Project Martin A-30 Baltimore

Hello Aleatorylamp,

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

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

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

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

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

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

- Ivan.
 
Hello Ivan,

Thanks for your post and your instructive thoughts and explanations on the Mitchell C power distribution. I agree that for the 600 Baltimore MkV units produced with the souped up 1700 Hp engines, an F10 WEP implementation is more fitting!

As you say, with the Baltimore, I was getting strong 250 Hp excesses at different altitudes. That´s why I had eliminated F10 WEP, although this of course then allowed for erroneous continuous use of Emergency Boost like you pointed out.

Nevertheless, as far as the power curve was concerned, the Baltimore .air file, like your Mitchell .air file, seemed to be closer to the correct power readings without F10 WEP in it, and these were still better than the ones I am getting now.

I have re-impemented F10 WEP, having managed to find possibilities for correction not only with Boost Gain adjustments like you said, but also with WEP Press Change Rate to curb the F10 WEP peaks, and this has now improved the .air file considerably.

The 250 Hp peaks you mention have long since gone, both in the non-F10 WEP version and the present F10 WEP version.

Now the only real problem-peaks are the 127 Hp excess at 15000 ft and the 85 Hp excess at 7600 ft, but in contrast, these peaks don´t affect the speeds, which lie within the expected performace range for the MkV model, so perhaps they are really not a big problem, depending on one´s appreciation of the whole thing, of course.

Although speeds are OK, RoC could be too high in some places, (which I still have to test), and I could go a bit more conservative and reduce the whole envelope by about 75 Hp (compensating with Zero Lift Drag to maintain the speeds), although this would make Hp go a bit under in some other places.

However, I don´t know if that is a good idea, because as you say, this simulator has a game facette which is also to be taken into account. What would you think?

So... F10 WEP or non-F10 WEP? It´s like the English say: "Sixpence of one or half a shilling of the other", although in this case F10 WEP is better, I suppose.

Cheers,
Aleatorylamp
 
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5 min. Emergency and Take-Off Power.

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

Hello Ivan,
In tune with your endeavour of fitting the whole power curve as opposed to only a couple of points on it, I have been tweaking the engine parameters, and with some minor adjusting (2.15 boost gain, 0.0625 Emergency Power Press Change rate, 0.54 Zero Lift Drag), I have managed to considerably reduce the excessive power in the areas where I was over specification. I also ever so slightly increased the friction graph, and gave the torque graph a tiny reduction. The results I believe look very pleasing indeed:

S.L.
WEP: 1701 hp 44 mpsi 309.5 mph (1 hp over)
Non-WEP: 1435 hp 38 mpsi 297.3 mph

4500 ft:
WEP: 1754 hp 44 mpsi 315.0 mph (54 hp over)
Non-WEP: 1482 hp 38 mpsi 305.3 mph

6700 ft:
WEP: 1787 hp 44 mpsi 318.5 mph
Non-WEP: 1511 hp 38 mpsi 308.0 mph (11 hp over)

12000 ft:
WEP: 1723 hp 41 mpsi 320.9 mph (23 hp over)
Non-WEP: 1582 hp 38 mpsi 316.6 mph

15000 ft:
WEP: 1483 hp 35.4 mpsi 315,6 mph
Non-WEP: 1533 hp 36.4 mpsi 317.3 mph (33 hp over)

Probably, it can´t get much better, I´d wager.
Thank you very much indeed once again for your inestimable and motivating help and comments!
Cheers,
Aleatorylamp
 
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WEP Parameter's ACTUAL Purpose.

Hello Aleatorylamp,

I must congratulate you for pointing something out that should have been obvious but that I and everyone else had overlooked.
SERIOUSLY: THANK YOU!!!!

Back at Post #78, you did some experimenting with "Emergency Power Press Change Rate".
Although you did not get the results you were looking for, it got me to thinking and experimenting a bit.
I now have some useful (though in hindsight rather obvious) information to convey.

This number (whatever it is called) has the same 0.5280 value in every single stock AIR file that has WEP with the exception of the stock FW 190A. This aberration can be easily ignored because it is pretty much common knowledge that the WEP doesn't actually work on the stock FW 190A.
If the stock AIR files were implemented correctly, this value should be 0.0000 for the P-47D which it is not.
Without basic knowledge, one has to study existing flight models and one has to presume that the existing values are as they should be.
This simple fact caused me to overlook the actual purpose of the value and conclude that the WEP implementation in CFS was simply incorrect.

