Project Martin A-30 Baltimore

[aleatorylamp]

Hello Ivan,

The massive P47 engine seems to have the best propellers to fit the impressive 2x1700 14-cyl supercharged engines (1700 hp at 2600 rpm) of the Baltimore. Ceiling appears to have been quite a considerable 25000 ft.

Putting in the cylinder capacity and compression ratio parameters, and adjusting the torque and friction tables, I get quite a close and possibly quite satisfactory 1720 hp at 2585 rpm.

The engines had a 2 stage supercharger, which for CFS1 will unfortunately have to be single stage, probably with only with approximations to fit performance at different altitudes.

I was looking for your thread on engine tuning, but haven´t had any luck yet.

As I have few details on the engine itself, I have to juggle around the P47 parameters relative to Boost Gain and Manifold Pressure a little. For the moment I have slightly reduced the P47 ones, but I feel like groping in the dark a bit.

I´m getting too much power at altitude, but reducing manifold pressure to adjust it, low altitude power drops considerably (of course...).

Without putting you out too much, perhaps you could recommend something, or maybe simply point me towards your engine-tuning thread?

Thanks a lot!
Cheers,
Aleatorylamp

[smilo]

at this point, this is the only document i have.
can you read or translate (i believe) Polish?
according to this document,
the MkV had 2xR-2600-29's
and farther down, notice
fuel...490 US gal=407.7 Imp. gal. at 2940.0 lb
oil...27.5 US gal=22.9 Imp. gal at 206.3 lb

[aleatorylamp]

Hello Smilo,

Thanks for your information - it definitely clarifies the type of engine and tank capacity!

As regards the attached document, I´m afraid the resolution is too low for it to be legible.
My only remaining doubt at the moment would be the top speed.

If you can make out the info regarding speeds, maybe it´s easier if you just tell me instead of trying to send a picture in higher resolution of the document.

If all fails, I´ll just take the present info as Max. speed 320 mph at 15000 ft and 308 mph at sea-level, unless of course, being a supercharged engine, the speed could be the same at any altitude... Hmmm...

Thanks!
Cheers,
Aleatorylamp

[smilo]

i can barely read it either
and i'm looking at a 48 inch screen.

i was able to google some of the words
and got a few,

predkosc=speed
maks.=max.
wysokość= altitude
therefore, max speed altitude[mph/ft]=320mph/15,000ft

przelotowa=looped or cruising
therefore,
predkosc przelotowa [mph] might mean
cruising speed[mph]=224mph

pulop(?) i can't get a translation
praktyczny=practical
ft=25,000

zasieg normalny [mile/lb]=980/2000
zasieg=effect_range
normalny=normalmight, therefore be,
normal effective range
of 980 miles with a 2000 pound load.

these values are all in the MkV column.

that's about all i'm able to come up with.


ps...i do see that 308***/13000
in the MkI and MkII columns
unfortunately,
i am unable to read the footnote.
but, i can see 284mph/ 457, 1 km/ft

[aleatorylamp]

Hello Smilo!

That´s excellent! Thanks very much indeed. There´s no doubt anymore and I can proceed with this data.Pulop should mean ceiling then.

I found an interesting page mentioning some performance data. As I know you like the plane, and for the event that you haven´t seen this info, here it is:

QUOTE
With bomb-bay auxiliary fuel tanks (as used during ferry deliveries from USA via the Equatorial Atlantic route), a range of 5-1/2 hours was possible. By fitting a 700 gallon tank in the bomb-bay
we cold range out as far as the Dardanelles and into Northern Greece on recon.

The Baltimore was an aeroplane all pilots feared before they started flying them, mainly because noinstruction was available. You were given a dossier on the aircraft and when you thought you knewenough about it you took off.

Landing a Baltimore required a special technique and we all had trouble with the landings until we developed this technique. A flying boat skipper could have landed a Baltimore easily; the technique was the same:Come in low with power, then at one or two feet ease on more power until the wheels touched, then ease off power. Once on the ground it was imperative you kept absolute control because she was a vixen for group-looping.

