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-   -   24-turn Spin RV-7. 47-turn Spin RV-8 (https://vansairforce.net/community/showthread.php?t=181549)

Tandem46 04-18-2020 04:20 PM

24-turn Spin RV-7. 47-turn Spin RV-8
 
Nothing new here, just consolidating these two impressive videos because I can never find them in normal searches. Interestingly, the RV-7 takes 5 turns to recover in this video.

RV-7 24-turn Spin
https://m.youtube.com/watch?v=mPsSJhM8xDk&noapp=1

RV-8 47-turn Spin
http://www.spatscheck.com/oliver/Spin.mp4

Snowflake 04-19-2020 10:24 AM

Also interesting is the prop that doesn't automatically start windmilling once gliding speed is achieved. Looks like it only took a slight dive to get enough additional airspeed to start it moving again, but if you held it at your glide speed it would stay stopped (or maybe flick over slowly as his did).

The annotations on the RV-8 video were useful as well... Looks like ~10000' for 47 turns, or about 4.7 turns per 1000' loss in altitude on average. Recovery was in about 2 turns on the RV-8, as opposed to 5 on the RV-7. Does anyone see why?

Marabou 04-19-2020 11:39 AM

Quote:

Originally Posted by Snowflake (Post 1423586)
Also interesting is the prop that doesn't automatically start windmilling once gliding speed is achieved. Looks like it only took a slight dive to get enough additional airspeed to start it moving again, but if you held it at your glide speed it would stay stopped (or maybe flick over slowly as his did).

The annotations on the RV-8 video were useful as well... Looks like ~10000' for 47 turns, or about 4.7 turns per 1000' loss in altitude on average. Recovery was in about 2 turns on the RV-8, as opposed to 5 on the RV-7. Does anyone see why?


Prop stops while spinning but it doesn't want to stay stopped at best glide speed. I kept it stopped intentionally and to do so I had to fly slowly. I mean about 75 knots top. A bit faster and it starts windmilling. I have fixed prop. May be CS behaves differently. Friend of mine intentionally stopped engine above airport and landed this way. Prop stopped first time already at roll out. He flies 7 taildragger with CS prop.

DeeCee 57 04-19-2020 12:17 PM

Quote:

Does anyone see why?
Guess multiple factors. Size of the tail feathers, length of fuselage, pro or con aileron position, CoG, recovery inputs, and many more...

Thanks for the links Tandem :)

skylor 04-19-2020 01:05 PM

Quote:

Originally Posted by Snowflake (Post 1423586)
...
Recovery was in about 2 turns on the RV-8, as opposed to 5 on the RV-7. Does anyone see why?

On th -7 the elevator remained slightly up or neutral for about 3 turns after opposite rudder was applied. Once elevator was deflected downward, the recovery was fairly quick.

Skylor

jrs14855 04-19-2020 02:47 PM

Spin
 
It is very important that full opposite rudder be applied followed immediately with elevator at least slightly down or significantly down as required by the individual airplane. I thought the 7 might have had a bit of out spin aileron but can not tell for sure due to the viewing angle. In high performance aerobatic airplanes recovery from a fully developed upright flat spin is almost immediate if one simply applies opposite rudder and simultaneously puts the stick in the opposite corner. Full power throughout. In the Pitts S2B and many of the monoplanes the spin stops in about 1/8 turn. I have no spin experience. In RV but would absolutely not recommend this technique in RV. The failure to apply proper elevator control and neutral aileron is typical of spin recovery mistakes. Many years ago two very experienced pilots spun a Pitts S2A into the ground. Intentional power off upright spin, would not recover because the stick was not far enough forward. Just before impact full power was applied, the spin flattened out. They both walked away.

gmcjetpilot 04-19-2020 08:36 PM

When the RV-7 kit came out around 2001-2002, Van had a test pilot do a flight test program. Before that Van did all the testing of previous models. I flew with Van once, he is a good stick. I caught one of his aerobatic routines at Arlington Airshow once. The result of RV-7 spin testing was RUDDER was increased in size. I recall recovery was 4-5 turns to recover with the original smaller rudder. It recovered but took too many turns. This is some back issues of RVator.

The original first RV-7 empennage kits Van sold had smaller rudder. Van later sent out the larger rudder to the original kit buyers who asked for it free of charge. I am sure some folks stuck with the original rudder. It is not that it would not recover just it took longer. The RV-8 came out after the RV-7 and all RV-8 kits came with the wider rudder.

I can't tell if the this Red RV-7 has original smaller rudder. I took screen shots of both RV-7 and RV-8 from video and scaled them. It is hard to tell if a rudder chord is a a few inches wider with this method, but it looks like the RV-7 rudder might have less chord than the RV-8 rudder.


PS the Piper Tomahawk I once had a partnership in was certified in utility category and approved for spins. I spun it a few times but only a three turns. It had a reputation of winding up and getting faster and steeper
https://www.youtube.com/watch?v=xzFgqtPVCZ0

RV8JD 04-19-2020 10:35 PM

Quote:

Originally Posted by gmcjetpilot (Post 1423721)
The original first RV-7 empennage kits Van sold had smaller rudder. Van later sent out the larger rudder to the original kit buyers who asked for it free of charge. I am sure some folks stuck with the original rudder. It is not that it would not recover just it took longer. The RV-8 came out after the RV-7 and all RV-8 kits came with the wider rudder.

Some of the above is not correct. The larger rudder that Van's adopted for the RV-7 to improve its spin characteristics was the RV-9 rudder. The RV-8 has a different rudder altogether. The RV-8 rudder is smaller than the RV-7/-9 rudder and has thicker skins (0.020" vs 0.016").

Here is the story on the RV-7's rudder change from Van's.

Below is a pic of an RV-8 rudder (on the left) next to an RV-7/-9 rudder (on the right):



Also, the RV-8 (first flew in 1995) came before the RV-7 (2001). When the RV-7 came out, the push for more common wings parts between the -8 and the -7 lead to the RV-8's 'Dash One' wing, which allowed for an increase in the Max Aerobatic Gross Weight of the -8, from 1,550 pounds to 1,600 pounds.

BillL 04-20-2020 07:41 AM

Quote:

Originally Posted by RV8JD (Post 1423742)
The RV-8 has a different rudder altogether. The RV-8 rudder is smaller than the RV-7/-9 rudder and has thicker skins (0.020" vs 0.016").

Below is a pic of an RV-8 rudder (on the left) next to an RV-7/-9 rudder (on the right)

Carl, I believe the 8 rudder (.020" skin folded TE) is the same as the final .020" skin 6 and the originally shipped 7 rudder.

If there is a dimension you believe is different between the 7 (short/original) a and 8 please post it and I will measure against mine hanging in the basement.

skylor 04-20-2020 08:59 AM

Rudder
 
Quote:

Originally Posted by BillL (Post 1423795)
Carl, I believe the 8 rudder (.020" skin folded TE) is the same as the final .020" skin 6 and the originally shipped 7 rudder.

If there is a dimension you believe is different between the 7 (short/original) a and 8 please post it and I will measure against mine hanging in the basement.

This is what I've always thought was the case as well. The -7 in the video appears to have the "early" rudder, based on the size and shape of the counterbalance.

EDIT: After seeing Marabou's later reply and watching the RV-7 video again, it's clear that this has the large (tall) counter-balance of the large -7 (AKA RV-9) rudder.

Skylor


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