The Best Trip Home That Didn’t Happen (Part 2)

The repair of the CTSW took about another week. The shop had run out of push rod tube seals, so we lost a couple of days waiting on some to arrive. The repair itself only took a day or so once they got there; but Houston swings between days of good weather and bad in cycles during the summer and the good days had passed while we were waiting. Between a couple of weathered-in days and my desire to limit work impacts as much possible, the next attempt to get the airplane home looked to be on the weekend. Most of our weather was due to afternoon thunderstorms firing up, so leaving Denton in the morning made the most sense. That meant I’d have to either get up there the night before and stay overnight or get up there early in the morning and try to get back as fast as I could. To make things worse, the shop said they didn’t have any way to assist with the trip up until the following week. Allowing the whole thing to drag out until then would mean impacts to both my work and personal schedules I wanted to avoid, so my wife and I started exploring ways to get me up to Denton to fetch the airplane at the lowest cost. We had enough points in our airline accounts to pay for a ticket on Southwest Airlines for only a few bucks, so we used it to buy me a ticket up on Saturday morning, July 8th. I got one for a flight that arrived at Dallas Love at 8:30 in the morning.

The shop didn’t typically work on Saturday; but they were trying to move some other work forward so there would be folks there who could let me have my airplane. I didn’t think there was much chance of getting a ride from them when they were manning with a skeleton crew and didn’t want to depend on it; after looking at what ground transportation was available and what each cost, it wouldn’t cost me any more to rent a car than renting a ride, so that’s what I did. It would be a one way trip and I’d drop the car at the FBO. Having a car would also give me some options about getting lunch or a room if things went awry and I had to spend the night.

My wife dropped me at Houston Hobby at a little before six thirty on the Saturday morning. I was carrying only my flight gear and had positioned it plus anything else that might trigger a TSA security alarm in my flight bag so I could send it through their X-ray. I breezed through security and got to my gate to find our 737 already there. There were probably only about 40 people total on the whole flight, so getting a window seat was not a problem nor was launching on time.

I was keenly interested in the weather on the flight up; most of it seemed to be active to the east of Houston, i.e. good news for me if it stayed that way. We landed at Dallas Love a few minutes early and I beat feet out of the Terminal to the car rental busses, barely missing the one for Hertz rental as I stepped outside. A good fifteen minutes later, one showed up again and I rode it to the Hertz rental counter where my car was already waiting. I spent a few minutes checking her for damage and a few more checking her controls before plugging in a route to the Denton airport on the iPhone. It said I’d be there in 38 minutes. That was a lie; I-35 North was destroyed for construction and it took me an hour and 45 minutes to roll up to the shop and get out, hoping the mechanics were still there. They were; but they didn’t know I was coming, so they spent a few minutes on the phone making sure letting me have the airplane was okay while I performed a very thorough preflight, including a visual inspection of the engine compartment with the upper cowling off. There were no oil leaks anywhere and the oil level was at the top, right where I wanted it to be. Having a full tank of oil meant extra time in the air in the event of another leak.

By the time I got the preflight and weather briefings done, it was approaching lunch time. I had only snacked at breakfast time, so I felt I needed some real food to take with me since it would take close to three hours to get home. I needed to top off the fuel in the rental car anyway, so I headed out for a Chevron gas station some few miles away that I knew also had a Subway sandwich shop. I fueled up the car, got a sandwich and a bottle of cold water, and hustled back to the airfield where I turned in the car at the FBO (with some qualms in case I had to return but couldn’t see a good way to both hang onto it and turn it in as promised). I walked down to the shop and the CTSW, got the cockpit and me ready, and started the airplane up. After completing the post-start checklist, including getting courses laid into all my nav gear and the Go Pro camera started again, I taxied out for takeoff as I had a week before except I had no intention of overflying the area to the south. My plan was to fly out to the southwest as I had before and not to request flight following to leave me freer to deal with the airplane.

After completing my takeoff checks and taxiing up to the runway, I called the tower for takeoff. The controller told me to hold short again and asked me for my direction of flight, to which I responded “southwest”. A few moments after a Cessna transited in front of me down the runway, the controller issues me a “maintain runway heading and no delay” takeoff clearance with traffic inbound at one mile, which I accepted as I gunned the airplane forward, hitting full throttle as I rolled onto the runway centerline. Everything felt good, and the little CTSW lifted off quickly, climbing up several hundred feet before I retracted her flaps while continuing straight ahead. When the tower controller called me for a right turn, I rolled into it at her command before acknowledging it on the radios. Like I had before. I continued climbing to 2500 feet while heading southwest, switching off to Unicom frequencies when outside 8 miles.

I continued southwest over Propwash and onward to Copeland, where I again started a climb to 4500 feet while turning southwest. I had altered my planned course slightly to make it direct shot from Copeland to Bourland, closer to but clear of the Class D airspace belonging to Fort Worth NAS JRB, which I like to call Navy Fort Worth. I punched up the tower frequency and was surprised by the number of requests to transit their airspace, many of which were from departures from Fort Worth Meacham’s airport immediately to its east. The climb to 4500 feet was completely normal, and I started to relax, thinking that my problems with the CT might be over at last. I flew out from under the Dallas Class B’s southwestern ring and, with Bourland in sight, pushed the throttles up for a climb to 5500 as I swung more southeast.

Once again, I felt the vibration, the slight skipping, that I had seen before. I pulled the throttle back and started a right hand descending turn to return the way I had come. It was back to Denton again, no matter how much I hated to do it. Like last time, the gauges were showing me nothing unusual, and the engine was purring along like nothing was wrong as long as the throttle was not at full. I leveled the airplane down at 3500 and went to full throttle to see what I would get; the vibration returned and the RPM seemed to hang. I backed off the throttle, putting her at normal cruise, and pointed the nose east of Copeland, trying to run more directly back to Denton. The direct line clipped the Fort Worth Alliance Class B which I could stay above; instead I elected to fly a little bit northeast of the line rather than risk any kind of infringement. My nose stayed ready to sense the smell of burning oil, but I never did. I pulled into the left downwind for runway 18 paralleling a Cessna inside my right wing; the tower had him turn in close and first and I followed him around the corner to another safe landing.

The hangar doors at the shop were still open but no one seemed to be there. I stopped my airplane and shut her down and found one mechanic working on a Cessna Mustang who I explained to what had happened. As I unloaded my gear again, I checked the nosegear and saw another oil leak running down the strut at the same spot as before. Whatever was happening was BUSTING the seal! At that moment, any doubt I had about where the problem was located disappeared. I was very certain the problem was in the head, something I told the head mechanic when I got him on the phone. We also now knew that the problem wouldn’t appear until the airplane had been airborne for thirty to forty-five minutes, suggesting to both me and the head honcho that it was related to the overall thermal load, i.e., heat soakback, in the engine; and we knew it was busting the push rod seal. He responded that he knew what it was, i.e., a valve sticking open that was overpressurizing the push rod tube and then causing the seal to leak. I had seen valve problems in cars when racing as a kid, and I concurred with his analysis. We now could explain every symptom we were seeing. If we didn’t have the exact cause, we were damned close to it! He said he’d talk to the mechanic on Monday and, in the meantime, see what he could do about getting me back home. Unfortunately for me, he wasn’t able to come up with anything; so I re-rented my car, got a hotel room in Denton for the night, and wound up buying a ticket home on Southwest Airlines. Not the outcome I was looking for; but I once again was happy both me and the airplane were okay and I was convinced we were now on the right track to solving the problem.

The Best Trip Home That Didn’t Happen (Part1)

Our 2006 Flight Design CTSW in flight near San Leon, Texas.

Our Flight Design CTSW had been up in Denton, Texas for about five weeks getting her yearly conditional inspection, some preventative maintenance I wanted done, and replacement of all the rubber hoses used to run its Rotax 912 engine. I was ready for the airplane to come home. It had taken several weeks longer than expected due to weather delaying my delivery of the aircraft to the shop, a training interval for the mechanic, and a nasty surprise that developed during the last part of the work. A spark plug in the number four cylinder head had stripped during removal. (More on that in Part 3.)

