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alpinelakespilot2000

Well Known Member
Tried putting the main gear on tonight for the first time...

I've scalloped the firewall flange all the way back to the firewall as per taildragger plans. The left gear leg will go in but rubs against the bottom skin and firewall web scallop once the gear leg is fully seated. The right leg will not even not go all the way into the socket because the interference is even worse. I only need probably another 1/32" on the left side and 1/16" on the right side, but the problem is that I cannot scallop any further or I will begin cutting into the WEB of the firewall. It appears that the gear leg sockets sit too far aft on the engine mount.

Has anyone had this problem and been provided with any solutions?

 
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Scallop back the flange as far as you dare and if that is not enough shim the frame forward. On my -6 I scalloped almost to the firewall and I already had some shims in place to level the frame relative to the firewall. You don't need much clearance here. I used a little Dremel drum sander for a neat finish that looks as if it's supposed to be there. I aslo used big steel washers as shims.
Jim Sharkey
 
What Jim said

You will take that flange off even with the firewall to make sure the gear leg fits in there. If you open up a hole in that corner, fill it with some fire seal. In my case I used some fire block from 3M.
 
Thanks guys. As I mentioned above, I have already scalloped all the way through the flange. Any more and I WILL penetrate the firewall web. I'm not sure how much I am willing to have a hole in the firewall there, even one that I can fill with sealant, but a little one may be unavoidable.

Shimming all six mounting bolt locations with large area washers between the motor mount and firewall might be a possibility, but I think that increases the bending force on those bolts, so I'll check with Van's on that.

Thanks again.
 
alpinelakespilot2000 said:
Any more and I WILL penetrate the firewall web.
Click to expand...

What are you calling the web? You shouldn't have to go beyond the plane of the firewall, but most or all of that flange will have to go. That will expose a small opening in the firewall that's already there, so just a little more proseal shouldn't be a big deal.

Maybe a picture of the firewall you are concerned about would help clarify things.

Cam
 
N916K said:
What are you calling the web? You shouldn't have to go beyond the plane of the firewall, but most or all of that flange will have to go. That will expose a small opening in the firewall that's already there, so just a little more proseal shouldn't be a big deal.

Maybe a picture of the firewall you are concerned about would help clarify things.

Cam
Click to expand...
Yes, I will have to go beyond the plane (or face) of the firewall. (That's what I meant by web--just like a rib has a flange and a web.) I can't do what it appears Bill was able to do. He seems to have just scalloped up to the face of the firewall but no further. What will end up happening in my case is that I'll be essential scalloping the lower face of the firewall a little as I previously did with the flange of the firewall.

Perhaps this will, as you suggest, just make the gap that already exists at the radiused corner bigger. So maybe it is just a matter of more high temp RTV or sealant.

I'll try to get a picture from the top on the forward side.
 
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Here's a pic from the top. A better way to explain this whole problem is that if I continue to scallop the bottom skin (which is what is interfering with the leg, I will open up a gap between the bottom skin and the BACK of the firewall. See below also for an unusually quick response from Bruce at Van's.



Bruce's reply: "The choice about what to do is yours. It is OK do take a little more material from the firewall even if you cut into the web. You can put a little fuel tank sealant around the cut to seal it off. It is also OK to add a washer at each engine mount bolt location."
 
Keep cutting Steve. That looks just fine. If you had to cut into the structure behind the firewall that would be different.

Cam
 
Resolution and Result

Well, it's done. Rather than cut any farther into the firewall and create a hole that doesn't need to be there, I just added a large area washer under each of the bolt locations. Fortunately, I have a builder buddy who just happened to have 6 of the right size! The original bolts even still work. In fact, they had been on the long side originally but now they are pretty much perfect!



Now I have plenty of clearance between the gear leg and skin...



And the end result...



Pretty cool having the thing up on its gear! I've always heard that the -9 sits tall because of its longer gear legs, but I was really surprised at how tall, given that I've never seen a -9 in person!

Another advantage of using those washers to solve the problem: by effectively moving the whole engine 1/16" forward I won't have any aft c.g. issues like many fixed-pitch RV-9/9As! :D

Thanks to all and thanks again, Bill, for all the extra suggestions. Time to get that new engine hung!
 
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