Air Racer Airframe & Wing Stress clues...

[BuckyD]

We know that the- "Fly Fast-Turn Left" high-speed/high-G scenario of the World's-Fastest Motorsport, is really tough on both man & machine. Stop-action photography sometimes reveals tell-tale hints of the stress effects on the airplane that appear on exterior surfaces (-Today's super digital photo resolution can really bring this into focus f/scrutiny & study).

Sliding canopies warping on their track rails; landing gear doors coming unseated; wing root fairings & access panels bulge & distort to make gaps; even aluminum skins 'oil-canning' over frame & rib interior structure. My old pal & photo guru- Neal Nurmi's (a.k.a.- 'Wingman') crisp & clear camera images brought out many instances of air race-induced aircraft form fatigue, which helped race crews address such issues when discovered in pictures. You can see why there's so much gap sealing w/aluminum tape going on, for drag reduction.

During my editing sessions of last year's Reno '09 shoot, I came across this particular example on Race #86's L/H wing's top surfaces, when the Yak was turning Outer 4 Pylon during Saturday's UNL Heat-3A...

DBD

[Stevo]

Re: Air Racer Airframe & Wing Stress clues...

[Leo]

Re: Air Racer Airframe & Wing Stress clues...

That is downright creepy.
If it was my plane I couldn't fly it again without opening it up for a look-see. I've seen a lot of flex in sailplanes but the glass structures never wrinkled!
Is that much movement in that small of a structure normal or is it slight movement exagerated by lighting?
Case in point, look at the skin just ahead of the wing on a B-52, wrinkled from the wing flexing (the joke used to be "Use preparation B-1 for removal of unsightly wrinkles").

[laminar]

Re: Air Racer Airframe & Wing Stress clues...

Yikes

[spacegrrrl]

Re: Air Racer Airframe & Wing Stress clues...

A number of airplanes exhibit "oil canning" of their wing skins but I have to say I'd be concerned as I expect the Yak is flying at speeds and loads way past what it was designed for.

Definitely an eye opener!

Michele

[Inverted]

Re: Air Racer Airframe & Wing Stress clues...

Ya there is nothing worse than looking out the side and seeing the wing of a metal airplane doing that under G load thats for sure.... Great shot!

[JET1]

did you hear that loud thud...?

...it was Sherm passing out!

[wolfee]

Re: Air Racer Airframe & Wing Stress clues...

I wonder is Sherm is even aware that his wing is oil canning like that.

Maybe he can pop in here and give us his point of view on it..


Awesome pics, and WOW scary at the same time.

[ignomini]

Re: Air Racer Airframe & Wing Stress clues...

Amazing shot. It would make me want to know more. Hope it's been passed on to the team.

[steve D]

Re: Air Racer Airframe & Wing Stress clues...

Great catch there Bucky! There's a well known photo(by whom I'm not sure) of Howards Bearcat with the wrinkled skin shown under perfect lighting conditions. During the rebuild years ago the wing skins were beefed up with thicker skins, about.080-.090 IIRC.
Also have you all seen the pics of the wing step being "pushed" down on the Sea Furys by the aerodynamics! Anybody familiar with Furys know that wing step has a strong spring to hold it up yet the airflow pushes it down!!
Amazing!!

[BaylesScott]

Re: Air Racer Airframe & Wing Stress clues...

Great Shot Bucky! Had to look twice at that picture.
Engineer would say "Bend, Don't Break." Like the T-tail on a Tomahawk(Traumahawk) Scarey to look at.

[Warbird5]

Re: Air Racer Airframe & Wing Stress clues...

Morning,

I'd be very concerned after seeing the close up of the wing section. Keep in mind that we are only seeing the top side of the wing in compression as it appears the wing is being loaded in an upward direction from the tip. The compression forces are being made visible at the section where the upper wing skin is not directly bonded to underlying supporting structure. Since the wing gets and maintains it strength from the intregity of the entire structure from the spar or spars. stringers, and external skins. It would be just as reviling to see the underside of the wing which is in tension.

If memory serves me there are some pictures of this aircraft's undersides taken last year that show lower skin wrinkling and stress being applied in the areas of the wing fuel tanks.

Loading of a wing in flight is normal and this stress and overload stress are factored in during the design process. I'm pretty sure the wing loading this aircraft is seeing around the pylons at Reno is way above what the original engineering planned for. My suggestion would be to open up the wing and due a detailed inspection to determine it's condition. Perform and engineering analysis to determine if the wing can continue to be operated in the racing enviroment with or without modification/repair.

