slartibartfast Posted February 12, 2009 Posted February 12, 2009 Just a quick flash I haven't thought through yet. How about driving the prop through magnetic induction? The engine directly drives a shaft inside the boom, and a free spinning prop hub is on bearings outside the boom. Electro-magnetic inside, permanent magnets outside. That would overcome many problems - prop strike would not affect the engine, no heat in the transfer, no harmonic vibration, the boom can stay one-piece, etc. There'd be some issues around getting it moving and synched. Smart electronics should solve them though. The technology probably exists - maglev trains for example. A lot of work to certify though - never heard of one before. If it works, I want the royalties. I agree that stones will be a problem though. How about a stone guard?
Tomo Posted February 12, 2009 Posted February 12, 2009 Now that is a brilliant idea... Some slashers and pump drives are done like that, no friction, if it jams it won't do any shock damage... Great Idea don't you reckon folks??
Deskpilot Posted February 13, 2009 Author Posted February 13, 2009 That's a brilliant, outside the square, idea, Slarti, but gee, it ain't half gunna be heavy. Think of all those copper windings. If it works, you get the royalties ok, but I get to sell the plans ;) ;)
Tomo Posted February 13, 2009 Posted February 13, 2009 No copper windings... using rare earth magnets... I can't seem to find any info on it yet, but I'll keep looking...
Deskpilot Posted February 13, 2009 Author Posted February 13, 2009 Ozzie, re ground clearance....use longer legs. Certainly longer than the Vampire. An alternative would be for a multi-short-bladed prop. Spats with soft extensions to the lower edges might stop stones flying. The grasshopper's OK, but all that drag on the engines ruins it's performance. I think the wing would have to be beefed up a bit to handle twice the speed. I haven't started to model the prop assembly yet so can we hang on that for a bit. I started doing a rough-up of the wing yesterday but got stymeed with the aileron mount tube and transition to the trailing edge. How to do it? Any ideas? Another wing problem. I've suggested tube into tube connection of wings to fuselage. If we have three tubes entering the fuse' in a straight line, ie, along the fuselage side, does that create a potential fold line? Remember, no outside support struts/wire. If so, then might stub wings, with say, a 'V' shape(viewed from top) be stronger? My reasoning is that if the main spar started to buckle, the forward and rear spars would still maintain some integrity/rigidity of the assembly. See sketch below. Your views people?
Deskpilot Posted February 13, 2009 Author Posted February 13, 2009 Tomo.......Er, wasn't this to be a CHEAP plane ;) Nice try but.
Guest ozzie Posted February 13, 2009 Posted February 13, 2009 have a look at how gliders attach their wings you will need a full spar carry tru for a cantilevr wing/ problem is it may tend to be heavier than the strut type wing spar. as per grasshopper type design you can drop the engine down behind the pilot and place the prop higher. or just fair the engine in. have to agree with doug the cost is blowing out. cantilever wing and the prop design will cost heaps. gotta stick to the KISS principle. i've seen this many times before it is to easy to get carried away. once you have a simple design out there and flying then you can look at taking that design to the next stage. many designs from the states that verge from the normally accepted principles have never gotton past initial prototypes. MJR mentioned this when he talked of the Arizona airraces. keep going tho it is good to see this happening and gives me a chance to reserect some old skills. ozzie
Tomo Posted February 13, 2009 Posted February 13, 2009 Tomo.......Er, wasn't this to be a CHEAP plane ;) Nice try but. Well..ah..yeah... spose it would cost a wittle bit much...:big_grin:
pylon500 Posted February 15, 2009 Posted February 15, 2009 OK Doug, just to reinforce what Ozzie said about cantilever tube spars, the 'Insert' spar to hold the tube spars on the BD-5 is HEAVY in section just to hang onto a 8 foot wing on each side. I'm talking a tube of nearly 10mm wall thickness, although it does go on the inside of the wing tubes. The system you've shown will work, but you will need at least two sets of sleeves inside the root of the wing tube to handle the bending loads. As for the prop location, it's a hell of a lot of work for no real benefit, but if you think about it laterally; You have a cockpit, a wing, and engine and as prop. Do you really need a tail? I had thoughts of how to use standard Vampire bits to build a swept flying wing, and it would have worked! (Cant remember how to drive Sketchup quick enough to add a quick drawing) Back to your wing design, I still think the front tube is basically redundant if you wrap a sheet around the leading edge. Remember, if the spar tube can handle the lift loads, it will easily handle the drag loads, although a drag spar would add a lot of stiffness to the wing. As for twisting loads, this is more a function of how the ribs are attached to the spar tube. As you will need a false rear spar to hang the ailerons on, this will serve to control twist. Arthur.
