Project Martin A-30 Baltimore

Hello again,
Of course, it is quite obvious what is happening here:
The two blower speeds, high and low, are not available in CFS1.
So if I set it for Sea-level, I don´t get enough power at altitude,
and if I set it for altitude, I get sea-level top performance way too high.
So I suppose there is no other way around it than to either accept a
too-high sea-level performance, or a too low sea-level power with
correct performance, which is whay the MitchellC .air file does...

Update:
Well... I finally figured it out how to fiddle around with Induced Drag/Zero Lift Drag to get a little more speed higher up, adjusting torque/friction accordingly.
For the moment, I´m getting with 44 Mpsi::
- Sea-Level: 1596 Hp, and 290 mph
- 15000 ft: 1825 Hp, and 319 mph
Performancewise it ties in quite well, but Powerwise there´s quite a great 229 Hp difference, which is most probably unaviodable, given the single-speed blower available.

Cheers,
Aleatorylamp
 
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Hello,
You were right, Ivan, it wasn´t that difficult to get the speed range within the desired range!
I just got another 2 mph to increase the difference between Top Speeds:
289.3 mph and 320.0 mph, at Sea-Level and 15000 ft respectively, as agreed upon earlier!
Hp figures as before: 1596 and 1825.
One is too low and the other, too high. In an ideal 2-speed blower world, it would be 1700 and 1450, but we make do with what we have. The MitchellC .air file, had a lower Hp difference, between 6018 and 1780 Hp, although speed difference was greater, 270 - 316 mph. Possibly the last 4 mph need proportionally more power... I don´t know.

Induced drag is now a bit on the low side at 3000, but with decent drag entries for flap and and undercarriage it should be no problem to slow down the plane for landing.

Anyway, this is better for the time being, until perhaps future propeller pitch parameter adjustments give rise to further improvements.
Cheers,
Aleatorylamp
 
Hey Guys,

Which propellers were used on the Baltimore?

Was it the Curtiss Electric?

I'm having trouble finding out the info. If it is, then I have it from the work I did on the P-36.

Update:

Found it. It is a Curtiss Electric.
 
Hello Blood Hawk,

From the photographs I have seen, the propellers look much more like Hamilton Standard Hydromatic types.
Attached is a typical photograph.
By the way, Why would the manufacturer of the propeller be useful for calculations?
I am thinking if you are going to build tables for the airframe / propeller combination, you would need
Diameter
Pitch Range
Activity Factor
and probably some estimate of efficiency which ties back to the airframe it is mounted on.

Hello Aleatorylamp,

I haven't looked at the AIR file yet, but it seems pretty close.
From my prior message, if you are testing at 500 feet, perhaps you want to scoot the sea level speed up a bit.
The 3000 Oswald wing efficiency number sounds WAY too low. I figure it should be a bit over twice what you have there.

The sea level power seems about right.
If *I* were tuning this file with what we know now, I would do the following:
1. Raise the induced drag value up to about 6500 or so. Maybe even a touch higher.
2. Adjust the Zero Lift Drag down a bit until you get 295-298 MPH or so at 500 feet.
3. Bump the Supercharger Boost Gain down a touch until your speed at 15,000 feet drops to about 320-322 MPH.

Right now, from the power numbers you are posting, I bet that 15,000 is NOT the altitude for Maximum speed.
It is probably a bit higher which is not really right.

By the way, after the prior post, my technicians protested.
The claim that WE have the best mechanics in the business.

Gotta Run. Time to prepare dinner.
Anna Honey just left for a trip and I am still a bit sick, so the energy level is low.
BTW, next month, Anna Honey will be in your area.

- Ivan.
 

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Latest Improvement

Hello Ivan,

Thanks a lot! I thought "Sea-Level" was for practical purposes 500 ft - but your latest indication allowing for a few more mph sounds just fine! Thanks for the detailed indications - I´ll make the necessary adjustments.

6500 Induced Drag allows a speed difference of about 28 mph and I was using it during my tests. It will also allow for slight the Boost Gain reduction.

