VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.


Go Back   VAF Forums > Main > Safety
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 09-09-2021, 07:43 PM
Traash Traash is offline
 
Join Date: Apr 2007
Location: Montgomery, TX
Posts: 56
Default Takeoff/Climb performance

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.
Attached Thumbnails
Click image for larger version

Name:	18123D1F-7FC8-4E86-BB52-59226AEBF493.jpeg
Views:	54
Size:	187.5 KB
ID:	15654  Click image for larger version

Name:	B6869F34-49BC-4E7C-8ED6-6587CB789EB2.jpeg
Views:	44
Size:	181.5 KB
ID:	15655  Click image for larger version

Name:	F2244649-85CF-48AD-8B8C-3D9A29BC15F0.jpeg
Views:	40
Size:	147.0 KB
ID:	15656  
__________________
Joe
Reply With Quote
  #2  
Old 09-10-2021, 06:11 AM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
Posts: 487
Default 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
__________________
Mike Vaccaro
RV-4 2112
Niceville, Florida
Reply With Quote
  #3  
Old 09-11-2021, 02:21 AM
gotyoke gotyoke is offline
 
Join Date: Jul 2020
Location: Placerville, CA
Posts: 50
Default

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%.
__________________
RV-14A Emp and wings kits ordered
Reply With Quote
  #4  
Old 09-11-2021, 01:35 PM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 295
Default

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.
__________________
RV6A in phase 2 as of April 2016
Donation made Oct 2020
Reply With Quote
  #5  
Old 09-12-2021, 07:25 AM
Tim Lewis Tim Lewis is offline
 
Join Date: Aug 2006
Location: Bristow, VA
Posts: 165
Default 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.
__________________
Tim Lewis
CFI, A&P
RV-10 N31TD - 1450 hrs
RV-6A N47TD - 1100 hrs (sold)

Last edited by Tim Lewis : 09-12-2021 at 07:47 AM.
Reply With Quote
  #6  
Old 09-12-2021, 08:03 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,543
Default

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
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019

Last edited by lr172 : 09-12-2021 at 08:09 AM.
Reply With Quote
  #7  
Old 09-12-2021, 08:09 PM
N427EF N427EF is offline
 
Join Date: Oct 2005
Posts: 1,555
Default 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.
__________________
Ernst Freitag
RV-8 finished (sold)
RV-10 IO-540 8.5:1
Running on 91 Octane E10 mogas since 2011
Don't believe everything you know.
Reply With Quote
  #8  
Old 09-13-2021, 12:34 AM
Traash Traash is offline
 
Join Date: Apr 2007
Location: Montgomery, TX
Posts: 56
Default

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
Reply With Quote
  #9  
Old 09-13-2021, 12:38 AM
Traash Traash is offline
 
Join Date: Apr 2007
Location: Montgomery, TX
Posts: 56
Default

Quote:
Originally Posted by Tim Lewis View Post
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.
__________________
Joe
Reply With Quote
  #10  
Old 09-13-2021, 02:01 PM
Tim Lewis Tim Lewis is offline
 
Join Date: Aug 2006
Location: Bristow, VA
Posts: 165
Default Flight Data

RV-10 N31TD, 31 Sep 2021, 2244lbs

Flight data: https://apps.savvyaviation.com/fligh...4-454f35c15144

Excel data: https://1drv.ms/x/s!AgyQUSm6uO_2hpMY...foi5Q?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, 65F, 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.
Attached Thumbnails
Click image for larger version

Name:	climb gradient.jpg
Views:	46
Size:	225.3 KB
ID:	15780  
__________________
Tim Lewis
CFI, A&P
RV-10 N31TD - 1450 hrs
RV-6A N47TD - 1100 hrs (sold)
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 12:05 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.