Project Martin A-30 Baltimore

Hello Aleatorylamp,

My point wasn't that our mechanics could not blueprint a couple good engines. These guys and sometimes gals are amazing.
The point was that these engines may not have been as tolerant of maximum power operation as some others.
As I commented earlier, the Nakajima Sakae and their equivalent for the Japanese Army were quite durable engines and tolerated over boosting quite well to the point that this fact was noted by the enemy who warned their own pilots.
In other words, maximum power / WEP for the R-2600 SHOULD be limited in some way.

So.... With that in mind:
WEP is 44.0 inches
Maximum Continuous is 39.0 inches
What is normal full power / military rating for this engine? Perhaps 41.0 or 42.0 inches Hg???
I haven't found it in the manuals yet.
I have my own interpretation but want to confirm it before trying to build to that specification.

- Ivan.
 
Hello Ivan,

I find it very interesting, how this thread on WEP is developing, and agree with you on some way of limiting WEP. At the moment, the full 44 Mpsi is limited to the normal CFS1 5-minute Full WEP Take-Off Power as noted in the SEFC, and its abuse will destroy the engine.

Following your line of thought on further limitation, and as the SEFC specifies an Emergency Maximum, also for 5 minutes, we could use this as full WEP in our model:

42 Mpi at 4500 ft and 41 Mpsi at 12000 ft.

So, there would be 2 questions:
1) Would this be a Military Rating?
2) Was Military Rating also a 5-minute thing?

Thus, it would be a matter of reducing maximum Manifold Pressure to 42 Mpsi: Normal at 39 Mpsi, with a WEP increase of 3 Mpsi. Although this will limit Take-Off Power a little, I don´t think it will matter as there´s enough power anyway.

Just by reducing the Max Manifold Pressure to 42 , without altering power or friction graphs, I´m getting WEP power with 42 Mpsi all round as follows:

500 ft: 1503 Hp
4500 ft: 1559 Hp
12000 ft: 1672 Hp
15000 ft: 1720 Hp

As speeds are all round a few mph lower than they were before, perhaps they should be pushed up a little by adjusting Zero Lift Drag.

Cheers,
Aleatorylamp
 
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My Own Experiments with the Mitchell

Hello Aleatorylamp,

I did a fair amount of poking around yesterday with engine parameters of the Mitchell.
First issue was that the last full engine test was done and documented 30. Nov 2008.
(Yes, the project is that old!)

It was on version 0.53.
I looked around a bit and confirmed that my current version is 0.58 modified in Jun 2013.

I also found that I was really building a generic "Early B-25 with no specific actual model.
The performance goal was more in line with a B-25B (Tokyo Raider) at a bit over 300 MPH.
The actual B-25C is more like 285 MPH to about 290 MPH depending on the source.

FWIW, for this version, the performance goals are the following:
264 MPH @ Sea Level
310 MPH @ 15,000 feet

What I actually got was:
267 MPH @ 500 feet ----- 1619 HP @ 44.0 inches Hg
310 MPH @ 15,000 feet ----- 1654 HP @ 40.3 inches Hg
Service Ceiling 27,200 feet (which is probably a bit too high)
As you noted, there was no WEP available.

My new goal was to make Take-Off power available (WEP) and duplicate the original performance as much as was reasonable.

What it does now is the following:
1631 HP @ 42.0 inches Hg. ----- 1718 HP @ 44.0 inches Hg with WEP engaged.
1690 HP @ 42.0 inches Hg at 5,000 feet
1763 HP @ 41.3 inches Hg at 12,500 feet <---- Probably Maximum Speed here.
1611 HP @ 37.3 inches Hg at 15,000 feet

Service Ceiling is now around 26,500 feet which is about 1,000 feet lower than the last version.

My guess is that I am 2-3 MPH faster at Sea Level and
probably 2-3 MPH slower at 15,000 feet.

I can move the service ceiling up as much as I want but right here seems reasonable.

- Ivan.
 
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Hello Ivan,

That is now looking absolutely great! It also seems like it could be very fitting for the MkV Baltimore.

So you actually managed to achieve the full 44 Mpsi at Take-off, and then have it go down to 42, 41.3 and 37.3 Mpsi as altitude increases. That´s what I was trying to do but never managed to get. How did you get there?

This way you also get reasonably more Take-off Power than I was getting, and your 15000 ft value also corresponds very well as it´s above critical altitude. I got maximum power here, rather than at 12500 ft.

