KX100 engine for aircraft

[Danappger]

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.

 

[NO HAND]

Are you sure you want to bet your life on the reliability of a kx100 engine?! I'm not sure the motor is going to hold up very long if you plan to keep revving in the max hp for a very long time. I would worry it might get too hot because it was meant to be ridden with on/off throttle application much like you find on a mx track.

 

[Studboy]

Your best bet might be to tune the motor for a lower peak RPM range than stock... revving at 12,000 RPMs for extended periods of time may lead to some excessive wear.

 

[Danappger]

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.

 

[NO HAND]

Sounds like fun, I thought it was a project more like the ultralight planes they are building with ultra unreliable rotax snowmobile engines. There had been a few catastrophies happening around here, all resulting from these rotax engines blowing up on take-off.

 

[Danappger]

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?

 

[CaptainObvious]

Hey Dana,

As an aircraft builder myself (an RV6) I have a lot of interest in this thread. I have also (successfully) test flown a few aircraft. Nothing gives me comfort like a good powerplant. Some things to consider:

The KX100 motor makes about 22 horsepower. Is this enough for your desgn? It might be enough peak horsepower, but a small bore 2-stroke makes its maximum torque and horsepower in a very narrow rpm band, say 500 rpm (I know, this is why you need a dyno) between – for example - 10,000 and 10,500. If you choose a 3:1 reduction, you’ll have a prop speed of 3,500 and 3,333. That’s only a 166 rpm spread! Are you using the gearbox as a reduction drive?

Because of this, you can’t assume that you will have both a climb and cruise power setting. If you choose a prop that climbs well you wont have enough torque to turn the prop at lower rpm. If you choose a prop to run at a reduced power setting for cruise, the prop will surly cavitate at full throttle. As you are aware, the airfoil on a paraglider only really operates at one speed, say 26 mph. Excess power is converted into climb and power in equilibrium with airspeed turns into a “cruise” setting. With a small bore 2-stroke, I see you climbing and descending…not cruising.

I think that you are falsely finding comfort with the increased airflow for cooling. That engine will be at high-load for most of its operation. This will generate heat that “may” overcome the cooling jackets in the cylinder. A KX100 will go much faster than your craft! I don’t really see the cooling advantage.

A small bore motorcycle engine, run at full throttle with a constant load, will need an overhaul as often as every 10 hours.

Having flown a few paragliders, I can see why the Rotax 682 is chosen as the (2-stroke) engine of choice. It is chosen because of its wide (for a 2-stroke) power spread. I just don’t see a 100cc engine providing enough excess power – and at the same time – allowing a cruise power setting.

I look forward to being proven wrong.

 

[Danappger]

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?

 

[CaptainObvious]

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.

Sure they do! I've had it happen on experimental props. A portion of the prop stalls, causing the prop to rev higher without "grabbing" air. It can cause the engine to surge beyond it's red-line. It's like a transmission slipping. Afterall, a prop IS a transmission, if you think about. For your application, I'd suggest a ground adjustable Ivo-Prop

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.

Nor have I...it's a 582! I have flown 2-place paragliders with this engine and the Rotax 912/914. The four strokes are much better (just like with dirt bikes :)) because they provide a much wider power spread.

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?

That number would be at the rear wheel...and it's an estimate.

 

[Danappger]

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.

 

[CaptainObvious]

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.

OK, I guess you have test flown more props then I have. I have about 15 under my belt on three different airframes. You?

Props cavitate. It happens at the root, not the tip. The root spins without grabbing air causing the prop to "slip". It happens more often on 3 and 4-bladed props than 2 blade props. In fact, I have never heard of it happening on a two-blade prop.

I can direct you to many prop builders that can fully explain the phenomena. Bernie Warnke and Clark Lydick are two that come to mind. I believe it is also explained in Tony Bengelis' books on aircraft construction. These books are available through the Experimental Aircraft Association.

Are you forgetting, air and water behave the same.

BTW, You are correct, I was thinking of a powered parachute which, due to its size and weight, have higher horsepower requirements.

 

[Danappger]

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!

 

[Green Horn]

Oh god, it's the dueling Rich Rohrich's of the paragliding world. :)

 

[dklink2000]

You say tomato…..engineers! ;)

 

[bikepilot]

If your KX100 motor is a newer powervalve unit you need to make sure the powervalve governor is properly assembled as many came from the factory with too much clearance which allowed the 8mm steel balls that ride in the ramps to open the powervalve to sling out and into the trans. Or better yet you could eliminate the powervalve governor and use a cylinder from an older model. I think they will bolt up to the newer cases, or if you have not purchased a motor yet just make sure to get a pre-powervalve unit. For your application I seriously doubt the powervalve would be anything but an extra failure point and maintence item. Also, just so you know, the KX80 and 100 have the same crankcases (for a given year at least) and crank but a different bore. One can be converted to the other by simply changing top ends. The KX100 (pre powervalve) is extreemly reliable in my experence. My little sister (who is a serious rider with many race winns under her belt) rode one in the Little Sahara sand duens several hours a day every day for 3 weeks without any motor work. Unlike most dirt riding, riding in the dunes is mostly continous high-rpm-high-load, especially for a small bore trying to keep up with KX250's and CR500's.

