Author Topic: Climbrate/climbspeed/time to hight??? (Read 1595 times)

Knegel · « **on:** February 26, 2006, 07:29:41 AM »

Hi,

once again i stuble over the strange discrepancy between climbrate and time to hight.

What i find strange is:

The max climb speed(rate) is given with just above 20m/s (1200m/min), while with same power(rpm) setting the time to hight curve show 3min to 5000m = 1666m/min and 5min to 8000m = 1600m/min middle climb rate.

Similar discrepancy between best climbspeed and time to hight we can see in the 109E manual, where max 15m/s gets displayed, but the time to hight show roundabout 2300m in 2min = 1150m/min(19,17m/s).

Also the Spitfire climbreports show this discrepancy, best climb of 4700ft/min(23,88m/s), time to 3000m is 2min = 1500m/min (25m/s)

While the SpitIXc BS.543(Merlin66) show a much better climbrate, its time to hight is much more bad.

Could someone please tell me the logic in it??

Greetings, Knegel

butch2k · « **Reply #1 on:** February 26, 2006, 08:36:05 AM »

Use the steig u. kampf curves and use the (non-visible on this copy) time-to-height scale which is 2minues/square

Knegel · « **Reply #2 on:** February 26, 2006, 03:27:31 PM »

Hi Butch,

i just remeber that i did stuble above this K4 table before, i simply forgot the solution.

Whats about the discrepancy in the 109E manual and the SpitIXc climb, between climbrate and time to hight??

Greetings, Knegel

justin_g · « **Reply #3 on:** February 27, 2006, 01:46:50 AM »

Time to altitude is actually measured - but the climbrate curves are "fitted" to a series of data points for climbrate, recorded at instants of time during the climb. Known or measured engine power and critical altitudes are used to fit the curves, I think. Eg: this climbrate graph for P-51B shows data points for climbrate that are scattered around the drawn curves.

Edit: well, that's my speculation, anyway. PS: Noticed your sig changed.

gripen · « **Reply #4 on:** February 27, 2006, 02:00:39 AM »

Hm... That K-4 chart comes from Mtt "projectoffice" papers so it's very probably a calculation.

gripen

Knegel · « **Reply #5 on:** February 27, 2006, 03:17:57 AM »

Hi,

there must be a reason why they give the 109E in the manual absolut constant 15m/s up to 3500m, what seems to be very strange, specialy if we see that they reach 3500m in 3 min, what is pretty hopeless with 15m/s(900m/min). Maybe the max climbrate show the steepest climb(climb with vx) while the time to hight show the most effective climb(climb with Vy)??

btw, since the 109K4 climb seems to be made as comparison between the climbperformence with "Grundeinstellung 1.8" and "Grundeinstellung 1.98", , not to get the best climb, the resulting climbrate could be made with a higher speed than Vy, to keep a more stable flight. Otherwise i cant understand why 500PS more result only in 5,5m/s more climbrate.

Greetings, Knegel

justin_g · « **Reply #6 on:** February 27, 2006, 07:13:06 AM »

Quote

Also the Spitfire climbreports show this discrepancy, best climb of 4700ft/min(23,88m/s), time to 3000m is 2min = 1500m/min (25m/s)

Well, the time to 3000m isn't exactly 2min. It is more like 2.1min(+6s), which makes the average climbrate = 23.81m/s - you can see that a small difference in time will affect the average climbrate by a noticable amount. If you calculate the time to altitude using the climbrate curves on the graph, the results are very close to those shown by the time curve. Eg: I calculated 2.17min to 10,000ft - a difference of 1% from the claimed time of 2.15min.

For the Emil I can only offer a link to this website which has more realistic times to altitude - note that the time to 5km is similar, but the lower altitudes are reached in more realistic(longer) times.

Quote

btw, since the 109K4 climb seems to be made as comparison between the climbperformence with "Grundeinstellung 1.8" and "Grundeinstellung 1.98", , not to get the best climb, the resulting climbrate could be made with a higher speed than Vy, to keep a more stable flight. Otherwise i cant understand why 500PS more result only in 5,5m/s more climbrate

The 109K chart is 99% sure to be calculated, so the climbspeed used would be = Vy, since no real plane was actually flown. Also note that the power at 0m for each curve would be:

___ 1.8ata/Grundeinstellg 1.8ata = 1850ps
__._ 1.8ata/Grundeinstellg 1.98ata = 1800ps
---- 1.45ata/Grundeinstellg 1.8ata = 1430ps
_.._ 1.45ata/Grundeinstellg 1.98ata = 1400ps

So increase in climbrate of 5.5m/s(for Grundeinstellg = 1.8ata) is acheived with a power increase of 420ps. In comparison, the Merlin 66 Spitfires gained about 800-1000fpm(4-5m/s) in climb with a power increase of 400hp, so the climbrate increase for the 109K would seem to be well within expectation.

Knegel · « **Reply #7 on:** February 27, 2006, 09:17:20 AM »

Yep, you be right, a smal mistake realy make a big different!

Thanks for the hint!!

