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High pitch C_THRUST table

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High pitch C_THRUST table

Postby pierreg » Sat Mar 10, 2007 1:03 am

Hi,

Aeromatic generate C_THRUST and C_POWER tables for 10-30 or 12-30 propeller pitch angles.

I thought high power engine with low propeller RPM need higher pitch angles. Is it right ?

If yes, how can I generate values for high pitch angles ?
(4591 HP, propeller 162 in. 4 blades, max RPM 1390, cruise RPM 1020)

Thanks

Pierre
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Postby tcbetka » Sat Mar 10, 2007 2:39 pm

Sorry...I don't know if I understand what you are asking. Let me take a crack at what I think you are asking though.

Propeller RPM is usually limited by a couple of things, for the most part--propeller tip speed and airframe vibrational issues. Check out this link:

http://www.ajdesigner.com/phphorsepower ... epower.php

...and note how engine RPM is a factor in rotational horsepower. So if an engine with a given displacement is to deliver a certain amount of horsepower, it may require turning the engine faster. For example, the Continental O-300 6-cylinder engine found in the early C172 was rated for 145hp at 2700 RPM, but the same engine (in a geared version) turning 3200 RPM generated 175hp in the C175. I have flown both aircraft many times and the engine was very smooth, even at 3200 RPM. But in the C175, the propeller was geared to only turn 2400 RPM for propeller efficiency.

http://en.wikipedia.org/wiki/Continental_O-300

While the pitch angle of a propeller does indeed have a significant effect on the RPM of the engine, these angles are generally variable via the constant speed mechanisms inherent to the propeller design. I don't believe I have ever seen an aircraft engine producing more than 200hp that did not have at least a variable speed propeller--indeed most had constant-speed mechanisms employing engine-driven governors. So by knowing the value for the *engine* RPM, you can calculate the (theoretical) horsepower of the engine. You might have to figure out the relationship between blade angle and engine speed for that particular installation though, but I don't know for certain how you would get that. Have you checked to see if there's a property tree node for blade angle? If so you could maybe plot the relationship and derive an equation...

TB
MD, CFII, A&P
(Aero Eng Student)
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Postby pierreg » Sat Mar 10, 2007 5:17 pm

Hello tcbetca,

Thank you for the information.

Let me give you more data:
Engine 13820 RPM turboprop, gear ratio 13.55, constant speed propeller, pitch 34 to 55 in flight (-7 to 92.5 operation).

With the high power and low propeller rotation speed, pitch angle is very high compare to small planes.

Like you suggest, I'm trying to find the relation with angles, but if somebody have the magic equation to extend thrust data to 55 degrees, your’ welcome.

Thanks

Pierre
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Postby tcbetka » Sat Mar 10, 2007 10:27 pm

I guess I might try to find a similar aircraft (like a Beech King Air, perhaps?) and look at the specifics for it...and then model yours like that. Otherwise I am not really sure what to tell you, as I am not that familiar with turbine engine propeller angles. I would think that you could Google that information and have some success?

TB
MD, CFII, A&P
(Aero Eng Student)
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Postby grtux » Sat Mar 10, 2007 10:43 pm

Hello PierreG,

We had a talk together, on the French Forum, regarding that topic :),

From the "tcbetka" answer an idea is coming up:

Probably you know the wonderful L410 model, to me it is the best exemple you could get for Propeller turbine Engine (and the best model Aircraft) , look at it

http://javky.rozhled.cz/index.php?id=fgfsl410&typ=P

Regards

Gérard
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Postby pierreg » Sat Mar 10, 2007 11:18 pm

Hello Gérard,

This is exactly the kind of data I'm looking for.
This aircraft is absolutly fantastic.

Thank you very much.

Pierre
pierreg
 
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Location: Montreal, Quebec

Postby pierreg » Mon Mar 12, 2007 1:29 am

Hi,

After the suggestion of Tcbetca and Gérard, with Aeromatic equations, I estimated the correction coefficient for various pitch angles using the data of the L410 propeller and apply to the Hamilton 54H60. The result seems good.

If somebody have the real tables for this propeller, your'e wellcome.

Good flight

Pierre
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Location: Montreal, Quebec


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