KX100 engine for aircraft

I've just finished building a KX100 powered paraglider (pix at the "plans" link at flyparafan d-o-t com. At this point I'm working on dialing in the appropriate propeller to get it into the powerband (best rpm I've achieved so far is around 9700). Anybody know where I can get a dyno chart for the KX100? You hear so much BS about horsepower but few hard facts.

-Dana

Place a half full glass of water before a pessimist, optimist and an engineer:

The pessimist says the glass is half empty.
The optimist says the glass if half full.
The engineer says the glass is too large.

Well, a couple of things. First, it won't be at full power constantly, only during takeoff and initial climb. Second, the airflow through the radiator will be a LOT better than on a bike. Also a steady rpm, even if high, is a lot easier on an engine (as long as it's not overheating) than a lot of power variations. There's also none of the bogging down or overreving due to inappropriate shifting you get in a bike.

Another guy is flying a paramotor with a KX80 engine; he's got it propped to max out around 11,300 with good results. After 35 hours of running it's still going strong. A KX100 should have it easier.

"bet your life"... well, this is a paraglider after all. When (not if; we all fly 2-stroke engines and they quit occasionally) the engine quits you simply glide down and land... and you don't fly in places where you can't do that.

-Dana

When authorities warn you of the sinfulness of sex, there is an important lesson to be learned. Do not have sex with the authorities.

Rotax may make snowmobile engines which at one time were used in ultralights but they also make aircraft engines that are a far cry from the snowmobile engines in terms of reliability... though their 2-stroke engines at least still require more attention than a 4-stroke.

Still wish I could find that dyno chart.

-Dana

Why is it called tourist season if we can't shoot at them?

RV-6, eh? I used to own a Taylorcraft before I got into paramotoring. My brother-in-law is building an RV-8... at this point he's planning on a turbine engine for it; wish I had just _some_ of his money!

22hp is more than enough. My old paramotor is only 14hp and gives good (if not breathtaking) performance. That engine is a 210cc Solo engine with no tuned exhaust, turning around 7000 rpm max with a 2.65:1 reduction. This is considered "old" technology. Another very popular paramotor engine is an 80cc engine turning around 11,000 with good reliability, I don't know the hp. A lot of the current engines are 100cc, in the 20-22hp range, with good reliability (some are aircooled and some are liquid cooled). 200 hour TBO is typical of all these engines... and as I said there is one KX80 powered machine still running well after 35 hours flight time (he replaced the rings at 20 hours but said it didn't look as though it was necessary). I heard about another guy who used a CR250 engine but it was so heavy he only flew it a couple of times.

I'm using the original 3.4:1 primary redution, with all the other gears and shafts removed from the gearcase, and running the prop drive off the gear that originally drove the clutch, so if max rpm is 11,500 then the prop RPM will be 3382. I've test run it (on the ground) with four different props (all to highly pitched for the engine) and gotten max rpm's between 8-10,000. Next step is a ground adjustable prop so I can dial it in to the right pitch.

An air propeller does not cavitate... cavitation is a phenomenon of water props, where the pressure reduction causes the water on the front surface of the prop to vaporize (boil). It may, however, be partially stalled. Because of the low speed, though, it'll be a fairly flat pitch (no need to pitch it for high speed cruise!), so that's unlikely to be a problem.

I'm going slower than the max speed of a dirt bike, but there's a prop blowing air through the radiator at all times, and the radiator is clean, not choked with dirt or mud as often may happen with a bike.

I've never heard of a Rotax 682... but I do know that Rotax doesn't make any engines small enough for paramotor use, which is a pity.

You mentioned the 22hp figure... is that hp at the rear wheel with the whole bike on a dyno, at the gearbox output sprocket, or at the crankshaft? How are bike engines normally dyno tested?

I too look forward to you being proven wrong. :laugh:

-Dana

Why is it called tourist season if we can't shoot at them?

No, it's still not cavitation which is a vaporization effect as I explained... and think about it, what happens at the stall? The lift (thrust in the case of a prop) falls off and the drag increases dramatically as the flow separates... which would limit the rpm, not cause it to surge higher.

Anything with a Rotax would be a powered parachute (PPC), not a powered paraglider (PPG). Though they look similar there are significant differences between the two: PPG's are small, 12-25hp, usually foot launched (some use carts) with relatively efficient elliptical wings, controlled by handheld brake lines and weightshift. PPC's are larger, 35-80hp, always on wheels, with inefficient square parachute wings (though some are going to ellipticals) and foot steered.

4 strokes are definitely better in all aspects except the the critical one fpr a ppg... power to weight ratio. The few 4-stroke ppg's that have been flow are low powered and very heavy.

-Dana

Giving money and power to government is like giving whiskey and car keys to teenage boys.

I've flown quite a few aircraft types (although, come to think of it, all with 2 bladed props), but in this case I'm speaking not as a pilot as an aeronautical engineer. Aircraft props don't cavitate. This is where air and water don't behave the same: water can vaporize (which is what cavitation is), whereas air is already vapor.

