Its a SPEED test not a climb test so what is the relevance of Vy. As discussed in the in the initial thread these are level speed runs looking for max TAS at each altitude tested.

OOPS, I was locked on the altitude you found FTH and started thinking climb for some reason.

Look guy, I did not ask for the TAS. I wanted to confirm that you did not convert the FTH data from your test to standard conditions.

Is the raw data showing the FTH to be 17,500 ft?

If it is then that is definative proof the atmospheric model is not agreeing with the Flight Models.

FTH is a function of density altitude. Your supercharger does not care what your altimeter reads.

Rather than using terms like "Look Guy" ... (pull your head in by the way ). I tactfully suggest you read the posts carefully before flying of on a tangent and throwing your two bobs worth in.

So far in the Spit and Hurris speed test threads the 3 tangents you have gone off on are:

1. Suggested using the dry Adiabatic lapse rates instead of the ISA Lapse rate.
2. Asked about Vy speed in a level speed test.
3. Suggested that airfield field elevations varied with pressure.

I clearly stated in all the posts no adjustments were made to standard conditions the data is as it is. I also indicated in the Spit test post the FTH quoted was as stated the Altitude at which during the Speed run I first noticed the Boost drooping off. So in the test case was the Rammed FTH. As I indicated in the Spit test no attempt at converting to a standard atmosphere was made ... and I invited anyone who wanted to to go for it !

There is no question or issue here. The atmospheric model is not correct or is using a very non-standard lapse rate.

That is fact. You cannot have an OAT of 19C @ Sea Level, a pressure of 992mb, and have a density altitude that equals 17500 ft with any standard lapse rate.


Find Pressure Ratio at Sea level,

992mb = 29.29inHg
Pressure ratio, delta , at sea level is 29.29”/ 29.92” = .978944

Find Pressure Altitude,

Usually we only know the pressure at sea level. We can use charts to find pressure ratio if we know pressure altitude. So Let’s determine Pressure Altitude. Using the rule of thumb, 1” Hg =1000 ft. This is an approximation, but it works pretty good. So with a barometric altimeter setting of 29.29 we can see how far off we are from Standard day. 29.92-29.29 = .63 “ which roughly equals 630 ft. Now, do we subtract or add? This is how I look at it, If I roll the altimeter setting to 29.92 what happens to my altimeter. Since I am increasing the setting, then I am increasing the altitude to get to pressure altitude. SO Pressure altitude is 17500 + 630 = 18130 ft

Find Pressure Ratio at Altitude,

Look in a STD Atmospheric table, 18130 ft equates to a pressure ratio of .4967475

Our value lies 130 feet above the 18000 ft level. You should be smart enough to figure out how to extrapolate it.

Find Temperature Ratio,

19C + 2 degree per 1000 ft lapse rate = 17500/1000 = 17.5*2 = 35 = 19C - 35C = -16C
-16C = 3.2F

Theta = T/To at sea level , where T = Actual Temperature in deg K or Deg R and To = Standard sea level Temperature in deg R or deg R.
At altitude Theta = (3.2F + 460R)/(59F + 460R) = .892486

Find Density ratio,

You can’t just read off the table. Temperature influences density. We use the ideal gas law relationship to find density ratio.

Sigma = Delta / Theta = .556589

Look in a STD Atmospheric table, 18000 ft equates to a density ratio of .56991

In case you don't know how to extrapolate on the table:

.56991-.556589 = .013321

19000 ft density ratio = 0.55112

.56991 - 0.55112 = .01879

.01879/1000 = .000019

.013321/.000019 = 709ft (Ti-89 uses 1.879e-5)

Density altitude at 17,500 ft indicated is 18709 ft

Do you think any Merlin II or III engine had a FTH of 18700 feet?????

NO...

Does anybody have weather reports from the Battle of Britian? They only possible explaination the data is correct is to change the lapse rate adding more moisture to the air. If it is dry, the FTH is even more out of wack.

Wrongggg! 1013.25 Mb or Hpa = 29.92 inHg, yet another example of lack of basic knowlege for an apparent professional pilot.

Wronggg!! 29.92 divided by 29.92 = 1

Why do I get the feeling the rest is pure comedy?

Our pressure at sea level is not 1013.25Mb....

It is 992Mb......

992mb = 29.29inHg or more precisely 29.2938592inHg

http://www.csgnetwork.com/pressinmbcvt.html

Start laughing.....

first of all I think you must mean 29.921373825 inHg

And how exactly do you figure? I suggested in a thread that perhaps the atmospheric model was porked by someone equating 29.92 to 992, but that does not mean it is equal to 29.92 inHg.

Chuckle worthy as it is

Ok....I see my mistake, forget it .92 looks an awfull lot like .29 when surrounded by numbers.

see that...humility, try it sometime.

And I will ease on the itchy trigger finger.

Amazingly, I do think Crumpp has a valid subsidiary point about rather oddly low pressure at sea level in CloD.
Most of BoB was fought in good - high pressure - weather.
Apart from one period of low pressure in August, I think.

Look here for great historical weather charts http://www.wetterzentrale.de .

56RAF_phoenix

Now if I could find my old link for the historical surface pressure charts we could work out the actual lapse rate...

(of course the 500hPa charts kind of measure atmospheric thickness, i.e. some sort of temperature variation)

56RAF_phoenix