Tweaking the different BMW132 engines for Auntie Ju
Hello Ivan, hello Smilo,
I am still not quite satisfied with the engines in the .air files of the different Ju52 models. Although maximum power and performance is quite OK, continuous power and performance seems high, so Iīm going to improve this, but first I checked for more exact information on the different engines, and stumbled upon some problems which donīt exactly help.
Some time ago, we put in the engine parameters for the FW200A Condor, aiming for the specified 720 Hp at 2050 RPM at S.L. We had found reliable data as to the 6:1 compression ratio, and the 1.2 ATA max. MP from the FW200A operating manuals. The engine type was referred to as a BMW132A or BMW132G-1. This engine is the same type as on the early Ju52/3m g3e and g4e versions, that had 660 Hp BMW132A and 725 Hp BMW132A-3 respectively, both rated at 2050 RPM at S.L.
Engine power on later military versions of both aircraft (FW200A and Ju52/3m) increased, as the BMW132 series was improved, Hp reaching 850 and over, and RPM going up to 2400.
I have always been intrigued as to how exactly the power increase was achieved. Apart from more better materials, more efficient cams, lubrication and refrigeration, the obvious candidates are compression ratio, and manifold pressure. However, there is surprisingly little detailed information on these facts.
So where did the 65 Hp difference between the 660 Hp and 725 Hp engines come from?
Some sources state different compression ratio, giving 6:1 and 6.4:1 respectively, although most quote the same 6:1 for both. Then, one source even mentions a MP value of 1.25 ATA instead of 1.2 for the 725 Hp engine.
Updated paragraph: Incidentally, some sources state the A-3 as giving 715 Hp, which is curious, because ifan .air file regulated to 660 Hp, with 6:1 compression and 1.2 ATA max. MP, were to be modified by increasing compression to 6.4:1 and MP to 1.25 ATA, we get 717 Hp.
Well, so maybe the militarized Ju52/3m 725 Hp engine needed more MP and compression ratio to get the 725 Hp, whereas the Condorīs civil engine, being newer, gave almost the same power with lower compression and MP?
Nevertheless, it is not serious, because the .air file can be made to give correct performance in both cases. I could just leave it as it is, given the fact is that the FW200Aīs 720 Hp engines had 6:1 compression and 1.2 ATA.
When the aircraft was later further improved to the g5e version, the 830 Hp BMW132T-2 engine was used. Here, I had overlooked the 6.5:1 compression ratio!
At least I have one realiable piece of information to make the necessary corrections.
All BMW132 engines with 800 Hp or above had 6.5:1, and power ranged from 800 Hp on the -L version to 850 Hp on the -Z Version. This last one also had direct injection and 3-bladed CV propellers. Apparently the use of CV propellers increased RPM to 2400 on these engines, which only did 2300 RPM with the 2-bladed 2-pitch props. There was even a civil version, the BMW132-Dc, that gave 868 Hp and had a compression ratio of 6.93:1.
Possibly manifold pressure also increased, but I have found no reference to this.
Update No. 2: As an afterthought, if the difference in power from the 660 Hp to the 725 Hp engine came from increased compression and MP, how would one account for the further increase of 105 Hp for the 830 Hp engines? ...apart from just increasing the Torque graph, of course! http://www.sim-outhouse.com/sohforum...s/confused.png ...or shall we just forget the whole issue?http://www.sim-outhouse.com/sohforum...s/positive.png Also, itīs quite doubtful whether itīd be noticeable when flying.
Anyway, Iīm managing to tweak the propeller tables in order to tone down normal performance a bit, and itīs going OK.
Cheers,
Aleatorylamp
Superchargers versus Manifold Pressure
Hello Aleatorylamp,
I believe you are working under a few misconceptions.... Or perhaps I am.
Here is my view of the way superchargers work:
Some basic background (which I am sure you know, but others may not).
Basic Engine Parameters:
Compression Ratio
Displacement (In CFS, we don't distinguish between long stroke and short stroke engines.)
Maximum Boost / Manifold Pressure
Then we have the Supercharger
We can have single stage, two stage, or even more stages.
This generally affects to what altitude the supercharger can maintain sea level boost pressures.