That doesn't mean you can't experience a phenomenon that looks like cavitation, but "cavitation" isn't the correct term. The key was when you pointed out it happened mainly on multi blade props. When the blade stalls (near the root first, unsurprising since the blade angle is greatest there) the drag increases. This could cause the air to be "dragged" around behind the prop instead of being pushed backwards, and since less energy is going into thrust, it goes into speeding the prop up, just as a boat prop does when it cavitates. Different mechanism, same effect.

This could also explain why many ppg props get higher rpm's during static runup on the ground than they do at full throttle in flight.

The Ivoprops aren't really suitable for ppg (and are heavier than others). I looked at Powerfin, but it looks like I'll go for a 2-blade adjustable from GSC in Canada (less than half the price of Powerfin) Now I just have to wait the 2½ weeks for delivery....

-Dana

And they shall beat their swords into plowshares, for if you hit a man with a plowshare, he'll know he's been hit!

I wasn't aware that they ever made a KX100 without a powervalve. I already have the engine at any rate; it's a 1998. I had the whole thing apart and it looks OK, and it seems to run fine as well, and the powervalve opens when it should; I'm just not getting enough rpm with the props I have available (9700 with a 49" prop and 10,000 with a 47½" prop with too much pitch). I've ordered a 47" adjustable pitch prop which hopefully will be the ticket, should arrive in a week or so.

A 618 or a 582... yikes! I suspect foot launching could be a bit problematic with one of those on my back! No matter how many parts you removed you'd never get them down to the size and weight (>30#) of a KX100 engine. Not to mention the danger of that much power.

-Dana

When Columbus came to America, there were no taxes, no debts, and no pollution. The women did all the work while the men hunted or fished all day. Ever since then, a bunch of idiotic do-gooders have been trying to "improve" the place.

Who makes spacers to take the place of the powervalve, Kawasaki? Why would you want to do that? Seems you'd lose a good bit of midrange torque which would be a big problem for a bike (but might not matter to me, since torque required by a propeller is proportional to the square of the rpms). I assume then the powervalve wedge simply gets removed?

Hard to believe a 550cc engine could compete in weight. The KX100 engine is under 30# with the gears removed. Overall engine length is also an issue.

-Dana

The difference between golfing and flying: In golfing you hear "whack... ****!" and in flying you hear "****... whack!"

Hmmm... the only powervalve spacers a web search turns up make the powervalve open later, not eliminate it.

I flew it for the first time a couple of days ago. With a prop that lets it turn around 11,200 on the ground I get pretty good thrust. Overall performance was pretty good... until the engine sagged and died about 10 minutes into the flight. When I landed, the engine was stiff to turn, almost like it was seized, but it loosened up and when I pulled the head, carb, and exhaust I couldn't see any damage. It's back together now and I hope to get it running again today.

My current theory (which I welcome comment on) is that it starved for fuel: Because the tank is below the engine, I have a Mikuni fuel pump to pump the fuel to the carb. The pump puts out enough pressure to force the float needle open and overflow the carb. It takes around 5 psi to overcome the needle, so I put a 2 psi relief valve in a tee on the line to regulate the pressure the carb sees, returning the excess to the fuel line below the pump. It seemed to run fine on the ground, but I'm thinking maybe that wasn't quite enough for an extended full throttle run, maybe 4 psi would be better. I've also seen reference to karters removing the float altogether, constantly pumping fuel through the carb with an overflow tube at the normal float level to handle the excess... anybody know anything about that?

-Dana

Son - you're going to have to make up your mind about growing up and becoming a pilot. You can't do both.

The theory about the pressure was that the pressure pulse (since it's not constant pressure) was over 2 psi so the bulk of the fuel went through the relief valve instead of up the line to the carb... a 4 psi valve would reduce that. The pump is more than adequate as far as flow goes; it's used on much larger engines. However, I'm not convinced now that fuel is the problem.

I started it up yesterday evening. Started right up, and died again within a minute. This time it's seized hard. I've pulled the head and it doesn't look like it's the piston, but I haven't pulled the jug yet (doing that tonight). At this point I'm suspecting it might be a main bearing. but we'll see.

I'm not sure about the jetting; the engine came from a bike salvage yard and the various parts may or may not have been from the same engine... but judging by the plug color the mixture is OK. The only gage on the engine is a CHT, not really applicable to a watercooled engine, I know, but if it was overheating I'd know it. When I landed, no more than a minute after it quit the first time, the CHT only read 200°... and the fact that it seized up so quickly the second time, before it had a chance to warm up, supports that.

I've learned a little more about the pump around modification... basically it uses a dual fuel pump. The float is replaced by a baffle (only to reduce sloshing) and an outlet is added at the desired fuel level in the bowl. One pump pumps fuel in, and the other one sucks it back out again through the new outlet, maintaining a constant level. Seems like it would work if the engine is level, but it's a level of complication I'd rather not go to.

-Dana

The speed of light is greater than the speed of sound. That's why some people seem very bright until you hear them speak.