Constant Speed PTO for prerotor???

[skyguynca]

OK, I am looking for idea for a prerotor drive unit that will run at a constant speed....regardless of engine speed over say 2000rpm on the engine but maintains a constant drive speed of 270 to 330 rpm for a prerotor? Any ideas?

[Victor Duarte]

david, sounds like you should use an electric motor or an hydraulic regulated motor, but needs an hydraulic circuit... apart the engine.
If you mean a mechanical system that acts from 0 to 2000 rpm, then maintains 330 rpm, I dont see for now a lot of devices, excepted torque limitators, but they may generate some friction above the given torque...
or a cenftrifugal "anti-clutch" that frees the shaft above a given rpm... but i dont think it exists ready made, you have to do it.
and i'm curious about the answers you get.
thanks

[skyguynca]

Really what I want the unit to do is take power from the engine and yet be governed to where it can not turn the blades faster than flight rpm regarless whether the engine is running at 2000 rpm or 5400 rpm, I was thinking there should be some hydraulic motor that might do it

[Victor Duarte]

Yes david, i understand what you want, so maybe an hydraulic motor...
there are sohpisticated torque limiters but $$$.
i also know there are magnetic clutches like http://news.thomasnet.com/fullstory/10864
or magnetic particules clutches
they are smooth, but the best seems an hydraulic motor.

as i see it, you re going for a semi-powred rotor... care about the couter-torque ;)

thanks

[Vance]

David if you reach close to flight RPM it will be easy to tell because things will began to shake and slide before you take off. Just back off the prerotor then. You could also limit the presure in a hydraulic motor so the motor wouldn't produce enough horsepower to accelerate the blades to flight rpm. Thank you, Vance

[KenSandyEggo]

Wouldn't a helicopter be what you want?

[Victor Duarte]

Looks like it is, ken.
What i dont get, David, is Why you want this device ? before flight, a prerotator is fine, then the rotor auto-rotates.. is it the fear to loose RPM ? or the will to ease the rotor ?
thanks

[Mike Hook]

They make a CST drive but it does not quite work like you think. A CST drive has a input shaft and a out put shaft and also a shaft with a brake rotor. You start the input shaft to full RPM and then the brake rotor spins freely. As you desire output RPM you apply breaking pressue to the rotor caliper. You can slowing bring the output shaft up to speed and then after the desired speed is acheived you just release the brake rotor and everything free wheels. They use this type of drive in the mining industry to start long belt drives. This system is also used in pulling tractors. I have thought about this system before but have no time to pursue it.

Mike

[Victor Duarte]

Mike, what you describe looks like a differential.. ? What is CST please ?
thanks

[quadrirotor]

I think that the simpler and lighter solution could be a second small engine (you need about 4 hp to prerotate a 25 feet rotor to 200 rrpm) let's say 15 hp solo engine (or equiv.) with a car cruise control governor...
As better rotor are used (4 bladed) the rotor fly almost horizontal, so a backup power is needed not to lose rrpm too quickly in a negative situation (negative Gs, negative AOA...).
Of course, the solution of Dick Degraw is the best (DeBird, RhinoGyro) but those gyros are in fact almost helicos...
Tip jet driven rotor is not bad at all! with a car cruise control on the waste valve of the turbo!

[skyguynca]

I am not familiar with Dick Degraw's solution, I have the the Rhinogyro but not the Debird......no I do not want a helicopter been flying gyros and helios for years and prefer the simplicity of a gyro. I just have a few experiments I wish to do and need a constant speed prerotor that can be engaged and disengaged anytime even in flight, that is why it must be able to make flight speed.

[Victor Duarte]

david, i agree with andre andre, tip jet prerotation is what you need, smooth, no iddle, no shock, no need for clutch, no torque .. or H2O2 rocketry for short power increases.
It implies ou nust have a specific design for tip jet, makable on a 2 bladed tiltilng rotor but its very inefficient, whatever you will have engine power eaten by the prerotation.