We can have single speed, two speed, or even more speeds in real life but in CFS, we can only simulate power curves for SINGLE SPEED superchargers. I believe I discussed this in the Engine Tuning Tutorial.
The issue here is that we can't really duplicate the power drop or "Jag" in the power curve from blower gear changes.
The point that I believe you are confusing here is that the static compression ratio really has nearly nothing to do with altitude performance.
Note that the Merlin had a 6.0:1 compression while the Allison had a 7.0:1 compression but the big difference was that the Merlin got a better supercharger earlier and then a two stage supercharger while the Allison usually had only a single stage and smaller supercharger.
Thus the compression ratio of a particular BMW 132 doesn't really tell you anything unless you know there is a historical link beyond what has been stated.
Note also that maximum boost pressure or manifold pressure also doesn't have much to do with altitude performance.
When the P-51A (Mustang Mk.II) got a two speed supercharger for its Allison engine, it had better altitude performance than earlier Mustangs even though the maximum manifold pressure was lower. The speed at Sea Level was lower because the maximum boost was lower but it could maintain that boost pressure to a much higher altitude (about the same as the Single Stage Merlin engines).
Thus a 1.20 ATA versus 1.25 ATA is also no real indication of a more capable supercharger or better altitude performance.
It is actually more likely an indication of improved engine parts and strength.
Some Ju 52 manuals are available on the Internet without cost, but so far, I have not been able to find anything useful in the ones I have accumulated. They are listing engines in the 620 PS range and happen to be very early manuals. I would send you a copy of what I have, but it is a bit too large to email and really doesn't provide the information you want anyway.
I checked in my copy of Jane's 1946, but found nothing at all on the BMW 132.
I have a very similar need for information for one of my own potential projects at the moment.
Regarding your comments about the kinds of engines I have been tuning:
I have actually spent more time tuning engines for your projects recently than for my own projects!
- Ivan.
Acceptable results with strange graph shapes.
Hello Ivan,
The specified Max. Power and MP settings for the 725 Hp BMW132A-3, at S.L. and altitudes upto 7200 ft as posted a few days ago:
1 min: - 2050rpm / 1.25ata - 725PS @ S.L.
5 min: - 2050rpm / 1.13ata - 640PS @ S.L., 660PS @ 2952ft
30 min: - 1975rpm / 1.06ata - 575PS @ S.L., 600PS @ 4600ft
max. cont: - 1930rpm / 1.02ata - 535PS @ S.L., 565PS @ 5600ft
cruise: - 1860rpm / 0.96ata - 485PS @ S.L., 515PS@ 7200ft
I have managed to get some more or less satisfactory results by making adjustments to the propeller table 512, which however also included some adjusments to the torque graph, where I have put in a "hump" before the 2050 RPM point, in order to to increase Hp for the lower RPM settings. This "hump" is probably not very orthodox, and may be questionable.
I found I could avoid it by compensating in Propeller Table 512, but the graph shape got very obnoxious, requiring a strange "valley" shape at J=0.4, also affecting J=0.6 a bit.
The "valley" in Propeller table 512 looks just as obnoxious as the "hump" in the torque graph.
Anyway, a summary of the results:
Results at S.L.:
---------------
Max. Power Hp and RPM are exact.
At lower throttles, Hp results are exact, but RPM tend to be 60-70 RPM lower than desired.
Results at 3000 ft:
------------------
Max. Hp and RPM are fine at 2952 ft.
5 min. power throttle is 9 Hp and 13 RPM low, but may be acceptable.
Results higher up, upto 7200 ft:
------------------------------
Hp and RPM tend to get progressively higher than desired with altitude, upto 34 Hp. and 200 RPM.
Well, I suppose it was to be expected... I wonder if you would have any comments.
Perhaps this can be regulated by reducing Boost Gain, which I havenīt tried yet.
Possibly the increase from 1.2 ATA to 1.25 ATA, which increased overall engine power, would require an equivalent reduction in Boost Gain.
Update: Reducing Boost Gain may be a way to fix the excessive power at higher altitude, but it may go against specs. Iīve just checked the model: Specs say full ATA is maintained upto 5900 ft, and in this case, MP starts going down a little before, just like on the 1.2 ATA model, so at least it canīt be said to be excessive.
