Project Martin A-30 Baltimore

[aleatorylamp]

Hello Ivan,

I have started to build the Baltimore - the muses have come back and the builder´s block is thankfully gone! Let´s see if I can be more successful with the model itself than with tuning the MkV engines for which insufficient information is available.

I may have done more research on the Baltimore than you, but by no means with any more success! The information on the Polish document relative to the different versions, MkI to MkV, ties in perfectly with two other old publications I have found, but what is lacking is more specific engine data regarding WEP power on R-2600-29 on the MkV Baltimore.

How they all of a sudden got 320 mph out of the -29 engine in my opinion implies an increased WEP, giving perhaps about 1800 Hp. For want of more specific information on the engine, one simple solution here would simply be not to build the MkV, but one of the earlier Baltimores, the Mk III for example, which had the -13 engines. This way the 320 mph mystery can be ignored.

Top speed would be fine at around 305 mph. Current flight test results would tie in perfectly well for the R-2600-13 engined Baltimore MkIII (of course), with the Mitchell-C .air file simply corrected for dimensions and weights.

For the moment, I think this will be the best solution.
Cheers,
Aleatorylamp

 

[aleatorylamp]

Tuning the R-2600-13 for a MkIIIA

Hello Ivan,
Out of interest, I tried out some tests for the R-2600-13 powered Baltimore Type B-2 MkIIIA, which is quoted with the following performance:
Vmax at S.L.(500 ft?): 284 mph
Vmax at 11500 ft: 305 mph

After Boost Gain and Drag adjustments, results for the MkIIIA are:
__500 ft: (____WEP) 44.0 Hg, 1721 Hp, 284.0 mph
11500 ft: (non-WEP) 37.9 Hg, 1597 Hp, 305.7 mph

To cite further altitudes quoted on the R-2600-13 SEFC (incl. speed results):
_4500 ft: (____WEP) 44.0 Hg, 1774 Hp, 297.1 mph
_6700 ft: (non-WEP) 42.0 Hg, 1716 Hp, 299.6 mph
12000 ft: (non-WEP) 36.4 Hg, 1631 Hp, 305.4 mph
15000 ft: (non-WEP) 32.8 Hg, 1398 Hp, 301.5 mph

The 4500 and 6700 ft readings are not really of much use given the lack of a 2-speed blower in CFS1, and are included just for information. Then, just for the record:
12500 ft: (non-WEP) 36.4 Hg, 1532 Hp, 305.0 mph

Again, and similarly to the MkV with its 320 mph, the high altitude Manifold Pressure readings here don´t tally very well with the SEFC either, and that would presumably be put down to the lack of a 2-speed blower.

Anyway, at the end it appears that although at first glance it seemed more probable that a MkIIIA tuning would be more exact because of the R-2600-13 engines, perhaps the previous tuning for a MkV adaptation to R-2600-29 engines is also quite acceptable, without any need for any additional WEP Boost, which is quite pleasing, I would say. Would you think so too?

Cheers,
Aleatorylamp

 

[aleatorylamp]

Two models with 2 different engines

Hello Ivan

I´ve been re-reading your posts from the last 3 weeks, and there´s indeed a LOT of information.

One thing that I had meant to comment on is related to your Post #99, where you mentioned the R-2600-13 as being incorrect on the Polish table: Would this mean that the R-2600-13 is SIMILAR to but not EXACTLY the same as the 1700 Hp R-2600-29 ? Perhaps this also explains the Mitchell-C´s R-2600-13 engines´ having a Cylinder Displacement 0.2 cu.in less, and a Compression Ratio 0.5:1 lower than the one I´m using - the only one I could find similar to the R-2600-29 was the GR-2600-C14BB. It´s not a terrible difference, but it amounts to about 1.5 mph at 500 ft.

Incidentally, the R-2600-29 apparently also had a 1850 Hp version, which is interesting.

Then, I´d forgotten to compensate the 5 mph speed difference between S.L. and 500ft for the IIIA version. It should be 289 mph instead of 284, but that´s easily fixed.

At the end of the day, the good thing that has come out of all this, is that we will most probably have TWO Baltimore models: An early one without a turret (or perhaps larger Boulton Paul turret, but preferably not), and also the later MkV with the smaller Martin turret, possibly in 2 different liveries, a desert-camo and khakhi-green-camo.

Cheers,
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp,

I see two issues with this plan:

1. As I commented earlier, I do not believe the Baltimore was ever equipped with the R-2600-13 and if it was, it was not the same engine we are seeing the SEFC for. The power ratings are too low for the one described in the Page 112 data table.
I am fairly certain it is a typographical error.

2. Also as I commented, the early R-2600 engines were not all that durable.
The engine obviously had a Take-Off rating at 44.0 inches Hg but I do not believe it was for use after take-off.
I believe that my idea of 42.0 inches Hg as normal maximum is most likely correct.
These engines only had a critical altitude of around 12,000 feet which means that they essentially have no additional boost available post that altitude. in other words, there is no high altitude WEP.

