Talking propellors

[jwocky]

Speaking of this, I so want some expansions to get JSB helicopters going. That would be really fun.

[sanhozay]

Sorry to drag up an old thread, but it is relevant to the Beagle Pup experiment ...

@Bomber, you gave a brilliant explanation of how to use JavaProp.

I found the weight of the McCauley 1A105 SCM 7053 is just 19.5lbs or 0.606slugs:

http://www.grummanpilotsassociation.com ... /P-918.pdf

So then I calculated the moment of inertia using the three methods (point mass, rod and disc) listed here: http://www.mh-aerotools.de/airfoils/pro ... nglish.htm

Diameter = 5.83', radius = 2.915'

Code: Select all

0.606 * (0.3 * 2.915)^2 = 0.463 SLUG*FT2 (point mass)
(2 / 3) * 0.606 * 2.915^2 = 3.433 SLUG*FT2 (rod)
(0.606 / 2) * 2.915^2 = 2.575 SLUG*FT2 (disc)

Calculating by this method: http://hyperphysics.phy-astr.gsu.edu/hbase/mi2.html gives

Code: Select all

0.606 / 12 * 5.83^2 = 1.716 SLUG*FT2

Which method did you use for your calculation (which I think was using a heavier propeller)?

EDIT: I don't see how the 2/3 * m * R^2 method is valid. I think it should be 2/3 * m/2 * R^2. The mass needs to be halved to calculate the moment of a blade and then the result doubled.

Code: Select all

(2 / 3) * (0.606 / 2) * 2.915^2 = 1.716 SLUG * FT2

[bomber]

An awesome find....

pm me your email addy and I'll send you my spreadsheet of prop design and known props...

I'm updating it with this new info as we speak.

[sanhozay]

Great, thanks.

I've also collected the data for the Sensenich propellers on the Pup 150 and 160. I think these specifications are complete, apart from perhaps the spinner diameter of the Sensenich propellers. In the absence of any data, I've also assumed the Pup 160 has the same max speed as the 150.

I've run all of these through JavaProp, as per your guide, to get the correct pitch and static RPM. I have the analysis but I haven't put those into my prop definitions yet. I assume it's just a case of copying the power and thrust tables and mirroring them top to bottom?

Code: Select all

McCauley 1A105-SCM-7053

Blades:             2
RPM (max):          2750
Diameter:           70" (5.83', 1.778m)
Spinner Diameter:   4 3/8" (0.11m)
Velocity (max):     110kt (57m/s)
Power (max):        100hp (75kW)
Weight:             19.5lb (0.606slug)
Geometric Pitch:    53" (1.346m, 17.8*)
Static RPM:         2300-2400
Moment of Inertia:  1.716slug*ft2

Sensenich 74DM6S5-0-60

Blades:             2
RPM (max):          2700
Diameter:           74" (6.16', 1.880m)
Spinner Diameter:   4 3/8" (0.11m)
Velocity (max):     120kt (62m/s)
Power (max):        150hp (112kW)
Weight:             34.5lb (1.072slug)
Geometric Pitch:    60" (1.524m, 19.0*)
Static RPM:         2200-2400
Moment of Inertia:  3.390slug*ft2

Sensenich 74DM655-0-62
Blades:             2
RPM (max):          2750
Diameter:           74" (6.16', 1.880m)
Spinner Diameter:   4 3/8" (0.11m)
Velocity (max):     120kt (62m/s)
Power (max):        160hp (119kW)
Weight:             34.5lb (1.072slug)
Geometric Pitch:    62" (1.575m, 19.6*)
Static RPM:         2200-2400
Moment of Inertia:  3.390slug*ft2

Notes:
Inertia calculated as m/12*D^2.

