50 / 600 Head Speed ???

[millerman]

what motor, pack, pinion?

edit this is the fusion i'm talking about as that is running 3400?

cheers

Only way I can see getting this HS is running 12s with an 630 kv motor and 129/17 gear combo this vastly exceeds recommended blade speed by 1000 Rpms (spin blades state 2600 max for 600mm blades)



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[raptorheli2]

Only way I can see getting this HS is running 12s with an 630 kv motor and 129/17 gear combo this vastly exceeds recommended blade speed by 1000 Rpms (spin blades state 2600 max for 600mm blades)



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the max pinion outrage sell is 16t so i'm curious how that 3400 was obtained hence the q.

also curious how it has not blown apart aswell!

cheers

[oneandonlyian]

Hi

They are both electric.

2300 on the Srimok is GREAT!

The reason I am asking about the fusion is that I maidened it and the head speed sounded crazy, so auto'd and tach'd without blades.....

Gareth

Did you get that head speed without main blades. Probably explains why its so high as there is no load. sorry if i misunderstood.

[jamiem]

Did you get that head speed without main blades. Probably explains why its so high as there is no load. sorry if i misunderstood.

If it's governed (not sure if it is, but i suspect gareht is using a cc or kontronik, so probably is governed) then load wouldnt matter. It's also worth mentioning that unlike a brushed motor, brushless won't (or hardly!) overspeed. It's a 3 phase motor and as such, it will only want to spin at the set rpm.

[Gareth-71]

Hi

Someone else built the heli, I just put the 12s packs on it and tested - turns out that the pinion chosen for build was the largest available (16t I think).

Ran it today at 65% throttle and it flies a treat.

The OP was asking what the top end rpm should be for a 50 sized as the test speed was ludicrous.

I'll change to the 10t pinion and then esc should run more efficiently.

Gareth

[raptorheli2]

10t is not available either-too small for the mod of the gear.

what motor is it?

you may have the wrong motor?

cheers

[Vic.P]

what motor is it?

you may have the wrong motor?

cheers

I would like to know that too
Was the heli set up to run a 12 cell flight pack?
It sounds to me judging by the ludicrous and very dangerous head speed, that it should be running with less cells to get the correct head speed for the Kv value of the motor. Perhaps it was set up to run 8 cells?

After considering the possible consequences of running such a dnagerously high head speed as yours, it got me thinking ................ it might be a great learning and safety tool to incorporate exploding heads and tails on simulators like Phoenix, Aerofly, etc when the head speed is over-clocked by the user.........something like a loud bang, a blade flying straight at the viewer followed by a lot of blood dribbling down the screen and finaly the sceen going black as the user dies

[moyesboy]

i think it gets to s stage where no matter how fats the headspeed is it wont make much more difference, the blade can only giv so much lift, no matter how fast its spinning

The lift will keep getting more, but the loads on the servos might mean you don't get the actual set pitch (more head speed means the blades have an increased desire to stay at zero pitch).
That is until the blade tips start to go supersonic at 343.2 metres per second
on a .50 size the radius at the tip is 670mm so the rpm to get supersonic tips is 343.2*60/2*pi*0.67 = 4891 rpm
out of interest if you do the same calc for a 12" propellor you get the blade tips supersonic at 21,000 rpm. The limit for efficient props is mach1 at the tips so you see how our motors developed for planks have ended up with the useful power band where it is just below that speed.

Thinking about this led me to do a calc on an M4 bolt thats holding the blade on a .50 heli.
for an M4 thread the stress area is 8.77 mm^2
The best m4 bolt will give you 1220Mpa UTS. or 10709 N
i just weighed my 600D at 125g with c of g at 290mm from the root.
mrw^2 gives w=sqrt(F/mr) so max rpm I calculate to be 5100 rpm

So at a normal .50 head speed of a bit over 2000 there is a safety factor of 2 to allow for boltr quality, damage etc. Gojng up considerably in head speed eats into that safety margin so you'd better have really top quality bolts and maybe replace them after crashes.

The bolt through the blade is loaded in shear with twice the cross section area loaded, but it is subject to flexing loads as well as the straight pull. I consider the weakest point is probably the bolt in the end of the feathering shaft.

[Rotorhead]

Remember the bolt is in double shear, so its cross sectional area is effectively double the figure you have there, plus I get 12.56 sqr mm for the area.

[moyesboy]

the cross section to be considered is the root diameter of the m4 thread. Then a bit less to allow for the stress raise from the thread cut.
I am cosidering the spindle bolt, which is direct tension not double shear.