Project Martin A-30 Baltimore

Hello Aleatorylamp,

As you saw by the SEFC for the Vultee Vengeance, even for the same model engine, there is quite a lot of flexibility.
Your opinion is as good as mine in this case considering that neither of us has found a SEFC for the Baltimore yet.
I have my own tuning preferences. Yours do not have to be the same.
I also have my own testing protocols (which are in a state of change for climb testing).
Again, yours do not have to be the same.

At the moment, you are playing with a parameter that I have never experimented with, so I am not in a position to give advice especially since I have no access to a simulator to even experiment to see if I can understand what is happening.

I knew what my goals were in my testing for the Mitchell and achieved the majority of them.
I have no idea anymore what your goals are with the various Baltimores.

- Ivan.
 
Hello Ivan,
Thanks for your post. Yes, I agree with you on the flexibility and the goals.

The testing protocols are easy to change and I can really use whichever are more convenient - they won´t change the shape of the curve anyway. 1000 lb lower weight is just 1 point lower on the Zero Lift Drag in AirEd. I´d just forgotten to empty half the tanks and was half way through the test before I noticed, so I just went on, also for the 2nd model, especially after your comment. So like you say, that really doesn´t matter. Next time I´ll subtract it from the .air file and that will prevent me from forgetting!

What does matter, is that the graph shape just doesn´t seem to want to come out right, even using some of the more obscure parameters that at first sight seemed to have been beckoning towards a solution.

How would one arrive at the best solution with single-speed blowers instead of two-speed ones?
What´s more important, the speed of the plane in the sim or its MP or Hp readings?
You said a while back that you were more inclined towards getting closer to the performance rather than the numbers, so that means Mph, and not Hp or Hg so much, and then, performance along as many parts of the curve as possible, not only at the beginning and at the end.

I thought that my goals were clear, even despite the non-existence of a SEFC for the Baltimore, but anyway, here they are again:
MkV: S.L.: 291-292 mph, 296-297 mph at 500 ft, 320 mph at 15000 ft, with a higher peak just at 12500 ft.
MkIIIA: S.L.: 284 mph, 288-289 mph at 500 ft, 305 mph at 11500 ft, with a higher peak just after.
PLUS: As few aberrations as possible along the rest of the line!

The fact that suddenly a 2nd Baltimore has come up is because I thought the performance curve on that one would be easier to achieve given its shorter speed-span, but in fact it´s even more out than the first one. So, I can forget about it and try to get the first one right.
Had the Mk.IIIA been easier I would have discarded the Mk.V.

Problems?
A) I didn´t understand the 44 MP Take-Off WEP thing you had in mind and put that into the 296-297 mph instead of leaving it separated from the curve. Solution? Try out further.
B) Boost Gain has lowered critical altitude and CFS ignores the parameter specifying it. Solution? I dunno! This is the condicio sine qua non. For the smaller wings, lighter airframe but similar engines this doesn´t seem to be coming through as nicely as on the Mitchell-B/C.
C) High speed Manifold pressure is to low, but has ALWAYS been too low. Solution? Not important for my goals, but MP must be correct at S.L. and until correct critical altitude which it is.

Conclusion:
The Baltimore is conditioned to the possibility of my being able to move the engine peak onto the other side of the correct critical altitude, in other words, my possibility of correcting the stupid position that the simulator incomprehensibly forces critical altitude into after providing the seemingly obvious solution of lowering Boost Gain for performance adjustments after Take-off. Like George Orwell said in 1984: "Two plus two is four. Once that is granted, all else follows".

Not to worry, and not to hurry! As they say here, "There are more days and more pots", so I´ll continue tinkering around until you get the chance to try out this "unused" parameter and see what you can say about it.

Update:
Maybe all these musings are useless beatings around the bush, a pile of codswallop, as the English say (best not to explain what it really means!), because most probably, what is in reality going on but nowhere to be found, is that the R-2600-29 has a critical altitude of 15000 ft, with WEP Hp rating of 1850 Hp, and a normal 1700 HP rating at 12500 ft! I´m quite certain that putting this into the .air file will work. Actually, it will be the only thing that works!
There being two editions of the -29 engine may mean that the 1850 Hp version had the 1850 Hp at 15000 ft in the normal max. rating, and was just a nomenclature change, not a real change, so it was the same, identical engine.
Bets anyone?

Then perhaps, the Mk.IIIA .air file not working for a completely different reason, being that I have not actually tested it yet using the normal approach without all the extra (for this case useless and even pernicious) new parameter experiments.

Cheers,
Aleatorylamp
 
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Hello Ivan,
Following on from my last message, to make sure how the normal approach would work on the MkIIIA beforeperhaps erroneously discarding it, I did a very precise test.

Aims were:
1) 500 ft: 288-289 mph with 42 Hg.
Experiment result: 1574 Hp at 288.8 mph - Fine!

2) 500 ft WEP at 44 Hg: 1660 Hp.
Result: 1660 Hp at 305 Hp. Hp is PERFECT!
Is a 15 mph increase over non-WEP fine? WEP MP increase is at 2, and Emergency Pressure Change Rate is at zero.

