teufelhund

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Hi All,
It's been a while in taking shape but it is recognizable as a twin now. The nacelles gave me the most frustration. I couldn't figure out how to get the strength I wanted to attach to the wing. I finally figured it out though. Here are some pics. I have two brand new OS max .91 2 strokes powering this one.

Flyboy Dave

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....that should have plenty of steam. [sm=thumbup.gif]

FBD.

NikolayTT

Nice looking but distance between engines is too big compared to the wing span. It seems easy to
enlarge the wings on both sides. Check for example Catalina picture for the ratio of wing-span
versus distance betwen engines. That will save your plane in case if one engine stops; Catalina
was designed to fly even on one engine. I believe you should almost double the wing span of
course the parts you add should go narrow to the tip; maybe it is good to scale some real
plane wing shape (seen from above).

NikolayTT

One thing more: - in hard landing some of your engine exhaust most likely will hit the ground and
the damage on plane&engine will be severe, isn't it; I would keep the engines with vertical head,
that has several other benefits too.

teufelhund

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Hi NikolayTT,
I thought about adding some length to the wing as well, but I thought that because the wing has such a broad chord I should be alright. I still don't understand what you mean about the hard landing damaging the engines unless you mean that I need to lengthen the distance between the main gear wheels. It has been my experience also that the engines should run perfectly fine on their sides when adjusted properly. Thanks for sharing your thoughts on the plane and please add more if you think of anything. Thanks for looking! Ben

teufelhund

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Hi Dave,
Thanks for looking. I was wanting plenty of power for this one as I plan to have it perform on floats as well. It may get a third engine also.[X(] It was originally designed as a trainer for a 25cc to 26cc gasoline engine. Ben

NikolayTT

Hi Ben,

I have twin of OS.91FX and that is quite heavy. Looking at your landing gear - it looks almost half of the strenght I have
unless you use some special metals there. Then with this wing surface you have, you will most likely come to about of
100g/dm.sq wing loading or more and then the stall speed will be maybe near 100 km/h, thus your main landing gear
will be "tested" because you haver to either land with high-speed (you seems you have no flaps) or almost stall the
plane very near to ground. I have about 210 cm wing span and wing loading is about 80g/dm.sq and still the landing
is not what I want especially if the engines are killed prior landing. Not to mention that there might be a cross wind
and then the story will get further more nasty and one of the wing tips will head to the ground - there is the engine
muffler which will hit first the ground and that is very bad if you land on asfalt especially; anyway I broke my engine
even on a grass ... and I will not place mufler near ground, maybe on contrary; I will place the engine in the way
that the muffler is on the top; yes it is a bit ugly while it is a safe solution.

In fact if you enlarge the wings, there you cam place the ailerons and your current ailerons you could control as
flaps and that would be pretty nice solution I would vote for.

Regards,
Nikolay

teufelhund

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Ok NikolayTT, I see what you are saying now about the landing gear and the wing span. I do have flaps on it(look closely and you can see them). The main landing gear was designed for a giant scale Sukoi (25-26lbs) so it should hold up. The Robart nose strut should also be adequate. It is rated for 15- 22lbs aircraft. My landings aren't that hard(most of the time).I still have quite a few more things to work out before she gets maidened though. I may go ahead and lenghten the wings a bit. I done the math before for the wing loading(22oz per square foot) with a 25cc gasoline engine(2.5lbs) and everything needed to fly so everything has changed now. I think now it would probably be closer to a 30oz psf loading on the wing. Thanks for your input again. Ben

TRoc

I like the mods to your Treehopper, Ben! Looks good, especially the twin rudders (besides the twin engines). Were it me (and this may not be wise) I'd see how it flys with the current wing; if it (survives and) needs more wing after that, build outboard wing panels and figure out how to attach them to the current wing (after removing the tips).

Twins are fun and I think it's good to have at least one in the stable (I have a Sportster 40 twin). When I fly my twin, a lot of time is spent wondering if both engines are running !

I enjoyed seeing your creativeness with the Treehopper![8D]

Tom

teufelhund

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Hey Tom,
Thanks for the compliments! I'm going to try the current wing and see. I still have to make up a balsa nose cone for the Treehopper also. Finished all covering now except the nacelles and ailerons/flaps. I was wondering about the wing loading on this one to. It may become a sesquiplane![X(] Thanks for your input again! Glad to hear you got everything straightened out with your motor. Ben

TRoc

Hi Ben,

This is just a guess, but I'm thinking the wing loading with two FX 91's will be about the same as the wing loading with one Zenoah G26; Two FX91's weigh about 25 oz each with muffler = 50 oz. A G26 weighs about 60 oz. which leaves about 10 oz. left for the weight of the two nacelles. While I wouldn't consider my G26 powered Treehopper to be a floater (maybe my CG is too far forward), it does well and has a gentle stall (actually I run out of elevator getting it to stall so maybe it's the CG thing again). I may be overlooking something, but I don't think the wingloading on your twin will be that much different from that of a "regular" Treehopper.