The stripped spark plug removed from the #4 head.

The mechanic informed me that Rotax had removed any kind of repair of the spark plug cavity from the approved procedures, implying his only recourse was to replace the head. That added a week to the overall timeline and, worse, about two thousand dollars of expense we were not prepared for. I didn’t see I had much choice if I wanted to fly the airplane out, so I approved the purchase and installation of the new head as he recommended.

Getting and retrieving an airplane from a shop some two hundred fifty miles away is always challenging, but I had taken it there because the mechanic was both Flight Design approved and Rotax certified. I had flown it up and my wife had arrived later by car to pick me up and continue a family trip to Missouri and Kentucky. Getting the airplane home became a bigger issue. It was a five-hour drive (another five hours to return), a ticket on Southwest airlines (that would cost about $250 and you still had to get to Denton) or someone in another small airplane had to fly me up.

My planned GPS course in and out of KDTO from KLVJ. It is designed to avoid any Class B or D airspace in case weather or ATC clearances preclude entry.

The shop had mentioned they had a 205 they might be able to give me a lift in; so, I asked about they might do that so I could go get the CT. That airplane wasn’t available but they had someone else with an airplane who might be able to come get me; we arranged for me and that pilot to meet me at the Pearland FBO at 9 a.m. on Monday, July 3rd. He would be flying down in a Bonanza; it was a VERY nice F33A. He arrived and we left Pearland closer to 9:30 a.m., sneaking out under the floor of the Class B past West Houston airport, before eventually climbing to 4500 feet and leveling off. It was a very smooth ride, disturbed only by a few bumps due to the heat of the day. I was looking at the cumulus clouds dotting the skies around us while thinking about my trip back; daytime heating would grow them upward like flowers stretching for the sun. If I was quick getting back, I could get above them and avoid traveling in the hot, bumpy air below, something that would be impossible if they merged into a broken layer. Light Sport rules forbid overflying a ceiling so that you couldn’t tell where you were over the ground by looking down. Once I got Basic Med under me, I could fly my Light Sport airplane under Private Pilot rules and cheat that, but for now…

David Shulman, the pilot and owner of the Bonanza, was a professional pilot, and he talked about how he got there as we headed north. He had every approach control frequency between Houston and Dallas memorized, and we monitored Houston and then Waco’s approach controllers as we made our way. He aimed the airplane directly at Arlington’s Class D airspace at the bottom of the Dallas Class B, descended to 2500 feet, and requested clearance through the area from the tower, which it quickly approved. As soon as we zipped past, we quickly descended to 1500 to crawl under the floor of DFW Class B as we headed toward Ranger VOR, just south of Denton. Flying slightly west of a direct line to the fix to miss the western edges of the Surface to 10,000 DFW Class B, we traveled only a few minutes more before Denton was in sight and we were talking to their tower. They had us run a left downwind to runway 18 at two thousand feet and follow in some other traffic, which David did in a quick and professional manner. Moments later, we were shutting down his Bonanza on the ramp to the shop where my CT was; my airplane was sitting underneath an open hangar door in obvious anticipation of leaving soon today. I hoped to do exactly that.

After thanking David for a pleasant flight, I made my way to my airplane, did a quick look over, dropped my flight gear in its cockpit, found its mechanic, and had a chat. We discussed what had been done and how it had gone; he told me the logs were in the cockpit and the removed parts were there, too. I took a look at them and reviewed the log entries; happy with what I had found, I paid the bill (which was a bit lower than I had expected), and started preflighting the airplane. I didn’t find anything unexpected, so I pulled the airplane out of the hangar and got the cockpit ready to go. I ran my weather brief from my phone, turned on my Go Pro, an external GPS, and an iPad mini, called “CLEAR PROP!” and started by airplane up. My main navigational instrument was a Garmin 496; when I powered it up, I could barely see its screen. Considering it unusable, I shut the airplane back down, popped the 496 out of its holder, and started stepping through its settings. The backlight had somehow gotten turned down; I ran it up, reinstalled it, and restarted the CT. Once I was happy everything was ready to go, I gave my airplane some throttle and started to taxi.

At the end of the ramp, I stopped and called Denton Ground for taxi, also informing them I’d be requesting flight following. Using flight following usually had given me the most direct routing to Pearland. Once I was airborne, Regional approach would ask me what heading I wanted; I’d tell them “one eight zero” and they’d clear me south just west of the DFW surface class B at 3500 feet. I’d hold that until I was out of their hair and then turn a bit southeast to point at the west side of Houston’s Class B. Denton Ground gave me clearance to taxi and came back quickly with a squawk and a frequency for Regional, which I dutifully repeated back. I taxied south to the run-up area near the approach end of runway one-eight, did my take-off checks (including a run up, which was normal), dropped the flaps to fifteen degrees, and then taxied forward to the hold short where I gave tower a call. The controller asked me to “hold short”, which I acknowledged, nudging the nose of the airplane to the right to be able to see down final better. One Cessna later, the tower cleared me to go; acknowledging the call, I pushed the throttle forward, steering a long arc to the left, and hitting full power as the aircraft reached the runway centerline. I rotated at 42 knots, and the airplane leaped off the runway, climbing away at about 800 fpm. Right at about a thousand feet AGL, the tower approved a right turn out for me and advised me to switch up to Regional departure. I turned, acknowledged, switched frequencies, and called Regional, reporting in passing seventeen hundred. Regional answered immediately, letting me know I was in radar contact and giving me the latest altimeter setting. I continued the climb up toward twenty-five hundred as the realization crept in that I wasn’t going to be offered my usual course south. Must be holiday traffic, I thought. No worries. The course I was on would carry me southwest to the western edge of the Dallas Class B, where I would turn south and eventually southeast toward home.

I overflew Propwash and continued at 2500 feet until I hit Copeland where the floor of the Class B moved up to 5000. I shoved the throttle full forward to climb to 4500 feet and raised the nose to hold Vy. And when I did, I noticed both more vibration than usual and a barely perceptible series of “skips”. In all the time I’ve flown the CT, I had never felt anything like it. At my target altitude, I pushed the nose over to level flight; and as the airplane accelerated, I pulled the throttle back to cruise rpm, i.e., 5200. The vibration and the skipping went away.

I didn’t know what I had, but I knew something wasn’t normal. I continued to cruise level for a few more moments, but then pushed the throttle up to full power to see what would happen. The vibration seemed to return, vanishing as soon as I backed off the throttle even a little. Did I have a real problem here or not? After all, I had been out of my airplane for five weeks and I knew I was a bit reactive, knowing the head had been changed out and the most likely time for any issue is after someone’s done major work on your airplane. I felt like something was wrong, and I needed more assurance there wasn’t before I continued to trek toward Houston. I rolled into a medium bank right and pulled the power back, called Regional to let them know I was stopping my progress but didn’t get an answer, and descended to 2500 feet before leveling off heading southwest again. Regional called and asked what my on-course heading was going to be; not yet ready to abandon the idea of continuing home, I responded I would be turning to 180 shortly and then shoved the throttle to full to climb back to 4500 feet. Oil pressure, oil temperature, and cylinder head temperatures all were normal; but once again, the vibration returned at full power. After a few moments of experiencing it, I turned right, arcing back to head back to Denton in a descending turn that leveled at 2500 feet.

By now, my gyrations had gotten the attention of Regional approach, and the controller asked me if I needed any assistance because she was showing me heading northeast. I told her I had a problem “but it wasn’t big” and I was returning to Denton. She asked me if I needed assistance there and I responded in the negative; I didn’t feel I was in “emergency” territory yet, though I was prepared to go there if needed. I pushed the throttle up to full power as I cruised back toward the field at 3500 feet; the RPM pushed up to 5200 but that’s where it stayed. I felt like I usually would see the engine creep higher than that at this altitude; I was more convinced than ever something wasn’t right.