The ceiling value would be fine for the Baltimore too, although it was only 25000 ft, but no mater.
What is most striking is the full 44 to 37.3 Mpsi range that the Manifold Pressure spans - fantastic!

Cheers,
Aleatorylamp
 
Very well-fitting results!

Hello Ivan,
Thank you for your interest and collaboration in sending me your new Mitchell .air file.
You will be pleased to hear that after some minor adjustments to account for the lighter Baltimore airframe, loading, tankage and slightly higher speed, I got some very good results!

Striking is the fact that the propeller diameter adjustment to 11 ft, down from the Mitchell´s considerably larger 12.58 ft, meant a drop of only a couple of Hp!

Also interesting, is how you established your engine supercharger parameters, so that the WEP effect disappears above critical altitude. This very well reflects an effective protection against engine damage and makes flying much easier with less risk of ruining the engine.
In the simulator, this 5-minute WEP implementation for Take-off and for 5-minute Emergency Maximum feels more realistic and safer at the same time.

Incidentally, is there a reason for using the methanol-water WEP option 2 rather than the Supercharger Boost option 3?

Sea-Level performance is also a little lower then what we had established initially, and fits in very well with the criteria of increasing engine protection against excessive over-powering. Then, as before, altitude performance still fits in very well with the speed specifications for the plane.

These are the numbers for the Baltimore now:
500 ft:
1716 Hp @ 44 inches Hg - 286.9 mph
1629 Hp @ 42 inches Hg - 282 mph

5000 ft:
1688 Hp @ 42 inches Hp
1778 Hp @ 44 inches Hg - 301 mph

12500 ft:
1761 Hp @ 41.3 inches Hg - 322.5 mph (maximum speed here)

15000 ft:
1605 Hp @ 37.3 inches Hg - 320 mph (exactly as per specification)

Interesting results, and quite realistic-looking, I must say!
Thanks very much again for your help.
Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

I am glad you are happy with the results.
If you had already done a lot of tuning to your AIR file, the only real changes in mine were

Record 505 - Supercharger Boost Gain, Manifold Pressure Limits
Record 508 - Engine Torque versus RPM
Record 509 - Per Cylinder Friction Loss versus RPM.

There were no other changes, so if you just copy these Records over to your AIR file, you have all the changes.

The Propeller diameter should and relevant tables Records 511 and 512 should not affect Engine Power at all.
They affect thrust and performance but not engine output.

If you want the original performance, you can still get it with just a few changes.

Try the following and see if it helps:
1. Reduce the Zero Lift Drag until you get about 295 to 297 MPH.
2. Reduce the Supercharger Boost Gain a bit until the power reduces enough to get down to 320 MPH.
3. If you need to adjust the Service Ceiling, adjust Torque versus Friction as per the Tutorial.

As a Confirmation that the results are good:
Take an engine power and manifold pressure reading at 12,000 feet.
It should be around 1700 HP and 41.0 inches Hg.

My version exceeds both these numbers by a fair amount at 12,000 feet but I needed to do that to get the performance I was looking for.
The numbers match pretty well a little higher at 12,500-13,000 feet which I attribute to Ram effects.....

The net performance changes to my own B-25C were pretty much negligible as compared with its earlier AIR file.
The only real gain was about 80 HP at Take-Off for a touch less speed at altitude.
If I were building a real aeroplane, I would have preferred the earlier version of the engine because the net effect of these changes was negative but I believe it is a bit more realistic for a B-25B/C.

WEP type 3 is probably more realistic. I just don't like the engine damage at 5 minutes 10 seconds.
I also needed more WEP duration for flight testing.
I am also pretty sure that even above critical altitude when WEP has no effect, exceeding WEP time limits will still destroy your engine even though there is no power gain at all.
That part is quite unrealistic if it is true.

- Ivan.
 
Hello Ivan,
Thanks for your additional info. The engines are getting better all the time!
I´ll just do the extra little adjustments to get the previous Sea-Level performance back again.
Cheers,
Aleatorylamp
 
Testing of B-25C

Earlier this evening I ran just one simple test of the Mitchell.

The earlier version was able to reach
310 MPH at 15,000 feet.

The new version only gets to
301 MPH at 15,000 feet.

The results were a bit surprising and tell me there is more work necessary.
There are some interesting explanations for the unexpected results; They have to do with the fact that the propeller tables are discrete points rather than continuous curves and the interpolation would sometimes arrive at slightly different results than one would expect from a smooth curve.