Greetings, Knegel

F4UDOA · « **Reply #8 on:** February 27, 2006, 10:03:35 AM »

IMHO there was some creative license taken with some of the climb rates listed by mostly manufactures but you can see it on some A/C more than others. Karnak posted some Mossie climb times with climb chart a while ago. They just didn't match and when you calculated the average rate of climb to 20K it became very obvious something was off.

In order to reach 20,000FT at these times you must average

8minutes
Average climb rate= 2500FPM

7 minutes
Average climb rate= 2857FPM

6 minutes
Average climb rate= 3333FPM

If this does not match the average climb rates shown in the corresponding climb charts then they might be testing zoom climbs.

HoHun · « **Reply #9 on:** February 27, 2006, 02:33:10 PM »

Hi Knegel,

>there must be a reason why they give the 109E in the manual absolut constant 15m/s up to 3500m, what seems to be very strange, specialy if we see that they reach 3500m in 3 min, what is pretty hopeless with 15m/s(900m/min).

Such diagrams were often simplified, perhaps in an attempt to make them easier to memorize for the pilots, perhaps to hide the unique engine technology (in the shape of the variable speed supercharger drive). The official Luftzeugmeister diagrams are most notable for this, but especially the climb rate below full throttle height is also simplified in British diagrams. Just like the Luftzeugmeister did in the Emil diagram, the RAF liked to draw climb rate below full throttle height as a constant figure though in reality, it wasn't.

There is more one should keep in mind about performance diagrams: For example, they were usually corrected to a constant weight (often, but not always, the take-off weight), and the time to altitude diagrams were (as far as I can tell) normally calculated from the climb rate diagrams by simple numerical integration. This leaves weight loss due to fuel burn as well as the requirement to add kinetic energy to the airframe unaccounted for, but for fighters, both effects are minor anyway. (The "climb rate" diagrams could more accurately be considered specific excess power diagrams as a result.)

Anyway, here is a calculation of the Me 109E performance I prepared a while back:

http://hometown.aol.de/WBHoHun/Me109E_DB601A-1_early.gif

It still features some simplifications, mainly the approximated power curve which leads to a somewhat angular graph between 1.5 km and 4 km. This should be a smooth curve realistically.

I'd say the climb rate in the diagram you posted is probably for 1.23 ata/2300 rpm, though it indicates a full throttle height that is too low for that. This is a bit odd, but considering the somewhat inaccurate nature of the simplified graph, nothing to worry about :-)

Regards,

Henning (HoHun)

elkaskone · « **Reply #10 on:** March 01, 2006, 03:43:39 AM »

This Russia or Polnish Document is from a BF109E3 with DB601Aa,
for me it looks like the Orginal Performance Figures!
The 500km/h at Sealevel must be the 1 Minute "Kurzzeitleistung"!

[/URL][/IMG]

Knegel · « **Reply #11 on:** March 01, 2006, 12:56:03 PM »

Hi,

thats how most other nations display their Vmax, no matter if its realy usefull while combat.

btw, this scans are new to me and very interesting(1st graph with 1min power i see, Looks like the 109E didnt need to fear the 12lb boost of the MerlinIII, thanks for sharing!!), but they are a bit OT here, cause i was looking for the often happen discrepancy between time to hight and climbrate.

OT.: Could the DB605A also increase the rpm above rated alt, better sayed, did the 5min powersetting of the DB605A turned to be the 30min setting above rated alt, similar to the DB601A???

Greetings, Knegel

elkaskone · « **Reply #12 on:** March 01, 2006, 02:23:24 PM »

Look here, at this Documents from DB601A & DB601Aa,
i think these will give you the right anser to your Question!

DB601A

DB601Aa

HoHun · « **Reply #13 on:** March 01, 2006, 03:35:19 PM »

Hi Knegel,

>btw, this scans are new to me and very interesting(1st graph with 1min power i see, Looks like the 109E didnt need to fear the 12lb boost of the MerlinIII, thanks for sharing!!)

I'm rather sceptical about the DB601Aa at 1 min power suggestion. As with the Merlin III at +12 lbs/sqin, you should see a marked decrease in full throttle height for this configuration, and that's just not there in that graph.

By the way, if I remember correctly, someone somehwere pointed out that the graph was of Yugoslavic origin. The German version was published for example in the Radinger/Otto/Schick books on the Me 109, but without any additional information, so that was fairly useless. I seem to remember dimly that more information was available on some other forum, including a scan of the original German graph, but if I saved it I lost it somewhere on my hard disk.

Anyway, I believe Me 109 performance with a DB601Aa would differ quite a bit from what's indicated on that graph.

Regards,

Henning (HoHun)

hitech · « **Reply #14 on:** March 01, 2006, 03:53:00 PM »

HoHun: Just for old times:)

That chart is correct, why you think you know more then the enginers who made the chart? You can't caclulate what the change in full throttle hight would be, that is way to complex for you to calculate it correctly.

Ok back to today.
Boy I don't miss that type of argument.

Sorry for the interuption. Now back to our real discussion.

HiTech