GregP
Major
A P-51 and Bf 109G-6 have almost exactly the same stall speed .... around 95 mph IAS. Unless the sources I used are incorrect.
Nice chart.
The Zero's Maneuverability
- Thread starter MIflyer
- Start date
Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
Nice chart.
Aeroweanie
Airman 1st Class
- 102
- Jan 17, 2021
Stall speed is not the important part, as it varies with weight. CLmax is the important parameter. Here is what I have estimated from the data I have uncovered. I have Bf 109G-6 fighting at 6,700 lbs, while the P-51B is at 8,167 lbs.
Aeroweanie
Airman 1st Class
- 102
- Jan 17, 2021
I have done everything at mil power, or its equivalent. These are the curves I have developed
My eyes are not young anymore. So I'd ask for clarifications:
- What engine's line is at 2000+ HP at 8000 ft, and 1700 HP at 23000 ft?
- Merlin 45 and Sakae make better power above 34000 ft than V-1650-7?
- 1650-3 makes 400 HP more at 30000 ft than 1650-7?
- What engine's line is just some 10 HP worse than that of the Jumno 213A's at 25000 ft?
Plus: are the lines with or without the ram effect?
Last edited:
Aeroweanie
Airman 1st Class
- 102
- Jan 17, 2021
My eyes aren't young either - hence the wide lines, but I do appreciate the difficulties in reading this jumble of data.
1 That is the data I have for the BMW 801D-2
2 Below is a plot of just those three. I tend to agree with you skepticism, but its the data I have found.
3 Another plot follows below. Again, its the published data
4 That line is the V-1650-7 (see plot below)
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
That was way easier for my ancient eyes.
I'm afraid that these lines are way too optimistic. Even with overboost (i.e. at some 1.58-1.65 ata), the power was about 1900 PS (minus 1.4% to arrive at HP) down low. 'Book' value for Notleistung of a fully rated engine (2700 rpm, 1.42 ata) were 1440 PS at 5.7 km (~18500 ft). Perhaps these few posts might be of interest: link.
Here is, among other lines, a line (top of the graph) denoting the total engine power, ie. power to the prop "Ne" (or "Nc"?) + power to the fan "Nluft", with minimum ram and overboost where applicable.
Merlin 45 data should mimic the Merlin 20 series data above 10000 ft? Here is the graph for the Merlin 20 series: link
Max power of the 20s is at 25000 ft is some 860 HP, where the V-1650-7 is good for ~1220 HP, and 980 HP at 30000 ft (see graph), ie.
Expecting that the 1-stage supercharged Sakae can even remotely compete with the 2-stage Merlins is, I'm afraid, not going to happen. Even against the Merlin 45 it is a long shot.
See again here (dashed blue line for the -7, full blue line for the -3) - the difference between hi-alt power values of the two Packard Merlins was minor.
Also please see here, total of 100 HP difference between the different 2-stage Merlins at 30000 ft (that is despite the -3 having a big 1-stage impeller, unlike the Merlin 61).
Please count to about 860 HP for the -3 at 33000 ft (~10 km), and about 840 for the 213A there (the best non-ram line).
Also please note that 2-stage Merlin on the P-51 was getting heaps of power via the ram effect (~300 HP extra above 25000 ft), while the Jumo 213A was gaining perhaps 150 HP at 6-8 km? The power figures with ram effect calculated in when doing speed, lift and drag calculations might be much more valuable when making calculations than the 'static' values.
Thanks for posting these power graphs. On first look the "DB 605" curve is very low and the V1650-5 and -7 look different to my references.
However, the DB 605 went through restrictions and upgrades so, I will have to concentrate on this with a clear head!
Eng
Aeroweanie
Airman 1st Class
- 102
- Jan 17, 2021
Here is the BMW 801D-2 data I used. My interpretation of the notation might be off. Assistance would be appreciated...
On another note, I am using uninstalled engine performance and bookkeeping installation effects as drag.
On another note, I am using uninstalled engine performance and bookkeeping installation effects as drag.
GregP
Major
The Bf 109G-6 will have CL max of about 1.6 for 0.4 of the entire span include the fuselage width due to the slats opening. The taper ratio at the edge of the tapered wing just when the rounded tip starts is 0.519.
I calculate that means 14% of the wing area has CL max = 1.6 (from slats) and the other 86% of the wing area (no slats) has CL max = 1.4. This area calculation includes the aileron area.
So, of the assumed 16.1 sq m of wing area, 13.846 has CL max = 1.4 and 2.245 sq m has CL max = 1.6.
Perhaps an update on the turning calcs? Perhaps not. Just curious, not nitpicking.
Last edited:
Greg Boeser
1st Sergeant
Mmmm. Rainbow spaghetti.
Aeroweanie
Airman 1st Class
- 102
- Jan 17, 2021
I tend to rely on test data for stall, as airfoil-based estimates often don't produce accurate results. You need to consider wing twist, tip effects, fuselage upwash, etc. And then, there is the question as to how much of the wing needs to be stalled before you get a real stall break.
