jchumley

My Feedback: (1)

If I were to build a three engine plane with two outer engines as tractors and a center pusher. Must all three engines be exactly the same? I would like to put 2 TT .25 GP engines on the outside because I already have them and buy a ball bearing engine to use as a pusher because the tt .25 won't run properly as a pusher. Would this work? I assume if I set them up carefully so that at cruising speed they were all running at approximately the same rpm, it should work pretty well.

Also, should I set the idle slightly higher on the middle one so that if one of the outboard engines died, I could throttle back and trim back until the other outer one died then go to full power with the middle engine and hopefully be able to limp home and land on one enting. Sound reasonable? (never flown multi engine before)

Jeff

evan-RCU

Yes to all your questions, sounds like you have it thought out niceley, what airframe and size are you looking at? I don't see much reason for a higher idle on the center engine, the important thing is you don't have the idles so low any will quit. If you have a larger center engine and one outboard dies you could kill the other outboard and fly it home on the center engine....

jchumley

My Feedback: (1)

THis is an odd duck of an airplane and perhaps even an odder implementation. It is a Caproni Ca.42 from WWI. A triplane bomber, the original had a 96' wingspan with 7.5' or so wing chord. All three wings are identical with ailerons on each. It had twin tailbooms, three full flying rudders and a center pod for the pilot, copilot and gunner. Another gunner stood at the top of a ladder at the rear of the center pod between the wing and the pusher engine.

I am making a stand-way-the-heck-off scale 1/16 scale with a 72" wingspan. I will build it very lightly. I think the .25s will fly it. I am looking for scale like performance. I would really like to put three small four strokes on it but they cost alot more.

evan-RCU

I think that with that span on such a lightly loaded airplane .15s would fly it scale, .25s would be more suited to a 100"+ size. I have 105" old timer Quakers that I fly with single Saito 56's and they are over powered. Three .25s are going to give you at least .60 pulling power, more like .75-.91 power. Looks like a great project, going to take you some time to do it....

jchumley

My Feedback: (1)

Actually, I plan to build it pretty fast. It is for use in a club event called the Dawn Patrol games using 1/8 scale WWI fighters flying missions including protecting a bomber. At the same time, I am working up plans for a serious 1/8 or 1/12 scale version of the Caproni. That one will take a few years. This one will take about a month once I start work on it, probably in about a week.

Thanks for the help:

Jeff

DICKEYBIRD

Geez, I couldn't cut out all those ribs in a month! Please post some pix as it progresses. Sound like a cool project. With all that wing span and the engines being so close together, I'll bet the only change in flying characteristics if you lose an engine will be a reduction in speed!

jchumley

My Feedback: (1)

Yeah. Ribs.

I have a method for cutting ribs that works pretty well. It requires a router table.

I cut out one rib form 1/4 ply or hardwood including notches for spars and leading edge and trailing edge sheeting if necessary. On one side, I stick sandpaper using either the sandpaper rolls that fit the Great Planes sanding blocks or 3M type 77 spray adhesive and regular sandpaper. I use the rib to mark a bunch of ribs on 1/8" stock or whatever is appropriate with enough room between them to cut them out a bit oversize (I use a band saw). I put a 1/4" edge trimming bit with a bearing on the end in the router table and use the following method to trim the ribs:

Lay down a rib blank. Lay the template on it sandpaper side down with the blank protruding a bit all the way around. THe bit must be adjusted so the bearing rids on the edge of the template and the rib blank below is cut by the blade. Press down on the template and run it around the bit for a neat trim. The spar notch and leading edge cutout need to be hand cut using the template as a guide. If I have many to make, I make two templates and sandwich a bunch of them between the templates to cut the spar and leading edge notches.

THis is much slower than buying laser cut ribs but much faster than any other way I have found. Probably comes out to about 1 minute per rib or a little more.

I may have to spend a little time making some jigs for this project. I think I will need about 120 ribs.

IF I take pictures that means I will have to clean up the shop. I don't know...

Jeff

fockewulf37

My Feedback: (102)

I am flying a 3 engine SM 79. The plane has a 110" wing span and weighs 22lbs dry. I am flying it on a 91 4-stroke center and 2 magnum 61's out board. I just make sure the 91is running great and I don't worry if the Rpm's match on the out board. I even have a occasional sag on an outboard engine. It does not hurt the flight preformance at all.I have not had an engine out yet but I do have the radio set up so if I have an outboard engine go out I can reduce the power to the outboard engines if the is a yaw problem. I do have constant glow on all of the engines.

By the way Magnum 4-stroke run great if you are looking to keep you cost down...
Ty

roydefiant

This Junkers 52 has a laser 80 in the nose and laser 70's on the outboard. If you lose one of the outboard engines the center engine helps overcome the yaw of the running outboaed engine

roydefiant

will try to upload