Vroom Vroom DUC Swirl Prop Video

[drdehave]

Guys:
I guess this doesn't exactly qualify as "Eyecandy"...but, I continue to love the DUC prop I put on my Sting Sport LSA last summer (and reported on to this forum earlier). However, now that it is coming up on 170 hours of near-flawless performance, I decided to memorialize the salient points in a video (while getting back to some flying basics and sounds):

https://www.youtube.com/watch?v=yyLt652 ... sIcQaBCQ_A

[FastEddieB]

That was fun!

Maybe one "Stick and Rudder" moment, however?

Why should headwind affect rate of climb once you leave the ground?

Hint: it doesn't.

Angle of climb, certainly, but not rate.

Right?

[Merlinspop]

Why should headwind affect rate of climb once you leave the ground?

I suspect it doesn't have much effect before, either.

Can it be that headwinds increase the time it takes to reach the end of the runway, so for a given rate of climb, one can be at a much higher altitude by that reference point, giving the impression of increased climb performance? Either way, noise sensitive neighbors appreciate it, I'm sure.

[drseti]

Bingo! And, the headwind tends to blow the sonic boom farther away from that noise-sensitive neighborhood.

[FastEddieB]

Can it be that headwinds increase the time it takes to reach the end of the runway, so for a given rate of climb, one can be at a much higher altitude by that reference point, giving the impression of increased climb performance?

Of course, which is why I stipulated that angle of climb would, in fact, be greater.

But, reducto ad absurdum, were he climbing into a 60k headwind he'd be climbing vertically...

...but at exactly the same rate as with a 60k tailwind!

Believe it or not!

[drseti]

Believe it or not!

I posted a rather extensive response to this just minutes ago, but it appears to have been lost in the propwash. So, I'll try to reconstruct it.

I believed this at first, Eddie, but upon further contemplation, your reducto ad absurdum led me to a different conclusion. So, let's do a thought experiment:

Consider an airplane, engine off, sitting on the runway, facing into that 60 knot headwind. Airflow across the wing is 60 knots, and angle of attack is below critical. That produces lift. In theory, the plane should hover off the runway, and climb vertically at 60 knots, no?

Now, add engine power to the mix. The added thrust from the prop increases the airflow across the wing, so it would seem airspeed should instantly increase above 60. To hold 60 knots, it would be necessary to convert that thrust into lift (that is, divert it toward the vertical) by hauling back on the stick. Conservation of energy suggests this would increase rate of climb, no?

Applying reducto sub absurdum, I would think that any headwind would allow us to divert some takeoff thrust from the horizontal to the vertical, increasing rate of climb. What am I missing here?

[drdehave]

...And, once again, this is exactly why I stick with you guys: To teach me something, by taking the simple, salient points way beyond what my feeble mind could ever contemplate.

[CharlieTango]

One more:

The claimed 'almost constant speed' prop effect is not to give you best climb and top speed because with the exception of the seldom used 5 min exception best speed and best climb are the same pitch setting. The 'almost constant speed' benefit is the same as a constant speed benefit and it would be to allow you to enjoy best climb ( and best speed ) when flat as well as good economy when coarse.

The compromise is economy vs performance not best cruise speed vs best climb.

[3Dreaming]

Believe it or not!

I posted a rather extensive response to this just minutes ago, but it appears to have been lost in the propwash. So, I'll try to reconstruct it.

I believed this at first, Eddie, but upon further contemplation, your reducto ad absurdum led me to a different conclusion. So, let's do a thought experiment:

Consider an airplane, engine off, sitting on the runway, facing into that 60 knot headwind. Airflow across the wing is 60 knots, and angle of attack is below critical. That produces lift. In theory, the plane should hover off the runway, and climb vertically at 60 knots, no?

Now, add engine power to the mix. The added thrust from the prop increases the airflow across the wing, so it would seem airspeed should instantly increase above 60. To hold 60 knots, it would be necessary to convert that thrust into lift (that is, divert it toward the vertical) by hauling back on the stick. Conservation of energy suggests this would increase rate of climb, no?

Applying reducto sub absurdum, I would think that any headwind would allow us to divert some takeoff thrust from the horizontal to the vertical, increasing rate of climb. What am I missing here?

Thrust is used to overcome drag. With a 60 kt wind brakes could overcome the drag while on the ground, but as soon as the airplane lifts off the drag would start moving the airplane backwards reducing the airflow over the wing and the airplane will come back down. So just like before the airplane will only climb because of the excess thrust available after it has overcome all the drag being created. The airplane will perform the same in the airmass regardless of how fast the airmass is moving. The only thing that changes is the pilots perspective in relationship to the ground.

[FlyingForFun]

Delete

[FastEddieB]

Consider an airplane, engine off, sitting on the runway, facing into that 60 knot headwind. Airflow across the wing is 60 knots, and angle of attack is below critical. That produces lift. In theory, the plane should hover off the runway, and climb vertically at 60 knots, no?

Without the engine producing thrust, I think not.

It would be lifted into the air for the briefest of moments, but then almost immediately begin moving backwards to move at the same speed as the moving air mass. And then just drop.

In that briefest of moments there might be a tiny, tiny effect, I suppose, but it would be negligible.

Anyway, all this assumes no treadmill within a mile of the aircraft!

Let me look for a video of a plane lifted by the wind, and I think you'll see what I mean.

edited to add: FfF posted while I was composing, and I think said the same thing in far fewer words,

[FastEddieB]

A video is worth 1,000 words!

http://www.youtube.com/watch?v=O-wjtP90d_g

Looks to me like that "briefest of moments" was about 3 seconds.

[Merlinspop]

Yikes! Eddie! A good reason to bring your own tie down ropes rather than rely on the weather worn ones at the transient spots (if they have any at all). Elevator locks would be nice, too.

[MrMorden]

I think to evaluate the prop performance in cruise we need to know what the Sting's WOT rpm setting is. The cruise test was at 5200rpm, and showed 120 knots. But depending on how the prop is pitched, WOT could be 5200rpm, 5700rpm, or anything really. 120 knots @ 5200 seems awfully fast if you still have another 400rpm to put to it. If however you are WOT or nearly so at the 5200rpm you were cruising at, that seems more in line with performance of other 100hp 912 Rotax powered birds.

For reference, yesteday at 2500ft in ~42°F temps (great temps for performance!), my CTSW was able to achieve 116 knots at 5200rpm, and 127 knots at 5650rpm (WOT). This is with a three blade Neuform prop at a flying weight of approximately 1220lb. Wind was very light and variable.

[drdehave]

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?