Take-off in a war machine like a Baltimore or a Spitfire is an exhilarating experience. The acceleration is so great you feel you are being punched along. The stalling speed was 118 miles per hour so you had to be doing more than that before take-off.

The single engine control speed - that is, the speed if one engine cuts so you can still maintain control of the aeroplane - was 165 miles per hour. so there was a 47 miles per hour gap to make up before you could consider the flight under control. This period lasted a few seconds only due to the high rate of acceleration.

The undercarriage which always is a drag when suspended, would retract in a Baltimore in three seconds, and by the time the undercarriage locked in the "up" position the speed was only a second or two away from 165 miles per hour. Once it raced past that speed it was a glorious aeroplane to control.
UNQUOTE

It must have been quite an experience to fly the Baltimore!
Cheers,
Aleatorylamp

[smilo]

that was interesting, thank you.
speaking of the ferry tank,
here's a fron and side view;

[aleatorylamp]

Hi Smilo,

Good, thanks. I had no idea it looked like this!

At the moment I´m tuning the engine to try and get the speeds right at low and high altitude. For the time being, I can only get one or the other to coincide.

I´ve finally found Ivan´s Engine Performance Tuning Tutorial again, and I´ve copied it all out to study it thoroughly. Upto now I could only get the gist of it, but now I´ll delve deeper.
With all that´s in there I should get the Baltimore´s performance bang on!!

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp, Smilo,

I have been occupied with other things and had not been following this thread for a while.
The PC still crashes at strange times, but at the moment it is a matter of reviewing the P-40 AIR files and much of that can be done on other machines.

There seem to have been a great number of developments.

I am glad you found the Engine Performance Tuning thread. Too bad it is not a sticky.
You commented earlier that you could not find data for the Wright R-2600 engine.
I have actually found that most of the really essential data can be found on Wikipedia among other places.
The only thing missing from Wikipedia is the Manifold Pressure settings.

One way to cheat a little is to just use the numbers I have in my AIR file for the B-25C Mitchell.
It has basically the same engine though altitude ratings may be a bit different they are still going to be very close.
I do not recommend using the entire AIR file because I made a lot of changes to tune for the Anhedral on the Mitchell's wings.
One way to confirm data is to find the manual for another aeroplane that uses a similar model engine or perhaps you can find the SEFC as a separate posting somewhere.
I would need to do some poking around to see what model of engine and whether I have data.
I am pretty sure I actually have lots of data on the Baltimore.

Regarding Propeller tables, it might be worthwhile to calculate the Propeller Power Coefficients for each of the stock aircraft and find out which one is actually closest to the Baltimore. Just eyeballing the sizes and such doesn't work all that well because of the Reduction Gear Ratios. Also, operating speed ranges are important.

I actually have a much better and readable copy of the Table of data that Smilo posted.
Let me know if you need it.
The 284 MPH listing as a footnote is a Sea Level Speed if my phonetic Polish to Russian translation is accurate.
Even though the listing is for the earlier Marks, the value should be pretty good for all the versions IMO because 100 HP is not going to make a significant difference. Also, later aeroplanes tend to have more power but also tend to have more drag from equipment additions.

1700 HP at Take-Off is probably the equivalent of a WEP rating.
Be very careful about assuming that the 1450 HP at altitude is actually a maximum rating.
The changes are that it is not a maximum.
It is more likely to be a Military rating.

Regarding Engine Versions:
My guess is this:
This aeroplane was originally used as an export model to the French and British.
The US military was fairly uptight about sending out their latest and greatest engine (especially supercharger) designs.
The Curtiss-Wright typically used a designation of GR for reduction geared radial engines and a simple R for direct drive.
This can be seen in the Brewster export versions of the Buffalo which had both versions.
The GR-1820 designation was probably a commercial designation of an export cleared engine and other than the supercharger and minor details that we don't care about in CFS, dimensionally the same as the US Military R-1820.

Hope this helps.
Email me if you don't have a version of the B-25 Mitchell to check out.

- Ivan.

[smilo]

making the Engine Performance Tuning Tutorial a sticky
is a good idea...it's done.

also, if you have a better and readable copy
of the Table of data, please post it.
is it in english?

