Project Martin A-30 Baltimore

[aleatorylamp]

Hello all, and Smilo and Ivan!

Smilo has given me the necessary prod towards deciding my next project, this will be the Martin A-30 Baltimore.
Thanks for the extra high-detail drawings, Smilo!

I also remember Ivan mentioning this model as an interesting one which indeed is conspicuous by its absence!

I was initially planning on doing the GR.V version with the stronger 1700 hp engines and the extra guns.
There are a few different and quite appealing colour schemes, so different versions will be possible.
See attached photos. The colour schemes are quire appealing.

Well, so let´s see how it goes!

Cheers,
Aleatorylamp

[smilo]

here are the MK V fore and aft views;

[smilo]

and top and bottom views;

[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 Ivan,

Setting the critical altitude to 12500 like on the MitchellC, reduced performance at altitude a bit, although the Mpsi setting still remains at 44.

I tried to get the Hp spanning from 500 ft to 15000 ft in a similar way to that on the MitchellC, arriving at following results:

500 ft: 1603 Hp with 284 mph.
15000 ft: 1830 Hp with 314 mph.

If this looks plausible, then it´s better, but unless of course it doesn´t, then it isn´t.
Now, in reality, I don´t really know what is correct any longer...

If I knew more about aircraft engines, it shouldn´t really be too difficult for me to decide which maximum speed to use - 305, 308 or 320 mph, and at what altitutude. I think the one entry I´ve seen for 329 mph can be discarded - that much, I suppose I know. But for the others... Maybe the Mk I-III units would be candidates for 305-308 mph, and the MkV, 320 mph? I really haven´t a clue.

Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,

Nice conclusion... What it clear is that there are several different pieces of information for the same parameters, but I don´t know enough about aircraft engines to deduce which of these pieces of information could be the most plausible ones, in order to discover which was the most reliable source.

I believe I´ve seen all the different specs I can get at, and the main problem is that the early and later models are not differentiated in some cases. The main information required for an .air file would be the maximum speeds, and here there are quite a few different ones. This is 305, 308, 320 and 329 mph, with or without some altitude reference.

Of course this is a rather lamentable state of affairs, proven by the impossibility of making speeds tally at different altitudes in CFS1.

2951 RPM max for all altitudes in CFS1 (2600 RPM on your computer):
This coincides with the criteria of a CV propeller, but the charts rather suggest Constant Horsepower and varying RPM.

I´d set critical altitude at 25000 ft, thinking that the ceiling would be the criteria, but I found out that it´s the altitude upto which the blower maintains its power, in this case the 44 Mpsi. Probably mistakenly, I´ve kept Mpsi at 44 for 15000 ft., so I´ll conduct some test correcting this.

The Specific Engine Flight Chart states an emergency maximum for 12000 ft at 41 Mpsi and maximum continuouus at 15000 ft at 41 Mpsi, so possibly the critical altitude setting for 44 Mpsi would be the 12500 in the MitchellC .air file.

Well, At the moment, with 2591 RPM on my computer (2600 on yours), and 44 Mpsi all round, I´m getting:

500 ft: 1670 hp - 294.3 mph (280.6 mph without WEP)
15000 ft: 1885 Hp - 320 mph (311.8 mph without WEP)

Looking at the performance of the MitchellC, which appears to have about 40 Mpsi for 15000 ft, so as I said before, I´ll see what happens if I reduce ctirical altitude to ther 12500 ft given there.

Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan!

I´m beginning to seriously doubt whether the R-2600-13 engine actually had WEP as such, given the difficulty in implementing it in CFS1. What kind of engine WEP did the CFS1 programmers have in mind when they implemented WEP with superchargers in this simulator? Of the 3 kinds available, water injection, methanol-water injection and supercharger boost, the only one that occurs to me as being of any use here is the supercharger boost, but perhaps that is also not really the case.

The blower on the R-2600-13/29 is in use all the time, either in low or high, for all different flying powers, so the blower itself is not a WEP thing, but seems more like a general booster without any extra WEP Boost.

Perhaps this would explain why it was working so well with the 44 MPSI Max Manifold Pressure setting, without any WEP implemented.

At the moment, with 39 MPSI Max Manifold Pressure and 5 MPSI Emergency Power Manifold Pressure Increase, even the Emergency Power Press Change Rate reduced from 0.52800 top 0.10000 is really helping only slightly.