Cheers,
Aleatorylamp
1 Attachment(s)
New 725 Hp engine for g4e
Hello Folks,
Looking at the BMW132 power vs altitude graph, it is safe to assume that the BMW132A-3 engine worked with a max. manifold pressure of 1.25, delivering 725 Hp at 2050 RPM for take-off.
Performance is as close as possible close to specification in as many positions along
the curve as possible. Altitude performance is very similar to the previous .air file.
Results, compared to manufacturerīs power chart S.L. - 7200 ft:
1 min power: 100% throttle, 1.25 ATA
------------------------------------
S.L....: 2052 rpm (+2 rpm), 725 hp (OK!), 165.6 mph (+0.6 mph)
2952 ft: 2153 rpm ( OK! .), 771 hp (OK!), 173.5 mph (+1.5 mph)
5 min. power: 89% throttle, 1.13 ATA
------------------------------------
S.L....: 1971 rpm (-79 rpm), 639 hp (-1 Hp), 160.5 mph
2952 ft: 2037 rpm (-13 rpm), 651 hp (-9 Hp), 165.3 mph
30 min power: 84% throttle, 1.06 ATA
------------------------------------
S.L....: 1903 rpm (-72 rpm), 575 hp ( OK! .), 154.9 mph
4600 ft: 2028 rpm (+53 rpm), 612 hp (+12 hp), 164.8 mph
max. continuous power: 81% throttle, 1.02 ATA
---------------------------------------------
S.L....: 1865 rpm (-65 rpm), 539 hp (+ 4 hp), 151.6 mph
5600 ft: 2023 rpm (+93 rpm), 590 hp (+25 hp), 165.4 mph
Cruise power: 76% throttle, 096 ATA
-----------------------------------
S.L....: 1797 rpm (-63 rpm), 485 hp ( OK! .), 146.2 mph
7200 ft: 2005 rpm (+145 rpm),549 hp (+34 hp), 163.1 mph
Restly altitudes:
10000 ft:
---------
100% Throttle 1.02 ATA: 2177 rpm, 644 hp, 176.0 mph
_83% throttle 0.90 ATA: 2053 rpm, 524 hp, 165.2 mph
19000 ft:
---------
100% throttle 0.72 ATA: 2073 rpm, 419 hp, 164.7 mph
_83% throttle 0.63 ATA: 1956 rpm, 350 hp, 156.3 mph
It isnīt perfect, but itīs as good as possible a balance achieved with micro-adjustments
on tables 512 and 511, as well as a convenient Torque graph shape.
Of course, as always, any suggestions will be welcome. If anyone were to be interested
in seeing or should have the time and gumption to try out the.air file, I will gladly attach
it to a post.
Re: 830 Hp BMW132T-2 engine for the g5e
Looking at the BMW132 power vs. altitude graph again, for this more engine of the g5e,
it seems safe to assume that the manifold pressure for take-off power would be 1.35 ATA.
I am adapting performance accordingly. As before, any warnings or suggestions will also be welcome!Thank you very much for your interest.
Hereīs another screenshot of the g4e just for eye-candy.
Cheers,
Aleatorylamp
1 Attachment(s)
New Spanish Supercharger too.
Hello Smilo, Hello Ivan
Thanks, Smilo, for your interest! OK, hereīs the .air file for the g4e night flier, attached to this post!Remember, it is the 725 Hp version recovered from the Norwegian lake in 1986, at present in a Norwegian museum, very nicely restored!
OK - now, apart from the other 830 Hp engine pending supercharger correction, the third model
also needs supercharger attention: The Spanish CASA 352L.
This Ju52/3m version has three Elizalde (ENMA) Beta B-4 engines, that deliver 775 Hp at 2200 RPM. They are Spanish licence-built American Wright Cyclone R-1820īs, just like the Russian Shvetsov M-25, of which the Spanish Air Force also had a number for their Polikarpov I-16 Rata/Mosca fighters.
I have found no information whatsoever as to these enginesī manifold pressure, and upto now I had 1.2 ATA (34.87 inches Hg) for want of anything else, and it has worked quite OK.
Nevertheless, I though Iīd try and get it better, even if actual model performance will stay the same. So, looking, I found a Power Chart, within a Wright Cyclone R-1820 Engine Overhaul Document - I canīt make head or tail out of it... so many different engine versions ranging from 575 to 1525 Hp... but I enclose it herewith. Perhaps someone can find some use for it!
