Better Prerotator!

[Coen]

Good day,
I have a problem! I want to opperate my sparrow hawk out of short strips and that means that i will have to make a plan with the prerotation currently on the SH.Or maybe take off tecknique. I operate at 3700' asl with warm summer conditions. Options that i am looking at are hydraulic or maybe a V-belt and jockey pully system like on many tandem gyro's. The brakes bother me a bit as well they dont want to hold the gyro at higher RPM settings? Any suggestions to better these will be welcome.
Thanks Coen.

[GYRO J]

jump takeoff is what we need yea!

[ptope]

i fly manufacturing offers several upgrades to include disc brakes. that may help hold you in place..

http://www.imflyn.com/sparrowhawk_options.htm

[Aussie_Paul]

A 32' rotor is what's needed for that sort of weight at that sort density altitude!!

Aussie Paul. :)

[Coen]

Fitting 32' rotors is good but this will just ad to the problem already existing in the SH, this being that having such long blades and poor prerotation system takeoff distances is long not because of disk loading but because the rotors need to be nursed to get good RRPM without getting bladeflap thus having a long takeoff roll. Like you have said some place about the magni(if i remember corectly) it took 4 seconds to takeoff,because full power can be applyed after prerotation, this is a good way of using the power one has. And in the above mentioned gyro it is a combination of good prerotation and brakes.

[Aussie_Paul]

Coen, the Raf style pre rotator is capable of exceeding the 170 rrpm needed for a full power take off like the Magni. With some of the Raf pre rotoators it is more difficult to get them set up correctly. The problems I have found are:

1) Clutch material needs facing to make it perfectly level and grip the entire
drive disc.
2) The lever on the joy stick not fitting the tube perfectly and "giving" a bit
when the pressure is applied.
3) Not starting pre rotation at less than 1000 engine rpm, and not increasing
power until the rrpm is 100 rrpm, and then gently as to not have the
clutch slip.
4) Not keeping the pre rotator engaged for a couple of seconds into the take
off run. If you let the pre rotator handle go, and then apply power you will lose 5 to 10 rrpm.
5) Not having the stick fully back from 120 rrpm to take advantage of any availible wind.


Coen, heat from the clutch slipping is the main culprit, after after you have machined the friction drive material flat.

I hope this helps.

Aussie Paul. :)

[Aussie_Paul]

Fitting 32' rotors is good but this will just ad to the problem already existing in the SH, this being that having such long blades and poor prerotation system takeoff distances is long not because of disk loading but because the rotors need to be nursed to get good RRPM without getting bladeflap thus having a long takeoff roll. Like you have said some place about the magni(if i remember corectly) it took 4 seconds to takeoff,because full power can be applyed after prerotation, this is a good way of using the power one has. And in the above mentioned gyro it is a combination of good prerotation and brakes.

.....with larger blades you will take off with less rrpm and airspeed, both of which help a shorter take off.

Aussie Paul. :)

[davreich]

Hi,
I think one of these kits would be adaptable or used to buy your own parts. Mechanical disk might be better. Think about the rotor in motion while in a taxi and being able to lock the brakes up with hydraulics. Hope this helps.

http://www.phantomaeronautics.com/

[PW_Plack]

Coen,

What is the minimum rotor RPM at which you can begin a full-power takeoff roll? In the Sport Copter Vortex II tandem trainer, which uses the same blades as the SH, 150 RRPM is about all you need to forget about flap and go for it.

[mceagle]

Coen,

What is the minimum rotor RPM at which you can begin a full-power takeoff roll? In the Sport Copter Vortex II tandem trainer, which uses the same blades as the SH, 150 RRPM is about all you need to forget about flap and go for it.G'day Paul. Blade flap is is not the only considertion when doing a min. rrpm take off. The bending stresses on a hubbar and rotors at higher forward speeds and low rotor speeds are extreme. This is very easily observed watching impatient beginners from side on during their take off run. The excessive coning angle is frightening.

Anyone that uses full power once the rotors reach 150rpm is asking for trouble, not only from excessive stress but also from the possibility of striking an untimely "gust" and sending the blades into unrecoverable severe high speed flap.

[PW_Plack]

Tim,

I have no experience with different blades and machines, so I have no reason to question your comment as good general advice. The blades on the SC tandem spin up mighty fast once the machine starts moving, making it hard to outrun them. I can see where a light, powerful machine with harder-starting blades could be different.

[Coen]

I just wont be happy before 200RRPM is reached without hasstle and without stressing whatever system i decide to use, there is just to many factors that play a role in the way that rotors behave before flightRPM has been acheved. And the magic 200 seems to be the best place to be to be safe in almost all conditions.
Regards Coen

[Aussie_Paul]

Anyone that uses full power once the rotors reach 150rpm is asking for trouble, not only from excessive stress but also from the possibility of striking an untimely "gust" and sending the blades into unrecoverable severe high speed flap.

Tim, that is an unfair blanket statement. :(

In my Hybrid 150 rrpm can be enough, BUT I use 170 rrpm as my minimum figure to avoid the problems you stated.

As I have said in another thread each machine has its own minimum rrpm at which it is safe to apply full power.

Aussie Paul.:)