I now feel quite stupid and a bit embarrassed for having made that statement so often and with such certainty.
At some point I will have to go back and post this in the Engine Tuning Tutorial as well as the Warhawk thread.

The supercharger implementation in CFS actually works reasonably well if the parameters are specified correctly.
The value you have been adjusting is actually the WEP Additional Supercharger Boost Gain.
It is the additional boost gain over the normal supercharger boost gain when WEP is engaged.
For gated throttles such as on the Spitfires and Mustang, it would have some fractional value because the critical altitude is increased when the throttle lever is pushed "Through the Gate".
On regular Anti-Detonant type WEP implementations, it should have a value of 0.0000 because supercharger boost gain does not change at all.....

I will need to go back and fix quite a few AIR files to correct for this factor.

On some AIR files, it makes almost no difference while in others such as the P-40 series, it makes a great difference.

- Ivan.
 
Sources of Information

Hello Aleatorylamp,

I am a bit curious as to where you are getting your performance data for the Baltimore Mk.V.
Specifically, I am wondering how you came to the conclusion that the Sea Level speed was something over 305 MPH.
What do you think of the accuracy of the Page 112 Data Table regarding Sea Level Speeds?

- Ivan.
 
WEP Additional Supercharger Boost Gain - and page 112?

Hello Ivan,
Thank you for your posts! I´m glad that I have been able to contribute with my little grain of sand, (as the Spanish say). It did seem a bit strange that with all the provisions available for superchargers, some aspects didn´t seem to work quite correctly in CFS1, and by chance or out of curiosity, I started poking around in this "new" WEP parameter, and discovered that it helped tremendously. I´m also glad that your P-40 will benefit from this find!

Now, contrary to my previous insistence, it seems that F10 WEP does actually work much better than implementing WEP in the last 10% of the normal throttle travel, like I was saying before with all my insistent certainty. I suppose it is normal that we all defend our arguments until new information appears which makes us change our minds.

Another example is the Baltimore 305 mph sea-level maximum speed.
I know that for the early Baltimore MkI it was 284 mph, and at altitude, 305 mph.
For the souped up MkV model, I have to say that I have found no concrete information about sea-level speed. My 305 mph speed here is an educated guess which well might be wrong, but is fundamented on the following:
Several sources state a max. speed of 320 mph for altitude (12000 or 15000 ft).
One source says even says 329 mph, but we can ignore that one.
Quite a few other sources just state a maximum of 305 mph for the MkV without specifying altitude, so I took this one to be the sea-level max. speed, and also, because of the statement about this machine´s top speed being generally above 300 mph.

At the moment my .air file is slightly over at 309 mph for sea-level and just under at 317 mph for 15000 ft, but now that I have found a way to separate WEP and non-WEP speeds, and I am still trying to get it down a little more for sea-level, and up a bit for 15000 ft, so I´m not quite there yet.

Update:
A better reasoning to calculate sea-level speed could be:
As MkI = 287-305 mph, diff.=18, then MkV = 320-18=302 mph.
But then again, we do not know how they souped up this engine to 1700 Hp. Was only by increasing WEP turbo-boost? ...or did they increase turbo-boost throughout? ...or also non-WEP power? Another detail could help: Cruise was 225 mph for the MkV, and 230 mph for MkI/II, so they must have increased non-WEP too...

But there´s a problem for the moment:
If I reduce S.L. top speed to 302 mph, the 12000 ft 320 mph speed also goes down to 315.5 mph, and the 15000 ft top speed even more, as it is already 3 mph slow.

Another thing: I´m afraid don´t have the Page 112 information you mention, to know the correct speed which it should have at sea-level. I´d appreciate your pointing out where this page 112 is.