[aleatorylamp]

Hello Smilo,
I actually thought it would be of interest to put all of Ivan´s Engine Turtorial posts into one document to make it more readable. I managed to put it all together, inverting the order of the posts to get the beginning at the top, also sifting out the off-topic material. Finally I made one .rtf format type document out of it - this way it keeps headings in bold type. Here it is, attached!

However, there were no longer any attachments contained in the thread, so there´s just the information in the posts themselves.
As regards the Table of Data: I´m afraid that´s not there either. ...however, maybe I don´t understand exactly what you mean...

Hello Ivan,
Thank you for your interesting (as always!) post on the Baltimore´s engines. They had a single 2-speed supercharger with a volume compression of 7 to 1 and 10 to 1. Early versions had geared props, but the Mk.V didn´t so there´s no problem as to the reduction ratio.
Thanks for the comments on altitude and power for these engines. So for maximum take-off power probably 1660 hp would be better, keeping 1700 hp for WEP.
The clarification on the sea-level setting being 284 mph is fantastic because it now coincides far better!
Conclusions from your comments:
1) Maximum speed of 320 mph at 15000 ft would then be without WEP.
2) One source quotes 329 mph at 15000 ft here, so perhaps this was achieved with WEP.
3) Possibly the widely quoted 305 or 308 mph max. speed refers to the sea-level performance under WEP.

Cheers,
Aleatorylamp

[smilo]

"I actually have a much better and readable copy
of the Table of data that Smilo posted.
Let me know if you need it."

is a quote from Ivan's #33 post above.
i was merely encouraging him to post
his "better and readable copy".

[Ivan]

Hi Smilo,

I will need to coordinate with Anna Honey to pull the image out of a rather large PDF.
She has a full version of Adobe Acrobat on her machine.
I do not have a PDF editor / extractor and getting something useful out of a PDF is always a chore.

Hi Aleatorylamp,

I believe you are misinterpreting my meaning about the GR-2600 as versus the R-2600.
Wright called their engines R for direct drive and GR for reduction geared.
The US Military did not make any such distinction. ALL of their models were R-something.

The point I was trying to make was that the early GR designation on the early Marks was because it was not a US military version of the engine, thus it used the Curtiss Wright commercial designation.
The Mk.V used a R-2600-13 or R-2600-29 which was the US Military designation of basically the same engine though with a slightly higher rating.

While the R-1820 was used as both a geared and direct drive engine in the Buffalo, the R-2600 was a much bigger engine and probably was never used as a direct drive engine.
The R-1820 in the early versions had a very low maximum RPM (about 2200) so a direct drive with a small propeller on a rather slow fighter would not be too far out of range.

I did a bit of poking around last night in my downloaded manuals and found this:
The R-2600-13 was used in the B-25C/D models. (The version I built.)
The R-2600-13 OR R-2600-29 was used in the B-25J.
The Pilots Manual makes no distinction between the two engine models in operation.
The power output is identical between the two versions.

Here is a link to a copy of the SEFC that I found. It is for the B-25C/D, but as stated earlier, there is no difference from our point of view.
http://zenoswarbirdvideos.com/Images/B-25/B25SEFC.pdf

Gotta Run. Need to go do some grocery shopping.
Email me if you still need the B-25C AIR file.

- Ivan.

[aleatorylamp]

Hello Smilo,
OK, I understand!

Hello Ivan,
Thanks for the B25 engine specs. Very detailEd and useful!
I thought I saw your B.25 in the warbirds library, in order to get at the .air file, but I was mistaken. It would indeed be useful, so I´ll e-mail you to have a look inside! Thanks for the offer!

