Hub Bars and Starter Motors

[Brian]

Never thought about being a gyro junkie BUT but I guess its pretty true.They have been a big part of my life since learning to fly back in 93 [gyros][]

[asra]

You've got to be kind, this computer has just been discharged from hospital.Brian, there is no "working out", I simply reported what we found, I also suggested someone else repeat the test to see if they could confirm or deny our findings, which astonished us as much as anyone else! Obviously the cushioning effect of twist in the mast and cheekplates softens the blow as Tim has pointed out in his beachball analogy. Obviously something or things are acting to let the working gyros miss out on the problem recently encountered, but are there problems ahead, waiting to be encountered? Don't forget that Cierva badly miscalculated the effects of rotor accellarations leading to an in flight rotor failure.Looking at RAF rotors is pointless in this context, as their preroator is clutched in and so does not have the impact we found.mrford61, I know thinner leads are reputed to soften the jolt, but I remain sceptical on the grounds that while they are cold they are going to carry the maximum current with minimum voltage drop, but as they warm up resitance will rise and so lessen the current and voltage available at the starter. It's really the opposite of what you want. I am even wondering if my old "harp" resistor would have given a better soft start if it was shorted initially to heat it up, even though subjectively it was very soft.John

[asra]

John, I believe that you will find that the average starter motor produces between 8 and 12 ft lbs of torque, that would equate to their hp rating of about 2 hp and +- 3000rpm. If you think in lb inches, you may be a little closer to your mark. Truck starters are about 11 hp.The shear applied to the bolts at a 1" radius, ie 2" dia would be 5 times that of the rivets on the rim of a 10" ring gear.cheersJonem

[asra]

jonem, obviously you are right, but if you read the original post you will find that's not what this is all about[)]John

[asra]

DeletedLlewella

[asra]

Interesting to read your arguments John.Impulse = mv(initial)- mv (final) Nm/sMass is in Neutons, Velosity in Rad/Seconds.So the problem with your test jig is that it only measures Torque not Impulse, as v initial and v final are the same. Also every action has an equal and opposite reaction maybe you should try this.Put a rotor head in the vice, mounted to 2m of 2 x 2.5 mast.Apply starter and measure the angle of twist at the rotor end and the Torque at the other.If you video it as well you could work out time and consequently velosity for the above equation. (important to note that the time would be taken from half way through the cycle when velosity is at its maximum)This would be reasonably accurate although I do realise that the moment of inertia of the mast and starter is not factored in. All this done I think it will be clear why hub block bolts do not sheer.ChrisCJL

[asra]

[asra]

Cool JohnWhat you did was good.What I can say after thinking about it for a while is that their are are relationships to concider as to the weight of the starter motor and the effect on the mass moment of inertia the weight of the starter motor has. (and the PCD of the bolts or dowls on the block for that matter)This is because an impact that takes place over 1/1000 of a second is 100x greater than one that takes over 1/10 of a second.Now lets talk reality, if people are going to measure their gyro for CLT then a deisel Land Cruiser starter improves the CLT when opposed to the Honda Civic starter.If you would like I can do some calculations as to the mass and pitch centre of the starter as related to the pitch centre of the hub bolts. (February)Anyway John have a good Christmas Denman is great for me form Sydney as it takes little time longer to get their and has a great setup.Hope to see you their. ChrisJudge yourself by who you include not by who you exclude, treat others as if you were them.

[asra]

[Tim]

John, I agree with you totally about the severity of the initial impact of a powerful starter motor, and that is why we always encourage pilots to give the rotors a reasonable hand spin before the starter is engaged. That seems to reduce the shock load many fold. I have also seen on many occasions pilots with a cable prerotator stall the engine with an abrupt pull in. Geoff Wilkinson in Vic did some tests with a cable type and after several tests he found that the head forks on the Higgins head had been distorted and were slightly twisted. Re CLT. I have an old PRA magazine approx 1990 that stated that within 2 years all Gyros in the world will be as the "big bird" design with tall tails. It seemed that did not come to pass. We have here different opinions of what "stability" entails. My personal opinion is that a Gyro should be able to be throttled fully up or down and there should be no sudden pitch changes. The further up you go with the C of G the more sudden the pitch changes are, even up to the extent that a dominator with a sudden engine failure could be lethal for a beginner, or even for an experienced pilot operating at "Birdys" height. There is a flaw somewhere in popular thinking that CLT creates no pitching forces. It still seems to happen regardless of the A of A of the stabilizer. I realise that this is only one aspect of "stability" but opening up the full book all in one hit will only create more confusion.Tim McClure

[birdy]

Hmmmm................ 5 hours and no bite from Paul,is he dead??Ignorance is bliss............but only till you realise you were.

[asra]

Hmmm.....Why would you say that Birdy?Aussie Paul. []www.firebirdgyros.com

[NiqueNaque]

Birdy,12:27 - 10:00 = 2:27...what are you infering?Cheers,Nick.

[asra]

[NiqueNaque]

John,I've heard the term 'aging fleet' used by yourself and Paul B.Out of curiosity, what is the average age of the fleet?And, what do you call a 'young' or 'old' gyro?Cheers,Nick.