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  #1  
Old 08-06-2022, 07:52 AM
MacCool's Avatar
MacCool MacCool is offline
 
Join Date: Aug 2020
Location: central Minnesota
Posts: 1,339
Default Advanced Flight EFIS - flying the AoA calibration

In the most current AFS manual, the AoA calibration protocol for the 5400 EFIS in my RV-9A recommends hanging a tennis ball or something and flying a maneuver until it’s weightless, then hitting the “record” icon on the AoA calibration screen to save that zero-lift condition. Do that maneuver for both flaps up and flaps down.

How did y’all fly that zero-lift/weightless maneuver?
__________________
RV-9A, 2011, bought flying
IO-320D1A (factory new), C/S
Dual Pmags
IFR equipped
AFS 5400/3500, G5, IFD440 navigator,
bunch of other stuff
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  #2  
Old 08-06-2022, 09:03 AM
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Ironflight Ironflight is offline
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 13,229
Default

Generally, a Zero-G parabola is fun to do, but not easy to do precisely without practice. It is more challenging to do with a non-aerobatic airplane like your -9A, because you have pitch limits to observe as to not go into the aerobatics regime - 30 degrees up or down. You also have a fairly narrow range of speed between maneuvering and stall, or in the case of “flaps down”, the top of the white arc and stall. This means you’ll only have a few seconds to establish and hold Zero-G and push the button. (The parabola is much easier to fly in something like a KC-135 because the entry and exit speeds are much farther apart on the ASI, and you can get 30 seconds of zero-G….)

The parabola is a wings-level maneuver, so you only have to dive to the max speed you can get, then pull up at about 2 G’s to the maximum pitch you can use (45 degrees works well for aerobatics, but 30 is the non-aerobatic limit), then push over to establish Zero-G. Make sure you are at Zero with you tennis ball - all the dust flying up off the floor might mean you’ve gone negative - and push the button, then recover before you get too nose low, indicated by pitch or by airspeed getting too high. This can be REALLY challenging with flaps down because the top of the white arc comes up real fast when the nose is low!

There is an ideal power setting to use as well if you want perfect unaccelerated Zero-G flight, but you’re going to be so busy, and the time is so short, don’t worry too much about it. Just don’t overspeed the prop on the down line if you’re fixed pitch. You want has much energy as you can get just before pushing over - time at Zero-G is directly proportional to entry speed.

Sound complicated? Find someone with aerobatic experience to do this with you (or for you) the first few times. Of course, in a -9A, you aren’t going to be doing “legal” aerobatics, so you don’t need a ‘chute for each person on board….

Paul
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Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
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Last edited by Ironflight : 08-06-2022 at 10:04 AM.
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  #3  
Old 08-06-2022, 09:35 AM
622BH 622BH is offline
 
Join Date: Nov 2011
Location: Albany, OR
Posts: 241
Default Get someone

Paul described the maneuver (except for that "die" part - I think he meant dive) well.
My suggestion is get someone to ride along and do the button pushing. Luckily, I live near Van's and AFS. Rob Hickman flew with me and accomplished the calibration.
Find someone near you that's "been there" and have them help you.
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  #4  
Old 08-06-2022, 10:34 AM
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MacCool MacCool is offline
 
Join Date: Aug 2020
Location: central Minnesota
Posts: 1,339
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Thanks to both of you. Not knowing how the 5400 uses the weightless maneuver for the AoA calculations, it seemed logical to assume that stalling the airplane was the “zero lift” point and push the button at full stall. I had a buddy along and he pushed the button, but I noted that the “tennis-ball-on-a-string” didn’t actually float, making me suspicious of my assumptions. Parabola it is then.
__________________
RV-9A, 2011, bought flying
IO-320D1A (factory new), C/S
Dual Pmags
IFR equipped
AFS 5400/3500, G5, IFD440 navigator,
bunch of other stuff

Last edited by MacCool : 08-06-2022 at 10:38 AM.
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  #5  
Old 08-06-2022, 10:57 AM
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MacCool MacCool is offline
 
Join Date: Aug 2020
Location: central Minnesota
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I just found a video that amplifies the technique a bit. Helpful. Obviously I didn’t go far enough into weightlessness. It does look like flap overspeed is potential issue.

https://www.youtube.com/watch?v=6AcYi3v_qmk
__________________
RV-9A, 2011, bought flying
IO-320D1A (factory new), C/S
Dual Pmags
IFR equipped
AFS 5400/3500, G5, IFD440 navigator,
bunch of other stuff

Last edited by MacCool : 08-06-2022 at 03:29 PM.
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  #6  
Old 08-06-2022, 08:29 PM
622BH 622BH is offline
 
Join Date: Nov 2011
Location: Albany, OR
Posts: 241
Default Zero Lift vs Airspeed

The calibration can be accomplished without exceeding Vfe or stall speed. Since zero lift is not airspeed dependent, you can perform the parabola between those two speeds 1) with flaps up, 2) with flaps down.
To the uninitiated, aggressively pushing over to achieve zero lift can be a bit disquieting. But it can be done in a relatively short period of time - if the button pusher is ready for it.
Go out and try flying along at say 75 Kts, pull the nose up and bleed off about 5 Kts, push the nose over aggressively until your shoulders are pressing against the straps. You'll see it doesn't take you anywhere near exceeding Vfe and you won't stall the plane either. And, it can all be done in about one minute.
Once you got the idea of "pushing over" you can take up the "button pusher" and get the calibration done.
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