Talking propellors

[IAHM-COL]

I've emailed you my spreadsheet...

I want it :"D

[bomber]

That's not a problem I think hosting design spreadsheets of various types for all to share and add too is something that could set FGMEMEMBERS as being different from the rest.

[IAHM-COL]

that'll be cool, too

If it's open we can get more people engaged that are interested in this very fast turning topic.

[bomber]

Well If we're brainstorming I'd like to think a web page with design tools of various types within in, like engineering toolbox.. would be a great addition.

[bomber]

As I lay in bed, sleepless, last night with the wind howling, I was thinking about the static RPM and I think what I'll try is adjusting the prop to the upper range of the static RPM then bring the actual static RPM down to the middle of the range using the engine parameters so the static RPM is part derived from the prop and part from the engine.

I'd be curious as to how this turns out.... Isn't the engine pretty much nailed down with a known HP at a known RPM at see level ?

[bomber]

. Now go back to the "Options" tab and load the file you saved. Et voila!

The load tab is greyed out on my aplet in windows 10..... bummer

[bomber]

This has the correct pitch of 17.8* at 75% and static RPM at the upper limit of 2400rpm. I may have used slightly different airfoils from the ones you usually use.

shouldn't a 7053 have a pitch of 18.7degs.

[sanhozay]

I think 17.8 is correct:

For reference: http://www.sensenich.com/files/document ... 966148.pdf:

Geometric Pitch (inches) = π (.75) D tan β
D is the diameter in inches, β is the blade angle, at the 75% blade radius station, measured from the plane of rotation of the propeller

Rearranging, and calculating in Python:

Code: Select all

Python 2.7.10 (default, Oct 23 2015, 19:19:21)
[GCC 4.2.1 Compatible Apple LLVM 7.0.0 (clang-700.0.59.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import math
>>> GP = 53
>>> D = 70
>>> (180 / math.pi) * math.atan((GP) / (D * 0.75 * math.pi))
17.814362405515663


I checked my formula against the Sensenich example and got the same answer as they did.

[bomber]

my gaff as my spreadsheet has asin instead of atan...

double checked formula here

http://www.pilotfriend.com/training/fli ... /props.htm

Simon

[bomber]

See how this one compares to yours....

2346 static rpm
thrust at 55m/s = 217lbs


Simon

Code: Select all

<?xml version="1.0"?>

<!--
**************************************************************************

Copyright (c) 2016 Simon 'bomber' Morley
simonbomber64 at googlemail.com

This work is licensed under the
Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
To view a copy of this license,
visit http://creativecommons.org/licenses/by-nc-sa/3.0/ or
send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.

Attribution,  You must give appropriate credit, provide a link to the license,
and indicate if changes were made. You may do so in any reasonable manner,
but not in any way that suggests the licensor endorses you or your use.

NonCommercial,  You may not use the material for commercial purposes.

ShareAlike,  If you remix, transform, or build upon the material,
you must distribute your contributions under the same license as the original.

**************************************************************************


Based on tables from JavaProp.


 -->

<propeller name="McCauley 1A105-SCM 7053, 70inch 2-blade aluminum prop. (Fixed pitch)">

   
   <ixx unit="SLUG*FT2"> 1.77 </ixx>
   
   <!--
   Prop Characteristics
   -->

   <diameter unit="IN">  70 </diameter>
   <numblades> 2 </numblades>
    <constspeed> 0 </constspeed>
   
   <!--
   <gearratio> is the gearing between the prop and the engine,
   Normally it's defined from the engine to the propeller and is a value below zero
   ie 0.78
   To specify from the propeller to the engine use 1/X = gearration = 1/0.78 = 1.28
   -->
 

   <gearratio>  1.0 </gearratio>
 
 
   <!--
   <ct_factor> is the props co-efficent of thrust 'tuning' factor
   <cp_factor> is the props co-efficent of power 'tuning' factor
   -->
   <ct_factor> 1.0 </ct_factor>
   <cp_factor> 1.0 </cp_factor>
 

   <table name="C_THRUST" type="internal">
      <tableData>
         0.00   0.126847
         0.05   0.119041
         0.10   0.125292
         0.15   0.122432
         0.20   0.118955
         0.25   0.114345
         0.30   0.108913
         0.35   0.102908
         0.40   0.096132
         0.45   0.088391
         0.50   0.080358
         0.55   0.072039
         0.60   0.063445
         0.65   0.054722
         0.70   0.045755
         0.75   0.036546
         0.80   0.027116
         0.85   0.017478
         0.90   0.007646
         0.95   -0.002453
         1.00   -0.012552
         1.05   -0.022384
         1.10   -0.032022
         1.15   -0.041452
         1.20   -0.050661
         1.25   -0.059628
         1.30   -0.068351
         1.35   -0.076945
         1.40   -0.085264
         1.45   -0.093297
         1.50   -0.101038
         1.55   -0.107814
         1.60   -0.113819
         1.65   -0.119251
         1.70   -0.123861
      </tableData>
   </table>


   <table name="C_POWER" type="internal">
      <tableData>
         0.00   0.05781
         0.05   0.059132
         0.10   0.05871
         0.15   0.059698
         0.20   0.060591
         0.25   0.061084
         0.30   0.06112
         0.35   0.060727
         0.40   0.059689
         0.45   0.057823
         0.50   0.055381
         0.55   0.052326
         0.60   0.04861
         0.65   0.044264
         0.70   0.039201
         0.75   0.033377
         0.80   0.026766
         0.85   0.019339
         0.90   0.011073
         0.95   0.001869
         1.00   -0.007335
         1.05   -0.015601
         1.10   -0.023028
         1.15   -0.029639
         1.20   -0.035463
         1.25   -0.040526
         1.30   -0.044872
         1.35   -0.048588
         1.40   -0.051643
         1.45   -0.054085
         1.50   -0.055951
         1.55   -0.056989
         1.60   -0.057382
         1.65   -0.057346
         1.70   -0.056853
      </tableData>
   </table>

   <!-- thrust effects of helical tip Mach -->
   <table name="CT_MACH" type="internal">
      <tableData>
         0.85   1.0
         1.05   0.8
      </tableData>
   </table>

   <!-- power-required effects of helical tip Mach -->
   <table name="CP_MACH" type="internal">
      <tableData>
         0.85   1.0
         1.05   1.8
      </tableData>
   </table>

</propeller>