Guest drizzt1978 Posted February 16, 2009 Posted February 16, 2009 Would be interested in speaking to an engineer, about that propeller rotating around that fuselage section, just inherently seems incorrect? Would it create turbulence of some sort??? Not trying to shot anything down..... Just asking?
Deskpilot Posted February 16, 2009 Author Posted February 16, 2009 Would be interested in speaking to an engineer, about that propeller rotating around that fuselage section, just inherently seems incorrect? Would it create turbulence of some sort???Not trying to shot anything down..... Just asking? Every one is asking 'why?', I ask, why not? Are you a sheep or a sheppard? I like to be different without being too controversial. I go my own way, and yes, sometimes that gets me into trouble. I follow 'most' rules, those I don't, I tend to bend. We all readily accept pusher aircraft so that should answer your question re turbulence. I believe it will give more control as there is always clean air going over the tail control surfaces, well at least, whilst the engine is running. Using the crucifix or H style emmpenage, also vitualy negates slip stream yaw as previously mentioned. Arthur, thanks for your input again. Let me deal with the swept flying wing first. I agree, less to build, but how many newbies would feel safe in one? People tend to have set ideas as to what makes a plane, see above. I want a conventional plane, with a twist, and I'm sure others have a like mind. Obviously, I have more research to do re the wing design. As for the front tube and ply covering, my initial thoughts were for foam sandwich ribs. A 'soft' structure. The ply leading edge was only meant to be very thin support for the covering and not the conventional 'D' box. Therefore the tube was designed in to add stiffness. As I've mentioned before, I personally see scalloped wings as less than desirable, and generally slow. BTW, what's your take on my 'stub' wings? Would it be stronger? I've spent the last few days modeling the prop hub and will be posting some pictures tomorrow. I need other, more expert opinion on this 'controversial' part of the design before I spend too much time and energy on it. Keep the questions, suggestions and helpful comments coming guys. Fly safe.
Guest ozzie Posted February 16, 2009 Posted February 16, 2009 The contra rotating prop drive that i was thinking about was the Twin Maximizer. it was used in several different aircraft. BUT it was for a twin engine setup driving thru a common thrust line with two counter rotating props. John Moody did use it on the easy riser. it was also used by CGS and several others in various versions. ozzie
Guest drizzt1978 Posted February 16, 2009 Posted February 16, 2009 Ok, The wheel is round for a reason, thats why people don't reinvent it...Im not saying NO it wont work or dont do it, and yes I am familiar with a pusher type plane, BUT Have not scene a a propeler that spins around the fuselage...probably wouldnt make a difference?? WAS just interested is all!! I might have to get ny mate (Enginer student to but in to this thread and tell my to shut up ;-) Ps You have got my support tho!!!