3a) Max speed 305 mph at 11500 ft, WEP making no difference.
Result with Boost Gain 2.27: 42 Hg, 1724 Hp, 330.1 mph. Hg/Hp good, Mph TERRIBLE!!
Result with Boosh Gain 1.85: 35 Hg, 1400 Hp, 304.7 mph. Hg/Hp low, Mph VERY GOOD!
Adjusting Boost Gain more finely, I´m sure exactly 305 mph can be reached, but there´s no point.

3b) Critical altitude is 11500 ft, i.e. peak performance is here.
Result with Boost Gain setting 2.27: Peak at 13500 ft. TERRIBLE!
Speed continues to rise to 331 mph at 13500 ft, and at 15000 ft it is still at 329 mph. There´s no point in investigating where it goes.
Result with Boost Gain setting 1.85: Peak at 7000 ft. TERRIBLE!
Exactly at 5528 ft, 305 mph max speed is reached too soon, and later, speed comes down to 305 mph again at 11500 ft, which should be critical altitude, after which it continues going down.

Obviously a Boost Gain setting that fits the required 11500 ft altitude does exist, and may be at around 2.2 or so, but it will also have a very high speed peak, so it´s not even worth trying out.

Comments:
Wahtever I do, the curve shape is very distorted. Obviously this, like you said, is the CFS single-speed supercharger at work.
I´m terribly sorry, this won´t do at all. Unless there is a way to get this reasonably bent into shape using whatever criteria may be useful or reasonably effective, which I don´t have, I can forget about this version again.

Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

It seems we are going around in circles. I think you are looking for a "Magic Bullet" and I doubt you will find it.
CFS is what it is and although it was a great improvement over FS98, it also has its limitations.

You brought up a lot of points. I will try to address a few.

Priorities are Performance, Manifold Pressure, Horsepower in that order.
There are a few cute little ways to do fine tuning but I don't want to bring those up because on this project they are almost certainly not necessary.
On something like the FW 190D that I used for my tutorial, I believe they would be unavoidable.

Don't worry if you are 3-5 MPH off.
The parameters in the simulator are not that granular and sometimes that is as close as you will get.
The fine tuning such as with Propeller Tables can help, but I do not recommend you go there.

Changing multiple parameters at a time is unwise.

For the SEFC we got from the B-25C/D, we can gather the following:
Take-Off Power is around 1700 HP at 44.0 inches Hg and 2600 RPM.
There is a small rise in power above Sea Level so that 1700 HP is reached again with only 42.0 inches Hg.
The 12,000 feet power rating is PAST its critical altitude because only 41.0 inches Hg can be reached.
Perhaps I am wrong and it is a limitation of the High Speed Supercharger gear, but I am treating it as beyond critical altitude.
The Aeroplane reaches a high speed of 315 MPH at 15,000 feet but this is way above critical altitude which is not uncommon.

For your Mk.III Baltimore, if it is hitting maximum speed at 11,500 feet, its engines' critical altitude is quite a bit lower.
(Otherwise it would go even faster if you went higher.)
From the SEFC of the B-25C/D, it appears to me as a reasonably educated guess that those engines had a critical altitude in High Blower of around 11,500 feet, so an earlier version with less supercharger would probably be below that.
(This probably is like saying the typical Basketball player is PROBABLY taller than I am.)

I have data limits on cell phone, so that's it for now.

- Ivan.
 
Circles, circles...

Hello Ivan,
Thank you for making me un-dizzy again, I must say! ...with the added merit of your message coming out of the the miniaturized Iphone technique which I´m useless at.

I´m glad that at least I tried to look through the tangles in the quagmire and decipher something, because I have learnt a bit about what some of the more obscure and unused (and probably useless) parameters can and can´t do, and what they really should do and don´t do!!

So where´s the magic bullet? It just crossed my mind that until someone else wrote decent CFS .air files for the Baltimores, I could provide simpler FS98 ones to do the trick for the time being! (Honestly no sarcasm meant). This way I could chicken out and just build...

However, I´d be missing out on how interesting it will be to see if, or rather how, eventually something usable DOES come out of a CFS .airfile for the planes. So, lead on, Mac Duff, the journey has yet to improve!

Cheers,
Aleatorylamp
 
Mk.IIIA back in production

Hello again, Ivan,
I was fearing that I was getting heavy with this business and that you were going to get fed up, so I am quite glad and relieved to have the sensation that this is not the case.
After your reassuring comments on the Mk.V and Mk.IIIA´s different engines, I have just made some small adjustments and conducted another precise flight test on the Mk.IIIA.