Next step is to check Sea Level speed. The method of adjustment also depends on how that number has changed.

Update: It turns out Sea Level speed is also lower which means Drag was altered since the test back in 2008. Or I could be working on an incorrect version.

- Ivan.
 
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Hello Ivan,

Sometimes it´s not as easy as it seems! At the moment I have quite a few different versions, and it takes a bit of an effort not to get them all tangled up!

Using the latest version I still haven´t been able to reduce the speed range between Sea-Level and Altitude.
I too have to conduct additional trials!
I´m still at 288 (S.L.) -320 mph (15K ft), when the goal is 296-320 mph.
Of course, increasing torque and reducing Boost gain works, but then the Manifold Pressure values come out too low higher up.

Strangely enough, if I use my own .air file and only introduce the new engine data, the S.L. speed goes up to about 309 mph instead of 296. In this case the culprit is my propeller, which doesn´t work as well as the your slightly cut-down Mitchell-C one!

Well, we´ll see what comes out!
Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

I am having some issues with my engine performance as well.
It turns out (it is actually in the notes) that my testing protocols have changed a bit since 2008.
Back then, I was conducting the Service Ceiling and Absolute Ceiling tests with a full fuel load (670 Gallons).
These days, I do it with about half fuel. (Start with 53% and it should drop down very near 50% by the time the test is done.
I found with my changes I was actually getting just over 28,000 feet Service Ceiling.
The Zero Lift Drag was also SLIGHTLY higher than it should be and that was easily corrected.
With a re-edit of the Torque versus Friction Records to bring down the Ceiling, I need to test engine power all over again.

Will update as I get some more test data.

- Ivan.
 
Hello Ivan,

I got a bit of bother myself just now... It was beginning to look promising after lowering Torque and increasing Boost Gain - I´d just got Sea-level speed at 196 mph and was going to test at 15000 ft when the graphics card went.

Luckily it was not on my main computer but on my re-furbished old dual-core laptop with upgraded CPU, memory and battery. Suddenly the screen filled with short lines! The graphics card is seriously deteriorating... pity about the wasted upgrade! Now I´ll have to get at the HDD data with a USB HDD box.

If it´s not one kicker, it´s another, sent to keep us on our toes...

Cheers,
Aleatorylamp
 
Hello again,

The auxiliary laptop is dead but I still have another p4 fall-back one - so all in all I´m not too badly off. I´m rather suspicious of the sudden failure of the graphics - despite a cooling platform. Programmed obsolescence? I wouldn´t put it past them!

Anyway, with the Baltimore engine tuning, it appears that there´s a limit to the Boost Gain without it boosting too much above critical altitude, and I´m finding it impossible to get the planned performance range - i.e. 296 mph with WEP at 500 ft and 44 inches Hg, and 320 mph with about 40-41 inches Hg at altitude. With correct S.L. performance it just falls 5 mph short higher up. The best I´ve managed is 300-317 mph upto now.

We´ll keep trying! Now it´s time to get my biological food from the farmer´s market. Have a nice Sunday! Tomorrow is a Canary National holiday, so that will also be nice.

Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

Sorry to hear about the first laptop. Glad you have another one.
It is funny how we can get attached to computers as if they have some kind of spirit in them.
I would be very upset if my old Pentium 233 were to die completely. It fails intermittently and that bothers me as it is.

Regarding the AIR file, I am wondering a bit why you chose to INCREASE TORQUE as your first step.
Depending on where you are starting from, that is probably not a good first step.
I did suggest adjusting Zero Lift Drag as a first step. Which way to adjust depends on whether your speed was high or low.
After that, the chances were that your speed at 15,000 feet would have been too high because it was correct earlier.
Now depending on which direction you needed to go, you could adjust Supercharger Boost Gain to correct it.

Life would have gotten a bit more interesting at that point because the actual Critical Altitude of the revised AIR file I sent to you was around 12,100 feet or so and you are trying to adjust performance ABOVE the critical altitude.

This would have been time for a service ceiling test and use Torque / Friction to adjust as needed.

- Ivan.
 
