Here's a slightly different take on using an AoA, even a very simple device, as a reference for certain speeds, such as Best Glide and Best Endurance.
David F. Rogers is a PhD, ATP and
Professor of Aerospace Engineering (Emeritus) at the US Naval Academy in Annapolis, MD. Dave has been greatly helpful to us and our Alpha project. In late Dec 2011, on the Beech Owners' List, he was explaining that... "...there are three angles of attack that are independent of density altitude and weight. Those angles are:
1. Stall
2. Best glide
3. Minimum power required (minimum sink / maximum endurance)
"Fly the Airspeed for best glide and you will be at the best glide angle of attack.
"The Airspeed for minimum power required/minimum sink (L/Dmax) is 76% of best glide speed. Fly that Airspeed and you will be at the angle of attack for minimum power required."
Old Bob Siegfried (Bonanza owner, retired UAL 747 Captain) then asked: "... how do I know when I am at the proper speed? It seems to me that if we had a good Angle of Attack instrument [in our light aircraft], the rest would be easy..."
Marc interjects, from Canada:
"Doc Dave was agreeing with you, Bob. He [was assuming that we already have an AoA installed and he] suggested that we ... fly the proper 'speed for the weight' airspeed for Best Glide and then record that AoA point; then do the same for Best Endurance. Once you have [found] the corresponding AoA, you would thereafter not need to know the weight and could just fly the AoA [target]."
... and Dave Rogers replied: "Exactly. This works because the angle of attack is independent of density altitude and weight. Do it once accurately, mark the [Glide, Endurance] angle of attack on the gauge and you are done.
"So ... If you have an angle of attack gauge ...
"
1. Look up the value in the POH for best glide speed. It will be given as an indicated or calibrated airspeed in the emergency section.
"2. Then get in the airplane and climb to some convenient altitude. Configure as the POH suggests, then establish best glide speed - use the value in the POH. I suggest using idle power in a glide.
"3. Mark the angle of attack gauge at whatever indication is displayed.
"4. That is the angle of attack for best glide at any weight and any altitude.
"5. That is all. You are done.
"If you want the angle of attack for L/Dmax (maximum endurance / minimum power required) then calculate that value as 0.76 times (best glide speed) and repeat Steps 2 & 3 above. That is the angle of attack for maximum endurance / minimum power required at any weight and any altitude."
in which, according to Bernard (Bud) Carson, another engineer at the USNA, the maximum duration speed is calculated as V-L/Dmax (best glide speed) divided by 1.316. So: 1/1.316 is 0.76 or 76%V-L/Dmax. He also defines a faster Optimum Cruising Speed ("Carson's Speed") in terms of the maximum speed per gallon as being V-L/Dmax times 1.316.
Walter from Germany suggests: "... assuming a Fuel Flow instrument is connected to a GPS and shows NM/Gal, and also assuming a no-wind day...then
play with the power to achieve a maximized NM/Gal. That will be equivalent to a Max L/D for that given weight. Then read the AoA indication; it then becomes a valid L/Dmax AoA point for all weights.". Bingo! It avoids the math, but it works!
John Collins concludes:
"...if best glide speed is 105 Kts, then max. range speed is 105 Kts,
and maximum duration speed is 105Kts X .76 = 80 Kts,
and optimum fuel flow/knot speed (Carson's Speed) is 138 Kts..."
Interesting discussion, isn't it? It is a privilege to know that these men are my friends.
NEVER FORGET that a AoA Display will NOT improve any aircraft's performance, not even a little bit! But an AoA will provide sufficient additional information to give the pilot confidence to operate safely closer to the airplane’s limits…and the AoA will enable a pilot to extract all--or, at least: far more of--the airplane's available performance. An AoA can definitely make a good pilot better and enable him to fly more precisely.
Disclaimer: The information provided in this website and AoA/Aircraft portion is provided free of charge. All information provided on this web site is provided 'AS IS'. No guarantee is provided for the accuracy of the information or the application of the information provided herein. I accept no responsibility or liability with regards to the accuracy or currency of the information provided. By using, reading or accessing this web site, you agree to be the user of the information provided. The user accepts full responsibility for all information provided. Although I try to keep the information on this site as accurate as possible, there is no guarantee that the reference materials or the material on this site is correct. This information is provided entirely in the spirit of helpful cooperation.
Incidentally, here's a summary of regulatory guidance clearly indicating that installation of an independent secondary advisory AoA like the "Legacy" is a "minor alteration" on the vast majority of light general aviation aircraft and here is a list of all the AoA manufacturers that I'm aware of.
Newly-published magazine articles, Spring & Summer 2011
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