I'll be interested to hear how your twin flys.

Maybe after a season or two, you may want to try another engine on the nose! <grin>

Tom

teufelhund

My Feedback: (2)

Tom,

I had thought about a third engine also! I'll just have to see about the wing loading when I get it finished and ready for maiden. I know that you had said that maybe the CG was off before in the other thread, did u ever try changing it? If so then what were the results or did you just change it back to what it was originally? Thanks for the info! Ben

TRoc

Ben,

I think I was focusing more on getting the engine to run well so didn't get around to experimenting with the CG; The plane actually flew fine where I had the CG from the start and I didn't change it. Plane is stable, tracks well although as I mentioned, it feels just slightly heavy to me on the elevator but not bad. It does take a lot of down elevator for inverted flight but perhaps a lot of that is due to the flat bottomed airfoil. Also (from the other thread), some time back I added down thrust because it would clearly climb when I added power from straight and level.

Regarding the third engine. Probably enough on your plate now with two engines; the third one can be for dessert later.[8D]

teufelhund

My Feedback: (2)

Hi guys!

For all of you waiting to hear if this twin flys or not, IT DOES FLY! It flys very well and tracks straight and true. I finished it up yesterday and began breaking in the engines in. All up weight came out to 18lbs 9 oz(dry). Today I took her out to the field at around 6:30 and knew if I was going to fly it wouldn't be for long as the sun sets at around 8:00 now. I got out there and tweaked the engines a bit more then decided to take her up as I thought the engines were good to go. I done some taxi runs at speed and then decided to go for it. I was pleasantly surprised as she gracefully lifted off after about 25 feet of runway(this was without flaps)! I got some altitude and began to trim her. Two clicks of up elevator and 3 clicks of left aileron had her flying straight as an arrow. I cant't believe how good this plane flys as I thougth she was a little overweight. The twin OS 91FX"s sound awesome as she is flying around, especially on the low passes. Like I said I cant believe how well she flys! Well after three or four circuits I decide to land and try the flaps for takeoff. Landing is smooth as silk and I start to taxi up to the pilots table, right engine quits. I refuel and taxi around a bit after tweaking the right engine a little(these are brand new engines) as it starts and runs very good on high end. I decide on takeoff again with flaps, this is gonna be the last flight of the day as its getting dark. I taxi out and begin my takeoff roll after probably 10-15 feet this thing leaps into the air and is heading right for me and my buddies on a right hand turn, I straighten it out and apply full power after I see its not going to hit anything with the nose at a 85 degree angle. She keeps climbing straight up(no shortage of power at WOT). Pucker factor dropping (lol) now and I do a few circuits and decide to bring it in for landing. I am on final still at around 50-60feet alt and both enignes die at the same time. No problem flaps down and I grease her in. Needless to say the engines need a little more running in and some tuning. All in all a great day as I got to fly and the plane is back in one piece. Pictures will be forthcoming in the next few days. Oh forgot to mention that this bird is fast when WOT. No tendency to pitch up when applying full throttle either. I attribute this directly to the down thrust I built into the nacelles on Troc's suggestion. (Thanks Troc!) See you guys later! Ben

TRoc

Good job, Ben! Way to go! You can feel good that you did something different by building a twin and being successfull at it! Sounds like it's a winner. Congratulations![sm=thumbup.gif][sm=teeth_smile.gif]

JohnBuckner

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Congratulations Ben you did a fine 'bash' and there is nothing more fun than kit bashing multi's. It appears you made some good decisions.

I would have second thoughts about a third .91 especially without adding a llittle on the wingtips perhaps around one bay each side to reduce the wingloading slightly. Just a thought.

John

teufelhund

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Alright guys as promised, some shots of her in the air and others. Nice to hear from one of the Master bashers also, Mr. Buckner. I don't think I'm going to put a third engine on this beast as it has plenty of POWER! Enjoy, Ben

ps2727

Ben,
Great looking twin!
Congrats,
Paul

teufelhund

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Thanks for your comments Paul. It looks like you do some great work too. I really like your landing gear designs. The LG on the f104 is a work of art! It must be really time consuming to get that complicated gear to work as it is supposed to. Some very nice machining work you have done there. Cya, Ben

JohnBuckner

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OK Ben I can see many happy flights and experimenting with that airplane but no practitioner in the art of bashology could ever last long without thinking about the next 'Big Bash'. See you have already been talking about the next big one in this thread with the third engine.

So whats it gonna be?

teufelhund

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Hi Mr. Buckner, I'm really not sure yet but i think I would like to put two engines on the wingtips and 1 in the middle of some typw of aircraft. I have seen a german design from WW2 with this engine arrangement, however the aircraft never made it past the design stage. Maybe time to change that, as I don't know of anyone that has built a model in this configuration. Ben

teufelhund

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A few more pics from this weekend.