A.K. Rotor's thread.

[birdy]

Oi,Jeff mateI put a measur'n stick on um today and they is 26'.You reckon it maybe slightly over rotored????

[asra]

Hi Birdy, sorry I didn't reply to your post earlier. My records show that I supplied a 25 feet and 28 feet set to you, can you please E-mail or phone me and give me the serial numbers of the Rotors so I can confirm or correct the records and which one of these sets did you purchase from someone else.Jeff H-S

[birdy]

Rito Jeff.

[birdy]

Hmmmmm.......... Jeff,did I send you those numbers??Also,not sure if you'v been follow'n the topic"teeter'n props",but theres some info I'm after for the same yarn on the yank forum.I'll post wot he asked,[the pitch limits for your blades.]In a 90-deg. bank (whatever the stick position) at 400 RRPM, you'd be flirting with precession stall if you could do a 180 in a single second. For each half-turn of the rotor, the body of the gyro would have turned 13.5 degrees. As the body turns, it takes the spindle with it. The spindle cranks 13.5 degrees of cyclic up-pitch into the advancing blade. That's enough to stall most airfoils if applied all at once, even if the foil starts out with a zero angle of attack (which it likely won't). The cyclic pitch change isn't really applied instantaneously; rather, it comes on smoothly during the blade's sweep from the fore-aft position to the "abeam" position. The blade has some chance to get out of the way and so dilute the pitch change, but that input rate is still scary. There's some evidence that a very fast, flat yawing turn (so-called "pedal turn") in a gyro can cause a cyclic or precession stall if the stick is held back as you suggest. It would be great if rotors could be rated by the maximum cyclic pitch change rate that they can tolerate without cyclic stall. Testing for these limits could be pretty spectacular. A rotor head mounted on top of an armored vehicle might be the appropriate test rig!Thanx Jeff.

[asra]

Yeah Birdy, I have been following your thread occasionally and I do have some reservations about the teetering Prop. Which would require quite a bit of explanation, sorry I don't seem to have the time to write my thoughts on the subject except that, Gyroscopic forces, teetering stops in sharp turns and manoevres, could be detrimental or possibly catastrofic.To your other question on precession stall on Rotors. Again I can't see it happening in a 90deg. bank and 180 deg. turn. Some years ago when I first started testing and experimenting with the extruded Rotors, it so happened I was also experimenting with a tall tail. The very first flight with the new tail (I realised after the event I should have had an anti servo on the tail) just after take off at around 100 feet I made a left turn as normal just using the cyclic, three quarters of the way through the turn as I had just passed over the house we were staying in at Denman, I decided to tighten the turn by using a bit of left rudder also to test it, to my surprise I did not realise the rudder would be so responsive, as I released the pressure on the left pedal the Rudder seemed to steer even more to the left, before I had time to instinctively push the right Rudder pedal. The Gyro at this time was still climbing gradually at a speed of around 45 knots.Immediately the Gyro rotated through 360 degrees and still going forward in what seemed like a split second, but at a guess and talking to witnesses directly below in reality it was around two seconds.No I have never tried it again nor do I want to. In my debriefing my thoughts and memory of this scare/fright I realised there were no ill effects or wierd pitching/oscillations, in fact I must have momentarily froze, I don't recall any bumps or stick effect or shake I don't think I even attempted to move the stick, just held on to it, all I did was jam the Right rudder pedal to straighten up and kept flying although it was just for one circuit, had to come in for a change of undies! Not really but for a calming cup of tea and inspection to the cause.It's late, [|)]Jeff H-S

[birdy]

Someone asked wot the noise woz that came from AK blades as they slowly spun down,or just teetered in a gusting breeze,I think It woz Brian.I'v been fiddl'n with me birds the last couple o days and one of the things I did was change the teeter towers to the later 'mushroom' type and switched to an identical set of spare 26' AK's,and now I'v got the same noise cum'n from me blades.For 500 hours the other set never made a noise.After a bit of ilimination I found it was the teeter bushes 'gripping',and the resultant vibration was eccoing down the blades.[theres no resistance in the teeter action,they are still free]Question,[to Tim Mc.,] are these bushes ment to be lubed???I'v heard of materials that don't require lube,and noticed the surfaces of these mushroom bushes had an odd look'n material onum.Also the fiber thrust washes,are they ment to be dry??Ignorance is bliss............but only till you realise you were.

[Tim]

G'day Birdy. The bushes are a "DU" self lubricating bush and need no further lubrication. In fact in the outback, adding grease shortens the life of the bushes to a very few hours. Once the teflon has worn off the bushes they have to be greased if they cannot be immediatly replaced. Once greased, they have to be cleaned and greased daily for the bushes to last, which is a pain in the freckle. The self lubricating bushes work best with smooth stainless steel mushrooms. The surface of the bushes is hydroscopic and the ingress of water makes them swell up and get tighter, also shortening their life.Currently we are having good success with sealed bearings instead of bushes, with the initial set with well over 1000 hours now and still "smooth". An added advantage appears to be slightly lighter joystick while doing "roll reversals", and weather proof.The fibre washers normally run dry and are fine if the rotors are smooth. If greased, they will attract dust and wear into the head forks. It is actually better to run a thin nylon washer (also dry), especially if you have a "rough" set of rotors, but the nylon washers are harder to come by and usually have to be made as a one off.Tim McClure

[birdy]

Thanx TimWhen Barb woz ere I niticed she put grease on the mushrooms,so I thought they were ment to be lubed.Is it too late for my bushes?? They'v only don a couple o hours.Mite go n clean em up.Ignorance is bliss............but only till you realise you were.

[mrford61]

G,day Birdy,If you dont mind my asking, how many hours did you put on the 25 footers?Thanks Mark.

[birdy]

25'ers???Only 25'ers I'v flowen were Rix rotors,[fabricated ones].My AK's are 26' ,and bout 8oo hours onum.Bout 200 hours on the 28'ers on the RAF.BTW,I still have the 25' R.,rotors if anyone wonts them.Ignorance is bliss............but only till you realise you were.

[mrford61]

I seen in post #2 in this thread that Jeff says his records were that he sold you some 25,s. Apparently the rotors I have now were once yours. The bloke I got them off also said they were 26ft but definitely are 25 and are definitely AK,s.No worries to me because they fly excellent [][]. I,m just interested in tracking their history is all.Mark.

[birdy]

Not mine Mark.I'd never sell a set of flyable AK's.So your fly'n again,wots news,you said you'd let me know how you got on.[I'll give you a bingle tonight,gota bolt now.]Ignorance is bliss............but only till you realise you were.

[birdy]

Just remembered that you'v moved Mark,you'll have to ring me,coz I don't know your new number.Not tonight tho,coz I'v left for camp already.Should be home tomorro night tho.Ignorance is bliss............but only till you realise you were.