Vroom Vroom DUC Swirl Prop Video

[CharlieTango]

The almost constant speed feature is especially attractive with light sport where constant speed is prohibited. In addition to demonstrating performance when the prop is under high load I would need to see evidence that when throttled back in cruise that the DUC is unloading and using a coarser pitch.

[MrMorden]

120 knots @ 5200 seems awfully fast if you still have another 400rpm to put to it.

That's about right--another 400 + or -, to go. I don't like running her that high, because I have the start of a water pump leak out the weep-hole at the bottom of the water pump, and putting the pedal-to-the-metal seems to make that little hole want to weep! But I'll go out today and briefly see what she pulls WOT SNL--and report back (the rpm, not the speed, naturally). What I do know, is that she pulls about 10 knots more speed than either of my Woodcomp SR200 props delivered, no matter where they were pitched.

And..just for comparison, Andy, what rate of climb, angle, and speed, were you pulling on take off?

Wow, that does seem like that prop is fast then...I bet you'll see 130 knots WOT.

In that nice cool air we were at 1000fpm yesterday, but I wasn't consciously trying for a max performance climb, and was often at a speed a little above the 78 knot best climb speed. When solo I have seen 1350fpm in the airplane.

[Merlinspop]

... I'll go out today and briefly see what she pulls WOT SNL--and report back (the rpm, not the speed, naturally.)

If that's because you don't want to appear to be busting the LSA speed limits, I don't think that's a problem, as long as at your test altitude WOT is greater than max continuous power. But then again, that's my interpretation of the rule and maybe you're better off just reporting how many RPM you have in reserve beyond your cruise RPM.

[dstclair]

Keep in mind the 120kt limit is at max continuous power (not WOT), CAS (not IAS), sea level and standard conditions. I've also been told by a manufacturer that the ASTM standards have an error tolerance of +/- 5%. So even an IAS of 125-130kts at below standard temperature would highly likely be within the standards.

[MrMorden]

Keep in mind the 120kt limit is at max continuous power (not WOT), CAS (not IAS), sea level and standard conditions. I've also been told by a manufacturer that the ASTM standards have an error tolerance of +/- 5%. So even an IAS of 125-130kts at below standard temperature would highly likely be within the standards.

I would not worry about it, if you are using a SLSA with all factory-approved parts. After all, the airplane is certified to meet LSA limits, if it does not, that's on the manufacturer, not the pilot. And it's not like there is some FAA speed trap up there with radar guns making sure you are complying with LSA limitations.

And you are totally correct, unless you are breaking limits while at sea level on a standard day (I've yet to see one) and using a calibrated instrument, I think you are safe.

[drdehave]

Comment: 120 knots @ 5200 seems awfully fast if you still have another 400rpm to put to it.

My Reply: That's about right--another 400 + or -, to go.

Wow! This is way better than I thought! This AM, @ 2,500', 12C, she zipped to SNL 5,630 rpm in a heartbeat, with still an inch or so left before the throttle-slide (i.e., pilot end) stop! Airspeed was locked on the majic odd number! I did not want to push her to the max, i.e., SNL WOT, due to added stress on the aging (1250 hrs and counting) water pump shaft seal, which is waiting to puke coolant into my cowling and belly of the aircraft, sometime in the next 200 hours.

But I have confidence that when that seal is replaced--if I wanted to--I could make her pull 5,800 rpm and 135-140 knots, SNL--WOT, with the DUC Swirl pitch set where it is right now.

Now, that would put her into the LSA Rocket Performance category I do believe.

[MrMorden]

Very impressive...what were your numbers with the previous prop?

[3Dreaming]

Depending on how your throttle is rigged you may have been against the stops on the carbs. I know that is how the CT is set up.

[drdehave]

..."you may have been against the stops on the carbs."

Negative. I did verify there was still throttle to go--I just didn't want to hold it there at WOT to see how much.

..."what were your numbers with the previous prop?"

My two different Woodcomp SR200s both pulled about 10-12 knots less speed--with significantly less T/O climb and T/O RPM rarely above 5,050.

[dstclair]

Very impressive...what were your numbers with the previous prop?

OK -- my Woodcomp was just about to TBO so I decided to replace the prop with the DUC Swirl instead based on feedback from a few Sting owners. I tested the Woodcomp at 7130' DA at 5100, 5250 and 5400 and on the return trip tested the DUC at 7070' DA at the same RPM. The Woodcomp gave me 111 KTAS at 5250 and the DUC did 119 KTAS. 6-8kts improvement across all the normal cruise settings.

At lower altitudes I had trouble staying out of the yellow

OAT's were not the same so I couldn't compare oil temperatures.

Also had a db meter and the DUC was 3 db quieter.

I'm sold!

Anyone know of someone or want my low-time Woodcomp SR200?

[FastEddieB]

Wow - that's tempting.

They make a pusher version that would fit right on my Sky Arrow.

Hmmmmm.....

[drdehave]

Dave Said: Anyone know of someone or want my low-time Woodcomp SR200?

Negative, Dave. But if you find a taker, see if he wants two more copies of the same, on the shelf in my hangar.

PS/ One thing I noticed with my DUC Swirl is that there was a break-in period of about 50-100 hours. During that time it got faster--and a rough spot (blade harmonics) it had during throttle pull-back, static position, after run-ups, gradually disappeared. And one more thing that I see: On climb-out, at 65-75 knots, WOT rpm varies 5150-5180; but, steepen the angle-of-attack to Vx55 knots, and rpm increases to 5200-5220. I guess this is that constant speed effect? On the other hand, during T/Os I see it definitely pulls the airplane down the runway differently than the Woodcomp. I must be patient, giving it plenty of time to grab bites--and I have discontinued counterproductive short-field T/Os involving throttle-up with brakes on.

After you have some serious hours with it, I would like to hear if you have similar observations.

Rich