RV-4 Engine Mount Length

I was wondering why the engine mount on the -4 seems to have undergone special efforts to keep the engine as close to the firewall as possible - for example the special drain fitting on the fuel pump and the inability to remove the fuel pump without pulling the engine forward, or moving the plane back if you prefer.

The Fwd CG limit is never a factor on the RV-4, only the Aft limit. It would seem that a longer engine mount would make access to the engine accessories easier AND help the Aft CG issues. A win win. Sooooo... does anyone know why Vans made it so short in the first place? I called Vans but they said that was done in the 80's and nobody there knew why it was done that way....

One thought I had was that moving the engine further forward of the main gear would cause a "lighter tail" and increase the risk of "nosing over" resulting in a prop strike, etc.

Does anyone have knowledge/theories on why the engine is so close to the firewall and the relevant effects of moving it forward?

Fastwind67 said:

r.


One thought I had was that moving the engine further forward of the main gear would cause a "lighter tail" and increase the risk of "nosing over" resulting in a prop strike, etc.

Click to expand...

On the other hand, moving the engine forward raises the height of the engine above ground and therefore increases prop tip clearance.

My thoughts are that keeping it tight keeps it light...less cowl material, less mount material, shorter hoses, shorter exhaust, shorter cables, etc. Perhaps Van made decisions based upon the popular engines of the time period, and perhaps the issues you mention did not show up often at the time. The effects of moving it forward are as you have already mentioned. Think about the guy with an aluminum CS on the nose vs the guy with a wood prop. The guy with the wood prop would have to move his engine 1-2" fwd (just a guess) to match the CG of the CS setup.

the fuel pump can be removed without moving the engine, its a pain in the a// but it can be done.


bob burns
n82rb
RV-4