IC Engine Testing

IIRC, it turned out to be because the upstroke of the wings also creates lift (by interacting with the vortex from the downstroke). I may have remembered it incorrectly of course. Whatever, it was a failure of understanding, not incorrect data. We all "know" what won't work, until someone makes it work...

It's the thermodynamics.

Bit unfair, since the inventor has worked on it for years and spent (only) his own money on it.

We'll do our best to oblige.

David

My point was not the direct comparison, but that the Atkinson Cycle has a short intake stroke, coupled with a longer power stroke. I may be wrong here, but if i was a spring I think id probably be expanded to full height at bdc, end of intake stroke( im sucking, so the pressure is very little, possibly less than atmospheric?), which effectivley raises the piston top. This means that the intake stroke is a spring height shorter. then squeeze, bang, Im fully compressed. I remain that way until the presure above the piston is less than the spring pressure. so at bdc power stroke I am likely to be lower than on the intake stroke, as there is residual pressure in the cylinder. thus longer power stroke -> conclusion variation on atkinson cycle. The weblink was intended to give the basics of the akinson cycle, rather than an exact mechanical layout. it did also seem to fit the description of nicks engine: Nick wrote

Dave

I would get me a "thumper" like a KTM LC4, a Yamaha XT 500, Honda X(L)R

600 or something like this. 500 .. 600 ccm, single cylinder, carb, ... Engines that do have power and not a lawn mower who's only construction goal was low production prize.

Nick

OK, so it doesn't draw the temper (titanium: no clue), but it still is the _working_ temperature. And 200°C is high enough to have a significant effect.

Nick

In article , snipped-for-privacy@bem.fki-et.com writes

OK, David, I think I can now see the analogy.

David

It doesn't look the same at all. But the intended effect is the same. Stretch the expansion cycle or shorten compression or something around that (even if unintended).

Nick

Thanks, Nick. Looking at motor/generator packages right now, but motor cycles/rolling road dynos are second option - just quite a bit more expensive.

David

Forgive me if I'm teaching granny to orally extract nutrient from Gallus Domesticus ova but there is a relationship between piston speed and acceleration that not many will be aware of.

It's commonly accepted that maximum piston speed is a limiting factor in engine design. In fact this proves to be very much correct and whether the engine be a tiny model aeroplane one or a massive ship's engine the maximum piston speeds tend to fall into a fairly close range. This is mainly a function of an engine's breathing ability although most people wrongly think it to be a function of the forces that the piston/rod/crank can withstand.

Let's compare a couple of engines. The largest in the world

and an average car engine. Peugeot 205 GTi 1.9

The ship's engine has stroke of 98" (2489mm) and maximum rpm of 102. Rod length is not specified but let's assume 1.8 x stroke as being a good average for engines.

The car engine has a stroke of 88mm and rod length of 143mm

If we calculate maximum piston speed and acceleration we get the following.

Ship's engine at 102rpm. Maximum piston speed 2717 feet/minute Maximum piston acceleration 181 m/s^2 or about 18.5g

Now let's calculate the rpm at which the car engine has the same piston speed and see what happens. This turns out to be 2862 rpm. However the maximum acceleration is a massive 5167 m/s^2 or 527g which is 28 times that of the ship's engine at the same piston speed. This turns out to be the same factor as the inverse of the ratio between the two strokes.

At 8000 rpm, which this engine can be made to run at quite easily, the piston speed is 7594 feet/minute and the acceleration is 4115g which is 222 times that of the ship's engine.

The rpm at which the car engine's piston acceleration is the same as the ship's is only 536 rpm which isn't even idle speed.

So the longer the stroke the smaller the piston acceleration, and forces, for a given piston speed. As it will be the accelerations that cause the most trouble for your design and have the most impact on the spring force required you therefore want to be dealing with very long stroke engines rather than very short stroke ones.

I meant just the engine. You can toss away the rest of the bike. If you want a new and cheap 4 stroke with between 50 and 125ccm that is better than any lawn mower*), get a Honda Monkey clone. The engine costs below 1000.- EUR new. And will be easier to start than a LC4. :-)

*) Again about these engines. It is no black art to improve such a primitive engine. Far away from pinging, the results will nothing have to do with modern engines.

Nick

In article , Dave Baker writes

Interesting thoughts, Dave. I am not the one who has been doing the simulations of the action, but I will certainly discuss it with Bill (who does this).

David

Here's an interesting engine. Cams instead of a crankshaft to transmit the piston forces to the gearbox.

This lot have at least managed to get the moving parts all into an area where they can be lubricated.

Cheers Trevor Jones

In article , Dave Baker writes

Hm, that was interesting; thanks, Dave.

David