XC#10 in a series, Giant Icon? - RC Groups
Jun 07, 2010, 12:53 AM
Master of the Wind
Discussion

# XC#10 in a series, Giant Icon?

#8 is a success with a 7 hour 90 mile flight, a 1 hour LSF 5 flight in the bag, and countless miles on the road with a variety of pilots. Max altitude 1522m, a full yank from a dive twice, and plenty of landings on various surfaces with never a scratch on the T-tail.

#9 should be in the hands of a customer shortly and I expect great things.

Now it is time to sit back, slow down, and really think about what the next one will look like. I have one more fuse in the corner, and this should be it for a while. I can stop anytime. Really.

This design will be data and analysis driven. JW has patiently pointed me in the right direction over the past few years and it is starting to sink in. I'm not an aero professional but the tools are public and anybody stubborn enough to stick with it should be able to go through this design process.

I have some very interesting first look results but I need to clear something up before I go on. Does the max visible height scale linear with the chord or does it follow some other function? As a starter I took the fraction of a degree that a given chord takes up in a circle and plotted it against the altitude for three different chords. If my math is right it is not linear, and the higher you go, the more advantage the 14" (red) chord has. Will haze make this curve more linear, or worse yet, bend it the other direction, and does the amount of haze matter? Open for discussion.

### Files

 Jun 07, 2010, 01:10 AM Registered User Congratulations, Greg. It sounds like all of you effort has paid off and you have a great recipe for building these ships. I would bet that the "visibility" (the light wave propagation) through the lower atmosphere is crazily non-linear. The variations in pollutants, dust, and other junk in the air vary on a daily, if not hourly, basis. Really looking forward to seeing this plane in action, Mike
Jun 07, 2010, 04:16 AM
Registered User
Quote:
 Originally Posted by G Norsworthy #8 is a success with a 7 hour 90 mile flight, a 1 hour LSF 5 flight in the bag, and countless miles on the road with a variety of pilots. Max altitude 1522m, a full yank from a dive twice, and plenty of landings on various surfaces with never a scratch on the T-tail. #9 should be in the hands of a customer shortly and I expect great things. Now it is time to sit back, slow down, and really think about what the next one will look like. I have one more fuse in the corner, and this should be it for a while. I can stop anytime. Really. This design will be data and analysis driven. JW has patiently pointed me in the right direction over the past few years and it is starting to sink in. I'm not an aero professional but the tools are public and anybody stubborn enough to stick with it should be able to go through this design process. I have some very interesting first look results but I need to clear something up before I go on. Does the max visible height scale linear with the chord or does it follow some other function? As a starter I took the fraction of a degree that a given chord takes up in a circle and plotted it against the altitude for three different chords. If my math is right it is not linear, and the higher you go, the more advantage the 14" (red) chord has. Will haze make this curve more linear, or worse yet, bend it the other direction, and does the amount of haze matter? Open for discussion.
my 2c. I think the most important thing for visibility is air quality and angle of the aircraft in relation to the pilot. I would not have thought my 50 something mark one eyeballs could see a 12" chord at over 5000 ft till I proved it to myself at the last Davis event. That had everything to do with the perfect air clarity that day and with the fact we kept our SBXC nearly straight overhead in cruise while that high up. When it is straight overhead (say within a 10 degree cone) you get the full benefit of the wide chord visibility when cruising or thermalling. When it is off to the side, say 45 degrees, for a given AGL you are not only further away in actual distance (hypotenuse of the triangle) but the angle of sight reduces the effective chord for visibility (bottom surface of wing is no longer perpendicular to the pilots eyes). a double whammy especially when there is crud and haze in the air like there is during the majority of flying days. and thermalling at high AGL and off to the side like that causes the plane to pretty much dissappear every half circle due to the angles. Now, we often dont have a choice when it comes to thermal location and end up following them off to the side many times but we do have a choice where to position the glider while in cruise and straight overhead is the safest place to be while at extreme altitude.

the problem I have with flying it directly overhead is it can become damned uncomfortable on my neck. I need a lazyboy recliner or something. two lazyboys bolted to a big flatbed truck.. now we're talking...
 Jun 07, 2010, 04:00 PM Registered User Greg - I think I know where you are going with this. I like your trend towards Icon planform As for chord - an example is the red on my Victor. In most instances at Davis it is far more visible than a comparable black bottomed aircraft of the same chord. So chord alone is one factor, but color and specturm of light shifted due to particulants is another. And you cannot account for all conditions - just how much you are willing to compromise to get your target AR
Jun 07, 2010, 04:09 PM
Registered User
Quote:
 Originally Posted by jgs99v Greg - I think I know where you are going with this. I like your trend towards Icon planform As for chord - an example is the red on my Victor. In most instances at Davis it is far more visible than a comparable black bottomed aircraft of the same chord. So chord alone is one factor, but color and specturm of light shifted due to particulants is another. And you cannot account for all conditions - just how much you are willing to compromise to get your target AR
Jack,

I had a different experience with the red bottom. Last year at Cal Valley there was a lot of dust in the air. The red bottom of Jim Rolle's SBXC was very difficult for me to see at 3000 ft. When we got close to Dean's MXC with its black bottom I could see the black was easier for me to see in dirty air conditions (we were both at approx the same height). Dark blue and black look the same to me at altitude.