Update:
OK, I´ve just done it.
I´m quite amazed at the precision with which you gave me the indications - they worked perfectly!
I got 297.5 mph at 500 ft, and then, with slightly lower Boost Gain, I got exactly 320.0 mph at 15000 ft with 42.8 Mpsi. Predictably, Hp numbers are now 1597 Hp for 500 ft (as before) but thankfully not as high for 15000 ft: 1761 Hp. (before it was 1828 Hp here!)

I was looking around to see where it would get any faster, and it didn´t below 15000 ft. Further up, the drop in manifold pressure gets stronger, and presumably it won´t get any faster there either, but I still have to test it there for speed.

Hello also Blood Hawk!
Just for the record, the new 297-320 mph .air file is attached to this post, to susbstitute the previous 289-320 mph .air file which I have just deleted.

Cheers, and thanks again for your guidance, Ivan!
Aleatrylamp
 
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Hello Aleatorylamp,

You're welcome. After doing a bunch of AIR files, the pattern is pretty predictable.
That was the original reason for doing the Engine Tuning Tutorial to begin with: To try to share the development steps that work so predictably.

Now I should let you in on a little "Secret".
(It isn't really a secret but sounds better if I call it that. ;-)
It really is just my testing process which is generally pretty quick.

My Test Altitudes are:
500 feet
2500 feet
5000 feet
7500 feet
.....
32500 feet
35000 feet
37500 feet
40000 feet.

You can see the 2500 feet steps.

The process is NOT to test for speed initially but rather to test for Engine Power at each altitude.
On the Baltimore, I would have tuned for Engine Power at 500 feet and also at 12,500 feet.
The Zero Lift Drag would have been set initially at 500 feet.
Once Engine Power was close at 12,500 feet, I would also run a speed test at 15,000 feet and adjust boost and drag slightly.

At this point, I would take an Engine Power reading at each 2500 feet interval and record it.
(This is necessary for later reference.)

The maximum speed at altitude will always be at either the altitude with maximum power or the next altitude above it.
The Engine Power readings are proof that what you have is REALLY the Critical Altitude.

So WHY test Engine Power rather than Speed????
A Speed Test generally runs 3-4 minutes per altitude.
An Engine Power reading can be done in about 10 seconds and gives as much information as you need while developing.

After that comes the Service Ceiling test which was the point of the Engine Tuning Tutorial.

Now it is time for dinner.....
Good Evening.

- Ivan.
 
It would seem that the MK I - MK III used the Hamilton Standards. MK IV are still unknown. Mk V's I found a listing for the Curtiss Electrics.

Its funny, I can find more info for the Maryland and B-26 then I can for the Baltimore.
 
Hello,
Out of curiosity and after your suggestion, I did the WEP power test with 2500 ft intervals:

500ft: 1596 Hp, 297.5 mph, - 44 Mpsi
2500: 1624 Hp
5000: 1662 Hp
6700: 1688 Hp, / 1397 Hp at non-WEP (to compare with SEFC)
7500: 1700 Hp
10000: 1740 Hp
12500: 1782 Hp, 318.6 mph
13500: 1799 Hp, 320.5 mph (critical altitude setting)
14000: 1807 Hp, 321 mph (a power peak here)
15000: 1761 Hp, 320.0 mph - 42.8 Mpsi
17500: 1590 Hp
20000: 1423 Hp, 34.8 Mpsi
22500: 1267 Hp, 31.8 Mpsi
25000: 1128 Hp, 28.2 Mpsi (specified ceiling)
27500: 990 Hp, 25.2 Mpsi
30000: 865 Hp, 22.5 Mpsi

I suppose this is looking quite pleasing, especially taking into account that we are limited to a single-speed blower, so there are bound to be discrepancies with the 2-speed blower in the SEFC.

Hello Blood Hawk,
Yes, it´s a bit frustrating with the limited information. Despite the Baltimore´s high production numbers (1575 units, only surpassed by the B-25 with 9816 and the B-26 with 5288 as per Wikipedia), I suppose it´s due to the fact that is wasn´t used by the US. Then, as its predecessor, the Maryland, was rather innovative for the time, this could account for the larger amount of information available here.

Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

I believe your testing at 6700 feet is not useful because that is the area that will show a serious mismatch because of the CFS single speed supercharger.
You should really be aiming for a match in three places with minimal deviations in between.
The three places are
Sea Level (500 feet)
Critical Altitude
Service Ceiling.

