fuselage layout

[Aj114]

Hi
I am building a rectangle long shaped fuselage with my brushless being at the front and using a kfm 2 airfoil with a conventional tail.
After i installed my hardware i realised that ny propeller doesnt exceed my fuselage by much... will that be a problem or will it be blocking my thrust power?
Also is it wrong to have a fuselage shaped rectangle or do i have to make it deeper than the width? And why?
Thanks

 

[Ketchup]

Could you post a picture of your plane? I have built planes with wide fuselages, but I don’t know how wide yours is compared to the prop. Also, you can try throttling up the motor while holding the plane to see if it creates thrust.

 

[Merv]

A rectangular fuse will work, there are many planes that use this design. The arc of the prop needs to exceed the fuse. Try a smaller fuse, one just large enough to hold the electronics.

 

[Aj114]

A rectangular fuse will work, there are many planes that use this design. The arc of the prop needs to exceed the fuse. Tyr a smaller fuse, one just large enough to hold the electronics.

Why is that so?

 

[Ketchup]

Why is that so?

The arc of the prop has to pass the fuse because if it doesn’t the air pushed back by the prop will just hit the fuse and stop, it won’t push the air back and create thrust.

 

[JasonK]

Why is that so?

for some actual metrics on this, I tried building a thrust testing method for my props, put the motor facing up, and weighted it down on my scale... got way less thrust then I thought... I extended the distasnce between the motor and the scale... everything else the same, thrust went up. basically the air moving down from the prop pushed down on the scale offsetting the lift. If your prop is blocked by your fuselage, it will end up in the same boat.

 

[Merv]

Why is that so?

I agree with @Ketchup, the thrust from the prop will be pushing against the fuse. The equal and opposite forces will offset each other. There may be some side thrust generated, but that's not what we are looking for. This principal is what makes a pusher setup a bit more efficient than a tractor setup.

Keep in mind that the thrust is directly proportional to the area, if you double the raidus you have about four times the area. The area increases by the square of the radius as you move outward, Pi x R squared.

 

[Aj114]

Thanks Merv, Jason K & Ketchup for clearing it up for me, highly appreciated.
Ill send you a photo once i put it together.
Ill definitely be in touch as this is my first time building.