Author Topic: RR Merlin vs the DB series (Read 9458 times)

niklas · « **Reply #45 on:** November 17, 2002, 09:34:18 AM »

Well gripen, isn´t it strange that the spitfire claim a gain of altitude due to RAM effect of 4000ft (from climb to speed), 1223m, while the germans claim only 500m? only 40%? And the air intake of the 109 was in a very good position, outside of the boundary layer, like the cooler duct of the P51.

Actually you could do a litte calculation:
Atmos. Pressure in 16k /5km: 0.54bar
in 18k: 0.505bar
in 22k: 0.428bar

Best possible RAM pressure (100%)
at 233mph in 18k: 0.0368bar
407mph in 22k: 0.1bar

now 18k: 0.505bar +0.0368bar = 0.542 = ~0.54 bar
22k: 0.428 + 0.1 = 0.538 = ~ 0.54

Can you see it? 100% efficiency in pressure gain. Sorry, they corrected for the standard day, somehow they corrected also for best RAM efficiency of 100%. Or the alittude indicator showed wrong values at those high speeds, a phenomen that can also observed for the spit14 dive tests.
6k more altitude (compared to 16k) due to RAM effect was definitly not possible for high speeds. Even the power chart lists only 2k for 400mph (assuming the base of 18k).
So i would be careful with those tests, very careful.

When the 109 tops out for climb in 5700m then it didn´t reached in this test the best critical altitude anyway.

It´s probably better to compare strictly the engine performance charts, this one was my source

niklas

gripen · « **Reply #46 on:** November 17, 2002, 04:53:18 PM »

HoHun,
Note that only the first Spitfire IXs had the Merlin 61, vast majority of production had later models ie 66, 70 etc.

For one reason or another USAAF had decided to use the Merlin powered P-51s for tactical fighter duties like the earlier Allison P-51s. So when the first P-51Bs arrived to ETO late 1943, these were allocated for 9th AF. This is probably the reason why they switched to the lower altitude engine variant.

Niklas,
I don't know if you fully understand that A&AEE test data. They simply recorded at which altitude the MAP started to decrease. There can't be big errors in altitude calculations (those were not a dive tests BTW) and you can find several other tests which confirms these results (see Morgan's and Shackladys book). Your chart combines engines with different gear ratios and appears to be somekind of calculation, not test data so it's pretty much useless for accurate comparisons.

Please prove that 6k RAM effect is impossible. Similar RAM effect is recorded for the P-51B too and actually several times.

Also note following note in the DB 605 power chart in the manual:

"Die Höhenleistungen sind abgestellt auf den Gesamtdruck (statisch + dynamisch) und ergeben sich ohne Berücksichtigung der Rückstoßenergie"

So the powerchart allready contains somekind of standard RAM effect (but not exhaust jet effect). And this RAM effect appears to be about same as at climb speed (I have test data). For max speed FTH I used again real world data, I've seen several charts and max speed FTH for DB 605A appears to be around 6-6,5km. But it had to be well over 7km to compete with the Merlin 66 because the Merlin 66 did 1580 at FTH and the DB 605A did 1355hp.

gripen

HoHun · « **Reply #47 on:** November 17, 2002, 05:26:05 PM »

Hi Gripen,

>Note that only the first Spitfire IXs had the Merlin 61, vast majority of production had later models ie 66, 70 etc.

I'm aware of that, but the history of the Merlin 61 nevertheless is interesting as apparently the RAF thought they could break the Fw 190 dominance with an engine with very high critical altitude.

Besides, the initial outpout of Spitfire IX aircraft seems to have been quite low so that while the Merlin 61 Spitfires were small in numbers, they were the only Spitfire IXs at all for almost a year. This underlines the importance of their role.

>For one reason or another USAAF had decided to use the Merlin powered P-51s for tactical fighter duties like the earlier Allison P-51s. So when the first P-51Bs arrived to ETO late 1943, these were allocated for 9th AF. This is probably the reason why they switched to the lower altitude engine variant.

I'm not sure this makes sense - in spite of being scheduled for low altitude duty, the P-51B arrives with a high-altitude engine that later is changes to a medium-altitude engine when the plane is used as a high altitude escort fighter, and never changed back again?

>So the powerchart allready contains somekind of standard RAM effect (but not exhaust jet effect). And this RAM effect appears to be about same as at climb speed (I have test data).