Because the Rotax 912 engine has twin carburetors that have to stay in sync, vibration issues are often due to the carbs being out of it. I had experienced that in flight when an air tube that keeps them together popped loose; there was a very increased vibration in the midrange, about 4000 RPM; at operation below or above that range, it smoothed out. It didn’t feel like what was happening; and though I couldn’t rule a carburetor issue out, I also knew that the most likely place for an issue was in the head since that component had been recently changed. It was a lesson I had learned not only as a pilot but as a NASA safety engineer dealing with the space shuttle; we often performed a risk analysis (though I didn’t do that one personally) to examine what a maintenance activity would perturb before approving its implementation.

The engine was producing good power and the gauges still looked good, but I was hedging my bets by staying at 3500 feet as long as possible. (The Class B floor was 4000 there.) My next checkpoint was Propwash, an airpark with a single north/south runway, and I could see its white block buildings clustered around the runway. Regional called, recommending I start a VFR descent, which I did. It was accompanied by the smell of burning oil. I had never smelled that before when flying the CTSW, and I now knew the situation was bit more serious than I had first thought.

Insert shows gauge location. Background shot shows start of approach into Denton. Look at where the “green” ranges are. Engine gauges are showing nothing unusual even though I’m smelling burning oil.

I dialed up the tower, reported my position, and requested a full stop landing. The tower gave me an immediate clearance to land. There were several aircraft in the pattern with me, and the tower controller mentioned as I swung into downwind that he had a departure to get out, which I thought I saw sitting at the hold short. The last thing I was going to do was allow a downwind extension to get a departure out…so I was keyed to declare an emergency as I passed abeam the approach threshold. Before I had to say anything, the tower asked me to make an immediate right base to help them with sequencing, and I happily and immediately complied. I kept the flaps up to keep up my approach speed and get on the ground sooner; I made an uneventful landing and taxied back to the shop the trip had started from.

I shut down the CT, got out, and opened the little oil door in the cowling to see the inside full of smoke.

I sauntered off to find some mechanics; mine had gone to lunch but the head guy was there, working on another airplane. After telling him I had experienced some “abnormal vibration and loss of power”, I pulled out my iPhone, texted my wife to tell her I had returned to Denton because of a problem, and looked over at the CT. Oil was flowing down the nosegear strut!! I took a picture and then fetched the head mechanic and he did the same as he also called my mechanic back from lunch.

The CTSW nosegear strut covered with oil from the leaking seal some minutes after landing.

When my mechanic got there, it only took him about a minute to pinpoint the oil leak; one of the push rod tube seals on the head that had been replaced was leaking. He said he had used seals that didn’t have a shelf life, pondering whether there might have been a material failure, and that pinching during installation was also a possibility.

The push rod seal after removal with damaged areas shown.

In any case, I left it up to him to go work. I wasn’t going anywhere else in the CTSW today; that was for sure.

While the head guy worked on getting me home, I grabbed my flight bag and my gear and walked up to the FBO that had some air conditioning to be comfortable while I waited. David agreed to run me back home later in the day; but he couldn’t get there until 6 p.m., so I spent the next four hours thinking that, while I was not happy about the problem or the additional delay getting my airplane home, I was very happy the incident had turned out okay and neither me nor my airplane had gotten hurt. I had discussed the failure with the mechanic; when I had suggested to him that the ultimate result of pressing ahead would have been engine oil starvation and seizure, he agreed and said he could not tell me how long I would have had before I would have encountered it. The one thing we both felt was right was…I would not have made it home without becoming a nightly news story, either because I performed an emergency landing (either successfully or unsuccessfully) or had chosen to use the airplane’s Ballistic Recovery System.

I had made the right decision…not only because of my experience as a pilot but because of my experience as a NASA safety engineer at the MER Safety Console during the Columbia accident. The engineer actually on duty when the crew was lost was Dave Witwer, one of my best friends, a fellow pilot and CFI who now flies for United. He and I had many talks about the value of following your feelings and taking action when you feel something is wrong. We are both strong believers in the value of intuition, which is often confused in the engineering community as operating on “emotion”. They are not the same. Intuition is the subconscious synthesis of your experience and knowledge; when the data is not there or is lying to you, it may be all you have. You ignore it at your own peril; paying attention to it can often save your life. In this case, it saved both me and my airplane.

And the role my intuition would play in getting this whole thing resolved was not over, yet…

Getting Lift Straight

As a pilot, an aerospace engineer, and an aerospace educator, I’ve been wrestling for at least the last year with how lift and aerodynamics were being taught. I’ve written a few blogs about it and protested to AOPA, the FAA, and the Civil Air Patrol in an effort to broach the problem. I have also dived back into my college aerodynamics books and other aerodynamics texts I own in an effort to re-examine what I knew and to see where I thought the holes were in my own knowledge. The timing was good. As I was doing this, I stumbled on Doug McLean’s excellent book: “Understanding Aerodynamics: Arguing for the Real Physics”. It has filled in a lot of the holes my college education didn’t. I’m still digesting the book; you’ve got to be interested in the subject to hang with it and is best digested if you have some technical background. That said, I STRONGLY encourage the above named organizations to go through section 7.3.3, “A Basic Explanation of Lift on an Airfoil, Accessible to a Non Technical Audience”. In particular, AOPA needs to bounce it off their “Essential Aerodynamics” course and the FAA needs to do so against their “Pilots Handbook of Aerodynamic Knowledge”. (I intend to take care of my CAP cadets, since I’m in the organization.) They are not the only ones by any means; many instructor written textbooks need to do the same.

Doug talks about the wing creating a downturn in the flow and that the wing’s reaction is lift (Newton’s Third Law). Most sources are interpreting this as the wing creating a downward “jet” of air (in the same way that a rocket engine reacts to a gas jet) and then confuse downwash over a wing as the downward jet the wing is reacting to. But his next statement points to the real meaning: “The aspects of the interaction that need to be explained further have to do with how the moving fluid actually pushes back.” He goes into that in the next section ( entitled “Lift is Felt as a Pressure Difference on the Airfoil Surfaces”. In other words, while the downward turning air is extremely important to the overall physics of the flow and lift generation, the lift is felt as a pressure difference that acts on the wing. (This is what I’ve been trying to say when I’ve protested against folks saying the wing pushes down on the air; it actually does…but…it doesn’t somehow shoot a big jet of air toward the ground that pushes the airplane into the sky. There are lots of momentum changes going on in the flow and engineers can calculate lift by analyzing that, but the answer is the same.)

Thankfully, even before I got ahold of Doug’s book, my own revisiting of the subject had convinced me that part of the issue was that the subject needed to be presented as a wing/air system instead of as individual pieces with more emphasis on the critical factors (like angle of attack) and less emphasis on poking the mechanical bear. I do agree that the cause and effect relationships of the flow need to be touched on; this was something that is lacking from every text I have (as Doug mentioned, college level aero texts tend to emphasize the math and skip the physicality, which drove me bonkers but I shrugged my shoulders and went on.) Like Doug, I am a big believer that technical subjects need to be taught correctly, that dumbing them down too much is a mistake, and there is usually a way to get to the right explanation if you try. Many people don’t, assuming that it’s okay to take any liberty; but the problem is often that doing so is like having an accident: everything appears to be okay until somebody gets hurt. As I said earlier, if you’re looking for a good explanation of how lift works, grab section 7.3 of his book and be sure to read and understand it.

Thankfully, the explanation of “Lift” on Wikipedia has already been updated while leaning heavily on Doug’s work, so the next generation of learners will be getting the right stuff. I’ll be putting together my own little pitch on this I can use with my own students, even while I go work on my Advanced Ground Instructor rating knowing I have to buy the FAA’s wrong answers on the aerodynamics portion of the test. Hopefully, this mess will get straightened out in the next year or so. We’ll hope truth can overcome the Internet and the current trend to believe in what you want to, even if it’s wrong. Otherwise, we risk running afoul of the words of Richard Feynman: “For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled.”

