I have a plane where the motor runs a little hot. I wanted to have a 3-blade spinner that was smaller than the current 1.75" spinner to let more air through. Previously, going to 1.5" spinner with 2 blade prop helped with cooling when hot but I wanted to stay with current 3-blade 11x5 Igor prop.

I 3D printed one based on recommendations Howard made in another post using a BadAss 1.5" spinner backplate. I also wanted to make it a little longer and more curved than the conical BA 2-blade. After creating this one, I found an aluminum one I had in my spinner box. It also fits the BA backplate. Sorry, I have no idea where I bought it from.

The spinner is 2 pieces. One for the body and one for the ring that glues into a slot at the bottom of the body and then slides into the backplate slot.

Page

Images
3 spinners - 3D printed, BA 2-blade, aluminum 3-blade.
3D Printed spinner with backplate
Inside of spinner
connecting ring between body and backplate

Nice. I'm a big fan of annulus air intake. Remember though the outlet is as important as the inlet. The outlet area has to be minimum 1.5 times the inlet and you need to be sure you have a clear passage to the outlet. As in no restrictions.

Quote from: Page Peterson on August 11, 2026, 03:59:18 PMI have a plane where the motor runs a little hot. I wanted to have a 3-blade spinner that was smaller than the current 1.75" spinner to let more air through. Previously, going to 1.5" spinner with 2 blade prop helped with cooling when hot but I wanted to stay with current 3-blade 11x5 Igor prop.

I 3D printed one based on recommendations Howard made in another post using a BadAss 1.5" spinner backplate. I also wanted to make it a little longer and more curved than the conical BA 2-blade. After creating this one, I found an aluminum one I had in my spinner box. It also fits the BA backplate. Sorry, I have no idea where I bought it from.

The spinner is 2 pieces. One for the body and one for the ring that glues into a slot at the bottom of the body and then slides into the backplate slot.

Page

Images
3 spinners - 3D printed, BA 2-blade, aluminum 3-blade.
3D Printed spinner with backplate
Inside of spinner
connecting ring between body and backplate

Can you share the STL files?

I also opened up the air exhaust even more with the current 1.75" spinner. The bigger hole was pretty unattractive and I had a timer wire come out during a flight. I printed this cover for the bigger hole. In addition to the two holes in the pictures, the plane has a 3"x3/16" exit hole at the back of the fuse as Bob Hunt does in some of his planes. I think I now have enough air exit area. The esc and battery are fine. The bigger exit cooled the motor by 10 or so degrees. It was best with the cover.

The STL is too big to post. I can email anyone that may want it. Message me with contact info. I will be back home middle of next week.

Page

Nice. Looks like its good to me. The very back of the airplane isn't the best place to put your exhaust hole. It is counterintuitive but that is the second or third highest pressure zone on the airplane, the highest being at the stagnation point on the wing. The lowest pressure zone is where the airplane as a whole is fattest which generally coincides near or on the wing maximum thickness. Somewhere close to that is the best place. It often isn't easy to get a good clear path to that spot so we do the best we can. As a powerplants engineer we have been through many debates on where and how to place the APU exhaust. Straight out the back isn't a good place and many jets put them exactly there. Then the APU windmills in reverse and has all kinds of problems including not being able to start in flight. More recent jets have the exhaust exiting the side and the intake has a deployable ram scoop to mitigate those issues.

Quote from: Mark wood on August 11, 2026, 06:54:39 PMNice. I'm a big fan of annulus air intake. Remember though the outlet is as important as the inlet. The outlet area has to be minimum 1.5 times the inlet and you need to be sure you have a clear passage to the outlet. As in no restrictions.

The annulus air intake looks like it's really effective. I also think it's butt ugly. I prefer a great big scoop right under the spinner, with a baffle to point the air at the front of the motor. I know that it's not as effective thermodynamically, but it sure looks better.

Well, you do want that air being forced to go through the motor, and then past the batteries and the ESC.

I have not built a lot of full fuselage electrics, but I have had pretty good luck by splitting the air intake, with about 2/3 of the air being directed at the motor, and the other third going past the battery and of the ESC.

You're not wrong the annular intake can be fugly as sin.  But it doesn't have to be great big to be effective. Spacing the spinner out a bit and making them 0.06" larger diameter makes a good balance between function and appearance. In combination with an airflow spinner is a great way too.

In light of Mark's posts, would further forward under the high point of the stab have the same effect?  All I have been able to read and a few AI searches tells me that they would.  Like a reverse scoop on a car hood. Unless I am wrong (it has happened) they do not produce so much "suction" as they do a smoother exhausting.  I will leave it up to the engineers to explain why there is a difference.  I also read that the trailing edge of an elevator/flap/rudder was a good place for venting.  Wouldn't the vertical slot in a tall thin fuselage qualify?  I also read that placing an external rear facing scoop/vent near the high point of an airfoil and/or the widest point of the fuselage had a better chance of producing the "Scavenging" effect.  So, in light of Mark's post, here are where I am placing my vents.  There is one more large vent over the ESC in the forward hatch and none in the aft. (hatches are off)

Ken

Quote from: Ken Culbertson on August 14, 2026, 10:21:18 AMIn light of Mark's posts, would further forward under the high point of the stab have the same effect?  All I have been able to read and a few AI searches tells me that they would. 

The exhaust hood idea certainly has coolness built in. I like it. Done right, adding heat in the cooling train they can produce thrust. The P51 radiator is a perfect example. In the cooling system we hope for reduced installation drag. Bottom line is if it makes you happy then absolutely do it.

Gotta be careful about what you're receiving from AI. Ask for specifics like sources. The term is relative. It's basically Bernoulli in application. The fatter the cross section' the lower the static pressure will be. We want to dump our cooling system into the lowest static pressure we can in order to realize the maximum mass flow. The way to think about it is to picture slicing the airplane into sections. The slice where the wing interfaces has much more area the the slice back at the tail. That means the static pressure at the section around the wing will have the lowest static pressure. AI is correct, moving the slice forward will reduce the pressure. However the  difference is slight. Especially when compared with the slice up by the wing.

I don't believe thinking about the lower pressure side as sucking the air out is quite the best way. It's more better to think of how fluids move. They move as the result of pressure differential. The greater the pressure difference, the faster it moves. The other part of the equation is the restriction in between. That is probably the more often overlooked part. I see lots of examples of large intakes coupled with small passages along the flow path dumping into what would be adequate exhaust. This happens very often around the battery which takes up a large piece of the cross section. It's also one of the biggest troubles we have with batteries. The motors have some self cooling ability provided they are given cool air.

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