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Sam M.
First Sergeant

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Posted Wednesday, July 7, 2010 @ 03:27 AM  

Hey Bob, can you elaborate on the Avalanche that you do?
Bob Grimstead
Captain

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Location: Perth, Western Australia or West Sussex, England
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Posted Wednesday, July 7, 2010 @ 08:02 AM  

This post, like all my aerobatic posts, is specifically aimed at American, Australian, Canadian, New Zealand and South African operators of Fournier RF4Ds on Experimental C of As. Pilots flying Fournier RF4Ds on EASA Permits to Fly or British or EASA Certificates of Airworthiness without specific approval to fly flick/snap rolls should first consult their Permit or C of A limitations or Owners Handook to ensure flick/snap rolls are allowed in their airplanes.

For information, and to assist other owners who might wish to get this arbitrary restriction removed, here is a letter from RenÚ Fournier himself on this topic:

[/URL]

Hi Sam,

You/we have to be very careful here, because the Avalanche incorporates a snap/flick roll, and these are not approved in some RF4s. They are allowable in my Australian one because it is certified Experimental Exhibition, and in my British one, which has an EASA Permit to Fly allowing my particular Fournier to fly flick/snap rolls. That is after all why RenÚ developed the RF4 from the RF3. Unfortunately different certification authorities view these things differently, despite the aeroplanes all having been built in the same factory to the same standards.

However, we do know (because we have film evidence) that RF4s and RF5s (but not RF5Bs) have been flick-rolled /snap-rolled safely for more than forty years.

After establishing that this manuver is legal in your airplane, make sure all your fin, stabilizer, elevator, wing, aileron and rudder attachments are secure, not only to one another, but also to the wood within the structure. DO NOT SKIP THIS STEP. Snaps may only register 3.2g or so, but they impose significant torsional stresses on the airframe.

Rene's test pilot Bernard Cheauvreau told us, "Never snap roll above 120kph" Work this out for yourself, but I seem to remember that 120 kph is around 65 knots or 75 mph BUT CHECK THIS VERY CAREFULLY FOR YOURSELF.

I tried many level snap rolls, starting at maybe ten knots slower and working upwards to that kick speed.

I found that the stick wants to move sideways in your hand, and that letting it do so improves the snap.

I found that if you 'unload' the snap stops immediately.

I found that if your nose is at all above the horizon the snap will stop before a 360-degree rotation.

I found it snaps better to the right than to the left (although it can sometimes be more reluctant to recover).

I found that, to initiate the snap, you need simultaneous full back stick, full right rudder and full right aileron.

I found that, to stop the snap, you need simultaneous full left rudder and nearly full forward, absolutely centered stick.

I found that sometimes, for no apparent reason, the snap will continue rotating into a full-blown spin and turn through another 180 to 360 degrees (with consequent height loss) before stopping. I don't know why, it doesn't often happen, but it's scary when it does. I suspect that it mostly happens when the stick is not dead central laterally during recovery

For the Avalanche I fly a tight loop from 130 mph, pulling quite hard all the way around, so that the nose is just coming down towards the horizon inverted as the speed gets to snapping speed. Then I hit the 'initiate' inputs at precisely that speed and no higher.

A second or so later, just before 270 degrees of rotation, I hit the 'recover' inputs.

This is not a proper Avalanche, because the snap is not symmetrically disposed around the top of the loop, but rather starts at the top and finishes in a vertical nose-down attitude 3/4 the way around the loop (and nearly stationary in the air). However, to fly a more symmetrical one I would need to snap at a higher airspeed, and that would be madness in a 43-year-old airframe.

That's all I can say Sam, except 'Don't do it'.

If your airplane flies apart, your folks, your buddies and lots of other people, myself included, would be horrified and appalled.

Take care, think very hard about this, and talk it through with your folks before trying an Avalanche.

Yours, Bob

[Edit by Bob Grimstead on Wednesday, October 5, 2016 @ 06:03 PM]

Sam M.
First Sergeant

Gender: Male
Location: Santa Paula, CA
Registered: Jul 2008
Status: Offline
Posts: 228

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Posted Tuesday, July 13, 2010 @ 03:55 AM  

I really appreciate you're reply Bob. Chances are i wont be attempting one. But In case I do i always enjoying reading you're description.

Sam

Jorgen
Captain

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Location: Lund, Sweden
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Posted Tuesday, July 13, 2010 @ 05:38 PM  

Hi Guys,
I have a confession to make: first time I tried a loop in the 4, I pulled too hard at the top; WhamBam- Voila; avalanche! Well, sort of....as I remeber I dished out badly since I quickly released back pressure. As they say: "-There I was, flat on my back..."

All went well (As the late Pete Goldin said "-It's one strong Airy!" but I haven┤t tried it consciously since. As Bob's description hints I think you have to work your way up to it methodically and feel confidently proficient in the aerobatic basics first.

May the 4's be with you/ J÷rgen

Sam M.
First Sergeant

Gender: Male
Location: Santa Paula, CA
Registered: Jul 2008
Status: Offline
Posts: 228

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Posted Monday, July 19, 2010 @ 01:05 AM  

Hey Bob, Did a few avalanches today, Worked out great. videos shortly. also did power at Idle level snap rolls from 70mph. came out 20 degress nose low but was very enjoyable. I used a different technique then the yank and stomp. I started skidding full left rudder and then brought the stick into the left corner after i had skidded a second or so. it broke cleaner then the normal technique.

-Sam

Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 1671

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Posted Saturday, July 24, 2010 @ 01:21 PM  

Hi Sam,

That's great. Well done.

Have you seen Bob Hart's composite footage of my Red Bull flying in May?

http://www.youtube.com/watch?v=pVHX0kJxGjU

It is very low resolution, but you can kinda see both my control inputs and the external result.

I will try your technique tomorrow, on my way to the Windermere display.
Washed out today, because I could not get over the hills because of low cloud and drizzle -- typical British summer weather!

Enjoy, but remember that 120kph maximum flick speed (and if you're doing them on a down-line, you want to be even slower for the kick).
And I use ten knots slower for the half-flick to the inverted, because that's all you need.

Have fun and stay safe.

Yours, Bob

Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 1671

Click here to see the profile for Bob Grimstead Visit http://www.redhawksduo.co.uk Send email to Bob Grimstead Send private message to Bob Grimstead Find more posts by Bob Grimstead Edit or delete this message Reply w/Quote
Posted Monday, June 9, 2014 @ 09:43 AM  

Further experimentation:

http://youtu.be/os_8oQiP_74

Bob

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