Interesting observation. I had always thought the standard charts to consider ram effect for high-speed flight. Would it perhaps be possible for you to post such a chart with the paragraph you quoted? (Sometimes "Schnellflug" appears in German documents to denote high speed flight.)

Regards,

Henning (HoHun)

gripen · « **Reply #48 on:** November 17, 2002, 06:58:52 PM »

HoHun,
AFAIK Spitfires IXs with other than Merlin 61 engines started to reach units February/March 1943, 7-8 months after the first Spitfire IXs started service.

I don't know about the sense of the USAAF decisions. There were only the V-1650-3 available 1943 and production switched to the V-1650-7 sometime early 1944. I don't know exact date but according to "Rolls Royce and Mustang" decision was made late 1943. The V-1650-9 (P-51H and some late P-51Ds) was a high altitude engine again.

I don't have a scanner but gatt posted part of the DB 605 manual some time ago, see this.

gripen

MiloMorai · « **Reply #49 on:** November 17, 2002, 09:42:10 PM »

Just an idea , but could the P-51 have had its rated altitude decreased because most LW fighters were encountered at a lower altitude thus needing more power at the lower altitude.

gripen · « **Reply #50 on:** November 18, 2002, 03:31:33 AM »

MiloMorai,
Yes in the case of RAF and RR, they saw Merlin powered Mustang as a solution against the Fw 190 and wanted lower altitude variant (see Rolls Royce and the Mustang). In the case of USAF I don't know definite answer; possibly they were happy with their current planes (P-38, P-47) until heavy bomber losses late 1943 turned their heads. Anyway, it's clear that in the beginning USAF allocated the P-51B for the tactical units and that was their policy at the time when the decision to change to the V-1650-7 happened (late 1943). Possibly only NAA saw the P-51 as high altitude fighter because they were developing light weight variants (F,G,H,J) for high altitude engines that time (winter 43/44).

gripen

niklas · « **Reply #51 on:** November 18, 2002, 06:30:21 AM »

Quote

Originally posted by gripen

Niklas,
I don't know if you fully understand that A&AEE test data. They simply recorded at which altitude the MAP started to decrease. There can't be big errors in altitude calculations (those were not a dive tests BTW) and you can find several other tests which confirms these results (see Morgan's and Shackladys book). Your chart combines engines with different gear ratios and appears to be somekind of calculation, not test data so it's pretty much useless for accurate comparisons.

Please prove that 6k RAM effect is impossible. Similar RAM effect is recorded for the P-51B too and actually several times.

Also note following note in the DB 605 power chart in the manual:

"Die Höhenleistungen sind abgestellt auf den Gesamtdruck (statisch + dynamisch) und ergeben sich ohne Berücksichtigung der Rückstoßenergie"

So the powerchart allready contains somekind of standard RAM effect (but not exhaust jet effect). And this RAM effect appears to be about same as at climb speed (I have test data). For max speed FTH I used again real world data, I've seen several charts and max speed FTH for DB 605A appears to be around 6-6,5km. But it had to be well over 7km to compete with the Merlin 66 because the Merlin 66 did 1580 at FTH and the DB 605A did 1355hp.

gripen

Maximum gain in dynamic is rho/2 *v^2. Now you still have some pressure loss effects at the inlet, in the piping system and so on. So they didn´t reached 6k in reality for sure. This is only theoretically possible with 100% efficiency in case of the spitfire, at the given altitude and speed.

For example in the P51-B / F4U comparison the critical altitude was 29k feet, this is some reasonable 2.5k feet higher than the "static" critical altitude of 26.5k. Ok, that was a 1650-3, but the P51 was flying much faster than the spitfire up there.
AH has the P51B in 29k too.
The topspeed of the P51-B in Rechlin was in 8km.