187 Baltimore Mk.IIIA Trial No. 3
Friction: 38
Torque: .535
Oswald: 6750
Zero Lift Drag: 73
Boost Gain: 2.0
Supercharger Low Altitude Boost increase: 1.0

100% fuel and 0% bombs trial

___16 ft 44.0 Hg 1663 Hp 283.7 mph
__500 ft 44.0 Hg 1669 Hp 284.1 mph >>>> Mk.IIIA 284 mph S.L. Spec. Speed very good
_4500 ft 42.0 Hg 1635 Hp 293.1 mph
_6700 ft 42.0 Hg 1665 Hp 299.8 mph
_8000 ft 42.0 Hg 1663 Hp 304.2 mph
_9000 ft 41.8 Hg 1690 Hp 308.2 mph >>>> peak better here than before at 7000 ft.
10000 ft 40.2 Hg 1627 Hp 307.1 mph
11500 ft 37.8 Hg 1533 Hp 305.0 mph >>>> Mk.IIIA Spec. Speed exact.
12500 ft 36.4 Hg 1483 Hp 304.0 mph
13500 ft 34.9 Hg 1426 Hp 299.8 mph

Evidently the difference between S.L. and 500 ft is not as much as I´d expected when I extrapolated data from what we had agreed on for the Mk.V´s 296-298 mph at 500 ft.

This has allowed an increase in Zero Lift Drag to get S.L. speed correct. I still don´t understand your comment on the low S.L. performance i.e. WEP or non-WEP for 500 ft, so I went for the specification S.L. 284 mph and tested over the water at a hair-raising 16 ft.

I got exactly what I needed, or think I needed, and discovered that speed increase for this aircraft from S.L. to 500 ft is actually only 0.4 mph. This makes 42 Hg tests here, in my view, irrelevant, unless of course I´m completely wrong, which can´t altogether be discarded!

This has also allowed an increase in Boost Gain to 2.0, thereby fortunately raising the CFS imposed critical altitude to 9000 ft, much better than the previous 7000 ft.

Performance at 11500 ft matches 305 mph specification speed as before, which is still a great satisfaction, but a greater one is that speed peaks below and above 11500 ft critical altitude have disappeared!

Can it be said that this is as good as it can get? If not yet, then I´m sure it can be improved, judging by your comments.
If so, we have the pleasing situation whereby the Mk.IIIA is back on the drawing board and will resume AF99 production.

The next step will in any case be to see about the Mk.V´s chances of achieving the same.

Thanks again, Ivan, for your steadfast and encouraging help!
Cheers
Aleatorylamp
 
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Sea Level Test

Hello Aleatorylamp,

Your Baltimore Mk.IIIA performance actually looks pretty good.
I don't believe you will significantly improve on the performance curve you currently have.

Here is an interesting thing for you to consider:
Your Sea Level speed run is ENTIRELY INVALID! <Grin> Unless you tested at Death Valley or some place below Sea Level.

Perhaps they go faster because swimming with the fishes scares them??? Naaah.
Here is why: Ground Effect.
Hubbabubba and I touched on a somewhat related subject a few years ago.
In Ground Effect, The reduction in Induced Drag changes the speed significantly.
No one actually tests at Sea Level. They test at a convenient altitude and use a mathematical correction to get equivalent Sea Level performance.

Another invalid test (The part Hubbabubba and I were discussing) is to go from a higher speed DOWN to the maximum speed.
It doesn't seem logical, but is how things really work.

During the wary, Bombers would climb a bit and then go down to sea level in a shallow dive.
When they reached as low as they dared, they would be in ground effect for long over-water flights AND
the speed would stabilize a couple MPH above where they would have been had they accelerated UP to that speed from below.
Whether it makes sense or not, this is what really happened.

Time to cook dinner.
My family just finished visiting at my mom's house about an hour ago.

- Ivan.
 
Hello Ivan,
What good news! I AM glad about this!

I was just doing a daredevil 16 ft test on the Mk.V to establish the basis for correct 500 ft performance.
It seems to have clarified WEP use and speeds for S.L. and/or 500 ft performance somehow, although the actual numbers for 16 ft height were not going to be respected by anyone!

Would 288 mph for 500 ft then have been indeed closer to the truth? It would however not have helped towards the correction of critical altitude. Anyway, thanks to this the performance envelope is pleasing!

So testing downwards can be misleading. I had that feeling, so when I do test going downwards, I let out the landing gear and pull it in again to slow down to a point where speed has to rise for that altitude. This way it´s quicker too, but it´s convenient to eliminate Landing Gear Pitch Moment for the test...

So bombers saved fuel in ground effect! Flying boats did as well. So it´s the Induced Drag that decreases. I always wondered why the dynamic air cushion under the wings could make Drag decrease.

Like the ekranoplan Caspian Sea Monster! I wonder if anyone would want a "Korabl Maket" KM4 for CFS1. Probably not... Extraordinary 500-ton Leviathans from 1964 as big as a 747 doing 500 mph at 40 ft above the water.
A breathtaking sight, these incredible machines. Take-off using 10 Turbojets, 8 of them just behind the cockpit, which had cups that could blow the jetstream downwards to increase ground effect under its short but wide wings. Once airborne, they cruised in Ground Effect on just the two tail engines below the tall T-Tail, with stabilizers necessarily above Ground Effect. The front ones were sometimes left idling to be able to use them quickly enough to "jump" over suddenly appearing obstacles.
The .air file has a stronger Ground Effect Graph 400, and a severe cut in peak of the Wing Lift Coefficient vs. AoA Graph 404 to prevent it from flying above ground effect. Flap control tandems flaperons with jetstream angle for Take-off. Wierd but effective.

