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JavaProp: Design for low-pitch, high-velocity twin  Topic is solved

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JavaProp: Design for low-pitch, high-velocity twin

Postby TheEagle » Sun Oct 02, 2022 11:23 pm

I'm trying to make the constant-speed 84 in diameter 2-bladed propeller for the Cessna 310A, which has it's high pitch stop at 22.5°, and at 5000 ft, with 180 HP, 2400 RPM it should cruise at 206 KTAS, and with the current flight model 458 pounds of total thrust (229 lbs per engine) are needed to achieve this speed with the current FDM. Problem is, when I do a Design in JavaProp for this data, it gives me a blade angle of 27.9° or so (at the 0.75 r/R station) - that's already past the high pitch stop !
I'm using Clark Y Re=100000 for all four airfoil stations. Can anyone help on this ?
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Re: JavaProp: Design for low-pitch, high-velocity twin

Postby S&J » Mon Oct 03, 2022 10:13 am

Screenshot your design page and lets see what you've got.
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Re: JavaProp: Design for low-pitch, high-velocity twin

Postby S&J » Mon Oct 03, 2022 12:09 pm

And that btw is a really low high pitch stop angle
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Re: JavaProp: Design for low-pitch, high-velocity twin

Postby TheEagle » Mon Oct 03, 2022 12:33 pm

S&J wrote in Mon Oct 03, 2022 12:09 pm:And that btw is a really low high pitch stop angle

I think so too, but that's how it is !

Here's my Design page:
Image

For the Airfoils I got Clark Y Re=500000 for all four stations.
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Re: JavaProp: Design for low-pitch, high-velocity twin

Postby S&J » Mon Oct 03, 2022 1:35 pm

reduce the angle of attack in the airfoils tab to

-0.5 = r/R 0.00
-0.75 = r/R 0.33
-1.1 = r/R 0.667
-1.25 = r/R 1.00

What values do you then get ?
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Re: JavaProp: Design for low-pitch, high-velocity twin

Postby TheEagle » Mon Oct 03, 2022 1:41 pm

Hmmm, that gives 22.4°,but i need these 22.4° at higher speeds - the highest cruise speed of this thing is 206 KTAS, at 5000 ft with 180 BHP and 2400 RPM each engine !
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Re: JavaProp: Design for low-pitch, high-velocity twin

Postby TheEagle » Mon Oct 03, 2022 1:45 pm

If I do a design for 230 lbs of thrust each, 2400 RPM, 106 m/s (206 KTAS), I get 27.3° ! Basically I think i need a different airfoil, that creates more thrust at low pitch.
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Re: JavaProp: Design for low-pitch, high-velocity twin

Postby S&J » Mon Oct 03, 2022 1:55 pm

Your velocity value is 84.524m/s

I'm using your input values
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Re: JavaProp: Design for low-pitch, high-velocity twin  

Postby TheEagle » Mon Oct 03, 2022 1:55 pm

Oh well, I've got what I need now, I think ! :) What I did was, I picked a high-Cl airfoil (MH 112 for the root section and MH 114 for the rest) which gave a very thin blade, then used the Modify tab's Change chord by and Scale chord by fields to increase the blade width until I get enough thrust - and the power required is about the right, too ! :) Perfect ! :) I guess I shouldn't trust all the automation features too much in the future ! ;)
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