References:
https://www.easa.europa.eu/system/files ... 0final.pdf
http://www.pilotfriend.com/aircraft%20p ... %20100.htm
http://www.pilotfriend.com/aircraft%20p ... %20150.htm
http://www.mccauley.textron.com/MAG.pdf
http://www.grummanpilotsassociation.com ... /P-918.pdf
http://www.mh-aerotools.de/airfoils/pro ... nglish.htm
http://hyperphysics.phy-astr.gsu.edu/hbase/mi2.html
http://www.sensenich.com/files/document ... 535087.pdf

[bomber]

I've emailed you my spreadsheet...

What we're doing now is what as a flight modelling community we should have done years ago.... swapping data, filling in the Island of knowledge that we can gather from the internet and other sources and using this to extrapolate data where we have none.... up until we find the data.

As opposed to aguing about about a persons intent. Hopeful;ly we can get more people here interested in flight modelling and have some real indepth discussion on how to advance our hobby.

what I have noticed is that the horsepower of the prop is the main driver for it's weight... if not the only driver.. I'm not convinced that an increase in diameter means an increase in weight for the same HP, it's just a means by which to alter the props performance curve.

I'll update the spreadsheet over the next week with the data you've supplied and see where it gets us.

regards

Simon

[bomber]

3 props showing that the difference between them is just 2 degs of pitch..

Climb 1B90/CM7150
Standard 1B90/CM7152
Cruise 1B90/CM7154

[bomber]

@Bomber, you gave a brilliant explanation of how to use JavaProp.

I'm not comfortable with javaprop and would welcome some sanity checking of what it seems to be doing.

[sanhozay]

I had been fiddling with it before I read your posts on it and I got as far as sticking the numbers in, picking the airfoils for real aircraft, and using the modify tab to get the correct pitch at 75% radius. I don't see much in those steps to question.

I wouldn't have figured out the part where you tweak it to get the static RPM but it makes sense. I think my only doubt is whether the prop model alone can derive the static RPM, or whether it's really a function of the prop/engine combination. I don't really know, just a nagging feeling about it and I don't have a better idea.

I put it in my model and it's certainly an order of magnitude better than the Aeromatic prop, which is to be expected, given the extra data that goes into it. I'm still trying things out but I'm getting into the right ballpark in terms of performance at low levels. Looking at the propeller thrust at max speed and using that to work out the drag is a great tip.

What will be interesting, when I make a bit more progress, is whether dropping the Lycoming/Sensenich combination into the same aerodynamic model ends up anywhere near where it should be. That's always been my theory with this set of aircraft: that the airframe is the same and the variants should drop out by substituting the engine/prop.

[bomber]

I guess I don't feel that the process as yet is robust enough for a challenge...there are simply too many unanswered questions.

for example...

On the front page... fill in the details for a cessna 172 prop 7553

2700 rpm
1.9m diameter
0.2 hub
108000kw
and put in an initial velocity of 60m/s

Add the airfoils and then go back to the front page and 'design it'

If you look on this page it tells you the beta angle at 75%.....if you calculate what it should be for a 53" it doesn't match..

So now lower the speed to 44m/s and 'design it'.... the beta angle now matches 17.5 degs.

I'm just not 100% confident as yet...

Simon

[sanhozay]

Certainly the front page isn't updated when you use the modify tab, but the geometry is. The only way I can see to check the pitch after using modify is using the geometry tab. The β value on the front page doesn't match.

I think pressing the "design it" button just resets everything back to the default settings from the parameters on that page. I took the "design it" button to be an "initialise" button, never to be pressed again, unless you mess up and want to reset everything.

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.

EDIT: Try this ...

With your prop design suitably tweaked, go to the "Options" tab and press "Save". Choose a location to save and enter a filename with a ".jpdata" extension. Go back to the "Design" tab and press "Design it". Note the pitch and static RPM are back to defaults. Now go back to the "Options" tab and load the file you saved. Et voila! The design tab shows the correct β, the geometry is as you tweaked it and the multi-analysis shows the correct static RPM -- you just need to analyze with P prescribed.