Anyway, here´s a picture of my FS98 Caspian Sea Monster meanwhile!

Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,

Check Record 400 for Ground Effect Graph.
The increase in CL will let the wing lift more at a lower angle of attack but drag is matched with angle of attack
so because of the reduced AoA, the induced drag is less.

Regarding lower SL speeds:
Remember that the engine power output curve does not really match a two speed supercharger power curve.
It peaks where in reality it should be pretty low.
I figure the best approach is to best match the two curves so it doesn't deviate too far at any one point.
It will then be too low at SL too high at middle altitudes and perhaps too low again at critical altitude.
Because of the ram effect and because of where people typically test for speeds, I will not reduce the critical altitude speed much if at all.

If you think your graph matches badly, look at the one for the FW 190D that is in my tutorial.
If there is a better way to do things in CFS, I don't know it.

Just think about it though:
In the history of CFS, developers generally have not cared much for duplicating actual performance or perhaps most folks really did not have any idea how to do it.
The fact that we spend a little effort along these lines and are getting fair results is a vast improvement.

Pity we can't meet for a long lunch or dinner discussion.
Typing responses is a bit slow.

- Ivan.
 
Hello Ivan,
Interesting, yes... and also, when coming down during test flying instead of going up, because of the lower angle of attack and the downward descending movement there might be an increased cushion of air underwing, causing what we could call a "Coming-down Effect" i.e. a pseudo Ground Effect.

A lunch would be great, wouldn´t it? Spring rolls, fried Wan Tun, and fried rice for me please. The last time my wife and I ordered this, here in a Chinese Restaurant, the Owner almost didn´t serve us, arguing unpleasantly that none of these were main courses, and only served us what we wanted because otherwise we would have left. Sweet and sour prawns (done in Tamarind sauce) would have been a good main course, but we weren´t so hungry that day.

My current experiments with the Mk.V seem, surprisingly and unexpectedly for me (but I´m sure not for you), to be going rather well. The lower S.L. performance resulting from my hair-raising 16ft test flying appears to be working!! ...sheer luck! Results resemble your current curve description:

- Slightly low at S.L. (exactly like the Mk.IIIA),
- Speed peak Critical Altitude at 10000 ft (this must go up to 11500 ft as yet by correcting Boost Gain).
- 317 instead of 320 mph at proper 15000 ft critical altitude. (this will go up to 320 if I correct Boost Gain).
(Update: Neither of them did...)

Interesting, how well this is finally going - and without either strange speculations or using other misleading and obscure parameters! I suppose I was a bit hard on our CFS, and I do thank my lucky stars that it still works in this day and age, and what it does is quite remarkable for what it is!

Time for breakfast and getting the kids to class. My wife is off to a practical cookery exam - the third in 7 days.

Update:
The kids don´t have to go to class, they´re studying for exams.
I´d forgotent that... My memory resembles a 2nd. hand EDO module.

So, here are the new results of the Mk.V flight test, and the shape of the curve is exactly as you said!
("Of course", you will say, ha ha!)
Increasing 15000 ft speed to spec. 320 would come at the price of an extra 3 mph at the 10000 ft peak. Now speed is nicely acceptable, so it may stay there. In after-thoughts predictably, I haven´t managed to move the peak to 11500 either...

187 Baltimore Mk.V Trial No. 6
Friction: 32.6
Torque: .535
Oswald: 6750
Zero Lift Drag: 68
Boost Gain: 2.076
Supercharger Low Altitude Boost increase: 1.0

100% fuel and 0% bombs
___16 ft 44.0 Hg 1694 Hp 292.9 mph >>>> This one just for fun now, but also helps to get my bearings.
__500 ft 44.0 Hg 1700 Hp 293.5 mph >>>> Predictably slightly low (should be 296-298 mph)
_4500 ft 42.0 Hg 1666 Hp 300.6 mph
_6700 ft 42.0 Hg 1696 Hp 308.9 mph
_8000 ft 42.0 Hg 1714 Hp 316.4 mph
_9000 ft 42.0 Hg 1728 Hp 321.2 mph
10000 ft 41.7 Hg 1729 Hp 323.2 mph >>>> Peak still here, but weaker.
11000 ft 41.0 Hg 1670 Hp 322.0 mph
11500 ft 39.3 Hg 1639 Hp 321.4 mph
12000 ft 38.5 Hg 1609 Hp 320.8 mph >>>> Critical altitude set at 12100 ft (but ignored?)
12500 ft 37.7 Hg 1579 Hp 320.7 mph
15000 ft 34.2 Hg 1431 Hp 318.0 mph >>>> Should be 320 mph. Probably I should go for it and raise Boost Gain ever so slightly once more. It would then possibly be 326 mph at 10000 ft. From what you say in your last post, I gather that it´s just what you would do in your case.