However, looking further, on an Air Tractor page I found a comment:
Someone was installing a Wright Cyclone R-1820-72 on his M-A1B Air Tractor. Apparently this power-house was going to be a bit much for the crop-duster! 1200 Hp at 2500 RPM, manifold pressure of 45 inches of mercury, would be overdoing it a bit, I suppose...
So, he decided to derate his engine to 900 horsepower, by limiting rpm to 2,300 and manifold pressure to 36 inches, for take-off and for continuous use. This way he was also going to increase its service life.
Interesting piece of information... I could further derate this engine to give me 775 Hp and 2200 RPM. The numbers donīt tally absolutely exactly, so Iīll strike a mean between the two results:
300 rpm less: 45 13.5 = 31.50 inches
425 Hp less: 45 - 9.5625 = 35.4375 inches
Average 33.46875 inches, the new Manifold pressure for the 775 Hp Elizalde Beta B-4.
With a slight adjustment on the Torque graph, I can get exactly the performance needed!
Would you think this could be a plausible, acceptable way of going about the matter?
Opinions will of course be very much appreciated!
Hereīs a screenshot of the Spanish Ju52/3m for more eye-candy.
Remember, the attached -.air file is for the armed night-flier bomber/transport.
Thanks again, and Cheers,
WEP by Methanol-Water injection
Hello Ivan,
Thanks for confirming! Iīll go about it that way then.
For practical purposes in the sim, I think it will be a simple and good solution.
I expect that Smilo will also agree!
Out of curiosity, I tested whether keeping the throttle at 85% would prolong WEP time allowed, but itīs the same 5 minutes as for 100%. Anyway, itīs partially realistic though, as 84% throttle was allowed for 5 minutes.
What happens with water-methanol injection? I think the engine rusts! ...If used at speeds above cruising, I suppose it would possibly interfere with lubrication and maybe quickly ruin the engine.
Itīs not such a stupid idea at all, actually, but do correct me if Iīm wrong!
The impression I got was that interestingly enough, methanol performance increase came with the penalty of greater heat, so they injected water to cool that, also obtaining the added thrust of the steam generated. The drawback of all this was I believe greater corrosion resulting in reduced engine life-span, but for military purposes it wasnīt important.
Later, the French did the same with their Turbomeca Bastan VIC turboprop turbines, with similar results, although here there was no methanol, just water. They were actually quite successful, and used them on the Nord 262 commuter/navy patrol aircraft for quite some time.
Hereīs a screenshot of one I made for FS98. The lines are quite elegant. (Youīll say Eeek! A jet!!). The Americans modified a few of these with PT6 P&W Canada turboprops and called them Mohawk-298, for use by Allegheny Airlines for some years.
Iīm curious as to what idea you may come up regarding water-methanol injection in the flight dynamics!
OK then, cheers,
Further to the Power Curves
Hello Smilo, hello Ivan,
For the moment, the power curves of the three engines (725, 775 and 830 Hp)
are very accurate at S.L. compared to the specified maximum and cruise powers
for S.L:
All are exactly bang on +/- 0 Hp, except the 830 Hp engine which
is 18 Hp low at 76% throttle.
However, further up, there is some discrepancy with specs:
_9-29 hp low at 3000 ft,
_8-12 Hp high at 4600 ft,
21-30 Hp high at 5600 ft, and
34-43 Hp high at 7200 ft.
Further up, I have no spec. data to go by.
I was trying to figure out a way of evening out the consistent excessive power
from 4600 to 7200 ft in the specs, but could only come up with the idea of
lowering Boost Gain a little, so as to reduce the excessive Hp at 4600, 5600
and 7200 ft., but this is not possible:
The RPM ranges involved overlap with the RPM ranges for 3000 ft, so any
reduction to correct performance further up would further reduce performance there.
The only thing that occurs to me is to either
a) leave it that way, as for simming, a little extra power at the altitudes involved will be fine, or
b) reduce power altitude power a bit the excess, at the expense of losing power lower down.
Iīd vote for leaving it as it is, unless you would have a different preference.
What would your preferences be?
Cheers,
Aleatorylamp