With my Mitchell, I was really going for B-25B level performance to have something capable of flying the Tokyo Raid mission.
I could not get the level of performance I wanted by staying strictly with the SEFC, so I adjusted a bit to get where I wanted.
Additional Detail:
I was getting 26,750 feet service ceiling with my current testing protocol but observed that this altitude was simply impossible (hate that word) to achieve when the aeroplane was flown manually.
I simply cannot trim quickly enough to keep the aeroplane headed in the correct direction for a continuous climb and practical ceiling was more like 24,000 feet or perhaps even lower.
I could get the aeroplane to go way over 25,000 feet but not in a continuous climb and formation flying would simply be hopeless.
So what IS the service ceiling now and how do I test to confirm it?
(The Russian term is actually "Practical Ceiling" which I used a few lines above.)

So, what should your target performance be?
I can't tell you. I have my own opinions, but I have already told you those.

- Ivan.

 

[aleatorylamp]

Hello Ivan,

Thanks for your interesting reply! OK, so it isn´t the R-2600-13 engine that was used on the Baltimore, but inferior ones for MkI to MkIV models, and OK too, that the R-2600-19 and the GR-2660-A5B were worse quality engines, for which the performance envelope developed here in this thread is more fitting.

Then, it seems that we can agree that once I fix the S.L. speed for the MkIIIA, this would be good to use for earlier the Baltimores. Then, initially, the faster version of the same .air file would serve for a MkV, as it has the speeds agreed on in our posts. No extra WEP!

There is a slight contradiction regarding the MkV´s R-2600-29, a later edition of the R-2600 engine: In fact, in the article about the R-2600 engine defects, there´s a comment on aircraft models from other manufacturers receiving a recommendation to change from the -13 to the -29 engines to cure the problems, so the -29 must have been more reliable and better than the -13. That would also explain its vastly improved top speed. Too bad there is no information on it - as I said, I have only found a GR-2600-C14BB. Possibly similar, but who knows?

Update:

As per the other two sources, the engines on the MkIIIA were R-2600-19, and on the MkIII, GR-2660-A5B, both giving 1660 Hp. I can try reducing engine torque in the .air file to get 40 Hp less, hopefully it will not make it more difficult to maintain proper power at altitude and it may be more fitting for the worse engines. Thanks for pointing it out (again).

The plan of making two models using two different adaptations of the Mitchell-C R-2600-13 engine .air file parameters comes from the fact that there are no other SEFCs available. The two models´ (MkV and MkIIIA) engine performances do not really match ALL the performance details in the SEFC that we have at hand - only some of them coincide, the aim being to correctly reflect the performances given in the documentation on the Baltimore MkIIIA and MkV aircraft types.

Regarding your comments on the Mitchell-B/C´Service Ceiling, I still have to do that test on the Baltimore(s). They definitely had a lower ceiling, and I wonder what the outcome will be. For the MkV it was 25000 ft, and for the MkIIIA it was 23300. I suppose the fitting term "Practical Ceiling" would entail the ability to maintain a 100 fpm rate of climb, as you once mentioned. The conditions under which such a test is to be undertaken would be 50% fuel tankage and 50% Bombload, perhaps? ...similar to a rate of climb test, maybe?

Cheers,
Aleatorylamp

 

[aleatorylamp]

Now correctly tuned MkIIIA/IV 1660 Hp engine?

Hello Ivan, again,
OK, I´ve just done it, and contrary to what I was fearing, the results for a 2x1660 Hp MkIIIA/VI Baltimore were unexpectedly easy to arrive at. There are corresponding adjustments to Zero Lift Drag, Oswald factor, Boost Gain (this at only 1.955, which apparently has a side-effect of lowering the set critical altitude), slightly reduced Torque graph and somewhat increased Friction graph, and results are probably (hopefully) looking quite satisfactory:

__500 ft: 44.0 Hg, 1660 Hp, 289.0 mph.
_6700 ft: 42.0 Hg, 1655 Hp, 303.6 mph (just for the record)
11500 ft: 37.0 Hg, 1464 Hp, 305.0 mph
12500 ft: 35.5 Hg, 1435 Hp, 304.6 mph
15000 ft: 32.2 Hg, 1306 Hp, 300.1 mph

What is not so pleasing (but irrelevant) are the WEP peaks or surges, but, as
you said, WEP would not be used other than at take off, so it can be ignored:

4500 ft: 44.0 Hg, 1713 Hp, 301.1 mph
6700 ft: 44.0 Hg, 1745 Hp, 309.8 mph
7000 ft: 44.0 Hg, 1750 Hp, 312.1 mph (absolute peak here)

Anyway, I thought this was quite interesting for the 1660 Hp R-2600-19 or GR-2660-A5B engines.
Thanks again for prompting me to do it. Hopefully this will be acceptable now.

Update: Problem!
The (irrelevant) WEP surges made me test some other altitudes at non-WEP, just in case.
There are some non-WEP points above 305 mph, just between the 6700 ft and 11500 ft
altitudes where I hadn´t tested before!