I'v read years ago that a small xtra engine (a leafblower or a grass-cutter) has been tried on a french gyro for prerotating , but what a mess ! it has built-in sprag clutch, but if ou wan to operate it in-flight you need an extra starter.. IMHO, drop it.

why dont you investigate hydraulics?, i remember i repaired a screw-elevator (not shure of the translation) that was used to suck corn from a truck to the silo, it had a small hydraulic engine i could hold in my hand, once the power off, the screw could spin freely.. interesting for you , but you need an Hydruilic pump.

looks you are going to test extreme manoeuvres ;)
cheers

[skyguynca]

That is what I am looking for Victor, I was thinking a hydraulic pump with a motor. Most hydraulic pumps put out a specific pressure at a specific flow rate which means the motor would run one speed. I am just not sure of which or where to look for it. I was hopeing someone on here has had experience with such items.

Yes Andre' I have thought of the small 15hp extra motor, several of the 4 cycle have come to mind because they have starters, are small enough and 4 stroke but the weight is about 100lbs.

[Victor Duarte]

That is what I am looking for Victor, I was thinking a hydraulic pump with a motor. Most hydraulic pumps put out a specific pressure at a specific flow rate which means the motor would run one speed. I am just not sure of which or where to look for it. I was hopeing someone on here has had experience with such items.

Yes Andre' I have thought of the small 15hp extra motor, several of the 4 cycle have come to mind because they have starters, are small enough and 4 stroke but the weight is about 100lbs.
David, just perform a search about hydraulic motors, the net is fulll of info.
http://www.parker.com/ead/cm2.asp?cmid=973

what i remind about the model i had in hands (looked like the one you can see in the link) is that it was pretty small and light. about 15 cm diam, 10 cm thick, cylindrical. it could easyly screw a column of 3 meters of corn, not bad. Adnd i remind i could spin the screw without any effort when off..

I worked with a pressure valve, constant speed, i dont know about the size and power of the pump, but it was actionned by an electric motor comparable to those you find on the column drillers (hope i translate it right).

you should have a go to an agriculture/tractor workshop or a caterpillar dealer.

cheers

[skyguynca]

thanks, I was playing on their pump and motor software and they make a motor and pump to do exactly what I want, thanks.

[quadrirotor]

David, the best is to use a small two strokes engine which is used in the paramotor domain and has a small starter. You can see also this 10hp:
http://www.engineeringsystem.co.jp/
You can use also an hydrostatique transmission, but that's more heavy and a lot more complex:
http://www.flexion.nl/hydraulics/trans/ld_trans.htm
http://www.fluidpack.com/
http://www.hbus.haldex.com/products/hpm.htm

[skyguynca]

I thought about a small 2 stroke but you have the exhaust which for tuned engines is quite large, then the hp is small for the untuned, residue from exhaust and most do not have the ability for a starter and the ones that do are as large as the 4stroke engines with starters and you still have to have a seperate gas tank for the 2 stroke fuel which leads the 4 stroke at a definite advantage, thanks for the ideas though.

[quadrirotor]

now you have to fit it, you add weight but you add power too! (it has a starter...)
http://www.baileyaviation.com/maincontent.html

[skyguynca]

Looks great, but look at the price too!!!! 3700 pounds sterling....lets see that is about $5500 US????

[quadrirotor]

It's a steal because this engine comes from a scooter...may be the Honda gc160 with a little work...

[Victor Duarte]

Nice engine Andre, good for a small two-aside prop.

David, let us know if you found a good setup, i am also interested in the best setup with that kind of stuff, and the price.
Thanks.

[skyguynca]

I will, this project is a experiment with the ability to drive the rotors thru takeoff for shorter field capability, heavy loads and cross country work and hopefully alot smoother than 2 blade systems.

[Victor Duarte]

David, this message i had in a french forum, the guy works on a variable pitch rotor and says he prerotates at 480 RPM
"Bonjour
Je suis en train de construire un autogire à décollage vertical voir le site :

http://perso.club-internet.fr/rvtpanet/Articles/Gyro_sauteur_Brun/Gyro_sauteur_Brun.htm

J'ai commencé les essais du prélanceur en mode autogire standard sans variation de pas, j'ai prélancé actuellement à 480 t/mn avec un rotor de 7m, mon but c'est d'atteindre les 600t/mn avec un rotor à plat ou légèrement négatif avec un rotor de 8,50m. "

as i feel it your project is ready for tip-jets, with the weight of the hydraulics, you can easily mount a supercharger feeding the blades(about 15 lbs), the advantage is NO TORQUE, no link to the frame so, a very smooth rotor... i posted a drawing for a variable pitch control on the rotor thread, imagine you replace the central control rod by a tube, driving air to the blade roots, could work.
thanks

[skyguynca]

I was at his site, very busy gyro he has going, using a drive shaft thru the head...has he flown it?