I´m looking for more precise information regarding the use of the 1700 hp military power. From what I have seen so far, it seems to have been 5-minute Take-Off power as well as 5-minute Emergency maximum, although the 5 minute are my own conjecture, as I haven´t seen any comments regarding the length of its use.

Have you got any rather more specific views on the issue of this particular engine?
By the way, I did notice the absence of any WEP implementation in the MitchellC .air file that you sent.

Not that I want to argue... I just find this rather confusing.
Sorry to be such a pain, but I´m starting to go round in circles.

Cheers,
Aleatorylamp

[No Dice]

Great choice,

Should be fun to watch its progress.

Dave

[aleatorylamp]

Hello Smilo,
Thanks for the extra drawings. It´s amazing how slim this aircraft was. I bet that helped with the performance it was famous for.

Hello No Dice!
Thanks for the moral support!
I hope to be able to post progress as it goes along. Ivan is much better at that, but I´ll try!
Cheers,
Aleatorylamp

[Ivan]

Thanks for the compliment, Aleatorylamp.

I am also a bit curious about how you will go about building this aeroplane.
James Ellwood started on a Handley Page Hampden a long time ago but didn't complete it.
He did make its AFX publicly available though.
The Hampden has a pretty good resemblance to the Baltimore in my opinion.

- Ivan.

[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]

Hello Ivan,
Given the impossibility of getting maximum speed in the flight envelope to span 284 mph to 320 mph, possibly it is a matter of interpreting what the specifications say.

I have seen at least 4 sources that state the maximum speed of the Mk.V Baltimore as 320 mph, and some include the altitude of 15000 ft here.

I have seen 1 source stating 312 mph at 11600 ft, then, several others state max. speed at 305 or 308, without stating the altitude or model, and two more which say it´s 305 mph at 11.500 ft but don´t mention the model.

Also, a few sources describing what the Baltimore flew like and the missions it did, don´t state specification details, but do say that the plane was capable of speeds above 300 mph, and that it had the performance of a fighters, being able to outrun some of them.

This could imply that this speed was also possible at sea-level, and would consequently lead me to discard the 284 mph maximum speed at sea-level that you had initially suggested after extrapolating from the Mitchell´s performance. This speed also does not appear in any of the sources.

So, for the sake of looking for a more realistic flight envelope, my exercise this time was to see if the speed range between Sea-Level and 15000 ft could span from about 305 mph to 320 mph, and I did a test. The result IS actually possible with procedural emergency power (no WEP enforced with F10):

Aimed Power: 1700 hp
Critical altitude 12500 ft
Max. RPM all round: 2590 (2600 RPM on normal computers and yours)

Sea-level: 1690 hp - 305.7 mph 44 Mpsi
12500 ft: 1867 hp - 322.5 mph 44 Mpsi < this is the critical altitude.
15000 ft: 1718 hp - 320 mph 40.1 Mpsi

This seems to tie in with the information given by most sources. I wonder what this would be in your opinion? Useful, or useless codswallop?

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

I was pretty sure tuning the maximum speeds to the range that you wanted wasn't very hard, so I decided to try it myself.
I started with the Mitchell C AIR file and took a few screenshots to show the numbers I am getting on a Pentium 3 866 MHz before and after some very minor tuning.

The picture of the Mitchell model has no real relevance but I thought it looked nice.

The only tuning I did was to adjust the Zero Lift Drag down to 62 using AirEd.
I did absolutely NOTHING else. No Engine Tuning was required to get this performance....

If your target performance was 284 MPH @ SL and 320 MPH @ 15,000 feet, this would be close enough I think.

The R-2600-13 on the B-25C and the R-2600-29 on the A-30A are close enough to be the same engine and you already have the AIR file containing my version of the R-2600-13.....

- Ivan.

[aleatorylamp]

Hello again!
Of course, critical altitude being 13500 ft, is just between the two reference altitudes with their Hp and MPSI values given in the Specific Engine Flight Chart, the lower one at WEP and the higher one at Maximum Continuous:
12000 ft, 1700 Hp, 41 Mpsi Boost, WEP
15000 ft, 1350 Hp, 39 Mpsi Boost, NON-WEP
Now the thing is to find the ideal Emergency Power Pressure Change Rate value (which affects WEP) and Boost Gain value (which affects non-WEP), to get both above mentioned Mpsi values right! Not exactly a piece of cake, but not an excessive mouthfull either, I suppose.

