Prop loading and unloading ???

[scottessex]

I have a few observations....when running the arctic cat dominator, it seems that the IVO prop gets to a certain rpm and then "unloads"
I have the prop pitched so the engine gets through the 5000 rpm area where it starts building torque, then it screams all the way past 7000rpm.
So I put the WarpDrive prop on and again, have it pitched so it gets through the area around 5000 rpm, and it holds the engine at 6500 rpm.

It seems to me that something is going on here with a flexibility issue or something, If I add more pitch to the IVO it cannot climb through the 5000 rpm area, as soon as I take some pitch out, wham, all the way to 7000! No in between.
The warp seems to be able to hold the engine at 6500rpm and still make it all the way through the rpm range.

Does this have to do with the IVO being more flexible?
The IVO is 4 blade and the warp is 3, I know I could take a blade off the ivo etc, but I am trying to get the engine dialed in and jetted etc

I just thought it was kind of a curious observation.

[Earthboundmisft]

Scott, my guess is the 4 blade versus 3. A fair comparison, as well as a troubleshooting
tool would be reconfiguring the Ivo as a 3 blade. Does seem wierd though. What is the diameter you are working with, and your gearbox ratio?

[scottessex]

Both props are 60" gearbox is 2.58:1

[GyroRon]

Not all Ivo props are the same. Besides the diameter and the rating ( such as Magnum ,etc.. ) , Ivo props also come in different HP ratings. You might have a prop made for engine with a either much more or much less HP than your sled engine

[NoWingsAttached]

I've written about this on a couple of other threads.

I did some thrust testing with my IVO and found it too flexible on the outer 1/3 diameter, making it harder to obtain repeatable data through variable loads. My conclusion was that the prop is not completely predictable in the higher RPM range. The blade tips flex in the opposite direction of travel and the air diffuses coming off the blades increasingly as loads also increase. This variation in thrust is unsettling in some take-offs I've noticed on my Bee. I have never noticed these variations on my Air Command, which has the stiff Warp Drive.

I published some related findings on this on another thread when I was describing the proper way to perform thrust tests in static ground set-up. I reported that according to my data (recorded using the IVO) if you gunned the motor you will get false readings, often 10-20% HIGHER than true thrust obtained by first properly "pre-flexing" the prop in stepped increments.

A few folks here scoffed at my conclusions, saying things like "what good does it do me to take thrust readings at RPM levels lower than you see when you are flying? All I am concerned with is maximum thrust." (Laughing to myself), I responded by saying that by doing a test this way - taking a reading every 500 incremental engine RPM, starting at normal engine idle, I found a thrust curve that did not match what it should be on the test prop - an IVO - and that by obtaining thrust results at the lower speeds you can accurately map a thrust curve to predict what should be found at the higher speeds, so long as the prop remains stiff and keeps its shape.

Sure, you can probably make a test run with an IVO on my dyno and record thrust 10 - 15 fp higher than a comparable Warp Drive, but is it reliable and repeatable throughout a range of data points? Not that I found.

A proper thrust test must be done slowly, and you must be sure to completely flex the prop before recording your results throughout the rpm range of your engine - not just a single number you jam into the dynomometer at full throttle. This is the only way you can really see what is going on with your prop.

OR YOU CAN JUST READ YOUR TACH - LOL!!!!

[RotoPlane]

It sure sounds like you nailed it Scott. The Ivo is flexing above 5000 rpm. Perhaps a a higher hp rated Ivo is stiffer……

[NoWingsAttached]

Not all Ivo props are the same. Besides the diameter and the rating ( such as Magnum ,etc.. ) , Ivo props also come in different HP ratings. You might have a prop made for engine with a either much more or much less HP than your sled engine

You printed this b4 I got mine out. So the higher HP-rating is a stiffer composite?

[GyroRon]

I don't know if it is stiffer or not, but they do offer different HP rated props.

[Earthboundmisft]

Glad to see you are sticking with the Artic, they have quite the two stroke heritage.
Careful carburation set-up, should give long service. Whats the HP on that bad boy?
Guess Im kinda partial to two-smokers!

[jcarleto]

I'm glad to see this thread. It explains what my testing was starting to show with the Bulldozer. That is, when I get the prop set for 5500 RPM, I can barely climb at all. When I open up the prop so that maximum RPM is 5000, I get much more climb thrust. Clearly, it should work not like that.

The conclusion I was "guessing" was the 4-blade, 68" PowerFin propeller, for whatever reason, is an inappropriate prop for the machine. The specific "why" wasn't clear, but the results were impossible to ignore. This thread makes the reason more clear to me.

I was going to keep trying to fine-tune the prop to try to find an absolute "best thrust" setting (lying somewhere between 4500 and 5000 RPM), but it may be I would be better off shopping for a more appropriate propeller for my application. It doesn't make sense to me that I should settle for losing 300-500 RPM of potential horsepower due to a prop deficiency. The Bulldozer needs all the help it can get moving itself and my sizeable carcass off of the ground. :D

[NoWingsAttached]

John, ye ain't all THAT large.

[gyromike]

Scott,

You mentioned that the IVO jumps from 5000 to 7000 with nothing in between.
Does the Warp do the same thing from 5000 to 6500? Or is it a more linear increase?

I am wondering if the Arctic Cat is just way more peaky than the Rotax.

[Friendly]

Roger has a K engine that does the same thing. It was belts slipping, but you have gear drive. His may still do so, we have not have the motor up that high for a while.

[dabkb2]

I will be interested to see where this thread goes.

[birdy]

Dose it still push wen the rpm takes off? [ if it dont, its stalln]
If it was just flexn [ depitchn ] under pressure, itll still be pushn.

[Jean Claude]

Sudden jump of 5000 rpm to 7000 rpm hears easy to the ear. If you hear nothing, change Tachometer!

[scottessex]

Mike, Yes the warp drive is much more linear.
It is almost like the IVO is flattening out.

And yes it is audible, there is nothing wrong with the tach, :)

[NoWingsAttached]

Do they sell IVO spacers to turn a 4-blade into a 3? heck, for the $12.00 they charge for spacers check it out as a 3-blade. I'd bet that is 80% of the prob

[scottessex]

Yes Gregg, I have all the stuff to change from 4 blade, to 3 or even 2,
It was easier just to swap out the prop and see if anything changed with the stiffer prop, and it did, so now I have other options.

[NoWingsAttached]

Are you driving down to B-Days? If so, when are you leaving?