Cheers,
Aleatorylamp
 
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Page 112 Data Table

Hello Ivan,
I remember now that Smilo posted a Page 112 Data Table, but unfortunately the resolution was such that I could not read it, and he mentioned a few things on it - translating from Polish.
You then mentioned that you have a better copy which would of course come in handy.
Incidentally, I also found another text, stating 320 mph for the MkV at sea-level, so there are all sorts of data which could well be way out, ...or not... I don´t know.
Well, we´ll see...
Cheers,
Aleatorylamp
 
Now for the discussion.
Hopefully I can finish this before I get kicked off the computer.

Up until last night when I edited it to put in changes in description, FDECtrl.txt had a note that this WEP Additional Boost Gain field was typically either zero or 0.528 but without further explanation as to function. Even AirEd does not have any useful help on this field.
It actually took me a little while to figure out what the actual effect of this field was after you gave the hint that it changed the WEP effect above critical altitude.

The AIR file still has a lot of things that are not readily done such as WEP time and effects, Direction of propeller rotation, etc.
Or perhaps we just don't know where to adjust things yet.

Time for more exploration into AIR files.

Hopefully this version of Page 112 Tables is more legible. I can read my copy fine but the upload may reduce quality.

Smilo already pointed this out: At the bottom of the table, it mentions the Sea Level speed of the early Marks as 284 MPH.

So what can we do with that information assuming that we believe it to be correct?

From a quick observation of the Baltimore in various versions, the shape is basically the same.
There are obviously some differences with the Mk.IV with a Boulton-Paul 4 x .303 cal machine guns.
The drag would be quite a bit higher with such a prominent gun station.
The Mk.V was a little better off with a Martin 2 x .50 cal turret in its place.
The bottom line is that from an eyeball analysis, the drag of all the versions was pretty comparable with a slight advantage to the very early version.

In looking at the Engine outputs, they varied from 1600 HP, 1660 HP, to 1700 HP.
The difference from low to high was not more than 100 HP or so.
So why was the Mk.V faster at altitude if the power output was similar?
The simple answer is that the critical altitude was raised presumably because of a better supercharger.
The same power in the thinner air gave a bit better speed.

So how do we estimate SEA LEVEL speed?
Air density is the same, and drag is the same, so the difference will be entirely due to power differences.
(and some negligible to minimal effect from Prandtl and Glauert.)
So with a maximum difference of 100 HP Take-Off / Emergency rating, the speed increase would be the cube root of the power ratios.

Assuming 285 MPH on 1600 HP, that would give approximately 291 MPH on 1700 HP.
Note that if it is really 285 MPH on 1660 HP, 1700 HP would only give 287 MPH....

This is on the assumption that drag is unchanged, but in reality, it is probably higher for the Mk.V because of the turret and also because it probably was a heavier aircraft and also the cube root estimate is an ideal case.

That is why I was guessing that the Sea Level speed was probably the same or pretty close.

Hope that makes sense.
I am curious about the other testing reports you mentioned.

- Ivan.
 
Hello Ivan,
Yes, the attachment is legible. Thanks a lot!

Your careful reasoning sounds very plausible too - more than just an educated guess. Actually, I remember a similar line of thought you expressed a few weeks ago along the same lines, only that I was still a bit stubborn in my idea of keeping the speed a bit above 300 mph.

Presumably the contradictory information available has its origin, as so often happens, in errors along the chain of reports coming from reports, or probably even worse, inventing information to fill in gaps where the data was only available for some models and not for others.

So, in a nutshell, you are suggesting a WEP 291-320 mph speed range between sea-level and 12000 ft for the MkV. In effect, the MitchellC .air file, with correspondingly adaptated weights and fuel, would give a very similar result of 270-316 mph for a MkI supposition.