ARC R&M-2361 gives a value of 1.4 for a Bf 109E, as does the Ackroyd and Lamont paper. I also found the value of 1.4 in a Finnish document concerning the Bf 109G-2.
This data for Bf 109 V24 (a 109F prototype) indicates 1.45
Title of the graph says that it denotes power available to the prop + power to turn the cooling fan ( 'Wellen- + Luefterleistung').
The thick lines are for 'Mit Stau' condition, ie 'with ram effect' - that means engine is not just installed, but the aircraft is moving at a very high horizontal speed. Another note says 'Stauausneutzung 70%', ie. engine uses 70% of ram effect out of 100% that is theoretically possible.
Thin lines are for the case without ram effect - 'Ohne Stau'. For the fully rated engine, and without overboost (= 2700 rpm, 1.42 ata), the best value in 2nd gear, total power plotted at ~18500 ft as 1560 PS. The fan required, at least on the BMW 801S, some 70 PS at 2700 rpm, so the actual power available to the prop is a bit under 1500 PS at that altitude. A bit more generous than the values from the manual, but we can probably live with it.
Graph denoted as 'mit Alkoholzusatz' - basically if MW50 is used - gives far better power values, however the MW 50 was not used operationally on the BMW 801.
Please note that German equivalent of 'military power' for the BMW 801 is the case of 2700 and 1.42 ata. The 'dry' overboost, as it was the case with allowing up to 1.65 ata operation on the fully-rated engine would've been called 'WER' on US terminology; water-alcohol use on US engine was called also WER, and sometimes 'WER wet'.
The line for the DB 605A on your graph is for the restricted engine - 2600 rpm, 1.30 ata max - that was good for 1250 PS at 5.7 km (1300 PS at S/L). For the fully rated engine, making 2800 rpm and 1.42 ata max, usually dated from October 1943 on, power was 1350 PS at 5.7 km, and 1475 PS at S/L.
Fellow members and yours truly have posted a number of graphs in this thread, FWIW.
Last edited:
GregP
Major
Actually, I was thinking of the outer wing area affected by the slats when they open. It is pretty well-documented that the area affected by the slats get a CL max of 1.6, but only that area. The rest of the wing is CL max 1.4 or so.
The slats don't just open at stall, but creep open as the airflow separates. You can see that in an F-86 in-cockpit video. I'm thinking they creep open when you load the wing at speeds below about 160 mph, or when you get close to stall at higher speeds.
F-86 slats can be seen in here:
View: https://youtu.be/jgpPyLoWeOc
Last edited:
I have had a good trawl through the Merlin/P-51 B data and found a complicated situation. No surprise, but I think it shows the difficulty in presenting performance comparison without very specific type data to define the specific machines. The situation is complicated by the vagaries of different superchargers, different carburettors in some comparisons, different airspeeds and RAM (above rated Alt) and different fuels with different Boost ratings at different times and tests. There are also the differences between the RR Merlin, Packard V-1650's and the Packard Merlin for RAF (eg Packard Merlin 266). These differences can be very minor, or great, but there does seem to be complication in the exact specification between some of these builds.
So, overall the V-1650-3 and -7 seems to have reasonable data to help. I do not offer my info as fully researched, just to illustrate what I think are some questions.
I started with my interpretations of your tables for theV-1650-3 and -7.
The -3 was a fairly high alt rating and reads.
1675@15,000 and 1420@27,000 with 1270@30,000. My comparisons here come from Lumsden, doc EO 10A-20A-2 and Eglin test 3 Jun '43. These come out with broad similarity, but some noticeable differences. In sequence these are,
1530@15,700/+16, 1300@26,500/+16, 1100@30,000.
1490@13,750/61", 1210@25,800/61", no 30,000. 61" equals +15.25.
1510@13,000/60.5", 1260@26,000/60.5", 1075@30,000.
These all WEP on 100/130.
The rated alt differences are possibly linked with RAM. But the noticeable difference is the powers. The graph powers are a minimum of +145, +120 and +170hp greater than the data.
Now, on to the -7. With this engine the supercharger drive ratio's were reduced to improve the performance at slightly lower altitudes, being similar to the Merlin 68 and 69.
The graph seems to show,
1670@11,000 and 1550@20,000 with 850@30,000. My comparisons are the doc. EO 10A-20A-2 again and Eglin P-51B test on 67" MAP,high octane fuel.
1590@8,500/61", 1370@21,400/61", no 30,000.
1695@10,300/67", 1390@24,000/67", 1150@30,000.
Here, the low gear power is in the bracket but the high gear power is +160hp minimum, and it would look like this would reflect a 67" (18.2lb boost) manifold pressure.
Additionally, the 30,000 power is 300hp low.
Eng
Aeroweanie
Airman 1st Class
- 102
- Jan 17, 2021
Thanks for the guidance. Here is the curve I have now. BTW, thanks for the link to the thread - I hadn't seen it.