... but it´s looking nice!
Thanks again for your summed-up indications! Now we can have 2 Baltimores! ...at least...

What blows my mind is how you knew that this was what the curve was going to more-or-less look like if done correctly... Flabbergasting!

Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,

Actually there is nothing that is really "Flabbergasting" about the end result.
For the most part, tuning the CFS engine is pretty predictable.
You actually were at this point a couple months ago when I first sent you my MitchellC AIR file and you modified it.
The differences between where you were then and now are pretty minor.

Keep in mind though that you have worked on flight models of this type a couple times,
but I have done this several hundred times.
It doesn't mean I know everything because I do not. There are things I have been meaning to experiment on such as the Propeller Tables.
I should be home this evening and if I am not too tired, I will try a couple things out.
First task is conduct a proper Service Ceiling Test for the B-25B/C Mitchell.
My current protocol is closer to an Absolute Ceiling Test.
I shudder to think of how the results and change of protocol will affect other projects.
I know for sure the Mitchell's flight model will change to some extent.

Recommend you increase Supercharger Boost Gain slightly because not only will it increase your speed at critical altitude, it will also bring the Manifold Pressure up a touch. Perhaps you will still not get to 41.0 inches Manifold Pressure but you will be closer.

Also as a side note, there is a "Critical Altitude" parameter in Record 505, but I don't think it actually does anything.
On my P-40N and others I have worked on, changing that number doesn't seem to affect anything.
Also, the actual critical altitude on my P-40N is around 12,100 feet but the parameter is set for 12,500 feet so the two don't really match though they are close.

Hopefully you are now getting a good "Feel" for how changing parameters affects engine power.
If you think back on all the things we have covered since you first started posting here, there is almost nothing regarding tuning AIR files that I know how to do that has not been discussed at one point or another.

Take Care.
- Ivan.
 
Hello Ivan,
On the way home on the tram (it´s impossible to park downtown so I don´t drive to work) I thought back on how similar the present .air file was to the one you have just referred to.

Back then, the 326.5 mph at 10000 ft seemed awful to me because I didn´t know much about supercharging in CFS, and stubbornly kept on trying out all sorts of different things to see if I could get it any better. Now it turns out that this new one is very similar, and "only" perhaps a bit better after my topsy-turvy investigation. However, it has been a very fruitful experience, as you also say, because now I understand much more about what is actually going on!

What I have learnt about engines in all this time since the beginning, represents a huge improvement for my FS FD building, and my knowledge about the development of aircraft engines since the early times, a subject that has always been one of my favourites. So thanks a lot for your patience in repeating things when I didn´t quite get them until I did!!

Next will come the building itself, and then some testing along the lines you are at present working on.
So, there´s interesting material on the horizon!

Later today I´ll post the new test resuts after slightly pushing up Boost Gain. I wonder if the "false ceiling" will also crawl up ever so slightly...!!

I have one more class this afternoon and then I´ll be free again.
Cheers,
Aleatorylamp
 
Hello Ivan,
Here are the Baltimore Mk.V new slightly-pushed-up-Boost-Gain Flight Test results,
with a little something interesting added below... Humm humm, what could that be now?

...but first the results:

187 Baltimore Mk.V Trial No. 7
Friction: 32.6
Torque: .535
Oswald: 6750
Zero Lift Drag: 68
Boost Gain: 2.125 This is the value for exactly 320.0 mph specified speed at 15000 ft.
Supercharger Low Altitude Boost increase: 1.0

100% fuel and 0% bombs

___16 ft 44.0 Hg 1694 Hp 293.2 mph
__500 ft 44.0 Hg 1700 Hp 293.3 mph >>>> (now 0.2 mph lower still),
_4500 ft 42.0 Hg 1666 Hp 300.7 mph
_6700 ft 42.0 Hg 1696 Hp 309.5 mph
_8000 ft 42.0 Hg 1714 Hp 316.7 mph
_9000 ft 42.0 Hg 1728 Hp 320.9 mph
10000 ft 42.0 Hg 1743 Hp 323.4 mph
10500 ft 41.8 Hg 1742 Hp 324.7 mph >>>> peak has moved 500 ft up! AND to 41.8 Hg!
11000 ft 41.0 Hg 1710 Hp 324.4 mph
11500 ft 40.2 Hg 1683 Hp 323.5 mph
12000 ft 39.4 Hg 1652 Hp 323.4 mph
12500 ft 38.6 Hg 1621 Hp 323.4 mph
15000 ft 35.0 Hg 1479 Hp 320.0 mph >>>> exactly as per spec.