11000 ft: 37.7 Hg, 1517 Hp, 306.0 mph
10000 ft: 39.4 Hg, 1573 Hp, 308.1 mph
_9000 ft: 40.9 Hg, 1630 Hp, 309.0 mph
_8000 ft: 42.0 Hg, 1674 Hp, 308.6 mph

Lowering these implies lowering the specified 305 mph for 11500 ft.
Perhaps not so good after all, and it´s not as easy as I´d first thought!
After this rather unexpected surprise, I decided to try out the MkV .air file, which was correctly giving me 320 mph at 15000 ft and 296 mph at 500 ft, for untested altitudes. Lo and behold! I ALSO get the same peak surge at 10000 ft, this time going up to 326.5 mph. Well well, another kicker!

Maybe I should just quit and built a completely different airplane that will give a decent performance envelope in CFS1, because what´s the point in building a plane that will do crazy things at illogical altitudes?

Cheers,
Aleatorylamp

 

[Ivan]

Crossing Posts

Hello Aleatorylamp,

I just noticed that our Posts 143 and 144 were done at nearly the same time and I know I did not read your post until just now.
I will try to address the issues you brought up there.

Are the R-2600-13 and R-2600-29 functionally similar?
At least from a power standpoint, I believe they are identical.
See the attached excerpt from the B-25 Mitchell Training manual.
This is the reason I was willing to use the SEFC from the B-25C/D as a guide for tuning the R-2600-29 in the Baltimore Mk.V.

Are the engines dimensionally the same?
I believe the Bore and Stroke are the same but the compression changed slightly in different models.
This is from memory but I CAN go back and check the dimensions when life slows down a bit over here and I get some time.
I do not believe from a functional standpoint that there will be any significant change requiring additional performance tuning changes in the AIR file though.

It sounds like the R-2600-29 came in multiple versions like the BMW 801D-2 did.
Although the designation didn't change, the equipment DID change for the better with the later versions.
My guess also is that because of the discontinuation of the Baltimore, it may never have seen the better engines.
Don't feel too bad, the same probably applies to the B-25B/C/D using the R-2600-13.

Just to really throw an even bigger wrench into the machine, check out the attached SEFC also for the R-2600-13 but for a different aeroplane. Note that this one actually specifies a Military Power setting and it is the same as the Take-Off setting.
No, they are not identical. It makes you wonder how the -13 may have changed during its production run.
Note also that the original MitchellC engine without WEP is closer to this one from the Vengeance.

So WHICH -29 engine did the Baltimore have? I have no idea but the time period is a pretty good guide.

- Ivan.

 

[aleatorylamp]

Hello Ivan,

Ha ha! I don´t feel so bad, it´s just that just when I thought I had it all sussed out, I got this unexpected peak at a completely unexpected altitude...

The two posts were done almost at the same time because I´d edited them. Sometimes it takes me a while until the penny drops! I´d missed the main point on the non-existence of the R-2600-13 for the Baltimore, wondering why we´d used the SEFC in the first place, so I edited it. Then, I added the second post so as not to make the first one even longer with the new MkIIIA results, which I´d thought were so good. Later, I edited that one too, twice in fact, once to include the MkIIIA kicker results, and again to add the MkV ones. So, it´s just as well that you didn´t read them sooner - they would have been incomplete or different. ... Oh, what a long story!

Very interesting, the 2 new attachments you provide. Thanks very much indeed! They are not really a bigger spanner in the works. On the contrary, I feel they would actually tie in quite well with the early MkI/II Baltimores that had their 308 mph top speed at 13000 ft.

The absence of War Emergency and there only being Military Power proves your point on not having WEP for anything else than Take-off. Then, would it be better to use WEP Option 3 once the .air file is not being tested any longer, to destroy the engine sooner, in order to deter simmers from using it while flying?

Thanks also for your clarification as to the similitude between the -13 and the -29. That´s 1 doubt fewer. And, we can then also discard the 1850 Hp version of the -29 engine - another doubt fewer!

Incidentally, one of the 2 old document scans I´d found mentions the R-2600-13 for the MkV! There does seem to be quite some confusion in the original old sources, doesn´t there?

Good, your moral support! So it´s not as bad as would deem dropping the project for want of higher performance envelope precision.

This peak at 10000 ft seems to come from the low Boost Gain setting, and I was thinking of ways around that, but increasing it again to make the peak coincide with Critical Altitude will cause the surges where top speed is correct now, which is exactly what I was fixing.

There´s a comment in AirEd Info for the Boost Gain parameter:
>Maximum MP/Ambient Air pressure
>Sets Max Speed/Max Altitude Factor

Well, at least your Mitchell-B/C´s flight envelope is backed by the information on the new attachment!

OK. I´ll keep on looking for a good way around for the Baltimores! (Can we have ALL 5 of them? - No, please... Ha ha!)
Cheers,
Aleatorylamp

 

[aleatorylamp]

Obvious but questionable solution.