Steve
 Jun 07, 2010, 06:15 PM Registered User Seems like for a given sprectrum we all have preferences That is something to keep in mind. You should time for me in next weeks TD contest if I can attend. Red is not red - there are significant differences in reflection, illumination etc....
 Jun 09, 2010, 12:52 AM Master of the Wind Here is a sketch of the geometry I used to calculate the visibility angle for a given chord. The equation for the angular portion of a cylinder taken up by the chord width as seen from the ground is Angle=2xArctan(0.5xchord/altitude). Also two graphs of the visible angle vs the altitude using 3 different chords, 12" 13" and 14". Note on the full scale the slope of the lines gets flatter as the altitude increases. If you look at the expanded scale, this means that for a given angle the larger chord is visible farther away not just in a linear fashion, but more. For example, at an angle of .014 degress the altitude difference between the 12 and 14" chord is 200m, while at .012 degrees, the difference is almost 250m. On a super clear day this means the wider chord has an advantage flying in the risky but worthwhile range of 1250-1750m. On a hazy day neither plane is likely to be comfortably visible above 1250 and the advantage may be less. For the purposes of this analysis, it is probably reasonable to assume a linear relationship between chord and max visible altitude.
 Jun 09, 2010, 12:57 AM Master of the Wind Does anybody have GPS data from the Sacramento contest or any other contest that shows a higher climb rate at higher altitude? I don't need the 3d, just the profile view as plotted by the SkyTrace software. I have both my first lap and some data from another contest that shows above 1000m the slope of the climb curve is a straight line. Meaning there is an energy advantage flying high but maybe not always a climb rate advantage. I know it "feels" like the lift is stronger way up, but is it really true in the ranges we fly?
Jun 09, 2010, 02:21 PM
Registered User
Quote:
 Originally Posted by G Norsworthy Does anybody have GPS data from the Sacramento contest or any other contest that shows a higher climb rate at higher altitude? I don't need the 3d, just the profile view as plotted by the SkyTrace software. I have both my first lap and some data from another contest that shows above 1000m the slope of the climb curve is a straight line. Meaning there is an energy advantage flying high but maybe not always a climb rate advantage. I know it "feels" like the lift is stronger way up, but is it really true in the ranges we fly?
Greg, I dont know if rate of climb is greater but obviously there is a tremendous potential energy advantage at 4000 ft vs 2000 ft which allows more selectivity. Can choose to fly straight thru weaker thermals with greater confidence that something stronger is within range. also, I think thermals are bigger in area at high altitude which is another energy advantage

in the Skytrace plot attached it seemed that once we were above 4000 ft AGL the lift was everywhere. the .stg file is too big to attach here

### Images

 Jun 09, 2010, 03:34 PM Master of the Wind Steve, Can you show the slope between 1800-2100 seconds vs the slope from 2900-3100 sec? This will show the difference between a lower, weaker thermal and a stronger, higher one. Greg
Jun 09, 2010, 04:29 PM
Registered User
Quote:
 Originally Posted by G Norsworthy Steve, Can you show the slope between 1800-2100 seconds vs the slope from 2900-3100 sec? This will show the difference between a lower, weaker thermal and a stronger, higher one. Greg
looks like average climb between 1800-2100 seconds was about 200 ft/min. average climb between 2900-3100 seconds was 655 ft/min

### Images

Jun 09, 2010, 05:31 PM
Registered User
Quote:
 Originally Posted by TrekBiker looks like average climb between 1800-2100 seconds was about 200 ft/min. average climb between 2900-3100 seconds was 655 ft/min
Steve, select the cross hair option (right), then select start and finish points and the program will tell you the climb rates.

JT
Jun 09, 2010, 05:40 PM
Registered User
Quote:
 Originally Posted by jtlsf5 Steve, select the cross hair option (right), then select start and finish points and the program will tell you the climb rates. JT
ok, that worked better.

for the 1800-2100 sec thermal avg climb was 217, max climb was 281 ft/min. 1075 ft alt gain in 5 min from 2885 ft agl to 3960 ft agl.

for the 2900-3100 sec thermal avg climb was 682 ft/min, max climb rate was 967 ft/min. 2127 ft alt gain in 3.1 minutes from 3135 ft agl to 5262 ft agl

thanks for the tip JT

### Images

Jun 10, 2010, 01:57 AM
Registered User
Quote:
 Originally Posted by TrekBiker ok, that worked better. for the 1800-2100 sec thermal avg climb was 217, max climb was 281 ft/min. 1075 ft alt gain in 5 min from 2885 ft agl to 3960 ft agl. for the 2900-3100 sec thermal avg climb was 682 ft/min, max climb rate was 967 ft/min. 2127 ft alt gain in 3.1 minutes from 3135 ft agl to 5262 ft agl thanks for the tip JT
Now you're usin' all the tools, compadre.
 Jun 10, 2010, 10:08 AM Master of the Wind OK there is my evidence I will keep cranking on the model.

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