Hi folks got another question,

My busa sopwith calls for side and down thrust when I install the engine.
I have built a lot of wwll aircraft and always set them up at 0 degrees to the centerline. and set the wing to zero also if it was a fully symetrical wing...and slightly neg if it was a semi symetrical wing.

This is my first quarter scale bipe and I was wondering if I really need that side and down thrust.

Also I was wondering has anyone tried to glue a piece of hard rubber to the firewall to absorb vibration.

My zenoah has a large flat surface that mounts against the fire wall.... seems to me that a piece of hard rubber about 1/8 inch thick and the size of the fire wall would help.

I don't know just asking the experts.

A plane all set up to zero angles will fly well. It will not fly at it's best, but it will fly well enough to get going until all small quirks are trimmed out. The need to trim out the plane depends on whether you have automatic thumbs that even out the plane's deviations, or whether you need it to be neutral through all manoevres. BTW, That is the holy grail of all plane designers. Some come close.

Most of your standard trainers and high wing planes have downthrust. The reason is because the wing is on top and creating drag. That drag is pushing back on the leading edge of the wing. Push the leading edge back and the nose of the plane comes up. So, downthrust is usually required.

Most low wing planes are opposite. The drag on the leading edge is pushing the wing back, but since it's on the bottom, that will tend to pull the nose down. Up thrust is needed.

Shoulder wing should come out with zero thrust up or down.

That's just the theory. Does it always work? I dunno. Ask an aeronautical engineer.

On the rubber:
Sounds good, in theory.

But consider this. By the time you get the bolts tight enough to secure the engine to the firewall--you will have completely smashed the rubber. It will not provide any vibration isolation after it's smashed down tight.

Forget the rubber and mount it directly to the firewall. Gas engines shake. Nature of the beast. You just make sure the airframe is glued correctly and add some tri-stock in strategic locations up front to prevent any flexing. You want a solid firewall and mount. The vibrations will be transferred through the airframe. The wings and the mass of the airframe will absorb the shock from the engine vibrations.

I dont have any experience with this model... but I guess the question that comes to my mind is.... if the plans suggest that then why go against it? I mean they designed the plane and are probably the best resource for engine mounting suggestions. A lot of planes already have thrust built into the firewall... maybe they didnt build it in but decided it's required after testing.

Jake, Thanks for the reply, yes I used to think that way also but on every model that I have built (which were low wing fighter aircraft) I zeroed everything out including the wing, and they flew a whole lot better.
basically I turned them into pattern ships. This is why I asked the question.
This is my first bipe and I wanted to get some first hand expert advise and I did,...this plane requires right and down thrust just like you suggested. This is why this forum is so great, before computers you had to do trial and error, this helps eliminate going back to the drawing board so many times.

Thanks everyone

Good that you found your info.. I wasn't trying to be smart. Every plane I have had I have always added washers to adjust the thrust. Def. a fine tunning process.

Just part of the fun

Jake, I'm sorry, I did not mean to sound that way.
I was just trying to let you know why I was asking that question.

RcPilet, Thanks for the info, you mentioned gluing the frame properly, I've always used white glue on all my nitro powered aircraft.
This is my first gasoline plane, would aliphatic resin glue be sufficient? I don't realy trust CA type glues

no worries... I wasn't thinking about yur response... I just wanted to let you know I wasnt trying to be smart in my original post. I re read it and thought it could possibly be taken the wrong way thats all

Regular ole carpenters glue works good on balsa wood.

Gorilla glue works good, but it foams and spreads the joints out. You have to clamp and then wipe the foam off about 3 times within the first 20 minutes. After 20 minutes, it's done foaming and swelling. But who wants to fuss with every joint for 20 minutes? Not me.

White glue works, but it's not my first choice.

I use CA on everything but the landing gear mount, wing joint and firewall. CA works great. Just make sure you sand good and have nice tight joints. A tight joint is the best thing you can do for making an airframe last a long time. CA practically fuses the joints together. But, I know some guys can't handle the smell.

Thank you jake, I thought my answer was misinterpreted, I definitely do not want to upset anyone, especially when I'm seeking help...Ha!Ha!

RcPilet, Thanks for the Info What you said sounds logical since I have used all of the glues you mentioned.
I think I will go with CA.

The side thrust is probably to counteract torque at high throttle settings.

I'm not a fan of any down thrust on any model. The problem with trainers is all of that extra angle of incidence put in when the leading edge is set higher than the trailing edge. Also, the flat bottom airfoil is at work too. So, downthrust is there to provide some sort of fix to keep the trainer somewhat level throughout the throttle range where it won't balloon up on you.

I've not owned a bipe from the era of your model, but I've seen enough flying to see that they have a lot of slow speed lift. Drag is probably very high. You can always use shims if the angle is too much.

Thanks blw, Thats what I was thinking, I hate down thrust also if you set the wing incidence to correct the extra lift problem then you don't need down thrust, this is true on single wing models, I wasn't sure on bipes.
But after I thought about it for a while..... (that is dangerous, me thinking).....The bipes have such a high drag what difference would it make to have a little side and downthrust, plus I'm not going to be flying it in a pylon race anyway.

I'm having to change my way of thinking after all these years.

If you do not put in right th. in it. your bipe. what you will get it a trim that is not at 0. You land your plane and walk up to it you will see you ailerons one up and one down just a touch to fly Laval. Right th will take that out. with it being a tail dragger you will need just a little more right rudder to keep it striate on the run way. With the down th the plane will tell you if it needs it if it blooms.

I know a lot of people that will put all at 0 and set up mixers to do the rest. I guess what I am saying is it is all in what you want to do with the plane.

Paul