[Victor Duarte]

appearently not yet, personnally i find the system a little complex... if i know more i will post it.

[mceagle]

In my opinion, if you loose enough rotor speed in flight that you need mechanical assistance to get them back to speed, then I would suggest that you have already made the first part of a fatal mistake.
If you did manage to get the "drive" into gear then the Gyro would spin so fast that maintaining control would be impossible.

[Victor Duarte]

Tim, the way I feel it, David is whishing to obtain a kind of coumpound like the "rotodyne", semi powered rotor, props, and gyro, but the way to get it is : tip jets , or twin rotors. BTW a power input will indeed create spin, fatal ? perhaps not, if the rudder has a large surface, the tail has a big lever and the power input not too brutal, but it's a bet i would not attempt.
thanks.

[Vance]

It is my understanding that in a Helicopter, even with all the power they have, a rotor blade stall is classified as a non- recoverable event. Thank you, Vance

[skyguynca]

OK guys your going alot further than I intended with this whole thing. First I will explain the background for my idea. Several hybrid gyros have been built with rotors that can be powered for prerotation and in flight and landings. If you study Bensen's notes and ideas he built 5..yes 5 powered gyro rotor systems from 5hp to 25hp and the 25hp one could hover with out.....read it again....with out a tail rotor, the direct thrust coming from the engine past the rudder gave him enough control to hover safely, and he could accelerate out of this hover into controlled flight with no transitional drop. He flew it many times and yes he also discusses the amount of hp and what to expect. It can be done as as he states, you must have a higher degree of experience to hover but you can learn it and it has been done. He also states that he gained a higher top speed and a much lower controlled airspeed that he could still maintain altitude and climb than he could without the powered rotor system. The power is not enough to create so much torque that the aircraft needed antitorque system other than engine thrust and rudder. The gyrhino did this also with its jump capability not to mention the two other certified gyros that can also jump. As I stated earlier (if you read the earlier posts) this is a experiment for short takeoff and landing with mulitblade rotor systems and heavier gross weights...I never ever said it was for zero or negative g manuvers or trying to recover from a area behind the power curve. It is just to enhance the short field capability with greater control. In order to do this the rotors must be just below flight rpm and accerate into flight rpm as the machine lifts off in it own length and to land this way you must also be able to engage the system in flight to use for landing really short with a higher gross weight and hold off rotor decay just a bit longer this way.This is all I am looking into.........ok read closely so there is no mistake again....this is not to recover from behind the power curve or blade stall. it is to make higher gross weight aircraft that can perform better stol capabilities with higher amounts of control. Ok?

[quadrirotor]

That's only a side effect benefit, and to underlign the necessity of In Flight Added Power...

[Victor Duarte]

David, i feel you are a little iritated, dont be please, i think no one intended to upset you. I and others are just enthusiasts and we like thinking about the subject you lauched. Did you began to build or still drafting ?
thanks

[skyguynca]

I am not upset at all, I just don't want this to be misunderstood as a attempt to make up for mistakes in flying. All I am trying to do is make a rotor system that will allow a great degree of control at lower speeds and stol capablilities. Please don't think I am upset. Just making sure the wrong impression of my experiment are stopped early. I have just about drafted the entire machine still working on the rotor drive though. I can not complete the head design and rotor drive until I figure out what engine or drive motor I will be using. The 4 bladed rotor head is done though and I believe it will work quite well with minimal tooling required. I am going to try and make most of the pieces with just standard shop equipment except for 4 parts that will have to be done at a machine shop.

[Victor Duarte]

thats ok david,
sounds you have quite everything ready for the rotor, how will you test it ? on the back of a truck or a tow ?
thanks

[skyguynca]

Actually tow once the airframe is together. The airframe I will probably start on mid November, I was building a 3DRV but I have decided I will do both at the same time so I am moving both projects to the last week of November or the first week of December as the starting date so I have time to aquire the materials and plans for the two seat airframe. I am going to try to make a drop keel Parsons Trainer, well that is if I can get the plans, if not I am going to wing it.

[Victor Duarte]

wing it ? (sorry moi francais) ;)

[Mike Hook]

Victor

Sorry took so long to get back here, yes the CST drive is like a auto differental,a input output and a pinion shaft with the brake rotor.