Holtzauge
Airman 1st Class
When it comes to the Zero not having a high internal fuel capacity, I have to ask the question in return: Where did you find this information? The US analysis states an internal fuel capacity of 140-145 gallons which seems quite impressive to me for an aircraft with an engine that is in the 1000 hp class.
I'm not saying 2600 rpm 35" boost was used operationally. But those speed numbers are the most optimistic figures I have seen so far (as in from flight trial data) for the Zero. The engine data comes from a Japanese chart for the Sakae 12 engine that only goes up to 2550 rpm and in which I have extrapolated the effect of running the engine to 2600 rpm. From this I reverse engineer a Cdo to tune the simulation model. But if more credible data surfaces then I will for sure update the model. But as it is, the best I've seen so far (and which I use) is from the data Mike Williams and Neil Stirling generously have made available at WWII Aircraft Performance. On the other hand, even if the power or drag was to be slightly updated with new numbers, this will only have a marginal impact on the turn performance I posted earlier. So the general trend in those figures should still stand.
Then when it comes to the 60" boost for the Allison, this was actually cleared for operational use later in the war, and in a letter from the 12th December 1942, the Allison Division at the GMC complains that even though 60" of boost is now officially approved, some pilots are not content with this and even ran it at 70" for "prolonged periods of time".
Again, the instantaneous turn chart I posted is only showing what both aircraft are capable off in terms of maximum performance and not necessarily how they were flown most of the time. And the example of a P-40 getting off a deflection shot on a Zero in the scenario I posted earlier is definitely quite possible even though this requires shooting without seeing the target: This involves getting into the "saddle" by rolling in to match the Zero's roll angle, then pulling lead and allowing the Zero to disappear below the nose and opening fire by "feel". May sound atrocious at first, but this was actually the modus operandi of the German ace Marseille in North Africa where he shot down a number of tighter turning Allied aircraft using this method. In addition, desktop aces all over the world are doing this (deflection shooting targets masked by the nose) in flight simulators like DCS and Il2-Sturmovik that have flight performance that is quite close to IRL performance. All it takes is practice.
Holtzauge
Airman 1st Class
I make the same estimate as you for the Bf-109, but where did you find a low speed Clmax as high as 1.5 for the Mustang?
The best I've seen so far is 1.4 from the NACA full scale testing documented in NACA report 829, and which is what I currently use in my simulation modelling.
In addition, I have a hard time understanding how the Mustang could have such a high Clmax as 1.5 on aircraft level? Both the Spitfire at 1.36 and the Bf-109 at 1.4 come in lower, and comparing the wing profiles on these aircraft (looking at things like camber lines and nose-radiuses) I would expect a lower, not higher, Clmax on wing profile level for the Mustang.
There is also a German report (FB 1712 by Doetsch) in which they only get a Clmax of 1.22 for the Mustang. And this is only on profile level, so I would expect a Clmax significantly higher than 1.4, or else it's difficult to explain that the Mustang is able to generate the 1.4 on aircraft level NACA recorded. But I suspect this may be due to Re effects, since the Germans only ran the tests at Re=2.7M. But I know from a paper you have done that you have studied the P-51's aerodynamics in detail, so maybe you have an explanation?
There are a few observations about the performance graphs and tables of the various Merlin engines that I have compared lately. Even when you find a quite original and "official" document, there are quite large differences in the quoted FTH's of what should be the same engines. Rolls Royce is not blameless here, with some grossly simplified graphs combining several engine types. Obviously, some data is for different Boost or MAP, and here the FTH should obviously be lower with a higher Boost or MAP on the same engine, but this is not always so in the data. RAM will make differences according to speed and the efficiency of the intake. Generally, the test-bed data is without RAM, but Trials are usually including RAM.
RAM can be estimated, but the with/without RAM is a complication, as the data is often ambiguous. For instance, there are Trials of a Merlin Spitfire IX that show increases of about +5,000' to FTH of both Low and High gear supercharge at about 400mph TAS. These effects are possibly corrupting data, and will make big differences between a high speed fight and a low speed fight.
Military power might be defined in some spheres. However, the realistic power level for manoeuvring combat is WEP or the Maximum power allowed, for the rating of the engine at that altitude and particular aircraft. Even for so-called slow speed combat, maximum power is usually used and advantage taken of any climb available. Cut power for strange manoeuvres or tactics is unusual and is a separate aspect of tactics.
Eng
RAM can be estimated, but the with/without RAM is a complication, as the data is often ambiguous. For instance, there are Trials of a Merlin Spitfire IX that show increases of about +5,000' to FTH of both Low and High gear supercharge at about 400mph TAS. These effects are possibly corrupting data, and will make big differences between a high speed fight and a low speed fight.
Military power might be defined in some spheres. However, the realistic power level for manoeuvring combat is WEP or the Maximum power allowed, for the rating of the engine at that altitude and particular aircraft. Even for so-called slow speed combat, maximum power is usually used and advantage taken of any climb available. Cut power for strange manoeuvres or tactics is unusual and is a separate aspect of tactics.
Eng
So the pilot flew 75-100 circles in a fight?, I'm struggling to believe that.