Oops, almost forgot.
Late last night, I did some testing with the Mitchell C Air file I had adjusted the night before.
Here are some results:

Sea Level: 1631 HP @ 42.0 inches Hg -- 272 MPH
Sea Level: 1726 HP @ 44.0 inches Hg -- WEP. No speed test was done because this is only a T-O setting.
5,000 feet: 1695 HP @ 42.0 inches Hg
12,500 feet: 1775 HP @ 41.3 inches Hg -- 316 MPH
15,000 feet: 1608 HP @ 37.3 inches Hg -- 310 MPH'

Service Ceiling was not tested but I am estimating it at 26,500 - 27,000 feet from power readings.
I quit testing when I got too tired to remember what to do. I was missing the points where I needed to collect data.

Speed is a couple MPH too high at Sea Level, but I am not planning on adjusting it.

- Ivan.
 
Hello Ivan,
Well, the surviving laptop also got a memory and CPU upgrade, so it´s quite pleasing. It´s an older single core 1.7 Mhz, and I do hope its programmed obsolescence will have a greater span... If this one goes, I could always buy my daughter a new laptop and use her present one for which WinXP drivers do exist (for AF99, of course)!

Baltimore engines: The thing is that I am working on two different .air files, to try and get the desired 296-320 mph speed range: Your originally MitchellC one, adjusting weight, loading and fuel to the Baltimore, and also my own, with the Mitchell engines and propellers, and they need two different approaches.

Mine gives me a too narrow speed range: 303 mph at 500 ft with WEP (too fast), and 317 mph for 15000 ft (too slow). Yours is somewhat better, but the range is too wide: 288 mph (too slow) at 500 ft and 320 at 15000 ft (quite right).

I also tried a balanced increase of torque and friction to see if there was any difference in the speed range, i.e. what the speed was at altitude with correct speed lower down, but I think this only made it worse on the MitchellC .air file, so I should really use this system on mine!

Speed range was 290-327 mph. Lowering Boost Gain to reduce the 327 mph at altitude then lowers Manifold pressure too much, but I suppose that will have to occur if I want to lower the speed, although I´ve been trying to keep my Manifold Pressure and Horse Power values similar to the ones you are getting.

Update: I just tried the balanced friction/torque increase maneuver on my .air file and got a 2 mph increase in the range. It was 303-317 mph and now it´s 303-319 mph. ...not enough, even though the friction/torque increase was tremendous.

Anyway, we´ll see...
Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,

If you need to adjust Sea Level speed and your engine power is already correct,
Adjust the Drag or Thrust to achieve the proper speed.....
Once you have this, and need to adjust the speed or power at altitude,
Use the Supercharger Boost Gain.

Most of the time this should work pretty well.

At this point, you should test Service Ceiling and balance Torque / Friction to adjust the altitude at which this power level is achieved.

This WILL affect engine power at lower altitudes, but since you are balancing to get the same Sea Level Power, the speed change there should be pretty much negligible.
The speed at critical altitude MAY change a bit, but it should still be near negligible.

The spread from Sea Level power to Critical Altitude power is controlled by Supercharger Boost Gain which is why I was recommending distinct steps.....

If those steps do not work well, there are other ideas but we have not gotten there yet because so far, this AIR file task is actually following the pattern pretty well.

- Ivan.
 
Hello Ivan,
OK, thanks for your patience and insistence on the correct procedure. Indeed I have been using this procedure all along. Sorry that I´ve been insisting on a point which seems not to have been a point anyway! I do apologize.

Because of the very low Manifold Pressure readings I get at altitude when speed is right, I sometimes invert the procedure to see what S.L. speed I would get with the expected Manifold Pressure readings and correct speed at 15000 ft. Of course S.L. speeds are incorrect because I have to change Zero Lift Drag for the trial.

As the speed span is larger in the Baltimore case, and from what you say then, it would be normal to expect lower Manifold Pressure Values values at altitude. That was what was throwing me off all the time.

Anyway, I see I´m on the right track, and I´ll do the ceiling check and see.
For the time being I´ll use the Mitchell-C torque and friction settings. Mine are a little higher, and I have also done tests with exaggeratedly high settings (of course at the desired Hp).

Incidentally, I did correct critical altitude as I saw you´d done in the .air file you´d sent. I also noticed that one of the things to get the performance more correct is that the Boost Pressure Change Rate is set at Zero. This obviously helps to prevent WEP from shooting up with altitude.

Update:
OK, I´ve just done the normal procedure for the originally Mitchel .air file.

