Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Knegel on February 26, 2006, 07:29:41 AM
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Hi,
once again i stuble over the strange discrepancy between climbrate and time to hight.
(http://www.raf-roy.com/share/knegel/Screenes/109k_Sp09climb2.jpg)
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
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Use the steig u. kampf curves and use the (non-visible on this copy) time-to-height scale which is 2minues/square ;)
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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
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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 (http://www.spitfireperformance.com/mustang/p51b-12093-climb.jpg) shows data points for climbrate that are scattered around the drawn curves.
Edit: well, that's my speculation, anyway. PS: Noticed your sig changed.:D
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Hm... That K-4 chart comes from Mtt "projectoffice" papers so it's very probably a calculation.
gripen
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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)??
(http://www.raf-roy.com/share/knegel/Screenes/bf109e-perf-chart1.jpg)
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
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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 (http://www.rolfwolf.de/daten/E4/Emil.html) 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.
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.
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Yep, you be right, a smal mistake realy make a big different!
Thanks for the hint!!
Greetings, Knegel
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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.
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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)
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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"!
(http:// [URL=http://img145.potato.com/img.php?loc=loc236&image=06114_Me109E3__Polnische_Grafik_01.jpg][IMG]http://img145.potato.com/loc236/th_06114_Me109E3__Polnische_Grafik_01.jpg)[/URL][/IMG]
(http://[URL=http://img143.potato.com/img.php?loc=loc118&image=06119_Me109E3__Polnische_Grafik_02.jpg][IMG]http://img143.potato.com/loc118/th_06119_Me109E3__Polnische_Grafik_02.jpg)[/URL][/IMG]
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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
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Look here, at this Documents from DB601A & DB601Aa,
i think these will give you the right anser to your Question!
DB601A
(http://img138.potato.com/loc171/th_45311_DB601A__Leistungsblatt_1937.jpg) (http://img138.potato.com/img.php?loc=loc171&image=45311_DB601A__Leistungsblatt_1937.jpg)
(http://img127.potato.com/loc248/th_45522_DB601A__Hoehenleistungen.jpg) (http://img127.potato.com/img.php?loc=loc248&image=45522_DB601A__Hoehenleistungen.jpg)
DB601Aa
(http://img13.potato.com/loc269/th_45317_DB601Aa__Leistungsblatt_1937.jpg) (http://img13.potato.com/img.php?loc=loc269&image=45317_DB601Aa__Leistungsblatt_1937.jpg)
(http://img133.potato.com/loc239/th_45525_DB601Aa__Motorleistung.jpg) (http://img133.potato.com/img.php?loc=loc239&image=45525_DB601Aa__Motorleistung.jpg)
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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)
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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
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Here ist another Russia Document from a Russia Handbook about the BF109E3 with DB601Aa with the same Performance!
I belive that is the same Performance that are on the Messerschmidt Charts, but however i never see the Orginal German Charts!
(http://img41.potato.com/loc24/th_50289_109E3_28.sized.jpg) (http://img41.potato.com/img.php?loc=loc24&image=50289_109E3_28.sized.jpg)(http://img14.potato.com/loc24/th_50294_109E3_10.sized.jpg) (http://img14.potato.com/img.php?loc=loc24&image=50294_109E3_10.sized.jpg)(http://img18.potato.com/loc24/th_50299_109E3_11.sized.jpg) (http://img18.potato.com/img.php?loc=loc24&image=50299_109E3_11.sized.jpg)
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Well, the Russian charts for speed seem refer manufacturers claims with 5% tolerance and apparently tested data; there is notable difference but it's unclear if the engine settings are the same (I'm too lazy to try to translate...).
gripen
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Originally posted by elkaskone
Look here, at this Documents from DB601A & DB601Aa,
i think these will give you the right anser to your Question!
Hi,
i know the different between the A and Aa regarding the poweroutput, but the discrepancys are very often in the same datasheet and not only related to the Me109!
The answer to my question seems to be: Sometimes there are mistakes included. ;)
btw. why there was a DB601A and a Aa?? What was the technical differents and which engine got used when??
