Blohm & Voss BV 141B-0

[Ivan]

Hello All,

Back in January 2003, I released the original version of this project.
It was done by request but by the time I had completed it, the requestor apparently had lost interest and I don't believe I ever heard from them again. It was not a particularly long running project (probably about a month or so) because back then, my standards and general knowledge were much lower than today.

The control panel was a direct alias to the stock FW 190A and the flight model was simply a heavily modified FW 190A.
The engine was a pretty similar model so the instruments fit pretty well, and the flight model was modified by very simple methods.
Engine Power was adjusted by changing the maximum manifold pressure (EeeK!)
Weight, Fuel, Cockpit Location, Aerodynamic Drag, and of course Engine Location were the only great changes.

The one thing that really bothered me at the time was that the Landing Gear Animation did not work.
Aircraft Animator sequences worked within the utility but not in the simulator.

******* Fast Forward to Today *******

A year or so ago, I decided to revisit this project because it occurred to me that although the visual model, by appearance, had generated correctly from AF99, it exceeded several AF99 resource recommendations.
I figured that if I could get the animation to work, I would re-release the project.
After a few days of adjustments and some minor parts tweaks, I found that the animation was working.
I figured I would also add in some of the features that I tend to use today such as an internal canopy frame.
THAT one feature made the project much more complex because to look right, it also needed to have a different display sequence from the internal view.

It then occurred to me that the textures could be improved a bit.
The original was a single colour but the real aircraft had a splinter camouflage and radio call letters, so both were added.

A couple months ago, I figured that since I now had a virtual cockpit, the unusual framing pattern that was already built could also serve as the basis for a more realistic panel.
A modified screenshot of the virtual cockpit now serves as the basis for the main control panel.
The panel and some smaller auxiliary panels still need to be completed.

The general handling seemed to be pretty good with the exception that the roll rate was better than many fighters.
This was probably a legacy from its origins as a FW 190A.
The roll rate was easy to tone down.
At this point it seemed to be almost done..... (Famous last words!)

In doing some quick handling tests, I finally noticed on the panel that the Manifold Pressure was much too high:
It was reading around 1.80 ATA while the real engine was limited to 1.35 ATA even at WEP.
In checking things out further, I found that other than general handling, almost everything else needed to be modified.

So now, after a few weeks of AIR file tuning with a misbehaving development machine, only a few flight performance tests remain to be completed.

The control panel is next but will need a bit more experimentation and knowledge to do properly.....

The original expectation was for a very simple model update but has expanded considerably.
This seems to be pretty common with my projects.

- Ivan.

[aleatorylamp]

Hello Ivan,
This is going to an interesting thread for an interesting and unusual plane!
Cheers,
Aleatorylamp

[hertzie]

Hello All,

Back in January 2003, I released the original version of this project.
It was done by request but by the time I had completed it, the requestor apparently had lost interest and I don't believe I ever heard from them again. It was not a particularly long running project (probably about a month or so) because back then, my standards and general knowledge were much lower than today.

The control panel was a direct alias to the stock FW 190A and the flight model was simply a heavily modified FW 190A.
The engine was a pretty similar model so the instruments fit pretty well, and the flight model was modified by very simple methods.
Engine Power was adjusted by changing the maximum manifold pressure (EeeK!)
Weight, Fuel, Cockpit Location, Aerodynamic Drag, and of course Engine Location were the only great changes.

The one thing that really bothered me at the time was that the Landing Gear Animation did not work.
Aircraft Animator sequences worked within the utility but not in the simulator.

******* Fast Forward to Today *******

A year or so ago, I decided to revisit this project because it occurred to me that although the visual model, by appearance, had generated correctly from AF99, it exceeded several AF99 resource recommendations.
I figured that if I could get the animation to work, I would re-release the project.
After a few days of adjustments and some minor parts tweaks, I found that the animation was working.
I figured I would also add in some of the features that I tend to use today such as an internal canopy frame.
THAT one feature made the project much more complex because to look right, it also needed to have a different display sequence from the internal view.

It then occurred to me that the textures could be improved a bit.
The original was a single colour but the real aircraft had a splinter camouflage and radio call letters, so both were added.