Understanding Aerodynamics

If you’ve been reading this blog and especially the ones written about aerodynamics and how it’s being taught, you know I feel like there’s a lot of disinformation that’s being taught by people who purport to know better. Understanding aerodynamics is not as easy as it might first appear, and I’ve been re-examining what I know about it and especially wresting with how to write about and teach it. I consider it crucial to teach it at the most basic level I can while keeping it technically correct. I am unhappy to report that many organizations I have approached about incorrect technical educational issues have shown me nothing but apathy. This needs to change, especially in this age of immediate and widespread information dissemination. The Internet is a great thing; but a lot of stuff you see out on it, especially dealing with aerospace education and aerodynamics in particular, is incorrect. It’s one thing to just be wrong; it’s another thing to line your pockets while doing it.

One of the people stepping up to discuss some of this is Doug McLean, a retired aerodynamicist and physicist from Boeing. (Thanks, Doug, for restoring my faith in physicists.) He has written a book entitled: “Understanding Aerodynamics: Arguing for the Real Physics”. I have seen a different (and I believe original) subtitle that said something like “Common Misconceptions in Understanding Aerodynamics”. Frankly, I wished it had stayed that way to call a spade a spade and raise a flag about what’s going on. Anyway, it’s a good read for anyone really wanting a better understanding of aerodynamics and helps fill in many educational holes even at the college aero class level, since the explanations there often take you through the math..but not the physicality. While that did the job, it often left me with a lot of questions; I’m the kind of person who needs to link the abstract to the real to get it. (And I feel that connection is especially important when you’re trying to teach this stuff to general audiences.) That said, the book is a bit heavy for the layman, so you gotta be really wanting to get into the science to stick with it. You can get a good and somewhat lighter preview of what the book says by looking at the first 29 minutes or so of this video, which is a capture of a lecture he gave an engineering class about the book:

This whole controversy (and it really shouldn’t be one) has been good for me in that it has forced me to re-examine what I learned, find the places where I had misconceptions, drill down into the various technical explanations for lift and drag and see where they were right or wrong. I am even revisiting the technical foundations of my education (physics, calculus, and differential equations) when necessary, and it’s a process I’m still continuing. I’ve got a ways to go before I’m going to feel like I’ve got it down; it’s a lot more work than I thought it would be, and there are days when I ask myself why I’m doing it. But I like both learning and teaching, the latter most of all. At my age, I take a strong look at anything I’m putting a lot of time into since the long term payoff for me isn’t clear; but if it helps me be a better pilot, engineer, or educator…helps me teach the right thing to one pilot or STEM student..then I am convinced it will be worth it, which is why I soldier on.

Spin Training

Author’s Note: This was originally written back in 2011 when I was working on my Light Sport CFI. For another way to get some spin training than the old fashioned “strap your tail into an airplane and then hurl it at the ground”, see the blog “Flying For Flyquest (Part 2 of 3)” dated Nov 27, 2016.)

The requirements for it were not really clear. Both me and my CFI, Dave, had looked at the regulations and they seemed to be saying that even for a Light Sport Flight Instructor, a spin training endorsement was necessary. Regardless, it had been a while since I had an excuse for any kind of flying that turned the world on end, so I agreed to it. On a Monday morning with a cloud-filled sky, Dave rented a Citabria and we launched in it to do some spins.

The cloud deck was a bit of surprise as it hadn’t been in any of the weather forecasts I had looked at. It started moving in from the south, the direction of the Gulf of Mexico, as we were preflighting the Citabria together. We decided to launch because we could see some breaks in the clouds to the east over Galveston Bay, and that was where we were going to do our training. Dave slid into the fabric airplane’s back seat as I tried to remember how to get into the front. Pulling myself up, twisting one leg in and around the stick, and sliding into the seat, I finally sandwiched in. I reached back and grabbed the shoulder harnesses, pulling them over to my waist to attach them to my waist buckle. Once in, I connected my headset to the intercom jacks and pulled the headset over my head, resting it on my shoulders until we got ready to start. My habit was (and is) not to put them on until after the engine and intercom are on in case some reason comes up we need to exit quickly.

I’d gotten a little big in the past decade (I’ve gotten back to “fighting weight” since) and felt scrunched up against the instrument panel, though the control stick still was in a good place and I had plenty of room for my feet in between the rudder pedals when I didn’t need to be on them. The metal stick began moving around on its own; Dave was checking out his control throw. He couldn’t get the stick all the way back up against my seat because it was hitting me, and he felt that we would need to do a wheel landing because of it. While I felt I had enough stick throw to do a three-point landing from the front, I had not flown any taildragger in several years and Dave flew a Pitts as well as this airplane fairly frequently, so I deferred to him and said he needed to do the takeoff and landing instead of me as we had briefed. He acknowledged the call and we started through the prestart checklist, with me controlling the engine start since I was in the front. The engine started on the first try, and I told him he had the airplane. He acknowledged and taxied us forward.

We crossed La Porte’s runway 12/30, heading for 12, though the windsock was showing a little bit of life out of the west. I informed him that the terminal forecasts had shown by ten a.m. that the winds would be two-two-zero at ten gusting to sixteen. That was a little less than two hours away, and he was confident we would be down by then. Still, we talked about the proper control inputs for a crosswind to the right, i.e. , full right stick at the beginning of the takeoff declining toward the center as we gained speed but enough to keep the wind from picking up a wing. We performed our pre-takeoff checklist at the hold-short for 12 and Dave then made a radio call announcing our departure. We rolled onto the runway, aligned with white stripe centerline, the control stick “magically” full right. Dave slid the throttle forward, the engine roared, and we advanced down the runway. The stick came back fairly quickly and we were airborne. The airspeed seemed kinda slow to me, i.e., 45 mph, and I said something to Dave and he thought it was, too, even though the nose attitude looked correct. I looked to my right to make sure the little metal bug cover over the pitot tube was retracted and it was and then looked back at the airspeed indicator and it was showing 60. We both felt the airplane was performing okay and Dave asked me to take the airplane and I did. I continued a shallow climb straight ahead toward an oil tanker sailing into the Houston ship channel while I looked for holes to get us on top of the cloud deck, being also mindful that the floors of the Class B airspace were at 2000 and 4000 feet MSL over the bay, depending on where we were.

Dave asked me to turn to the south to align with some islands he wanted us to use as visual landmarks during the spins. The cloud base was at about 2000 feet and looked to be only a couple of hundred feet thick, but we both discussed our location and concurred we had crossed into the shelf where the Class B floor was at four thousand. I climbed us up through a couple of breaks in the deck, flying east and then south, and as we got glimpses of the shoreline to our east we could tell where we were. Dave asked me to climb to thirty-five hundred to give us some room above our imaginary three thousand foot recommended recovery height. So, I did as we continued cruising south toward what I thought might be a break in the clouds. We found a clearing in the clouds above one of the small islands Dave wanted to use.

“Hey let’s do them here,” he said. “Let me know when you’re ready and give me the airplane.”

“I’m ready,” I said. “You’ve got the airplane.”

He acknowledged he had control and immediately brought the throttle back and the carb heat on.

“I’m going to demo a spin to the right,” he said, as he held the nose where it was and let our airspeed bled off. The airplane didn’t have a stall warning horn; but as we slowed down and I started feeling like we were close to the stall, Dave said he was pulling the stick full back, ailerons neutral, and kicking in full right rudder. He did and the nose rotated right and down; I was suddenly looking straight down at the island below as it whipped around in a blur! As we rotated into the heading we gad started on, the rotation stopped, leaving us diving straight-nose down! As Dave pulled us out, the G-meter needle rolled to 3 g’s; the power came up and we moved back into a climb and I heard: “Your airplane!”.

“I’ve got the airplane,” I said, taking the stick back and continuing the climb. I had noticed as we were spinning down that there was more of a hole to the north than to the south, and that hole gave me more ground reference to work with. So, as we climbed, I turned us back to the north and steadied up in the direction.

“Your turn,” Dave said. “I want you to demo a one turn spin and recovery.”

“Ok,” I said, just as we hit our altitude. I immediately throttled back and brought the carb heat on while slowly bringing the stick back to hold the nose in a level flight attitude, telling Dave what I was doing as as I did it. We slid slower, slower, and NOW! Stick full back, I kicked full right rudder and held it in; the airplane rolled over like a dying hippo and spun, heading straight down! About a quarter turn before I hit my entry heading, I kicked full opposite rudder, quickly kicking it back to neutral as the rotation stopped while I simultaneously came forward on the stick, a bit too aggressively. We kicked into a very slight zero-g dive, which I quickly negated by beginning the pullout, shoving the throttle to full as the nose came up through the horizon.