Somewhere i did read the Aa was the export version, but is it possible that the HQ sell the better engine, while the own Luftwaffe get the crap??
Greetings,
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Output at given rating seem to be about the same for both engines. There is some difference in weight and lenght so differences might be somewhere in output gearing (apparently strenghtening) and possibly also in supercharger.
gripen
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I have no Documents which I can show you,
but what i have read about the Bf109E makes me that picture:
BF109E1 = DB601A
BF109E3 = DB601Aa (maybe a few early with DB601A)
BF109E4 = DB601Aa
BF109E4B = DB601Aa
BF109E4N = DB601N
BF109E7 = DB601Aa
BF109E7B = DB601Aa
BF109E7Z = DB601N with GM1
I dont think the DB601Aa is the export version, it was the Series engine since the BF109E3!
Focke Wulf has a engine export version for the FW190A3 for the Turks,
it was labelt Fw190Aa3 with BMW801D but slower performance.
The point is, i believe that the 500km/h at sealevel and the 570km/h at 5000m, are manufacturer data from Messerschmidt for the BF109E3 and DB601Aa!
If anybody has orginal German speed charts for the BF109E, please post it will make a smile to my face.
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Hi Hitech,
>That chart is correct, why you think you know more then the enginers who made the chart?
I'm aware that you are joking, but that chart wasn't made by engineers :-)
The graphical data does not even match the tabulated data.
The speed table shows an anomally high speed at 0 km and a kink in the speed graph between 2 km and 3 km that probably indicates the action of the variable speed supercharger drive.
The climb table shows climb rate fluctuating slightly around a high average below full throttle height, but the climb graph shows the climb rate dropping continously from sea level up.
Regards,
Henning (HoHun)
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Hi Elkaskone,
>Look here, at this Documents from DB601A & DB601Aa,
i think these will give you the right anser to your Question!
Thanks a lot, I hadn't seen a DB601Aa power graph before! :-)
Based on my above calculation from the Me 109E-1/E-3 Kennblatt, I ran a preliminary analysis using the DB601Aa data from your graph and came up with the following results for 5 min power:
Altitude - Calculated Speed - Tabulated Speed
0000 m - 490 km/h - 500 km/h
1000 m - 514 km/h - 510 km/h
2000 m - 540 km/h - 530 km/h
3000 m - 559 km/h - 540 km/h
4000 m - 577 km/h - 555 km/h
4300 m - 581 km/h
5000 m - 575 km/h - 570 km/h
6000 m - 568 km/h - 565 km/h
7000 m - 559 km/h - 560 km/h
As you can see, the 500 km/h at sea level from the chart don't seem to make sense - maybe that's really the value for 1 min power as it seems too high for 5 min power.
The rest of the tabulated data is slower than it should be, and lacks the relatively low full throttle height with the relatively high top speed evident in my calculation. (No surprise here, the DB601Aa has a low full throttle height, so a top speed achieved at 5 km is obviously unlogical.)
Regards,
Henning (HoHun)
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Huhun,
as elkaskone wrote, its the 1min speed. Looks like he own more of this datapackage!??
So the Db601Aa was the 'normal' engine in WWII?!
Greetings, Knegel
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>Altitude - Calculated Speed - Tabulated Speed
>0000 m - 490 km/h - 500 km/h
>1000 m - 514 km/h - 510 km/h
>2000 m - 540 km/h - 530 km/h
>3000 m - 559 km/h - 540 km/h
>4000 m - 577 km/h - 555 km/h
>4300 m - 581 km/h
>5000 m - 575 km/h - 570 km/h
>6000 m - 568 km/h - 565 km/h
>7000 m - 559 km/h - 560 km/h
Your speed calculation is in the bounds of possibility,
personally i think that the Top-speed (5' rating) between 4000m and 5000m could be nearly the same,
that is which me at the speed diagram also looks a little bit doubtful!
>as elkaskone wrote, its the 1min speed. Looks like he own more of this >datapackage!??
Sorry for the misunderstanding,
it is a pure speculation of me, i forgot the (!?) or (maybe) in my formulation.
But 500km/h at sealevel it a very high speed for BF109E and i dont believe it can be reach at the 5' rating!