S

scottw

Member
Two questions I have in skinning the fwd fuse:
1. F451 lower fairings as received from Van's look kind of like a parrallelogram(ends not square). Dwg 27 shows it square at least in front(by square I mean parrallel with the firewall), anybody installed these recently?
2. When laying out the fwd side skin holes I am stuck on how F421(the fwd top skin) attaches to the upper longerons in the vacinity of the upper firewall weldments, screws and nutplates at 2" centers attach it but what did you guys do in the corner where there are 5 tightly spaced dash 4 rivets that attach the upper longeron to the weldment?
 
Hi Scott,

As for the F-451, if I understand you correctly, you're talking about the forward end of F-451 where the little bulkhead (the one that's flat on 2 sides & then curved for 90 degrees) fits. I just looked, and mine isn't perfectly parallel. The F-451 SKIN is about 1/2 inch behind the plane of the firewall on the outboard edge, but almost an inch aft of the firewall on the inner side where it starts to form the wall of the exhaust tunnel. I installed the little bulkhead itself so that it IS pretty much parrallel w/ the plane of the firewall, both vertically as well as in the inboard-outborad direction. It is NOT installed so that the flanges of the little bulkhead are perfectly aligned with the front edge of the F-451 fairing (at least mine isn't).

Remember, that later on, when the fiber-glass instersection fairings for the gear legs are made, they will cover this area, and any slight mis-alignment of the front end of F-451 will not be visible.


Your 2nd question gave me a chuckle because I scratched my head for a quite while over that one myself!! There are AN bolts in the top of the longeron, and as you say, rivets on the side. There didn't seem to be enough room for adding any nut-plates in the FWD corner for screws!

In fact, you have to be pretty careful and drive the rivets first, then install the AN bolts & nuts. Otherwise the nuts will block access for the bucking bar. I suppose if I were smart enough & planned ahead better, I could've planned it so that the rivets which hold the nut-plates also hold the longeron to the outer leg of the upper firewall weldment, but the plans didn't give me any hints there, or I missed it.

My solution was to rivet a 3/4 x 3/4 x 0.063 angle to the top of the longeron between the firewall & instrument panel stations, with one leg of the angle pointing UP. This angle is flush w/ the outside of the main longeron, so it essentially doubles the width of the flange & gives plenty of room for nutplates without having to worry about the small size of the weldment flanges in the FWD corner. It also means that the bottom edge of the upper FWD skin will butt to the top edge of the FWD side-skin rather than over-lapping it. I'm hoping this will pay off later when fitting the cowl cheek extensions. I've seen other RV-4's at fly-ins where the FWD upper corner of the fiberglass cheek extension had to be trimmed-down a bit in order for it to clear the overlap area and sit flat against side of the fuselage. If it wasn't trimmed, then a small part of the cheek extension would overlap the joint where the top skin overlaps the side skin near the firewall, and there would be a small gap there under the fiberglass flange of the cheek extension.

Anyway, I hope that helps a bit.
All the Best on your project!!
 
photos

Here are some photos of my project. I agree with Les. The nutplate spacing on my longerons are not exact; just the best I could do since I didn't plan for them when spacing the skin rivets. Countersink the screw holes before the nutplates are attached. I forgot and had to remove a few, then re-attach. Hope this helps break your log jam.

Sincerely,

 
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great pics Brian, thanks, where did you get those gussets on top, are those .062?did you put them at the bottom too?
 
Gussets

Can't take credit for the gussets; I copied another builder. Not sure if they are necessary or not? Seems like the general RV-4 owner/builder consensus is for beefed up firewall bracing. Can?t hurt anyway. This is one of the very few deviations from plans that I have made. I believe the gussets are .062; home brewed from flat stock. Not difficult to fabricate and install.

 
Steve

Dear Steve Sampson,

I'm excited to see your butterfly about to emerge from the cocoon!!! Thanks for being so good about updating your website and letting us all see your RV builder life. I really enjoy reading about, and viewing your progress. I've learned so much from you about my own project; big thanks for thinking out loud in your narrative. You have contributed to my project more than you will ever know. Wish I could be there for the first flight!!!

Very sincerely,
 
Nice gussets

Brian Vickers said:
Can't take credit for the gussets; I copied another builder. Not sure if they are necessary or not? Seems like the general RV-4 owner/builder consensus is for beefed up firewall bracing. Can?t hurt anyway. This is one of the very few deviations from plans that I have made. I believe the gussets are .062; home brewed from flat stock. Not difficult to fabricate and install.