This allows us to share JavaProp designs, and include them in our aircraft for reference and editing later :

McCauley_1A105-SCM-7053.jpdata

Code: Select all

<?xml version="1.0"?>
<JavaProp>
   <OptionsCard>
      <Count value="5"/>
      <Density value="1.221"/>
      <Viscosity value="1.4607E-5"/>
      <SpeedOfSound value="340.29"/>
      <Language value="en"/>
      <Country value="US"/>
   </OptionsCard>
   <DesignCard>
      <Count value="9"/>
      <Name value="McCauley_1A105-SCM-7053"/>
      <Blades value="2"/>
      <RPM value="2750.0"/>
      <Diameter value="1.778"/>
      <Velocity value="57.0"/>
      <PowerThrust value="75000.0"/>
      <Spinner value="0.13"/>
      <Design value="Power"/>
      <Shrouded value="No"/>
      <SquareTip value="No"/>
      <OpenHub value="No"/>
   </DesignCard>
   <AirfoilsCard>
      <Count value="4"/>
      <AirfoilIndex value="9"/>
      <AngleOfAttack value="3.0"/>
      <AirfoilIndex value="10"/>
      <AngleOfAttack value="3.0"/>
      <AirfoilIndex value="11"/>
      <AngleOfAttack value="3.0"/>
      <AirfoilIndex value="13"/>
      <AngleOfAttack value="3.0"/>
      <ZeroDrag value="No"/>
   </AirfoilsCard>
   <GeometryCard>
      <Count value="21"/>
      <beta value="0.0"/>
      <beta value="0.0"/>
      <beta value="1.0470223799940044"/>
      <beta value="0.9085645086788687"/>
      <beta value="0.7931993616555554"/>
      <beta value="0.6988623028323309"/>
      <beta value="0.6220547139504232"/>
      <beta value="0.5592639393709082"/>
      <beta value="0.5075017508311436"/>
      <beta value="0.4643962683778196"/>
      <beta value="0.4281183883825201"/>
      <beta value="0.39727059142975313"/>
      <beta value="0.3707843216392971"/>
      <beta value="0.3478377253031364"/>
      <beta value="0.32779332762336066"/>
      <beta value="0.31015190107157753"/>
      <beta value="0.2945185762470889"/>
      <beta value="0.2805779325512062"/>
      <beta value="0.2680755990680819"/>
      <beta value="0.2568045652492013"/>
      <beta value="0.24659490937698567"/>
      <chord value="0.0019292692515972185"/>
      <chord value="0.0019292692515972185"/>
      <chord value="0.09418302814893137"/>
      <chord value="0.14461971094668213"/>
      <chord value="0.1702003687038978"/>
      <chord value="0.17519062140266753"/>
      <chord value="0.1678626005318237"/>
      <chord value="0.15871072898051825"/>
      <chord value="0.15404742943431013"/>
      <chord value="0.14696422279378274"/>
      <chord value="0.1385977612290283"/>
      <chord value="0.12958585635545505"/>
      <chord value="0.12025152704363394"/>
      <chord value="0.11071910668645069"/>
      <chord value="0.10447686479440665"/>
      <chord value="0.0992245770680976"/>
      <chord value="0.09274171170793492"/>
      <chord value="0.08433422969556262"/>
      <chord value="0.07267674754184164"/>
      <chord value="0.05454046296240341"/>
      <chord value="0.002727023148120171"/>
   </GeometryCard>
   <ModifyCard>
      <Count value="9"/>
      <AngleDelta value="0.000"/>
      <AngleScale value="1"/>
      <ChordDelta value="0.0"/>
      <ChordScale value="1.005"/>
      <ChordTaper value="1.0"/>
      <VelocityRoot value="1.0"/>
      <RadiusRoot value="0.5"/>
      <ThreadingLine value="33.0"/>
      <ThicknessTE value="0.5"/>
   </ModifyCard>
</JavaProp>


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.