“Nice job!” Dave said.

“Except for the part of floating you a little bit,” I laughed.

“I’d rather see you recover aggressively than not aggressive enough,” he countered.

Well, it was, as flying often is, a matter of “how much”. It had been just a small float, and I had essentially just “unloaded” the airplane which amounted to giving Dave a free, one-to-two second weightless ride he probably hadn’t anticipated. But a harder negative g recovery in another airplane, like the Pitts Dave often flew, could flip the airplane into an inverted spin. Ok, so it would take a LOT to get there; but still, it was a matter of degree.

We climbed back up and Dave took the airplane to demo a spin to the left. The nose did the same familiar slice and roll, and again tucked into a fast, rotating, near-vertical dive. Propeller driven airplanes often spin faster to the left than to the right because the engine torque adds to the rotational force with a leftward spin, but I didn’t really notice any difference. All I knew was that once it broke loose, the nose attitude down ad the rotational rate was steeper and faster than I remembered it. Despite my anxiety at not having done anything like this for quite a while, I was enjoying the hell out of it!

Dave gave the airplane back to me and as I set up, he emphasized that in this airplane the rudder force to get full left rudder was much higher than it was to go right. I acknowledged that as I immediately throttled back (initially forgetting the carb heat until reminded) and slowed us down and down, until we hit the stall and I kicked full left rudder. Again, the airplane rolled over and spun down; and again, as I neutralized the controls and stopped the spin, I floated us for a second before beginning the pullout and bringing us back up into a climb. During both his set of spins and mine, we were averaging five to six hundred feet altitude losses. We climbed back up toward thirty-five hundred feet as Dave talked to me about doing “incipient spins” next.

“I’m going to pretend I’m a student doing stalls and then do something wrong that starts us into a spin,” he said. “I want you to take the airplane and recover it.”

I acknowledged I was ready and watched as he leveled us back at thirty-five and began slowing the airplane down. Everything was going fine as we slowed into a stall but at the break, the airplane began rolling right, the nose slicing into the now ever-familiar signature of an upcoming spin. I called “My airplane!” as the bank hit about forty or fifty degrees, taking the stick and pulling the power back, rolling wings level, and then executing a pullout, adding power to get us back into a climb. Dave complimented me on the recovery and then took it and did it again, this time getting the airplane to break left. I took control of the airplane and got us righted again, losing only a couple of hundred feet…if that. Again, Dave complimented me on the recovery.

“Well, that’s all the training we have to do,” he said. “Is there anything else you want to do?”

“Yeah!” I answered. “Let’s go do another spin!!”

I started climbing for our altitude, looking forward to doing a spin for fun!

Dave asked me how much gas had in my left wing. I leveled the wings and the gauge needle was bouncing around close to a quarter of a tank, but the right wing gas gauge was bouncing between quarter and zero. While we didn’t think we really had a gas feed problem, we both agreed that the prudent thing was to knock it off and head back to the field where we could check it out on the ground. I dived us northward toward home field through a hole in the clouds; and once the airspeed and attitude was stable, the right wing showed about half a tank, closer to what we had been expecting. By that point, we were closer to home than not, so I decided to call it a day anyway. I felt good about what we had done.

I leveled us at a thousand feet about six or seven miles out from the airport and turned the airplane back over to Dave since he was performing the landing. We initially set up for a crosswind landing on 12 but then changed to runway 23 once we saw the windsock and that the winds had changed. Dave couldn’t see the airspeed indicator, so like I had done in my F-14 RIO days, I called airspeed for the pilot as he brought us down the approach. With just a slight “clunk”, Dave did a really nice wheel landing, brought the nose down once we had slowed, and taxied us back in.

I have to say that even though I had been an aerobatic pilot in my past, taking spin training for my Light Sport CFI was well worth it, required or not, and something I recommend to anyone going for their Light Sport rating, whether as a pilot or CFI. You probably will have to look elsewhere than where you are training in your Light Sport to find a spin certified airplane, though light sport aerobatic planes are hitting the market now, so who knows? No matter, have your favorite flight instructor or one he/she recommends to conduct this training and go with tim to spin around. It’s one or two hour of flight training that can save your life.

Eyeballs Out!

I saw the yellow J-3 Cub fly into the downwind and then, when abeam the threshold of runway 14, turn left and nose down onto base leg. The airplane was close aboard and arcing quickly over to intercept the final approach to the runway. It was approaching the threshold and only about one hundred feet in the air when a Cessna 152 sitting at the hold short pulled out onto the runway in front of it. I couldn’t hear the Cub’s engine, but its pilot reacted immediately; the Cub leveled off, flying over the top of the Cessna. The Cessna sat frozen, its pilots made aware by the Cub’s shadow and its presence overhead that they had almost caused a collision.

I didn’t have my handheld radio with me, so I was uncertain if the Cub had broadcast its position in the pattern. If it had a radio at all, that is. It was probably not equipped with one. Even if it had been, the fact that the pilot didn’t use it was irrelevant. No one is required to make any radio transmissions in the pattern at a non-towered field, something many pilots either aren’t aware of, forget, or ignore.

When you’re engaged in a dogfight, you quickly learn the only thing that’s going to keep you alive is your visual lookout, no matter what technology is onboard. I call that being “EYEBALLS OUT”! (Yes, the term is used more routinely to describe the direction of g-forces one is experiencing in the cockpit; but it’s appropriate to use it here to distinguish where one is looking.)

Yes, the Airman’s Information Manual and other aviation safety materials recommend radio protocols for pilots to use to stay informed of each other’s position in the traffic pattern. That communication is very helpful and certainly best practice. But I’ve often heard comments that make it clear we EXPECT other pilots to use the radio and often consider it poor form when they don’t. Well, it is, but that expectation is OURS and can be and often is unrealistic. Your best advice in this matter comes from the movie “The Princess Bride” where the Dread Pirate Roberts tells Montoya, “Get used to disappointment”. If you have become dependent on radio calls to keep you safe in the pattern, the problem is yours and you are likely to find out the hard way when your belief and your practice is badly placed.

The only thing that’s going to keep you safe in the pattern…or in flight…is your EYES! If you’re taxing around the airport or flying the pattern convinced that the radio is going to keep you safe, you have, as we also used to say in fighters: “your head up and locked”.

I was taught when checking traffic at a non-towered field to do a 360 on the taxiway before pulling forward toward the runway for takeoff. I teach this to my students. That said, my CTSW has a very wide turning radius and some taxiways at smaller airports don’t support it, so I’d be lying to say I always perform it. What I always do, however, is make sure I visually sweep the entire downwind and then turn my airplane enough to ensure I can see all the way down the final approach and about twenty to the thirty degrees to the side opposite the pattern before pulling forward toward the hold short. This ensures I not only see anyone coming down the final approach but anyone who has overshot final and is correcting back or is approaching the final from the other side. This is especially critical at airports where there is helicopter activity, where they may be flying downwinds on the opposite side of the pattern to the fixed-wings. (This is a strong reason to take the time to perform the 360 sweep, as long as you’re really paying attention to it and not just going through the motions assuming no one is there.) And anything you choose to do to assist your visual lookout MUST take into consideration the blind spots in your aircraft; it’s up to you to know where they are and do what you need to in order to work around them.

It’s no less critical to stay “eyeballs out” at towered fields. Most mid-air collisions happen within 5 miles of an airport; and whether the field is towered or non-towered seems to make no statistical difference. The radios can help you get or maintain situational awareness for things you can’t necessarily see; but, in the end, it’s your eyes and your reactions that are going to keep you safe. The regs require you to “see and avoid” even if you are flying IFR (as unfair as that might sometimes seem.). Additionally, today’s technology laden cockpits lure us all to be “eyeballs in”, a problem that’s going to be made worse by ADS-B. It’s great to see that target you can’t see on your iPad and maneuver early to avoid it, but if you smash into the airplane not displayed while doing so, you haven’t gained a thing.

