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Takeoff/Climb performance

Traash

Well Known Member
Flying IFR in high Density Altitude conditions reminded me that I needed a better way to calculate takeoff and climb performance. I used the online interactive Koch chart (takeofflanding.com) to tabulate performance changes to takeoff distance and climb rates. This gave me percentage changes from sea level performance. I took the Vans published sea level takeoff distance and Vy numbers and developed an Excel spreadsheet to calculate TOD (Takeoff Distance) and CLB (Climb rate) adjusted for Density Altitude. Since Vy is close to 90K for most RV's and my initial deck angle of 10* gives me 90k, I calculated the feet per nautical mile at that speed which can be compared to Departure Procedure requirements. Using the known length of the runway centerline stripes (200' between stripes) and the Density Altitude and climb gradient displays on the G3X I did 4 comparisons of TOD and FT/NM at DA's from 7 - 10K'. They all compared favorably. The table is a bit on the conservative side. I found out that I can't takeoff into minimum IMC at Gunnison, CO and must use the VCOA (Visual Climb Over Airport) method to depart IFR.

The tables are derived using Van's published numbers. If you test your aircraft and find different results, you can change the sea level TOD and CLB entries and the excel spreadsheet will do the remaining calculations for you.
 

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Another Resource AC 90-89B

Another resource for estimating takeoff performance is Figure 1 in AC 90-89B Amateur-Built and Ultralight Flight Testing Handbook. The chart is based on wing loading and is also conservative.

One other consideration is runway surface. The British CAA publishes an informative leaflet on turf operations here with some performance effect rules of thumb here: https://publicapps.caa.co.uk/docs/33/20130121SSL07.pdf

Fly Safe,

Vac
 
Frankly those climb rates look disappointing to me. At max gross, it looks like you're looking at 100 FPM between 12,000 and 13,000 feet. That would therefore be the plane's service ceiling, over 3,000 feet less than the brochure (the 235 HP engine), barely enough to fly into Tahoe, and right about where an old Cessna 172 is. You say conservative. I hope you mean conservative on the order of 20-30%.
 
Looking at a C-172N manual, takeoff distance at 7000' - at 20C is about double the distance at SL at 20C. Which would be way higher than 7000' DA. So right off the bat something looks amiss. Your calculations show greater degradation in take off performance than the 172N POH.
 
Nicely done

Joe,

Nicely done. Gunnison is an eye-opening example. An excellent first approximation. Thanks for posting this.

If we're trying to get out of Gunnison (for example), I think we could possibly achieve a little higher climb gradient (higher feet/nmi) by flying Vx rather than 90kt. (Although Vx and Vy converge at high altitude, to 90kt will be pretty close).

Did you intend to attach the Excel sheet? You mentioned it in your last sentence, but I don't see it attached.
 
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While the TOD numbers seem in line with expectations, the FPM rates seem really low. Even at full gross, I get substantially better than 350 at 10,000' at 130+ KTAS. I don't think I am even that low at 14,000' and that is while climbing at 130 KTAS, though I suppose that may be at 90 KIAS (never really noticed).

I took off from Erie, CO one afternoon at full gross. Runway was around 5K' and DA was 11.5K. Didn't really measure, but was off the pavement, in ground effect by less than the half way point of the runway.

Larry
 
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Fully agree with IR172

I fully agree with Larry on this.
I very seldom use "90kts" or Vy for climb out and as Larry pointed out, climbing at 130kts you still climb well over 300 fpm at full gross.
I am one to err on the side of caution but limiting your performance with
numbers that are off by 30% is not helping you or anyone else.
The only real numbers for you to use are those that you have acquired during your 40 hours phase one tests at full gross.
I flew 10 of my 40 hours at full gross and in my RV-10, climb rate at full gross is well above 350fpm at 10,000.
 
This falls into the category of "Something is better than Nothing".

The tables aren't based on any testing. They are derived from Van's published numbers and a standard Koch chart.

My takeoff distances were very close. I got better than derived climb rates. Accurate testing that is corrected for DA will surely give better accuracy.
 
Joe,

Nicely done. Gunnison is an eye-opening example. An excellent first approximation. Thanks for posting this.

If we're trying to get out of Gunnison (for example), I think we could possibly achieve a little higher climb gradient (higher feet/nmi) by flying Vx rather than 90kt. (Although Vx and Vy converge at high altitude, to 90kt will be pretty close).

Did you intend to attach the Excel sheet? You mentioned it in your last sentence, but I don't see it attached.
Forums don't accommodate posting of an Excel spreadsheet.
 
Flight Data

RV-10 N31TD, 31 Sep 2021, 2244lbs

Flight data: https://apps.savvyaviation.com/flights/5238942/97225197-56f5-4724-aaa4-454f35c15144

Excel data: https://1drv.ms/x/s!AgyQUSm6uO_2hpMYz5ubITmJNfoi5Q?e=Orfsqb

Climb gradient graph and data attached (.jpg)

Observation: RV-10 flight data shows climb rate well in excess of what Koch chart predicts. Example: at 8224' PA, 65°F, Koch predicts ~78% rate of climb reduction. I saw rate closer to 48% reduction (from Van's sea level spec).


Caveats: Just one flight. Airspeed a bit wobbly. Formulas came from Google searches. I'm not a flight test engineer. Peer review welcome.
 

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Tim, your real world testing and data posting was exactly what I was hoping for by posting my original info.

Your data seems in line with my experiences although I didn't log anything since I was on a vacation trip. I plan on doing some real world testing later on.
 
Reviving this old thread about takeoff and climb performance at high DA.

Does anyone have the spreadsheet that is referred to in the 1st post in this thread. I sent a PM to Joe but haven't heard back yet. Alternatively, has anyone found a takeoff/climb calculator that can be customized for an RV-10 (outside of using the Koch calculator)?

Thanks,

Vas
 
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