Hello Ivan,
Looking at the numbers of the unexpected 10000ft Hp and Speed Peak, an obvious solution comes to mind, which works, but comes at a price: 7 mph lower WEP speed at 500 ft, but exactly maintaining 1700 Hp there. I´d already lowered it before from 1721 Hp, to improve the situation.

I increased Drag to reduce 500ft WEP speed from 296 mph to 289.1, and raised Boost Gain from 2.085 to 2.24, getting a max. speed of 319.6 mph at 15000 ft with 36.9 Hg.

Then I went down to 10000 ft to check for the bad peak, and although the 1743 Hp Hp peak was still there, the speed peak was gone, speed staying happily at around 319.5 mph.

The next step is to adjust this "solution" to exactly 320 mph at 15000 ft.

A similar solution can be obtained for the MkIIIA/IV .air file, which, with its lower bad speed peak will lose less speed at 500 ft.

So the million dollar question here is: Can we accept this 7 or 8 mph reduction in the previously agreed 296 or 297 mph max. speed for 500 ft? I would say yes, but I would like to know if you would agree.

Thanks in advance for your always valued opinion!
Cheers,
Aleatorylamp

 

[Ivan]

Been off the net all day. on iPad right now.
Power and speed peak is unavoidable: CFS Single Speed Superchargers.
You are only moving it around. It will not go away.
You will see if you test at more altitudes in between.
Hopefully peak is not too much higher.

I don't understand why sea level speed dropped so much.
Performance tuning is to whatever goal you decide.

- Ivan.

 

[aleatorylamp]

Undesired 10000 ft peak

Hello Ivan,
It´s nice of you to answer being off the net but using your Ipad with its typing inconvenience. You don´t have to worry if time passes until you can answer more easily from your computer.
Thanks for confirming that the problem is the single-speed CFS1 turbocharger.
Let me see if I can explain a little better how I´m trying to get around this and what is happening right now:

We are not only moving things around, but also taking out speed peak which was completely out of place, 2100 ft below critical altitude, which was also much higher than the normally expected critical-altitude peak. Another way of interpreting it is that the critical altitude dropped by about 2100 ft because of the very low Boost Gain setting. AirEd info refers to this in a very vague way.

The only way to correct this is by increasing Boost Gain, and to do this without a resulting speed surge above critical altitude, we must reduce Drag. This of course entails reducing speed at 500 ft to aproximately S.L. Speed, and consequently S.L. Speed unavoidably also goes down. Also, mid-altitude speed goes down, but high-altitude Hp and Hg readings are more in line with reality.

Granted, I agree that the useless peak is still there, but without the speed, and also, that with the Drag increase, I´m moving the whole envelope down. However, then I can increase the excessively low Boost Gain again to recover the desired power at 15000 ft, eliminating the speed surge at 10000 ft. The unwanted peak has the same Hp as before, but speed is slower by aproximately the mph subtracted from the 500 ft speed due to the Drag increase. This way the plane doesn´t shoot off at 326+ Mph, 2100 ft under critical altitude, now obediently staying put at 320 mph, the same speed it has at 15000 ft, before and now. Then, the restly critical altitude peak is as before.

Here´s a comparison chart. The two side-by-side values in each column are before and after the Drag/Boost Gain increase. (I put Boost Gain up from 2.085 to 2.221).

You will notice that the low Boost Gain had not only lowered critical altitude, but also given poor power levels above that, which is now corrected. Of course speed there has stayed the same, which was mandatory. Speed below critical altitude was exorbitantly high, and correcting this was the objective.
I did some more tests for 8000, 9000 and 11000 ft.

__500 ft: 44.0-44.0 Hg 1700-1700 Hp 296.0-290.0 mph. - Now 6 mph under
_4500 ft: 44.0-44.0 Hg 1754-1755 Hp 309.7-302.8 mph. - Now 7 mph under
_6700 ft: 42.0-42.0 Hg 1696-1695 Hp 313.7-304.8 mph. - Now 9 mph under
_8000 ft: 42.0-42.0 Hg 1715-1714 Hp 320.5-310.5 mph. - Speed surge removed
_9000 ft: 42.0-42.0 Hg 1728-1728 Hp 324.2-316.8 mph. - Speed surge removed
10000 ft: 42.0-42.0 Hg 1742-1742 Hp 326.6-319.9 mph. - Speed surge removed
11000 ft: 40.2-42.0 Hg 1674-1757 Hp 324.9-322.3 mph. - Speed surge reduced
12000 ft: 38.6-41.2 Hg 1612-1735 Hp 323.7-323.7 mph. - Speed same as before
12500 ft: 37.9-40.4 Hg 1586-1703 Hp 323.1-323.5 mph. - Speed effectively same as before
15000 ft: 34.3-36.5 Hg 1447-1555 Hp 319.8-320.0 mph. - Speed effectively same as before

Notice the low previous Manifold Pressure at 11000 ft is lower than it should be, as it´s below critical altitude. Also, if you press the WEP button here, you should get 42.9 Hg, but it was ineffective previously, which also shows how critical altitude was incorrectly low before.