A couple months ago, I figured that since I now had a virtual cockpit, the unusual framing pattern that was already built could also serve as the basis for a more realistic panel.
A modified screenshot of the virtual cockpit now serves as the basis for the main control panel.
The panel and some smaller auxiliary panels still need to be completed.

The general handling seemed to be pretty good with the exception that the roll rate was better than many fighters.
This was probably a legacy from its origins as a FW 190A.
The roll rate was easy to tone down.
At this point it seemed to be almost done..... (Famous last words!)

In doing some quick handling tests, I finally noticed on the panel that the Manifold Pressure was much too high:
It was reading around 1.80 ATA while the real engine was limited to 1.35 ATA even at WEP.
In checking things out further, I found that other than general handling, almost everything else needed to be modified.

So now, after a few weeks of AIR file tuning with a misbehaving development machine, only a few flight performance tests remain to be completed.

The control panel is next but will need a bit more experimentation and knowledge to do properly.....

The original expectation was for a very simple model update but has expanded considerably.
This seems to be pretty common with my projects.

- Ivan.

Ivan,

Sounds great! It's one of my favorites. Do hope you'll upload it someday.

hertzie

[Ivan]

Hello Aleatorylamp,

Yes, this is an interesting aeroplane.
One of the odd things about it is that when attacked, the pilots would put the aeroplane into a steep left bank when then gave the gunners a very wide field of fire.
I suspect the shape of this aeroplane is what inspired the Star Wars B-Wing ships.


Hello Hertzie,

I am glad there is some interest in this project. As I mentioned, it has been released once before and I probably can find an older version if you want one immediately. I would have to look to be sure.

- Ivan.

[Ivan]

The Blohm & Voss BV 141B-0 was designed to be a short ranged Reconnaissance Aircraft / Light Bomber.
(Aufklarer / Hilfsbomber)
This competition was ultimately won my the Focke Wulf FW 189.

This aircraft was to have great visibility from the crew compartment which was addressed by Focke Wulf by using a twin boom design and by Blohm & Voss by offsetting the main Fuselage to the right.
The offset engine location was also intended to compensate for the effect of engine torque and propeller wash that would make an aircraft pull to the right in a conventional design.

My own observation is that Richard Vogt, the designer, had a tendency toward other asymmetrical designs for no apparent reason other than novelty.

The offset engine according to flight reports actually overcompensated a bit for the engine torque effect which tended to make the aircraft pull slightly to the left instead of right.

(This idea of offset thrust also inspired me in my flight model for the P-38 Lightning which used opposite rotating propellers to compensate for torque. As a result, my version of the Lightning's AIR file has no noticeable engine torque if both engines are running at equal settings.)

This aircraft reportedly handled and performed very well with its main problem being that of a weak and unreliable hydraulic system.
Unfortunately, this aircraft was not mass produced with only about a dozen pre-production examples manufactured.
The Germans used the -0 (dash zero) subtype designation indicates it pre-production status.

I completed and released the initial version of this project back in January 2003.
At the time, I could find no detailed drawings of the aeroplane but that lack of data never would slow me down at the time.
This means that although the overall dimensions are correct and the model looks pretty good (at least to me), there are probably some pieces that may be slightly off in their location. Since then, I have acquired a pretty good book (by Schiffer) on the aircraft and have found some pretty good drawings but am not about to go back to redesign the project.

For weaponry, handling and performance, my references for this reword are
Wings of the Luftwaffe by Eric Brown,
The Schiffer Book I mentioned earlier,
various reports on the BMW 801 engines,
and
the Service / Operation manual for the BV 141B-1 aircraft.

- Ivan.

[aleatorylamp]

Hello Ivan,
Fascinating information! The similitude with the Star Wars B-Wing ship is quite apparent.
I bet the torque-overcompensation resulting in a left pull helped the steep left banking counter-attack maneuver, and must have been rather sudden and quite unexpected for the attacker!
But as usual, the unconventional did not appeal to the RLM - the Reichluftfahrtsministerium - for mass production.
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

My understanding of the story is that the RLM really didn't have a problem with the unusual configuration.
The issues were the following:
1. The aircraft required the same BMW 801 engine as did many other aircraft.
The Focke Wulf design required two small Argus engines which were not in such great demand.
2. Although the BV 141B had excellent handling and performance, the FW 189 had enough performance to accomplish the same mission.
3. Blohm & Voss also built the Focke Wulf FW 200 Kondor. Building the BV 141 would adversely affect FW 1200 production.

