Fire Wall Construcion and Engine Selection

[spitzy]

Hi All,

 

I'm about 3 or 4 months into my Cozy project and am almost done with CH4. Pretty much just need to build the firewall and it's on to CH5. Before I get into building the firewall I want to verify I'm not creating re-work for myself should I end up using the Deltahawk engine instread of Lyoming.

 

Any Cozys flying w/ Deltahawk engines?

Any Gotchas I need to know about?

 

Thanks,

Mike

[Jerry Schneider]

Any Cozys flying w/ Deltahawk engines?

Any Gotchas I need to know about?

None that I'm aware of.

 

The only gotcha I'm aware of, is most builders say they wish they'd made the aluminum inserts 2x2" vs. 1x1". I'm not an engineer, (and there isn't even a Holiday Inn Express in my neighborhood. ), but I'd think no matter what power plant you use, it would still have to push the plane in the same spot.

[Jon Matcho]

The only gotcha I'm aware of, is most builders say they wish they'd made the aluminum inserts 2x2" vs. 1x1".

Thanks for the reminder Jerry... my "real" firewall (AeroCanard sized) still isn't done yet.

 

...I'd think no matter what power plant you use, it would still have to push the plane in the same spot.

I'm not an engineer, but I read a book once, and I'd say you're exactly right. The engine will require a mount specific to the Cozy Mark IV, which should be provided (or approved) by DeltaHawk. Given that the first flight of their prototype was in a Velocity, I would bet that they'd be willing to at least provide drawings for how to fabricate a mount of the Cozy Mark IV.

[spitzy]

Thanks for the information guys!

 

If I'm lucky the details will be worked out when I'm ready for an engine.

 

Why 2" inserts instead of 1"?

[Jerry Schneider]

Why 2" inserts instead of 1"?

To allow for slop.

[Nathan Gifford]

Is that 2" mod discussed anywhere? Are there downsides?

[argoldman]

Is that 2" mod discussed anywhere? Are there downsides?

Weight penalty of about 2 oz and increased cost of the additional aluminum

[Wayne Hicks]

I know I discuss it on my website. I was surprised when I drilled the engine mount holes. Two holes were off center. The third hole was so off center that it just barely fit within the 1-inch square laminate. Now I will confess my engine mount is not from Brock. Mine is custom made. (The brock mount won't fit my IO engine.) But I did verify the footpads as being correctly placed.

 

The point is, the welding can and does tweak the engine mount. Your footpad locations may be slightly off from the plans. That's why I recommended wider laminates.

[Steve Innova]

If I recall, isn't the AL supplied in 2" flat bar? So it's actually easier to cut it 2x2 than to make them 1x1. Generally speaking, rather than order your AL flat stock chapter by chapter, just go ahead and calculate all the flat stock required and order it at once, +25% to allow for mistakes.

[Nathan Gifford]

One builder suggested 2" SS. Good/bad??

[argoldman]

One builder suggested 2" SS. Good/bad??

 

You could possibly use SS, however, I don't know if you would gain much.

 

What you would loose is the ability to easily drill.

 

SS, especially at 1/4" is a bear to drill free hand, as you will be doing when you mount your engine mount. I believe it needs slow speed and much pressure. If you could affix your drill press to the FW, that would be another matter.

 

Aluminum is so much easier to drill.

 

Additionally, the stresses put on the FW at those points is distributed through many layers of fiberglass on it's way to the fuselage. I'not sure if the material was chosen for it's tensile strength, as much as it's resistance to hole elongation -vs- the wood firewall (this is merely conjecture).