Instructors have to work twice as hard at keeping a lookout; trying to keep tabs on what their students are doing pulls their eyeballs in; so, if you’re flying with one, keep your eyes moving and help make sure you both come back from the flight alive and unhurt. And, Instructors, all of us get engaged with something they are doing and keep our eyes too much inside; but we are also supposed to be setting an example and keeping things in perspective. During many flights, we are the Pilot in Command; so, if anything unfortunate happens, it can be ultimately on us.

There were two people in that Cessna 152.

Safety Standdowns for General Aviation

After a significant accident or incident involving flight operations, my Navy squadron would halt all flying to conduct a day-long review of various safety subjects as closely related to the accident or incident as prudence allowed. This break in our operational routine was called a “safety standdown”; and it was designed to make sure we had our heads screwed on right about taking risks. It was one thing to lose aircraft and aircrew due to combat; it’s quite another to lose them to preventable accidents. It was an effort to reinforce “better dead than look bad” or “it can’t happen to me” really doesn’t work, something some folks in aviation just don’t get.

We all have accidents, sometimes minor and sometimes, serious, happen at our airports. I don’t know about you but all that often happens afterwards is I pick up gossip about what went wrong, at least until the NTSB report comes out…if there is one. Too often, though, even when an accident reaches Part 830 thresholds to become reportable, unless it makes the evening news, we pilots hear nothing. (And that’s even MORE true for accidents that don’t trip the 830 threshold.) That’s exactly the opposite of what would make for a safer community. Over and over, in the safety world, we learn that open and honest communication about what went wrong is what helps the world become safer, though it still only occurs when the practitioners of whatever dark art we’re talking about take the lesson provided to heart.

Just before the holidays, we had four significant accidents associated with operations at our airport within about six weeks. Two of them were fatal and one involved significant injuries. Three of them occurred during or shortly after takeoff and one during the landing phase (the most risky parts of the flight profile). The latter was the only one not involving an injury or fatality but did disable the aircraft. The accidents involved both flying clubs on the field and one private individual not based there. Though these were certainly not the first fatal accidents that had occurred out there, the number and severity of the accidents within the short timeframe got lots of folks’ attention, including mine. The initial lack of response from anyone appeared deafening to me, and I brought up the subject with some of my compatriot instructors, some of whom also have military and/or safety backgrounds. Everyone thought a safety standdown was a good idea. Eventually, one did happen…almost. A FAAST event was put together at one of the flying clubs, though the notification announcing it was not widespread or much in advance. The flying club involved in one of the fatal accidents had an instructor give a brief review of stall/spin factors (though it was too rushed for my liking); a pilot’s organization rep gave a brief on airport pattern operations that was, unfortunately, tainted with incorrect gouge (something another flight instructor next to me agreed with me on); a helicopter training school gave a helpful brief on helicopter operations (they were fairly new at the airport so the fixed wing guys were adjusting to their presence); and a group of formation flyers introduced themselves. I felt some of it was helpful, some of it was better than nothing, but the whole experience could have been improved with more focus. A “safety standdown” is different from a safety seminar in that the latter may cover related accident causes (or suspected accident causes if the probable cause has not been established) but a safety standdown is aimed right at them. That does not exclude it from including other safety related material that might be relevant, but its primary focus is aimed at the events that triggered it.

Because we’re talking about this in relation to general aviation and not a centralized authority (like a military command), someone has to take the bull by the horns and get it going. Any flight school or flying club can decide to do it, and it will achieve maximum impact if associated flight operations are halted during it. This would have to last long enough to send a strong signal that safety is being taken seriously, i.e., a minimum of two to four hours, depending on the quantity of relevant material and the significance of the trigger event(s). In the event there are multiple clubs or schools, the airport FBO or management could call for the standdown and act as the focal point for putting it together and hosting the activities. Each flight school or flying cub could provide safety officers, CFI’s, or other knowledgeable pilots to a working group that would discuss the events and trends they have been seeing and then decide on the content, timing, and location of the event. FAAST/FAA Wings credit for attendance should go without saying; FAAST subjects that might relate to the events could well be prime candidates for inclusion, even when the probable cause of the trigger events are only suspected and not known. This is not the same as speculating on the probable causes; that needs to be avoided; but there is little new in the causes of most general aviation accidents. Related safety information will be available.

So, okay, that’s the ideal. Not every airport manager, FBO, flight school, or flying club is going to be willing to stop all flight operations. While doing so will provide maximum benefit, you can still make it work by letting flying continue and making attendance at it totally voluntary. The other logistics of it need to remain the same, i.e., the agenda needs to be matched up with the events being targeted. Take video of the presentations and make them available for those who wanted to come but couldn’t for whatever the reason. If you have a newsletter, either electronic or paper, you can include information about the highlights of the events, including any lessons learned or changes to operations that might come out of them.

Additionally, maximum benefit can be gained by making the event, as much as possible, an interactive exchange between the presenters and the pilots in the room. It’s an opportunity to not only impart wisdom from the podium but gain some from the folks in the room. Almost every gathering of this type will be filled with pilots from a myriad of backgrounds…some military, some general aviation, some from the business aviation community, and some from the airlines or some with parts of them all. Encourage those with experiences that relate to the topic to share them; it not only helps us get to know each other better but it opens the door to tapping the wealth of experiences whose depth we would otherwise have no knowledge of. It also reinforces the idea that anything can happen to any of us; and, if it does, knowing how someone else handled it, good or bad, might help us make the outcome go our way.

(Author’s Note: Thanks to Jim Gardner,ATP/CFI and Russell Lewey, Educational Director for FlyQuest, for their input to this article.)

Flying the Circular Pattern: Thoughts from a former F-14 RIO and current Light Sport CFI

The University of North Dakota and AOPA’s Air Safety Institute is performing a study of the use of the circular traffic pattern at general aviation airports. This type of pattern has been in long use by the U.S. military, with the Air Force and Navy using it as the emergency approach pattern and the Navy using it as the pattern of choice…at least since the British pioneered its use to get the F-4U aboard ship. I’ve flown the pattern as both a pilot and a RIO and use it today when flying simulated engine out approaches in my Light Sport Flight Design CTSW. I also work as a part-time safety analyst for the Flight Safety Office at Jonson Space Center, so I‘m content to wait for the study’s results and seeing their recommendations before formulating aa position. What I’m going to do here is detail some caveats centering around the Navy’s operating environment that affect its use and how that translates into the environment at a non-towered airport. Hopefully, the students conducting the study have some ex-Naval Aviators and USAF pilots at their disposal; not sure if the Army uses it, but if they do, then some insight from some Army pilots cold be helpful as well.

The Navy’s primary use of the pattern is to safely get aircraft aboard ship. It provides enhanced visibility of the landing environment (i.e., the ship and its position) and allows for smaller, more gradual, and continuous adjustments of your position to arrive on a final approach with consistency, something critical to the tight requirements needed to get aboard. Crews can and do use altitude gouges to judge glideslope at the 90 degree degree “to go” turn point (450 ft AGL) from downwind pattern altitudes in the same basic range as general aviation patterns (slightly lower than most actually; the F-14 NATOPS pattern was at 600 feet AGL). The pattern is intended to provide a stabilized approach beginning at the downwind abeam point. The aircraft hits that target “on speed” (green chevron on the AOA indicator, 15 units Angle of Attack for the Tomcat) and in the final landing configuration. That is gear down, flaps down, speedbrakes out (if applicable); no other major changes in aircraft configuration are made after that point since any changes in aircraft configuration can cause a major upset to an otherwise stabilized approach. Variables for the Navy pilot to deal with are therefore narrowed to controlling altitude and angle of attack and judging the rollout onto final (which will be slightly to the right of the ship’s wake to line up with the angled deck), followed by “Meatball; Lineup: Angle of Attack” until touchdown or bolter. The aircraft’s “locked down” configuration MUST be taken into account when discussing the stability and precision of the circular approach and before applying it to general aviation where that is often NOT the case. The FAA Flying Handbook instructs pilots not to go to full flaps until established on final and some preceding amount of flaps are applied sometime after the downwind abeam point, not ahead of it. While this is to give you the best glide possible in case of an engine out, it still means you’re going to make one of the most significant configuration changes you can make while also trying to get into an airspeed and descent rate stabilized approach. While the impact is more a function of the aircraft being flown than the type of pattern, but understanding the impact of configuration changes is a necessary part of evaluating the overall use of the circular approach and its for stability. You could decide to put the airplane in its final config and then count on the power being there as the Navy does and get all the benefit; but it’s unlikely that would be the case, even if the probabilities were to tell you that protecting for an engine out in the pattern might not be a good trade considering the safety gains of approach stability. This must be considered by the team conducting the study.

