Scratch and Kit Built Aircraft Discuss and share your scratch built or kit built aircraft as well as building techniques, methods, mediums and resources.

Compute your prop thrust angle in degrees

Old 12-18-2021, 03:06 AM
  #1  
Marc
Member
Thread Starter
 
Marc's Avatar
 
Join Date: Sep 2008
Location: East Texas
Posts: 167
Default Compute your prop thrust angle in degrees

The formula is:
((L - R) / D) * (180 / pi)
where:
L is the distance from the horizontal prop tip to the leading edge of the left wing
R is the distance from the horizontal prop tip to the leading edge of the right wing
D is the diameter of the prop
(180 / pi) is the conversion factor for radians to degrees or you can just substitute the constant 57.29578

A positive result will be a very accurate measure of the right thrust angle in degrees.

Last edited by Marc; 12-18-2021 at 03:08 AM. Reason: formula
Marc is offline  
Old 12-18-2021, 10:05 AM
  #2  
solentlife
Super Contributor
 
solentlife's Avatar
 
Join Date: Oct 2010
Location: Ex UK Brit now in Latvia west coast - Ventspils
Posts: 12,887
Default

Just to be clear ... this is to calculate what you have as angle - not to determine what it should be ?

My way of finding or setting the angle is to use a straight edge along fuselage and also helps to make sure prop centre is actually on centreline of fuselage. Its not unusual to find a models motor mount has thrust angle that results in prop centre not on models C/L ... Would that not cause error in the formula result ?
solentlife is offline  
Old 12-18-2021, 08:13 PM
  #3  
Marc
Member
Thread Starter
 
Marc's Avatar
 
Join Date: Sep 2008
Location: East Texas
Posts: 167
Default

To be honest, I had to get out my college trigonometry textbook to derive the formula. It uses the sine function to compute the angular deviation from perpendicular to the wing leading edge. The sine function is defined as the side opposite the angle to be computed divided by the hypotenuse. (L - R) sets the side opposite the angle in standard position. The hypotenuse is the diameter of the prop. The x-axis is the leading edge.

The prop center does not need to be at the center of the fuselage, but the leading edge should be straight and perpendicular to the fuselage. If the plane of the prop center deviates significantly from the plane of the leading edge (i.e. high wing or low wing), the computed angle will be somewhat diminished.
Marc is offline  
Old 12-19-2021, 09:25 AM
  #4  
solentlife
Super Contributor
 
solentlife's Avatar
 
Join Date: Oct 2010
Location: Ex UK Brit now in Latvia west coast - Ventspils
Posts: 12,887
Default

Trig is my deal ... having studied not only plane trig - but also spherical trig as part of my Certification as a Ships Navigator ... before coming ashore and into the Shipping and Petroleum World.

Polynomial Differentiation slowed me a bit ... but got there in the end.

For me the adjustable 'set-square' is the tool for this job ... then matter of wings L/E is not a factor. But only if I really need to measure. Otherwise I find the 'eye' is a good judge after all the years ... if I can detect a slight right and down - thejn I'm happy ... its amazing hopw good the eye is.
solentlife is offline  
Old 12-20-2021, 04:07 AM
  #5  
Wildflyer
Past President of PSSF
 
Wildflyer's Avatar
 
Join Date: Sep 2009
Location: Lacey WA, 1 mile E of Mushroom Corner
Posts: 2,258
Default

I have used a similar formula for thrust angles, if you want to be a little more accurate, rotate the engine 180 so that you use the same prop tip. Some props are not perfect.
Wildflyer is offline  

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
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


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

Copyright © 2022 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.

Page generated in 0.09731 seconds with 12 queries