Remember...Fly safe.

Willie

[BuckyD]

Re: Air Racer Airframe & Wing Stress clues...

Thanks for your comments & look forward to any additional input that's both objective & informative in nature on the subject.

Well, most of us 'plane people' understand the fact that aircraft wings like to flex a bit, whether flying in bumpy air or just taxiing & hitting a bump in the taxi surface. Everyday airplane passengers know it as well,-when they look out to observe from their window seat.

I believe this particular example of skin warping due to wing-flex under g-load, is located near where the outer wing panels attach to the Yak's rigid center section assembly.* The wing skin panels riveted onto the ribs appear to be buckling there. Probably not a good sign, w/repeated stress to the wing skins (including the lower skin which is stretching more during flex, as Willie pointed out) near what's known as a- 'shear-point'. But then, I'm not an aeronautical engineer or expert on the subject of metallurgy either. (I'd like to think that I do know a little bit, having worked around seaplane airplane maintenance & restoration up here in Ketchikan, Alaska for almost 20 years now.). *Note: Yak-11 doesn't have a wing ctr-section as I erroneously-noted. See post #23 of this thread f/Chris UK's correct description of wing construction notes f/the Yak-11 aircraft. Thanks, Chris! DBD

Anyway, you can see skin stress examples on the airframe & wings of other Unlimiteds in photos (as Michele & SteveD noted), especially on sunny days,-when there's alot of highlighting running along the skin surfaces of the race planes. Look at your shots & you'll notice it.

The plane owners & crews are probably aware, but ya never know, as things aren't so obvious on the ground or from far off vantages. Just thought it was interesting enough to pass along in a thread post. Hopefully others will come forth and add their two cents or post other similar-type photos.

During Sat. UNL HT-3A (when the posted photos were taken)- Race #86 Czech Mate was averaging just over 460-mph (w/o the 12-sec. pylon cut penalty factored-in; #7 Strega was averaging just under 496-mph w/o the cut penalty). Decided to check my photos of Race #86 during the following day's Sunday UNL Gold Championship final for some comparison views of what the same wing was doing in Czech Mate's next race.

Here's a couple more photos in sequence from the '09 Gold Race (again, w/enlarged detail views). For the 8-lap Gold Race, #86's average speed for a 3rd-place finish was 464.312-mph (to Strega's blistering 1st-place 491.822-mph!). Sherm was going a little bit faster than he was during Sat. HT-3A, but not a whole lot. These Gold Race photos were taken from the same vantage (Outer 4 Pylon), same time of day & under similar lighting conditions, w/#86 turning in a similar bank angle.

You can readily see that the LH skin location in question, shows much-less warpage, than evidenced in the previous HT-3A photo. One point worth noting- both sets of photos were taken a few laps into each race, when wake turbulences are churning up along the UNL racecourse flight path. There's a good possibility that Race #86 hit a good chunk of rough air while passing Outer 4 in HT-3A, at the precise moment the photo was shot, w/the wings getting some serious flexing right then. Czech Mate's turning bank angle certainly wasn't that extreme, but she's running much faster than ever before, hauling a big & mighty R-2800 around the race patch, aboard those short & thin orig. Yakolev-design wings...

DBD

[stuntflyr]

Re: Air Racer Airframe & Wing Stress clues...

The top skin is unloaded in these pictures, all of the stresses of consequence are being taken up by the tensile load of the bottom skins and of course the spar. There is very little to be afraid of by seeing these wrinkles.

Along with the apparent misplaced concern of the language of sheet metal wrinkles in flight, there seems to be an incredible misunderstanding about air speed.

These airplanes operate in flight by indicated air speed, or IAS. Groundspeed doesn't mean much except to the clock and the record books, in flight the IAS is what is going over the wings. The typical really fast speed for an unlimited racer is about 390 to 410 knots indicated air speed, or IAS. That is about 450 to 490 mph on the course using the stopwatch. When Dago Red was going 511 around the pylons, or Strega and Voodoo were going down the straight at 540, the indicated airspeed was well below the 505 redline of the P-51, or just a little bit over that for the Bearcat and Yak stock plane airspeed limits.

Chris...

[John]

Re: Air Racer Airframe & Wing Stress clues...

Bucky, is that the location of the Gun bay(s) on that model of Yak?

One has to root for the little Yak to win Gold someday!

Sherm S. mentions on an AirRace.org Podcast that they plan on more mods to the cowling as the spinner to cowling gap is more than needed.

It could do 480+ mph laps someday!