Go Back  RCU Forums > RC Airplanes > Questions and Answers
Reload this Page >

Forula for determining engine size?

Questions and Answers If you have general RC questions or answers discuss it here.

Forula for determining engine size?

Old 08-15-2016, 06:05 AM
Thread Starter
H5487's Avatar
Join Date: Dec 2005
Location: Houston, TX
Posts: 1,088
Likes: 0
Received 0 Likes on 0 Posts
Default Forula for determining engine size?

I've seen the info on RCU before but I can no longer find it. What are the formulas for sizing nitro and electric motors to an aircraft? I remember that the formulas were based on the model's weight vs the desired performance. This is something I need to print out for my Holy Binder of R/C Knowledge.


Old 08-15-2016, 06:28 AM
My Feedback: (6)
Rafael23cc's Avatar
Join Date: May 2002
Location: Junction City, KS
Posts: 2,961
Likes: 0
Received 4 Likes on 4 Posts

Here's a little reading for ya:


And if you keep in mind that "WATT" is a unit of power, you could easily convert to nitro engines:

Old 08-17-2016, 01:59 PM
Join Date: Dec 2006
Location: Fort Worth, TX
Posts: 7,266
Received 35 Likes on 30 Posts

Getting the watts/horsepower requirement right is the easy part. Determining how to use that power is what's tricky. Take my J3 Cub for example. The manufacturer suggested a .46 2 stroke engine for it. That engine was rated for about 1.6 HP, and realistically probably made 1.1-1.2 HP in actual use. It spun an 11x6 maybe 12k RPM and flew the plane ok. I then switched to a Saito .72 which is rated for a bit less HP, but has a lot more torque. It turns a 12x8 around 9600 RPM and flies the plane much better.

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 - Manage Preferences - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.