bilko

I wasn't sure if this should be under RC humour or here.

I have the remains of an Irvine Tutor 40 and as I have already replaced it I thought it might be a laugh to rebuild the original as a twin engine trainer. I recon hanging a couple of 36's or 40's under the wing might not alter the C of G to much, and the tail surfaces are pretty large on the trainer so single engine control would be OK. As its a high wing I thought that thrustlines would be straightish with the engine below the wing chord.

So should this be in the humour section or what.

Any advice, including don't be stupid, will be welcome....

Regards
Bilko

AR196

Many moons ago, RC Modeler Magazine had Joe Bridi do up a trainer, which was really an advanced trainer.

It worked very well too, the wing was very thick with a symmetrical airfoil, tail size and moment were good too, so slow speed handling was excellent as were overall flying qulities.

It came out in a 40 size as well.

So along came a chap who did with the 40 essentially what you are contemplating. It's called the RCM Twin Trainer. Power was 2 40s, instead of the original single engine.

You can see a photo of it at RCM's web site in the illustrated plans section.

Naturally the construction article said it was a great flying plane as a twin. IF it was close to the single, that would be true.

Good luck with your project. It sounds to be well worth a try.

twinman

My Feedback: (2)

bilko
There are few actual twin kits out there, so most trainers are bashed singles. No, this is not a joke and no one will laugh.....not the with posts on twin, triple, and five engine KADETTS!!!

Welcome to the BASH WORLD. Personally have not done the Tutor , but in this forum there is a wealth of information about bashing a kit.
Suggest checkout the following posts in this forum.

http://www.rcuniverse.com/showthrea...971&forumid=220

http://www.rcuniverse.com/showthrea...971&forumid=220


http://www.rcuniverse.com/showthrea...215&forumid=220

Good luck,
and send pictures,
Twinman

William Robison

My Feedback: (3)

George:

Your links aren't working.

Bill.

bilko

Thanks twinman.

I was thinking of a couple of ASP 36's but the original trainer is rated for 40 - 46's. Would they be OK or could I save money and use a couple of 25's. Are there any guidelines?

By the way the links don't work....

Thanks again

Bilko

twinman

My Feedback: (2)

!$^%@%@#%!!! new system is in test stage at rcu.
Do a search for
How to Kit Bash to a Twin
Twin Engine trainer
Bashing an ARF into a twin (and/or triple)
I think those were the references I used.
Sorry for the problems.
Twinman

twinman

My Feedback: (2)

bilko
I would strongly suggest go with the recommended .40-.45's. It will be a lot more fun,and you DO NOT WANT A PLANE THAT CANNOT STAY IN THE AIR WITH ONE ENGINE!!! I would prop these sizes with 11x5 or 12x4. Make sure the engine spacing is wide enough to clear the props. My twin fuse Long John 40, I built with only 12" prop centers.....have to grind 1/16" ( Approx 1mm) from the props now. You are not looking( I think) for speed, but want thrust.
Good Luck,
Twinman

vtol_guy

bilko, i'm no hot shot with twins but 2 size .40's!!!?????

thought you wanted a twin??? not a bloomin' vertical climb performance!!!!

i would've thought 2 .25's max.?

if it is origanally for a .40 then 2 .25's just abouit matches that?? :stupid:

bilko

Well there seems to be 2 schools of thought here.

1 You need enough power to keep going on 1 engine, more weight and cost.

2 You need to roughly match the original single engine power rating with 2 smaller ones which are more efficient as there is more propeller area therefore more thrust. Less weight and cheaper, but will a smaller engine keep the plane in the air. I would have thought that the time you need power most is on take off, thereafter you could get away with less.

Given the small cost differential between 25's and 40's and the fact that you can allways throttle back, it seems to me that 40's would be the way to go......Unless I'm missing something.

I'm sure that there is a "golden rule" out there about this.

What am I missing, or is this one of these questions to which there is no correct answer?

William Robison

My Feedback: (3)

Bilko:

As much as any, the "Golden Rule of Thumb" for twin conversion is to use two engines each of2/3 the size of the original.

Your Tutor, originally having a 40, should then have a pair of 23 sized engines.

The size and power over 50% compensates for the added weight of twin engines and associated equipment.

Bill.

vtol_guy

yey i was right!!

also, if you have a deadstick anyway you gonna want to land it more or less straight away, and you'll be kinda forced to anyway unless you have one big huge rudder control surface

twinman

My Feedback: (2)

Let me ask this. How do you want to fly this conversion?
The added weight of the extra engine, nacell, fuel tank, fuel, and servo is significant to the weight of the plane. I once had the same idea of smaller engines for a twin conversion on a Ugly Stick 60. I put two good .40's on it, and is did not fly well at all!!! It should have, at 50% over kill on engine displacement, but it did not and will not fly as well as the original. I changed to two .60's and became on of my favorite planes.
Imagine flying your plane with a .25. Now add another engine and associated weight of accessories AND now put it into a drag induce yaw during engine out, which will happen. Can you say ROCK?
I would also really consider to extend the wing length to reduce wing loading......or at least add end wing plates to increase wing lift.
My two cents is still go with .40's and you will be happier in the long run.

twinman

bilko

Well that got interesting.

I hope we are still all friends.

