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tail stall?

DEWATSON

Well Known Member
I've been flying my RV8 for almost 400 hours. I have done acro quite a bit in those 400 hours, but never with a passenger. A friend with acro ability and I put on our chutes today and he flew from the front seat. I have done several hundred split ess maneuvers by myself. He pulled up to slow to 80mph and rolled right to inverted and started the down side allowing the speed to build. There was a violent shake and some strange noise from the tail. Scared me....never happened before. We talked about what happened for a minute and then I did the maneuver to the opposite side. The same thing happened. Scared me again. We landed and took a real good look at the airplane....mainly the tail. Everything was tight and normal. Was the tail stalling because of the aft CG?
 
Probably boundary layer separation on the tail. It also happens when doing loops at too high of a gross weight and too many Gs pulled. Lighten the plane up and reduce the g loading.
 
Not Tail Stall

In an -8 with mid to aft CG (i.e. passenger in the back) it is very unlikely that you were experiencing tail stall in a split S. More than likely, the pull over was a little too brisk for 80 mph and you were experiencing some accelerated tail-buffet from the wing root boundary layer separation characteristic of the -8 due to the landing gear intersection at the wing root leading edge.

Skylor (lots of acro in the -8)
 
In an -8 with mid to aft CG (i.e. passenger in the back) it is very unlikely that you were experiencing tail stall...........

Concur. Tail stall is a very specific aerodynamic term. It is highly unusual, and normally unrecoverable. Barnaby Wainfan did an article on the subject in KitPlanes magazine a while back. If I can find a link or reference, I will post it.

It made for interesting reading.

IIRC, the gist of the issue is: the tail is providing "Lift" in a downward direction at all times. If the tail stalls, the plane will pitch violently forward, which exacerbates the tail stall, and essentially renders recovery impossible. In the vast majority of aircraft, it is not possible to stall the tail before stalling the wing, which is a Good Thing.

Now, would a real aerodynamics expert take over please? I think I am in way over my head!! :rolleyes: Steve Smith????
 
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Two questions:

1) What was the GW?

2) Where was the CG?

I guess a roll intiated at 70 KNOTS (mph is for cars, knots is for airplanes... ;)) would result in a low speed entry.
If the CG and/or the GW where near the acro-limit, it would easily result in an accelerated stall if the pull when inverted was initiated too abruptly.

Do you recall or could estimate at what speed he started the pull?
 
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Shake

Happened to me during my phase one testing. Solo, CG slightly forward, don't remember the weight but probably around 1500 lbs.

The Wierd shake and funny noises made me decide, OK----I've done a split ess, don't need to do it again. Sign it off and continue the rest if the testing!
 
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shake and noise

I'm with you. No more acro with a passenger for me. Like I said in the original post.....I've probably done over 200 splits by myself and never had a problem. My RV 8 has never surprised me, but this rumbling and shaking really got my attention. I took it back up today and all was normal. Splits are really fun to me....no more with a passenger though. Thanks for all of the comments and answers.
 
Tail stall

What amazes me was after the first split S noise that scared you , you decided to do another ! I think I would have determined what the sound was on the ground after the first one .
Tom
 
probably several flight conditions apply.....?

........ If the tail stalls, the plane will pitch violently forward, which exacerbates the tail stall, and essentially renders recovery impossible. In the vast majority of aircraft, it is not possible to stall the tail before stalling the wing, which is a Good Thing.QUOTE]

my check pilot inadvertently did this in my -9a early in my 'training'.
Just pointing out it's possible.
I think we were nose high, full flap, full power straight ahead.
I almost went thru the canopy.:eek: not fun....but recovery was/did occur as soon as airflow was re-established.
 
disrupted flow

Hey Fellas:

The -8 has a known flow problem around the wing root that can shake the tail. This happens at high alpha conditions, kinda like what would happen if the CG were shifted aft and maneuvers were repeated in the normal single pilot manner.

Falcon Lead, Stu McCurdy, has some vanes attached to his fuse that stops this flow issue. Dunno where he got 'em, but it sounds like they might be a good addition the those using their -8s for aggressive (high G, or high alpha) maneuvering.

Thread drift, sort of:
IMHO, high alpha/low speed maneuvering is something we should all explore, with the proper mentor on board. These airplanes are capable of far more aggressive low speed maneuvering than many of us can imagine. Seems to me it's safer to KNOW about this capability then not...

BTW the -8 is not the only ship out there with this flow disruption issue!

Carry on!
Mark
 
This just sounds like a power on stall in an rv.

my check pilot inadvertently did this in my -9a early in my 'training'.
Just pointing out it's possible.
I think we were nose high, full flap, full power straight ahead.
I almost went thru the canopy.:eek: not fun....but recovery was/did occur as soon as airflow was re-established.
 
........ If the tail stalls, the plane will pitch violently forward, which exacerbates the tail stall, and essentially renders recovery impossible. In the vast majority of aircraft, it is not possible to stall the tail before stalling the wing, which is a Good Thing.QUOTE]

my check pilot inadvertently did this in my -9a early in my 'training'.
Just pointing out it's possible.
I think we were nose high, full flap, full power straight ahead.
I almost went thru the canopy.:eek: not fun....but recovery was/did occur as soon as airflow was re-established.
What you just described here is not a tail stall. You described the normal behavior of an airplane in a full power stall. The nose dipped violently forward because the only way the airplane could fly again after such an aggressive maneuver was to have the nose go down abruptly once the stall occurred.
 
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'Tail stall' sounds more sensational though. ;) ...and apparently can be used to describe simple buffeting of the tail from turbulence coming off the wing at high AOA, as well is the nose dropping from a normal stall. Next topic - 'tip stalls'. :)
 
strakes

Does anyone know where to get a pair of the fuselage strakes described here? I've seen them referenced here a couple of times.
 
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