Posted by: =worr=

Posted on: 16:16:54 11/11/98

Message:

Stimpy I hate to do this to you, but you keep posting away on this to your own embarasement and soon you would confuse the masses. :(

Remember to always do your homework before you bring an accusation of "IMOL porked my favorite ride." And don't be ashamed to ask a simple question without stating that you have all the facts and need no further help. "Pride goes before the fall."

NO, it doesn't mean "always trust the data as presented" But since when is skepticism a sole virtue? At least give them the benefit of the doubt that they are at least smarter than you or me in these matters since they are investing more into than we ever will for a much larger audience.

You have data for the 47-25-RE that states top speed is 375 MPH (TAS) at 10,000 feet. This is minus the usually pressure density, temeperatures and weights that can always put some variation in this. I can cross check this very same data for the 25-RE (Mind you we model the 30-RE and I have no data for that.)

Anyhow, you proceeded to tell us the WB 47D was off by some 40 MPH!

Here is your exact post:

+++++++++

Just for example...

The top speed of the D at 10k in real life is 375, in WB it is 337 by

the tables. That ain't a small descrepency... Then it has 308mph at 15k in WB, while in real life at 20k the speed is 406mph. Though 15k and 20k are not the same (doh :), it shows the speed should go UP from 10k to 15k to 20k... Here the P47 loses performance as it goes higher...

+++++++++

Blah. It is ugly so no one likes to fly it so who cares...

Double blah...

stimpy

Rogue Gryffons -BYA-

++++++++++++++

To obtain TAS from IAS you need to multiply IAS by 1.167 at 10,000 feet. (curtiousy of Jeffery Dillweed)IAS if you do some reading means indicated air speed. TAS means true air speed which is in all those nifty books for land dwellers. FWIW, pilots live and die by IAS because of its constancy. My stall speed ias at sea level is the exact same at 30K. But TAS it goes all over the place...hence planes are build with IAS indicators.

So a light 47D at 10k gets 331ias times 1.1.67 and you get...oh oh :)

Heavy you get 319 times 1.167 and you get the picture. Add to that wep and you are right off the charts because nobody does wep like the JUG.

To your benefit I think we should have something out there on the warbird links for IAS to TAS conversions. This foilable jumps up on the boards every six months or so and could possibly save additional embarasement.

Live and learn....

Worr, out

N.B. Attached for you old vetrans of WB is the most infamous chart of Jeffery! I found it with dejanews...and had to chuckle. Just cut and paste the below and enjoy. :)

Re: Warbirds planes 

Date: 1996/05/18

Forums: comp.sys.ibm.pc.games.flight-sim

>Hawkey:

>I have been flying WBs since it came out. U seem to have info on the performance of these birds.

>It seems impossible to get these planes to fly any faster than 330 IAS at any altitude. At 10K feet the P51D should be flying at a minimum of 375 or according to Green it should fly at 395 TAS. I add 2 miles per hour per 1K of altitude. Applying this to WBs P51B u get 330 IAS plus 20 fo raltitude and u get 350 TAS!!! Same for FW190A-4 and other plances.

>I welcome your comments and analysis.

>ROland N. Cataldo

The book figures for a P-51D say 437 MPH top speed.

The ceiling is supposed to be 41,900 feet. Try it in WarBirds and see what you get. :)

Here is the file convert.txt explaining a little bit about IAS and TAS and how to convert. Remember WarBirds speedometers are in MPH and they are inaccurate. For an approximation though while flying, you can use the table. It's not as complicated as some would have you believe. For a closer determination of top speed you can climb to the altitude you want and time how long it takes to fly between 3 grid lines on the map. This is a distance of 40 miles.

Example: (Distance/time in seconds) *3600=Miles Per Hour.

As far as speed being off in the P-51, it is a little slow.

A bigger concern is fuel consumption which may be off by about 30%. This forces you to carry more weight which reduces performance. Total flight time involving takeoff and climbing to 26k and throttling back to about 335 MPH TAS is only 1 hour and 17 minutes with half a tank of fuel.

It makes one wonder how a P-51D could have made it to Germany and back, even with drop tanks, at this rate of fuel consumption. The ceiling is also lower then book figures with the P-51 in WarBirds.

Here is the table you can use with the speedometer.

AIR SPEED CONVERSIONS

The following table facilitates IAS to TAS, TAS to IAS conversions. Simply multiply IAS, or divide TAS by th altitude factor to convert. This lets you compare data between games, or to real world data.

A circular slide rule type flight computer was used to obtain data. Density altitude was set to desired altitude and TAS was read from IAS. In other words density altitude and pressure altitude were assumed to be equal. You can read the temperature at which this happens off "whiz wheel" opposite pressure altitude. True altitude is very, very close at this setting. This is what I believe Microprose did to get the factors used in their text file. TAS was divided by IAS to calculate "altitude factor."

Numbers in parenthesis are from Microprose file f15spd.txt.

Differences are probably due to: my 50 year old eyes, differences in E-6B flight computers, and the difficulty in reading a non-precise device like a mechanical circular slide rule. I used reading glasses AND a magnifying glass. If anyone finds any glaring errors, let me know.

Jeffrey Dillman

Alt. factor Alt. factor

1k 1.017 21k 1.394

2k 1.031 22k 1.417

3k 1.047 23k 1.443

4k 1.063 24k 1.470

5k 1.078 (1.077) 25k 1.497

6k 1.097 26k 1.523

7k 1.113 27k 1.551

8k 1.130 28k 1.576

9k 1.149 29k 1.609

10k 1.167 (1.164) 30k 1.634 (1.635)

11k 1.186 31k 1.669

12k 1.203 32k 1.697

13k 1.223 33k 1.733

14k 1.244 34k 1.763

15k 1.263 35k 1.798

16k 1.286 36k 1.833

17k 1.303 37k 1.880

18k 1.329 38k 1.923

19k 1.349 39k 1.970

20k 1.373 (1.370) 40k 2.018 (2.016)

Jeffrey Dillman