Regarding "oilcanning"

[wingman]

There was some discussion last week of some of the things that happen to aircraft structures under stress. This shot was done at the 1985 Bakersfield Air Race held at Minter Field. It was done from home pylon, so the aircraft is not pulling Gs. My understanding is that there were some structural problems with the Bear's fuselage at that time, that were eventually dealt with. Note also that the landing gear door was open quite a bit. Despite all this and much more Lyle ran laps well in excess of 430 mph at near sea level. Quite something for that time...

Neal

[wingman]

Here's a more recent example. This was done from the "Valley of Speed" during qualifying at Reno 1991. Very distinct ripples can be seen from the wing back...

Neal

[AAFO_WSagar]

Neal, some of this (though not nearly as evident as in the first photo!) is still there on the airplane..



From what Bill Rogers said makes this happen on the Sea Fury, similar things might well happen on the Bearcat.. As the airplane goes faster, the tail has to push down harder to keep the nose up.. putting the top skin in tension, bottom skin in compression..

The above photo was at Vegas last year, I don't know what speed they were doing there but obviously, less than full race speed...

Wayne

[wingman]

And one more -- This time Reno 1992, from pylon 3, so the aircraft is under some G loading. This is during qualifying -- John running close to 490 mph just before torching a piston and maydaying. Along with the fuselage dimpling, note how much the engine torque is rotating the cowling...

Neal

[flynride]

Bear @PRS

The RARA close-up pics from home pylon at PRS show it too:

http://www.airrace.org/gallery/web/prs2003/112c3298.php

[AAFO_WSagar]

It's evident in the pix I took in April also and we were only doing something like 150kts..

Situation normal methinks..

Wayne

[bearfan1]

The more I see about this, the scaryier(sp) it seems to be to me. and now it seems that there are 2 forces at work, the engine torque and the elevator being forced down. Am I correct in thinking this ? Or is it still the result of one thing. I would imagine that there would be some form of fatigue that would occur having this happen over and over that would evidently lead to some form of failure. Can anyone elaborate on what was done to the Bear, early on, to attempt to cure this situation ?

Duane

[Leo]

Is this a function of actual structural stress or of the pressures at the wing/fus. joint? My old V-dub bus used to oil can along the sides just from the airflow above 70 (downhill) and made a hell of a racket.

Leo

[stuntflyr]

Aerodynamic structures have a certain amount of elasticity to keep them from fatigue and cracking. The oilcanning seen in the photos on this thread are the outside skin deformation from stress loads imposed by normal flight. The fuselages on these airplanes are a semi- monocoque structure and the flexing the skin shows is a reflection of a small amount of movement the underlying structure of longitudinal keel and stringers, plus vertical formers have displaced. The wings wrinkle like this too. If they didn't they would fatigue and fail. If the airplane has no wrinkles on the ground, it will in the air.
Normal flight is the G load range and airspeed range the airplanes flight envelope allows. For most of our racers it is a G and airspeed that is not exceeded all week.

[Randy Haskin]

Originally posted by AAFO_WSagar
It's evident in the pix I took in April also and we were only doing something like 150kts..

150?? Isn't that right close to the Bear's "across the fence" speed?? It's gotta be tough to keep good formation with that kind of slow speed.

(P.S....it is in the F-15 and the T-38!)

[AAFO_WSagar]

Originally posted by Randy Haskin


150?? Isn't that right close to the Bear's "across the fence" speed?? It's gotta be tough to keep good formation with that kind of slow speed.

(P.S....it is in the F-15 and the T-38!)

Randy,

Yep, that's what both "John's" said.. fast for the Seneca with the door off, darn slow for Penney in the Bear!

Formation work for the Bear, even in a T-6 is a challenge... apparantly, the airplane does not like to go slow!!

I believe at PRS, John was going to form with Mary Dilda and Scott Germain and the airplane started going auto rough when he slowed... After Friday's "attention getter".. John called off the flight.

Now talk to me about how fast 150 is with both doors off the Seneca in the middle of April, several thousand feet above the freezing level..

Wayne

[Randy Haskin]

Originally posted by AAFO_WSagar
Formation work for the Bear, even in a T-6 is a challenge... apparantly, the airplane does not like to go slow!!

Maneuverability is, of course, tied to airspeed, and with you're in the "negative P-sub-s" region (fighter pilot speak for the back side of the power curve), the airplane just doesn't respond as crisply to control inputs.

This is why many military fighters have a waiver to the FAA minimum speed limit of 250 knots below 10,000 feet: they just can't maneuver to avoid other aircraft as well at 250 as they can at 300 or 350.

I can only imagine how an aerodynamically slick airplane with small wings and control surfaces like De Bear flies in formation!

[AAFO_WSagar]

Originally posted by Randy Haskin
I can only imagine how an aerodynamically slick airplane with small wings and control surfaces like De Bear flies in formation!

Actually, I think Critical Mass has a tougher time of it.. Tom "stalled" off us twice at Grass Valley last year.. one second he's there.. the next, gone..

Even the Hughes Racer had trouble keeping with us in their Bonanza at 160 (unknown if kts or mph)

Jim Wright said at that speed, he was on and off the throttle from idle stop to some throttle constantly to not outrun us, and had to keep a bit of nose up attitude.. which we did not want for the photos..

John Penney seems to do OK with keeping in formo at that speed, I've not heard him talk much about that but the engine does not like running at that speed, apparantly, especially with race fuel in the airplane.

Just once, I'd love to just go along for the ride on an air to air and just watch.. it's fascinating when you put down the camera and watch for a second.. something I'm sure you're familiar with but even more so with no "glass" between you and the subject.

Did we find you a parking slot for your "hen" at R2K+3 yet???



Wayne

[wingman]

Structural deformation at speed is not confined to radials. This was taken at Phoenix 1995. There is major deformation of the reskinned ammunition bays, as well as what looks like a gap opening up at the left flap leading edge. I'm not sure whether this is actually "oilcanning" or not. I remember something like this turning up in my photos of Dago Red in 1982, and being told that in that case the wing was somehow being pressurized at high speed, causing the bays to bulge. At least I think that's what I remember from so long ago... Maybe I really have consumed too many recreational intoxicants over the years!!

Neal

[Mluvara]

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