small_rcer

Good day All:

Am building my DNU and have chosen to move the firewall forward to keep the prop in line with the prop line on the plans. Will be using a Sure Start.

In reading over the posts and looking at the pictures, I find some keep the air intake tube and others do away with it. I have found that if you do away with it, the needle valve stem will break from vibration unless you shorten it up.

What are others doing? And if you keep it what soultion do you use to simplify mounting?

TIA

Jim H

gcb

Jim,

The backplate without choke tube has been used on many, many product engines so it runs well without it. The choke tube facilitates choking, supports needle and provides clearance for intake. You can do without these if you so desire. Your choice.

Since you are moving the nose forward anyway, why not make provisions for it. I think most just use spacer blocks on each side of the tube. Spacers can be made of maple (preferably) or plywood, or even pine or spruce. These spacer blocks are mounted on the plywood firewall, usually.

Here is a pic showing Sure Start, three product engines with that backplate (came in various colors) and one product engine with another type backplate.

George

ptulmer

My Feedback: (5)

Jim,
If you leave the choke tube on, it's doesn't hurt the performance. I've use 1/4" square hardwood before. The firewall may need to be relieved a tiny bit right behind the tube. If you take it off you'll need to do two things. Shorten the needle as you noted and remove some material from around the intake. It's awful close to the firewall, otherwise. If you use covering on the firewall, and leave the backplate stock, you can do a pretty good blimp imitation. Just make sure you drive seven hours and are surrounded by understanding friends...

PS, I've used surestarts on two DNU's built straight from the plans. Lengthening the nose probably won't hurt, but it's not really necessary. One had 3oz of battery/tank up front and the other had half that.(300mah nimh and balloon tank) Both balanced somewhere on the spar. (which is good)

Have fun with it! It's a pretty darn sporty airplane!

dieFluggeister

As Ptulmer stated clip off some length of the needle to reduce the vibrating needle syndrome. Some of us also remove the needle spring and the crappy plastic seal at the needle base and replace it with a small length of fuel tubing that fits the needle and the base snugly. It stops the vibe and eliminates air leaks at the same time.

propbuster

My Feedback: (1)

I've been taking the choke tube off and trimming the intake back a little for clearance. I haven't been shortening the needle valve,and so far,haven't had any problems.

combatpigg

My Feedback: (3)

I found the steadiest needle settings after I took the time to steady the needle, makes sense? There is a packing of fuel tubing under the plate that keeps the needle from moving around. It is tight enough that I need to use tiny channel locks to turn the needle, but once you find your setting, you don't need to move it.