sthudson

Hello,

I have a H9 60 size Corsair that I have done an electric conversion with. It has thrust angle built into the firewall and comes with pencil marks to align the motor mount. I checked the alignment with the factory marks and it was centered left and right. Unfortunately I didn't check it to be centered up and down. Well it turn out that it is about 1/2" from center (height). Will this cause any noticeable issues in flight?? I may just go ahead and change it, but it won't be easy with it already drilled with blind nuts epoxied in.

Thanks for your time,
Scott

meaden

If it was my plane and it was a 1/16th or an 1/8th off I wouldn't worry much about it but a 1/2" is quite a bit. I can't say for sure how it would fly (not good would be my guess.) I would change it.

alfredbmor

Yes it will affect the performance since the line thrust is much altered (1/2"). Engines should be placed with right or up thrust as well as right and left thrust. Some ARFs come very well tuned in this matter, so you only place the engine and you will have very acceptable flying characteristics. In others ARFs, you will have to tune this thrust adding some washers to the engine mount-firewall place. We are here talking about a very close distances from zero, the maximum amount of right, left up and down amount that I have changed in an ARF is about 3/32". As Meaden told I would change it, no matter how much time this task will take.

meaden

It shouldn't take that long to fix. Pry the blind nuts off carefully with a screw driver (or other sharp, metal, pointed stick) and fill the wrong holes with bits of dowel and epoxy. Sand flush. If the wood chips off on the blind nut side fill that with more epoxy. Re-drill the holes. Right as rain...

EZer

I to have the 60 size Corsair and just got done mounting a 20cc on it. When I slid the cowl over, I then notice the 1/2 different.

sthudson

Alright then. It's coming back apart tonight for the fix. Thanks for the advice! It's just frustrating when your so close to being done... but I have taken my time and worked on it here and there all winter, so a couple more nights is no big deal.

Thanks again,

sthudson

EZer: I think the factory pencil marks are wrong. Have you flown yours yet?? or did you too just notice as your finishing?

meaden

I was just thinking that there may be a design reason H9 has it a 1/2" off center. I'd look through all the documentation and see if it is mentioned. Or even call them.

It doesn't sound right to me but all I can give you is my experience with scratch building, kits, and an ARF or two. Most have the thrust line on the center of the firewall. Then it's corrected in one way or another.

Just don't want to steer you wrong...

EZer

sthudson,
the plane was all done and I was fitting the cowl when I notice the center line different. dont really know what I'm going to do with it, might just fly it and see had it handles.

acejinx

You know, I don't think the 1/2 will affect it that much. Look at the seawind, or catalina, or a number of other 'high mount' engines. Yes the horizontal stab is built for it, but they fly power off just fine. The horizontal stab creates the downforce for stability. If your motor was high, you would have a little more downforce, which in turn would be a minute increase in drag at high power settings. If the motor was low you could have a little less downforce at high power settings. This might make the plane feel 'pitchy' but hey, at high power settings you want the manuverablity. Either way coming in on approach you are going to have low or no power and it is going to fly just like it would otherwise. It's true that engineers take a lot of time to calculate this and that, but in real world application, I just don't think it matters that much. Heck, it might fly better!

alfredbmor

Yes everything may work here, and maybe that is why trim exists in our transmitters. I would change the motor position and let the trim for something else IMO.

sthudson

Thanks for all of your advice. I have taken it apart and am working on making the change. It would be tough to live with just knowing it's not right...