Hello everyone,
I have an old Eaglet (50?) that has a stated engine range of .09-.21 or so. Unfortunately, the engine that used to run that plane (a Supertigre .29) is dead, so I had a thought... I have a Megatech .46 engine that runs well, and I was thinking about mounting it on the old trainer. Obviously, the center of gravity will move forward, but I wanted to know if anyone has had experience with such intentional engine/plane mismatch (assuming corrected balance, etc). I'll bet that the stall speed will increase, but hey, so will the speed- it might even be fun to try some crazy tricks with this combo. Does anyone think such a proposition is flyable? I would love to hear of past experience. Oh- one last thing: I REALLY don't want to buy a new engine (tryin' to save a bit of cash). Thanks in advance.

Like almost anything in this world there are no rules set in stone. You can make it fly fine as long as you keep the CG in the same place as before. You will notice and increase in speed specially in the vertical direction. Just remember that the wing structure was setup for a TRAINER kind of performance so no high G maneuvers at max speed. Otherwise, have fun......thats the idea of this hobby.

Mores law applies if some is good more is better! Like it was said willl the airframe take it! I have a LT-40 Sig! I'm running a magnum 91 fs in it! I sheeted the top and bottom of the lead edge of the wing! I aslo fiberglassed the wing saddle! I do banner tows with it and other fun stuff like parachute drops!
Peel some coveriing off the center of the wing and glass the wing saddle. If you ambitious strip the whole wing and beef up the spars add some shear webs! Make sure you tail feathers are good and tight. Also seal your control surfaces to eliminate chance of flutter! And most of all have Fun

If you're not a beginner then sure, why not! ! !

One possibility that may crop up. The engine may not want to idle low engough to let you land. If so then go for a prop with less pitch.

Scoff if you will but a bunch of years ago I was helping a new flyer with his first jumbo build. It was a Goldberg Cub with a 2 stroke OS 61 in it. I'd fly it down and try to land and it would just climb out on idle. I thought I just had too much speed so I tried to feed in some up pressue a LONG way out in the hopes of getting the model into that prestall mush where it settles in nicely. Nope, it just continued to gain altitude.

Go for the bigger engine but if this happens to you be sure you can cut the engine on final once you know you're going to make it.

http://www.rcuniverse.com/forum/Spee...1183832/tm.htm
I had the same question. But i was discouraged to do it???

PaPa-NeGeorgeo - On reading both threads I would believe that the strength of the wing was the major concern in it not being recommended. It is a valid concern. If you beef up everything before flight it is going to be OK, with some exceptions.

It depends on the airplanes pitching moment verses speed curve shape. A flat bottomed wing with incidence setup is going to vary quite a bit.

I remember seeing a mid side Goldberg Falcon with a .40 on the front fly - it did but the wings could get some awesome dihedral in a quick pullup. I flew the same sized Skylark (low wing version of the Falcon) with a .40 but with sheet covering on everything that was fine.

I fly a engine size or two bigger on most of my fun airplanes but those are the ones I have built and know personally that they will be strong enough, they also all have symmetrical wings. They just go faster.

You're right Papa, I'd forgotten about those very valid concerns.

OK, I'm changing my vote. Ixnay on the big engine. I guess I didn't see the bit about it being an Eaglet. Those models don't have a lot of wing spar in the first place. Adding that much power is asking for problems.

I suppose IF you're carefull not to exceed some basic performance limitations then you can do it but if you figure you can just blast 'er about the sky with total abandon then I think you'll find it disintegrates in mid air.

For example the ONLY time you should probably use full throttle is when the nose is pointed upwards at least 30 degrees. IF you can hold yourself back the rest of the time then yes you can get some more life and flying time out of the old airplane.

Papa this last bit goes for you too. Fly it with some degree of respect for the limitations of the airframe and you'll do fine. Ignore the limits and fly it like a Piper Cub with a twin row Wasp and it'll "blowd up reeeeal guuuuud". (10 points to anyone that can tell me where this last bit of comedy trivia is from)

John Candy in a sketch he used to do on "Second City Television"

Very good. You win. The prize is the accolades of your peers....

I'm impressed that Second City made it down to Kentucky. Not bad for a Canadian show...

Ok thanks Bmathews for clearing that up.
Ive already installed a old .25 sf on it and im really hoping it run well. If not, i was thinking of taking the halves of my sig four star 40's wing putting them back together with very little dihedral on it and try and fly it with a semi symtrical airfoil? Then id put a .40 la on it run it at 3/4 throttle. Since its a really light model i think it should be very aerobatic for a high winger? Can anyone think of any major flaws or problems with this, (except for the fact my wing is blue and yellow and my fuse is red and white).

