Hydraulic prerotor

Just setting here thinking on the threads on prerotors and wonder if anyone has tried to use a relief valve on their hydraulic prerotor. I think that you could set it so it would dump if the torque was too high as to cause blade flapping. If the dump releif was set right you could just leave the prerotor on and crank the engine right on up and still would allow the rotor to come up to speed in a controllable manner without the issue of blade flapping like in the Dragon Wings.

Any thoughts????????


Mike

I reckon a relief valve should be fitted anyway.Mind you,I'v never see a hyd setup so couldn't realy say if there's a need for one.
That said thou,it wouldn't prevent flapping.Flapping is caused by the opposing rotor airspeed differential becoming too great so as to make the blades teeter beyond their teetering limit.The amount of toque applied to the systm will only determine the rate of rpm gain.[and strain on the mast]
But I reckon it would simplify the prerotating proceadure as you stated ,and be a safty against overstressing the systm.

Mike, mine is not vented and it is not a problem to prerotate up to 200 R's. Flapping has never been a problem either.

Thank you for your replies Birdy and Chuck.

Birdy made a point I never thought about the tourque that is applied to the mast tube. Has anyone every done a study to see what the limit of tourque on a mast tube?? Either redundant or single tube masts aluminum or 4130 steel.

Mike

Mike, I have run my hydraulic pre-rotator on both 1 x 2 redundant and 2 x 2 masts. There was no ill effect on either. Both were 6061-T6. However, my blades are only 24' long and very light (DW's). As far as I know, no one uses a steel mast.

I had never considered the possible problem of Mast Twist. The Sportcopters w/ 912 are being built with a Steel Mast I believe.

Hello Todd. That is interesting. I assume that it is constructed of relatively thin wall 4130. If you find out what the dimensions are, I would like to know.

Todd see if you can come up with a pic too of that 912 mast set up please.

Thanks Mike

Chuck,

Is your prerotor assembly made by Dominator? Do you have any specs on the pump and motor displacement and the rpm ratings??

thanks

Mike

Chuck,

I think the Sport Copter 912 mast is a milder steel than 4130. It makes a really sweet setup, comes with the engine mounts, suspension mounts welded on, for a no-holes installation. If I understood correctly, the whole mast is then treated inside for corrosion resistance, sealed airtight, heat treated as one piece and powder-coated. Jim says it weighs seven pounds more than the aluminum mast it replaces, but saves much of that back by eliminating the need for most of the structure behind the mast.

Look at the picture of the Vortex 912 ULS on his website, and you'll see all the tubing gone from the rear: http://www.sportcopter.com

The engine literally hangs from the back of the mast. I wondered if that would hold up, but Jim's got a couple hundred hours on his tandem with the new design, with an NSI Soob 2.2 and cockpit-adjustable prop hanging there, and everything's been fine. The steel also pretty much ensures that the mast will fail near the top, at the folding hinge or the shock mounts, in a blade strike.

Mike, yes, my pre-rotator and the rotor head are built by Ernie, but I have no specs.

Paul, That is quite interesting. Thanks a lot for the info.

Thanks Chuck

I was going thru the Granger catalog last night and was looking at air motors.
they make a vane air motor that produces 1 3/4 hp on 100 psi, 75 cfm and it is small. I wonder has anyone expermented with this type of motor. All you need is a small tank and a valve to dump to the air motor. I think you could use a small electric compressor to charge the tank or maybe the exaust off the engine itself.


Or better yet just spend the money on a factory built one,, buttttttttt then that takes all the fun out of it.


Mike

Mike, I personally don't think you would be happy with the air motor. On the other hand, I am very well pleased with the hydraulic pre-rotator on the Dominator. I have an extra pump that I could let you have for half of what a new one would cost. I may even be able to help you on getting some new parts. Just let me know what you decide on, and I'll be more than happy to help if I can.

Mike H.,I looked into an air motor prerotor setup when I was changing the RAF over to the 914.
Got all the specs off a manufacturer and did the numbers for an exhaust driven setup and it added up right.Can't remember wot I did with the numbers,and can't remember why I didn't do it.
Probably coz I had the RAF prerotor already and couldn't be stuffed with the headakes.I just wanted to fly.

Thanks Chuck I will keep that in mind.

Birdy I was just playing with the idea, glad to see I was not the only one that has thought of using air motors. I have not had a chance to run any numbers on a sub 2.2 but as soon as I get the chance here. Been very busy with work and just get a few to check the fourm. Hope to head out to Mentone Friday night here if -hit dont go down hill on the job.
Mike