richardgerardi

Can the Kougar do 100 mph with an OS46 AX with a 10x7 prop. Just finished one and hopefully she will maiden tomorrow.

still4given

Maybe with an Ultra Thrust or Jett stream muffler.

ProBroJoe

Can the lowly AX turn that prop to almost 18k?

lfinney

My Feedback: (44)

mas nitro...lol mucho nitro

MJD

My Feedback: (1)

I bet it flies 85-90ish in level flight, but I'd be glad to be proven wrong*. Good luck!

MJD

* in either direction

combatpigg

My Feedback: (3)

If he can get 15,000 rpm with that prop, the pitch speed is 99.4 mph. About as fast as a VW Bug pushed off of cliff.

wildnloose

The wing is too fat, he'll be lucky to push 80-85 in a dive. I thought about trying all kinds of mods to make it fly faster, but its such a fun plane to fly why bother....makes a nice windy day plane, can take all kinds of abuse. I really doubt you can get more speed out of it.

I actually won this plane on a bet. I bet the owner I could land this plane on a 5ft circle 10 times in a row...guess who won (well, I did 9 but he was so impressed he gave me #10 and the plane).

ProBroJoe

That's assuming the prop is 100% efficient, right?

Does that mean that my Sig Kavalier with a piped Mag Pro .45, turning an APC 10x7 @ 15,250 RPM static (which it does) will break 100? Nah... I didn't think so. Even though a lot of the prop calcs (which figure in prop efficiency and drag) claim 85-87MPH for my setup, it sure looks more like about 70 in the real world.

Or do you just ignore efficiency & airframe drag when bench racing and assume that since the prop will unload in the air and gravity is on your side, that will make up for any losses?

I'm sorry, I don't mean to come off as being confrontational - it's just that I've seen several instances here where folks are claiming MPH #s higher than the pitch speed of the prop (using realistic RPM #s now) and I'd like to know how that's possible... Do these engines unload that much in the air? Are the airframes simply outrunning the engine in a dive? What are the physics involved here? If you try to go by pitch speed alone, it's going to take a whole lot of RPM to make it happen, which I have a hard time believing even the best engines out there can do. Are these guys really spinning 10" pitch props to 24-25K to get 200 MPH?

Flying freak

The prop is a aifoil, yes it has pitch but just the fact its an airfoil mean that its alot more than just prop pitch.

richardgerardi

She maiden this past weekend, 100mph not even close. I think 65 at most. Will play around with different prop sizes and maybe a tune pipe see what happens.

MJD

My Feedback: (1)

All he said was that the pitch speed was 99.4 mph, not that the airplane would do it. That's a big difference between reality and calculators right there.

It is true that may props are not exactly as marked, but close. Engines can unload 500,1000, 1500 rpm in the air depending on setup. Some highly tuned piped systems go through several stages of pipe resonance and result in enormous rpm gains in the air when they unload. The most extreme example of this, as an illustration, would be F2A c/l speed, where 2.5cc engines are launched at 20-22k, then progressively unload through several pipe stages up to the high 30's.

But none of this is any good of course if the combination of pitch speed and horsepower are insufficient to pull the aircraft that fast. However if it is, you can achieve flight speeds higher than the combination of static rpm and pitch speed would suggest.

The Eurocup speed guys and those doing that kind of flying, are indeed spinning 10" and higher pitch props at over 20k. It is not unusual for .60 powered speed aircraft to unload to 25k, and the prop pitch may range from 10" to 13" or so. 8x12, 8x13, 8.5x10, these are the sorts of sizes used there.

QM pylon guys are running pitches what, about 7" or so?, but spinning in the high 20's to achieve flight speeds somewhere south of 200.

MJD

jplavoie

I tried To have my Kougar flying fast too. Even with a tuned pipe on your .46 the speed will remain well under 100 mph. I tried different props with the Mac's tuned pipe (APC 9x8, 9x7, 10x7 10x6) and in I even tried it with a Jett .50Lx, but it was still in the 70-85 mph range. My top speed was a 92 MPH downwind level pass (wind was about 20 mph) but I almost roasted my 46 ax as it was running pretty lean.

My conclusion is the airfoil is just to thick and creates too much drag when the speed goes over 65 mph. Despite its jet-like look, this is obviously not a plane designed for speed. It is much a pattern-like plane. You'll enjoy more flying it as such than trying to make it fast.

If speed is really what you'r looking at, this runs almost twice the Kougar speed:

http://www.jettengineering.com/sundowner.html


JPL

bob27s

My Feedback: (19)

For the Kougar......

with the stock muffler, go with a 9x7 prop. Allow the engine to turn up a little.

Add a jett-stream muffler to the 46AX
9x7, 9x8 prop, ground peak rpm around 15,500 - 16,000 is what you want.
That is about the best you will see speed wise on the Kougar (unless it has retracts in it)

As noted, the plane has a thick wing. But that is one of the reasons it flys and lands so great. Also has a lot of frontal area. But the Kougar is a classic for a reason ..... good looks, great flying, and just a great sport plane.

MJD covered the "prop speed" subject well. Best thing to do in most cases is leave the calculator in the drawer. Aircraft performance is a balance between prop/engine/aircraft/pilot. Pitch x RPM does not tell much of a story.

Brief example I have posted before.
We know that a well built, well trimmed 424 sport Q-500 plane can reach level flight speed of 120mph (time, radar, air data confirmed on a number of occations).
That speed obtained not on the race course, but in extended level flight where turning is not involved.
Q-500 is quick.... semi-low drag, but very basic, boxy ..... so it can be considered a fast sport plane.
Powered by a TT40pro, stock, stock muffler, turning a 9x6 apc prop, at ground peak somewhere around 16,500 rpm.
We also know the engine can get up around 17,000 rpm in flight.
Using that, you can back out what the "pitch x rpm" speed would be.
You can see the disconnect.

combatpigg

My Feedback: (3)

PBJ, "The rich get richer and the poor get poorer" applies to the amount of unloading that any airframe allows. A model like a typical AMA Fast Combat model will unload to 10% higher rpm and drag will knock off 10% to bring the actual speed down to the mathematical speed. I've got RC models that do likewise.
I've personally never seen a Kougar that was fast enough to make you say, "WHOA!!!" It would make the subject of an interesting speed contest to see how fast anyone could make one of those sleds go.

Electric Delta

My Feedback: (13)

Back in the day, very late 1980's, I had a Kougar with an OS .50 FSR and Mac's full-length quiet-pipe set-up. Can't remember which Master Airscrew (gasp) prop I had on there (10x7?, 10x8?), but I remember ground rpms in the 16,000's. I would estimate that my Kougar just barely got into the 100-110 mph range, in level flight, but no higher. At the time, it seemed scary fast...