VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics


Go Back   VAF Forums > Avionics / Interiors / Fiberglass > Steam Gauges
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 04-27-2007, 09:18 AM
Kevin Horton's Avatar
Kevin Horton Kevin Horton is offline
 
Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,342
Default Errors in Kitplanes "How Fast is Fast" - ASI calibration, Apr 2007

The table of ASI reading vs water manometer height in the "How Fast is Fast" article in the April 2007 issue has errors. The errors are small at low speed, but there is about a 4 kt error at the highest speeds in the table. I'm not sure where those numbers came from. Does the author have a reference for them?

The CAS for a given pressure is equal to asl*SQRT(5*((P/Psl+1)^(2/7)-1)) [reference test pilot school notes].

where:
asl = speed of sound at sea level (661.48 kt or 761.22 mph)
Psl = atmospheric pressure at sea level (407.513" H2O at 20 deg C, or 10350.8 mm H2O)

The above values are from NASA Reference Paper 1046 (14 MB pdf), Measurement of Aircraft Speed and Altitude, Tables A19 and A27.

Corrected ASI vs water manometer height:
Code:
Speed     in.     mm                    Speed     in.     mm
(mph)     H2O     H2O                   (kt)      H2O     H2O
 15      0.11     2.8                    15      0.15     3.7
 20      0.20     5.0                    20      0.26     6.6
 25      0.31     7.8                    25      0.41    10.4
 30      0.44    11.3                    30      0.59    14.9
 35      0.60    15.3                    35      0.80    20.3
 40      0.79    20.0                    40      1.04    26.5
 45      1.00    25.3                    45      1.32    33.6
 50      1.23    31.3                    50      1.63    41.5
 55      1.49    37.9                    55      1.98    50.2
 60      1.77    45.1                    60      2.35    59.7
 65      2.08    52.9                    65      2.76    70.1
 70      2.42    61.4                    70      3.20    81.4
 75      2.78    70.5                    75      3.68    93.4
 80      3.16    80.2                    80      4.19   106.4
 85      3.57    90.6                    85      4.73   120.1
 90      4.00   101.6                    90      5.31   134.8
 95      4.46   113.3                    95      5.91   150.2
100      4.94   125.6                   100      6.56   166.5
105      5.45   138.5                   105      7.23   183.7
110      5.99   152.1                   110      7.94   201.8
115      6.55   166.3                   115      8.69   220.7
120      7.13   181.2                   120      9.47   240.4
125      7.74   196.7                   125     10.28   261.1
130      8.38   212.9                   130     11.12   282.6
135      9.04   229.7                   135     12.01   304.9
140      9.73   247.2                   140     12.92   328.2
145     10.44   265.3                   145     13.87   352.4
150     11.18   284.1                   150     14.86   377.4
155     11.95   303.5                   155     15.88   403.3
160     12.74   323.7                   160     16.94   430.2
170     14.41   365.9                   170     19.15   486.5
180     16.17   410.8                   180     21.52   546.5
190     18.05   458.5                   190     24.02   610.2
200     20.03   508.9                   200     26.68   677.6
210     22.13   562.0                   210     29.48   748.8
220     24.33   617.9                   220     32.44   823.9
230     26.64   676.7                   230     35.54   902.8
240     29.07   738.3                   240     38.80   985.6
250     31.61   802.8                   250     42.22  1072.4
I have created Excel and OpenOffice spreadsheets that will convert back and forth between ASI reading and water manometer height.
Excel and OpenOffice spreadsheets
__________________
Kevin Horton
RV-8
Ottawa, Canada
http://www.kilohotel.com/rv8/
Reply With Quote
  #2  
Old 04-27-2007, 10:12 AM
KPmarc KPmarc is offline
 
Join Date: Apr 2006
Posts: 138
Default

Thanks, Kevin.

I have attempted contact with the author, but his inbox has been full for a few days. I'll keep after it and see what his reference material was.

--Marc
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 01:31 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.