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Great question: quite a bit, actually. We did engine-off testing at altitude to determine the amount of residual thrust the fixed pitch propeller provides in the test airplane. We determined that actual glide angle with the prop windmilling and engine off was within a couple of tenths of a degree of glide angle with the engine IDLE and flaps 40 set; so we use flaps 40 during low altitude testing to simulate actual engine off glide performance. This is a light-weight Catto prop. With the engine off, it will windmill at L/Dmax (maximum range glide) but will naturally stop ONSPEED (maximum endurance glide). Previous CAFE testing determined that the pilot should make no effort to intentionally try to stop the prop below 3000's AGL. With a light weight, fixed pitch prop, physics takes care of it--different story with a metal constant speed propeller. If you still have control over RPM after engine failure, drag is substantially reduced at LOW RPM (i.e., pull the prop control all the way aft to reduce drag and improve glide performance).

Max, 45 degree banked gliding turn performance. 45 degrees of bank is optimum for a "turn back" maneuver following power loss on the takeoff. We are working on validating the glide performance modeling in the TLAR app. Part of the debate is airspeed reference vs AOA reference. Most airplanes don't have an AOA system, so we are looking at the difference in turn performance "on the buffet" (i.e., maximum instantaneous turn, which occurs at the aerodynamic [stall] limit), essentially Vref, not slower than stall warning; and ONSPEED (maximum sustained turn). Pilots brave enough to fly without AOA have a harder tactical problem when trying to "max perform" the airplane with a windscreen full of trees...there isn't any direct feed back of how hard the wing is working, save for any aerodynamic (buffet) cues and stall warning (if equipped), since that is, in fact, the only real AOA cue they have available. 🤔

That's great! A big part of our mission is education, and it's always nice to hear from folks in the field.

Ground effect in aerodynamics is the effect the wings have with a nearby fixed object. In this case the ground. The air being pushed under the wings against the ground causes the plane to rise. This can be dangerous when it occurs before climbing speed is reached, as nosing up will cause the plane to fall back down. In this video it appears the lighter tail end of the plane was pushed up, but the front end was not.

Close, the first part of the reply above is correct. The purpose of the demo is to show how AOA momentarily increases as you climb out of ground effect. It makes true back-country pilots cringe when they see folks like me "raise the tail" during takeoff, since the airplane has conventional gear (a tail wheel); but the part to pay attention to is the change in actual angle of attack just after rotation/lift-off. In ground effect, critical angle of attack (the angle at which the airplane stalls) is lower. Ground effect occurs within about a half wingspan of the ground, in this case about 12 feet (the RV-4 has a 24 foot wing span). My AOA system uses two pressures to compute angle of attack. One of them is dynamic pressure, the same pressure that is used to measure airspeed. I rotate at an angle of attack condition referred to as "on speed." It's the AOA used for best angle climb and is equal to 1.73 L/Dmax AOA. In video, an on speed condition is a steady tone, green "doughnut" lit in the AOA visual display (indexer), and 60% lift. % lift is the ratio of actual coefficient of lift to maximum coefficient of lift (stall). Notice that just after lift-off, AOA momentarily increases, so I make a slight pitch adjustment (nose down) to compensate. Thanks for asking, and @statboy, thanks for helping to answer. Fly safe, Vac

Hi Dale! Poor wording, I meant "what is the effect of sideslip on the accuracy of the AOA [solution]." The only wind tunnel testing was conducted by Dr Rogers using a different type of commercial probe a while back; so we are testing in the wild. Unfortunately, it's tough to have an accurate reference system to compare against since our GNSS/INS solution isn't valid under those conditions and the air data boom is suspect. Ultimately, we'll have to go back to the wind tunnel. However, the important thing to notice is that a properly calibrated coefficient of pressure system still accurately captures the stall, even when I'm generating maximum yaw.

Good to know it works at maximum yaw! Any news on V4?

Yes it is. Sorry for the delayed reply.

Max, good observation. I had Lenny dial it back a bit to suit me. Don’t know how practical it is to make it user adjustable.

Ouch--I apologize for the delayed reply! You can find contact information on our web site at FlyONSPEED.org.

Hi Jacob, it's a Van's RV-4. Cheers, Vac

@mikevaccaro1248 very nice! Brilliant aircraft!

Thank you! Not as sporty as it looks--the key is an accurate AOA system with good performance cues...if I know when I'm at L/Dmax and on speed, I can takeoff, climb, maneuver and land with more situational awareness than I can by using airspeed. AOA responds immediately to G inputs, and provides precise "stall margin" information...I'm not smart enough to do the cockpit math real-time to adjust indicated stall speed, and our -4's provide limited buffet cues. 'Course our system uses the pitot tube, so it won't compensate for leaving a cover in place. Good thing I'VE never done that ;)

@@mikevaccaro1248 Yeah well said..! I still take a beating every time I admit my "foul up "...! Cheers...!

Hey Max, Great question. Just trying to baseline Flaps 0 so we can run a transient response analysis on the IMU-based calibration for now...engineering in progress :)