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Old Jun 19, 2011, 11:36 PM
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Montague GPS Data Analysis

One of the side benefits of using the GPS loggers for scoring is the ability to analyze the logs and then use that analysis to improve your next flight. It might also give us additional information on the various glider designs we are using. With this in mind I did a quick review of four logs for four days of flying. I wanted to see if I could get some idea of the performance of the XC#10 racer and the Super Supra compared with the MXC. Attached is a chart showing the cruising speed in sinking air of 4 different teams.

I choose this data because I think speed between thermals is one of the most important performance aspects of any XC glider. When we cruise between thermal we are typically in sink and we should try to fly the glider as fast as possible. The problem is as we speed up the glider's sink rate increases rapidly. A glider that can go fast and still maintain a reasonable sink rate will have the advantage.

I don't know if the data is sufficient to make solid conclusions but the XC #10 racer was sure able to go fast, especially on Friday. I have looked at many of logs over the years and I do not recall seeing a cruising speed in sinking air of over 40mph. While the Super Supra did not seem to go as fast its hard to tell if that was because of the design. The Super Supra and its team did quite well throughout the contest. Keep in mind this is the speed in straight flight in sinking air over the entire flight while on course. The L/D's may seem low but these were measured while in sinking air and at higher than best L/D speed The data has been corrected for wind. There are many variables unaccounted for so its hard to say anything definitive but interesting none the less. Please feel free to comment.

John
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Old Jun 20, 2011, 12:58 PM
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Converted to a PDF in case you don't have WORD

- Bob -
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Old Jun 20, 2011, 02:11 PM
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I took your data and did a simple average on them to see if it was easier to see the trend.

MXC Team 647 L/D 10 MPH 34
MXC Team 273 L/D 9.75 MPH 31.5
SS Team 593 L/D 10.75 MPH 29.5
#10 Team 461 L/D 10.5 MPH 35.35

The Super Supra had the highest L/D but also at the lowest speed. If you bump it up a couple mph to a comparable speed with the rest then the L/D would drop off. The result would then be that #10 would have the highest L/D at the highest speed. That's quite dramatic.

It would help if they were in the same air at the same time but the four data points do help to make it a legitimate trend. Good Stuff !

Mike
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Old Jun 20, 2011, 02:45 PM
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Thanks for looking at this. It all validates my designer's ability.
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Old Jun 20, 2011, 03:45 PM
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Originally Posted by ThermalSeeker View Post
I took your data and did a simple average on them to see if it was easier to see the trend.

MXC Team 647 L/D 10 MPH 34
MXC Team 273 L/D 9.75 MPH 31.5
SS Team 593 L/D 10.75 MPH 29.5
#10 Team 461 L/D 10.5 MPH 35.35

The Super Supra had the highest L/D but also at the lowest speed. If you bump it up a couple mph to a comparable speed with the rest then the L/D would drop off. The result would then be that #10 would have the highest L/D at the highest speed. That's quite dramatic.

It would help if they were in the same air at the same time but the four data points do help to make it a legitimate trend. Good Stuff !

Mike
John, Mike...

I wonder how these factors figure into this analysis with regard to Super Supra. We never used reflex speed camber between thermals the entire 5 days, the only time we used reflex was on the final speed run to the finish on days 1,2,3 and 5 (landed out on day 4). Also, we miss-judged the altitude needed and the time to start each of these speed runs and ended up in reflex with a lot of down trim flying very fast and very innefficiently due to too much altitude. I would say that the day 5 short course flight between thermals would be a good one to look at and chop off the speed run past the last thermal we caught before turn 2 on the way back. All other days we were just in survival mode to make sure we finished the course.

Steve
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Old Jun 20, 2011, 04:15 PM
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Steve,

If you were not in reflex mode when cruising between thermals that would certainly account for the lower speeds shown.

It can be misleading to draw definitive conclusions from the small amount of data used for this analysis. Also, there are many unknowns and variables not taken into account. Each glider was flying thru different air at different times. One pilot may have been trying to fly faster than other pilots by pushing down elevator more or in your case not going into reflex mode.

Having said that, the data does show a fairly large speed advantage to XC #10. I guess this is not surprising since I believe Greg set out to design a fast glider. What is not clear is what kind of climb performance XC#10 is giving up in order to achieve the superior cruise performance. There were times at Montague this year our team needed every bit of climb performance we could muster in order to keep the flight going. If we had landed out even once we clearly we would not have won. So, depending on conditions climb performance can be critical.

The best way to really figure out the performance of the different planes would be to do testing of the type Dan Edwards and I did on the SBXC to obtain sink rates at any given airspeed. It might be worthwhile to meet out at cal valley one weekend just to do flight testing with all different XC designs. We could spend the evening crunching the numbers to see which plane is really the best. Of course "best" for one set of conditions might not be "best" for a different set of conditions.
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Old Jun 20, 2011, 04:40 PM
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Originally Posted by John Ellias View Post
Steve,

If you were not in reflex mode when cruising between thermals that would certainly account for the lower speeds shown.

It can be misleading to draw definitive conclusions from the small amount of data used for this analysis. Also, there are many unknowns and variables not taken into account. Each glider was flying thru different air at different times. One pilot may have been trying to fly faster than other pilots by pushing down elevator more or in your case not going into reflex mode.

