The Bucket Foundry

[Flettner]

just a foot note on vibration, my twin originally had no balance shaft, with the spindlyness of aircraft construction, I would be too frightened to do a circuit with it. BUT after the shaft was fitted, night and day, happy and smooth now. I would love to build these commertialy but I'm too small, as it were.

[WilDun]

I've been holding out, but ok I reply, yes I've seen all these engines for microlight / autogyro flight. Often getting requested to build gearboxes for these fourstroke twins. Not interested as there is too much trouble with heavy tortional cyclic loads, ..............Usually centrifugal clutches or peak load slipping clutches or fluid couplings, all very complicated. ( read expensive)
I put a lot of research into drives for aviation applications ( because thats my business),...........

As I said before, I sat in a light aircraft with a 4 cylinder Rotax boxer 4 stroke engine and probably without a prop this engine would be relatively smooth, but at a certain number of revs (a bit above idle), the torsional vibration (seemingly caused by prop flex) was probably knocking the shit out of the airframe but the guy piloting it didn't seem to notice!
I don't know a lot about these setups of course, (as you'd expect from me), but I am interested and want to know! - I don't think they are direct drive and I was wondering just what sort of damper they employ (if any) and how do they get away with allowing things to shake that much??.
So maybe in light fixed wing aircraft, it's the flexing (whipping) of the prop which has to be dealt with?
I dunno if this would apply to the autogyro but then I guess it's prop wouldn't be very different??

On the other hand two strokes are torsional easy, light, smooth and now with TPI relatively fuel efficent. Add to that an internal reduction, balance shaft, electric start and an output set up for a pre rotator (gyro), the future of gyro / microlight propulsion. The Autoflight engine, dunmmy.

That's the spirit! - you have convinced this dummy - now you need to convince all the other dummies! - especially those who actually don't like two strokes (but have no idea why!)
BTW I think fuel injection which you intend to use is one answer for the survival of the two stroke - I don't think that either that V-Due or the Wankel mentioned earlier would have made it with the setups they were using.

If I had money, an aeroplane and a pilot's licence, I'd buy the first Autoflight engine, to set the ball rolling!!

[Grumph]

From memory - mid 1990's - when I was shown the local Pegasus Aviation half a VW aero engine, the prop was driven off the end of the camshaft.
The cam drive rather than the normal VW gears was a wide toothed belt. They reckoned the belt had enough "give" to absorb the torsional effects

Do commercially available props come dynamically balanced ?

[Flettner]

Two to one is generaly not a good idea.
Always should be hunting tooth, not exact divisions ie two to one, three to one. Indivisible tooth reduction puts the prop in relation to engine in a different spot each cycle, important to dampen any accumulation of resonance.

[Grumph]

Two to one is generaly not a good idea.
Always should be hunting tooth, not exact divisions ie two to one, three to one. Indivisible tooth reduction puts the prop in relation to engine in a different spot each cycle, important to dampen any accumulation of resonance.

Ha, yes you're correct of course - but have you ever tried to time up a Velocette single ? They loved the hunting tooth principle - to the point where the timing marks line up - if I remember right - every 40 turns.....

[guyhockley]

Two to one is generaly not a good idea.
Always should be hunting tooth, not exact divisions ie two to one, three to one. Indivisible tooth reduction puts the prop in relation to engine in a different spot each cycle, important to dampen any accumulation of resonance.

Two to one...like a cam drive for instance...

[QUOTE=Grumph]Ha, yes you're correct of course - but have you ever tried to time up a Velocette single ? They loved the hunting tooth principle - to the point where the timing marks line up - if I remember right - every 40 turns.....[/[QUOTE]

Not unique to Velos, of course. At least Triumphs had the idler pinion.
Not cams but I remember reading a story about a Frankenstein/bitsa engine that the builders were having terrible trouble with the ignition timing. Turned out, where they'd used bits from different sources, the magneto sprockets didn't match up and the timing was changing one tooth per revolution.