Update:
-------
There are two more reference altitudes, also with WQEP and without WEP, namely:
4500 ft (WEP
6700 ft (NON-WEP)
...albeit with LOW-Blower (the higher altitude reference numbers were for HIGH Blower) - but we only have ONE Blower speed...
Also, There seem to be 2 types of extra boost (WEP): Take-off, with 44 Mpsi, and then Emergency Maximum, with 41 or 42 MPSI depending on altitude, but only one WEP is possible, so it will have to be with 44 Mpsi. Some values are just not possible to get, because there is only one blower speed, and one WEP. However, despite this, the results of my efforts are quite pleasing:

Performance Aims:
WEP (For take-off and Emergency Maximum):
Sea Level: 1700 Hp, 44.0 Mpsi, 305 mph or higher
4500 ft: 1700 Hp, 42.0 Mpsi
12000 ft: 1700 Hp, 41.0 Mpsi, approx 320 mph
15000 ft: 1547 Hp, 36.4 Mpsi, approx 320 mph

NON-WEP max.
6700 ft: 1500 Hp, 38.0 Mpsi
15000 ft: 1350 Hp, 39.0 Mpsi

Entered values:
Boost Gain 2.15
Max Manifold Pressure: 38
WEP Pressure Change rate: 0.0625
Manifold Pressure Increase for WEP: 6

Performance Results:
WEP:
Sea Level: 1701 Hp, 44.0 Mpsi, 310 mph
4500 ft: 1757 Hp, 44.0 Mpsi, 316 mph
6700 ft: 1785 Hp, 44.0 Mpsi, 320 mph
12000 ft: 1726 Hp, 41.0 Mpsi, 323 mph
15000 ft: 1547 Hp, 36.4 Mpsi, 318 mph

NON-WEP max:
Sea Level: 1481 Hp, 38.0 Mpsi, 302 mph
4500 ft: 1485 Hp, 38.0 Mpsi, 307 mph
6700 ft: 1558 Hp, 38.0 Mpsi, 310 mph
12000 ft: 1584 Hp, 38.0 Mpsi, 318 mph
15000 ft: 1497 Hp, 35.4 Mpsi, 317 mph

So now this is a little bit better, I would venture to say!
Cheers,
Aleatorylamp

P.S.
An interesting next step would be to fill in the speeds corresponding to the rest of the operating Conditions indicated in the Specific Engine Flight Chart, below the Take-Off, Emergency Maximum and Maximum Continuous, like Economical Maximum, Minimum Specific Consumption, Minimum Cruising and see what happens with the Conditions to Avoid.
A.

[Ivan]

Hello Aleatorylamp,

A couple days ago, you pointed out that my B-25C Mitchell AIR file did not have WEP implemented at all.
You are of course correct.

Please take a look back at Post #48.
I was stating back then that you needed to make a few choices as to what you were trying to achieve.

A Take-Off Rating IS a an emergency rating of sorts.. Typically it is of very limited duration.
I chose to ignore the time limitation on my implementation of the MitchellC AIR file, BUT
I also left the Sea Level power only at 1618 HP instead of the 1700 HP Take-Off power level.

The reason I did this is (as I have stated in many places) that I want a "Best Fit" of the power curve rather than an exact match at only one or two points. This is the reason I don't like the "1%" solution of matching performance very closely at just two points in the altitude range.
With only 1618 HP at 500 feet, the power at intermediate altitudes will still be way over 1700 HP.
Of course it will also be a touch low at Critical Altitude but the PERFORMANCE will be a closer match in most places.

You are going for 1700 HP at Sea Level and are not far off 2000 HP at intermediate altitudes which is why I think it makes sense for you to have a limit of some kind.
I figure that at worst, I am about 80 HP too high or too low.
I figure that your AIR file is more like 250 HP too high in places which is why a WEP limit makes more sense.

My goal is generally to use this game as a simulator. I want a 400 MPH Japanese Zero but also realise that it makes no sense from a historical or tactical perspectie, so I have never bothered to create it.
Just keep in mind that the Baltimore was an early war commercial bomber.
It wasn't a world beater and it wasn't a speed demon.
If it were, it may have remained in service much longer than it actually did.

- Ivan.

[aleatorylamp]

Hello Ivan,

The Hampden has a similar layout to the Baltimore although the shapes are a bit different.
(I found lots of pictures, but not James Ellwood´s AFX).

It is peculiar to see how a lot of English twin-engined designs are quite ugly. It appears that American designers came out with sleeker and more elegant designs all round. The Germans also had some quite ugly twins.

Anyway, I was thinking of building it using the distribution and grouping of parts that I used for the Curtiss AT-9 Fledgling for a start, and see how it goes.