The reason for my thinking that only earlier versions of the Baltimore had geared engines was in the different spec sheets where I found the following mentions:

- Powerplant: 2 × 1700 hp Wright GR-2600-A5B geared radial engines.
- Engine: 2 x Wright-Cyclone R-2600-19 (1660 hp) (Mk.V: R-2600-29 1700 hp)

...but then a 3rd mention says:
MkI to MkIII: 2x 1660 hp Wright Cyclone GR-2660 A5B
MkIIIA and MkIV: 2x1660 hp Wright Cyclone R-2600-19
MkV: 2x1700 hp Wright Cyclone R-2600-13 or 29

The fist mention does not mention the model the geared engine was used on, and the second one probably omits it altogether, but the third mention does clearly state the geared version for the earlier ones. Also I see the number on the two mentions of the geared engines are different! Maybe unreliable?
Then, wouldn´t the B25 engine spec sheet state the fact that it was a geared engine if it was in effect geared? But as you said, perhaps the American specs did not make any distinction.
Anyway, geared or not geared, I suppose it wouldn´t make much difference in the .air file.

Thanks a lot again!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp.

Check your email.

The reason I do not believe the Mitchell's AIR file is useful to modify into one for the Baltimore is because although the weights and performance and engine may be the same, I did a lot of odd tuning for the Mitchell.
The Anhedral of the outer wing panels resulted in a strange yaw to roll coupling that I was trying to duplicate.
There were a LOT of changes to get there and I believe you would do better to start fresh.

As for geared versus direct drive, there should be a serious difference in performance in real life.
Although it may not be shown in CFS, the large propeller and a high RPM direct drive means the blade tips will be supersonic and very very poor efficiency.

I still have not had a chance to borrow Anna Honey's computer for Adobe Acrobat yet.

- Ivan.

[aleatorylamp]

Hello Ivan,
Thanks for the Mitchell B25-C .air files. They are proving very useful.

I did not mean to use the whole .air file. Actually, only the engine manifold pressure and boost gain parameters, the torque and the friction tables, and the propeller efficiency and thrust coefficient tables.
The propellers on the Baltimore were smaller: 11 ft. The Mitchell´s were 12.58 ft, so perhaps they were not geared on the Baltimore?.

At any rate I´ve done some quick preliminary testing, trying them out as geared, and the performance seems to be fitting nicely within more correct speed ranges. One thing is good, I´m not getting the huge Hp increase any longer from 1700 Hp at sea-level to 1985 Hp at 15000 ft. Now it´s between 1660 and 1680 hp.

Tomorrow I´ll have some more exact results.
Good night!
Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,

Here are some more exact test results after finer adjustments in Zero Lift Drag and Torque Table. To have some basic reference for the MkV, I was using full throttle.

Performance aimed for:
1700 Hp
2600 RPM
284 mph at Sea-Level
308 mph at 15000 ft
Please correct me if the aimed performance is wrong.
I increased it a little from the Mitchell data because the Baltimore, being lighter and smaller, was perhaps faster, especially with the 1700 Hp engines instead of the 1600 Hp ones.

And this is what I got:
Sea-Level:
1679 Hp
2592 RPM
286.5 mph
44 Mpsi
1678 Thrst

15000 ft:
1716 Hp
2592 RPM
310 mph
40.3 Mpsi
1586 Thrst

I´m not sure exactly how to get it down to 1450 Hp at 15000 ft and keep the speed the same. I was looking in the tuning tutorial, but for the moment increasing both torque and friction tables hasn´t been working.

Engaging WEP I got a considerable increase, too much in fact, but I´m not exactly sure what I´m looking for here. I got 294.8 mph and 1853 Hp at SL and 327 mph with 2050 Hp at 15000 ft.

Anyway, I was wondering if you have any comments, which I would appreciate very much!
Thanks in advance.
Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,

I thought I´d try and get it a bit closer to what I was aiming for.
Now I got it at exactly:
1700 Hp with 309.1 mph for 15000 ft and
1672 Hp with 286.3 mph for sea-level,
both at 2590 RPM.

But, perhaps I´m under a misconception here... still...

If as you said the 15000ft Maximum speed reading of 308 mph is not at Maximum power then it is a Maximum Continuous power. Also, the most reliable source states 320 mph as Max. Speed, and this is the speed I should be aiming for with flat-out accellerator performance.