Deskpilot Posted February 17, 2009 Author Posted February 17, 2009 Ps You have got my support tho!!! Cheers '78
Deskpilot Posted February 17, 2009 Author Posted February 17, 2009 Prop-hub assembly OK, here we go. The most difficult, technical and controversial part of this design. I'm not an engineer so don't shooting me down without thinking about an improvement first. I've based this all on a 6 inch boom tube of whatever wall thickness is most advised. We start with the Hub inner. Hub-inner-sleeve.jpg Made from suitable, thick walled tube. The grooves are too close together in this model and I doubled the between groove measurement later. As there is no movement of this part, would alloy so? Internally machined to be an 'interference fit' with the boom tube. To fit part together, slowly heat the sleeve in an oven to as hot as possible, then sweat same to tube over a coating of epoxy. Once on, never to come off, well, that's the intention any way. Mustn't crush the boom either. Boomtube-sleeve.jpg Next fit the bearings. These are commercially available, fully sealed, high temperature with Solid Lubrication. That means that the 'grease' is a solid substance that melts very slightly with heat and returns to solid when re-cooled. Currently I have them at 40mm wide(ignore the center line on individual bearing, modeling error). Should these be Ball or Roller bearings? Boomtube-sleeve+bearings.jpg The outer sleeve, is ideally made from a solid piece of material rather than trying to match, mate and align separate parts. This is easier to achieve with the chain drive than the the belt, both of which are shown (just for fun). An internal stop is required to position it over the bearing, plus a cir-clip to stop it being pulled off. In use, thrust from the prop is trying to push it on, not pulling it off. I don't have the necessary info to be able to model the blade recesses as yet. Just for Example, I have use the Brolly type fitment. Hub-outer sleeve.jpg Hub-mounted.jpg An end cap is still to be modeled and bolt holes etc added. Shoulder bolts into blind holes and wire locking completes the assy, except for a couple of 'thrust bearings' which will be mounted on the main frame and run against the open end face so that the thrush load is taken else where apart from the internal bearings alone. Over to you gentlemen, will it, or will it not work? Re as to why again, I'm trying to find a photo of a Navy (I think) design from back in the 20/30's. The only type ever top have flown as far as I know.
Deskpilot Posted February 17, 2009 Author Posted February 17, 2009 Damn, how does one insert pictures into text.
Tomo Posted February 17, 2009 Posted February 17, 2009 Looks good... I reckon that should surely workout... Will you need a thrust bearing of some sort??
Deskpilot Posted February 17, 2009 Author Posted February 17, 2009 Tomo, read the text, don't just look at the pictures. (not having a dig, really)
Deskpilot Posted February 17, 2009 Author Posted February 17, 2009 Here's a temporary set-up, just for anyone who dosen't understand what I mean.
Tomo Posted February 17, 2009 Posted February 17, 2009 Whoops! sorry about that Doug, should've fully read the text through... Concerning the thrust bearings, would it be better to actually use one thrust bearing around the tube, fitted like the main bearings... that way its a lot less fiddly, maybe? Just a thought...
Guest ozzie Posted February 17, 2009 Posted February 17, 2009 just been in contact with a friend in th states who has an extremely large collection of information on hombuilts and ultralight tells me that there were at least 3 ultralights that had props rotating around the boom. he is now going thru his archives to find some photos. be interesting to see if he comes up with something. Vintage UltraLight Association this is his website ozzie
Deskpilot Posted February 17, 2009 Author Posted February 17, 2009 Some of my inspiration Bjorklund, Filip
Deskpilot Posted February 17, 2009 Author Posted February 17, 2009 Concerning the thrust bearings, would it be better to actually use one thrust bearing around the tube, fitted like the main bearings... that way its a lot less fiddly, maybe? Just a thought... Tomo, do you have the facilities to post a sketch of what you mean? Just hand drawn over one of my images will do.
Tomo Posted February 18, 2009 Posted February 18, 2009 Ok, I've printed out your picture, and then drawn in what I thought (very roughly mind you!) then scanned it, and hopefully it's attached it self... I Just thought of this idea because, it might be easier to do this than try and put some sort of shaft out the side of the tail beam for the other small bearings to attach to. It would probably nearly all weigh the same when you consider the bits required to do both designs... I hope you can understand my scribble.
Deskpilot Posted February 18, 2009 Author Posted February 18, 2009 I hope you can understand my scribble. Would have been easier if you'd rotated the picture I guessed this is what you meant but I see several downsides. 1, thrust is still side on to the bearing, not good in my opinion. 2. You'd have to remove the trust bearing to be able to remove the hub outer housing should it become necessary. 3. My 2 bearings would be mounted on another part of the airframe in order not to weaken the boom tube. A cir-clip groove in that is a definite no-no. Anyone else got any comments? Silence is almost a vote in the affirmative. Been re-reading Bill Whitney's note on a/c design this morning. I think I'll have to view the CD again as well. First time through, about 2 years ago, it all seemed so easy and straight forward. Now I'm not so sure.
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