If i were to connect the normal output shaft of a torque converter to a crankshaft moving at about 13000rpm, would it blow the converter apart? The casing of the converter would be connected to a fan, so the fan would be moving at whatever speed the blade angle permits it, and it would absorb as much power as the engine can provide. This would eliminate the need for a gearbox surely? This is purely speculation! However there are some cheapo one on ebay atm, and it would eliminate the need for a gearbox / belt drive...
Don't you mean connect the input shaft of the torque converter to the crankshaft? At any rate, whether it'll work or not will depend a whole lot on where the torque converter came from, as some will be rated for higher RPM use than others. However, I would be willing to bet you'll have a hard time finding one with a high enough redline - the practical limit for torque converters in cars is around 7500 RPM, for instance. However, if you could find a converter rated to take anything like those speeds, then yes, it would eliminate the need for a gearbox, in the sense that the converter will allow the fan to start, stop, and slip fairly gently. However, if the fan is slipping a lot relative to the crankshaft, you stand a fair chance of burning out your torque converter. More details provided will get you a more detailed answer.
I think the main issue with the torque converter would the torque rating. I believe it could spin at 13k however the oil in it will get hot. I would say buy one thats from a small engined car such as a honda civic or so, then try it. The worse that can happen is that the torque converter cooks. I think the simple answer would be the old try it and then implement it. However dont forget that the torque converter will consume power from your engine therefore reducing output, and at certain rpm will not spin the shaft but at higher rpm will virtually lock. Think of it as a huge clutch, witch may be a safer route. Clutch and flywheel setup could work too.
I'm trying to get a horizontally mounted axial fan spinning at about 3500rpm (it's about 550mm dia), and absorbing 20-30hp. The engine has to be as lightweight as possible (it's on the front of a hovercraft), so i was looking at 2 strokes. However the 2 strokes in that hp/weight range are all low cc (125 or so) so rev at about 14000rpm. I need to convert this speed into the lower fan speed. As the power curves on these engines is so peaky, i can't run them at lower revs. One way that this is done is with a belt reduction drive to the fan; however this is REALLY expensive. I was thinking of using an aprilia rs125 (fits the spec perfectly), but with the gearbox still attached as this would provide a decent output rpm, and the output sprocket has good bearings that could take the fan load. the problem is: what happens when a gearbox is run on it's side? i would assume the oil comes out of the sump and kills the oil seal on the bearings, so the torque convertor could be used in this orientation as it has no air inside. The ratio would be constant as the fan would virtually always be kept at the same speed, and like on a boat it doesn't need to change gears - i was thinking maybe remove the selector drum from the bike gearbox and weld the dog gears in place to keep it in one gear and reduce weight perhaps?? Lots of ideas, but the more the merrier! Can anyone give more info with the gearbox on it's side - as jag said it's gonna be a try it and see if it works thing i think.
You could the gearbox on its side, but consider filling it with oil, and adding a breather system to the top? OR Could you convert the bike engine to a dry sump?
How would you convert it to a dry sump? i guess use grease? the pulleys for the belt are expensive (along with the belt). a chain drivecould be used, but i don't like the idea of the drive cog going at 13000rpm, and the chain at that speed, when i'm 30cm away from it in the same plane! Xen0: i was going to try the breather thing; I think it should be ok, but other people are concerned with the lower bearing being under hot oil, so the seals would die, and the top bearing becoming dry! I think as others are saying it's going to be a trial and error thing
I think the torque convertor idea is a none starter, trying to slip ~10000rpm across it for considerable periods isn't going to work. Instead of turning the entire engine/gearbox on its side, just turn the drive through 90degrees at the output. You could utiliise the bevel gears (and possibly parts of the housing) out of a car differential.
if you use a 2 stoke engine you cant convert to dry sump. in reply to who asked how to covert to dry sump. there is still sum oil in the sump it just collects the oil used lubcate the cranshaft and pistons usally then the oil is then pumped away from the sump to spearate holding tank(smaller than sump) then is pumped back into the engine,there is usaly some kind of oil run which directs oil to crank. i woudl expect that with a motor bike engine there would be not much gain from useing a dry sump. ps feel free to correct any mistakes ive mad e
I think BjD is onto the best idea with the bevel gears. Do you actually need 20-30bhp? I read a few hovercraft build logs and they were all 6-12bhp lift engines. http://cgi.ebay.co.uk/Briggs-and-St...ryZ50377QQssPageNameZWDVWQQrdZ1QQcmdZViewItem http://cgi.ebay.co.uk/Husqvarna-Min...ryZ50377QQssPageNameZWDVWQQrdZ1QQcmdZViewItem Daresay you could tune one of those to a degree if needed.
Yeah, a torque converter isn't suitable for this at all. Try to think of a torque converter as an automatic clutch - you don't want to be slipping it that much all the time or you'll toast it. Despite the high cost, it seems a belt drive would be ideal. However, you could also use the stock gearbox from that engine, and then just worry about turning the output 90° with a few bevel gears. You'll probably be able to leave the engine in 1st or 2nd at all times, so you wouldn't have to worry about shifting gears; just figure out what ratio you'd use on a belt drive and then leave the transmission in whatever gear is closest to the same ratio.
The hover i'm building is F1 type, and will be taking about 160hp thrust - a large volume of air is needed to fill the skirt, as the forwards motion leaks a lot of the cushion air out the back, and it's also relatively small (so higher pressure needed). Also you want a nice hard skirt at these speeds to keep it steady. You want as little weight as possible at the front - a large 4 stroke at the front would cause the nose to dip, esp when skirt pressure is reduced (e.g. to slow down), which is very bad as it could easily snag into the ground / plough in resulting in rapid user ejection. One thing i did look at was using an outboard gearbox, as the prop shaft would have suitbale bearings etc on it, but this could become really complicated connecting them up - there's not that much room for whatever will be used etc: The hole at the front is where the lift fan goes. What would happen if i ran it with grease on the bearings or something radical like that?
Wheelbearings work with grease, so I suppose that could work. What do the other F1 hovercraft builders use as lift engines?
An engine would quickly spit any grease out of any bearing at the speed a crankshaft turns, Are there any suitable lawmower engines out there. there designed to give a hozontal output(sorry for my horrific spelling) isnt there a hovercraft motor sport furum out that could help better than us lot. By the answer so far i dont think any of us realy have a clue.
two stroke engines do not rely on oil in the crank case, they can be run in any direction you want. The oil is generally mixed with the fuel and th bottom of the crank case is used to compress the AF before it gets recompresed into the top of the piston and therefore lubricating the engine. To slow down the engine you could also use a flywheel as well as experiment with the carb to attain higher torque from lower rpm. The lawnmower engine idea is ideal however, but you wont get 20bhp out of it but you will get around 7hp but the motor is torquey in those things. a piece of a rear axle could do you well with both reduction of rpm and situate the engine better and even situate it in the back with a long driveshaft.
