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question

MrTommymxr avatar image
MrTommymxr asked MrTommymxr commented

Prop twist is reversed?

Greets,

I've noticed that the "prop_mod_aoa_twist_delta_deg" variable is reversed.
When increasing the twist, the tips provide more thrust.

We all know the twist that props require to provide good thrust and efficiency blah blah blah.1647717495101.png



More twist would (should) mean that the outer part should have less AOA and less thrust on the tips, as that is how props are twisted. They don't twist the other way


I made some tests here below.



Here with the standard +6° of twist. Tip AoA 12.7°1647717742371.png


Here with +10° of twist. 14° of tip AoA1647717863543.png
And here with -6° of twist. 7° AoA

1647718041842.png


Im confused. Are we supposed to use the positive (wrong) value, because when using the negative all high speed performance goes down the drain.


Looking for insight and feedback.

-Tommy


flightmodel
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1647718041842.png (3.5 MiB)
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Simbol avatar image
Simbol answered

Following..

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FlyingRaccoon avatar image
FlyingRaccoon answered MrTommymxr commented

Hello @MrTommymxr and @Simbol

The naming of the variable is confusing. Allow me to explain a bit more.
prop_mod_aoa_twist_delta_deg doesn't allow you to adjust the twist angle, it allows you to add a beta angle while keeping the same twist.

So, you will first use the prop_mod_aoa_lift_delta_deg to define the angle at a specific position of the propeller (75% by default). You're defining the angle in green here:

1648557049959.pngThe twist is automatically computed from this to have the alignment shown in this drawing

And then, prop_mod_aoa_twist_delta_deg will add an additional angle, constant on the whole length of the blade, without changing the twist.

@Nocturne will have a look at the parameter description so it's a bit more clear.

Regards,
Sylvain


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Thanks Sylvain,


Yes it is hard to understand what we need to do without becoming a full aeronautical engineer hahaha.

Appreciate the effort to make the documentation more user friendly for everyone.

Best,
Raul

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Yeah, that's kinda confusing.

So the twist calculates itself automatically depending on the radius, and prop_mod_aoa_twist_delta_deg is a linear offset from that calculated twist.

What's the difference then from just setting a different min and max beta? If have a min beta of 10 and prop_mod_aoa_twist_delta_deg of 5. Do i then get 15° at the defined point (default 0.75). If i set a min beta of 15 and twitch delta of 0?


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