Pre-rotators

[asra]

One for Tim (and/or anybody else who wants to jump in).I thought it was 15 years, but now that I look, it is 17 years since I started buggerizing around with these things (gyros).

[bones]

Fred,I agree with you there about winding the blades up and then flying over a strip, i have about 1800mt of bitchem strip here so most of the time i just get the blades to about 150rrpm, then start a roll, this also lets the motor,oils,ect warm up properly before lift off.I know there has been talk of certain gyro instructors not teaching to pat the blades up, and then learning the student how to bring the blades up to flying speed without the prerotator, what happens if the prerotator fails. This happened to me yesterday,i hadd taken off 3 times no drama, just that with the very humid conditions the blades didnt really want to play the game, my last take off was about 3.5 hrs ago, was needing a leak and smoke and strech the legs, now since a have this RAF prerotator on, i can get off bloody short, and was nearly going to sit down beside the mill, and have a talk before heading home, but i had people waitinig for me, so i decided to just go and land on a dirt road on the way back, landed no problems, took care of stuff, strapped back in hit the button, motor running, pulled the handle to start the rotors, and next thing the teeth on the ring gear were singing to me, WTF , tried again same thing, so stopped the motor climbed up on the seat, and the whole top of the preroator was gone, and as soon as load was applied the teeth would slip, after a few colourful words(lots actually) i rolled another smoke and went for a walk in the hope that it jumped off when i landed, not to be.So it was back standing on the seat patting the blades up to about 50rrpm, then bring them up take off and fly home, it was only after i got off the ground, that i got to thinking, it would really suck to have to get a trailer out to pick me and the gyro up just because i never knew how to hand spin rotors, glad i was taugh how to fly properly, just my 2 cents worth.

[Brian]

I reckon there has to be some extra pressure on heads and bearings if they are being spun up to say 300 revs for every takeoff although you dont hear of any problems with the Magni /ELA/ MT which all have the capability to spin rotors in excess of 200 revs.There was a lot of discussion back some time ago with the effect electric pre rotors would have on heads re the sudden impact when the button was hit eg, the Rosco type set up with no soft start like many use today. Doc Evans argued that there was a tremendous impact and Rosco

[bones]

I reckon there has to be some extra pressure on heads and bearings if they are being spun up to say 300 revs for every takeoff although you dont hear of any problems with the Magni /ELA/ MT which all have the capability to spin rotors in excess of 200 revs.There is a few other names capible of well over 200rrpm also remember,also anyone can build a prerotator capible of going over 200

[birdy]

My personal view is that it seems silly to screw the bum out of the head and pre-rotate to high speed to take off and then fly over a few hundred metres of runway, Ditto.Recon its got sumthn to do with ego. >and the whole top of the preroator was gone,???????????????????Like you said, WTF.You recon them brain surgions at RAF woulda figured a way of keepn that lid on by now, iv had one blow off, and have heard of a few others.Is yours threaded in, or just burred "center punched" in?

[bones]

Birdy threaded in, it was just goooooonnnne

[Greg Mitchell]

Good to see you posting again FW and I too agree with most of what you posted.Testing the the 3rd Aussie Monarch the other day resulted in 280 rrpm ( heavy 23 1/2 foot Patroney Blades) with plenty more "up the sleeve" so to speak.All three Monarchs have the MLS high torque pre-rotators which bring the USA manufactured, 23 foot Dragon Wings to 325 rrpm.Having a few hundred meters of perfectly good runway under you after take off can come in handy if one has an engine out on take-off, especially if the strip is the most friendly bit of dirt in the area.I dont support screwing the bum outta of anything However,

[birdy]

Just a coupla rough figures for sum clarity.To spin a set of 27" 8H12 rotors to 500 rpm, youll need sumthn like 140 foot lb of torque.So if your only spin"n up to 250, youd only be applyn bout 35lb torque.Buggerall if you think bout it.

[Brian]

Yeah, I didnt mean to say that only the MT/ELA/Magni could spin fast, only using them as an example but you are correct Bones, there are plenty of makes now with the over 200 revs so heads/ bearings etc are getting lots of workout without, seemingly, much in the way of problems. Hopefully, within a few years, most gyros will have the capability to spin over 200 revs if needed, reliably and efficiently and not cost an arm or a leg !!You are right there Mitch, the less time spent on rough ground, the better it is for everything, at say 80 revs on rough ground, take a look at the head & the rotors and see the movement happening, they say rotate to 100 revs before taxing but if you rotor wont go that far then you just got to taxi and get them blades going ASAP [without flapping].Always good to get height before the end of the strip, particularly if the country ahead isnt friendly. Its been said that most engine failures [FW] occur at the first reduction in power so its something to keep in the back of the mind.

[bosca]

And the larger the rotors the higher the Torque??

[bones]

And the larger the rotors the higher the Torque??

[Tim]

Would the torque be higher on start up than spinning those rotors at say 250 rpm? Two different torque values to be added here Kym. The first is the trorque required to accelerate the mass of the blades, and that varies with the rate of acceleration, not with the rotor speed where that acceleration takes place.The second is the torque required to turn the blades at a specific speed, and that varies considerably with the rotor speed (ie it takes a lot more torque to maintain the blades at 200rpm than it does at 100 rpm)Ultimately the torque required to turn the blades depends on the rate of acceleration of the blades and the speed that the blades have to be accelerated to. That total combination should more correctly be referred to as horse-power rather than torque.

[asra]

All good stuff, Gents. Everything said kind of agrees with my original concept that

[birdy]

I found that the prespinners are the week link.The more you ask of it, the less life youll get outa it [ duh] .Specialy the leclec ones.The one on the wasa [ origional RAF] is still like brand new, and the machine has just passed 1100 hours, and iv had to screw the nuts off it a few times too, but usualy only to bout 150-180, then full noise with the 914.The one on the ferel has over 1000 hours onit, and cept for the pinnion snagn in mesh and shagn the shaft once, its been faultless, and very effective.

[asra]

I found that the prespinners are the week link.The more you ask of it, the less life youll get outa it [ duh] .Specialy the leclec ones.The one on the wasa [ origional RAF] is still like brand new, and the machine has just passed 1100 hours, and iv had to screw the nuts off it a few times too, but usualy only to bout 150-180, then full noise with the 914.The one on the ferel has over 1000 hours onit, and cept for the pinnion snagn in mesh and shagn the shaft once, its been faultless, and very effective. Thanks David. Sounds good enough for me. If the wear is in the rotator, and not the head, then it aint a real problem. As a matter of interest, is the head on the ferral just a standard Roscoe (or something of that caliber?)CheersFred