Firewall Question

[rnbraud]

Hello all, I have a quick question about the Aerocanard firewall. I was wondering that since the AeroCanard is 3 " wider in the back seat, does that mean the firewall is 3" wider?

 

The Cozy plans show the firewall to be 18 1/2 inches x 2 = 37" wide at the bottom of the main spar, and 15 1/4 x 2 = 30 1/2" wide at the top of the spar "between" the longerons. If you measure outside the longerons it would be 17" x 2 = 34".

 

Is the Aerocanard firewall wider than these dimensions?

 

The reason I am asking, it if I widen my Cozy MkIV firewall three inches I was wondering if I could get a engine mount and cowling from AeroCad pre-built.

 

Thanks for the info.

[Jon Matcho]

I was wondering that since the AeroCanard is 3 " wider in the back seat, does that mean the firewall is 3" wider?

The AeroCad Web site reports that the AeroCanard is 3.5" wider in the back, yet I found the bulkheads to be even wider when compared to those of the Cozy. Answering your question, the firewall is also wider, but I've never checked by how much. Maybe it's 3", and maybe not, but either way the contours are NOT the result of adding width right down the middle. The shape of the AeroCanard firewall is different from the Cozy's. They have also moved some things around slightly on the firewall.

 

The reason I am asking, it if I widen my Cozy MkIV firewall three inches I was wondering if I could get a engine mount and cowling from AeroCad pre-built.

The engine mount hardpoints on the AeroCanard are in the same places as on the Cozy Mark IV, so your standard Cozy Mark IV engine mount will work.

 

In terms of getting an AeroCanard cowl, or any other prefab AeroCanard part to fit a plane that's neither a Cozy nor an AeroCanard, I would rule that hopeful thought out. If you want the options in the future, build the exact size as the AeroCanard or keep the same size as the Cozy -- AeroCad sells parts for both.

 

If you want to widen per AeroCanard specifications, call them up and see if they offer a deal on "upgrading" from Cozy Mark IV plans.

[rnbraud]

John,

thanks for the information. I was really hoping for the cowling to fit, oh well.

 

I am curious about the engine mount Aluminum hardpoints. If the rear is wider, and the hardpoints are in the same place, ie right next to the longerons, how can the engine mount be standard width? Do the hardpoints extend inward to meet the mount?

 

Thanks.

[Jon Matcho]

If the rear is wider, and the hardpoints are in the same place, ie right next to the longerons, how can the engine mount be standard width? Do the hardpoints extend inward to meet the mount?

I may very well be mistaken when I say that engine mount hardpoints are in the same place. The longerons move outward slightly, which means the hardpoints most likely move as well.

 

Do the hardpoints extend inward to meet the mount?

I'll try to compare both drawings tonight and let you know what's up.

 

John, ... Thanks.

You're welcome Rich.

 

Jon

[Jon Matcho]

If the rear is wider, and the hardpoints are in the same place, ie right next to the longerons, how can the engine mount be standard width?

I confirmed that the AeroCanard FG hardpoints are in the same position, relative to the Center Line, as the Cozy Mark IV.

 

Looking at the structure, I'm not concerned about any strength issues. The engine is being mounted to the firewall, which is strong against the main spar. The longerons on the AeroCanard FG are only out ~2.5" at the firewall. I'm just going to take the reinforcing layups that far, and add another 2 or so if I ever get paranoid.

 

Alternatively, the hardpoints could be moved further out, but then you need to custom-order an engine mount. A worthwhile benefit of the Cozy Mark IV and AeroCanard is that many parts are interchangeable, and I want to keep the one-offs to a minimum.

[Wayne Hicks]

I'm not concerned about any strength issues.

 

----> You should be. A plywood firewall with 1 bid each side is nowhere near strong enough. It's not just the weight of the engine, it's the weight times 6. Jeff told me himself that he widened the aluminum laminates, extended all engine mount reinforcing layups that the Cozy had, plus he added the cuppers. Better find where that is in his plans and stick to them.

[Jon Matcho]

I'm not concerned about any strength issues.

 

----> You should be.

What I wrote began with "Looking at the structure..." To be clearer, I mean that I am not concerned about being able to address any strength issues relating to keeping the hardpoints at the same positions.

 

A plywood firewall with 1 bid each side is nowhere near strong enough.

Is the Cozy Mark IV engine mount design okay? Did you use that, or an improved version?

 

Jeff told me himself that he widened the aluminum laminates, extended all engine mount reinforcing layups that the Cozy had, ...

Sounds like a good idea.

 

...plus he added the cuppers.

What's a cupper?

 

Better find where that is in his plans and stick to them.

I am sticking to the AeroCanard plans. The problem is that the AeroCanard plans do NOT have any of this information in them. I'll check in the text, but if it's not in the modified drawings, I seriously doubt it's in there at all.

[Wayne Hicks]

I followed the plans exactly for the engine mount reinforcements. No one's ever reported an engine falling off, so I'd say the mounts work as intended.

[rnbraud]

John, thanks for looking into this.

 

Another quick question. Is it fair to say that the Aluminim hardpoints, which the engine mount connects to, is stronger or equally strong as the fiberglass layups which surroud it.?

 

The reason I am asking, is if the Aluminum hardpoints are enlarged or extended, the intent is to maintain the strength of the connection to the longerons while at the same time accomodating a standard-sized engine mount. If the Aluminum isn't as strong as the surrounding fiberglass, then I would revert to utilizing a custom engine mount.

 

Thanks.

[Marc Zeitlin]

..... Is it fair to say that the Aluminim hardpoints, which the engine mount connects to, is stronger or equally strong as the fiberglass layups which surroud it.?......

The aluminum is far stronger (and heavier, hence the use of small bits).

[Wayne Hicks]

The aluminum hardpoints won't crush when the bolts are tightened. The wood firewall would. The loads are carried by the many plies applied inside, outside, and around the 4 engine mount reinforcements.