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Tim,I wouldn't by any measure discount what John has discovered.318,000 psi x 7 kPa / psi = 2.26 MPa, no where near riduculous, since aluminium has a shear stress of 70 Mpa these figures are not unreal.John's measurements are for impulse, the momentary power is enormous, so 99 HP is possible, no risk. He is not talking about the first 100 RPM of rotor speed, but the first 1 to 2 degrees of movement when the starter is engaged, even after it is given a pre-spin from ground crew, if there is one.Hope this helps,Nick.
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Me too thinks theres a flaw in the workings out. Working gyros get spun up many times during the day and when you have rotors that have 4/5 thousand hours up, getting spun up with starter motors then something should have shown up well before now. So far, has been one 3/4 inch hub bar and the RAF hub bars causing any problems. RAF, well, what can you say when you see how they make their hub bar and the 3/4 inch hub bar was made out of 2021t, not the better 6061t so I rest my case.
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Paddy Whack,You must learn to read post more thoroughly before you comment. As stated, an impact force can be reduced by multiplications of "X", (being the distance that the force is spread over).Would you not agree that the force would be better measured as "in situ", complete with torsionally flexable mast and moveable head and rotors?If you doubt the spreading out of the force factor, try sitting your finger on a beach ball and hitting it with a hammer, and then sit your finger on an anvil and hit it with the same hammer. When the bleeding stops, come back and tell us which hurt the most.It is obvious that the "theoretical" force is not there because it is way over the shear strength of the bolts. Even Albert Einstien Sikorsky could have worked that out.An DC electric motor does mot necessarily develop anywhere near max HP at zero or low rpms. If this were the case, manufactures would gear them to turn slower, but in fact the opposite is true - modern geared starter motors are geared so that the electric motor turns faster (approx 4.5 : 1). There are two starter motors that have been fitted to the EJ22 Subaru. The low powered one is 1.0 kw and the high powered one is 1.4 kw (1.8667hp).Tim McClure
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Tim,Image Insert:
9.71
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Nick, whenever a torque is applied to the ring gear, (rotors) an equal and opposite torque is applied to the mast. Look up next time you are pre-rotating and the amount of twist is very apparent. The starter motor is trying to run around the ring gear and the only thing that stops it is that it is fixed to the head, which in turn is fixed to the mast. This is why helicopters have a tail rotor. If the gyro was hanging from off the ground and the pre-rotator was enguaged, the whole gyro would start to spin from the torque transmitted through the mast.Tim McClure
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One small problem Tim.No pre rotator on my gyro.I appreciate what you are saying.Cheers,Nick.
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For further conviction of what Tim is saying, hit the Pre-Rotator while taxiing, with mine you could end up off the strip if you take it cheap.I have heard a thinner power lead will soften the blow ????
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Dose that mean your fly'n again Mark??,[you radio star.]
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Nick your drawing is great but your apreciation and understanding of physics leaves a lot to be desired...once again please engage brain before putting mouth into gear. If you tie the rotors to a pole and hit the prerotator i asure you the mast will twist and if your gyro was suspended it would do the rotatingEven Albert Eienstien Sikorsky could figure that one out!!!
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And even a SCG too Alby.............sorry,Albert
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You know what I like about Tim?He Builds Gyrocopters and he knows what he is talking about!
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quote:Originally posted by Mark HoranYou know what I like about Tim?He Builds Gyrocopters and he knows what he is talking about!And , unlike most , is humble about it.Birdy,No, but very close. If I had a spare 2 days I would be just about airbourne. Have had to pack it all up along with the rest of my gear to "move house".We will be almost neighbours, just across a thousand or so klm,s of desert. [8D]
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So, Albert..Are you saying Tim and Brian could be wrong?IE, if the starter pinion engages the crown wheel in flight?Cheers,Nick.
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Nick, I have engaged the prerotator in flight and like the nice man said, nothing happened !! Didnt fall out of the sky and didnt see any increase in rotor revs [unfortunately].People in cars do the same thing occasionally and in that case, the motor could be idling around 600/ 700 revs and nothing happens except a bit of noise.Tim and a number of his friends were flying gyros before some of us were born.I remember watching those madmen from Broken Hill down at the fly in at Lake Culluleraine back in the mid 80's throwing their gyros about in an awe inspiring manner and being hooked on the wopping of the blades.For a long while the BH mob could and mayby still, boast of having the best gyro pilot in Oz and there would have been at least 6 or more gyros around back in the days when a great flight was to do a circuit.
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So, you're confessing to bveing a long term addict... a 'g' junkie.
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