Mike

[Victor Duarte]

Thanks mike, no problem with delay.
have you a link or something ? when you have some time, looks to me an interesting thing for coax choppers.
cheers

[Not Yet]

Dave
What you need is a, pressure compensating flow control valve. This valve keeps a constant flow regardless of pressure or volume. This valve is usually mounted in the tank line (the line from your motor going to the tank). However in this case I think that it would be better to set it up in the pressure line, so that it dumps the excess oil at higher engine speeds to the tank.
Speaking of tanks, back in the late 60’s or early 70’s there was an add on oil tank cooler for the VW engine. It held 1 quart, was cast aluminum, and hade fines on it for cooling. I think that one of these might make a good tank for your partially powered rotor.
:)
another Dave :rolleyes:

[skyguynca]

Thanks another Dave, I will look into it.

[skyguynca]

Well at the moment I am still checking all options

[Mike Hook]

Hangardebris
while looking thru their hydraulic software take note of the required cooling capacity of the units as of tank size and cooler.

Mike

[Brent_Brown]

Skyguynca did you send me a message if so send me an real e- mail at ezgb@earthlink.net I have a copy of the parsons trainer but he didn't have some key parts in it so you would have to buy them from him. Some numbers are flipped again I think this was done to make it hard to do on your own. Two models the Mac and the Arrow motors, one long and one short back seat space. I have the short back seat with the front mast right aginst the seat tank. One other thing I known he made a longer torque tube and control fork for this thing with the light Mac motor the rootr head is far forward and the push tubes cant reach it. I will look for the plans for you today and make copies at work next week. OK

Did I miss the rotorhead your making four blades where did you post that?
I have a plan to use a 43cc mopedhead motor belt drive to the head. That should get 250 rrpm with the right gears.

[skyguynca]

Sent you email off forum, thanks

[Brent_Brown]

I just won this 43cc ele start motor and will see if I can do a update of that powerhead Dr. Bensen had. I think this will work best on a singel mast gyro but I will see what I can do with it on the parson type I have.

Now where I put that fan belt?

[skyguynca]

GREAT!!! Keep us updated!!! If you end up with the same results as Bensen did it will have shorter takeoff, better cruise and very very short landings.

[Rotor Rooter]

skyguynca wrote;

"OK, I am looking for idea for a prerotor drive unit that will run at a constant speed....regardless of engine speed over say 2000rpm on the engine but maintains a constant drive speed of 270 to 330 rpm for a prerotor? Any ideas?"


An idea;

Install a constant speed propeller. Connect the engine, to the propeller, to the rotor; at fixed ratios. Once the desired rpm of the rotor (and the propeller) has been reached, all additional power will go to the propeller.


A question;

I wonder if the advantage of constant mechanical power to the rotor during flight is offset by the power required to offset the torque of the powered rotor?

Dave Jackson

[skyguynca]

No power will be required to offset torque in flight. As I found out in 1980 while I was crewing UH-1H's we lost a tail rotor drive shaft, at 60 knots the aircraft flew just fine, it weather vane's even though the vertical is not a whole lot of area...also in Bensen's book he talks about how he flew his BM8 with a 25 hp engine for a prerotor, it few fine and he could even hover it just using prop wash over the vertical to control it. He said it required a bit more experence but once acquired it was second nature.

[Rotor Rooter]

The amount of torque that is transmitted to the main rotor from the fuselage (i.e. from the engine) will result in an identical counter-torque. This counter-torque may be handled by a tail-rotor, or by the redirection and drag of a deflected rudder, but in both cases it will consume power.

A long tail boom will reduce the force (power) required, but there is no free lunch.
The closest thing to a free lunch might be a propeller with lateral cyclic (yaw) control. It might even get close to allowing vertical take-offs if it was also capable of providing reverse velocity on the side of the retreating rotor blades.


Just some thoughts.


Dave Jackson

[PW_Plack]

Some sort of continuously variable transmission, like those used in small cars like the Subaru Justy, might work. They're usually used to keep the engine in its torque peak while wheel speed varies, but could theoretically be arranged to work the other way.

[Timchick]

How does Dick DeGraw's Gyrhino do his lift off? I saw it fly several years ago at Bensen Days. I was just getting into gyros then and didn't know too much about prerotators or anything else at that point. I should have a short video clip of the Gyrhino in action posted on the web soon.