The remark in the german manual seems to be taken out of context. Do you have the whole manual, all pages? 5.7km - and this is the listed critical altitude - did not include the dynamic pressure, this altitude is listed in all DB-manuals who simply could NOT know at what speed the aircraft will fly, what influnces dynamic pressure of course.
Maybe this sentence refer to another picture in the book that we can´t see, maybe it´s just an error, maybe dynamic pressure is something different than RAM effects - i don´t know.

niklas

gripen · « **Reply #52 on:** November 18, 2002, 07:39:41 AM »

Niklas,
We don't know the area of the inlet nor aerodynamic qualities of the inlet (it was a boundary layer scoop system BTW, Spitfire and Hurricane had it long time before Bf 109) and it's a dynamic system. So there is no simply way to calculate max possible RAM effect. What we have is several sets of test data which all claim that the Merlin 66 powered had high speed FTH around 20-22k at +18lbs boost, actually even 18k would give a clear advantage over the DB 605A and is enough to make it about equall with the DB 605AS. Try to live with that.

The V-1650-3 had critical altitude around 23-24k without RAM depending on source (P-51 manual, RR lists etc.). Again there is several sets of data which claim that the P-51B had high speed FTH around 28-29k.

There is an original DB 605A manual in a museum nearby and I have copied it. It seems that DB listed FTHs with somekind of standard RAM effect and this is what manual text says. Comparison with test data shows this clearly or another possibility is that they gave "optimistic"values about the output of their products.

gripen

niklas · « **Reply #53 on:** November 18, 2002, 10:14:54 AM »

According to my source the V-1650-3 topped out in 26.5k while the 61 topped out in 24k.
But well, 24k would explain the results from Rechlin.

There exist a page in the net whith flight manuals for spit-V - XIV and also P-51, but i don´t find it anymore. Do you or anybody else know the link? What P-51 manual do you mean?

The air inlet depends also a lot from the distance to the frame. The inlet of the 109 was much more outside. For the Do335 they found out than increasing the distance of the inlet from 80mm to 120mm brought a significant increase in critical altitude.

The german engine table is definitly not for RAM effect, because in case you should have the G-6, G6/R2 and G6/AS table you can see that for topspeed slightly lower power numbers are listed (1260PS compared to 1310 at sealevel for combat, 1440 compared to 1475 for emergency power).
If you use the chart i posted, start at 16 with a parallel line downwards, and interpolate it to 33k (a bit difficult due to the log-scale) then you will end very close to 800PS in 33k.
Everything else (flight test, error correction) becomes difficult to compare because noone knows how the individual tests were corrected in each country. And i already said: In Rechlin the P-51 topped out in "only" 8km.

Maybe "dynamic" pressure simply characterizes the pressure due to the massflow in the piping system, what is a function of the velocity (RPM, Volume) and density , and not RAM pressure.

Edit: It should be noted that for the Mc.205 topspeed is listed at 7.5km (605A) in some sources. Don´t ask me why it was so high, but this allows a much better comparison with the spit tests.

niklas

gripen · « **Reply #54 on:** November 18, 2002, 04:35:42 PM »

Niklas,
My numbers come from USAF P-51D manual which contain ratings with and without RAM for the V-1650-3 and -7 and these are supported by RR data, Wright field test data and A&Aee data. In addition AHT contains some data (some values there are mixed). BTW what is your source? IIRC a German report stated that the supercharger of a tested P-51 was not working correctly. One possibility is that they were not using RAM air but another intake.

The Merlin 61 is physically different if compared to the V-1650-3. The diameter of the first rotor in the charger is 10,1 inch in the 61 while it is 12 inch in the V-1650-3. And FS gear ratios are different; 8,03:1 vs 8,095:1. Also ratings are different, the Merlin 61 was rated at +15lbs while the V-1650-3 was rated at about +18lbs (67"). And the FS gear FTHs without RAM are following (RR data):

Merlin 61 1390hp at 23500ft +15lbs
V-1650-3 1330hp at 23300ft 67"

I don't know why you are continously trying to argue with a chart which appear to mix together Merlin variants with different supercharger gearings and which appear to contain just calculations? Generally there is lot of good and reliable test flight data available and it's mostly created by professional and experienced test organisations.

About air inlet it should be noted that the Merlin powered Mustang did not have a boundary layer scoop for intake air but somewhat larger area intlet which did pretty well as test data shows. Also piping was quite long but again it did well despite this. BTW the Bf 109G6/AS with the DB 605AS had a larger inlet scoop than the G6 with the DB 605A, quess why...

