Weird thought and question #4 - autorotators

[serverlan]

Are

prerotators electric or hydraulic? (I presume that hydraulics would run from engine oil pump pressure? They don't seem to do much of a job, from what I've read. They reduce takeoff distances a bit, but no greatly. If they are hydraulic, is it possible to get decent shaft-drivedn hydraulic pumps capable of delivering real power? or would the weight be prohibitive?

Don

[le-wardy]

Don, the hydraulic prerotators used by some gyro pilots on their machines, are made up of components using a power steering pump from a car. As much as we'd all like to have gyros which could take off like a helicopter, the complexity involved rears its ugly head.
The weight factor involved between hydraulic or electric prerotators is negligible. Electric prerotators are limited by their designed output, whereas the hydraulic option is determined by the pumps oil flow rate, pulley wheel size on the pump, and the engine powering it.
As the rotor blades are fixed pitch. Trying to attempt to spin the rotor faster than the rpm's required in flight while on the ground, will have you dancing your machine across the paddock like a swaggering drunk. Not good !The best thing is to remember, although we still need a take-off run of some distance. It's still a hell of a lot shorter than a normal fixed-wing does.

[rotor]

The reason we use a pre-rotator is yes to shorten our take off roll

BUT

what it really does is help us get the blades rotating to about 80-100 rpm. When ground rolling in a zero wind situation without a pre-rotator it can sometimes take a bit of effort for an inexperienced pilot (even experienced pilots can have trouble) to get the blades to wind up to this point. You also lesson the risk of hinging your blades (or your trainers) if you try to go to fast to quick without waiting for the blades to wind up. Of course this can happen at any speed with some blades.

After the blades get past this point they are easy to get up to flying speed.

Yes, pre-rotators do the job they were designed for, and in my opinion do it well.

I hope this answers your question. I'm sure some one will let me know if I'm wrong

[joey]

How difficult is it to use the main driving engine with a gearing system to the main rotor that has some simple pitch control. The rudder then would need to use the downwind from the rotor to keep the craft 'straight'. Engine power is then 'transferred' to the rear prop while pitch is reduced or simply flattened.

Are there any craft built like this? It would reduce take-off distance and increase the risk factor. However wouldn't still have blade twist effect as helicopters do so will still be relatively safe if on engine failure blades are flattened and engine disenganged from rotor...

any info..

I am interested in building a gyro but my budget is very very limited so cost would need to be at a minimum. i can do some engineering myself though..

[Aussie Blue]

Saw at the Dubai Air Show a Jordanian gyro. The pre-rotator was a 'manually coupled idler wheel' that coupled to the flywheel. This was connected to a worm drive that spun the rotor. Coupling was done by a lever next to the seat. Oh, the gear on the rotor was also coupled in some way.

[rotor]

Did this gyro jump off like the Pitcairns and Ciera's or was it just a prerotator? They used a mechanical type similar to what your saying and ran the rotor up to flying speed getting off with next to no airspeed.

[Echo 2]

Art Spink sent me a DVD he filmed while in the States , it includes a machine called the Gyrhino(?) , this thing is amazing - it is jump take off with no ground roll. I think it has mechanical drive up to a modified Hughes chopper rotor head , the pilot gets the blades up then pulls on pitch. ( there may be more to it than that ,but it sure is impressive)

[rotor]

When I first saw a picture of this machine I didn't realise it was so versatile. I didn't know what it was - thanks for the update


Linked to Gallery Pics:


http://www.rotorcraft.com.au/photoplog/file.php?n=95



http://www.rotorcraft.com.au/photoplog/file.php?n=93

[Echo 2]

It looks a bit weird but once you see it flying you'll want one...thanks for the pics.

[Bob]

Joey :
You can build a gyro for next to nothing IF .. you scrounge up a good engine and are good at building stuff yourself....
I got my gyro in a bunch of pieces at a yardsale..for 900 bucks ... the engine was just gone over by a shop and still had the tag on it ... the rotor was dammaged and only one of the landing gear was there.... but the Assembly instruction book and instructions came with it ... within a month I had it ready to test out.... the gyro was ready but I was far from it ( un known to me at the time )
.... so yes you can do it cheeply... Dirt cheep if your realy carefull !
I am presently makeing my new set of rotor blades, prop and repairs because I flopped the silly thing over about 2 weeks ago....
the gyrobee is a great little Gyro and the instructions are available over the internet for free
though buying the metal is not cheep it isn't near as expensive as buying a kit ....
the most expensive part of your gyro will no doubt be the motor ... so start building your gyrobee and keep an ear to the ground for a good cheep motor ... in a year or so you'll have your bird ! .... you can do it if your willing to do everything if your broke ... I know because I'm broke and I have rebuilt this gyro 3 times now ! hehehehe
while there are those that will question my sanity in doing this and not buying all new pieces to repair with , I have no doubt my gyro will get me home ... if you don't have the skills ... get them ... its cheeper to learn how to build one than it is to buy one !
there is no reason your dream of flying should be held up because of cash when a gyro is so darn simple.... but plan on and do get qualified instructions... its expensive ! so plan on it !
and hopefully you won't be rebuilding your gyro as much as I

my 2 coppers !

