Motor mount advice please ...

[MICKEYDSC71]

Just purchased the Power Pack C with the GT2215/10 motor, and was hoping someone could recommend a good motor mount for it. I don't have the exact measurement in front of me right now, but I'm anticipating the prop being around 6" forward of the firewall. My mind's been rolling over ideas of building my own out of tee nuts/bolts/washers/etc., but all the little bits can add up, so I figured I'd ask for the community's recommendation ... thanks in advance!

 

[FDS]

Not sure what you are after. The motor mounts directly to the firewall, which fits on the power pod, you mount the power pod in the fuselage to get your motor in the right place. You do not want the motor mounted on any structure that isn’t firm and flat, the torque will make a mess of any long standoff mounts.

 

[MICKEYDSC71]

Not sure what you are after. The motor mounts directly to the firewall, which fits on the power pod, you mount the power pod in the fuselage to get your motor in the right place. You do not want the motor mounted on any structure that isn’t firm and flat, the torque will make a mess of any long standoff mounts.

While I've debated going the power pod route, I'm leaning towards a more permanent mount to the firewall, but I need the 6" or so extension out from the firewall to accommodate the cowling. I was looking at the Great Planes mounts (see attached), but wasn't sure which of these would work with the GT2215/10. Would that mount be a good one for the motor?

 

[Mad_Mechanic]

I'm rather confused why your prop placement is ~6" forward of your firewall, necessitating the need for a firewall standoff.

Are you building a Flite Test designed plane or a custom plane?

 

[MICKEYDSC71]

I'm rather confused why your prop placement is ~6" forward of your firewall, necessitating the need for a firewall standoff.

Are you building a Flite Test designed plane or a custom plane?

It's custom ... I'm doing a Grumman AA-1B, and scaling from a line drawing. I'm following the firewall layout of the real plane, which has the engine suspended on a mount in front of it.

 

[Mad_Mechanic]

Ah, ok, interesting.

The cowling you are using, is it something already made? My first thought would be to move the firewall during your scaling process to avoid an extension/standoff. However, if you have parts already made that restrict this approach, then I think you would be better served by the firewall standoff you posted a picture of, it's looks pretty solid.

I would personally avoid an approach like using really long screws and washers or stacking a bunch of threaded standoffs.

 

[MICKEYDSC71]

Ah, ok, interesting.

The cowling you are using, is it something already made? My first thought would be to move the firewall during your scaling process to avoid an extension/standoff. However, if you have parts already made that restrict this approach, then I think you would be better served by the firewall standoff you posted a picture of, it's looks pretty solid.

I would personally avoid an approach like using really long screws and washers or stacking a bunch of threaded standoffs.

I haven't made the cowling yet, but was planning on carving a plug and then heat gunning a plastic bottle into the shape. The perceived benefits would be that the cowling would weigh hardly anything for its given size (and not be load bearing). I suppose what I should do next with the build is attempt to make that cowling and if it's successful, go the route of that mount with the cowling dressed around it. If not, I may just try extending the fuselage so that the cowling is load bearing, with the motor mounted to it.

 

[Mad_Mechanic]

Well, I think you could still have a cowling. The tricky bit is keeping the cowling scale based on your motor selection.

You said you ordered a Power Pack C, when that comes in I would suggest measuring it and trying to incorporate that into your scale designs for fitment.

Are you using any CAD software for the scale design work? If not, it might help. I would recommend DraftSight because despite what the website says it is free. However, I can understand not wanting to learn a computer program if you aren't already familiar/comfortable with CAD software.

It sounds like the concern is that the motor will interfere with cowling fitment?

 

[FDS]

I would move the firewall forward. People fit cowls to FT type planes all the time. The new Corsair model even has a compound curved foam one! Check out the build video, some of the techniques might be useful in your design.
If you want it to fly well then usually the motor and battery need to be further forward to counter act the mass of the tail.
That mount is designed for a more rigid airframe, you could manage it if you made the area behind solid enough not to allow the fixed firewall to detach from the surrounding structure.

 

[Merv]

I was looking at the Great Planes mounts. Would that mount be a good one for the motor?

If the mount you suggested fits it, should work fine.
I'd check the dimensions to see if it will fit under the cowl. It's hard to tell from the picture, it could be a larger mount for a glow engine.

One advantage if the power pod route, you can easily slide the motor forward or aft, to accommodate a cowl.

 

[MICKEYDSC71]

Well, I think you could still have a cowling. The tricky bit is keeping the cowling scale based on your motor selection.

You said you ordered a Power Pack C, when that comes in I would suggest measuring it and trying to incorporate that into your scale designs for fitment.

Are you using any CAD software for the scale design work? If not, it might help. I would recommend DraftSight because despite what the website says it is free. However, I can understand not wanting to learn a computer program if you aren't already familiar/comfortable with CAD software.

It sounds like the concern is that the motor will interfere with cowling fitment?

In a way, yes. I think the clearance of the motor to the top of the cowling will be close to scale vertically (the AA-1B's used a horizontally opposed Lycoming engine which put the drive shaft fairly close to the top line of the cowling). My biggest concern would be the forward placement of the motor so that it's to scale horizontally as well. I have the fuselage fabbed up to where the line of the firewall on the real plane exists (see attached, you can see that line just forward of the front windshield). The cowling starts on that edge and continues forward. My thought was to fab a plywood firewall to close off the front, with the mount extending forward of that.

 

[MICKEYDSC71]

I would move the firewall forward. People fit cowls to FT type planes all the time. The new Corsair model even has a compound curved foam one! Check out the build video, some of the techniques might be useful in your design.
If you want it to fly well then usually the motor and battery need to be further forward to counter act the mass of the tail.
That mount is designed for a more rigid airframe, you could manage it if you made the area behind solid enough not to allow the fixed firewall to detach from the surrounding structure.

I'll watch the build video tonight. I saw the maiden video this weekend and noticed how they tucked that pod in there. There may be a way to make that work here as well.

 

[MICKEYDSC71]

Thanks everyone for your input. Just finished watching the Corsair build video and you all have sold me on the power pod route. Truly impressed with how a material as flimsy as foam board can be fabbed into a structure that can handle a powerful motor. I'll order the power pod firewall and start working on a complimentary structure for the AA-1B.

Additionally, I was really impressed with the foam bending technique and I'm going to try that with my build, for both the wings as well as the cowling. The real Grumman has a wing profile with a little positive camber on the lower surface, so that curving would be great to have. Thanks again!