OS Engines,
I am in the process of finishing a model started some time ago and I need help in the engine selection. Tha engines were the main reason I put the model asside but now I am determined to finish it.
The model is of a JU52 a German Tri-motored transport designed in the 1930's and used extensively by airlines in a lot of countries and the German military.
The orrigional plans call for a .61 engine in the nose and two 1/2 a's (.049's) on the wings. The .049's were to simple to be bolted to the wing nacells and with there own fuel tanks and no rc carp aparently just run full throttle, probbably mostly for show. I'm not sure what would happen when one quit.
The model was built this way and would require some rebuild of the wings and nacelles to add glow engines now, but it could be done.
My problem is I do not fell that the .61 engine in the nose will be powerfull enough by itself and I do not know how to determine engine sizes for a model other than when building a kit useing the kit manufactures recomendations. There must be some guidlines for matching engine sizes to models I'm hopping you can help me with my engines,perhaps with a sugestion for the fuselage engine or perhaps a sugestion for the three engines. I have been thinking about a glow engine in the nose and two electric motors on the wings as this would require the least modifications to the wings and nacells.
The model has a wing span of 96 inches, a wing area of about 1130 square inches. and it weighs now without anything in it no electronic,batteries,reciever,servos etc. I expect a weight of about 13 pounds, but if any electric batteries are needed mabe as much as 15 pounds.
I would really appreciate your help. If it maters all but one of my model engines are OS and I have a new in the box .61fx .
Thank you for your help

1) Scale models are not intended to be "rockets". You'll need to ask about how well it flew. Try asking in the Scale forum. Maybe the original builder has comments about it. Are you building from a plan with a construction article? Don't be afraid to build the airplane dead-stock. Engines were usually selected for a reason. Just because the airplane is large doesn't mean you have to go to a "big" engine to make it fly properly. Many 1/4-scale airplanes will fly very nicely on a .61-.91 size engine. It's just that today's modelers think they have to go to 35-50cc engines on large airplanes, and then they get too much weight and vibration for the airframe.

The small engines on the wings were for show, and would cause very little change if one quit in the air. In fact, I'd bet the model will fly just fine without them.

The wing loading at the area and weight you mention will be about 26.5 ounces/sq. foot. Not bad. Similar to many advanced trainer types, and with the size, should make a nice-handling model. 13 pounds is not an unreasonable amount of weight for a ,61 to carry.

Bil Baxter,
The plans came from the January 1972 issue of RCModeler. My attempts to contact the fellow who designed it (JIM PYNER ) have not been successful also, I have not found anyone else who built the model to find out how it worked out.
There was another JU52 plan published by RCMagazine some years later that used three .25 glow engines but it was smaller.
I built the model just as it was designed however it wasn't quite finished ,radio and engines were not installed ,but for family reasons it was put aside for quite some time.
Now that I am attempting to finish the model I am having second thoughts about the power.
I thought that maybe with the changes in our hobby since 1972 there would be better choices for the power plants. I looked for models in this weight range and could not find any that recomended a .61 for power.
I didn't think to relate weight and sq.in of area in my search, maybe I should have searched more. I am also going by advice of some of my club members
I've so far gotten advice that ranges from three .25 glow engines to all electric, all seeming to come from people who know what they are talking about, but I'm getting is more confused.
Scale flight for a WW11 transport with reliable power plants is all I'm looking for.
Certainly the .61 in the nose is the easiest and most practical way for me to go, I wish I had more confidence that it would be ok.
Thanks for your help Bud

Bax,
I have a question concerning your reply to my inquiry. How did you come up with the 26.5 oz per sq ft? I'm trying to do some comparasons and I don't come up with the same answer so I must be doing something wrong.
One thing that I probably should have stated and it might make a difference is that the wing has a semi semetrical type of airfoil.
Thanks Bud