The maximum performance specified in the Mitchell engine chart for
Maximum Take-off power is 1700 Hp with 44 Mpsi at SL.
Strangely enough, their Emergency Maximum power is also 1700 Hp, but with:
42 Mpsi at 4500 ft and
41 Mpsi at 12000 ft.
BOTH these power settings are only to be enjoyed for 5 minutes!

So there is no WEP in reality, only just flat-out on the accellerator. Question: How do you select Mpsi, or does it just happen with the altitude?

Then: Maximum Continuous power appears to be completely different:
It is at 2400 RPM,
1500 Hp with 38 Mpsi at 6700 ft and
1350 Hp with 39 Mpsi at 15000 ft.

Now the thing is to get the engine revs to coincide with the power for the lower settings.

Update:
The problem with the 1500 Hp at 6700 ft and the 1350 Hp at 15000 ft is that the revs always stay the same, at 2590 and won´t go down to 2400 RPM.
Then: Getting the maximum full flat-out, 5-minute 1700 Hp speed up to 320 mph instead of 305 or 308, now brings up the Maximum Continuous speeds upto around 295 mph at low altitude and 305 mph at higher altitude. Perhaps this is correct?

Anyway, I´ll keep on trying.
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

You have brought up a LOT of subjects.
Hopefully I won't miss anything significant.

Regarding the Wright R-2600 engine being direct drive on the Martin Baltimore:
The specifications given thus far pretty much guarantee that this is not the case because....
The Propeller is 11 feet in diameter.
Maximum Engine Speed is 2600 Revolutions Per Minute.
This combination means that even with the aeroplane not moving, the Propeller Blade Tip would be travelling at 1497 feet per second or 1021 MPH.
Considering that the Speed of Sound is 762 MPH at Sea Level and only decreases with altitude, it means the Propeller Blades would be Supersonic which simply would not work well if at all.

Check your propeller specifications. If you cannot achieve maximum RPM of 2600 with 1700 HP and an 11 foot Propeller, there must be something wrong.

How are you configuring WEP?
If 1700 HP @ 2600 RPM with 44.0 inches Manifold Pressure is Take-Off and the Normal Maximum, how are you getting above that?
44.0 inches is THE HIGHEST Throttle Setting for this engine. There should be no higher.
The question is whether you allow it as normal full throttle or require that WEP be engaged to achieve this is your choice.
What is WEP is a subject I have discussed before in a thread specifically on the subject.

I do not know where you are getting Mpsi from.
The Specific Engine Flight Chart (SEFC) Table shows everything in Inches of Mercury (inches Hg) which is the same unit used in the AIR file.
With other nationalities, there may be a conversion of units required but not for the United States.

How do you select Manifold Pressure?
With the Throttle control on your Joystick. (No, it is not all that precise.)
How do you select Engine Speed?
Use <Control>Function Keys 1-4.

As I commented earlier, the 1450 HP at Altitude was probably not a maximum rating.
It probably is not a "Maximum Continuous" rating either.
My guess is that it is the "Military" rating of the engine.

Regarding the performance of the Baltimore being better than the Mitchell, I would rate them as quite similar.
The maximum speeds are pretty near identical for the Baltimore as compared to early Mitchells (such as the C).
The two aeroplanes were fairly comparable in size though the Mitchell was a bit bigger.
The A-20 Boston / Havoc was almost exactly the same size with the same engines and also considerably faster.
The Mitchell was slightly bigger and was not a particularly sleek aeroplane which would imply that the Baltimore was considerably worse from the standpoint of Form Drag.

Hopefully I addressed a few of the issues.

- Ivan.

[aleatorylamp]

Hello Ivan,
Thank you for your pacience. Yes, you have addressed all the issues!

Thanks about clarifying the propeller details. I´d just thought, as it was 1.6 ft smaller there might have been a chance it wasn´t geared, but my doubts are cleared.

Mpsi would be Manifold Presure per square inch, and in the Mitchel spec sheet they call it Manif.Press.(Boost). Then they also add a column with the blower speed as being High or Low. Beckwith´s guage calls it Mpsi, so I called it that... but we´re talking about inches of Hg in any case, so that will be OK.