Likewise, the team needs to consider the fact that few Naval aviation operations take place in a nontowered environment. The closest thing to it are operations at Navy Outlying Fields (NOLF) used primarily for pattern training and that often have someone on duty and on the radios. While they are primarily there to make sure no one lands gear up, they also act as a traffic advisory service. Operations at other Navy airfields (and some NOLF’s and aux fields) are run by Navy air traffic control towers; aboard ship. the Air Boss and his staff take on the roll of an ATC tower. This significantly limits the opportunity for traffic conflicts due to someone making an unexpected/unannounced straight in or unorthodox pattern entry. When applying the circular pattern to nontowered genreal aviation operations, then, this means a very big question is, for the pilot in the pattern as well as anyone approaching the pattern, whether it introduces more risk to “see and avoid” than the rectangular pattern does.

For pilot in the pattern, since the transitions to each leg are performed in a constant turn, visibility of incoming traffic will be directly affected by whether the aircraft is high wing or low and the amount of bank used. Belly checks (rolling wing down in the direction of possible incoming threat…uh….traffic) may be employed to look for traffic blocked by the upturned wing; and, if used, become a factor that can destabilize the approach. (Scanning for someone on final approaching from the outside is done by just turning your head in a rectangular pattern.) This can be mitigated by using shallower angles of bank, which would be more necessary in a low or mid wing than a high but can mitigate the issue. Of course, the shallower the bank, the more stretched out from the runway the pattern becomes; but my guess is it would probably still be significantly less than the stretched out rectangular patterns I see too often at nontowered fields. For the pilot approaching the pattern, the additional turning of the aircraft in the pattern may them a bit easier to spot; in a rectangular pattern, there are large portions of it where the airplanes in the pattern may be climbing or descending but are wings level and not the easiest to spot.

These are things I expect the study to evaluate. Personally, I like the circular pattern; and as I’ve said, I will often fly it when performing simulated engine out approaches in my CTSW. I have also demonstrated it to students and friends who are curious about how the Navy does things. I don’t tend to use it when flying a Remos GX; its higher approach speed and less effective flaps make flying a rectangular pattern a more comfortable thing to do and what I need to teach my students to do. While I’m content to wait and see what the study arrives at, with the investment the community has in both training and operations in the rectangular pattern, I think it’s going to be a “hard sell” to move us to a circular pattern. There must be a very significant benefit not otherwise achievable to make it happen. I also think there are bigger fish to fry; the factors that drive loss of control in the pattern aren’t things that this protocol are going to affect. The collision risk may be another story; but it seems to me that could go either way. If we were to switch to a circular pattern, you could probably expect accident statistics to initially get worse until pilots got trained and comfortable with the new way of doing business.

No matter what pattern we ultimately fly, good headwork, situational awareness, and skill are what we need to determine whether flying on any particular day goes well or goes bad. When those things fail, all you’ve got left is a little luck. Hopefully, it goes your way…

Flying a CTSW with Flat Plate Wings: Analyzing “Impact Lift”

I wrote a blog a little while ago entitled “One Form of Lift” which talked about the generation of lift and how there was, from an engineering standpoint, no such thing as “impact lift”. Classical engineering analysis only uses lift (which is primarily generated by pressure flows around the wing) and drag. My assertion is that most or all of the force people are calling “impact lift” is really drag, but was there a way to prove it by using a real world example? To take a look at that, I decided to analyze what happens if I stick a set of flat plate wings on my light sport aircraft, a Flight Design CTSW.

We will assume that the wings on the CTSW are mounted so that they are at zero degrees angle of attack (and angle of incidence) when the airplane is sitting level. The wing area of a CTSW is 107.4 square feet and the airplane’s max gross weight is 1320 pounds.

The equation for lift is: Lift = ½ D V2 S CL where D= air density, S = wing area, V2= the velocity squared, and CL = the coefficient of lift.

The equation for drag is of the same form, i.e., Drag = ½ V2 S CD where = air density, S = area being analyzed for drag, and CD = coefficient of drag.

For these formulas, lift=weight, the density of air at sea level is used, and S= 107.4 sq ft.

A flat plate has a lift coefficient, and the curve maximum hits a CL = 0.7 at an angle of attack of approximately 12 degrees.


At twelve degrees’ angle of attack, then:
Lift = ½ (.002378 slugs/ft3) V2 (107.4) (0.7)

For the airplane to fly, lift must equal to weight, so:
1320 = ½ (.002378) V2 (107.4) (0.7)

2640/(.002378*107.4*.7) = V2

2640/0.17877804 = V2

14,767 = V2

121.5 = V (feet per second) or 72 knots

This would get my CTSW with a flat plate wing off the ground at 72 knots while nibbling at the stall. Let’s say you understand this will be the case and elect to back off on the liftoff a bit, flying off at approximately 8 degrees angle of attack. (I believe you will either strike the tail of the CTSW at 12 degrees or be very much at risk of it.) So, when would you want to rotate? At that 8 degrees, you have a lift coefficient of 0.6. That gives you:

2640/.153238 = V2

17,228.1 = V2

131.25 =V (fps) or 77 knots

Since the CT actually gets airborne as low as 42 knots with flaps and about 50 without, you get an idea of the work a good airfoil design (using Bernoulli’s) is doing for you. You can “reverse engineer” the lift coefficient at those speeds by substituting them in for V and solving for CL.

Doing so for the no flap configuration and 50 knots yields a CL = 1.45; in other words, the shaping of the airfoil increases the “flat plate” lift coefficient by slightly over 100%. (The use of flaps yields a lift coefficient of 2.06…which is part of the reason why it leaps off the runway and feels like you’re in an elevator going straight up…)

But, let’s go back to flying by the flat plate alone since our real target is to examine the idea of “impact lift”. As I said in an earlier blog, the only way to do this from an engineering standpoint is to use drag as the “impact lift” force. There is no accounting for such a thing in conventional performance analysis (which should tell you something in and of itself about the rigor of the idea, despite some folks trying to discount how engineers do it).

Let’s see how we might be able to generate enough “impact lift” (drag) to fly. A flat plate has a drag coefficient of 1.28. Since the equations for lift and drag are the same and we’re considering the same area in both equation sets (i.e., only the area of the wings), then we can shortcut the calculation of the total drag force the wings can generate by simply taking a ratio of 1.28/0.7 = 1.83. Then, that same 1320 lbs of total force…now as drag instead of lift…would be generated at 72/1.83 = 39 knots. But this would be for a CTSW wing deflected at 90 degrees to the windstream (and the fuselage). Since we’re just trying to use “impact lift” (i.e., drag) to get airborne, the max lift would occur at a wing inclined 45 degrees to the windstream. The “lift” would be equal to the sine of 45 degrees times the total force. The sine of 45 degrees is 0.707. So, then the speed at which you’d have just enough drag acting vertically to lift off would be: 39 knots/0.707 = 56 knots.

However, for this to occur, the drag acting in the horizontal direction would also be 1320 lbs (sine and cosine of 45 degrees…the horizontal and vertical force components would be the same). Let’s see if the Rotax 912 can get there.

Using Thrust = (HP*efficiency*326)/KTAS and assuming we have a 0.8 propeller efficiency:

1320 = (100*.8*326)/KTS

1320 KTS = 26,080

KTS = 19.75

This is the speed the Rotax could attain in this “lift/drag” configuration. This is a conservative answer since the airplane will have more drag area than this, i.e., we did not account for the frontal area of the fuselage or other components. This puts us well short of the approximate 56 knots it would take to get airborne. To see how big an engine it would take, let’s use the same formula and solve for HP.