Bob......

[Bob]

On the subject of pre rotators and Jump starts...
Igor Benson experimented alot with the system and I guess did fairly well with it ...
though I have never gotten even close to a jump start with my gyro its v-belt system works extreamily good ! getting the rotors well into flight speed if i so desire its power is taken from just behind the prop hub from a v-belt pully and goes into a 2:1 90degree gear box from there it goes to the rotor head via a swivel socket ( universal joint) and slip joint to a pully with a one way clutch in it that then drives the large pully on the rotor blades ...
its simple, light and works well,
however sense i don't have brakes on my gyro I have a hard time spinning the things up because it wants to go ! hehehehe but brakes are comeing soon to cure that problem.

here's a pic of it if anyone cares ...
C ya !
Bob.....

[jonem]

Greetings all,

I am also looking into a high performance prerotator, as I see it ,there are two options (I presently have a Wunderlich) A Poly v belt drive to deliver sufficient HP through a flexible shaft drive or a prop shaft with a spline and universals complete with a o degree pitch adjustment on the prop is one reasonable bet. Another option is a seperate motor, ie a tuned mini 2 stroke coupled through a shaft to the bendix, no problem with the prop! I saw a video of one in use and it was quite impressive. Has anyone in OZ tried it?

cheers...jonem

[Brian]

Anything that is used to pre rotate that gets the revs up around the 200/ 250 mark AND is simple and reliable as well as light is going to be a winner.
As yet, there doesnt seem to be anything that meets this requirement.

I question the real need to have a 'jump takeoff' for a gyro, is the complexity and the associated risks involved, really worth it ?? Most people that have a gyro, have a bit of ground to takeoff on and I know from personal experience, that having somthing to be able to spin the blades up to say 200 or 250 would be great and enable a very short takeoff roll.

Of course, you could wait till conditions like we have here today with the wind up around 30 knots, that should equate to around 200 revs, only need 10 knots forward airspeed and she's flying. :blowme:

[Scorpion]

Hi there members,

I've read a lot of the threads about prerotor's and jump-takeoff, but haven't found anything that suggests the power required.

Can any one talk numbers to achieve the results needed.

I have a unit I'm looking at using which is 17 HP and weigh's in at 3.9kg. To that I have to add other bits and pieces which would probably double this weight, but it would certainly be under 10kg complete and should spin up to full flying RRPM.

Any ideas?

Graeme

[Fencing Wire]

Hi there members,

I've read a lot of the threads about prerotor's and jump-takeoff, but haven't found anything that suggests the power required.

Can any one talk numbers to achieve the results needed.

I have a unit I'm looking at using which is 17 HP and weigh's in at 3.9kg. To that I have to add other bits and pieces which would probably double this weight, but it would certainly be under 10kg complete and should spin up to full flying RRPM.

Any ideas?

Graeme

G'day Graeme,
I hadn't given it that much thought, BUT from a simple blokes perspective, If it takes me 75 hp to take off horizontal, why would I bother when I can take off vertically for 17 hp? I don't see any helicopters (which appear to specialize in this "jump take off" sort of thing) that use a 17hp motor. My suspicion is that you are going to be at least 50 horses short. But some-one (like young Nick) will have a formula that will allow you to calculate the power required for lift-off. If it's 7hp, then I'm going to sack my 75hp motor for bludging on me.:D:D

Cheers

[Scorpion]

Thanks, Fencing Wire.

I wasn't looking for VTO just a prerotor with a bit guts for VSTO (Very Short Take Off).

I have heard that around 12hp would be sufficeint but then there are others who have said much the same as you.

There are many who have already experimented with different types of pre-rotor, but no one seems to divulge the HP they needed to achieve it.

Hoping someone might enlighten us with the hard facts.

Graeme

[rotor]

Graeme,

take a look at this site -

Peroxide Propulsion :: Peroxide Propulsion (http://www.peroxidepropulsion.com/)

Power your rotors up with hydrogen peroxide rockets on the rotor tips

[Mitch]

Scorpion,

Have a look here at the Metro Launch System......

The Butterfly LLC (http://www.thebutterflyllc.com)

Mitch.