[guyhockley]

Vague memory that Lotus or Cosworth played with an aviation engine with cam/prop drive.

[guyhockley]

Maybe the Oldtimers disease hasn't got me yet! The engine details are further down the page.

http://stargazer2006.online.fr/aircr...microlight.htm

[Grumph]

Two to one...like a cam drive for instance...
Not cams but I remember reading a story about a Frankenstein/bitsa engine that the builders were having terrible trouble with the ignition timing. Turned out, where they'd used bits from different sources, the magneto sprockets didn't match up and the timing was changing one tooth per revolution.[/COLOR]

I was involved on the fringes of a guy's embarassment locally of the same kind.
Speedway TQ engine - Kawa Z1000J - he'd sent the crank to the US to get the good rods fitted at some expense, and the camchain sprocket on the crank recut to take roller camchain. Not uncommon - the J uses morse camchain and recutting it for roller chain gives you a better drive setup.
Anyway he couldn't get the cams to time up at all. Pulling it down and counting teeth revealed that the crank sprocket now had an unusual tooth count needing special cam sprockets to match....Nothing's easy.

[guyhockley]

Did they cut the sprocket to the same number of teeth as the Hy-Vo gear/sprocket? You can't just change the centre shaft for the old model one, then?
Speedway TQ, that's an oval track car, direct drive, no gearbox, or am I confusing yours with an american formula?

On the balance shaft thing, the club I raced with in the 80s had a Production 250 two stroke/400 four stroke class and there were a pair of very competitive Superdreams that had been relieved of all their balance paraphernalia (allegedly)
Recently I read a story about a custom KZ400 twin that the builder's mate took a great fancy to so they built a replica. When they checked the engine they'd bought - no balance shaft. They went ahead and tried it anyway and claimed you couldn't tell the difference! Custom built frames, though, so, who knows.

[Grumph]

Did they cut the sprocket to the same number of teeth as the Hy-Vo gear/sprocket? You can't just change the centre shaft for the old model one, then?
Speedway TQ, that's an oval track car, direct drive, no gearbox, or am I confusing yours with an american formula?

AFAIK, the morse sprocket was recut with the same tooth count. From what I was told examining the bits, the J has a bigger center shaft OD.

Yes, pretty much the same formula for TQ's here as the US. There are chain drive variations too. We used to have an international series here where a team of USAC TQ's would come over every summer. GSXR750's I built won it 3 years running. The last year I participated, I'd done my next door neighbour's engine a bit differently. He won the first race in the series comfortably - very comfortably - and post race in the pits I had the engine cover off checking it over when the current USAC #1 came over for a look. I saw him looking and said "Doesn't go bad for a little 750 does it ?" He was running a 1000cc SOHC Honda.
Next race the US #2 team man put him in the wall causing severe damage...
Another engine customer won the series anyway, LOL.

[speedpro]

Z1000 Mk2 had a larger centre shaft and one tooth extra. Presumably the later J models did as well

[Flettner]

I know this is not relevant to this thread but its all gone quiet anyway. 700 twin has now done two hours flight time (including a lot of taxi time) so far trouble free. Fitted a new Ignitech last flight because I just didn't trust the old one, new one runs just the same but at least I trust it. Certainly flying close circuits just in case of engine failure, I don't want an out landing just yet. Too many cows to land on.
There is a need now to build up a second engine but I need new cylinders for it. My foundry is just too crappy, I need to invest in a more permanent one.

[ken seeber]

Hello, anyone there ??? Long time between drinks fellers.

Have a look at this vid. Casting using a PLA print in investment plaster. Really good video. Almost so that I’d like to buy him a new plastic bucket, you’ll see why at the end. I think the trick might be the investment plaster rather than just regular “plaster of paris” / casting plaster; sand or no sand added.

https://www.youtube.com/watch?v=HVgPM1ojyLw

[EssexNick]

I'm still here. Just sitting quietly in the corner, hiding my ignorance behind a vail of silence.