Very well, as the Spec sheet calls it Emergency Maximum, I´ll implement WEP with 44 iches of mercury Manifold Pressure so that you have to press F10 for take-off, and leave normal Maximum Contimuous at 42 inches of mercury. That will be a very practical solution, so we can avoid going into Emergency Maximum just by giving full throttle. Excellent idea! I´ll make the necessary changes and report back (hopefully) improved results!

Interesting how the Havoc and Mitchel compare to the Baltimore!

Thanks, and
Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,


It´s unfortunately not working.
The main assumption is that the engine parameters in the Mitchell B-25C .air file would be adequate, but perhaps not the propeller tables, as the Mitchel propellers are 12.58 ft in diameter, so I´ve exchanged the propeller efficiencuy and cthrust coefficient tables for the stock Fw190a´s 11 ft propeller tables.
However, the main problem is still remains, that performance is too high at altitude when set correctly lower down, and if set correctly for at altitude, performance is poor lower down.


Perhaps it will be best to go back to square one, so I will sumarize the settings and the aims that would be used to start off with. The main thin is that these parameters should be the correct ones.


1) 1700 hp with 2600 RPM is WEP (at all altitudes). (Are the present 2592 RPM good enough?)
2) 1450 Hp is military power - presumably at 2400 RPM?
2400 RPM with 1350-1500 Hp (6700-12000 ft) is specified as continuous power,
PROBLEM: The .air file will not lower the RPM.
3) The props are geared (no problem).
4) WEP is with 44 Mpsi and normal Continuous Power is with 42 Mpsi.
4) 284 mph at SL is at Maximum Continuous speed.
5) 305 mph at SL would presumably be with WEP.
6) Specified 320 mph max. speed at 15000 ft would obviously be with WEP.
7) 305 mph (or 308 mph) at 15000 ft would be with Maximum Contimuous speed.


Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,

It´s unfortunately not working.
The main assumption is that the engine parameters in the Mitchell B-25C .air file would be adequate, but perhaps not the propeller tables, as the Mitchel propellers are 12.58 ft in diameter. So, I´ve exchanged the propeller efficiencuy and thrust coefficient tables for the ones of the stock Fw190a. However, the main problem is still remains: Performance is still too high at altitude when set correctly lower down, and too low lower down if set correctly at altitude.

Perhaps it will be best to go back to square one, so I will sumarize the settings and the aims that would be used to start off with. The main thin is that these parameters should be correct.

1) 1700 hp with 2600 RPM is WEP (at all altitudes). (Are the present 2592 RPM good enough?)
2) 1450 Hp is military power - presumably at 2400 RPM? ...but the .air file won´t lower ther RPM.
3) 2400 RPM with 1350-1500 Hp (6700-12000 ft) is specified as Max. Continuous power, but the .air file won´t lower the RPM.
4) The props are geared (no problem).
5) WEP is with 44 Mpsi
6) Max. Continuous Power is with 38-39 Mpsi. (Oops! I had 42 here!)
7) 284 mph at SL is at Maximum Continuous speed.
8) 305 mph at SL would presumably be with WEP.
9) Specified 320 mph max. speed at 15000 ft would obviously be with WEP.
10) 305 mph (or 308 mph) at 15000 ft would be with Maximum Contimuous speed.

It should get better now I´ve seen my mistake in the Max. Contimuous Power Manifold Pressure setting.

Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,
I seem to be progressing... It´s a bit difficult as this engine is very different from the old slow ones from the Great War that I´d got used to!

I finally had success after some futility trying out something you mentioned in the tuning thread, i.e. reducing the excessive surge of performance at altitude with balanced increases in the torque and friction tables. This surge has now become appreciably smaller: I increased the torque from 0.585 to 0.637 and the friction from 39 to 60.
I have the feeling that this has also caused a convenient increase in the difference in power between WEP (44 Mpsi) and the normal Maximum Continuous Power (39 Mpsi) which is at full throttle.

All in all, the performance envelope looks better now:
I´ve included some intermediate altitudes that are mentioned in the B-25C Spec. Chart.

Max RPM is always 2593 RPM... high altitude, low altidude, WEP, non-WEP... (no way to correct this for the moment).

