Unleaded Avgas


enjoy your very good magazine quite a lot, but…I just read your editorial in November’s issue, “Bravo Foxtrot Delta,” as well as your reply in December’s UNICOM.

You discuss in both cases the added weight’s effects on unusable fuel for empty weight only. Clearly the bigger issue is the added weight’s effects on full-fuel takeoff weight and useful load. My 160-hp PA-28-161 Warrior II holds 50 gallons of fuel. Clearly, the new weight and balance (W&B) calculation for unleaded fuel will now add 12½ pounds to the fuel load.

For a modestly powered airplane, 12½ pounds is not negligible. It’s more than my flight bag and all the coats and emergency kit, and a lot more than all of the pencils, pens and detritus in the airplane. The sales person at the car dealer has a similar argument for explaining the extra four percent fee above MSRP (extra $2000 or more) as being negligible. Your article, after explaining that four percent is negligible, added that, in fact, yes, you do need to calculate a different W&B for the new fuel. Well, yes of course, because in fact it’s not negligible.

ForeFlight is updating their W&B for the new fuel. The STC I’m sure will discuss the weight delta, as well as the flight manual and all other materials. Even on the empty weight, the FAA defines negligible weight changes as under a pound, so not even there is the change negligible in your example.

I believe that nothing about this new fuel is negligible, including its price, since it will be a quintessential unregulated monopoly. I understand that avgas is somewhat that already, but this will be dramatically the purest form. It may present as modest initially, but AOPA’s Mark Baker has a saying about once you allow the camel to stick its nose in your tent….

In terms of less maintenance, I have never had spark plug fouling issues of any kind, ever. The plane starts and runs fine every time.  At every annual the plugs get pulled, cleaned, tested, inspected and rotated whether the pilot wants it or not. I don’t expect that routine to change at all with the new fuel. No, I don’t expect my annual costs to suddenly and dramatically decrease. That is fantasy. Same for oil changes. So the new fuel appears to solve maintenance issues that don’t appear to need a solution.

I did read somewhere I believe, that the new fuel does excel as a paint remover, so when you spill fuel all over the wing on your $26,000 paint job, yes, that could be an issue that might need a solution.

In summary, it would seem then that the new fuel will cost more—probably a lot more at some point—decrease useful load and may (if commentary is correct) damage the paint on your plane.

I understand the environmental issues, and they are real, and the current politics of supply in some states and the eventual metastasizing of those issues everywhere. We do need an unleaded fuel, and this is a start, but this offering has some warts, the complete market monopolization to the purest degree being a big one. These should be openly discussed.  

As mentioned, I do like your magazine and get a lot from its very good articles, but not on this subject. On this specific subject, your articles feel to me like a trip to the car dealer.

Tony Esteves – Via email

Thanks, Tony. We’ll have to agree to disagree on a few things. For example, you’re running your engine well if you have no spark plug fouling, but it’s a real thing for other operators.

Regarding the monopolistic aspects of GAMI’s G100UL avgas, several other companies have attempted to come up with an unleaded fuel meeting the industry’s goals of interoperability, distribution, etc., including one (not GAMI) whose solution proved to be the excellent paint remover you mentioned. None has achieved GAMI’s approval levels yet. And we’re guessing you won’t be impressed to learn the four percent weight increase is at least partially offset by there being more BTUs in a gallon of G100UL than 100LL.


Regarding Jim Wolper’s article in November’s issue, “Propeller Theory 101,” raising the tail during takeoff of the PA-16 Clipper required an application of right rudder properly timed and in proportion to how quickly the tail was lifted.  It took me a little time to sort through why reducing P-Factor required more right rudder to keep things going straight.

Harry Shannon – Bartow, Fla.


Jim Wolper’s article covered P-factor and its characteristics fairly well, however, slipstream and gyroscopic effects came up short. The spiraling slipstream is real. The propeller constantly provides a rotation to the air, which continues to rotate as it is pushed rearward by more rotating air, hence the corkscrew. One may observe this helix at times during another plane’s run-up or takeoff in dusty or snowy conditions. Consequently, any time the engine is producing power, spiraling slipstream exists, and it is the dominant airflow over the empennage in the initial takeoff phase until the airplane achieves enough airspeed to minimize its effect. A little right rudder, please.

Gyroscopic effect happens when a force is applied perpendicular to one edge of a rotating disc (gyro) and results in that force reacting perpendicular at 90 degrees in the direction of rotation. Consider the powered propeller as the rotating disc. Raising the tail of a taildragger is equivalent to applying a force (push) to the top of that rotating disc, which reacts 90 degrees clockwise as a force (push) on the right side of that disc, swinging the nose to the left. More right rudder!

Wolper’s example is really an example of torque, which also is propeller-related and deserves some understanding as well.

Frank L Miller – Ninilchik, Alaska


The article “Propeller Theory 101” (November 2022) states that “angle of attack is higher during climb.” This is true only if the airspeed is reduced in the climb, but that’s simply because reducing airspeed always requires a higher angle of attack. If airspeed remains constant, the angle of attack in the climb is practically the same as in level flight (see PHAK, Chapter 4, “Forces in Climbs”).

In fact, the angle of attack in the climb is marginally lower than in level flight because thrust is counteracting part of the aircraft’s weight. A detailed explanation is beyond the scope of a reader’s letter, but to aid intuition, consider the case of a high-powered aircraft in a vertical climb: Its angle of attack is zero.

I enjoy the insights I get from Aviation Safety every month: Keep up the good work!

Martin Brænne – Via email


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