Go Back  RCU Forums > RC Airplanes > Aerodynamics
Reload this Page >

Placing the motors in Pull or Push configuration?

Notices
Aerodynamics Discuss the physics of flight revolving around the aerodynamics and design of aircraft.

Placing the motors in Pull or Push configuration?

Old 12-18-2020, 09:13 AM
  #1  
makehobbyrc
Junior Member
Thread Starter
 
makehobbyrc's Avatar
 
Join Date: Dec 2020
Location: France
Posts: 8
Likes: 0
Received 0 Likes on 0 Posts
Question Placing the motors in Pull or Push configuration?

I need some advice... about my RC Foam Home Made Seaplane (I hope will fly one day...).
About the motors... I will have 2 at least maybe 3. I have bought 2 ducted fans but also 2 simple brushless motors (with 15cm = 6 inch props...). I might use 2 ducted fans or / 2 or 3 propeller motors...

My questions are: 1) Any preference in putting the motor in Push or Pull configuration? Propeller in front or behind then motors...
2) And any need to put the motors at a slight angle from the longitudinal axis of the aircraft... It is a Seaplane, and the motors will be placed slightly above the CG, to be above the wing and fare from the water... Any need to have a slight angle pitching downward (for the rotational axis of the motors) to compensate for the "nose down pitching effect" whilst accelerating....?
Thanks a lot!
PS: pictures will come as soon as I am allowed to post
Old 12-22-2020, 01:26 AM
  #2  
BMatthews
 
BMatthews's Avatar
 
Join Date: Oct 2002
Location: Chilliwack, BC, CANADA
Posts: 12,398
Likes: 0
Received 17 Likes on 15 Posts
Default

Objects in front of the prop tends to reduce their effectiveness. Props work best when they see clear air free from turbulence that occurs from parts of the model. So I vote for normal tractor use.

And yes, you will want to angle the motors so they face up by a good angle. On the flying boat I built last spring I went with +2.5 incidence in the wing and the motor pointed up another +2 more than the wing. It still had a slight tendency to dig in the nose when on the water during the slow part of the takeoff run. But in the air it was just about right. No strong tendency to climb with throttle.

I thought the prop was up high enough too. But the nose digging in even the amount it did caused water to come up around the nose and into the prop. So plans are to add on a pair of 1/4" (6mm) wide by 1/2" (12mm) tall extra chines on the nose both to aid with floatation in the nose as well as act like to direct the water more to the sides. I learned my lesson. LOTS Of flotation up front ! ! !

Bubbles original design flying boat.

Bubbles flying boat.
Old 02-05-2021, 07:50 PM
  #3  
mithrandir
My Feedback: (2)
 
mithrandir's Avatar
 
Join Date: Jul 2003
Location: adelanto, CA
Posts: 1,167
Received 1 Like on 1 Post
Default

there are books written... multi-volume... addressing these very questions....

Tractor: clean air in, accelerated air causing thrust loss as it sweeps over the fuselage and tails....

Pusher: No fuselage to funk up the accelerated air... but a lot of crudded up air going into the prop from fuselage and tails... actually can be an irritating source of noise and potential prop fatigue...
there is a theory that pushers have added pitch stability if the prop is at the back of the plane....

Trying to run the thrust line through the CG is a myth..... you want to align the thrust line with the center of DRAG. (As much as is practicable)
this can be attenuated if you have a simple gyro on pitch, or even a throttle-elevator mix....

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.