Need advice with motor mounting

[Bobbydog]

Hey everyone,

I'm in the final stages of putting together my Fliton Extra 330 Mini and have ran into a problem with the motor mount location. The problem is that if I use the centering hole thats precut in the mount then the motor shaft sits too low in the cowling cutout. This is a problem that I've run into before and have always just moved the motor around the mount or added a new mounting plate to get the shaft centered in the cowling cutout. I figured now is a good time to find out the proper way to deal with this. Do I...

1. Make a new motor mount plate and center the motor shaft with the cowling cutout.
2. Mount the motor in the precut motor mounting location and cut out more of the cowling.

The other question I have is, when adding right thrust, should I move the motor mount to the left to keep the motor shaft in the center of the cowling cutout? Or do I just leave the motor mounted in the center of the mounting plate, and have the motor shaft not centered in the cowling cutout but instead closer to the side of the hole...

I know this is damn confusing and I hope that someone whos had a few beers or other can decifer this post enough to help me out here. Thanks in advance!

Bob

P.S. If you need more pics or info just ask

[Bobbydog]

I guess its a question of how important it is to maintain the designers thrust line. I cant see the builders making a mistake in the motor mount hole location, but I can see them making a mistake in the cowling hole location. Follow me? If I cut out some notches in the cowling for the landing gear, I can get the holes to line up better. I'm thinking that this is probably the best answer. Anyone agree?

Bob

[F3AFlyer7]

The best idea here would be to stick with the manufacturer's center line. The cowl has little effect in how the airplane flies other than a little streamlining, but if the motor isn't centered properly then you can run into poor flight characteristics. I would suggest just moving the cowl to fit the proper center line, and not moving the motor or firewall.

Also, If you are trying to add right thrust, you should move the motor to the left slightly. That way it will keep the propeller on the centerline of the airframe. You can figure out exactly how much you need to move it by using trigonomy. On very small motors, however, it is almost too small of a change to really matter.

[1trumpet]

You have it mounted by now. I have electrified several different models. BVM Astral XX, Trejro, Oxai Pennicle and a Show Time. The Show Time is probably like your application. I used the factory center line markings to center a box I built out of ply wood. My motor mount frame was square and I marked the center line both directions on it. The offset was pre-determined so I used thiers. I built both sides of my box the same leingth. I planned in advance to use nylon spacers, 4mm, I purchased at Ace Hardware. They are Black and come in various leingths including shims. Using them and the spacers I was able to tweek the thrust after I flew the plane. You can cut slots instead of holes in the box and move the motor left and right or up or down. Use a plywood back plate to run your 4mm bolts through. I ended in a prepisition...........oh well. Anyway it works well. I used that techneque on the Trejro also. Verticle climb at full power in calm air will tell you how many shims to the right or left. Half throttle in level flight will tell you how many shims up or down. Straight down dive, power off, will let you know if your stab or wings are aligned. Knife Edge will let you know if the CG is correct. Canopy out or belly out is corrected as far a possible before you tweek the transmitter. Fine tune with the transmitter. Same goes for straigt flight. All throttle positions need to be tweeked with your condition mode on your transmitter. Rudder fine tunning the same. It may pull more to the left or right at different throttle setting. Go to conditions and adjust the rudder to fit the throttle possition. Good Luck. !trumpet

[Highlights]

Bob man, what I do( and this will go right up to any size stuff)
Remember , you can cheat the cowl on the smaller stuff. However if the model is good then the manufacturers would /should have already taken this into account.

From the cross buck on your fire wall( or if it is just a circle cut out) you must establish the centre of the thrust line. From here you must project forward to the prop. ie. the bigger the motor , the farther to the right the thrustline will deviate from it's original centre of the fire wall.So yes you need to move the motor to the left to compensate for this.

I use a staight edge taped to the fuse for both top and side . from there I eyeball the prop shaft to fall on centre of these lines. Voila. Perfect every time. No matter how large the motor.

Hope this helps.

[Bobbydog]

Thanks guys, some great advice. I have a good grip on the fundamentals now. I ended up just cutting some slots for the landing gear to fit into, just small cuts and then everything lined up perfectly. The plane flew great, at least for the first 3 flights lol. Then somehow a tree jumped out in front of me and grabbed the damn plane! Anyway, its a long story. The ending of the story is that the plane is now back to 100% but it wont fly again untill my proper runway is finished. Should be in about a month. Check out my "building runway, need advice" thread Mark, I started it about 2 weeks ago. I cant wait! Its been ALOT of work but it'll be worth it. Thanks again everyone. Peace.

Bob