Having said that, the data does show a fairly large speed advantage to XC #10. I guess this is not surprising since I believe Greg set out to design a fast glider. What is not clear is what kind of climb performance XC#10 is giving up in order to achieve the superior cruise performance. There were times at Montague this year our team needed every bit of climb performance we could muster in order to keep the flight going. If we had landed out even once we clearly we would not have won. So, depending on conditions climb performance can be critical.

The best way to really figure out the performance of the different planes would be to do testing of the type Dan Edwards and I did on the SBXC to obtain sink rates at any given airspeed. It might be worthwhile to meet out at cal valley one weekend just to do flight testing with all different XC designs. We could spend the evening crunching the numbers to see which plane is really the best. Of course "best" for one set of conditions might not be "best" for a different set of conditions.
John,

The only direct comparison between SS and #10 happened on day 5 on the way from TP2 to TP9 when both of us were flying thru the same air at roughly the same altitude. SS was fully loaded to 5kg, #10 was unballasted (I dont know the wing loading of #10 unballasted). Both of us were in cruise, no speed reflex. We were pacing them fairly even so clearly the higher wing loading of #10 when at full 5kg wieght is a factor in the 6mph advantage it has between thermals. SS wing loading is just under 15oz at full wieght and I think #10 is around 17oz fully ballasted.

I agree that good thermal ability is a hard thing to give up as over a multi-day event it is almost certain that a team will find themselves scratching at very low level, during day 4 we struggled below 200 meters most of the way from TP6 to TP7 which is a good testimonial to SS's low level thermal capabilities. Also, in order to get the higher wing loading you would need to go with less chord (#10) or with lower aspect ratio (MXC) which means you give up visibility in the case of #10. The 5 kg limit really is pushing us with the design compromises.

maybe the morning before the first Cal Valley task when there is no wind and very little thermal activity we could do some tests.

Steve
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Old Jun 20, 2011, 09:55 PM
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I have done some "for fun" full size glider testing. We would meet at the same altitude, eyeball to eyeball maybe 100 ft. apart flying at the same airspeed gradually speeding up to see who had the advantage. Being in close to the same air is essential.

I purpose we dial in and test our individual gliders between now and Cal Valley. Mostly camber/elevator settings. At Cal Valley we can compare our prepared planes in close to the same air.

It would be great to dedicate a day before the contest to do this as that is the only way it will happen.

Greg has an advantage in that the designer has shared camber settings.
I'm guessing the MXC settings but with serious testing it should get better.

Regards Dean
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Old Jun 20, 2011, 11:04 PM
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Steve,

I took a look at your flight on Saturday and the numbers are:

Avg. Speed in straight flight in sinking air - 36mph, L/D 13

The Super Supra looked much better that day than on the other days. Was there any major differences with how you flew on Saturday?

John
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Old Jun 21, 2011, 12:10 AM
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Originally Posted by John Ellias View Post
Steve,

I took a look at your flight on Saturday and the numbers are:

Avg. Speed in straight flight in sinking air - 36mph, L/D 13

The Super Supra looked much better that day than on the other days. Was there any major differences with how you flew on Saturday?

John
The only difference on day 5 with the short course is that we went full out knowing that it would be easy to take a second round if we landed out. The long tasks on the first four days we were simply trying to finish and milking every thermal we could find which meant we were not too concerned with speed, just distance, and there really wasn't much of a chance of doing a second round. The FAI scoring, similar to the Winscore program, means that finishing the course becomes the number one priority.

one thing that skews the numbers on day five is that we hit large amounts of lift between thermals so we really need to test this during zero lift conditions in early morning....

Steve
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Old Jun 21, 2011, 12:40 PM
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I could not understand why #10ís speed was so much lower on Wednesday but then I remembered that was the day we missed the start gate so all that time milling around at the field (while we thought we were off the cource/clock) was adding time and no millage so that may have been what brought our stats down for that day. Or depending on how those stats were calculated off the GPS tracks, the number may be legit, but poor because we would not have been aggressively flipping into speed while milling around at the start gate. What do you think?
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Old Jun 21, 2011, 02:07 PM
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Tuesday and Wed we flew with the old trim settings on cruise and speed, more up. Thursday and Friday we flew with some more down trim which I think fully optimized the capabilities of the plane. Saturday I backed off a bit because it was cloudy but the GPS was destroyed anyway.
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Old Jun 21, 2011, 04:14 PM
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Bob McGowan wrote...... I could not understand why #10ís speed was so much lower on Wednesday but then I remembered that was the day we missed the start gate so all that time milling around at the field (while we thought we were off the cource/clock) was adding time and no millage so that may have been what brought our stats down for that day. Or depending on how those stats were calculated off the GPS tracks, the number may be legit, but poor because we would not have been aggressively flipping into speed while milling around at the start gate. What do you think?
Bob, when I get a chance I will double check the Wednesday flight. I tried to use the portion of the flight beginning after the glider crossed the starting line for the last time and ending when the glider crossed the finish line. Also, the numbers reflect only those portions of the flight where the glider is flying "straight" and sinking. It does not include any "circling" flight. I used those portions of the flight to try limit the analysis to the times when we were trying to fly fast. There should be no meandering time included in this analysis.

John
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Old Jun 21, 2011, 04:23 PM
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Originally Posted by John Ellias View Post
I tried to use the portion of the flight beginning after the glider crossed the starting line for the last time...
My understanding is that on this flight we crossed the starting line while trying to thermal up. Our intention was to cross it again later after we had gained good altitude (to get that "last time" crossing clean racing start) but we flew wide of the start line missing it.

(I think John knows this, but I thought I'd clarify for the other readers out there.)
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