Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
October 19, 2017, 03:47:14 PM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: [1]   Go Down
Print
Author Topic: Measuring prop pitch  (Read 1358 times)
0 Members and 1 Guest are viewing this topic.
Pete Fardell
Titanium Member
*******

Kudos: 51
Offline Offline

United Kingdom United Kingdom

Posts: 3,658


Topic starter


Ignore
« on: April 17, 2017, 02:19:01 PM »

If I want to get a quick, approximate figure for a readymade plastic prop's pitch, how far out from the centre should I be measuring at? Sorry if that's a daft question.
Logged
tross
Gold Member
*****

Kudos: 23
Offline Offline

United States United States

Posts: 565




Ignore
« Reply #1 on: April 17, 2017, 02:57:16 PM »

If you mean P/D and close counts then you can use these.

@75%  23°=1
           24°=1.05
           25°=1.1
           26°=1.15
           27°=1.2

And so on.
Quick and approximate of course.

TR
Logged
fred
Gold Member
*****

Kudos: 2
Offline Offline

Canada Canada

Posts: 260



Ignore
« Reply #2 on: August 13, 2017, 10:26:36 PM »

IF ? this is important to you. Then Google and hunt down Plans for a DIY prop Pitch gauge.
 Invaluable imo. as Few! props are what they claim to be.
 Build one ...and be astounded at what you discover :-)
Logged
LOUCRANE
Bronze Member
***

Kudos: 5
Offline Offline

United States United States

Posts: 39



Ignore
« Reply #3 on: August 17, 2017, 02:56:16 PM »

And, what may be a minor thought, most pitch gauges I've seen measure the angle of the - usually flat - 'bottom' of the prop blade.

All propeller blades have some form of airfoil, even "flat plates" due to their angle to the airflow.

Airfoils may have their 'zero lift angle of attack' above the line of the 'bottom' surface, even if the blades are very thin but have a curvature. Thickness and possible leading edge radius may contribute  to the zero lift AoA deviation from the 'bottom' surface. A thick airfoiled blade with the same nominal pitch as a thinner blade airfoil may perform differently. The camber line is halfway between the upper and lower surfaces, thus usually curved, unless the airfoil is symmetrical. A thicker airfoil will have a greater camber line curvature compared to the straight line from furthest point on leading edge to the furthest aft point on the TE.

(In the 1940's Raul Hoffman released a book called Model Aircraft Aerodynamics Made Simple, or something very similar. He apparently passed on before he had a chance to organize the content into more usable, legible, sensible format. The book, as it is, ain't easy, but much can be mined out of it.)

Either Hoffman or Frank Zaic , in his Annual Yearbooks, suggested a way to SWAG a propeller's zero lift AoA: For a typical flat-bottom-type airfoil, split the angle between top and bottom surfaces, at the trailing edge. Most likely too crude, but it does convey the idea that the zero lift AoA occurs when the LE looks below the angle of the bottom surface.

Few of us need to consider the usually small differences this  presents, but much of what we do survives because of the tolerance of imprecisions. We can't, or very seldom can try to, approximate precision. Too many variables we can't control: Wind, height above Sea Level, temperature, even humidity, and variations in flight and power adjustments. Yet, we do fly - and usually pleasantly well!
Logged

/LOU
Hepcat
Platinum Member
******

Kudos: 206
Offline Offline

United Kingdom United Kingdom

Posts: 1,668



Ignore
« Reply #4 on: August 17, 2017, 06:28:45 PM »

Lou,
Thanks for reminding me about Hoffman's book.  I haven't looked at it for some years but I hope it is still on the shelf in the Garden room next to the Zaics.  Does anyone know anything of his background, in particular what he did for a living, because (although I don'r want to run down Frank in any way) I think Roul was more knowledgeable about the fundamentals of aircraft design.
John
Logged
Pages: [1]   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!