500 ft:
44 Hg, 1720 Hp, 295.8 mph
42 Hg, 1633 Hp, 292.1 mph

5000 ft:
44 Hg, 1782 Hp, 312.4 mph
42 Hg, 1692 Hp, 305.5 mph

12100 ft: 38.5 Hg, 1628 Hp, 324.0 mph (I was hoping for 41 Hg and 1700 Hp)
15000 ft: 34.3 Hg, 1466 Hp, 320.1 mph (I was hoping for 37 Hg and 1500 Hp)

2nd Update:
I tried the procedure with my own .airfile with the considerably higher friction/torque settings, but for settings that keep Hp below 1800 at altitude, with correct Boost Gain so as not to have a WEP power increase above critical altitude, speed falls very short at altitude, so I prefer to use the .air file coming from your Mitchell-C.

Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,

I actually am not insisting that you take ONLY the path that I am recommending.
I am still learning as well.

The actual part that I am objecting to is your comment that something is "impossible" when the path to achieve that goal is pretty clear.
Now if there are additional goals, the process becomes a bit more complicated, but I believe it can still be achieved.

The real problem as I see it with the results that you are getting is that your path is a bit scattered for direction.
You adjust numbers that I believe should be used for fine tuning in an effort for major tuning.
The reason I keep recommending a particular path is that I am fairly certain that it brings the result RELIABLY toward the goal whatever that might be. The order of tasks is selected so that there is minimal backtracking as opposed to the jumping around which tends to undo earlier things that may have been satisfactory before.

If your real goal is experimentation, then it is working.
If your goal is to arrive at an AIR file that meets your specifications, then the wandering around will not get you there with any reliability.

There are a few other fine tuning steps but I have not suggested them yet because they only fine tune the basics.
If you use them for major tuning, you will probably get serious unintended side effects.

One of the other issues I need to figure out is a better protocol for conducting climb and service ceiling tests.

- Ivan.
 
MkV - 320 mph: WEP with Extra Boost?

Hello Ivan,

If you are also learning then I´m glad and relieved that it is not a pain for you! It shows that the tuning of the R-2600-13/29 radial engine is an interesting subject for both of us. The Mitchell-C and the Baltimore will definitely benefit from our discussions!

Thanks for your comments and thoughts. The last test results were conducted using your recommendations, and apart from the experimentation bit, which is of course interesting for me to see what happens, the goal is indeed to get a decent air file that will fit the plane.

In reality, the difficulty in reaching the desired numbers at altitude is giving me something to chew on, an a "what if" thought appears. The somewhat vague specifications for the Baltimore are just not specific enough.

The thing that bugs me is the 320 mph top speed specified only for the MKV model, whereas the earlier models were all much slower: MKI/II models with 1600 Hp were quoted with a max. speed of 308 mph at 13000 ft, and the heavier MkIII, with 1660 Hp and 302 mph at 11000 ft. The also heavier MkIIIA/IV with also 1660 max Hp are quoted with a max. speed of 298 - 305 mph at 11500 ft. ...and then comes the MkV, with 1700 Hp and suddenly 320 mph at 15000 ft...

How on earth they get this huge power surge with only 40 Hp extra?!! Was it because they just increased the Turbo Boost and really went for it? This would then indicate that the 320 mph was a WEP speed, and also that the MkV had an additional Boost Gain with WEP - i.e. a small percentage in the Pressure Change Rate parameter.
320 mph is then not a speed attained with Max. Continuous - not non-WEP.
Should Maximum Continuous speed at altitude perhaps really only be about 311-313 mph?

What would you think about this line of thought?

Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

The things I am learning about actually have little or nothing to do with the Wright R-2600 or even Engine Tuning in general.
That part is pretty easy at this point. Even the WEP Boost Gain did not really change any of my prior methods.
I was thinking more of the flight testing and creating a testing protocol that is both useful and reliable.
The Reliable part is done but the big question is whether or not the protocol really provides any useful measurements
That is the part I am working on now.

With all the changes over the last couple weeks on the Mitchell-C AIR file, the net result is that there isn't any great performance difference other than having another 80 HP or so available at Take-Off. At this point, I am satisfied with the R-2600-13 engine for the B-25C; I know I can fine tune it in either direction for ceiling without any other significant effects.

Regarding what the performance was on the Baltimore, I think we have gone over the subject a couple times already.
I have done very limited research. You have found more performance tests than I have so perhaps you also have reached some conclusions.
As you have already seen, tuning doesn't take very long if you know your target. Building the model takes much longer.

- Ivan.
 
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