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HomeAircraftHelicopterHelicopter Main Discussion › blades bending.
10-13-2010 10:55 PM  8 years agoPost 1
munkey nuts

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wales uk

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i have scale helicopter, im using vario 875mm blades and the heli weighs 12kg. im running 950rpm on headspeed.

i flew it over the weekend and the blades bend up whilst it flying. i assume its the weight of the heli. what i was wondering is, what is bending? is it the feathering spindle, blades grip holders(they are plastic) or the blades themselves.

is this normal with heavy helicopters?

thanks

gaz

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10-13-2010 11:11 PM  8 years agoPost 2
airdodger

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Johnston USA

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It is called a coning angle, normal. It was normal with glass and wood blades, the new carbon blades are so stiff they hardly bend.

Chris

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10-14-2010 12:17 AM  8 years agoPost 3
FenderBean

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Fort Hood TX

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thats actually very scale!

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10-14-2010 02:53 PM  8 years agoPost 4
AirWolfRC

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42½ N, 83½ W

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Increase your RPM ! Centrifugal force is what keeps the blades from bending up / coning too much . . . or put some more weight in the blade tips.

There's a way to calculate the minimum RPM but it requires measuring the downwash velocity at the outer 1/3 of the rotor disk.

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10-14-2010 03:18 PM  8 years agoPost 5
chopper_crazy

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Delphos, Ohio

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thats actually very scale!
sounds to me like it is

It's a complex, costly, glow powered anti-gravity machine!

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10-14-2010 07:58 PM  8 years agoPost 6
munkey nuts

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wales uk

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airwolf rc

the blades have a maximum rpm that vario give you and this cannot be exceeded.

gaz

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10-14-2010 08:57 PM  8 years agoPost 7
Adaboy

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Maricopa, AZ, USA

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That is one heavy chopper!

What is your power plant on that beast?

Sounds like were cooking with gas....

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10-14-2010 09:13 PM  8 years agoPost 8
munkey nuts

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wales uk

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wren 54.

gaz

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10-14-2010 09:59 PM  8 years agoPost 9
Justin Stuart (RIP)

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Plano, Texas

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Those are some long blades you're spinning.

Avant RC
Scorpion Power Systems
Thunder Power RC
Kontronik Drives

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10-14-2010 10:05 PM  8 years agoPost 10
AirWolfRC

rrProfessor

42½ N, 83½ W

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You say that there is a max. RPM on the blades
and you also say that you are running at 950 RPM.

Am I supposed to assume that those two conditions are the same ?

875 blades at 950 RPM is only 0.28 Mach tip speed . . . darn slow . . .

If 950 is the manufacturer's limit on those blades,
. . . I'd be looking for some better blades ! !

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10-14-2010 10:05 PM  8 years agoPost 11
Adaboy

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Maricopa, AZ, USA

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Please post some pictures of the bird and if you can get some profiles so we can see what kind of bends your talking about.

Thanks

Sounds like were cooking with gas....

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10-17-2010 02:58 AM  8 years agoPost 12
clink69

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Gtown MD

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Are they CF blades, also agree increase RPM some.

"A house is just a place to keep your stuff while you go out and get more stuff." G Carlin

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10-17-2010 06:28 PM  8 years agoPost 13
AirWolfRCrrProfessor - 42½ N, 83½ W - My Posts: All  Forum  Topic

In my view, model heli baldes should be rated to at least Mach 0.5 tip speed.
Here's a quick table for what that means;

Size . . . RPM
500 . . . 2920
550 . . . 2660
600 . . . 2440
680 . . . 2150
710 . . . 2060
875 . . . 1670

Full size blades typically run at about Mach 0.65 tip speed with a limit higher than that.

Robinson R22
- - - - - - tip speed of Mach 0.60 on it's 25ft-2in diameter rotor disk at 510 rpm.
CH-47D Chinook
- - - - - - tip speed of Mach 0.63 on it's 60 ft diameter rotor disks at 225 rpm.
H-60 Black/Pave/Sea Hawk
- - - - - - tip speed of Mach 0.65 on it's 53ft-8in diameter rotor disk at 258 rpm.
Bell 222A (AirWolf)
- - - - - - tip speed of Mach 0.65 on it's 42ft diameter rotor disk at 348 rpm.
V-22 Osprey
- - - - - - tip speed of Mach 0.59 on it's 38ft diameter rotor disk at 333 rpm.
- - - - - - - - or depending where you look
V-22 Osprey
- - - - - - tip speed of Mach 0.70 on it's 38ft diameter rotor disk at 397 rpm.

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10-17-2010 07:27 PM  8 years agoPost 14
FenderBean

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Fort Hood TX

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nevermind

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10-17-2010 07:30 PM  8 years agoPost 15
AirWolfRC

rrProfessor

42½ N, 83½ W

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OK

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10-17-2010 09:58 PM  8 years agoPost 16
munkey nuts

rrApprentice

wales uk

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i havnt got the pictures/video it was on my friends phone.

vario do recommend the blades at this speed only.

it must be fine.
but does look rather perculiar on his phone.

gareth.

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10-18-2010 12:49 AM  8 years agoPost 17
billiano

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Greece ,Patras

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AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

My Posts This: Topic Forum Increase your RPM ! Centrifugal force is what keeps the blades from bending up / coning too much . . . or put some more weight in the blade tips.

There's a way to calculate the minimum RPM but it requires measuring the downwash velocity at the outer 1/3 of the rotor disk.
Can you please explain this theory and also give a pic to understand it better.
Give also the type of maths for the calculations
Thank you

Esprit Model Flight Team
Kasama Srimok 90N FBL
TDR Rigid 90

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10-18-2010 04:17 AM  8 years agoPost 18
The man

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at home

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The RPM limit may not be for the blades but for the grip and hub/bolt.

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10-18-2010 03:34 PM  8 years agoPost 19
AirWolfRC

rrProfessor

42½ N, 83½ W

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Can you please explain this theory and also give a pic to understand it better.
Give also the type of maths for the calculations
Thank you
If there is no lift being produced by the rotor disk, there is no cone angle. As lift starts being produced, the blades move up into a "cone". Centrifugal force acts to oppose the "coneing". 710 blades at about 1800 rpm have a centrifugal force of around 600 lbs. With the centrifugal force (horizontal force vector)and the lift (vertical force vector), you can calculate the cone angle. The centrifugal force will also tell you how much force the blade root and blade grips needs to be able to handle.

For centrifugal force calculation, see my post here;
https://rc.runryder.com/t287507p1/?...p=1287412441#RR

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