Click to expand...

I really liked your gussets. Mine don't have the neat little bend on the front. Wish I'd thought of that. Did you also do gussets at the other end of those braces, near the spar box? It really bothered me that the landing load was being transfered to the spar through a 3/4 angle and a couple of -4 rivets. I got out my old RV6 plans and found that they added gussets there, too.

The pictures were great. Speaking of which -- has anyone else noticed that there seem to be no RV4 sites out there that show early construction? I've been struggling with all things having to do with that damned firewall for the last month. Some pictures would have really helped. For instance, has anyone actually managed to somehow rivet the 413 floor webs to the firewall stiffeners? I decided to use bolts and asked the factory if that would be a problem. Their answer was that they designed it for rivets and couldn't comment on whether bolts would be an acceptable substitute. Obviously, the lawyers are now firmly in charge back at the mother ship.
 
No other gussets

Jon,
I don't have additional gussets beyond what is shown in the photos. I am not familiar with the RV-6 construction. Again, I am just monkey see, monkey do!!

I don't quite follow what you are describing regarding the F-413 and firewall connection. I just went down to the shop and looked at my airplane(?).

I would be more than happy to photograph and post anything you or anyone else might need since my project is very accessible and the airframe is essentially complete. I have followed the plans on everything. My mission profile is a simple, easy to maintain, light weight and fun VFR sport plane. I just ordered an MT fixed pitch prop for my overhauled O320D1A. Not much left to purchase. I'm so bare bones in the cockpit that my big concern is aft CG.

Sincerely,
 
So how did you do it?

Brian Vickers said:
Jon,
I don't have additional gussets beyond what is shown in the photos. I am not familiar with the RV-6 construction. Again, I am just monkey see, monkey do!!

I don't quite follow what you are describing regarding the F-413 and firewall connection. I just went down to the shop and looked at my airplane(?).

I would be more than happy to photograph and post anything you or anyone else might need since my project is very accessible and the airframe is essentially complete. I have followed the plans on everything. My mission profile is a simple, easy to maintain, light weight and fun VFR sport plane. I just ordered an MT fixed pitch prop for my overhauled O320D1A. Not much left to purchase. I'm so bare bones in the cockpit that my big concern is aft CG.

Sincerely,
Click to expand...

Well don't leave me hangin', man! How did you do it? There's less than 7" of clearance down there in the footwells where the F-413's attach to the firewall. There's no way to get in there with a rivet gun and it's too deep to reach with a long offset rivet set.

I saw some bolts in a picture on someone's site (maybe Steve Sampson's), which gave me the idea that maybe bolts were the standard solution.

On the other gusset issue, the RV4 firewall gussets are patterned after the RV6. That's what got me looking at my RV6 plans, where I noticed that they'd also added gussets where the 3/4" and 1" angle frame members attach to the F-404 spar box. My 6 was a quickbuild or I might have noticed it sooner.

That 3/4 angle that forms a triangle between the spar and the bottom of the firewall is there to transfer the landing load back to the spar. It's attached to the F404 flange with two rivets. I don't remember hearing about any failures at that point, but it sure seems a little puny. On the six, it gets a gusset, and the bottom 1" angle has a gusset as well.
 
F-413 to firewall attach mystery

RE: "Well don't leave me hangin', man! How did you do it? There's less than 7" of clearance down there in the footwells where the F-413's attach to the firewall. There's no way to get in there with a rivet gun and it's too deep to reach with a long offset rivet set."

Jon,
Your question really had me head scratching... until I looked at old photos of my fuselage construction (see below). The angles were attached to the F-413's prior to installing them. Riveting the firewall on was after the angles were attached via the hand squeezer to set the rivets. You can see in the photo that the firewall is clecoed to the F-413 angles underneath. At that point in the photo, the angles were already riveted on. I was working on the longerons, I think(?). Long time ago; 2004 I think. I'm a sporatic builder.

 
Firewall - top longeron & steel corner brackets

Hi Brian,

I like your "old" pictures.

I am working on my first RV-4 project.
We have just placed the firewall assembly onto the front of the fuselage jig.

When I place a 3/4" angle into the upper steel corner brackets, the end of the 3/4" angle would have to be bent outerward and down at the steel corner bracket to have the longeron rest on the fuselage jig in the correct location.

Is anyone else having to bent the longeron at the steel corner bracket to get the longeron in the correct location at the main spar bulkhead?

Jim Ayers
 
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