Note that the Operations manual was for the BV 141B-1. This was not a typo. Apparently the aircraft was expected to go into production which would have changed it from a dash zero designation.

The RLM made other choices that made good sense overall but were not so good for us modelers today:
The FW 190D series was selected for production thus effectively terminating the following projects:
Me 209
Me 309
Do 335.

That reminds me, I should build a FW 190D someday.......

- Ivan.

[Ivan]

The BV 141B-0 was powered by a single BMW 801A 14 cylinder two row radial engine.

Specifications were as follows:
Bore: 156 mm
Stroke: 156 mm
Compression: 6.5

Engine Output was as follows:
Take-Off: 1580 HP @ 2700 RPM at 1.32 ATA Manifold Pressure presumably at Sea Level
Emergency Power: 1585 HP @ 2550 RPM at 1.30 ATA at 15,750 feet
Climb Power: Output not listed but throttle is 1.27 ATA @ 2400 (+40) RPM
Maximum Cruise: 1280 HP @ 2300 RPM at 1.15 ATA
Economy Cruise: 1150 HP @ 2100 RPM

Maximum Sea Level Power is also listed as 1538 HP but without an RPM specified.

Note that this data is gathered from several sources and may have slight conflicts.
One of the engines tested for these numbers was from a Dornier 217E and not the very rare BV 141B.
These engines were supplied as a "Kraftei" or Power Egg with engine, cooling fan and cowling supplied as a single unit and ready to be mounted to the aircraft, so the outputs are not likely to differ greatly.
One thing to consider is that the Propellers may be quite different between aircraft.

From a design standpoint, the integrated cooling fan was brilliant.
It allowed a very closely cowled engine and still provided sufficient cooling.
The cowl diameter was only about two inches greater than the engine itself.
At low speeds, the fan cost about 70 HP but at higher speeds, the air flow was sufficient to drive the fan and power cost became negligible.

*******

ATA Conversions for ease of comprehension:
1.32 ATA -- 38.36 Inches Hg
1.39 ATA -- 37.78 Inches Hg
1.27 ATA -- 36.91 Inches Hg
1.15 ATA -- 33.42 Inches Hg

As can be seen from the conversions, there is not much difference between the Emergency and Non Emergency manifold pressure settings. The difference is mostly in the RPM limitations.

This kind of engine cannot be simulated with perfect accuracy in Combat Flight Simulator because CFS War Emergency Power depends entirely on Manifold Pressure limits.
One has a choice: Either allow 2550 RPM as a maximum and not have a Take-Off rating or allow 2700 RPM always and depend on a very slight manifold pressure limitation and the operations guide (Check List) to be the limiting factor.

The choice here was to allow 2700 RPM because that is what the pilots actually could use and provide information in the Check List.
My opinion is that the Germans tended to be overly conservative in their specified operating limitations.
An example of this was in the testing of Arnim Faber's captured FW 190A. It also apparently had a de-rated engine but the British test pilots operated it as if it were not with no great problems other than fouled spark plugs.

*******

The engine tuning I did back in 2003 was quite simple and effective though not necessarily accurate.
The engine was pulled directly fro the stock FW 190A and modified as follows:
Manifold Pressure was increased until the proper output at Sea Level was achieved.
Drag was adjusted to give the proper maximum speed.
The Supercharger Boost was then adjusted until the aircraft reached proper maximum speed at altitude.

I had hoped to do things a bit more accurately with this update.

.......

- Ivan.

[Ivan]

The first attempt at revising the Engine Power and Performance gave reasonably satisfactory results.