The new criteria for WEP is now Take-off Power only, and not for flying around all the time, so I only did tests with WEP for lower altitudes. Nevertheless, perhaps the new criteria could include a permitted WEP power climb upto 6700 ft? This could also compensate the lower performance.
4500 ft, 44 Hg, 1755 Hp, 302.8 mph - WEP perhaps allowable?
6700 ft, 44 Hg, 1786 Hp, 311.4 mph - WEP perhaps allowable?

Curiously and expectedly, using WEP now at 8000 and 9000 ft gets very close to max. speed, so definitely no WEP there!
8000 ft, 44 Hg, 1805 Hp, 317.6 mph - WEP not allowable.
9000 ft, 44 Hg, 1820 Hp, 319.5 mph - WEP not allowable.

Use of WEP further up, at 10000 or 11000 ft would seriously distort the flight envelope of the plane - albeit not as much as before... co convenient comments in the Readme would perhaps make simmers abstain from using WEP after say 7000 ft. I haven´t tested WEP for 10000 ft or 1000 ft yet.

Anyway, I think all in all it´s much better. Of course, now it´s a little slower lower down, but 326 mph at 10000 ft was terrible! ...unless of course it wasn´t... (!!), and the critical altitude was all wrong!

I know you perhaps don´t like the lower S.L. performance, but maybe this is the lesser of evils.
Anyway, we are trying to curb the shortcomings of CFS1 ´s single-speed blower, so we could interpret the use of WEP here as a manually implemented extra boost, only to be used below 7000 ft.

If we permit it for take-off and prohibit it later, we might as well include it upto 7000 ft to compensate for the lower power at lower altitudes. I´d say it´s a valid argument, whouldn´t you agree?

Cheers,
Aleatorylamp

 

[aleatorylamp]

Hello Ivan,
Sorry about the long post.
I was trying to argument things as best as possible, and it just kept getting longer! The idea of course isn´t perfect and has its flaws.
On the MkIIIA it´s not working - Boost Gain here is lower still, with a shorter speed-span, and everything just gets worse.
I´ll perhaps try the balanced increase in torque and friction graphs, to see what happens higher up.
Cheers,
Aleatorylamp

 

[aleatorylamp]

Hello Ivan,

I was just testing your Mitchell-C .air file to see what you mentioning about the peaks.
From the speed information you quoted in one of your previous post, I deduce your testing protocol for speeds as being perhaps 80% fuel and no bombs, or perhaps 50% bombs and 50% fuel.

I see the your point. It doesn´t look like the peaks are too bad, which would mean that the peaks in my case wouldn´t be so bad either! If I could only somehow correct the erroneous peak 2000 ft below critical altitude, it would be perfect.
The performance curve on the Mitchell-C does look very good!

As the Baltimore is lighter and wing area smaller, the change in dimensions and weight required Drag and Boost Gain adjustments that have originated the current problem.
I´m working on it, to try to avoid sacrificing in the S-L. performance.

Cheers,
Aleatorylamp

 

[aleatorylamp]

Hello Ivan,
At least the increased Boost Gain has eliminated the "false peak" below critical altitude, and following on from the possibly acceptable peak criteria, I lowered Drag a bit to push up the whole envelope a bit. This got me an extra 3 mph at 500 ft., and is at 292.8 mph now, still 3.2 below the desired 296, but nonetheless slightly better.

I couldn´t push it up any further, as the altitude peak, previously already at 323.7 mph, has now increased by another 4.3 mph.The shape of the pèak starts at 9000 ft with 320 mph, progresses up to 328 at 12000 ft, and dwindles slowly down to 324 at 15000 ft again.

So, for the Mk.V, we have a possibly acceptable speed envelope:
- 8 mph faster at peak,
- 4 mph faster at specified max. speed 15000 ft
- 3 mph slower at 500 ft

Then, for the MkIIIA, it still won´t work! Any Boost Gain increase to kill the "bad peak" makes altitude performance shoot up so much that it can´t be compensated with a Drag increase. As soon as I find a balanced way to eliminate the peak, I´ll post some numbers. ...but not as extensively as last time, ha ha!

Should you have any suggestions or ideas, I would be glad to hear them. Possibly you may have mentioned something before, which I have missed. Thanks very much in advance!

Take your time - there´s no hurry at all for an answer!

Update:
By the way, I had already tried to compensate the 2100 ft loss in critical altitude due to the low Boost Gain by raising Critical Altitude to 15000 ft (overcompensating just to be safe), but it had absolutely no effect.
Cheers,
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp,

I am back home again tonight but will be heading out again tomorrow morning.

The shape of the power curve (and thus the performance curve) for a CFS supercharger is going to be the same shape in all cases as I understand it.
I see no way of getting around it.

There will be a low at Sea Level at a particular MP level.
There will be a critical altitude at which the same MP is achieved as at sea level. (This is the engine's critical altitude.)
There will be a peak about 2/3 (somewhere around 2/3 from my vague interpretation) of the distance between Sea Level and Critical.

The fitting of the curve to best match the performance of your project is up to you.