1320= (HP*.8*326) / (56)

1320 = (260.8HP)/ (56)

1320*56 = 260.8 HP

73920 = 260.8 HP

283.4 = HP

So, it would take an engine producing almost three times the horsepower the CT has available which would increase the weight and cause us to do all these calculations over again. Keep in mind, too, that we are only talking about the power it would take to get the CT into the air since climb rate is a function of excess horsepower. The engine would have to be bigger still. (At least a 300HP IO-540…) What the numbers are telling you is that the idea of impact lift doesn’t work, and that’s before we try to consider the flying characteristics and design of the flight controls for such a beast. We know that increasing camber (curvature) of an airfoil causes an increase in lift and that’s what makes ailerons and elevators work; how do you explain what’s happening if “impact lift” (drag) is the only force?

“Impact lift” is a misnomer and a popular myth, like saying you can discount Bernoulli’s principles and just use Newton’s laws to easily explain how airfoils work. Good luck with either. From both an engineering and piloting standpoint, it’s better and proper to see lift as a result of Bernoulli’s (i.e., pressure distributions) principles and drag as something that needs to be overcome and is not your friend (except when trying to slow down). You’ll not only stay safer that way but you’ll teach your kids the right concepts, making sure it is “as simple as possible but no simpler”.

AUTHOR’S NOTE: Many thanks to Dave Witwer, Jim Gardner, and Matt Zwack for their review of the drafts of this blog. They’re all pilots and aerospace engineers (Dave, Jim and I worked at Johnson Space Center and Matt works out at Marshall Spaceflight Center.) Great guys I’m honored to know as colleagues and friends!

Fuzzy Aerodynamics

A week or so ago in an aircraft owner’s forum, the exact thing I was concerned about happened, i.e., a pilot trying to explain how an airplane creates lift to a newer pilot started talking about “the downforce” under the wing that pushes an airplane up into the air (you know, because that’s how the reaction force…referred to in Newton’s Third Law is created…and the airplane reacts by going up!). I’d think it was funny but AOPA’s current iteration of “Essential Aerodynamics” also says that a wing pushes down on the air, creating a misperception that will probably take a decade to clear up. It’s not that Newton’s Laws are not involved; they are. The popular misunderstanding of what that means is fostered by the incorrect idea that somehow only Newton’s laws apply and Bernoulli’s laws are somehow incorrect and is all pure nonsense. So, I’m going to give you a technical explanation of why and do it without going into a lot of math. (I’m going to assume you’re not too dumb to follow what I’m saying, unlike some other folks who say we don’t need to teach aerodynamics like engineers do it because we’re not designing airplanes and then screw the whole thing. If you’re new to this controversy of befuddlement and want to get completely spun up, see the blog entitled “When Simpler Becomes Dumb”, another entitled “Only One Form of Lift”, go through AOPA’s “Essential Aerodynamics” presentation, and come back here. Otherwise, just read on; I’ll explain it in enough detail where you can grasp the core issue.)

The text we used in my aerospace engineering classes discussing aircraft performance was “Airplane Aerodynamics” by Dommasch, Sherby, and Connoly. Section 2:4 “Development of the Bernoulli Equation” explains how,by analyzing a small packet of air as it moves using Newton’s Second Law (F=ma) (Spoiler alert: Newton’s Third Law is not involved here) and assuming no mechanical or thermodynamic losses (conservation of momentum and conservation of energy),one derives Bernoulli’s equation. For incompressible flow (a good assumption for flows less than 200 knots or 230 mph), Bernoulli’s equation is:


where p=Pressure, D = air density, and V2=velocity of the airstream squared. P is the “static pressure” term and “D(V2)/2” is the “dynamic pressure” term. So, as the velocity of the airflow increases, the dynamic pressure (pressure in the direction of the airstream flow) increases and the static pressure (pressure of the mass of air and measured perpendicular to the flow) decreases.

Section 4.3 of that text is entitled “Development of the Lift, Drag, and Moment Equation”. It starts out with this: “…the only forces that can act on an object moving through a fluid are those produced by friction (shearing stress in a fluid) or those produced by pressure. Except for when minimum drag is considered, the pressure forces are by far the most important and completely responsible for the production of lift”. (NOTE: I know the reference to “minimum drag” creates a question; I’m researching that and will post an answer here once I have it.) It then goes on to discuss the generation of the force equations associated with deflecting a small packet of air using Newton’s Second Law (F=ma) to calculate the force produced. After showing you the answer, it states: “An airfoil..produces lift by changing the momentum of a given stream tube of air and is capable of producing a force greater than that predicted by the use of simple energy solutions.” In other words, an airfoil produces more force than can be attributed to this simple calculation (F=ma) alone.

So, the blind use of Newton’s second law doesn’t account for the total amount of force generated by an airfoil (or a wing). Notice, too, this analytical approach uses a “microscopic” viewpoint to derive the equations, a common practice when starting at the bottom of an engineering or scientific analysis. How can you figure out what the lift is practically? By stepping back and examining the pressure distributions around the airfoil and calculating the forces they generate. This is easily done, which is why it’s routinely used. (This is using Bernoulli’s principle, folks.)

Have we disregarded Newton’s laws? Not at all! And in doing so, we have generated Bernoulli’s principle, which gives us a more practical and easier to understand approach to working with many aerodynamic problems. Not only does its use make engineering solutions easier, but using Bernoulli’s principle makes for an accurate and easier to understand explanation for the layman. How Newton’s laws apply to aerodynamics is not intuitive; and as we’ve already discussed, often leads to misperceptions, especially when understanding of the subject is incomplete. It’s easy to jump to incorrect conclusions based on what we are familiar with, and most people seem to latch onto Newton’s Third Law, which we see in common thrust/acceleration relationships. Because of that, it jumps into the forefront of thought much more than Newton’s first (i.e., an object at rest tends to stay at rest or continue moving until acted on by an outside force) or second (F=ma).

There’s a more important reason to talk about Bernoulli’s principles when teaching aerodynamics to pilots. When I use Bernoulli’s to explain what’s happening with lift, I not only stick to a technically accurate explanation; but I continue to make a linkage back to airflow around the wing, which for a pilot is the critical thing to control. It’s easy to see the case surrounding controlling the angle of attack to keep from disrupting the airflow controlling the lift. If you try to explain how a wing works using Newton’s Third Law, you will probably think the wing creates a downward jet of air as our wayward pilot did. It does in the form of downwash around a wing but its primary effect on lift is to create induced drag by canting the lift vector rearward and decrease the effective lift the wing produces; to use Newton’s Law second and third laws to find the lift you have to calculate the TOTAL change in momentum of the flow field around the aircraft (and not all of that is going to be in the vertical plane). Want to teach that in your pilot information classes? Better be ready for calculus and lots and lots of work!) If you have a pilot thinking he can create more lift by increasing the wing’s “upward” reaction, you also just created the potential for having a pilot INCREASE back pressure when he encounters a stall to increase the downward force of the “jet” or create “impact lift” (if you teach that concept, too). Poo-poo that possibility if you want; but you can never predict how someone with the wrong idea will react or when you plant the wrong information on their head. I believe it’s a very bad idea to teach anything that is technically incorrect or that can be easily misconstrued into a bad result.

So, the next time you hear that only Newton’s laws apply to aerodynamics and Bernoulli’s don’t, hopefully you’ll understand there’s no way that can be true. Explain that Bernoulli’s equations COME FROM an analysis of the behavior of an airstream using Newton’s laws (Newton’s second, mainly), and you CAN’T DISCOUNT ONE WITHOUT DISCOUNTING THE OTHER. In fact, trying to make the case that “only” Newton’s laws apply can only be correctly understood by PERFORMING a very in depth technical analysis as I have discussed; and that makes understanding the subject harder, not easier. As Einstein said: “Make things as simple as possible. not simpler.”

Because when you take it past that point, you make it wrong.