Deviating a bit at critical altitude makes sense because of unknown ram effects which would not affect manifold pressure but would increase power slightly.

Keep in mind that sometimes we might need to ignore the manual to produce something that fits its tactical niche.
An example of this would be the P-40N.
The testing shows speeds at military power 44.2 inch Hg (IIRC) which means its sea level speed is barely above 280 MPH.
Above military, there is Take-Off power at 52 inches Hg and WEP at 57 inches Hg.
My choice was to allow T-O power for normal maximum which put speed at 500 feet at about 310-315 MPH which is still slower than earlier Warhawks.

So is my flight model realistic?
I don't know but it is what I am building.

Hello Blood Hawk,

Attached is a photograph of the last Baltimore Mk.V.
Its propellers still look more like Hamilton Standards than Curtiss Electrics.
The Mk.IV also appears to be equipped with Hamilton Standards.
How does the propeller manufacturer affect things?

- Ivan.
 

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Hello Ivan,

Nice photo! I like the no-monkeybusiness stance of this airplane, and its impressive intake scoops!
The production batch of the MkV (final production version) was the most numerous, reaching 600 units.

The 6700 ft test was only out of curiosity, by no means anything to go by for adjustments or anything.
The general flight envelope is already adjusted as good as it can be, I suppose.

Just like with the Warhawk, some practical measures are necessary for adjustments in CFS1 so that the model can retain the character of its performance. With all our efforts, I´m sure that we can get it as realistic as CFS1 lets us, and the results I´m sure will be quite acceptable!

I was just musing what a FS98 simulation of this model would be like... Without any way of keeping power up at altitude, the performance realism would be totally useless. Any kind of compensation would involve either having to overdo power lower down, or just underpowering it higher up! The only other solution would be to implement a jet-engine .air file, the only FS98 way not to lose power at altitude, although it would be a bit messy.

You mentioned the RAM effect - Correct me if I´m wrong... an increase in power due to pressure build-up in the scoop, perhaps? This RAM effect, unless I´m very much mistaken, also influences ground effect with pressure build-up between the ground and the wing - the Russian Ekranoplans really took advantage of that...

Cheers,
Aleatorylamp
 
I don't think it will matter so much on this aircraft. I only found the one reference to the Curtiss Electric. On the P-47 it matters a lot. As it used both on different models. They seemed to bounce between the two.

That is the first picture that I've seen to show a clear view of the props. It a nice clear picture too.

I don't like the way section 512 came out in the airfile. I'm going to run the numbers again. I think I missed some data in the worksheet.
 
Hello Blood Hawk,

Now you got me curious.
Yes, the P-47 used both Curtiss Electric and Hamilton Standard propellers.
There was a performance difference depending on whether the propellers were high activity factor or not.
There were smaller differences depending on propeller pitch range.
The paddle blade Curtiss Electrics did not look much like the Hamilton Standard versions.

So what else was different depending on the propeller manufacturer???

- Ivan.
 
I know that when the B-26 used them they had some runaway props due to the Curtiss Electric failing and going to a flat pitch. It would seem that they needed a more rigorous maintenance cycle.

There are some pitch differences. I believe the Hamiltons had a narrower blade. But they did have the paddle prop. Actually it looked more like a boat oar.

There were a few differences. Which may make a difference on a real aircraft. But since we can't make a prop profile to include all of the angles and twist in the blade, I just try to get the pitch as its listed. Might not be as important as on a fixed prop.

I have some info on the Curtiss. I found it while working on the P-36. If I remember, I'll send it out to you.

'til Later,
John
 
Hello Blood Hawk.

There is actually a lot more to that story about runaway props on the B-26 Marauder than most people have heard of.
Some problems may have been due to the Curtiss Electric propeller itself, but consider how many other aeroplanes used a Curtiss Electric propeller and did NOT have a history of runaway propellers.
My belief is that most of the problems were due to other issues in the use of the aeroplane.
I am pretty sure that the F4F Wildcats used a Curtiss Electric propeller and even in a harsh naval environment were not noted for problems.
Many models of the P-47 Thunderbolt also used a similar Curtiss Electric propeller also without a great deal of problems.