Cheers,
Aleatorylamp

[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 Ivan, again!

Before moving the Friction or Torque Graphs, it occurred to me to lower Boost Gain from 2.54 to 2.4, which in turn lowered the Manifold Pressure slightly at altitude.

Now the results are very much closer:
500 ft: No change: 1618 hp, 284 mph, 44 Mpsi
12500 ft: 1770 Hp 326.2 hp, 43.5 Mpsi
15000 ft: 1615 hp, 322.6 mph, 39.5 Mpsi

This seems to be acceptable, I´d wager.

Cheers,
Aleatorylamp

[aleatorylamp]

Hello,
Just a short correction: I missed a very obvious indication on the R-2600-13 Specific Engine Flight Chart in the right column, stating a maximum of 5 minutes for TAKE-OFF and EMERGENCY MAXIMUM operating conditions. Sorry about that!
Cheers,
Aleatorylamp.

[aleatorylamp]

Hello Ivan,

Good heavens, how easy that was! A nice surprise, to say the least, thank you very much.

The Germans say, "Why easy, when it can be done complicated too?".
("Warum einfach, wenn es auch komplitziert geht?").

So for a start I´ll just take the whole MitchellC .air file and do the same. Then I´ll shift over the Wing section and adjust the weights, and fuel, but nothing else just in case something breaks!

I was wondering about the 284 mph maximum speed at SL you had recommended, because it contradicts the information reflected in all the sources. As far as I can see, it comes from a calculation derived from the Mitchell, that had the same 1700 hp engines and similar performance, although it was a bit slower.

Well then, let´s see how it goes now! Thanks again.
-Yes, the picture does look nice! ...I like the slightly negative dihedral.

UPDATE:
I used the MitchellC .air file and transferred the weight, fuel and main wing parameters over.
I also had to transfer the smaller propellers diameter: 11 ft instead of 12.58 ft.
Zero Lift Drag is at 69 and induced drag is at 6800, as opposed to your 62 and 6750.
The results I got are as follows, all at 2592 RPM:

500 ft: 44 Mpsi, 1618 hp, 284.0 mph
12500 ft: 44 Mpsi, 1788 hp, 327.4 mph (speed considerably higher than yours)
15000 ft: 40.3 Mpsi, 1654 hp, 326.0 mph (speed slightly higher than yours).

Obviously the smaller propeller is giving the higher readings.
I could perhaps try reducing torque and/or increasing friction a bit.

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

Perhaps you don't care, but I think you should check out the Yaw-Roll coupling if you plan on developing from the MitchellC AIR File.
There were a lot of factors that were tuned to make that happen and offhand, I don't remember where they all were, so that is why I was recommending against it.

I get the distinct impression that you did not really understand the Engine Tuning Tutorial.
I am not saying my method is the ONLY way, but if you are intending to use it, it helps to be consistent.

Without getting into the extreme detail, here is the basic idea:

1. We need to tune THREE points on the graph of Power versus Altitude:
They are at Sea Level, Critical Altitude, and Service Ceiling.

2. Tuning the Sea Level Power should be done first.
We need to match Three Pieces of Data: Manifold Pressure, RPM, and Horsepower.
I usually do this by adjusting Torque.

3. Next is the Power at Critical Altitude.
This is done by ADJUSTING SUPERCHARGER BOOST.

4. Last is tuning the Service Ceiling / Absolute Ceiling and this is done by adjusting Torque and Friction and balancing their effects so that the Sea Level Power is not altered significantly.

.....So....

Leave the Torque / Friction alone at this point and just drop the Supercharger Boost a little bit.

Did you notice the choices I made as far as tuning the power curve for the Mitchell?
Note that the Sea Level Power and Critical Altitude Power are both a touch lower than one might expect.
This was done so that the power curve would not be too high at any point in between.

There are other ways to tune the performance without affecting the power curve but there are other side effects.

For what it's worth, earlier versions of the Mitchell were slightly faster than mine.
I built the B-25C/D or Mitchell Mk.II because I thought it was a good balance of combat capability and flight performance.
Later versions were even slower.

Perhaps it is worthwhile for you to post a little of the development and service history of the Baltimore.
Various conflicting information simply did not make sense until I read a bit about the history and put together the most likely scenario.
That history and logical developments is why I do not believe the Page 112 Table is correct.
Also worthy of discussion is how the Baltimore derived from the Maryland and perhaps a little speculation as to why the US military gave it an official designation but never used the aeroplane operationally.

- Ivan.