Very good. I´ll see what I can do.
At the moment, after increasing Drag to get sea-level speed down to 291 mph, of course the problem remains that altitude speed is too low, and not even playing with Induced and Zero Lift Drag, does it improve. The low manifold pressure specified at 41 for WEP at 12000 ft is the culprit here, I increased that to 44 there, like it is in the specs for lower altitudes, but of course, then the Hp shot up from 1723 to 1851, which is a bit much, and I´m still 6 mph under the desired 320 mph for 12000 ft.
Update 1:
---------
What I´ll have to do then is to reduce power and drag. This way I´ll get the speed up and reduce the power peak at altitude, although it will reduce sea-level power a bit, but as speed will be OK, it won´t matter there. Well, we´ll see how it goes.
Update 2:
---------
The best I can get is 292-316 or 295-317 mph, and that with only 1628 Hp at SL and a surge of 1791 Hp at 12000 ft - a difference of 163 Hp.
The difference here is similar to that in the MitchellC .air file, which was 1618-1780=162 Hp.
I would tend to be reluctant to accept CFS1´s lack of capability in reproducing an accurate engine performance envelope, but, what is amiss here? Why can´t we get 1700 Hp at sea level with 291 mph and 44 Mpsi, and 1700 Hp at 12000 ft with 320 mph and 41 Mpsi -(OK, I´m flexible and allow 44 Mpsi here...). Something must either be wrong with the published specifications, or with the simulator aerodynamics.

Now I´ll try putting friction at 125 and adjusting torque accordingly... I wonder...

Anyway, it is turning out to be a very interesting exercise indeed, the Baltimore supercharger implementation!

Thanks very much again,
Cheers,
Aleatorylamp
 
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Snow use...

Hello Ivan,
I´ve tried everything possible, but I can´t get the difference between S.L. speed and altitude speed any larger than about 13 mph, without creating a tremendous Hp difference as well.
The Torque and Friction increase didn´t work either. Nothing works. What I want to avoid is having 1620 Hp at Sea-Level and 1780 Hp at altitude. Why does it need such a huge discrepàncy with reality? A simulatioin is supposed to simulate something that´s real, and this isn´t. It´s uncanny - it seems that the air or its oxygen content in CFS1 is completely different.
Cheers,
Aleatorylamp
 
Hey Guys,

Question; Are you able to adjust the drag?

If you can adjust the parasitic drag or fuselage drag in anyway then you might be able to gain the extra that you need.

Something else to look at if you are able is the Prop.

I'm not sure what you can and can't do in CFS1 but thats what I've got. If you need the prop specs let me know. I can work on one for you.
 
Hello Blood Hawk!

Thanks for the suggestion. Yes, it´s possible to gain a little by playing with the induced drag as opposed to the Zero Lift Drag - from what I gather, this one reduces with altitude so it gives a greater difference higher up. I´ll have to try that.

I suppose you mean to reduce the pitch. The prop pitch angles are adjustable in CFS1 but it´s so complicated that I´ve only had a go at fixed props, not CV ones. A scalar parameter to manage all angles at once would of course be of great use, but I think scalars were introduced later into .air files.

However, there´s a flight dynamics Editor called AAM that shows all the graph curves for the prop blade angles, so one could change the pitch angle of each curve, moving a weaker curve to a stronger angle, I suppose. I´ll have to look into that.

Cheers,
Aleatorylamp
 
I'll pm you my email. send me a copy of the airfile and I'll run the numbers. I'll need as much of the engine and prop data as you can get. From there I can get rather close. I've done this on some of my WWI airfiles and had great results.
 
Hello Blood Hawk.

Welcome to the show.
I would also be interested in your propeller tuning process.
I have a couple projects stuck for lack of a proper propeller.
I believe I have a workable method, but the tuning is all manual at this point
It is mainly Table 512 that causes all the difficulty.

Hello Aleatorylamp.

Please check back on Post #58.
I believe you already had a pretty good result back then that only needed some minor tweaking.
The Sea Level Speed just needed to be up by a couple MPH and the Critical Altitude speed needed to be down a couple.
Both were easy things to tune.

More Later.
Gotta Run.
- Ivan.
 
Hello Bloodhawk,
Out of curiosity, what exactly would it be that needs to be done on the propeller tables? Is it that it has to be generally more feathered, or more efficient? As the problem I have is altitude-related, I suppose that the propeller gives too much power in the thinner air hhigh up, or alternatively, too little in thicker air lower down.

Hello Ivan,
Re. my post 58: The problem with the results here is the very low Hp at Sea-Level and the rather high Hp at 12000 ft, which is what I´m trying to avoid, because I can´t imagine that the numbers should be so way out on this simulation. It must be possible to get it better... but of course I may be completely wrong.

What I´m trying to get is a maximum WEP power of 1700 hp at 2600 RPM, both at Sea Level and at 12000 ft,
but the Sea-Level speed would be 291 mph with 44 Mpsi and the 12000 ft one,320 mph with 41 Mpsi.