We are also going way off topic at this point, so I propose we move this part of the conversation to the "Conspicuous By Their Absence" catch-all thread.

- Ivan.
 
Hello Ivan,
Intresting, how the war effort brought along its own technical problems.
I remember you mentioning how the Japanese Zero´s engines also gave trouble, and that they were far from ideal. However, I wonder how extensive the shoddy workmanship on the R-2600 engine models really was, and if all models were affected. It also appears that corrective measures were indeed undertaken.
Now, to what extent this would require adjustments to the engine performance parameters in the Baltimore .air file is a bit obscure, so I don´t really think I´ll do anything about it.
Also, the article doesn´t specifically mention the R-2600-29 or the Baltimore, and it appears that is was more the earlier units of the engine that had problems, which were then solved.
Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

My interpretation on this bit of history is that the Take-Off / WEP was not really useable for much beyond getting an overloaded bomber off the ground.
I am re-thinking the use of WEP for achieving maximum level speeds.
At altitude, it does not matter because there isn't any effect but perhaps it wasn't available for a sea level sprint either.
It also sounds like the problems were never resolved during the production run of the Baltimore and probably not of any of the Mitchells before late 1944.
Certainly the B-25C Mitchell would have had the same issues so perhaps I should rework it for lower power.

Regarding engine problems with the A6M Type Zero, I don't recall that there really were any functioning problems at all, especially with the A6M2 which had very well made engines. The only real issue with later engines were that they were not quite as well made and were not much of an improvement, but the equivalent engine in the Ki-43 Hayabusa series was noted for "Very High Flash Performance" with their pilots running constant over boost with no obvious consequences. This is a paraphrase from an Allied tactical report. It would also explain why the Hayabusa was in service throughout the war.

- Ivan.
 
Hello Ivan,

I´m so sorry, I must have got the name of Japanese plane you´d mentioned quite wrong.
It was about a model whose prototypes had German engines and were fine, but war-production units had Japanese versions of the same engine, and left a lot to be desired. They were less reliable, consequently less powerful because they couldn´t be pushed as hard.

You´d also mentioned that nonetheless, you were more inclined to reflect the designed qualities that the aircraft was designed for in the .air file instead of landing the simmers with the poorer qualities of some of the production models. I´m afraid I really don´t remember the model you were talking about. It could have been the Hayabusa, because I also remember a comment about high peak performances.

Well, so now the prize question that remains, is whether or not to leave the Baltimore WEP performance in the 297 mph at S.L. and 320 mph at 15000 ft range as quoted in the apparently more reliable sources.

Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

The Japanese fighter I was describing was the Kawasaki Ki-61 Hien (Allied code name Tony).
Its prototypes had Daimler Benz DB 601Aa engines but production models used the Japanese Kawasaki Ha-40 engine which was generally poorly made.
It is the project I am using to work on propeller tables and so far the Warhawks have prevented me from going back to finish.
The fairly simple camouflage scheme also has me stuck.
You are quite correct: The flight model for the Ki-61 reflects an ideal version of the engine instead of one with all the problems of the typical example.

Regarding the Baltimore and the Mitchell, My version of the R-2600-13 does not have WEP but also does not give Take-Off power at Sea Level.
At 15,000 feet, WEP and normal full power are the same so it makes no difference.
I was debating on bringing down the Manifold Pressure at sea level and bringing down the power slightly but also including WEP for easier take-off.
The general flight performance won't change much so it is really an exercise in engine tuning.

- Ivan.
 

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Hello Ivan,
Thanks for reminding me - it was indeed the Ki-61. My philosophy on the defective engines is somewhat similar:
The article mentions that some R-2600 engines, indeed it seems to have been quite a number of them, had engine failures, but by no means was it the majority, meaning that R-2600 engine failures weren´t the typical situation.
This would incline me towards fitting the Baltimore with two of the better engines, which can comply with the performance specifications.
It is very clear though, that both Take-Off Power and WEP are 5-minute enjoyments, after which a cooling period must be allowed for, otherwise the engines WILL be wrecked!
Cheers,
Aleatorylamp
 
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