Now for the little new something:

If we enter -15000 (minus fifteen thousand) into the Supercharger Low Altitude Boost increase parameter
- yes, negative values are indeed allowed - then we get the following:

___16 ft 43.1 Hg 1653 Hp (WEP)
__500 ft 41.1 Hg 1574 Hp (WEP)
_4500 ft 41.1 Hg 1626 Hp
_6700 ft 41.1 Hg 1655 Hp
_8000 ft 41.1 Hg 1673 Hp
_9000 ft 41.1 Hg 1686 Hp
10000 ft 41.1 Hg 1701 Hp
10500 ft 41.1 Hg 1708 Hp

Entering -16500 would have given exactly 1.0 Hg less, but my maths was wrong, (typical!) because entering -33000 you get 2.0 Hg less. (Mpsi = Manifold Pressure per Square Inch perhaps, of mercury being implied)

And from the Peak upwards, i.e. the critical altitude which for this plane seems to be 11.000 ft, the Manifold Pressure and Horsepower values remain unchanged.

So! Can this be true? Is this really our Low Blower Speed here, for low altitudes?
I knew it had to be somewhere, but the question is, can we use it?
Oh yes! Probably... But with what values?

Of course, perhaps there are different planes that have a High Speed Blower for low altitudes, for which then positive numbers in this parameter are obviously intended. But do High Speed Blowers for Low Altitudes really exist? I wouldn´t know. If not, the intention behind this parameter has been misinterpreted in the info file.

This could well be used to limit power on the throttle gated Gotha Grossflugzeuge and Staaken Riesenflugzeuge, setting Boost Gain so that critical altitude were only at 4000 and 7500 ft, below which full throttle was not allowed.

Here´s a picture of the toy Baltimore racing along at 16 ft above sea level just for fun. It´s made of wooden blocks and blue cardboard, with transparent gelatine canopy, turret and cabin, all very primitively shaped, just to get the feel of the looks and the stance. Terrible, you would say, but at least the props turn!

Cheers,
Aleatorylamp
 
Possible Baltimore Mk.V low altitude Booster correction

Hello Ivan,
My mechanics and engineers have been doing their homework, or rather their work-shop work, tinkering with the pressure regulating mechanism on the blower, so that below critical altitude, the blower RPM go down to deliver less MP than before, and if WEP is engaged, the RPM increase is higher than before, so the MP delivery for WEP is the same as before. Then, at critical altitude, the blower automatically reverts to its normal state, which doesn´t change with WEP.

What they don´t know exactly yet, is how much the MP reduction should be below critical altitude, and they eye-balled and said "OK, let´s go down 1 Hg and see if it works.", though I´m sure your engineers will know more exactly what it should be for the Baltimore Mk.V.

Anyway, previously we had at S.L.:
non-WEP: 42 Hg.
WEP: 44
Settings:
1-Manifold Pressure: 42
2-Supercharger Low Altitude Boost related: 0
3-Emergency Power Change Rate: 0
4-Emergency Power Manifold Pressure Increase (inches): 2

Now, below 11000 ft critical altitude, for the case of a
1 Hg MP reduction below critical altitude:
non-WEP: 41 Hg.
WEP: 44
New Settings:
1- Manifold Pressure: 42 (same as before)
2- Supercharger Low Altitude Boost related: -16500. (This will reduce normal MP by 1 Hg below critical altitude).
3- Emergency Power Change Rate: 0. (This remains unchanged. Using this for WEP here to compensate the 1 Hg reduction for seems not to work, at least not at S.L.).
4- Emergency Power Manifold Pressure Increase (inches): 3. (This compensates the reduction of 1 Hg normal MP, so that we get the full 44 Hg MP with WEP at S.L.).

This seems to work very well, and the Beckwith Testing Gauge gives the readings!
A rough climbing test gives 5 minutes to 10000 ft, but I haven´t got a stop watch and will have to check better.
One of the Specs I have says 4.8 min. to 10000 ft

Here are 2 pictures of a single-stage and a 2-stage supercharger, just out of curiosity.
The single stage one looks like a simple one without modifications for 2 speeds. Would they connect an altitude sensor to a slip-clutch mechanism? Maybe it was manual, and not automatic in reality, or perhaps even a turbocharger that would be altitude-regulated acting on the waste gate, but I don´t know if they existed at the time. Interesting anyway... The parameter in the .air files seems to cater for both.

Cheers,
Aeatorylamp.
 

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Hello Ivan,

Firstly: OOooppsss!
My post #173 has a mistake in the 500 ft line with the lower manifold pressure values.
In the second line power corresponds to a non-WEP setting. Sorry!
With WEP, MP would be 43.1 as well, and Hp would be almost the same as for S.L.

Later, I conducted another test with the reduction value for 1 Hg (-16500), WEP power at 500 ft delivered 1700 Hp. exactly and was almost the same at S.L.

Anyway, the subject of this post now:
Practically and mathematically, the "possible Boost correction" with a -16500 (-1 Hg) reduction entry is possible, but as I said, only an approximation. It gives a Normal Max. MP of 41 Hg below Critical altitude.

I have the sensation that it is bit insufficient to achieve correct RoC, but engine power is too much for Ceiling, so evidently, a ceiling adjustment will be mandatory first. You had already mentioned the need for a ceiling test several times in the last few weeks, and I can anticipate your answer to my question yesterday, which could probably be "The correct reduction setting will depend on what RoC you want to achieve with engine performance corrected for ceiling."