[darrellwittke]

I believe DeGraw uses a hydraulic pump with a splitter. 1/7th of available engine power goes to gyro during flight (thereby making it a gyrodyne) and with the variable splitter, more of the flow can be diverted to the prerotator for his jump take-offs. Dick also has a variable pitch head so that he can overspeed his rotors then pop off the ground pulling collective. At least that is what I recall reading, set me straight if I'm wrong someone.

[Timchick]

I'm sending Rotor-Head a video clip this week of the Gyrhino doing a jump takeoff at Bensen days 2 or 3 years ago. He's going to put it on his website. Those of you who haven't seen it are in for a treat.

[Dean_Dolph]

I don't know if it is relevant to this discussion or not but in the September '99 issue of Rotorcraft (the PRA magazine) Dick DeGraw was interviewed on the topic of the 'DeBird'; the machine he built for his wife. The 'DeBird' won Grand Champion Rotorcraft and Best New Design awards at Mentone '99 and Karol DeGraw won the "Man and Machine" award flying this machine. The award presenter commented at the time that since Karol was the first woman to win the award; they might have to change the award's name!

The interview write up is a little ambiguous in this area but Dick is driving the rotors thru a differential off of the prop with 14% of the engine power going thru a right angle gear drive to the rotor. He alludes to the fact that this is more than he provided the Gyrhino rotor. He doesn't provide any details on the differential other than "at the normal flight RRPM of 350, the differential internal parts do not turn, just like a car going down the road - both barrels turn at the same speed"

He is quoted as saying they can get 260 RRPM but usually takeoff when it reaches 220 - 230. He goes on to say that since the rotor is always powered it won't slow down 'catastrophically' (my interpretation!) during negative 'G' or in a full power push over situation and as such is an inherently safe design. He also mentions that with the driven rotor they cruise at 85 mph versus 70 mph when it is not driven. Top speed is around 100 mph but the fuel burn at 90 mph is 6 gph vs. 5 at 85 mph. The DeBird's powered rotor flies at a 4 degree angle of attack vs. 8 - 10 degrees unpowered like a standard gyro. The power to the rotor increases the RRPM by only 10 rpm over unpowered.

[skyguynca]

Thanks for the info, backs up what Bensen said about driving the rotors.

[Brent_Brown]

14% that is what 10 to 12 HP? if it had a 80hp motor?

[skyguynca]

I know, sounds great doesn't, Bensen said he could hover with 25hp no problem and 15hp was the limit with no torque tendencies or problems at all and he could take off with 10 to 15ft roll everytime, he said with the 15hp rotor drive he could takeoff anywhere he could land and that with the motor stopped in flight (no overrunnning clutch) he would slow down 15mph to drive the rotors engine.

[Brent_Brown]

No overriding clutch is not the way I would do it but, I guess it he did it. If the rotor motor stops and is free to turn is one thing but, if it locks up with a rod out the side of the case. that is not going to be good. You might slow down more than 15 mph.

[skyguynca]

LOL....very very true, I was thinking one of those heavy duty centrifical clutches like they use on the C box on rotax 582's, it should do the job

[Brent_Brown]

That is what I had in mind too. That will be a soft start also. I think the PPG motors are what we should look at. they are getting lighter and clutched at about 20 hp

[skyguynca]

Do you have a link?

[Brent_Brown]

Here are some not all
http://www.radne.se/Store
http://www.miniplane.com/inglese/top80.htm
http://www.simonini-flying.com/mini2plus_ita.htm
http://www.jump-air.com/
http://www.tn-prop.com/

[skyguynca]

Hmmmm, those alternatives are a bit pricey...I have a couple of ideas though, will post them later.

[rtfm]

Hi,
Just checking in to see what (if any) progress has been made in the way of partially powered rotors. Seems definitely the way to go.

Cheers,
Duncan

[skyguynca]

Afraid not, I am so busy with work I haven't had time to think of anything but food and sleep.......oh and the occasional comment on here.

[CypherNinja]

I lightly skimmed this thread so I know it was mentioned once, but I'm not sure if it was discussed more in depth.

I gave the problem some thought and I concluded that a hydraulic system would be the best way to go (my opinion). The system I envision would have a hydraulic pump similar to this one (http://www.northerntool.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=6970&productId=30936&R=30936) attached to the engine or gearbox output (possibly with a pulley, or maybe even using a gearbox with a PTO).

