True Airspeed in RV-10 - Page 5

Kevin Horton · #41 10-24-2006, 05:48 AM

Quote:

Originally Posted by aadamson

Kevin, maybe I'm just not thinking straight (wouldn't be the first time), but doesn't the 3 legs of the triangle factor out the wind? Maybe the formula needs to be changed to use the triangle calculator on various websites to provide TAS. You could average your 5 numbers, then plug each average into the calculator to give you your corrected speed, then use that. That would negate the wind effect I believe.

You can do runs in as many different directions as you like - if you average the results it will not equal the TAS. For example, using the 3 runs 120 deg apart method touted earlier:

Let's assume the TAS is 180 kt, with a 30 kt wind from 270. The runs are done with headings of 360, 120 and 240. If do the calculations, you'll find the ground speeds for each run are:

360 deg: 182.5 kt
120 deg: 206.5 kt
240 deg: 154.7 kt
average = 181.2

This isn't far off the 180 TAS, but the error goes up substantially as the wind speed increases. If the wind speed is 50 kt (not unheard of - I've see more than 50 kt at 6000 ft many times), the average ground speed is now 183.5 kt.

cstanley · #42 10-27-2006, 09:49 PM

A few months ago, I read a thread which I can only characterize as a "rant" about excessive heat under the belly and in the tunnel. I'm wondering whether those of you with completed -10's and apprciable hours are seeing this issue repeated, or if it was an isolated incident. I've been planning for how to deal with it, but don't want to add the weight/time/effort/cost to do so if it is not a typical condition in the design.

n2faith2 · #43 10-28-2006, 12:12 AM

While building my 10 I became concerned about tunnel heat because of all the posts. I considered all the options presented (even those in left field) and decided I'd wait and see if I actually experienced the problem before trying to "fix"it. I'm glad I waited. My tunnel is actually cool to the touch. Front and rear. I attribute that to two things.........RPV around the heat box and Vetterman exhaust. My addl 2 cents..........My MT prop is as smooth as silk and my Barrett Precision Engine purrs. My numbers are the same as Vics'.

Bill Stegemann
N545RV

Jim & Julie Wade · #44 10-28-2006, 07:44 AM

My 2 cents worth!! In intalled heat valves no sealer. Used 5/8 foam insulation from Aircraft Spruce in all the floor and walls of the tunnel. NO HEAT PROBLEMS!!!!!!! Have Vetterman exhaust. Used the heat once this week, works GOOD!!! Have also flown in 90 degree weather no heat problems.
Jim
40383
N369JW

glenmthompson · #45 10-30-2006, 05:17 AM

Quote:

Originally Posted by cstanley

A few months ago, I read a thread which I can only characterize as a "rant" about excessive heat under the belly and in the tunnel. I'm wondering whether those of you with completed -10's and apprciable hours are seeing this issue repeated, or if it was an isolated incident. I've been planning for how to deal with it, but don't want to add the weight/time/effort/cost to do so if it is not a typical condition in the design.

Hey Stanley...Come on by FD38 sometime, fly our 10, look at the build, feel the still very warm tunnel after several fixes, see the scars on my leg and see if you can still call my thread a rant. I guess Vans was also ranting when they came out with one of their rare SB?s addressing this very problem...... I also thought this thread was about TAS in the 10...??? And once again, our numbers are BETTER than Vans....Oops, I fell off my soap box.
Glen

ScottSchmidt · #46 11-27-2006, 02:50 PM

This weekend my wife and I went to Tucson AZ for a fun trip and this was also the first flight that I had my all my wheel pants and fairings on. I put them on the night before the trip and took the plane out for a quick flight and I could not believe the difference in airspeed. At 24.5 inches and 2500 RPM my TAS was 181 knots. They definately add around 10 - 15 knots.

Here are some numbers from the trip.

I was cruising at 10,500 ft., 19.4 inches, 2340 RPM, 13.4 GPH, (around 60 deg. rich of peak) and I was seeing TAS of 165 to 167.

Coming home from Tucson on Sunday I had a nice tailwind and saw ground speeds around 190 knots the whole way. I can't tell you how much fun we were having cruising at 218 mph.

dan · #47 11-27-2006, 04:18 PM

Question about crosswind calculations/indication... In one of those photos it shows winds as 057 at 3, but a xwind component of 4? Am I not interpreting that correctly? Rounding error?

Kevin Horton · #48 11-27-2006, 04:33 PM

Quote:

Originally Posted by dan

Question about crosswind calculations/indication... In one of those photos it shows winds as 057 at 3, but a xwind component of 4? Am I not interpreting that correctly? Rounding error?

I'm betting that the two items are calculated at different times, and the sensed conditions changed ever so slightly between the times the wind and cross wind were determined.

This is very much a case of "measure with a micrometer and cut with an axe". The precision of the wind calculations is very dependent on the heading and airspeed accuracy. There is probably enough error in both of those to make the wind values plus or minus several knots.

ScottSchmidt · #49 11-27-2006, 05:01 PM

I might have bumped the rudder a little, or the wind may have changed a little but it seems like the X-Wind component should never be more than the absolute no matter what type of calcuations are going on unless they are different algorithms that are being processed at the same time and one is not a function of the other.

All I really know is I had some great tunes playing, my performance numbers were exactly what Van's promised, and the scenery was to die for.

Big Cottonwood Canyon

Lake Powell

Grand Canyon

Sedona

Monument Valley

Randy DeBauw · #50 11-29-2006, 10:14 PM

When I flew with Ken Kruger to do a speed run we flew my plane at 8000 adj. alt., full throttle, 2500 rpm. We flew a box pattern and use the ground speed of the gps to get the speeds. He used those numbers to come up with top speed. At 8000 ft. full throttle is very close to 75% power. As it turned out my speed was low because my ailerons were not set correctly and was adding extra drag. I have not rerun the box since the ailerons have been set correctly. By the way flying at 8000 ft. adj and full throttle we were burning 19.2 gph. Randy DeBauw 40006.