Maximum Altitude ?

[Inseckt]

At least supplement 3 - climb gives a good RL approximate and context sensitive prediction of the ceilings with the charts at the end.

 

All I have to do now, to compare predicted RL ceilings, with those ingame, is:

 

1. Start a DCS session

2. Calculate my gross weight at altitude

3. Figure out my drag index

4. Make a note of the ceilings reached.

5. consider the temperature deviation from "normal day" (is that 20 deg celsius at sea level?)

6. Compare with the charts for the given variables

7. Profit

8. retire

 

 

Am I on the right track?

[Inseckt]

What are your weather settings?

 

I'm sorry I didn't take the time to read all the post. A lot of manuals and charts for aircraft performance are based on a standard day. That is 15C and 1013.25 milibars of mercury at sea level. I hope this helps with testing. If it already hasn't be said.

 

Yeah, thanks, you sniped my post in which you answered one of my questions, but I got a follow up: How does milibars translate to QNH?

[Krebs20]

Pressure altitude

 

From wiki.

 

In aviation, pressure altitude is the indicated altitude when an altimeter is set to an agreed baseline pressure setting. The baseline pressure is 1013.25 hPa, equivalent to 1013.25 millibar, or 29.92 inches of mercury. This setting is equivalent to the air pressure at mean sea level (MSL) in the International Standard Atmosphere (ISA). Pressure altitude is primarily used in aircraft performance calculations and in high-altitude flight (above the transition altitude). In radio communication, the baselinepressure settingis referred

 

to by the Q code QNE. [1]

 

 

 

I wouldn't know how to explain it anymore than that. There's a whole chapter in my ifr book about this stuff. It gets confusing very quickly.

[Inseckt]

Hmm, to reply, I just found and read this: http://forums.eagle.ru/showthread.php?t=76273&highlight=qnh. (cleared up a lot for me, I previously thought that QNH and so on was a unit of measurement, lol)

 

If I understand correctly, I realise that QNH in the mission editor, is given in hPa/mb, but in-game (ATC and Altimiter) it is given in inches of mercury?. So to set a standard day in the ME, i put temperature @ 15 and QNH to 1013.25? I have noticed also that the altitude at which pilots switch between QNH and QNE is called "transition altitude" but sometimes also "changeover altitude"?... Hmm, a bit confusing, but I'll make it through:thumbup:

Edited December 26, 2011 by Inseckt

[Krebs20]

I was playing around with this while waiting for the arma 2 update to finish. I managed 41338 with the weather at 20C and 760 in the ME. I'm wishing now i would of checked it before I tried to see how high I could fly. I think 42k is doable when I drop 5C off.

[Inseckt]

But how did you calculate the desired mach number? I'm struggeling to find out the changeover altitude.

 

Was 41338 absolute ceiling? (climbrate @ 0 when climbing at desiered mach)

[Depth]

Then use the ejection seat for those vital few feet needed for the world record.

[Inseckt]

Then use the ejection seat for those vital few feet needed for the world record.

 

well, I don't know if you're joking or serious, but if you read my post's in this thread, you would see that I'm trying to determine combat, service, cruise and absolute ceiling for a given set of variables in the simulator, for comparison with numbers in the dash-1. I am certainly not going for the world record, but if I was, ejecting would be a good idea indeed.

 

I have learned a lot since the beginning of this thread, but I'm still waiting for someone to explain how to aquire the mysterious "desiered mach number". If you know anything about it, please contribute fellow landsmann. :)

[Depth]

Yeah I was being hilarious again :(

 

But in all seriousness it's interesting, the desired mach speed for high altitude climb. What makes climbing at this mach speed more effective?

[Inseckt]

The speed of sound varies with temperature, and temperature is dependent on pressure, which again varies predictably with altitude. At lesser pressures, you encounter less drag, but engines becomes less efficient due to less oxygen into the engine, so if you keep at the desired mach number, my guess is that you stay at the mathematically optimal speed for less drag vs engine performance. :)

[BlueRidgeDx]

Forgive my brevity, but I'm responding with my iPhone from the Starbucks' WiFi...

 

Don't get hung up on the changeover altitude. While it can be calculated, the changeover point is of little consequence. You'll know when it happens because as you climb at a constant IAS, the Mach number will be slowly increasing.

 

Simply continue climbing at the desired IAS until that airspeed equals the desired Mach. When the two are equal, increase your rate of climb slightly so that the IMN stays constant while the IAS slowly decreases.

