Helicopters C

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daydreamer0023
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Re: Helicopters C

Post by daydreamer0023 » February 11th, 2018, 11:29 am

If we want to experiment with increasing overall rotor pitch, by what increment is a good increment to change between test models (eg. one degree, two degree, etc.)?
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Re: Helicopters C

Post by bjt4888 » February 12th, 2018, 6:13 am

Daydreamer,

I would recommend 2 degree increments. As I'm sure you have measured, on the FF kit, one degree at the center rib is accomplished by a 1/16" incidence change. We have this much variability amongst the 11 Helis weve built so far this year and they all fly about the same.

Good luck and congrats on testing rotor variables,

Brian T

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Re: Helicopters C

Post by Ten086 » February 12th, 2018, 7:40 am

Has anyone tried to modify the Chinook kit so the rotors are on top instead? :0 Would the stabilizers still be necessary in this case? And do you think having two disks would be okay because technically they’re both still at the highest point of the helicopter? I’m not really sure how that would work so I just wanted to check if anyone has tried already.
Just trying my best...

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Re: Helicopters C

Post by coachchuckaahs » February 12th, 2018, 7:57 am

I believe some of Dave's early prototypes had rotor on top, and the fuselage was very similar, indicating that the stabilizing panels were still needed. The rotors would then beat on the ceiling, though you could make a spinny disk to prevent that. I think the bottom rotors probably protect the rotors more, and the device tends to stay more stationary on the ceiling.

If you offset one motor stick slightly higher I suppose you could get away with a single disk.

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Re: Helicopters C

Post by daydreamer0023 » February 12th, 2018, 8:01 am

bjt4888 wrote:Daydreamer,

I would recommend 2 degree increments. As I'm sure you have measured, on the FF kit, one degree at the center rib is accomplished by a 1/16" incidence change. We have this much variability amongst the 11 Helis weve built so far this year and they all fly about the same.

Good luck and congrats on testing rotor variables,

Brian T
Thank you so much Mr. Turnbull! Another question, I'm slightly confused on what exactly you mean by a 1/16" incidence change. Can you please explain this?
"I am among those who think that science has great beauty. A scientist in his laboratory is not only a technician: he is also a child placed before natural phenomena which impress him like a fairy tale." - Marie Curie

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Re: Helicopters C

Post by bjt4888 » February 12th, 2018, 9:55 am

Daydreamer,

The FF kit rotors have 7/8" vertical separation between the leading and trailing edges (I am doing this from memory; so be sure to double check). As the center rib length is 2.125" (approximately) this pitch angle (as measured radially) is 24.3 degrees (arcsin 7/8 divided by 2.125). A 1/16" increase in the LE/TE vertical separation would change the pitch (or incidence) angle to arcsin 15/16" divided by 2.125", or 26.18 degrees; an increase of 1.88 degrees.

I see that I did the math wrong in my earlier post. So, we are not seeing significant flight time differences with a variance of 1.88 (or so) degrees of rotor pitch (or incidence) angle.

Sorry for the earlier error.

Brian T.

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Re: Helicopters C

Post by retired1 » February 12th, 2018, 12:00 pm

Ten086 wrote:Has anyone tried to modify the Chinook kit so the rotors are on top instead? :0 Would the stabilizers still be necessary in this case? And do you think having two disks would be okay because technically they’re both still at the highest point of the helicopter? I’m not really sure how that would work so I just wanted to check if anyone has tried already.
At our regional on Sat I saw 6 FF choppers (from the same school) that all had the rotors facing up instead of down and they had very poor flights. (height and stability)
I talked to Dave and he says that is the nature of this model.
I mentioned it to one student and he had no clue what I was talking about, so he must not have read the instructions.

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Re: Helicopters C

Post by Ten086 » February 12th, 2018, 3:37 pm

retired1 wrote:
Ten086 wrote:Has anyone tried to modify the Chinook kit so the rotors are on top instead? :0 Would the stabilizers still be necessary in this case? And do you think having two disks would be okay because technically they’re both still at the highest point of the helicopter? I’m not really sure how that would work so I just wanted to check if anyone has tried already.
At our regional on Sat I saw 6 FF choppers (from the same school) that all had the rotors facing up instead of down and they had very poor flights. (height and stability)
I talked to Dave and he says that is the nature of this model.
I mentioned it to one student and he had no clue what I was talking about, so he must not have read the instructions.
Oh... :/ Why would they be more unstable though? And did you happen to see any original designs with the rotors on top?
Just trying my best...

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Re: Helicopters C

Post by daydreamer0023 » February 12th, 2018, 3:47 pm

bjt4888 wrote:Daydreamer,

The FF kit rotors have 7/8" vertical separation between the leading and trailing edges (I am doing this from memory; so be sure to double check). As the center rib length is 2.125" (approximately) this pitch angle (as measured radially) is 24.3 degrees (arcsin 7/8 divided by 2.125). A 1/16" increase in the LE/TE vertical separation would change the pitch (or incidence) angle to arcsin 15/16" divided by 2.125", or 26.18 degrees; an increase of 1.88 degrees.

I see that I did the math wrong in my earlier post. So, we are not seeing significant flight time differences with a variance of 1.88 (or so) degrees of rotor pitch (or incidence) angle.

Sorry for the earlier error.

Brian T.
I understand now. Thank you so much for your help!
"I am among those who think that science has great beauty. A scientist in his laboratory is not only a technician: he is also a child placed before natural phenomena which impress him like a fairy tale." - Marie Curie

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Re: Helicopters C

Post by bjt4888 » February 12th, 2018, 6:38 pm

Daydreamer,

One last thing. I am thinking that exploring less pitch might be more productive than more pitch.

Brian T

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