Engine Mounting question
 

First post here from a "born-again" RCer. It's been about 15 years since I built a kit or touched a transmitter, but have just recently decided to jump back into it. I used to me involved in High Power Rocketry, but after the ATF restrictions on the hobby after 9/11, it just wasn't fun anymore, so I needed something else to do. Back in 1991, my father purchased a Great Planes Trainer Sixty, along with the "then" new narrowband Airtronics radio. He got as far as building the wing and most of the fuse before he lost interest and packed it away. I recently ran across the kit and that's what re-kindled my interest in RC. I have finished the kit have all the control systems installed and am ready to mount the engine. But it's been so long since I've built a kit, and the instruction booklet was missing, I'm not sure the proper way to mount the engine anymore. I seem to remember being told before that the engine should not be mounted perfectly straight in the motor mount, but should be pointed slightly to one side to counteract the torque of the motor.

So, here's my question.

What IS the proper way to mount the engine? According to the technical data that I downloaded from the Great Planes website, is says that the engine thrust is zero to the right and down. Does this indicate that the firewall isn't offset and provides for zero deflection? Do I need to mount the engine (a .40 by the way) pointed slightly to the left (port) or straight?

Thanks
Connery Carroll
Chandler, TX

RE: Engine Mounting question
 

From my experience your fire wall should be fine if built straight most modern kits today already have the correct position built in when the fire wall is set in place. So with that in mind I would mount your engine straight and go fly after a good pre-flight of course so have fun.:D

RE: Engine Mounting question
 

Looking from the cockpit forward, you want to angle the spinner right slightly and downthrust. Most trainer kits have the downthrust built into the firewall installation. If not, put a 1/16" thk. washer between the top two engine mount holes and the firewall.

I hope it was a typo when you said you were putting a .40 engine in a sixty trainer.

RE: Engine Mounting question
 

No, it wasn't a typo, this ond trainer was designed for a .40 as a minimum or a .60 for more performance. Since I have the .40 sitting around that's what I'll use to get used to things again. Since I didn't get the construction manual, just the plan and I didn't do most of the fuse construction, what's the easiest way to check to see if the proper downthrust is built in or not?

RE: Engine Mounting question
 

It'll fly fine with the forty , just not very aerobatic. My first r/c airplane was a
Jensen full size Ugly Stick with an Enya .45 . It flew fine , just didn't have enough
power to do anything other than learn to fly.

tommy s

RE: Engine Mounting question
 

Install the engine mount on the firewall, then set the engine in place, just as it will be mounted. Using a long piece of twine or some type of cord that doesn't stretch, hold one end of it on the front of the engine shaft, then move the other end to the tip of the left elevator (as looking from the back of the plane) and mark it where it touches the elevator. Swing the end of the string over to the right elevator tip and the mark should end up slightly further back, if there's right thrust built in.

If there's no right thrust, then add a washer on each of the left engine mount bolts (between the mount and the firewall). That will give you a couple of degrees of right.
Dennis-

RE: Engine Mounting question
 

Connery, I am in the process of building this exact plane from an updated plan. There is 2 degrees of right thrust. The plans tell you to offset the engine on the mount to get the 2 degrees. You could mount it up and just shim the mount some on the left side to get the right thrust. I am going to try mine without the right thrust first. If it needs it then I will shim some in. There is some down thrust that is built into the fuselage. The firewall gets glued to the sides at an angle set up by the fuse doublers. Just mount up the engine and have at it. You are right, a 40 to 46 for training. A 60 for airobatics and advanced training. I have a brand new Irvine 61 for in mine. I converted it to taildragger configuration. Going to use a Dubro vibration reduction motor mount. I am going to have to modify the cheeks to fit the mount. Also using Robart hingepoints and Robart control horns. Otherwise building it stock. Good luck with your trainer 60

Mark Shuman

RE: Engine Mounting question
 

Mark,

Thanks for the reply. I was hoping someone MIGHT have this same plane and have the specs. I went to the Great Planes website and the specs they list just say Right 0 (zero) and Down 0 (zero). No explaination if this meant the kit had the right/down built in and needed zero offset on the engine mounting, or if it meant that the kit has zero offset built in.

Connery

RE: Engine Mounting question
 

Connery I forgot to mention. The plan calls for 2 down and 2 to the right (Degrees thrust). This plan is from RCM. The trainer series is based off this plan. I wanted a kit for years couldn't find one until this plan came out. So I am scratching one up from the plans. It is the same as the kit except they added a bolt on wing. I can't wait to get it in the air. Right now I am fighting with the cheeks. They interfere with the motor mount. I am afraid they will have to go. Good luck with your plane. A freind of mine had one many years ago. Seeing his fly made me want one.

Mark Shuman

PS: check the plan you will see the built in down the fuse side doublers have it built in.

RE: Engine Mounting question
 

i have a question too..Im trying to mount my first motor and all the other ARF's i've got had the fire wall predrilled at the factory for the mount. Im building an Extra up that has a BOX type of fire wall at the front and a hole slightly at the top for the fuel tank to come through.. Do i mount my motor's crank in the middle of the hole in the fire wall or do i find the center of the whole fire wall and mount it there so it would be in the centre of the plane?

RE: Engine Mounting question
 

The motor will be mounted horizontal, does this afect where it need to be mounted?

There is no need for the thrust to be done as its built in to the box.