500 ft:
Max. cont: 1460 hp, 291.4 mph
WEP: 1700 hp, 304.5 mph

6700 ft:
Max. Cont: 1543 hp, 304.5 mph
WEP: 1794 hp, 314.5 mph

12000 ft:
Max. Cont: 1624 hp, 313.5 mph
WEP: 1886 hp, 322.1 mph

15000 ft:
Max. cont: 1670 hp, 317.3 mph
WEP: 1937 hp, 325.9 mph

Where to go from here?

1) I could try and reduce the whole envelope by about 5 or 6 mph. That way the sea-level Max. Continuous setting would get down nearer the 284 mph you had mentioned, and also the high-altitude WEP power would fit into the 320 maximum specified. But we wouldn´t be getting the 305 Mph top speed with WEP for sea level (although that was only an assumption on my part, and my not be real anyway).

2) I could continue with the balanced increases in the torque and friction tables and see what happens.

Anyway, that´s the situation at the moment, just in case you have any comments!
Cheers,
Aleatorylamp.

[Ivan]

Hello Aleatorylamp,

I still see some serious problems in your numbers.
(Most notably the 1937 HP at 15,000 feet.)
I am guessing that your Supercharger Boost Gain is way too high still.
I would suggest swapping in the MitchellC AIR file I sent to you and see how the engine behaves.
There is something strange going on if you cannot ever hit 2600 RPM.
It is probably the Propeller Tables.

I believe the main problem is that you are tuning too many things that all affect each other.
Get the power curve right before you start tuning performance.
I am pretty sure it can be done because the Mitchell I built is just about even with the Baltimore in terms of speeds and altitudes.
If it wasn't for having to undo all of the Yaw and Roll Coupling, it would be a simple task to convert it for the Baltimore.

I believe you are still a bit confused about what the different power ratings actually mean.

The Take-Off / Emergency setting on some engines requires a power adder or anti-detonant such as MW50, or Water Injection such as on the stock FW 190A (doesn't really work) or stock Thunderbolt
On other engines it is just an increased supercharger boost setting as found on the stock Mustang.
I don't like to use WEP as found on the P-51D because it is way too short and because there is no warning before catastrophic damage.
Still other engines such as found on the late FW 190A used fuel as anti-detonant which means it simple does not run out.

Unless it is a limited supply of anti-detonant, and WEP can't be used without it, engines generally don't self destruct after 5 minutes 10 seconds of WEP use. It is an operating procedure thing which is specified by the engine manufacturer in the hopes that the engine will reach its expected service life before overhaul.

On some engines, the manufacturer may be overly conservative as I discussed in the P-40 Warhawk thread.

As you noted, the use of Emergency Power is discouraged and procedurally may be limited to 5 minutes.
The question you need to answer for yourself is whether the engine is durable enough for this procedure to be meaningless or how you go about enforcing a limitation.

Military Power or Rated Power is one of the "maximum" ratings. It may have different names depending on which military you are in.
Sometimes it might be called "Climb Power" and be limited to 10 to 30 minutes.

Maximum Continuous is just as the name implies. You are permitted to run at this power level as long as you have fuel.
This is maximum Cruise Power. Maximum "Cruising Speed" is achieved at this setting, NOT MAXIMUM SPEED.

Only WEP and "Maximum non-WEP" are important as far as the AIR file is concerned.

Now to address the points you brought up in your previous post:

1. 1700 HP should be maximum at all altitudes. You need to determine whether it is Maximum or WEP enforced and how.
The reality is that you will probably be a bit higher between Sea Level and your Critical Altitude but hopefully not too much higher.
2592 RPM indicates a problem of some kind.

2. 1450 HP is PROBABLY Military Power in my opinion, but it is Military Power at 15,000 feet.
It would be at 2600 RPM.
To adjust RPM downward if you must, Use the Propeller Pitch Control on the Throttle Panel.

3. Maximum Continuous is an interesting piece of information but really irrelevant as far as developing and AIR file.
I typically include this information in the Check List.
Use the Propeller Pitch Control to adjust RPM.

