Hurricane Speed Test in game

[MiG-3U]

The full throttle height is function of pressure altitude as seen directly from altimeter, given the altimeter base level setting. Supercharger increases manifold pressure and that ability depends on outside pressure and dynamic pressure on intake regardless density of the outside air. Air density is, of course, funtion of pressure and temperature but supercharger only sees the pressure.

BTW Gaming wise it's more important that the relative performance of the planes is about right and that is pretty easy to test regardless atmospheric model of the game, given that all the planes can be tested in the same conditions.

BTW2 I just looked in my crystal ball a saw that soon my sayings will be denied and scans from various books will be posted with thick, red underlinings

[bongodriver]

BTW2 I just looked in my crystal ball a saw that soon my sayings will be denied and scans from various books will be posted with thick, red underlinings

I'd hate to dissapoint so here goes.

No it is a function of density altitude, a supercharger produces an excess of pressure which it can only maintain until it reaches a certain level of air density due to volumetric efficiency,atmospheric density is very much affected by temperature and atmospheric pressure is not, if conditions were ISA exactly then density altitude would equal pressure altitude, inevitably temparature varies and whenever things are on the hot side performance is reduced and vice versa, so it stands to reason performance is dependent on density, you only have to look at aircraft performance charts to see this is true, jet engines have the same problem, after all a supercharger is just a centrifugal compressor just like you find on some jets.

[MiG-3U]

Originally Posted by bongodriver

I'd hate to dissapoint so here goes.

No it is a function of density altitude, a supercharger produces an excess of pressure which it can only maintain until it reaches a certain level of air density due to volumetric efficiency,atmospheric density is very much affected by temperature and atmospheric pressure is not, if conditions were ISA exactly then density altitude would equal pressure altitude, inevitably temparature varies and whenever things are on the hot side performance is reduced and vice versa, so it stands to reason performance is dependent on density, you only have to look at aircraft performance charts to see this is true, jet engines have the same problem, after all a supercharger is just a centrifugal compressor just like you find on some jets.

I'm glad to be corrected on this, preferably in layman's terms without underlined scans

My thinking is that supercharger keeps constant pressure up to the FTH and the mass flow through the engine and power is at maximum at FTH. Below FTH intake air is warmer and hence density at the intake manifolds is lower at given pressure and mass flow and power lower than at FTH, above FTH supercharger can't keep the pressure which reduce mass flow and power.

Let's assume that pressure altitude is keeped constant but temperature is higher. Then the mass flow through engine is reduced due to lower density and less mass flow is needed through supercharger to keep constant pressure due to same reason. The power is, of course, lower at this situtation, however, pressure ratio between manifolds and outside is still unchanged and hence the FTH unchanged as well.

[Crumpp]

it is a function of density altitude

Correct

I'm glad to be corrected on this, preferably in layman's terms without underlined scans

It would be nice if people would not stick to their guns when they are wrong so that such things are not required.

My thinking is that supercharger keeps constant pressure up to the FTH and the mass flow through the engine and power is at maximum at FTH. Below FTH intake air is warmer and hence density at the intake manifolds is lower at given pressure and mass flow and power lower than at FTH, above FTH supercharger can't keep the pressure which reduce mass flow and power.

Let's assume that pressure altitude is keeped constant but temperature is higher. Then the mass flow through engine is reduced due to lower density and less mass flow is needed through supercharger to keep constant pressure due to same reason. The power is, of course, lower at this situtation, however, pressure ratio between manifolds and outside is still unchanged and hence the FTH unchanged as well.

Unfortunately, that is not the case and people continue to argue their point.

[Crumpp]

'Full throttle height' is defined as that altitude above which the supercharger is unable to compensate for the reduced air density and both the BHP and airflow decrease in direct proportion to any further increased altitude.

http://www.keenzo.com/showproduct.asp?ID=3192182

Most of the flight data and engine data you guys argue about is converted to standard day conditions.

On non-standard day's FTH will change true altitude to maintain the same density altitude.

[IvanK]

Courtesy of Klems data tool and his work it has been established that the basic CLOD atmospheric temperature lapse rate is 1.97 deg C per 1000feet (corrected to 2 decimal places). This has now been measured up to 26,000feet. So its only 0.01 deg C per 1000 feet out ... not much and well and truly in the ball park to the ISA value of 1.98 deg C per 1000feet.

[bongodriver]

Originally Posted by IvanK

Courtesy of Klems data tool and his work it has been established that the basic CLOD atmospheric temperature lapse rate is 1.97 deg C per 1000feet (corrected to 2 decimal places). This has now been measured up to 26,000feet. So its only 0.01 deg C per 1000 feet out ... not much and well and truly in the ball park to the ISA value of 1.98 deg C per 1000feet.

You beat me to it but a squad member from the dogz and I have been doing a little experimenting and found something interesting, much like you we have found the lapse rate to be in the 2 degrees per thousand feet but in addition we stumbled upon an element in the FMB that changes the the atmospheric temperature not sure of its function but it is the mission parameters box, there is an option for 'Breeze/Thermal Activity =0/10' with a sliding scale, default seems to be 0 and this gives an ambient temparature of ISA +10, but if the slider is set to 10 the temp almost lines up with ISA, so far no indication that the temps can be brought to an ISA - figure.

I have attached a screenshot of the FMB tool and a graph showing the results of our quick test today.

p.s. I mean to add the test mission was done on a clear day at 12:00 midday, no other tests done to check for diurnal variations.

p.p.s. also added a usefull graph for density altitude calculations.