OK, then. Don´t hurry for an answer, take your time, as I´m sure you are conducting your own tests.
There´s no hurry in the hobby - it wouldn´t be a hobby if there were any hurry!

Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,

Nice pictures of a Single versus Two Stage Supercharger arrangement.
It isn't really relevant though because the issue that causes us grief is the Single versus Two SPEED Supercharger.

My Engineers actually took a different approach to finding out more about this parameter.
First of all, it is pretty much a given that an old copy of FDECtrl.txt is incomplete at best and misleading at worst.
The same applies to AirEd.ini.

In poking around at a more recent version of AirEd.ini, the parameter is labeled "Minimum Manifold Pressure" or something to that effect.
I do not believe than anyone other than myself is even updating FDECtrl.txt any more, so there was no point in looking there.
The "Minimum MP" description made some sense because it came immediately after "Maximum MP".

These parameters in Record 505 are now located in the Aircraft.CFG file in more recent versions of MS Flight Simulators.
A description of the meanings of these parameter can be found here:

https://msdn.microsoft.com/en-us/library/cc526949.aspx

A description of this field is as follows:
"If a turbocharger is present, this value indicates the minimum design manifold pressure of the turbocharger (inHg)."
Please note how consistently other parameters line up with the ordering of parameters in the FDECtrl.txt and AirEd.ini.
To me, this is pretty good confirmation that this description is accurate.

As such, I suspect that further experimentation with this parameter will probably not yield useful results.

- Ivan.
 
Hello Ivan,
Wow! Thanks! I do have the latest AirEd.ini, and it´s my own fault for not using it (because of all the complicated-looking letters preceding line-names...). So, my mechanics deserve a clout on the head for not having looked in the right place before. But now they are intrigued... you probably feared as much! They want to continue their experiments after adjusting the ceiling.

It is interesting that the Vultee has Take-Off MP at 44.3 and Normal Mp (incl. Military) at 41.5 for low altitudes and the Mitchell has these at 44.0 and 42. So I wonder what will be best for the Baltimore, but I can only find out what the simulator will set it to after a ceiling adjustment.

From the fact that a) a normal MP of 42 without the low altitude Boost factor setting aka Minimum Manifold Pressure, makes low-altitude performance too high, and b) from the way the curve looks now with the tentative alterations:

--Alt----Hp--Hg
0-500: 1700 44
_4500: 1622 41
_6700: 1651 41
_8000: 1668 41
_9000: 1682 41
_9500: 1689 41
10000: 1696 41
10500: 1704 41
11000: 1710 41
11500: 1683 40.2
12000: 1652 39.4
12500: 1621 38.6

and c) including current approximate slightly low RoC test results (which only include some speeds which are not on this list, and the 15000 ft readings are missing as yet too), and from d) the present excessively high ceiling, I would deduce that a more correct low altitude setting could be found using the "new" parameter.

Maybe a new normal MP setting of 41.5 to be aimed for could be correct, because after a Ceiling correction, involving a small power reduction at altitude (balanced increase of Torque and Friction), would make low RoC come down even lower, this would call for less boost reduction.

I may be mistaken of course, and the difference will most probably not be noticeable while flying anyway, but it looks like an interesting experiment.

The illustrations of the Single- and Two-Stage Superchargers I found could possibly help to imagine how a Second Speed on the Two-Speed Single-Stage Supercharger could have been achieved by having an altitude-sensor-controlled slip-clutch on its single axel to make it automatically change between the 2 speeds, or perhaps how the pilot manually controlled this slip-clutch to select High or Low Supercharger Speeds.

I find all this fascinating!
Thanks for your extra input, clarifications, thoughts and advice!

Cheers,
Aleatorylamp
 
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Turbocharger lag

Hello Ivan,

It was quite straight forward to follow the last part of your tutorial to find the approximate power required at ceiling, and then set the torque and friction graphs accordingly. Now I remember doing it for the Staaken following your instructions!
As expected it took quite a long time, but it worked very well. I´m getting a RoC of 99-104 fpm for 25000 ft. As it is not such a high ceiling as the FW190´s, I had no problem using the autopilot.

Torque and Friction graphs needed to be substantially increased to lower the ceiling from 32000 down, but it worked. I did not alter the Boost Gain as it would have changed critical altitude, and I want to see the performance curve first.

I fixed the Power for 500 ft to 1705 Hp, so that S.L. Power is exactly 1700, and then Ceiling is correct now with only 23.0 MP. I´ll do another speed check.

I noticed that the keyboard throttle positions won´t work for fine adjustments if the Booster Low Altitude Reduction is implemented. There is a very strong lag effect, even for small movements on the throttle lever, causing large differences in power. A big let-down, I must say.