 

You can display the Mach number on the HUD via the IFFCC display menu.

[Inseckt]

Thanks for your reply in the middle of the holidays!

 

So if I understand you correctly, I must simply choose a desired mach number? Lets say .50 mach? Won't the results vary widely depending on what mach number I choose?

 

I will try to get some testing tonight, I will try to choose different mach numbers and so how it affects the results...:joystick:

[BlueRidgeDx]

Inseckt,

 

I'm afraid I might have led you astray with regard to Mach number. I assumed that - like every other jet I'm familiar with - there is a point in the climb profile where a change from IAS to Mach occurs. It looks like I'm mistaken when it comes to the A-10.

 

From the performance supplement to the "Dash 1" manual (you can find it here: http://forums.eagle.ru/showpost.php?p=1015425&postcount=3), you should utilize IAS all the way up to the absolute ceiling.

 

It's easy enough to remember: At Sea Level, climb at 200KIAS. Subtract 1kt for each 1,000ft of pressure altitude above Sea Level. For instance: at 10,000ft, subtract 10kt which gives a climb speed of 190kt. This is valid all the way up to point that the jet stops climbing.

 

In any event, the performance supplement contains charts to determine the Combat, Cruise, and Service Ceiling. The charts are based upon Gross Weight, Drag Index, and Temperature Deviation (from ISA).

 

As an example, a lightly loaded airplane (30,000lb) with a Drag Index of "0" at standard temperature will have Service Ceiling of 38,000ft.

[Inseckt]

Thats absolutely great! Now I can finally do some proper testing. Thank you for taking your time to clear this up. I am aware of the charts you are talking about, since I read them, but I must have missed the part where it says how to climb properly! I will report back shortly with some results. :)

[Inseckt]

Results from ceiling test in DCS and RL comparison

 

Report:

So, here it is. I have conducted a flight ceiling test using the procedure provided by BlueRidgeDX. I'm assuming this is a correct procedure for reaching the defining ceilings and the validity of the results depend upon it. Furthermore , please forgive the long post, but I wanted to do this with some level of seriousness. (sorry for completely hijacking your thread EventHorizon)

 

Settings:

In the mission editor, I have set up a standard day using "normal weather". This includes; 0 wind and turbulence; no clouds or fog; no precipitation; 15 deg Celsius @ SL; QNH=760 @ SL (given in mmHg and corresponds to 29.92 inHg which was set on the altimeter in the cockpit). On the load out-page, I set 100% fuel, no ordinance, 0 % ammo, 0 chaff and flare. This load out gave the total weight of 36 054 lbs and drag index = 0 (which includes pave penny pod and all the regular stuff attached to the hog). Before embarking on the test-flight, I prepared a speed chart to aid in keeping the proper speed at the different altitudes. This chart is presented in figure 1 below.

 

Execution:

I started from minvody and headed south. At FL 5000ft I went full throttle and started a climb while trying to stay at the recommended speed dictated by figure 1. In the beginning this proved to be somewhat difficult to execute with satisfactory accuracy, but when my climb rate started to come down, it got gradually easier. When nearing the first ceiling (combat ceiling @ 500 FPM) I was able to maintain the proper speed plus minus 1 KIAS which was satisfactory. Furthermore, given the inaccuracy in reading off the climb rate gauge, it wasn't a specific second where I "hit" the ceiling, there was always some variation in climb rate, as I was trying to adjust for speed. Therefore I made two measurements per ceiling, one on the first instance when all variables met the requirement for the given ceiling, and one where I was barely able to maintain the parameters. In the results I refer to these two measurements as "lowest measured altitude" and "highest measured altitude". Using the mean of these two numbers, i calculated an approximate error for each ceiling. These errors are probably not statistically correct, but serves to give some image of the accuracy. The biggest error of any of the ceilings should in reality be considered as the true uncertainty for every ceiling.

 

Documentation:

I possess a screen-shot of every measurement (both the low and high for every ceiling) showing KIAS and FL on the HUD, the climb rate gauge, the left MFD showing CDU-POS page with IAS, the fuel quantity gauge (needed to determine the weight of the aircraft) and also the barometric altimeter (although not as accurate as the readout on the HUD). I was also going to save the track but I always forget, and this time was no exception. :doh: My plan was to include the screen-shots and track, but instead I decided to hold them back until/if someones wishes to see them to avoid unnecessarily cluttering this thread with multiple screen-shots in case no one really cares.