In the first case, your peak was below the aeroplane's 15,000 feet critical altitude (Aeroplane's not Engine's critical altitude).
In the second case, your critical altitude was higher but the SL power started lower, so the peak was closer to where you wanted it.
The choice of 6 mph faster at medium altitudes or 6 mph slower at SL is entirely up to you.
Pick the one that appeals to you the most.

As for WEP, I believe the WEP Boost Modifier set to Zero makes the most sense, but again, it really is up to you.
The big problem is that this simulation of "Through the Gate" really doesn't make much sense when compared to reality.
On a real aeroplane, running Through the Gate at Sea Level will stress the engine.
Running Through the Gate above Critical Altitude makes much less difference and above a certain altitude makes no difference whatsoever.

It really is your choice.

- Ivan.

 

[aleatorylamp]

New experiment!

Hello Ivan,
Have a nice day out again!

Thank you for your helpful comments and your long answer!
So at the moment, that seems to be the state of the situation.
Interesting, and it will obviously require a decision as to what approach will be more appealing.
Thanks for the clarification about the 2 different critical altitudes - one for the engine and one for the plane... I get the gist, but it seems rather odd. Then, ceiling is yet another different thing...

Meanwhile, back at the workshop, there is some mysterious new activity going on:

Record 505: Parameter "Supercharger Low Altitude" Related?
-AirEd info:
>Usually 1.0000 if Turbocharged
>Large values (~100000) Inc MP/HP at SL

I looked into this in my current Baltimore Mk.V experiment, where:
- normal max. MP= 42
- WEP increase = 44
- Boost Gain = 2.221
and found that the following WEP and non-WEP MP readings came up at S.L. and/or 500 ft for the following different Supercharger Low Altitude increase entries, and have listed their corresponding MP readings:

Original setting and MP values:
_____1: 42.0 and 44.0

Testing new settings for their MP values: (all at S.L. or 500 ft, first non-WEP and then WEP))
__2500: 42.2 and 44.1
__5000: 42.3 and 44.3
_10000: 42.6 and 44.4
_20000: 43.3 and 45.1
_30000: 43.8 and 45.7
_33000: 44.0 and 46.0 This +2 Hg setting could be of use? Perhaps a cunning plan...
_40000: 44.4 and 46.4
100000: 48.1 and 50.1

First of all, 3 comments:
1) It seems that if throttle is at 99% instead of 100%, all values will default to 48.1 and 50.1 !!
2) The altitude at which only 0.1 Hg WEP/non-WEP difference happens, was 10000 ft. With Boost Gain at 2.27 like on the Mitchell-C, this difference occured was 10500 ft.
3) At and after critical altitude, also for the second Boost Gain setting, MP readings matched those obtained prior to any changes in the Supercharger Low Altitude increase parameter. Now I´m waiting for my mechanics and engineers to build some modifications into the supercharger, to see if and how this effect can be of any use. At the moment, there is a huge argument going on.

The idea is to try to use a 33000 setting and reduce Normal Manifold pressure from 42 to 40, so that with WEP for Take-off, they will get the required 44 Hg, but later, without WEP of course after mid-altitude (we continue to prohibit WEP for normal flying higher up), expectedly the pre-critical altitude peak will be 2.0 Hg lower!!! Now some of the staff are still shouting, but a few have just scuttled off to the drawing board, lathes and planes, to quickly build something before the place gets burnt down!

At least they are happier with the new plan than with the previous Drag trials... Let´s see what happens!
Another thing have just asked, is how about an Emergency Power Pressure Change Rate MINUS value instead of Zero?. Would that vary with altitude? I told them we can only try one thing at a time. That will have to come later.

Let´s see about the Low Altitude Supercharger effect first.
Cheers,
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp.

It is hardly a nice day out. I am trying to take care of my mom and she does not have computers or Internet access at her house.
She is barely mobile at this point, so life is not so easy. Not to mention that she tends to constantly ramble about a lot of odd things, but the rambling is pretty much the way she has been for decades.
She is pretty old but still coherent so that part isn't so bad.
I have my laptop computer, but no Internet unless I set up my cell phone as a wireless hotspot.
Problem there is that the communications speed would be VERY slow. It probably is not quite enough for easy browsing.
I tried it in the car a few months ago when we were doing a college visit for my daughter.

I know of the parameter you are describing but have never experimented with it.
I have always wondered if this was a "Supercharger as versus Turbocharger" setting.

If you are getting increasing MP values with altitude, I cannot see how this is beneficial or even useful.
What you are really trying to tune is the Engine Output because the MP settings that stay constant with increasing altitude are not THAT much of a problem.

You asked about my speed testing protocol.
I actually start with 100% Fuel and Zero Bomb Load and do not worry as I burn off Fuel during the test.
Weight does not seem to matter very much when testing speed, but matters a lot more when testing climb rates.

