Wing skin thickness

TTAero

TTAero

Member
BEAE7981-B242-4C31-9F0E-8A5302D13932.png Let me start with saying I am not trying to stir a pot in anyway. I respect the designer and what he has created.Home building is about learning and that’s all I am doing with this question. I saw this pic on Instagram of the 5 and noticed a lot of oil canning on the upper skin. Is this normal? Would a skin thickness change help? Has anyone done any mods other than the recent stiffener recommendation on a patrol wing? I flew a C-208b Caravan hauling 9 crew out to the canyon for 5 years and as far as I know maybe it’s 52’ wings looked like this too, I don’t know . I’m just curious of opinions and insight. Would increasing skins from .020 to .025 be worth the weight penalty to fix this ? I’m building a Patrol and thinking waaay ahead.


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Interesting photo. I am skinning my BH5 wings right now. Skin thickness are as follows. #1 - 0.032, #2, 3, & 4 are already 0.025. #5 & #6 skins are 0.020.
As the story goes those wings are QB wings. Wonder what is up because the location of the oil canning /dimpling is on #3 skin which should be 0.025
 
Yes that is normal.

It's not specific to Bearhawk's too. It just takes a combination of an external view and the light hitting the wings on a shallow angle.
 
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FYI - Bob has had us do a running change on the upper wing skin at the kit factory. The same kind of channel that runs span wise that Bob had us place in front of the main spar - we are now placing two channels running span wise aft of the main spar. At about 10 & 20 inches aft of the main spar. According to Bob - there are no structural issues as it was. Just a desire to clean up the airflow a little and theoretically maybe make another MPH or two. It does stiffen up that upper skin. Mark
 
Sadly of course a person jumping to conclusions posted a negative remark about that photo online, basically stating don’t fly in this airplane because of it.

Often it’s Pandora’s box to refute it with real information without opening a bigger can of worms so I just let it be. A few will sadly assume he was correct but more will ignore it.

pb
 
My partner in crime "wife" is a professional digital designer. So I showed this photo to her. She laughed & said I can make any photo to look however you want it to. You want the Bearhawk to look like an F18 it can be done. Seriously that is what she said.
Can we find out who took the photo?
 
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Interesting this topic came up. While fueling the other day I noticed some oil canning on my wings. Coulda been the lighting but I was going to take some pictures and compare them with pics I have from a while ago.

Lots of planes have oil canning in the wings while the plane is in flight but very few even notice because they can’t see it. I imagine all the span-wise stringers Cessna uses is to stop the oil canning.
 
Mark, will we be seeing that as a change notice soon? I’m just thinking ahead so I’m prepared to do all the upgrades when I start my wings this winter.
 
That is a picture that never should have been posted. Yes it is normal for aluminum skinned wings. Several years ago a similar picture made it into a magazine and at least one competing kit company used it as advertising against the Bearhawk.
 
I did a ton of research on EVERY high wing STOL-type/bush capable plane, no one had a wing as good and versatile as the Bearhawk wing.

Wing length-WIN
Wing cord-Win
Speed-Win
Stall-Win
I ordered a Bearhawk QB kit for a reason.
 
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I saw this and gave it some thought, can it be that the temps in the workshop when drilling the skins might differ from the temps when we eventually rivet the wing, lets say we went from winter to summer to complete the process of drilling, dimpling and eventually riveting, Body shops take dents out of cars by heating the area and then cooling the skin down with ice cold water. I use to straighten large structural steel beam by heating the longer side of the bended area and cooling it down. Maybe this process can sort this out and take the uneven stresses out of the skin.
 
Some finicky RV builders use electric blankets or other method to heat the wing skins while riveting, resulting in tighter skins at cooler temperatures.
 
rodsmith said:
That is a picture that never should have been posted. Yes it is normal for aluminum skinned wings. Several years ago a similar picture made it into a magazine and at least one competing kit company used it as advertising against the Bearhawk.
Click to expand...

That photo above is not bad. I have seen others which are much worse "aesthetically" oil canned. It is not a problem.
 
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I don’t dispute any of that. I love the Patrol and that’s why I’m building, but I’d just like it to be a little less lumpy in flight if possible.
 
Sir Newton said:
So what do guys think these stringers are going to look like?
I am literally skinning BH5 wings right now, so you can understand my interest in the subject matter of this photo.
Click to expand...

I think the stiffener will be fabricated like the stiffener used on the Patrol, that is found in a Patrol Engineering change dated February 2020. http://bearhawksafety.com/Patrol/february2020.html

From that document, it says you should make the skin stiffener channel and lay it on top of the nose ribs. The Patrol has only one that is 4 inches in front of the main spar web. I would place additional stiffeners to support the areas that show distortion in the photos. These Patrol channels are fabricated from .020 2024-T3 Aluminum, 3/4 inch wide with 5/16 inch flanges. Notch flanges of the stiffener 3/4 inch wide at ribs. Rivet to ribs and along channel to skin at approximately 1.5 inch rivet spacing with AN426AD3 or AN426A3 rivets. (those A rivets are soft and squeeze like butter.)
 
A very similar photo is in print in the August issue of Sport Aviation in the excellent article by jaredyates .
IMG_20210820_063300063.jpg
I noticed the oil canning and thought the light angle was unfortunate. A lot of wannabes read that magazine and will come to the conclusion that it looks silly or defective. Of course I don't believe it is but it may be perceived as such.
In the spirit of stirring the pot, because that's what we do on the internet, here's my "fix": add washout to the wing. Perhaps this would pre-stress the skin similarly to twisting cargo straps on a flatbed trailer.
There's no way I would attempt this without a redesign signed off by Bob.
 
Yes, I have friend who is a professional aircraft sheet metal mechanic. He also has a foot in custom building of light planes. He knows guys who build show planes. For cosmetic purposes they sometimes use halogen lights to heat up the metal prior to riveting. It “sucks” the skins tighter and flatter as they cool. Makes no difference to strength, he says.
 
Beware adding stiffeners where they are not needed. You may think it can't do any harm but it can transfer the load to a place where it's not meant to be taken.

There was a story (apocryphal or not) concerning (IIRC) the F18. They were having trouble with an aerial mount cracking on the VS. So they added a doubler. Then they found that the VS attach bracket was cracking so they beefed that up. Then .... etc etc :p
 
I agree with Paul, beware of adding stiffeners where not needed. In Post #13 I said "I would...." I should have left any recommendation out, and just described the stiffener that the Patrol now has as part of its design.
 
Good morning to the World Wide Bearhawk Aviation Forum. Chatting with the chief engineer on the project. He reminded me that if you have purchased plans for any Bearhawk Model. We always have an opportunity to buy another set of plans from Bearhawk for $35.00
Which in turn will show any updates that have been made. How awesome is that!
Personally I think BB is an excellent person. Just passing on the information.
 
Mark, is the change requiring 3 wing stiffeners (1 forward and 2 aft of the main spar) something I should be doing on my build? The plans I have dated 2020 just show the one stiffener forward of the main spar. Is there more current info on this? Thanks, Jason
 
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