The Baltimore didn´t have a turbocharger, and superchargers I presume have no lag, so it feels completely wrong and I won´t use it. It´s a pity because after correcting the ceiling I had got MP without WEP above critical altitude to 41.5 Hg and Full WEP to 44 Hg by setting -8500 into Minimum Hg (Booster Low Altitude reduction), but I won´t bother to test this feature any further.

So here they have a wonderful parameter that reduces the excessive performance below critical altitude which was driving me nuts all this time and giving you a headache too, and then they go and limit it to turbochargers! It also has a very clear altitude limit between the two speeds, whereas Superchargers have a greater range where they use one or the other speed depending on throttle.

Then, unfortunately, after having changed AirEd.ini to the new one, I also checked another AirEd.ini - one from Mudpond. This is more laconic in its Info and line naming, so I took it out to use the others again, but now AirEd hangs and gives error messages. I remember this happening before but I don´t remember the fix. There was something else I did apart from deleting it, cleaning the registry and and re-installing it, because it still won´t work. Apparently in the error message it says in the hex dump that there´s something in the wrong format in the clipboard, and then I pressed the wrong button ant it sent the message to Microsnot, but so what.
So, BEWARE!, NEVER use Mudpond´s AirEd!!!

For the moment, to continue tuning the Mk.V, I can use FDE and AAM, (ADE98 is only for FS98 .air files), so I´m OK.

OK then, it seems to be going well despite everything... which is very good!
Cheers,
Aleatorylamp
 
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Turbocharger versus Supercharger

Hello Aleatorylamp,

From the description in Microsoft's documentation, it seems like the authors didn't distinguish between Supercharger and Turbochargers.
They DO behave differently at times but everything is described as a Turbocharger.

The end of the school year and other issues are taking up quite a lot of my time, so I have done no testing or other development recently.

Anna Honey should be in your neighbourhood in a few hours. She is flying to Lisbon tonight.

- Ivan.
 
Hello Ivan,
Don´t worry about the testing. The kids come first!
My own daughters are doing very well at university, one of them is finishing physics (!!!), so it´s nice to see how one´s genetics are vastly improved upon for the next generation!

So Microsoft supposed that it would be useful for both kinds of boosters, and maybe there´s something that I´m not doing correctly. For the moment, the CFS Turbocharger lag effect makes the slightest downward movement of the thrust levers drop power so much that you haven´t a chance of getting 80 or 90% throttle. Oddly enough, it´s as if you disengaged the Turbocharger altogether. No good for the Baltimore unless I can avoid the lag, but it´s not a priority, as it turns out that the performance curve is quite acceptable after all. Maybe Low Altitude Boost Reduction (it sounds clearer then Minimum Hg) should be experimented on with a proper turbocharged model with correspondingly correct performance entries in the FD. No hurry! We can do that another time.

I went through your Tuning tutorial yet again, and also through your comments on this thread, and got out some more information to do the tests. It often happens that one has to re-read things often because as one slowly understands more, one discovers that one has missed things that have been there all along!
I had to repeat the ceiling test because of a confusion with the Boost Gain using AAM, which didn´t want to save the modifications, but eventually did. I managed to get AirEd working from the back-up CD, and I deleted the faulty HDD one. Overwriting or copying from another one on another HDD partition wouldn´t work!

The performance curve looks quite OK on the the speed test after the ceiling test, at least for a start.
I was limited to only pulling up friction and torque so as to get the desired S.L. Horsepower, without reducing Boost Gain because this pulls down critical altitude quite strongly. I´m learning a lot, and I hope I won´t forget very quickly...

Without low-altitude boost reduction - I didn´t like the pronounced lag effect at all.
Normal MP: 42, WEP Boost Increase: 2, Boost Gain: 2.125

-Ceiling test: RoC at 24900 ft: 99-106 fpm. Level flight at 25000 ft: 874 Hp, 23.0 Hg, 297.4 mph

Now the three key positions during speed tests are as follows:
-At 500 ft: 1707 Hp, 44 Hg, 293.3 mph (aim: 1705 Hp and 276-298 mph)
-At Engine Critical Altitude, 10500 ft: 1755 Hp, 41.8 Hg 325.3 mph (here is the peak)
-At 15000 ft:1445 Hp, 35.0 Hg, 318.4 mph (aim: 320 mph)

Would you recommend any of the following possible maneuvers in this case?:
-1) Pull down the torque graph to correct +2 Hp at 500 ft would further reduce speed at 500 and 15000 ft - but although a Drag correction would compensate, this would lower ceiling RoC to under 100 fpm.
-2) Increase Boost Gain to increase performance at 15000 ft by 1.6 Mph would also pull up critical altitude a little, but would also further increase the peak at critical altitude.
-3) Decrease Zero Lift Drag would correct the slightly low speeds at 500 ft and 15000 ft, but would further increase critical altitude peak.

From your tutorial I can deduce that you would prefer to be slightly further up on the peak than to be low on specified altitude performance, but in this case, perhaps it will be better to leave it as it is.

I hope Anna Honey will have a successful visit to Lisbon and a happy flight "crossing the puddle", as they say here.

Cheers,
Aleatorylamp
 
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