I don't know if you fully understand why max power ratings of the DB 605AS decreased if compared to the DB 605A. The DB 605AS had simply a larger diameter supercharger from the DB603 and therefore it was able keep wanted MAP at higher altitude. But larger rotor used more power and therefore max power ratings decreased. Also the altitude where the variable speed system started to work increased a bit (from about 2km to say 2,3 km, I don't know exact height, the chart is unaccurate) because the supercharger was able to keep wanted MAP up to higher altitude at it's min speed (max slip). So if you think this carefully, you might be able to figure it out... BTW this phenomena has pretty little to do with the RAM effect, it is there with and without RAM.

So how you explain the text in the DB 605A manual and test flight data which contains also MAP graph (Finnish Bf 109G-2 test and several German charts roughly support these)? These show quite clearly that the output chart contain some RAM effect or the service engines could not reach unrammed FTH height claimed by manufacturer without some RAM. For me the first explanation is far more believeable.

I don't know about the Mc.205 but in the FAF tests the performance of the Fiat G.50 was quite far from the performance promissed by manufacturer. While performance of the Bf 109G-2 in FAF tests was pretty much exactly same as claimed by manufacturer and tested by LW.

gripen

Angus · « **Reply #55 on:** November 18, 2002, 08:11:24 PM »

Gripen:
Niklas will argue to the death. You have to understand: 109 + 109's engine rule all. Wing design, engine, armament, whatever.
If there is any data indicating something else, it is either wrong, or 109 is porked in AH.
In case of that not being good enough, 190 will enter the fray.

Hence the

"niklas

__________________
only a burning spitfire is a good spitfire"

;

:D:D:D:D

gripen · « **Reply #56 on:** November 18, 2002, 11:59:31 PM »

Angus,
So far this has been just a bit of fun; if the arguments are in the level like that DB 605A vs DB 605AS stuff presented above, they are pretty easy to shot down

gripen

Angus · « **Reply #57 on:** November 19, 2002, 07:19:09 AM »

Gripen:
Nothing brings out a better reflection of things than a little "teaser", or as in the core of a good essay, a thesis.
Especially in this excellent forum of AH.
I once put up a post named "WW2 Powerplants", where I was asking for information about ww2 airplane engines, - I got no reply at all.
Now, post something like "DB sucks" and I will have a floodwave of DB information. Post "109 sucks" and I will het a megatsunami of various information (statements, charts, quotations, diagrams, pictures and links) indicating that not only does the 109 NOT SUCK, but indeed RULE.
So, Indeed, a humble "A vs B" thread is maybe the best thing. This thread was quite a success, with you and Niklas, also HoHun contributing a very good amount of data, - something worthy of an essay really.
I am very grateful for being able to access this kind of community, so a big "S!" to you all.

P.S. The DB sucks anyway

niklas · « **Reply #58 on:** November 19, 2002, 07:20:57 AM »

My 1650-3 data was for +16lb this explains the higher altitude.

I´d really like to know how a supercharger that is connected to an engine with a fixed gear can´t work correctly.

Test flight data is an aircraft comparison. To compare engines we have to leave that out.
You said yourself the 66 tops out in 16k. Now how much power would be available in33k withour RAM.

I still doubt that engine performance is given for a kind of RAM effect in case of the DB605. Noone would know the climb speed, the aircraft and so on. RAM effect has very low influence at lower speeds, naturally. And the propeller disturbs the airflow even more actually.
But it´s an interesting aspect, i won´t forget it.
The G6 table lists climb in crit. alt at 5.8km - some lousy 100m more, but it´s a bit more.

The max slip altitude was not a inlet/supercharger size problem. It was determined by the maximum oil temperature, and could be adjusted afaik.

The larger air intake of the AS can contribute to the higher mass flow at high altitudes and/or at higher boost, because MW-50 was almost standard now.

niklas

P.S Ok, it took the allieds 6 years to beat germans fighting in completly inferior material and numbers. Somehow i could also live with the conclusion you can draw out of this point of view

hazed- · « **Reply #59 on:** November 19, 2002, 08:09:43 AM »

If i remember robbie coltrains programme on TV on this very subject correctly it was agreed the DB had a better form of/designed supercharger mechanism but the merlin was the better engine and also the fuel injection system was far better for maneouvering than the merlins version (neg G effects)although there were quoted some benefits to the spits version in cold weather I think it was.great programme and ive probably remembered it all wrong but it goes right through the developement of both engines and speaks to restorers of these engines and the ones used in racing cars of the time(very similar).

wish i had it on tape but its bound to come on again on satalite.