 

Results:

The results are presented in figure 2 below. As you can see, it begins with the low and high value for each ceiling, followed by the mean value with suggested error. This value is considered to be the actual result. Next I have made an approximate read-off of the remaining fuel for each ceiling. I was then able to calculate the total weight when I was back in the mission editor. I then proceeded to find the values predicted by the TO 1A-10A-1 for each corresponding ceiling. The charts from which I extracted this information is found in the performance data supplements (TO 1A-10A-1-1) part 3 entitled "climb". If someone wants to check the numbers in the TO and don't know how to read the charts, or want to check that I did so correctly, then this is how I did it:I began by selecting the proper gross weight, (as calculated by remaining fuel), along the bottom horizontal axis. Then I followed a line upwards until I hit the drag index = 0 curve. Then I went straight left to read of the predicted ceiling as no weather correction was needed. I included and error of plus minus 500 ft considering the inaccuracy reading the chart, and the inaccuracy in reading off remaining fuel. The TO does not include a chart for calculating absolute ceiling, marked in figure 2 with "no data". Last, I intended to present the difference value between the values measured in DCS and the values obtained from the charts, however there where no considerable difference for any ceiling if you consider the error boundaries of the given values. This leads naturally to the conclusion.

 

Conclusion:

The DCS environment and FM accurately depicts the hight and climb performance of the A-10C as it is in RL, IF you postulate that the A and C model have equal performance profiles. (Paulrkii or someone else in the "know" might confirm or dis-confirm (is that a word?) this postulate (I thought that the A-10 got an engine upgrade somewhere between A and C?)). This result surprised me. As I said earlier, I had always felt aircrafts in ED products to be "underpowered". It only goes to show how useless "feeling", "thinking" and "believing" is when dealing with such a sophisticated simulation (the force failed me), and how only a serious endeavor into the simulation can reveal it's accuracy. To sum up, there are two postulates that these results rest upon, namely that; the speed profile of the climb supplied by BlueRidgeDx is an accurate means of testing an aircraft's ceilings, AND; that the A and C model have equal performance profiles.

 

End notes:

Again, sorry for the long post. Wonder if anyone will bother reading the whole report? :D But it doesn't matter, as it was extremely satisfactory and great fun doing this anyway. :thumbup:

 

Attachments:

Figure 1: Figure 1.pdf

Figure 2: Figure 2.pdf

 

- Inseckt:smartass:

 

Edit: I have noted an error in figure 2 under "results" and "combat ceiling". Here it reads 32 250 (plusminus 250) ft, but it should in fact read 32 650 (plusminus 250) ft.

Edited December 31, 2011 by Inseckt
error in figure 2

[rayz007]

Inseckt, I have to compliment you on a most entertaining late night read. I just so happened to get a surprising desire to see if I could get to the maximum stated altitude of the A-10C. (45,500 apprrox) I made it to about 34,000 and was learning on the fly (pun intended) I was like oh yeah, maybe i should jettison all that dead weight. Then I was like ok, I cant climb without that annoying stall warning alarm, so i'll set my trim to right before the alarm goes off. This got me only so hight,then I was like wait, I have 1150 rounds of CM. Shoot them off and I get some more room to push higher. I even tried to jettison the lightning Pod and the TGP but couldn't figure that out? Is it even possible? So again, thanks for the interesting read. This sim is so impressive. Thank you so much for this ED, you guys rock! I even think Inseckt was trying to say that too in his own way.

[Wrecking Crew]

Nice rayz007! That's up there... I've been up to over 27,000 loaded going into battle. I'll have to give +30K a go here soon!

 

You cannot jettison the pods AFAIK. But you can start w/o them...

 

Wrecking Crew

[Inseckt]

I even tried to jettison the lightning Pod and the TGP but couldn't figure that out? Is it even possible?

 

No it's not possible, but you probably knew that by now... If you want to go for a high altitude, start with no ordinance. If you are getting the stall alarm, you should level off and build speed before attempting to climb further...

 

Thank you so much for this ED, you guys rock! I even think Inseckt was trying to say that too in his own way.

 

Of course I was:)

[Jona33]

My record is 39,000 feet and a long ride in the ejection seat.

[Pelmo]

My record is 40.880 feet or 11.194 meters. I set season winter, temperature -50°C, no weapons, no guns, 25% fuel and starting from Sukhumi runway. Climb time was about 20 min.:thumbup: Screenshot at: http://forums.eagle.ru/showthread.php?t=93358&page=2

Edited August 25, 2012 by Pelmo