When differentiating between different models of the Baltimore, keep in mind what the differences were in reality.
I ran into this problem also with my P-38 Lightning:
The claim is that the WEP speed of the J Lightning is supposed to be around 445 MPH.
The F Lightning is slower at maximum speed but actually has less drag than the J because with the same power settings and very similar engine output at cruise settings, it is faster.
The problem is that with the SAME drag in the AIR file, the F is way too fast.
This tells me that the actual WEP speed of the J is probably not quite as fast as the reports claim because the numbers simply do not add up.
The alternative ideas simply do not add up very well.

Whenever we build an entire series of aeroplanes, we run into this problem where the test reports do not match exactly with the physics that we know MUST be true and sometimes with the aeroplanes' reputations.
I hit this with the P-40 series as well and that is why the flight testing with the P-40N is so strange.

Need to go find a few things before I leave the house for the day.
- Ivan.

 

[aleatorylamp]

How interesting!

Hello Ivan,
Thanks for your detailed reply!
What you say about different models of a plane is definitely the case!
This whole supercharger business is not only getting very interesting but also very exciting!
The truth is, that I only want to increase Power at low altitude, to recover S.L. speed, and then, try to get the altitude peak down!
So the Low Altitude Supercharger increase parameter is just what we need.
Boost Gain is now even lower than it was before, and this helps mid-altitude speed, and also, it will not warrant WEP after Take-Off! So we must prohibit that because using it will give more than specified maximum power as of 5000 ft!!

My workers have all run into town to party with their family or girlfriends to celebrate. They are all criticizing the test pilot because did the tests with full tanks and half the bomb load, but they decided to let him off...Here are the results of the test-flights:

187 Baltimore Mk.V Trial No. 5
Friction: 32.8
Torque: .535
Oswald: 6750
Zero Lift Drag: 64
Boost Gain: 2.065
Supercharger Low Altitude Boost increase: 33000
Emergency Power Pressure Change rate: 0.000

100% fuel and 50% bombs and 50% ammo trial

__500 ft 44.0 Hg 1700 Hp 296.7 mph >>>> WEP only here. Take-off, and a little while after...
_4500 ft 42.0 Hg 1666 Hp 305.2 mph
_6700 ft 42.0 Hg 1696 Hp 315.1 mph
_8000 ft 42.0 Hg 1714 Hp 322.6 mph
_9000 ft 42.0 Hg 1728 Hp 324.4 mph
10000 ft 41.5 Hg 1718 Hp 326.8 mph
11000 ft 39.8 Hg 1655 Hp 325.8 mph
12000 ft 38.3 Hg 1598 Hp 324.8 mph
12500 ft 37.5 Hg 1568 Hp 323.8 mph
15000 ft 34.0 Hg 1431 Hp 320.1 mph

I think this is quite a lot better than before!

Now my own family is angrily calling me to lunch.
Back later!

Update:
Well, lunch was wonderful. My wife being in the middle of her 2-year cookery course at a technical high-school downtown has its advantages...

Looking after old people is hard. At least your Mom´s mind hasn´t gone like my mother´s did. We were lucky enough to get a place for her in a social-security old-people´s home specialized in caring for cases of senile dementia in her last few years. I remember when my 2 brothers came to the Island to visit for a week each, one after the other, she recognized them, but the day after they were gone she´d forgotten the visit. However, I suppose there´s an emotional memory that somehow works when the conscious one doesn´t. Then she broke her hip at 85 and the unavoidable operation was too tough for her. Anyway, such is life. Everyone agrees, old age is only good if you are reasonably mobile and lucid...

I don´t know much about cell-phones because mine doesn´t even have a camera or a touch-screen, and I wouldn´t know how to use one which did... I´m sure they are useful... but I need my reading glasses for the phone, so it puts me off.

Anyway, you can try the "new" parameter on the Mitchell-C - maybe you can iron out the high altitude peak after critical altitude.
What I still want to figure out is how to compensate the other peak about 2/3 before critical altitude, although in this case, it helped with getting S.L. and mid-altitude speeds back in place.

I wonder what approach the MkIIIA will require - this has a speed envelope very similar to that of the Mitchell-C, but it´s more difficult because very similar speeds need to be achieved with slightly weaker engines, but with a considerably lighter and smaller airframe and just over half the payload. I´ll see.

Cheers,
Aleatorylamp

 

[Ivan]

Mobile Hotspot Operational

Hello Aleatorylamp,

Using my Cellular Phone as a Mobile Hotspot definitely works because that is how I am online at the moment.

You don't have to follow MY testing protocol.
If you want to do testing under different conditions, that is fine as long as you are consistent.
One thing we have not discussed is how long to wait for the maximum speed to become stable.
I generally record the value if it has not increased in 15-20 seconds.
If you wait longer in your tests, your speed reading may be 2-3 MPH higher.

Which value are you actually changing now for the supercharger?
I don't happen to have AirEd on my laptop but if you tell me what the Record:Offset value is, I can look it up in my copy of FDECtrl.txt which I do have here.
I am guessing it is Record 505 Offset 64 as a Double Precision Floating Point.

