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  #1  
Old 06-04-2021, 03:06 PM
PhatRV PhatRV is offline
 
Join Date: Mar 2018
Location: Buena Park, California
Posts: 607
Default Impossible Turn (RV4)

AOPA just released a new video showing a variety of real world testing using the SuperCub, C172, RV4, and the Bonanza, performing the "impossible turn" using a variety of altitudes when the engines failed.

What surprise me is the RV4 failed to make the turn-back 1 out of 3. I had assumed the RV4 excellent climb rate is advantageous for this kind of maneuver. The C172, despite its low climb rate, made it back from all altitudes, as low as 600 ft.

Link to the video:
https://www.youtube.com/watch?v=dFVFKq3QqXo

RV4 in the video:
https://youtu.be/dFVFKq3QqXo?t=290
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Last edited by PhatRV : 06-04-2021 at 03:08 PM.
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  #2  
Old 06-04-2021, 03:28 PM
BobTurner BobTurner is online now
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,859
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As the narrator said, about the Bonanza (but also somewhat true for the RV), the issue is a relatively (compared to the cub and 172) higher best glide speed. The higher Vglide means a larger radius turn, so more distance to be covered to return. Note the test was done from various altitudes, not various times since lift off. If done, say, 30 seconds after lift off, the RV would have an advantage since it would be higher than the others.
As an aside, I think it would have done better if a steeper bank had been used. This needs to be done carefully, as you are pushing closer to an accelerated stall, but I think best results are obtained by banking the plane until the AOA starts beeping. Iím pretty sure that with the cub, I could hear the stall horn occasionally chirp in the turn.
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  #3  
Old 06-04-2021, 03:43 PM
swjohnsey swjohnsey is offline
 
Join Date: Nov 2018
Location: Kingsville, TX
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Yep, a steeper bank angle! I practice the turnback about once a week from 600' AGL, wait five seconds, keep 90 mph and a 45 degree bank, prop to low rpm. I make it back easily in RV-4. 600' AGL usually catches me ready to turn crosswind at around 110 - 120 mph flaps up.
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  #4  
Old 06-04-2021, 03:44 PM
PhatRV PhatRV is offline
 
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Location: Buena Park, California
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I think the test was preformed from the takeoff to the turn back altitude. With the anemic climb rate of 172, it would be located far away from the runway at a specific altitude where as the RV4 with a much higher climb rate, would be closer to the airport when compare to the 172. But the video also mentioned of the RV4 constant speed propeller slowing it down during the glide.
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RV8 standard build: Empennage 99% completed
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Firewall Forward -- Cowl completed. Baffle 90%
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  #5  
Old 06-04-2021, 03:45 PM
wawrzynskivp wawrzynskivp is offline
 
Join Date: Feb 2018
Location: Incline Village Nv
Posts: 92
Default AoB

Nice posting!

It didn't look like a solid 45 degrees in the video.

I have procrastinated these tests in my RV-7 so I guess it's time to get them done.

Guidance I have heard from the chicken coop is 60 degrees for the AoB. I'll try that.

Last edited by wawrzynskivp : 06-04-2021 at 03:48 PM.
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  #6  
Old 06-04-2021, 03:52 PM
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donaziza donaziza is offline
 
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Location: Atlanta
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Really interesting. Here's my results---and I'm respectfully not pushing this on anybody, this is just me.
I regularly practice this about every 6 months. (Had originally done this at altitude of course, for obvious reasons) I have an 8. At my home airport, if one has an engine failure on T/O, there's absolutely no place to go, except into the side of buildings. Bummer. So I normally climb with my nose at about 18 to 20 degrees nose up. Then I pull the throttle, leave the nose there, count 1001, 1002, 1003, 1004 for the startle factor. Then of course, I push the nose down. I found that I can't go over 45* bank, or slower than 85 Kts indicated, or the plane starts rumbling meaning stall is right there. I'm also cranking out full flaps at the same time. Pulling my prop to full course pitch would help the glide ratio of course, but I'm afraid to try that so low, in case it doesn't come back. I found I can make it from 700' agl, but I've decided to not try it unless I have at least 1000'. (Fudge factor) Practice it both ways left and right. One other trick, at least at a non towered airport, is to take a 20 to 30 degree left or right cut right after takeoff for maybe 5 seconds, or whatever, the come back to runway heading. Then you're already sorta getting set up, so one doesn't necessarily have to make that full 270* turn to come back, if your engine does indeed fail.

If anyone has any better ideas, I'm all ears.

Last edited by donaziza : 06-04-2021 at 03:59 PM.
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  #7  
Old 06-04-2021, 03:55 PM
swjohnsey swjohnsey is offline
 
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Making your turn into any crosswind helps.
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  #8  
Old 06-04-2021, 05:25 PM
xblueh2o xblueh2o is offline
 
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I was giving a BFR in an RV-8 the other day and we tried this up at 4000AGL.
Long story short, 1000' is what it took.
Granted, we were right up near gross weight and up in altitude a little but it was probably a fair representation of the average capabilities.

Could we have got that number down had we done it multiple times? Absolutely.
The problem I see with that is if you do it 6 times one day and get the number down to say 600' then set that as your personal base line, you need to continually practice it so you can maintain the proficiency in what frankly can be a very dangerous maneuver when you have the bad day.

Don't misinterpret my intent. If you have figured out what your number is and practice it regularly then I think keeping the impossible turn in your back pocket as a viable option is a fine thing. If you do it once or just take somebody else's number and never practice it, please just aim for something soft and cheap that was between the wingtips when the engine gave up.
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  #9  
Old 06-04-2021, 05:33 PM
BobTurner BobTurner is online now
 
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Quote:
Originally Posted by donaziza View Post
...... I'm also cranking out full flaps at the same time. ...
I think you can do better with flaps retracted.
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  #10  
Old 06-04-2021, 05:34 PM
David Paule David Paule is offline
 
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It would be interesting to do a whole series of 360 degree turns at various bank angles and flap settings and speeds, to see what the lowest altitude loss is.

Dave
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