Hi, the plans for a plane I'm building show the engine mounted off centre a good half inch towards the (right) side of the firewall. There's about 2 degrees down thrust and 1 degree right thrust.

I was just wondering what this would do to the thrust line and why the designer would set the engine off to the side? Is this done so that the engine head will clear the side of the fuselage for better cooling? (strange?)

Originally, the plans involve a beam mounted engine, but I'm using a dave brown model. I've already cut/drilled out all the necessary holes but took a moment of pause before assemblying the fuselage to ponder this design. Should I stay with the original design or just cut another firewall with the engine in the centre?

Thanks.

It depend on the plane but I always found that right thrust is good for helping you at take offs.
What kind of plane is??
Give as much info you can and for sure you will find a good answer here between the 1/2A gurus.
Saludos.

[8D] If these engine thrust angles are what the plans call for, I'd go with them to start with. If the plane sucks on ice as a result, then you can always re shim the engine to correct it. My suspicion is though, that these are the necessary engine thrust angles recommended for decent flight, that is if your building entirely according to the plans. Some planes with a short nose moment, or spinning bigger props have a considerable amount of gyroscopic torque induced upon them by the propellor. The propellor spins to the right (when your looking at it from the cockpit) and hence the aircraft, thanks to Sir Isaac Newton, "every action has an equal but opposite reaction" wants to bank left, and incidentally fly into the heads of any innocent bystanders. Sooooo, long story longer, one way to counter act this "torque to the left" effect, is to put in a bit of right thrust in the engine alignment. The right amount will effectively counteract this torque effect and provide a more level and controllable flight attitude. The down thrust in the engine is similar but different, in that it is also there to counteract a tendancy, this being uncontrolled climb. Some high lift aircraft need this down engine angle to counter act the high lift they produce, so instead of flying around with your thumb on "down elevator" all day, you can alter the dynamic for level flight and better penetration in this manner. Another way to do this same thing is giving your horizontal stabilizer some positive incidence. Either way, its there for a reason most likely. Follow the instructions to a "T", and then see what happens.

Good Luck!
ZZ.

Thanks guys; this forum is the best learning tool I've come across in my RC adventure.

I understand the need for right and down thrust, but in this case, the whole engine is mounted towards one side of the firewall. i.e. it's not just pointing one way but its actually mounted off centre.

Don't think this produces right thrust; if anything, I would have thought that this would create a moment of force that would yaw the plane towards the left!

The plane is a marutaka Mini Devil. Pretty sure its unknown to most, and for some reason, I can't seem to post a picture of it at the moment. However, you can see a picture of it here:-

http://www.udisco.com/hobbies/desc/100029.htm

I'm pretty new to this, but its the first time I've seen an engine mounted off the centre line of the firewall. Just a little concerned cuz if it doesn't work out, I'll probably have to cut out the firewall to remount the engine.

Ideas.....?

Thanks.

That is odd. I've never seen that before.

The only thing I can think of is that the mount specified in the original plan has a non symetrical hole pattern that makes it look like it's offset but once the engine is fitted it all ends up centered. But it's a safe bet to say that you should correct this and mount the engine on the centerline and with the offset angles only.

Thanks Bruce. I thought the offset was because of the beam mount design, but after measuring and measuring and checking both plans and parts, I still end up with the engine mounted off centre!

I've had the fuselage sides and all the formers laid out on the table for the last 2 days while I agonised over this issue.

Should have come here first! Will get cracking and put together another firewall when I get home.

Thanks again everyone.

Woops, sorry efish, my bad. I didnt realize you meant the WHOLE ENGINE! That really does sound wierd, and your right. It will probably induce left thrust as a result. Bizzare. Bmatthews is on target though. Ditto what he said!

ZZ.

The engine is mounted off to one side so that the spinner can line up better with the front of the cowl. It won't make any difference with how the plane performs, it is done for appearance. I've never run into a 1/2A design that needed right thrust to fly straight, you will see the need in larger models, though. Some guys indicate a tiny bit of right, just so a tiny bit of left thrust doesn't get accidently built in. I would rather just build straight and get my impressions about what the plane needs after flying it. Up/down thrust angles are far more important to pay attention to, these make much more difference.

I think CP has got it right. If the engine is side mounted (like it appears in the pic) then moving it off center may help it to line up with the centerline of the cowl and centerline of the plane too. I also wouldn't worry too much about right thrust with a 1/2a motor either.

Oh, by the way that's a nice looking plane too!

Thanks CP, propbuster; the engine is side mounted so that does make quite a bit of sense.

To be safe, I've already made another firewall with the engine mounted in the centre. A quick comparison suggests that the centrally mounted engine may actually be better aesthetically as the offset one had the muffler protruding out of the cowl by about 1/8". so I think I'll go with the engine in the centre.

Propbuster, in gratitude, if you're interested, think my LHS may have a kit left. Only problem is that it's in Singapore, and I have no idea how to get the kit to you. Alternatively, if you know how I could scan the plans with an A3 scanner, I could email you a copy. (I think the kit is way overbuilt, anyhow) I believe the Marutaka company is now defunct, so I don't think there'll be any infringement of intellectual property rights.

efish, I'd sure like to have a copy of the plans for that kit only I don't know much about scanning stuff other than my scanner for my PC. I usually take a set of plans to a copy store here called Kinco's and make a copy there for $5 to send to other guys. There is some way to copy plans in a tiled format where you tape a bunch of 8" by 11" pages together for the whole plan but I don't know anything about how to do it. Thanks for the offer!

Well, if you're savy with photoshop,I could send you a few A3 scans that you could stitch together. Heard from a friend that they do graphics like that. Not sure how accurately it would work with a plane, but you're welcome to try!

I've been hunting around locally for a store to print my plans, but I can't seem to find one! They must exist, since we have plenty of architects etc, but it seems a DXF print to A0 or A1 is just asking too much....