Then you would use a variable flow control valve like this (http://www.northerntool.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=6970&productId=22211&R=22211) to regulate the flow volume to the rotorhead, which would regulate the rotational speed to anything you wanted.

At the rotorhead, you would have a gear drive much like what you see on many prerotators (maybe beefier, though) driven by a hydraulic motor like this (http://www.northerntool.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=6970&productId=25132&R=25132) with a clutch bearing like this (http://www.mcmaster.com/ctlg/DisplCtlgPage.asp?ReqTyp=CATALOG&CtlgPgNbr=1024&CtlgEdition=&sesnextrep=532852553335955&ScreenWidth=1280&McMMainWidth=1016).

This way, the rotor would free rotate with no interference from the hydraulic system. However, lets say your gyro is sitting on the ground and you give the blades a little push start. Your engine is turning along at an appropriate speed and you begin creeping the flow rate of the hydraulic system upward. As long as the hydraulic motor is turning slower that the rotors, the rotors are freespinning. As the motor begins to rotate faster, however, the clutch bearing will grab and and the rotors will begin accelerating in sync with the motor.

I think this type of system would do what you guys are thinking provided its beefy enough and it was properly designed to not have much parasitic drag on the engine when its not operating (maybe with the use of an electric clutch at the pump).

This type of system would be pretty convenient when used as a regular prerotator, as well. You could warm everything up, use the valve to prerotate, and then leave the valve set as it is. This way you could sit on the tarmac, taxi, or do whatever you needed to do, and the blades would never drop below whatever speed you set them at. :cool:

You wouldn't have to mess with a separate engine, it would be much more efficient than an electric setup, and trying to get the variable speed ability in a mechanical system would be majorly complex and probably alot heavier.

There's no way you'd make Part 103, but it'd make you pretty popular.:D

[rtfm]

Hi,
This is what makes this group so great. I'm not at the point of needing to fit the prerotator/partially powered rotor system yet, but it is sure comforting to read of a system which could very well work when the time comes. Like most designers/builders, I can't stop worrying about future design problems. Now that I have something which seems eminently sensible, I can start planning along these lines.

Thank you very much for the help.

Regards,
Duncan

[Mike Hook]

Hydralic pre-rotors are great but to use one as a partially powered rotor ,one has to take into consideration heat build up. You will need a larger fuild supply and a hydralic oil cooler.

Mike

[rtfm]

Hydralic pre-rotors are great but to use one as a partially powered rotor ,one has to take into consideration heat build up. You will need a larger fuild supply and a hydralic oil cooler.

Mike
Hi,
Yeah. But that's a pretty simple thing to add. And if you look at the prices in the links provided by CypherNinja above, it works out to be a pretty cheap package, too, all up.

Duncan

[CypherNinja]

Hi,
Yeah. But that's a pretty simple thing to add. And if you look at the prices in the links provided by CypherNinja above, it works out to be a pretty cheap package, too, all up.

Duncan

Just don't forget, I was only pointing out examples of key components. There are many components I didn't list that could drive up the price by no small amount. The price of hoses, fittings, coolers and resevoirs like Mike Hook mentioned, and other necessities should not be underestimated.

Also, other considerations such as heat, duty cycles, and weight could drive the cost of components up even further.

Parts made for ground machinery may not all be appropriate for an aircraft. ;) But at least I got the concept across with examples of what I'm talking about. :D

EDIT: The total weight of just the components I listed is ~32 pounds. The rest of the system could easily drive that figure up to 50+ pounds. When you select parts appropriate strength and duty cycle (triple checked:D), they may be even heavier than the ones I listed. There may be lighter weight alternatives out there for select components, but this system will be far from a "lightweight". You better be sure that that fits into the performace specs of the airframe your using. :eek:

[mike marckel]

Hi guys, great posts.I thought you might like to know about the prerotor on my gyro.( photos on the flying photos/raf 1000 thread)The prerotor uses a 6.5hp lawboy engine,serp.belt drive to a gearbox with a three disc wet clutch.After the gearbox power is transfered thru a pair of sealed u-joints ,the splined slip joint,then into the rotor head. A steel shaft supported by two small bearings takes the power to the sprag bearing mounted on top of the bearing block ,which is whatthe teter towers mount on....tests as of today..150 rpm,no torque transfered into the control system,no need to trim rotor system to compensate for hoses,or flex shafts!!! I expect much better results as i fine tune the system