Talking propellors

[bomber]

If you're into horse racing you don't enter a steeplechaser into a flat race and visa versa.

So do you think that a prop designed for best climb is used when wanting to run a speed test ?

[bomber]

Type test for the beagle pup which gives us some clues as to a possible prop design.

https://www.google.ae/url?sa=t&source=w ... yl8FyER9xw

McCauley 1A105 SCM7053
Diameter range 70” max. -68.5” min.
Static r.p.m. at maximum possible throttle setting (cross wind) :
Not over 2400, not under 2300 r.p.m.
No additional tolerance permitted

[bomber]

So here's the existing prop for this engine type the McCauley_1A105-SCM-7053.xml

Code: Select all


<?xml version="1.0" encoding="UTF-8"?>
<!--
**************************************************************************
McCauley 1A105/SCM 7053 Propeller
Copyright (c) 2015 Richard Senior
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
**************************************************************************
-->

<!--
Configuration notes:
Original configuration generated with Aeromatic:
Inputs:
                horsepower: 100
                     pitch: fixed
            max engine rpm: 2800
        prop diameter (in): 70
The last four digits in the designation of a McCauley propeller give the
diameter in inches and the geometric pitch of the propeller.
The geometric pitch is the circumference of the propeller disc at the blade
station multiplied by the tangent of the blade angle at that point. The blade
station is the point at 0.75 of the radius.
The blade pitch angle can be calculated using this Python snippet:
GP = 53
D = 70
(180 / math.pi) * math.atan((GP) / (D * 0.75 * math.pi))
The pitch angle has been rounded to the nearest degree.
References:
1. Continental Overhaul Manual for Aircraft Engine Models C75, C85, C90 & O-200
  http://www.culvercadet.com/manuals/C85_overhaul_manual.pdf
2. McCauley Propeller Systems Owner/Operator Information Manual
  http://www.mccauley.textron.com/mpc26ow.pdf
-->

<propeller name="McCauley_1A105-SCM-7053">
  <ixx>2.31</ixx>
  <constspeed>0</constspeed>
  <diameter unit="IN">70.0</diameter>
  <minpitch>18.0</minpitch>
  <maxpitch>18.0</maxpitch>
  <numblades>2</numblades>
  <gearratio>1.0</gearratio>
  <p_factor>5.53</p_factor>

  <table name="C_THRUST" type="internal">
     <tableData>
       0.0   0.0339
       0.1   0.0325
       0.2   0.0311
       0.3   0.0286
       0.4   0.0257
       0.5   0.0227
       0.6   0.0183
       0.7   0.0139
       0.8   0.0075
       1.0  -0.0026
       1.2  -0.0133
       1.4  -0.0240
     </tableData>
  </table>

  <table name="C_POWER" type="internal">
     <tableData>
       0.0   0.0228
       0.1   0.0228
       0.2   0.0222
       0.3   0.0217
       0.4   0.0204
       0.5   0.0187
       0.6   0.0172
       0.7   0.0144
       0.8   0.0118
       1.0   0.0042
       1.2  -0.0067
       1.4  -0.0203
       1.6  -0.0344
     </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
    2.00   1.4
  </tableData>
</table>

</propeller>



[IAHM-COL]

is the xml above a copy of the current, or are you suggesting changes?

[bomber]

that's the currect 'existing' file..... I'll talk you through any changes required...

[bomber]

So the first question is how heavy is a propellor ?

Do you know of one that comes with a weight ?
Yeh it might be a different overall size but if your new propellor is only 90% the size of it then you could assume (materials being equal) that the weight is 90%...

luckily I think I might just have a reference propellor...

Simon

[bomber]

Ok I have some prop data.. it's for the cessna 172 but we can use it as a reference prop.

Propellers Tested:
McCauley 1A200DFA 82/42. 82” 2-blade aluminum prop. (Fixed pitch)

Weight:
McCauley 2-blade w/spinner 48 pounds

Static Thrust (2700 rpm):
McCauley 2-blade (2450 RPM) 750 pounds

Cruise performance ** (6000’ MSL, full throttle & 2400 rpm)
McCauley 2-blade 95 Kts TAS

[jwocky]

I think, I miss here something

if you hang a propeller with a max rpm for 2400 on an engine with a max rpm of 2750, you don't have a gear ratio of 1.0
the other thing is, this is wood, the ixx appears a little high and you have a high p-factor, so that explains this enormous torque. Can it be, you work here with a too high propeller weight?

Or maybe I just need more coffee to understand it ...

[bomber]

I think, I miss here something

if you hang a propeller with a max rpm for 2400 on an engine with a max rpm of 2750, you don't have a gear ratio of 1.0

yes you've spotted what I agree is an error in the existing propellor file....(and I was getting to that, kinda ruined my thunder there)

the other thing is, this is wood, the ixx appears a little high and you have a high p-factor, so that explains this enormous torque. Can it be, you work here with a too high propeller weight? .

The inertia and how we calculate it is what I'm talking through... you say the prop is wood.... you got any proof ?

Or maybe I just need more coffee to understand it ...

move onto red wine ?

[bomber]

ok its an alluminium prop then it's

70/82 * 48 = 41lbs of prop

Anyone see a challenge to that thinking ?