How to build tight fitting cowl doors.

[whee]

Several Bearhawks I’ve seen in person, mine included, have had not great fitting cowl doors. I made two attempts at making mine and and thought the second set fit really good and tight but both doors now have bulges at the top/front.

So, you guys with tight fitting cowl doors on your flying BHs, how’d ya do it!?!

I’ll try to take a pic from the outside soon.

[svyolo]

I would think the air pressure inside the cooling tins would tend to push the sheet metal up/out in flight. Maybe a couple of stiffeners, just fore and aft of the cooling tins, following the lines of the cowling?

[whee]

Mine are bowed out all the time.



I formed the curve on both doors and they used to fit very well, no so much anymore. I think making new ones and rolling a slight lip in the front edge will get it done.

[Bdflies]

I can try to describe how I did mine. Because the radius at the nosebowl and the radius at the firewall are different, I made a template for each. I don't have a slip roll big enough to roll the doors, but I bugged enough folks till I found one I could use. I brought a bunch of pieces of .032" strip with me when I went to roll the doors. I should state that my cowl parts are all .032", so that you'll understand the previous statement. Because of the different radii, The roll is essentially a cone. I adjusted the left end of the roll to roll a curve that matched the nosebowl radius. Next, I adjusted the right side of the slip roll until I rolled a strip that matched the firewall, about the correct distance from the left side, to match the length of the cowl door. Then, it was a matter of rolling the sheet JUST ENOUGH to make the curve. The bottom curve was bent over my knee.
After the doors were trimmed to satisfaction, I rolled a slight edge break onto every edge, except the hinge line. The doors were attached to the top hinge and strapped very tightly to pull them tight to the nosebowl and firewall. At that point, I drilled pilot holes for the Camlocks and installed same.
Frankly, it was challenging to fasten the camlocks at first. Now, after 80 hrs, everything fits as perfectly as I could ask.
Pics attached.

As usual, the explanation makes sense to me, but could be less than perfect to read. Any questions will be answered to my best.

Bill

[BTAZ]

I used the same approach. I think it would be difficult to get them to fit correctly without a slip roll.

I used some thin rubber C channel on the back edge of the nose bowl and the front edge of the firewall to snug/seal "just a bit more" at final assembly.

[BravoGolf]

Very nicely done..

[Mark Moyle]

Perhaps using piper latches...they can be adjusted to tighten up the cowl to lay flat.

[Mark Moyle]

To adjust....add or subtract washers to the upper latches to adjust how tight you want the cowl door to the nose bowl and boot cowl.

[Gerhard Rieger]

Hi Mark, what is the material thickness

[corefile]

not much help but another reason I would love to see a complete carbon fiber cowling like the carbon cub

[stinger]

Different strokes, here is the way I did Lil Bears Cowling . Flight time 100Hrs . Stinger

[Bcone1381]

Stinger;

The text associated with photo number two indicates it is adjustable. How does that function work?

[stinger]

Brooks, each locking hinge has a upper and lower section. The upper half is the swing over locking arm. The lower half looks like a hook that one can adjust up or down . I built little boxes that each half is secured to. Works great if you want more pictures send cell number to 386 361 0467 . Stinger

[whee]

Thanks for the ideas guys. I tried to find a slip roll to use but couldn’t. I could pay someone to make the doors for me but where’s the fun in that.

I’ll think on it some more and try again. It’s just so ugly and I’m about ready to take the plane out into public...

A carbon cowl would be pretty cool especially with a bigger engine. However, I don’t want to lose any weight off the nose as that will decrease my load carrying capacity. I’m actually looking for ways to add weight up front.

[zkelley2]

not much help but another reason I would love to see a complete carbon fiber cowling like the carbon cub

I'm going to have randy at carbon concepts do one up for me... probably this winter.

[corefile]

Ooohh I can't wait to see how that turns out - hopefully he will make a mold and it's something others could order if they are so inclined - make sure you post a picture

[Bcone1381]

If you want to fly to Jackson, MI the local EAA chapter has a slip roller no one ever uses.

But if you flattened out the aluminum one you have, could it be used as a template for a carbon fiber copy? You know, wax it up with a mold release agent, then lay on the cloth/epoxy, trim it before it cures. I really don't know what I'm talking about. probably wouldn't work. But i might have to ry it some day.

[Battson]

It was easy, I have made the doors three times now, each time they have come out tight.

Use two strops to hold the metal in place to mark, measure and here's the key, wait until the hinges are installed on the cowl doors and clecoed in place before you match drill pilot holes and cut the edges to length. Use the strops again when match drilling. Locate the strops at the 30% and 60% locations on the cowl,

Another key point, remember the match drilled holes can move, or "wander" when you up-size them with a step drill. Make sure to draw extended witness lines, so you can see if they are moving. You can control the drill so they wander to make the cowl tighter, not looser. I did this to ensure a good fit, realising the fasteners have some sloppiness in their design.

Be careful not to crush the cowl metal with the strops, but be sure it's held firm.

Don't bother with stiffeners or bending the doors, it is not necessary.

[robcaldwell]

Check out Battson's video beginning at the 20 second mark to get an idea what he is referring to. You can see how the cowl door has almost no bend after it is opened.