For the moment the best I´ve been able to get is:
Sea-Level, 1678 Hp with 309.5 mph and 44 Mpsi, and at
12000 ft, 1700 Hp, 320 mph and 40.9 Mpsi

If I set it for 1700 Hp at Sea Level with 291 mph, then it increases to 1721 Hp at 12000 ft, which wouldn´t be too bad, but then it won´t get above 303 mph. To do so, it needs 44 Mpsi, and Hp soots up to 1863 Hp, but maybe this power difference can´t be helped...

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

Part of the problem is that your goals are not really correct in my opinion.
Here is a slightly larger version of the relevant table from Page 112.
The important things to note here are:
1. The Red Circle marks the single piece of data I believe is incorrect on this table.
2. You are trying for 320 MPH at 12,000 feet while the data shows 320 MPH at 15,000 feet.

The maximum speed is achieved quite a bit above the engine's critical altitude.
One doesn't know the Ram effect on this aeroplane and how it might affect things.

Here are a few interpretations using my pidgin Polish based on my mediocre German and phonetic translation of Polish to Russian. Use at your own risk!!!!

Footnotes:
* Turret Boulton-Paul Mk.III
** Turret Martin 250 CE
*** Speed maximum at level of sea 284 MPH

Note that the Mk.I and Mk.II show 308 MPH at 13,000 feet
Note that the Mk.III loses 6 MPH presumably because of the Boulton-Paul turret.
Unfortunately we do not know the altitude.
Note that the Mk.IIIA is only 3 MPH down with the change to the Martin turret.
Note that the Mk.IV shows basically the same speed with the same power.
Note that the Mk.V shows 320 MPH but at a much higher 15,000 feet instead of 11,500 feet.

Note that your testing will be at 500 feet instead of Sea Level.
Figure the difference is worth perhaps 5 MPH, and of course your mechanics are the best there are, so if you get 295 MPH to 300 MPH, it should be about right.
Figure that the actual Sea Level speed of a Mk.V is only about 288-290 MPH by my guess.

BTW, All of my numbers are "Educated Guesses".
If you have actual reliable test data use it instead.

- Ivan.
 

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Hello Ivan,

Thanks for your preoccupation, I definitely appreciate that.
Not to worry, my "Sea-Level" testing is at always 500 ft, ever since I ran into a hill with the Zeppelin Staaken Riesenflugzeug RVI back then!

The problem with the 15000 ft max. speed is that setting it at 320 mph there, with the lower Manifold Pressure there, the power surge just before critical altitude is even greater, and things just get out of hand. It was just an "educated" fiddling... But anyway, I´ll keep on trying.

You also have a point about the Boulton-Paul Turret of course, and this would set S.L. Speed a little lower to what we decided a couple of days ago. OK. I´ll note that as well.

I´ve just tried something out along these lines (WEP):
15000 ft: 44 Mpsi, 1917 hp and 316.6 mph
12000 ft: 44 Mpsi, 1870 hp and 312.6 mph
Sea-Level: 44 Mpsi, 1701 Hp and 289 mph

Trying to squeeze out another 3.4 mph at 15000 ft would mean increasing Sea-level speed to just over 292 mph. Not a piece of cake, this exercise!

Trying to set altitude speeds with 41 Mpsi for 12000 ft (1724 Hp) as per the Specification Chart only gives 307 mph, and leaves only 36.4 at 15000 ft (1546 Hp), with 304 mph, although the Hp readings are really very good!
Incidentally, lowering the critical altitude from 13500 to 12500 ft makes no difference.

You mentioned feathering the propeller a bit a week ago, I believe. Would this be manually done, something like reducing the 15º and also perhaps 20º column and moving all the others one or two columns to the right (or is it to the left?) on both propeller tables?
Let me see if my reasoning is correct: At altitude the propeller needs a greater pitch-angle than at Sea Level because the air is thinner, so the J values in the columns have to be increased, but if I´m trying to reduce the power surge there, I have to reduce the values corresponding to certain pitch settings, but which ones? The 15-20º ones or rather the 40-50º ones?.

Cheers,
Aleatorylamp
 
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