Papa

Mixing colors will cause a whole lot of drag, it probably won't get off the ground.

I doubt it would fly properly with those colors.......

Ill just have to make sure everyone at my field closes their eyes until im a couple 100 feet in the air.

Actually Papa that wing-fuse combination could lead to a nice model for that 40 size engine. As long as the tail feathers are very secure and the hinge gab is minimum you might get a really fast trainer. Have fun with it.

Papa, I think what threw me off the track was your post was intending to fly that Eaglet as fast as you could. THAT set off the alarms. In this one he only wants to get back in the air for a few more hours. I didn't make the connection until you posted here.

And actually it's a known fact that truly ugly multi colored models fly best........ The Earth wants to keep them as far away as possible...

<quote> And actually it's a known fact that truly ugly multi colored models fly best........ The Earth wants to keep them as far away as possible <quote>
Thats a very good theory.
About the eaglet, originally what i wanted, like you said was to get the fastest plane out of it as possible. When i found out that it might now be the best idea i just made it a normal trainer so i could get back into the air. But now im really thinking maybe after a couple flights switching the wing & engine and see how it goes.
I got just one problem that i just want to discuss here (i know its not my thread so i apologize) but i installed the engine with about 2 degrees upthrust by mistake will this make for any real problems. Especially if a change the wing and make it a faster plane?
Thanks alot,

Papa

Hahaha, I like your theory Bmatthews...... no wonder all the pretty ones end up in small pieces. [sm=lol.gif]
Papa, as far as your upthrust you better change it to downthrust for the flat bottom wing or maybe you can get away wtih zero thrust when using the semi-symmetrical. If you leave the upthrust as it is your model would want to balloon as soon as you add power to it. What could be interesting is your slow speed might get slower from the added vertical thrust vector component. Instead of an ultra fast trainer you could have the slowest landings out there.

What he said. Fix that thrust line. It doesn't matter what wing you have upthrust is always a bad idea...

.... well, there WERE some hot shot rudder only models back in the late 50's or early 60's that used upthrust but that's a special case. Forget I typed this last bit....

Does anyone know of anyway to get rid of upthrust in exchange for downthrust without totalling killing my firewall or destroying my entire plane?

You can make up some wedges from either aluminium or a good hardwood like maple. Adjust the angle to remove the upthrust and add a further 2 or 3 degrees downthrust. If you're using a radial mount make a single wedge out of 1/8 or 3/16 ply to fit between the firewall and the mount. Some folks try to just use shims but that often distorts the firewall and the engine mount if it's plastic . If you DO want to try just shimming it be sure the shims are right down by the screws. You may also need longer screws to fit.

The shims are a good idea even if you only use them to check on the angle required before you make up the better option of the wedge. Just use ply or hard balsa bits and snug the screws without tightening them for measuring. When happy make up something more robust that is permanent.

Or you can also add washers to the upper bolts holding the engine mount. Add them between the firewall and mount. Quick, easy, CHEAP. [sm=biggrin.gif]

Ok i got it down to about 0.5 degree upthrust. I think im going to use the washer idea but unitl then do you think i can maiden with just using a bit more elevator trim down? I really wanna get this flying soon and i dont have any washers that would fit.

You really need downthrust.....elevator down will become a lifting tail and that can be problematic as well. The forces involved on a trainer with flat bottom wing are downwards on the engine thrust and horizontal stab, then upward on the wing. Changing that format could give you an uncontrollable ship or one thats a pain to trim.

I just tryed running my .25 sf and was unsuccessful. So unless i can get it working im going to have to switch to my .40 la. Could i use a 9.5/5 prop on it or should i use a 10-6? Ive found two washers so im going to put in the downthrust.

Well, I took the Eaglet out today with the Megatech .46 onboard (after remounting the radio and battery within the rear body), with an 11-5 prop, and got her airborne. It acutally flew pretty well, execpt for the fact that it came in at about 100mph for landing! Seriously, I got it back on the ground in one piece, but man, it came in fast. Kind of like a "trainer deluxe." I ran it fairly rich, and rarely went to full throttle (mostly kept it at about 1/3). So, to answer my own question, yes, the .46 will work on the Eaglet. Thanks to everyone who posted!