I am not so sure I agree with your results though.
From what you have listed, it seems like your current results are quite a bit worse than what you were getting before.
Your engine's critical altitude is only at 9000 feet.
You are getting your target airspeed at 500 feet but you need WEP engaged to do it. It wasn't needed before.
Your Manifold Pressure is way low at 12,000 feet.
You reached target airspeed at 15,000 feet, but the power and speed before that are quite high.

Gotta Run.
- Ivan.

 

[aleatorylamp]

Hello Ivan,
Glad your Mobile Hotspot is in operation. Modern technology at work indeed! As yet, out of my abilities...
I also did Mk.IIIA trials with 100% fuel and 50% payload, for the sake of consistency. From what you said it seems OK for the purpose. It´s about 1000 lb heavier than with no payload + 100% fuel, which we will use once climb tests start.
I forgot to thank you for helpful suggestion on the 15-20 seconds for speeds to settle during test flights. I have adopted this method too and it makes life simpler, but usually a final check is 30 seconds just to make sure it stays put.

In AirEd.ini, in record 505, it is:
11=40,double,*Supercharger Low Altitude Boost Related ?
11h=Usually 1.0000 if Turbocharged|Large values (~100000) Inc MP/HP at SL

In FDE it is Unknown 505 - 64, so it is the one you say. Default is 1.

This value won´t affect critical altitute. In fact I thought it would help correct it, but it doesn´t.
The one that lowers critical altitude is the Boost Gain, which unfortunately has to be low so as to keep high altitude speeds (11000-15000 ft) from shooting up beyond spec. speed.

I don´t understand your present comment that I now need WEP for 500 ft and didn´t before.
I thought that we were aiming precisely at 44 Hg for Take-off, as well as for 500 ft with 296-297 mph, for which we need WEP. Otherwise we only get 42 MP.
Was that not precisely the point we needed - to have WEP only for Take-off? It would not be used to for the rest of the flight envelope you were describing so as to protect the engine, and that would be non-WEP at 42 Hg until it went down.
So I understood something quite different from what you meant.

There is already so much power in the engines with 42 MP that it wouldn´t really need the 44 Hg WEP for take-off anyway... or anywhere else, for that matter, but OK... So, in a nutshell, do you mean that the 296-297 mph at 500 ft should happen under 42 MP?

This will probably unfortunately distort the envelope even more, because Drag will have to go down further, to get S.L. speed without WEP up to what it is now with WEP. Reducing Drag always creates havoc at higher altitudes. Boost Gain will have to go down even further, so critical altitude will drop even lower. It is really set for 12100 ft, but CFS only respects it if Boost Gain is more or less at or above 2.25 - otherwise it either ignores it or multiplies it down.

My manifold pressure is way down low at 12000 ft. Yes, it is, and I have mentioned several times before, that it was a real the problem: With higher MP values there was excessive power, and speeds rise to beyond 330 mph. Curing this with Drag caused very low S.L. power and speeds, so it was a big problem.

Power and speed at 15000 ft are OK but before that, quite high. Yes they are, but I can´t find a way to iron that out. You had mentioned in your last post that the 2/3 altitude peak is impossible to eliminate, so I really don´t know what you mean. If I could find a way to iron that peak out or put it up a bit without messing other things up, I´d do it. I did say that I was still working on it. I thought you said it was a problem inherent in CFS.

Without lowering Boost Gain and without using the Low Altitude Boost increase, we get a different type of flight performance envelope that is has problems elsewhere, which I have mentioned several times before.

Anyway, I finally did manage to get the Mk.IIIA .air file going in a similar way to the last Mk.V one.
However, from your comments I gather that you won´t really like this one either, but here goes:

187 Baltimore Mk.III Trial No. 2
Friction: 38.3
Torque: .530
Oswald: 6750
Zero Lift Drag: 69
Boost Gain: 1.955
Supercharger Low Altitude Boost increase: 33000

Aims:
288-289 mph at 500 ft (284 mph specified for S.L.)
305 mph at 11500 ft

100% fuel and 50% bombs and 50% ammo trial

__500 ft 44.0 Hg 1660 Hp 288.0 mph >>>>WEP only here.
_4500 ft 42.0 Hg 1626 Hp 296.0 mph
_6700 ft 42.0 Hg 1656 Hp 303.5 mph
_8000 ft 42.0 Hg 1674 Hp 308.4 mph
_9000 ft 40.9 Hg 1637 Hp 308.6 mph
10000 ft 39.3 Hg 1576 Hp 307.0 mph
11000 ft 37.7 Hg 1517 Hp 305.7 mph
11500 ft 37.0 Hg 1492 Hp 305.1 mph >>>> Mk.IIIA Spec. speed
12500 ft 35.4 Hg 1435 Hp 303.3 mph
15000 ft 32.2 Hg 1306 Hp 299.6 mph

With the even lower Boost Gain required here to keep speed from shooting up at altitude, critical altitude for the engine is also very low - 8000-9000 ft!

Well, so much for that. Let´s see if it will be possible to adjust both .air files to get the 500 ft speeds happening with 42 Hg MP instead of 44. So WEP boost is meant to be independant from all this... Hmmm...

Let´s see how it goes.
Cheers,
Aleatorylamp