Thanks everyone for your imput, it has helped me.

On the whole it seems that a couple of 40's will be of more use to me after this twin trainer gets trashed.



Regards
Bilko

vtol_guy

fair point twinman but bigger engines mean extra weight anyway, ok i know there isn't a great deal of difference in the weight between a .25 and a .40

also, the .40 will consume more fuel than the .25

i have to side with will robinson on this, sorry.

William Robison

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Vtol:

Thanks for the back-up, but DO NOT DISREGARD Twinman's advice. He probably has more (model) twin time than the rest of us combined.

I'll stay with the 60% size engine selection, though.

Bill.

twinman

My Feedback: (2)

bilko
Never say "Trashed", You will love this plane.
Keep the engines close to the fuse. Suggest center of engines at 5.75". If you have good .40's, suggest 11x5 props for more thrust than speed. If really good .40's can go to 12x4, but must increase distance from fuse to compensate to 6.125 or 6.25" to clear props.
Make sure the wing has vertical sheeting between the spars, as the wing loading is going up. Vertical grain also on the sheeting.
Suggest keep engines upright for easy and safe starting. If you mount sideways, don't forget that one of the engines is near the fuse and glow plug connection must be considered.
Consider to enlarge the rudder surfaces to aid in control if the Unthinkable happens and one engine quits.
If you decide to not lengthen the wing, consider the wing plates I discussed earlier for more lift.....it also helps with knife edge.
We are all friends here and hope it stays that way.
When you finish..please send pictures.......uh before the first flight...tee hee......Sorry!!!
Remeber and burn into your brain the vertical test for engine stability!!! EVERY FLIGHT!!!
YOU decide how the plane flies and for all in this forum, let us know.
Best Of Luck.
Twinman

Robby

My Feedback: (18)

he he he.. This is funny...
There is a certian Twinman who recently saw some nutcase who
has a couple smaller twins going on..
It seems the rudders were a tad over kill and the motor size was
just a tinsey winsey little bit over size...

My normal rule is a .40 size plane converted to a twin gets two
.40s plop'd on it... And because I like to fly the rudder the
surface is enlarged.. Can we say 3D Tiger II with two ST.45's..
Tiger II is a .40/.45 size plane..

Where there will be added weight <wing loading> and the
chance of more speed capabilities than what the plane can
handle, there is a left stick on most TX's.. Learn to use it in both
directions...

Twinman reminded me of an item that can help should one not
wish to extend wing.. Add wing plates..

So, my vote goes to the more the merrier.. As V-Tol asks:
"A twin or a bloomin' vertical climb performance" Go for the latter
as it will help should a problem arise..
As T/M says, under power and you have a ROCK when that same
problem smacks ya in the face..

vtol_guy

will, its ok im not disregarding his advice, heck i havent flown a twin before and i am definatly NOT a cocky person


i have a lot of experience in aerodynamic studies and thats where i thought a couple of size .20's or .25's would be good for it.

I suppose at the end of the day it all depends on what performance you want from it, also, i was told once that whenever you try someting out for the first time in this hobby, eg, autogyros, twins, jets and whatnot.....always have plenty of reserve power

i suppose i'm kinda hypocritical in a way as my new twin is about the same size as the Irvine Tutor 40 and i have 2 .38's in mine ....then again though mine is a vtol... lol

xlr82v2

My Feedback: (1)

Also, when considering engine selection....on a twin...

Keep in mind that if you lose 1 engine... you do not lose 50% of your performance, but more like 80 to 90%!!!!!

Also, a larger engine will increase Vmc (minimum control airspeed, single engine) because of the increased thrust. So, if you have the good engine making maximum power, you have to maintain higher airspeed to stay in control than if you had a smaller engine. So, in other words, more power is not necessarily a good thing. NO SINGLE ENGINE GO-AROUNDS....or else be very very careful doing it. Vmc demo's close to the ground are spectacular, but you can usually only do it once.

Also know that the single-engine performance will be different depending on which engine quits... if the right engine quits, you will have better performance than if the Left engine were to fail. The left engine is called the "critical" engine on airplanes with left-hand rotating engines(facing the front of the prop). It all has to do with P-factor and torque.

Just wanted to throw some more stuff in to chew on[8D]

lions

Hi Fellas,

Just thought I'd add my 2 cents worth based on experience, not theory. Wanting to build a 4 engined bomber (I know, heard it before) a friend donated a Sterling Gazariator to play with. Shoulder wing, 4 channel, about 70 inch wingspan, designed for a 60.

Fitted 2 x OS 40's inboard, 2 x OS 20's outboard, total 1.20. Whilst performance was sprightly it was by no means a missile, use the throttle. Biggest problem was the glide, just like a stone because of the drag of 4 props, just land with some throttle on like the full size big multies. After more than 100 flights the 4 motors were removed (bomber built, flown & now almost 10 years old) & 2 x Enya 45 cx motors fitted.

These things put out more power than the type of 60's that the model was designed for but again no problems, sure it would go like a rocket but throttle back. The big difference was single engine performance which very rarely happened. Airspeed is the key word. With 1 engine out the remaining (powerfull) engine would fly the model fast enough to maintain control. It would roll, loop, touch and goes,even take off (almost full rudder needed) on one engine. End of argument.