They were as follows:

Take-Off Power: Target 1580 HP -- Actual 1595 HP.
Without WEP Boost but at 2700 RPM, engine gives 1524 HP -- There is no target value here but it is a note for future tuning.
At normal maximum engine gives 1448 HP @2547 RPM.
Setting the RPM is not terribly precise. Sometimes it is 2548 RPM but it does not make a significant difference in output.

At 15,750 feet, Target is 1585 HP @ 2550 RPM. -- Actual is 1582 HP @ 2548 RPM

Engine power is slightly high at Sea Level / 500 feet but is otherwise a pretty fair match.

With these settings:
Maximum Speed at 500 feet (2550 RPM) is 227 MPH
Maximum Speed at 500 feet (2700 RPM) is 230 MPH
This appears to be a bit slow because 229 MPH should be achieved at Sea Level.

At 16,400 feet (5000 Meters) Target is 272 MPH -- Actual is 277 MPH on 1545 HP @ 2548 RPM
This is a touch fast but I like them to be a couple MPH fast when flown on Autopilot.
It would be hard to achieve this speed with a human pilot.
It is also quite possible to bring the speed down a bit by p;aying with various drag tables but I chose not no do so.

Maximum Climb Rate with Full Fuel is a bit over 1700 Feet per Minute at about 140 MPH IAS at 5000 feet.
This number seems to be reasonably appropriate but I have not found good data on climb rates.

I made an attempt to test Service Ceiling and got some inconsistent results on the first try.
The problem was that the aeroplane was terribly unstable longitudinally at altitude.
A small edit to record 1205 - Horizontal Stabilizer improved stability and allowed a test to be completed

I try test Service Ceiling with 50% fuel and almost achieved it.
A full Fuel Load is 268 Gallons, so the goal is to start the test with enough fuel so that 50% remains when the aeroplane's climb rate drops to 100 FPM.

Actual results were
32,700 feet
241 MPH TAS
778 HP
124.2 Gallons

(Climb took a bit longer than I had expected though I started with 54% Fuel.)
My test computer locked up at 32,700 feet while Climb was still about 120 FPM, so it might have gone another 50 to 100 feet.

I wonder if this is still worth editing?

- Ivan.

[Ivan]

Here area couple screenshots to show the previous version of the BV 141B.
The shape really has not changed much.

The obvious changes are:
A slightly different paint scheme
Non Doubled Triangular Glass pane on the Starboard side of the Nacelle.
A modified Boarding Ladder.

The Landing Gear animation also did not work and it does now.
There have been a lot of changes to the way the project fits together, but the Polygons have no changed other than those mentioned.

- Ivan.

[aleatorylamp]

Hello Ivan,
Looks like a pretty close match to the real performance!
Cheers,
Aleatorylamp

[Ivan]

Hello Ivan,
Looks like a pretty close match to the real performance!
Cheers,
Aleatorylamp

Hello Aleatorylamp,

For the altitudes checked, it is a pretty good match, but as you know from your projects, the middle altitudes will be quite a bit off, so I decided to do a bit more tuning to see if I could reduce the low level power just a touch and increase the service ceiling by a few hundred feet.

- Ivan.

[Ivan]

One thing I forgot to mention is that the original BV 141B would reach 570-580 MPH TAS in a vertical dive.
I did some adjusting for that and now the limit is 488 MPH which seems more reasonable to me.

As mentioned earlier, I believed slight improvements were possible with tuning.
By balancing Torque and Efficiency as described in the Engine Performance Tuning Tutorial and doing it so that Sea Level power is slightly reduced, the low altitude numbers are now:

At 500 feet Altitude:
1443 HP @ 2550 RPM -- 228 MPH
1511 HP @ 2700 RPM -- 231 MPH
Take Off Power is now 1582 HP @ 2700 RPM

The Supercharger boost needed a very slight adjustment upward to compensate for the slightly reduced low altitude power.

At 15,750 feet Altitude:
1583 HP @ 2550 RPM which is awfully close to the 1585 HP target.

At 16400 feet Altitude:
1546 HP @ 2550 RPM -- 279 MPH.....
This is a bit higher than before but still reasonable in my opinion.
I am guessing the actual maximum speed is more like 290 MPH at whatever altitude the engine gives peak power.

