Hello,
I am considering front mounting Cobra3815/18 to the double sided copper clad laminate that will constitute the firewall.

The green part of the motor (stator) will touch the copper cladding (heat sink) directly for better heat dispersion. The motor will be mounted with four screws to the firewall.

Your comments are appreciated?

Thank you,
M

Hi Matt,

I use the same motor than you and in my plane it doesn't really get hot. I fly 6 cells and Igors 12x5 narrow blade 3-blade prop, use a 2200 mAh battery only and at 5.2 sec/lap energy consumption isn't that high, thus, the motor as well remains cool. In comparison, an AXI with same weight and same rpm/V but less diameter gets much hotter. I believe that more diameter helps with dissipating heat at our low revs. The slightly larger diameter of the Cobra 3515/18 also helps internal cooling.

I have however, when building also thought about using a heat sink formy front mounted Cobra and what I did was using a 2" wide aluminium U-profile that has approx. 1.5" long sides. These sides are then glued against the plywood reinforced balsa fuselage sides. The height of that piece of aluminium is approx the diameter of the Cobra, ca. 42 mm. I have drilled many small holes into the sides to give enough surface and contact for glueing aluminium to plywood.

I hope you can imagine how I mounted the Cobra-motor but as I said, it is uncritical with temperature, I even don't have a fan mounted. The aluminium heat sink stillhelps a bith though, maybe you fly in warmer spheres then Wolfgang and me here in Germany.

Christoph

Hi Christoph,
Please see the attached.
Is this what you use?

If yes: what is the thickness of the material used for the mount (bracket)? About 2 mm. I assume.

If the front part of the bracket is extended down, say 1", this extension can be used as a very effective heat sink. Imagine this extension cut vertically into four or five narrow rectangular fins and than twisting these 90 degrees. Such fins will be exposed to the incoming air and, at the same time, the air resistance will be reasonably minimized. Igor designed something like that some time ago - please see the second attachment.

What are you using your Cobra3515/18 for? What is the RTF weight of the plane?

Hi Dennis,
I use two 3.25" long, 0.25"x0.25" maple mounts epoxied to the 1/64 ply doublers that are epoxied to 3/32 medium balsa fuselage sides in my eParrot.
The mounts are thinned gradually from front to aft to save weight.
The firewall (0.18" ply-epoxy laminate) is screwed to these mounts using two 1" long aluminum wood screws and the entire length of the firewall (3") is epoxied to the 1/64" ply. In addition, four maple beams having the triangular cross-section (perpendicular sides: 0.2"x0.2") and 3" length are epoxied on both sides of the firewall-ply interface.

When the fuse front of eParrot was built like that and closed with the bottom and top 3/32 medium balsa, it created the tube that easily survives the motor's torque and the gyroscopic moments in sharp corners. I am using Cobra 2820/12 and APC Multirotor 11x5.5 prop on 4S 3000 mAh battery.

Regards,
M