Semi Retired Aviator

I'm about to launch into building a Dornier 335 from Al Masters plans, 64" span.

A note on the plans says, and I've read elsewhere, that weight aft of the CofG is critical, i.e., it's very easy to end up tail heavy, so I'm looking at a couple of things that may make it easier, and would welcome any input from experienced builders, not necessarily those who have built this model, but any constructive (pardon the pun) input.

Possible changes

1. Extend the nose by about an inch thereby putting the forward engine out further, easing the problem of an aft CofG;

2. Moving the rear fuel tank forward (it's close to the tail), and whilst the model is balanced with empty tanks, just moving the empty
tank would make balancing easier. How far from the engine can I safely have the tank without installing a pump?
If I put it way forward, I could put an oscillating pump on the front engine for the rear tank (I don't want to add even the weight of
a pump at the rear). If I did that I would need to run a fuel line forward to the pump about 24-30", and then back to the rear engine, a
total of 84-90", and I'm thinking the friction in the line wouldn't make that worthwhile. Any comments on either of these proposals?

Extra weight shouldn't be a problem as I'll be using more power than I believe I will need, an OS .70 FS up front and OS .52 FS down the back. Just the weight of a four stroke up frnt should assist, but may be offset by a four stroke down the back.

The 56" plan, 600 sq in wing area, calls for two .25 two strokes (2 X 4 strokes about .40 would be a rough equivalent) and I think it would be a slug with that little power.

Wing area of a 64" model is 840 sq in, so two .52 4 strokes should be about OK, but with a .70 up front the power should be adequate for even a heavy build.

I'd appreciate input from anybody with building experience, and input from anybody who has built this model would be a bonus.

Steve Collins

My Feedback: (8)

The Y.S. .63 four stroke is the same or very similar size to the O.S. .52 since it was originally in the .52 size range. The advantage it has, besides lots more power, is it's pressurized fuel system. I believe you could have the tank for the rear engine right behind the tank for the forward engine due to the pressurization provided by the Y. S. engines.

Another thought is that the rear engine could be a brushless electric motor with the battery in the nose.

Semi Retired Aviator

Thanks Steve.

I have a YS .53 (not .63) which could be used I suppose, but it is a heavy engine. It has a stack of power, but I've found a little finnicky over the years; one day it runs great, another it doesn't, and there's no apparent reason for it. In a twin engined aircraft I'd prefer reliability first. I hadn't given the pressurized fuel system on the YS a thought.

Now the electric idea is something I hadn't though of, and could just be the way to go.

vertical grimmace

My Feedback: (1)

Maybe get a Cline regulator for your rear engine. I think having the tank for the rear engine as far forward as possible to be imperative. I would not lengthen the nose. Also maybe a drive shaft of some kind could be fabricated to have the rear engine moved forward. I have also seen a marine engine used to allow the use of water cooling and overheating which can be an issue with this design.

Semi Retired Aviator

Thanks VG. There is an air scoop under the fuse to take cooling air to the rear engine, so provided the exit is sufficiently large cooling should be OK.

A colleague mentioned the Cline reg a few days back and I'm looking into that.

I could perhaps have an oscillating pump on the front engine drawing from a single tank up front, and increased diameter fuel line to the rear engine to overcome frictional losses.

So many choices starting to emerge!!

vertical grimmace

My Feedback: (1)

Exit air is just as important. Keep that in mind.