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Author Topic: Piston Engine Modelling..... including it's prop.  (Read 13720 times)

bomber

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Re: Piston Engine Modelling..... including it's prop.
« Reply #15 on: April 14, 2015, 10:34:52 am »

Read this....

http://www.pilotfriend.com/training/flight_training/fxd_wing/props.htm

If you take nothing from this document other than there being 3 types of propellor.... no not fixed pitch, constant speed, variable pitch....

but...... Climb, Cruise and Speed props....

So when you're aiming for a plane that 'hits all the numbers'..... ask yourself how's that even possible if I can only use a single prop at a time ?
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

bomber

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Re: Piston Engine Modelling..... including it's prop.
« Reply #16 on: April 14, 2015, 01:47:32 pm »

Now have a little look around the next tool....javaprop

http://www.mh-aerotools.de/airfoils/jp_applet.htm
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bomber

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Re: Piston Engine Modelling..... including it's prop.
« Reply #17 on: April 14, 2015, 03:31:37 pm »

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bomber

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Re: Piston Engine Modelling..... including it's prop.
« Reply #18 on: April 15, 2015, 03:09:48 pm »

If you're unlucky to have very little information about the prop.... which depending upon your era could be all of your planes, you're going to need to do design your prop to the known values you could have of the plane... ie it's engine, top speed etc...

First question is "how big is my prop"

So I've added the next tab on the spreadsheet which determines the maximum prop size you can have without running into helical tip issues...

http://target4today.com/_posted_files_/Cesna_172/Prop-Cesna_172.xlsx
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

bomber

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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

bomber

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Re: Piston Engine Modelling..... including it's prop.
« Reply #20 on: April 17, 2015, 03:20:29 pm »

More stuff to read

http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node86.html

hahahah don't worry, just go right to the bottom and look at the graphs..... the shapes of these graphs are important, if your results don't look like these then how can they be right.
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

bomber

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bomber

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Re: Piston Engine Modelling..... including it's prop.
« Reply #22 on: April 18, 2015, 07:17:51 am »

ok so let use the prop

McCauley 1A200DFA 82/42. 82” 2-blade aluminum prop. (Fixed pitch)
McCauley 2-blade w/spinner 48 pounds
McCauley 2-blade (2450 RPM) 750 pounds
McCauley 2-blade 95 Kts TAS

so we're looking for a static test (0m/s) of 750lbs (3.34kN) of thrust at 2450rpm, using all the grunt the engines got, ie 145hp (108kW)

Adding these values into the first tab and using the magic of javaprop we get this....


producing a set of tables like this


and a nice set of graphs for Ct and Cp that look like this


However this is the current prop graphs for the jsbsim Cessna



I guess we need Ron to explain the differences.

Regards

Simon
 p.s. updated
http://target4today.com/_posted_files_/Cesna_172/Prop-Cesna_172.xlsx
« Last Edit: April 18, 2015, 07:22:46 am by bomber »
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

bomber

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Re: Piston Engine Modelling..... including it's prop.
« Reply #23 on: April 18, 2015, 01:38:28 pm »

I've been thinking about it and it seems that it could be linked to a windmilling prop.
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

bomber

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Re: Piston Engine Modelling..... including it's prop.
« Reply #24 on: April 18, 2015, 04:09:26 pm »

creating the same spread on the V/(nD) of 0.05 and using xcel to mirror the values for windmilling we get the following...

I need to understand why the Cp is negative on the previous chart

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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

bomber

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Re: Piston Engine Modelling..... including it's prop.
« Reply #25 on: April 19, 2015, 07:58:04 am »

more reading on stationary vs windmilling props

http://lancair.net/lists/lml/Message/44132.html?Language=
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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell

bomber

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Re: Piston Engine Modelling..... including it's prop.
« Reply #26 on: April 21, 2015, 02:45:53 pm »

MT MTV-15-B/210-58. 83” 2-blade composite prop. (Constant speed)


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"If anyone ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me - it's all balls" - R J Mitchell
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