|
Here's a question I haven't seen addressed at all: Why not use motorcycle engine units for light aircraft? You can very easily find a whole motor kit that's the same size and weight, and has all the accessories strapped in. The shipping weight of a hayabusa motor with EVERYTHING bolted on (including battery) in a crate is 175lb. Add a few pounds for oil. They're also designed to run near redline for a long time. The "needs reduction gearing" is moot because the transmissions are built in. You could easily run a chain drive to a thrust bearing and not worry about modifying the engine cases at all. It may also be beneficial for cruising to leave the transmission in and just upshift to put yourself in a more efficient engine range, then downshift back into the powerband for TO/GA. Is this crazy talk?
|
#
¿
Jul 29, 2012 21:00
|
|
|
|
| # ¿ Apr 29, 2024 18:41 |
|
|
Nerobro posted:It's only "sorta" crazy talk. There's a lot to consider though. Thanks for the input, and let's consider. I just found a hayabusa crate motor ship weight very quickly, I wasn't intending to use one. I was thinking an older oil-cooled with external cooler and CV carbs. I've got this bandit 1200 right here.... Tuning/detuning the motor so it has useful power at less than redline is ideal. I know I can jank around with cams and heads and get a stupid-peaky torque spike right around 6k on a 10k redline, producing roughly 113HP. That sound perfect for a light plane. Super peaky, centered someplace where you're not flogging the motor all the time. As far as changing gears, it wasn't like having to bang up through gears to get on the interstate, more like you trim the gearbox to only have two (very wide and beefy) gears; one for takeoff, one for cruise. But if your motor's peaky anyway, there's not much point. Then, you can just get a single-speed gearbox (layshaft, mainshaft, and countershaft permanently engaged, with arbitrarily large gears). Or, like you say, get a two-unit design and lose the gearbox entirely. Prop speeds are only about 2k-3k rpm, right? A 2:1 sprocket/chain size is enough of a "reduction gearbox." You could even go with one of those grotesque Harley 3" primary belts to get some of the damping you need. This is another reason why having a motorcycle engine seems ideal: they're already designed with an output sprocket/belt in mind, and their bottom ends are designed around bumps and thuds given by chains already. So, to recap: Start with some 140hp oil/air-cooled motorcycle engine. CV carbs, with "enrichener" choke system. ECU(if any) that only does ignition advance based on throttle position. Tune it with heads and cams to have a narrow powerband around 100hp in the middle of its rev range. Get this rev speed to be in the 1:1 - 3:1 range with the prop you want, and mount a nice cushiony thrust bearing to the firewall, then drive that with chain/belt/whatnot from your engine. Since you're in the middle of rev range and below peak HP, leave the gearbox (if any) as it is; it'll probably be fine. Leave it in 4th or whatever, and don't connect the shifter to anything. Leave the clutch, maybe with some kind of emergency handle so you can let your prop windmill when your engine detonates. Also, since you're in the middle of the rev range, you should never have to worry about overspeeding your engine, right?
|
|
#
¿
Aug 3, 2012 04:14
|
|
|
I'm going to be falling into a big pile of money soon, and figured I might as well build an airplane now that I've got ASEL. Old issues of EAA have planes in them, and I've got a parts list going for a fully skinned fuselage and wings for about $1500 for a two-seat low-wing aircraft. Engine and avionics are obviously a big extra cost on top of that. I guess I'm asking for a sanity check. Is building this thing really just as easy as meticulously following the prints to the limits of precision and not accepting any shortcuts? The alternative is renting, and that makes phone sex addiction seem cheap in comparison.
|
|
#
¿
May 28, 2013 23:56
|
|
|
ehnus posted:Yup, 4130 fuselage and aluminum wings. The control surfaces and fuselage are all fabric covered. Kids get used to noise if they're exposed to it. They get tired and have to sleep; it's a biological imperative.
|
|
#
¿
May 30, 2015 05:40
|
|