Sport Pilot Talk

MrMorden wrote:
I guess it's a common Aero Engineer joke...

Let's put it this way: it wasn't original with me - or your ex-brother in law.

dstclair wrote:There are several reasons your S4 did not match speed with Rich's StingSport:
Weight - The S4 probably weighs 60lbs more than a StingSport. In the particular video, Rich could've been 200lbs lighter than you, which would make 5-10 knots difference.
Design - the S4s wingspan is about 2 feet longer with a slightly different design. Supposedly doesn't affect cruise speed but it seems to with anecdotal reports.
Density Altitude/temperature - big factor in performance.

We definitely were at close to gross so significantly heavier than Rich at that point.
I will try the same scenario solo, at different altitudes etc ... see if I can come close to replicating Rich's numbers.

It may indeed be the case that , despite factory cruise numbers, S4 variants are just simply slower ( which would be a bummer )

Thanks

The altitude that provides best performance is right around 7,500' DA. Higher and power is lost due to lack of O2 and lower speed is lost due to drag.

Warmi,

Check out http://sportpilottalk.com/viewtopic.php?f=3&t=3627 for some actual numbers and conditions for my Sting S3. I suggest you replicate the conditions and compare.

Two major factors. Hull design and prop pitch. You're stuck with hull design, but prop pitch can go a long way to help. At 5400 rpm at WOT you are over pitched. There are absolutely no redeeming qualities in being over pitched. You lose climb, cruise and fuel economy, plus higher engine temps.
Set the prop to get 5600-5650 rpm WOT at you average altitude. You will increase all the above performance deficits.
With two Sting aircraft side by side and one only getting 5400 rpm WOT and the other getting 5600-5650 at WOT the 5600 rpm one will always out perform the 5400 one.

Backed up by real time testing.

roger lee wrote:Two major factors. Hull design and prop pitch. You're stuck with hull design, but prop pitch can go a long way to help. At 5400 rpm at WOT you are over pitched. There are absolutely no redeeming qualities in being over pitched. You lose climb, cruise and fuel economy, plus higher engine temps.
Set the prop to get 5600-5650 rpm WOT at you average altitude. You will increase all the above performance deficits.
With two Sting aircraft side by side and one only getting 5400 rpm WOT and the other getting 5600-5650 at WOT the 5600 rpm one will always out perform the 5400 one.

Backed up by real time testing.

Roger, he said cruise RPM of 5400. He said it has a take off RPM of 5400. If anything I think he may be under pitched with take off RPM that high on a slick airframe.

I will try again and record all numbers more carefully.

He said almost full throttle at 5400, but then says take off rpm was 5400. That part made no sense. If he was really at 5400 rpm at take off then his WOT in level flight would be well over the 5800 max. I took his 5400 at almost full throttle as more correct.

No matter which is correct to set up his Sting with the "BEST BALANCED" all around performance specs will be in that 5600-5650 rpm range in level flight. Since we don't have in flight adjustable props whatever take off rpm is what it is. For most of us that puts us around 4950-5050 +/- rpm at take off.

Since he said it would turn 5400 during take off I took the 5400 at almost full power to be in relation to the 5500 max continuous power, rather than having the throttle almost wide open.

OK, after doing some more flying here are the numbers for my sting:

- takeoff ground roll : 5400
- takeoff and climb - 5150-5200
- cruise WOT : 5450-5500 ( yellow )

Seems reasonable from my limited understanding of Rotax.

Warmi wrote:OK, after doing some more flying here are the numbers for my sting:

- takeoff ground roll : 5400
- takeoff and climb - 5150-5200
- cruise WOT : 5450-5500 ( yellow )

Seems reasonable from my limited understanding of Rotax.

When you say WOT is that what you really mean, or are you limiting it to 5500? For it to turn 5400 on the take off roll and then only turn 100 rpm more when you level off just doesn't sound right.

Well, that's what I saw yesterday and I was paying attention this time

I had 5400 on the ground when accelerating at full throttle, around 5180 or so when climbing out (taking off ) and then around 5500 ( +- 50 rpm ) at WOT at cruise. - basically every time with throttle jammed all the way forward as far as it could go.

We , again , were close to full gross and at 2200 feet we were getting about 105-108 KTS at WOT at cruise.

My takeoff RPM is ~5100rpm, and I am flatter-pitched than any other 912 flyer I know. My WOT rpm at 2000-3000ft is 5700-5750rpm if not a hair higher.

5400rpm on takeoff doesn't sound plausible, you'd have to wind it out to 5600rpm+ get any decent cruise speed out of that airplane, and WOT would be past the 6000rpm redline. If this is at all correct, that prop needs to be adjusted to be significantly more coarse.

Well, the takeoff speed was at about 5180 ( when lifting off ) ,the 5400 was on the ground when accelerating prior to lifting off , if that makes sense.

Was that 108 KT Indicated (IAS) or already computed to True (TAS). Also, approximately temperature?