4. Information clearly indicates Reduction Gearing. You need to do some research to determine the ratio.

5. 44 inches Hg is Maximum. You determine whether this is procedural Emergency Power or whether it is enforced WEP.

6. Maximum Continuous rating specified in the SEFC is pretty much irrelevant as far as the AIR file is concerned.

7. 284 MPH at Sea Level is Maximum Level Speed at Sea Level. It is NOT Maximum Cruising Speed.
In CFS, there is no limitation on duration of maximum power but it is not a factor we can control.

8. 305 MPH at Sea Level should be impossible. 284 MPH at Sea Level is with 44 inches Hg and 2600 RPM IMO.

9. 320 MPH at 15,000 feet is with whatever maximum power level the supercharger is able to maintain at that altitude.
Without experimenting a bit, I have no idea what the Manifold Pressure should be.

10. 305 MPH or 308 MPH has no meaning at 15,000 feet if you are trying to build the Baltimore Mk.V.

- Ivan.

[aleatorylamp]

Hello Ivan,

Thank you for your time and detailed answer. I hope it isn´t putting you out too much, or putting you off!!

Directly using the MitchellC .air file certainly was a good idea:
This .air file also displays maximum revs at 2593 RPM at all times, so it must be an error caused by the computer, which is too modern for CFS1. It would be the equivalent of 2600 RPM on a "normal" computer. So, I´d suggest we ignore this, take it as 2600 RPM, discarding any propeller blade problems or further adjustments.

I saw from the .air file that no WEP is implemented, all powers throttle-controlled. OK, I´ll implement it in the same way. I could also set it as Emergency Maximum Power with Methanol alcohol instead of the short-lived WEP, but I think it´s better the other way.

Taking into account that the Mitchell´s maximum speed is lower than that of the Baltimore, the MitchellC. .air file gave the following performance results at 3 different altitudes under full throttle (Max. revs always 2593 RPM):

500 ft: 1618 hp, 262.8 mph, 44 Mpsi.
12000 ft: 1780 hp, 306 mph, 44 Mpsi.
15000 ft: 1654 hp, 305 mph, 40.3 Mpsi.

Thank you for your answers to the 10 points. I´ll go by that.

Update:
I made the necessary modifications, and have arrived at the following results:
500 ft: 2593 RPM, 1700 Hp, 44 Mpsi, 284.1 mph
15000 ft: 2593 RPM, 1735 hp, 40.2 Mpsi, 308.3 mph

Presumably now it´s looking better. I´ll see if I can manage to increase altitude performance now, which should be possible with a balanced reduction of torque and friction - inversly as I´d done before to lower it.

OK, then! Your continued assistance is excellent and I definitely appreciate it!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

Your comment about the MitchellC AIR file had me a little worried.
I decided to run a quick test to see if my earlier testing was correct.

The numbers I am getting are consistent with earlier testing as far as I can remember.
I will confirm when I can find the Testing Sheet I wrote up a few years back.
I had no problem getting a consistent 2600 RPM at all altitudes from 500 feet to 15,000 feet.

I am getting slightly different numbers from your testing and I do not believe it is because of the speed of the computer because the results were the same on another faster computer.

1613 HP for 264 MPH @ Sea Level
1789 HP for 310 MPH @ 12,500 feet <-- This is Peak Horsepower reading.
1654 HP for 306 MPH @ 15,000 feet

All were achieved with 2600 RPM.
In fact, if left alone for the time it took to write down the data, the Speed would slowly climb up to 312 MPH at 12,500 feet and 308 MPH at 15,000 feet.
(My testing protocol is to record a speed as maximum if it does not change for 15-20 seconds.)

I wanted to post some screenshots so you could see what I am seeing but the only flash drive I have by the development machine does not seem to be readable on this HP laptop. (My regular Flash Drive is very near where Anna Honey is sleeping and I do NOT want to disturb her.)

As for actual numbers, You can do anything you want. It IS your project.
Implement WEP or not as you wish. What *I* chose to do may not be the same as what you choose to do.
The question is whether you want to restrict the use of 44 inches Hg Throttle setting.

- Ivan.