Michael's Sonex #145

[gammaxy]

Great report.

At first glance, your performance seems to be similar to mine. Probably a touch faster in cruise and climb which is expected with your larger engine. Where you say 120knots at 3100rpm, I need ~3150rpm with my 54x46 propeller which is WOT for me.

Is the 152knots you list for WOT a typo? I wrote up a long response in amazement of your truly awesome speed, hoping I'll be able to replicate it when I realized it was more likely to be a typo. Oh well... I can still dream :-)

[MichaelFarley56]

Congratulations on completion of Phase 1 Michael! Your airplane looks fantastic!

[rizzz]

Great report.

At first glance, your performance seems to be similar to mine. Probably a touch faster in cruise and climb which is expected with your larger engine. Where you say 120knots at 3100rpm, I need ~3150rpm with my 54x46 propeller which is WOT for me.

Is the 152knots you list for WOT a typo? I wrote up a long response in amazement of your truly awesome speed, hoping I'll be able to replicate it when I realized it was more likely to be a typo. Oh well... I can still dream :-)

Its not a typo, 152 is what I have experienced.
I have a 54x48 Prince P-Tip, WOT straight and level @ 2000ft I see about 3400-3500rpm.\

Edit: I'll reconfirm the 152 as I realize it is quite high, perhaps I misread the IAS?

[WaiexN143NM]

Hi Michael,
Wow! Very nice! What kind of paint? Very professional report.
Not to nit pick but check a few dates. A little ahead in the calendar.!
Congrats again!
Waiex143NM

[gammaxy]

Edit: I'll reconfirm the 152 as I realize it is quite high, perhaps I misread the IAS?

Since the power required in cruise flight approximately increases with velocity cubed, I was using the rule of thumb:
Power Required Ratio=(Velocity Ratio)^3

I used 120knots as my max speed, so the velocity ratio is 152/120=1.26
Power Ratio = 1.26^3 = 2.03

I don't think you have twice the power available at WOT (or that I have THAT might extra drag).

I believe I'm probably leaving a few knots on the table due to slightly too course of a propeller (according to Sonex's dyno sheet), so if we assume our drag is about the same and assume I should be able to go a little faster, then I estimate your max speed should be about:
123 knots * (2400cc/2180cc)^(1/3) = 127 knots.

I noticed that your accelerated stalls were all at the same airspeed. Were these level turns? Were you pulling 2G's in the 60 degree turn? If so, I'd expect the airspeed of the stall to be ~36knots*1.41=~51knots. Your video showed how the static port on the wing leads to altitude errors while maneuvering. It seems like your data might be showing the same effect for airspeed.

It does make me curious about your Vx calculations, since a static error at slow speeds would probably make your true airspeed calculation incorrect, and yield too steep of an estimated flight path angle.

Anyway, thanks for sharing the report. It's really well done. Certainly better than what I did. Only reason I'm nitpicking is you have presented so much interesting data so conveniently.

[rizzz]

Edit: I'll reconfirm the 152 as I realize it is quite high, perhaps I misread the IAS?

Since the power required in cruise flight approximately increases with velocity cubed, I was using the rule of thumb:
Power Required Ratio=(Velocity Ratio)^3

I used 120knots as my max speed, so the velocity ratio is 152/120=1.26
Power Ratio = 1.26^3 = 2.03

I don't think you have twice the power available at WOT (or that I have THAT might extra drag).

I believe I'm probably leaving a few knots on the table due to slightly too course of a propeller (according to Sonex's dyno sheet), so if we assume our drag is about the same and assume I should be able to go a little faster, then I estimate your max speed should be about:
123 knots * (2400cc/2180cc)^(1/3) = 127 knots.

I noticed that your accelerated stalls were all at the same airspeed. Were these level turns? Were you pulling 2G's in the 60 degree turn? If so, I'd expect the airspeed of the stall to be ~36knots*1.41=~51knots. Your video showed how the static port on the wing leads to altitude errors while maneuvering. It seems like your data might be showing the same effect for airspeed.

It does make me curious about your Vx calculations, since a static error at slow speeds would probably make your true airspeed calculation incorrect, and yield too steep of an estimated flight path angle.

Anyway, thanks for sharing the report. It's really well done. Certainly better than what I did. Only reason I'm nitpicking is you have presented so much interesting data so conveniently.

Thanks for the detailed analysis Chris,

As mentioned before I will need to re-confirm the number as I realize it is quite high.
However I can assure you it is more than 127KT, If you look at the detailed flight reports in my document you'll see that I only did the WOT tests once or twice, however, I have pushed well beyond that 127KT number on a few occasions.
Anyway, I'll make sure I've got the GoPro running when I do the test again, I'll put it on YouTube.

[rizzz]

Edit: I'll reconfirm the 152 as I realize it is quite high, perhaps I misread the IAS?

Since the power required in cruise flight approximately increases with velocity cubed, I was using the rule of thumb:
Power Required Ratio=(Velocity Ratio)^3

I used 120knots as my max speed, so the velocity ratio is 152/120=1.26
Power Ratio = 1.26^3 = 2.03

I don't think you have twice the power available at WOT (or that I have THAT might extra drag).