Did your brother see the turbine RV8 at Oshkosh last summer? I think ATP built it. I might have some pics if you want.

btw, rotax did make a 618 for a while and they still make the 582. Perhaps that's where the 682 confusion came from. (both of which are much too big for your application, unless perhaps if you tuned them to run best at around 3000rpm and did away with the gear box, then you might acheive similar power and weight as a KX80 motor, but with a much longer TBO. I dont know if this has been tried, its just an idea.

 

[Danappger]

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.

 

[CaptainObvious]

Did your brother see the turbine RV8 at Oshkosh last summer? I think ATP built it. I might have some pics if you want.

Saw that...wish I had an extra $30,000 sitting around :(

 

[Burtonridr250]

get a banshee motor in that beast

 

[berudd]

Dana,

check out http://www.rpmsbigbore.com/ They do engine mods and have some dyno charts for various bikes. His charts and all other dyno charts I have seen are at the rear wheel.

 

[bikepilot]

I am not sure if there ever was a KX that came directly from the kawasaki factory with a non-powervalve 100cc motor, but Kawasaki did offer a big bore top end option that could be installed very easily. The cylinders were the same casting with a different bore. The cylinders could safely be bored to make the motor displace 107.2cc. I dont remember the actual bore diamater though. If you wanted to I belive you could swap a older KX100 cylinder onto your new cases to eliminate the powervalve completely. Also they make spacers to take the place of the powervalve. The governor can be removed from the trans very easily (its directly under the trans oil fill plug and can be accessed by removing the right side case cover).

You might be surprised how light some larger engines are. I know the 550cc twin cylinder in my little kawasaki jet ski is very light, I have not weighed it, but It can easily be carried around by hand. Definately not heavier than a standard KX100 motor, but perhaps heavier than one with the trans parts removed. With direct drive if keep the rpm's at normal prop speeds (<3000 or so) I doubt such a motor would make any more power than the KX100 mill. I dont claim this to be a good idea, just a quick thought.

Enjoy:)

Have a look here for my powervalve failure pics
http://www.postwhore.biz/thumbnails.php?album=85

 

[Danappger]

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!"

 

[bikepilot]

I dont remember the company name, but they advertised the spacers on e-bay. I have both a non-powervalve KX107 (overbored, slightly lower exhaust port than stock) and a powervalve kx105 (bought used - don't know anything about the porting - probably stock). To my surprise the older non-powervalve motor feels stronger, which could be due to better porting or the extra 2cc. However, this illustrates that the powervalve is not very effective on these bikes. Still, I am sure you would loose a little low-mid rpm power, but probably not enough to notice. I would want to remove the powervalve in an aircraft application inorder to improve the reliablility of the motor, as the KX100 powervalve is a known failure point. Also, you would loose a litttle rototing mass (govener) and weight. If you keep the powervalve, make sure the govenor halves are pressed together close enough so that the balls can not fly out at high rpm. Also, I would recomend upgrading the powervalve actuator rod/lever (the part that goes from the clutch cover to the cylinder) to the 04 spec part as it has a different design that is supposed to lessen failures. Lastly, there is a small pin that holds the actual powervalve to the actuator rod in the cylinder. This pin is known to fail which allows the powervalve to drop into the exhaust port resulting in pistion damage. Look at www.buykawasaki.com for exploded views of the motor if this doesn't make sense to you.

Overall engine lenght would probably be a problem with the 550, if you need I can take measurements. I can not easily get the weight though as its in the ski and I don't really want to pull it out. The main reason it is so light (IMHO) is that it does not have a transmission and large engine cases like a motorcycle motor, its just the crankcase and top end. Also, no reeds or powervalves.

good luck:)

 

[Danappger]

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.

 

[bikepilot]

I don't know much about the spacers, though I have definately seen ones the eliminated the powervalve.

The theory about the fuel pump not being able to flow enough is possible, though I doubt that increasing the pressure would do any good. If the fuel pump doesn't flow enough to maintain 2psi at full throttle, then it will not be able to flow enough to maintain 4psi. Also, I would be concerned about why the motor was hard to turn over. Did you do any jetting work prior to installing the motor, or are you running stock KX100 carb and jetting? If so, it will probably be too lean for constant duty running which could lead to seizure or overheating. Does it have a tempature gauge? Any indication that the motor got to hot? I have seen a KX100 be run so hard in sand dunes that it boiled its antifreeze and then got stiff enough to turn over (the piston expanded enough that it was too tight in the cylinder) that it would not stay running very well. Once it cooled down (and was re-filled with coolant) it was fine. Perhaps that is what happend to you?

The plug and piston should give you a good indication of wether its running too lean.

I don't know anything about running it without floats, though it sounds like it would work provided the return was sufficiently large that it wouldnt over fill the float bowl at low rpm/power settings.

good luck

 

[Danappger]

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.