Mark L wrote > I talked to Steve Makish again last night, and he said he'd had one stocker> break and a Scat 4340 break.>
Exactly why or how did they break? Was it failure of the taper due to gyroscopic forces? > I think if you'll ask around, you'll find more. If you want to talk strong> crank, check out the Corvair. > stock case, crank, and rods. I know y'all never imported Corvairs to SA, so > I understand why you wouldn't consider that option. Quite the contrary mark, we apparently did either import them or build them here (we did have a Chevrolet factory here in those days), the problem is, as far as I am aware, that only the early ones were sold here and not that many either. I know someone who found one at a local breakers yard.Believe me if I could find a "desirable" model corvair motor lying somewhere here I would'nt hesitate to defect purely for the extra power and smoothness reported. but I don't see the problem with > the stocker, assuming you use the "double thrust" bearings that almost > everybody uses (use the thrust half from two sets of bearings, so it works > from either direction. Now here is the reason why I belong to this group, I have never heard of the "double thrust system". Sounds very promising. Now you have really thrown a spanner in my works, I must learn more about this motor! > But the largest forces are gyroscopic (which are trying to bend the crank > repeatedly in opposite directions, leading to fatigue), not torsional. > You'll be testing for something that will probably not be the primary mode > of failure. Mark, respectfully I think you have missed what I plan on doing. I have designed a support structure that will house a double ball race, self aligning, sealed bearing situated just behind the prop hub that will handle just about all of the gyroscopic loads. All the crank will see is the torque loads and a very small amount of side load due to the relation between the length of the "drive shaft" ahead of the bearing compared to the length behind it.This side load probably wouldnt come near what a over tensioned belt would impose on the crank in a car.Here I am taking an educated guess so I welcome any information that will show me that my reconing is flawed. > You think a one in twenty risk of eventually having a forced landing is > acceptable? Absolutely not!What I am saying is that those one in twenty failures were probably due to fatigue caused by gyroscopic loads on that little taper at the end of the crank. If with my system I can eliminate the gyroscopic loads on the small taper of the crank I have no reason to believe that my system won't be as successful as the force 1 hub(provided the standard taper can handle the torque) I can't help but wonder why you wouldn't start with something proven, > like the GPASC Force One setup (although price would be a good guess). You are right on the money here, I am working on a shoestring budget and only have limited resources when it comes to machining. What I do have at my disposal at practically zero cost is a good friend who is one of the best tig welders I know of who just happens to be rated for aircraft welding. He also has a fairly good lathe and mill so most of my engineering work revolves around what we can do in-house at his shop. I searched the web for some shaft design stuff, and got bogged down > in everything but what I was looking for. Then it occured to me...the > reason I ditched the Type4 VW and went with the Corvair was because I didn't > want to have to design a drive shaft. Unfortunately I am stuck with the VW for now so I will just have to do the best I can with what I have at my disposal. > He echoed my sentiment to "go with the proven" GPASC Force One > system. I have no quarrel with this, remember , this hub is still on the pulley end and as long as it is kept as short as possible (I don't know how long a force 1 hub is) you shouldnt have any problems??? The reason I started all this redesign work was to have a substantially longer hub in order to achieve a really streamlined cowling. My friend's KR2 was a beautiful plane but I always thought it could do with a sharper more streamlined nose. It used a home made copy of the force 1 hub. I know of one aircraft engine company that paid an > engineering company to design a shaft drive system for them, and the first > example stuck on a customer's Type 4 self destructed in minutes! As I am NOT an engineer of any kind, my training is electrical and instrumentation, I won't even try to argue with you or anyone else more knowledgeable than I when it comes to things like tortional vibration, fatigue life, etc. The best I can do is compare my designs to things that have already been tried and use what was successful in the past, (or a combination of successful designs). To this end I will test a design using a significantly longer shaft than the force 1 hub attached to the crank using the existing taper ( subject to the taper performing well in the torque test ). To eliminate the mode of failure prone to the other hubs attached in this way in the past, I will be building the bearing housing support as mentioned above. I hope you'll decide to do something that's been proven already. > I know that sounds funny coming from me, but you've got to draw the line > somewhere. You are welcome to prove me wrong and crow about it, but I'm not > going to encourage it... Mark I am not aiming at proving you or anybody else wrong and I certainly won't crow about it if by chance I do succeed, but it should be noted that I am literally miles away from having anything to attach this motor to in order to go flying behind it. My 2S is a long way from flying and I certainly won't stick a motor on the front of it that I was'nt reasonably sure will pull me around the skies as safely as I can make it possible. As William says "flying is risky", all we can do is keep that risk down to a minimum by not being irrisponsible by thinking we know it all no matter who we are or how many qualifications we have.( Please don't take that as a stab at you because it honestly isn't) I am a very humble person and don't feel threatened by someone who can teach me something. I value yours and everyone elses input regarding my idea and read each and every response to it.Since I started this thread, before I sit down in front of the PC I put on a second hand nomex flight suit and install a welding screen between myself and the monitor! I might try some sunblock as an added UV protection soon. I thank you for your help and patients up to now. I will post the results of my torque test as soon as it is done. Cheers guys dene.coll...@telkomsa.net