I believe I'm probably leaving a few knots on the table due to slightly too course of a propeller (according to Sonex's dyno sheet), so if we assume our drag is about the same and assume I should be able to go a little faster, then I estimate your max speed should be about:
123 knots * (2400cc/2180cc)^(1/3) = 127 knots.

I noticed that your accelerated stalls were all at the same airspeed. Were these level turns? Were you pulling 2G's in the 60 degree turn? If so, I'd expect the airspeed of the stall to be ~36knots*1.41=~51knots. Your video showed how the static port on the wing leads to altitude errors while maneuvering. It seems like your data might be showing the same effect for airspeed.

It does make me curious about your Vx calculations, since a static error at slow speeds would probably make your true airspeed calculation incorrect, and yield too steep of an estimated flight path angle.

Anyway, thanks for sharing the report. It's really well done. Certainly better than what I did. Only reason I'm nitpicking is you have presented so much interesting data so conveniently.

Thanks for the detailed analysis Chris,

As mentioned before I will need to re-confirm the number as I realize it is quite high.
However I can assure you it is more than 127KT, If you look at the detailed flight reports in my document you'll see that I only did the WOT tests once or twice, however, I have pushed well beyond that 127KT number on a few occasions.
Anyway, I'll make sure I've got the GoPro running when I do the test again, I'll put it on YouTube.

Well I'm pretty sure I can not have been that far off with my 152KT number.
I have no video footage from that particular flight when I did the actual extended WOT test, however, I just went through the other video footage I made over various previous flights and found one where I actually pushed the throttle wide open, I've taken a short clip and put it on my dropbox account for now, I'll put it on YouTube as well when I get home (at work now :oops:), here's the link:

https://www.dropbox.com/s/4vxsogj38altt ... d.mp4?dl=0
(with dropbox, it's probably best to download the video before playing it, if you play it in your browser it will reduce in quality)

Edit: I just got home and uploaded the video to YouTube as well, here's the link:
https://youtu.be/tqVj2IJEbHI

Although it's hard to see the actual numbers on the airpeed indicator, they go up in 20KT steps so you you can make out where the needle is.
I start off at just below 120KT climbing to 1800ft, then I open the throttle wide open, maintaining 1800ft (close anyway), the airspeed approaching 145KT within 30 seconds or so before I decide to back it off (I probably did not have the courage yet at the time to push it further, also one of the EGT alarms started going off on the MGL which can be seen as well).
The final number might not be 152KT but I believe it will be closer to that than to 127KT ;) .
As promised, I will make a video of a more extended test when I get the chance.

[gammaxy]

Great video. You've definitely got a fast VW-powered Sonex.

I picked out some landmarks and calculated your average speed over 0.98 NM (once you had accelerated). It took you 28 seconds (+/- 1) for an average groundspeed of 126 knots (+/- 4).

Your airspeed calibration table shows your ASI reads about 10.5% high at 125 knots, so at 145 knots, your calibrated airspeed would be 131 knots. This seems consistent with the ground speed in the video (and the peak speed should be higher than the average over those 28 seconds), especially since I have no idea what the winds were :-)

I flew in a sport air race behind a Jabiru 3300 Sonex who only beat me by 10mph. I think his carburetor was not tuned very well, or he might not have been pushing it that hard. You might be able to beat him :-)

[rizzz]

Great video. You've definitely got a fast VW-powered Sonex.

I picked out some landmarks and calculated your average speed over 0.98 NM (once you had accelerated). It took you 28 seconds (+/- 1) for an average groundspeed of 126 knots (+/- 4).

Your airspeed calibration table shows your ASI reads about 10.5% high at 125 knots, so at 145 knots, your calibrated airspeed would be 131 knots. This seems consistent with the ground speed in the video (and the peak speed should be higher than the average over those 28 seconds), especially since I have no idea what the winds were :-)

I flew in a sport air race behind a Jabiru 3300 Sonex who only beat me by 10mph. I think his carburetor was not tuned very well, or he might not have been pushing it that hard. You might be able to beat him :-)

All sounds like a plausible explanation, thanks fr that. I am certainly indicating high at that speed as my CAS calculations suggest.
At least I'm pretty confident now I was not seeing things when I did my WOT tests the other day, I'm going for a fly tomorrow so I'll reconfirm things and try to get over 150 again, plus my new Clarity Aloft headset arrived yesterday, gotta go test that one out too :) .
You've got me wondering now about my accelerated stall tests although I'm pretty sure those were accurate too, I remember watching the airspeed very closely while flipping pretty much upside-down when I stalled :). I might do them again as well while I'm at it, they're fun.
It looks like I'm not the only one having come to this conclusion though, have a look at this guy's POH, page 12:
http://sonex883.com/Sonex%20pilot's%20operating.doc

[gammaxy]

I re-watched your video and noticed the airspeed does seem to respond immediately to angle-of-attack change at the beginning of your maneuvers.

It's kindof tricky, because you expect to slow down at a loop or roll entry, but it seems to respond so immediately and stop decelerating so suddenly when you unload that I bet its mostly caused by the same static system error we noticed before.

I haven't watched the ASI during an accelerated stall closely before, but after reproducing the other effects I noticed in your video, I believe what you saw is correct.

To me, the interesting detail is that at least up to 2 G's the airplane seems to stall at the same IAS. This might be a desirable "feature" and cause the ASI to work more like a lift reserve indicator.