Bearhawk Patrol Update - February 2020

[jaredyates]

Bob has issued an Engineering Change for the Patrol only:

http://bearhawksafety.com/Patrol/february2020.html

This update relates to a wing skin stiffener, to be applied to new construction going forward.

For technical questions about this update, please contact Bob at 540-473-3661.

[sjt]

channel.jpg
stiffener channel stiffener is .020 2024-T3 Aluminum, 3/4 inch wide with 5/16 inch flanges.

Is this correct?

[Chewie]

That's my understanding. I figure 134.75 inches between the centers of each end rib. If two sheets of .020 skin fit on a 4x12 there will be margin material available to make these.
Regarding 4" in front of the spar web... I would have to look at the existing flutes on the nose ribs and just find the closest rivet.

Was this in response to a single occurrence, or is it a known issue with every Patrol flying?

[sjt]

skinsheets2.jpg 020 material of this length is possible if wing skin sheets are cut long ways first
trailing edge was cut from 025 sheet used for ribs and is not shown.

[Chewie]

Nice graphic! You're making your tip ribs from .032?

[sjt]

The 032 is for the root. For some reason I numbered the sheets from right to left. I guess the small color differences wash out in the picture. The color was meant to show what goes where.

[Chewie]

No it's not the color, it shows up great. I just see two full-size outlines on the .032 sheet. Just happened to notice it, made me double check what I made mine out of!

[Mark Goldberg]

A little background on this engineering running change. It is non mandatory and not a safety issue. In some pictures taken from above a flying Patrol, some oil canning of the nose rib skin was noted. This is not structural but aerodynamic. Bob feels like this oil canning is slowing down the Patrol by some small amount of MPH.. Bob also has seen the same nose rib skin oil can as it sits on the ground in the heat of the day with the red paint (on Bob's Patrol) getting hotter than the white rest of the wing. This skin stiffener will cure it.

For those of you flying your Patrols - I would not worry about it. My new Patrol will not get anything done to it. If you have a set of wings from the kit factory (with the nose rib skin already closed up) - it is possible to bond in (not rivet) a skin stiffener in the place Bob calls for. One in each bay - not a long piece as Bob shows for new construction. In the bays on both sides of where the wing strut attaches where you have access.

Bob and I have discussed how this might be done on our existing kit wings, and if builders are interested I can detail how to do it. Mark

[Pbruce]

I will be starting on my QB wings soon and would like details on how to accomplish this. Thanks. I will watch this forum for details and I will contact you directly if I get to close-out before you have published them.

[geraldmorrissey]

Wondering how this .020 lump is going to look on an otherwise smooth leading edge. It might fair out but I'm somwhat concerned.
Gerry
Patrol #30

[Mark Goldberg]

At the factory we tested this and found it invisible. The only thing is to not place rivets close to where the "transition" is. We had seen something similar many years ago when we used to place an .032 "shim" on the flange of the false spar behind the fuel tank. But we found that with even a strip of .032 missing (to level out) that it was not noticeable if the rivets were placed away from the "step". Mark

[kauaicuda]

Mark, would the best method for installing this be to flush rivet the strip to the rib flanges first and then skin it along with everything else?

[Mark Goldberg]

There is a drawing with Bob's engineering change that shows what he wants when building up a wing. Not sure who you are. If you have our kit wings, then another strategy would be required since the nose section is closed up more or less. Mark

[kauaicuda]

Rob Hansen, Frederick MD

I have a rib and spar kit.

[Mark Goldberg]

Bob's drawing with this engineering change should answer your questions Robert. Mark

[Pbruce]

I have just cut and bent channels and am ready to glue them into my quickbuild wing. Mark suggested Proseal (a polyeurethane glue used to seal Vans RV wing tanks together). It’s $55 for 6 ounces! I think its overkill since I’m not doing a fuel tank. I’m planning to use 3M 5200 marine sealant, available at Home Depot. It’s also a polyeurethane adhesive, used to glue the decks on sailboat hulls and other marine applications requiring a permanent bond. it needs to be held in place for a couple of days. I plan to use a corplast panel jammed between the inside of the u-channel and the lower wing skin as a light-pressure clamp. One consequence of using it is it will not come off, ever. If I knew of something inexpensive which would provide a reliable bond which could be removed if required, I would use it. Hopefully, I will never find a need to remove the stiffeners, because they are on for good.

I am assuming that stiffeners would not be helpful in the first couple short bays next to the wing root. Also, I don’t intend to use them in the last few bays adjacent the wing tip, since any bending loads are far less, and so should the tendency of the skin to to “oil can”.

[Chewie]

In the last Beartracks Bob mentions that shorter stiffeners are okay as long as they're centered around the strut attach location.

[whee]

I have just cut and bent channels and am ready to glue them into my quickbuild wing. Mark suggested Proseal (a polyeurethane glue used to seal Vans RV wing tanks together). It’s $55 for 6 ounces! I think its overkill since I’m not doing a fuel tank. I’m planning to use 3M 5200 marine sealant, available at Home Depot. It’s also a polyeurethane adhesive, used to glue the decks on sailboat hulls and other marine applications requiring a permanent bond. it needs to be held in place for a couple of days. I plan to use a corplast panel jammed between the inside of the u-channel and the lower wing skin as a light-pressure clamp. One consequence of using it is it will not come off, ever. If I knew of something inexpensive which would provide a reliable bond which could be removed if required, I would use it. Hopefully, I will never find a need to remove the stiffeners, because they are on for good.

I am assuming that stiffeners would not be helpful in the first couple short bays next to the wing root. Also, I don’t intend to use them in the last few bays adjacent the wing tip, since any bending loads are far less, and so should the tendency of the skin to to “oil can”.

I just had my first experience with 5200 yesterday so I know basically nothing about it. I found it messy, runny and not great to work with. No doubt it will do the job though.

If it were me I’d use some 3M structural double sided tape. That stuff is strong and will last a lifetime.

[Pbruce]

Ok. Never heard of it. 5200 is a PITA to work with for all the reasons you just gave. It actually requires a system to place it, keep the mess contained, and hold it in position. I went to get it today only to find that all the stores were out. Permanent tape sounds like a really good idea. I’ll have a look around. Never heard of it so I don’t know what it’s normal application is. One thing about the 5200 is that it has enough body to run over the flange at the top of the rib. I presume the tape would require cutting the stiffner short of the rib flange In order to get reliable contact.

[whee]

I had never heard of the tape till a friend bought new enclosed trailer. All of the lap joints are put together with tape. It lasts the life of the trailer. The aluminum tears before the tape fails. Semi trailer have been made with it for a long time. It’s really cool stuff. There are lots of variations for different applications. Some have some sort of foam body so maybe that’s what you’d want.

I bought a roll to attach the nose ribs and hat sections in the wing tips I was building. I think it is going to work awesome.

[svyolo]

5200 is great for some things but working with it sucks. The regular stuff can take a week or more to completely cure. It is mostly used on boat hardware that you don't want to move - ever. Basically you assemble things (often threaded) and then don't ever plan on them coming off without destroying them.

All that being said it doesn't have great physical properties. It "creeps". I would not consider it a structural adhesive.

I did use some dabs of it on my kit to keep small aluminum clips from rotating or translating. They are captured and cannot come off or fail.

It is god-awful to work with. I makes a mess and sticks to everything.

[Bdflies]

Sounds like as much fun as Pro-Seal.