Service Ceiling:
32,850 feet
774 HP
242 MPH
136.2 Gallons Fuel remaining which is pretty close to 50% (134 Gallons).

At this point the performance is where I want it to be.

I also found that trimming for straight and level flight was quite easy.

- Ivan.

[Ivan]

This is a screenshot of the Virtual Cockpit view to the front.
The framing is a bit distracting but the general visibility is quite good in all directions except to the left.....
The Engine gets in the way there.
The original release did not have any canopy framing visible from inside.

What remains on this project is to create a Check List and a Control Panel.

- Ivan.

[aleatorylamp]

Hello Ivan,
It´s looking great and adds a lot of atmosphere!
It will look even better when you have the bitmap of the control panel on it!
Cheers,
Aleatorylamp

[aleatorylamp]

Merry Christmas Ivan, and a Happy New year!
Cheers,
Aleatorylamp

[Ivan]

It turns out that there were still a couple changes needed in the AIR file.
The Performance is about where I wanted it, but a few things needed to be changed to make Trim Adjustments easier.
About an hour tonight was spent testing whether or not the aeroplane could be trimmed for straight and level flight without the autopilot.

The answer (with some adjustments) is "Yes", but burning off the fuel doesn't just change Longitudinal Trim, it also changes Lateral and Directional because the Fuel Tanks are offset to the left of the aircraft centerline (assuming that the term "centerline" can even be applied to this kind of aeroplane).

- Ivan.

[aleatorylamp]

Hello Ivan,
I think it´s looking beautiful indeed. Very clean, tidy, and elegant.
It´s one of my all-time favourrites, this wonderful assymetrical fighter.

I´m looking forward to trying out the .air file. Perhaps I can learn something
from it from my own planes, especially regarding adjustments for level trimming
without autopilot. I have always had difficulty with that.

Nice!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

The BV 141 was really a light bomber rather than a fighter.
There really isn't any one thing in particular that is strange about this project except that the virtual cockpit 3D model shows a very odd arrangement.
The rest of it is pretty much normal except that the Engine and Fuel Tanks are offset.
The problem though is that with a Combat Flight Simulator model, if a designer really wants to offset the CoG a bit, it has to be designed into the model and the exact amount of offset is not easily predictable.
As you know, moving the CoG is not easy especially if the model has already had the SCASM treatment. That is the big lesson from this project.

As for setting Trim for straight and level flight, there isn't anything to learn from the AIR file that isn't already stated in the record descriptions of the AIR file editors. It is just a matter of choosing how you want the aeroplane to behave and then making adjustments until that effect is achieved.

In the case of the BV 141B as I have tuned it:
Lateral Stability is medium.
Longitudinal Stability is VERY Low.
Directional Stability is low.

Longitudinal stability and trim are easy to check with Trim Gauges under autopilot.
Lateral and Directional trim are just a matter of checking and recording the result on paper WITHOUT the autopilot because apparently, CFS is just like FS98 in that there isn't a Token Variable that can be displayed on a gauge.

The Checklist should be easy now but finishing up the Panel may take a bit longer since I really don't know what I am doing there.

- Ivan.

[aleatorylamp]

Hello Ivan,
Sorry, I made a mistake there, calling it a fighter instead of a light bomber. It´s a bit big for a fighter...
The powerful ca.1500 hp radial engine must have made it quite exhilerating to fly.
Thank you for the stability details on the flight dynamics.
I´ll be interested to be able to look into the .air file as soon as you upload the model!

Good luck with the panel. As you most probably know, it seems to have been a rather simple, narrow
affair fixed to the cabin-roof, leaving an unobstructed forward view for the pilot.
Very unusual, but quite appealing for the sim. I´ve seen a description of the instruments and the
cabin in German, so if you haven´t seen it or need some help, I could jump in!

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

Above the front glass is a row of indicator dials which could be considered the main "Panel".
That part is already done though the background could use a few edits.

The problem is that there are many more instruments that are "essential" for a CFS aeroplane.

There is the Throttle panel which would have a Throttle of course and also have (in this case) a Propeller Pitch control.

There would have to be at least one more "Sub Panel" to hold other gauges such as
Fuel Switch
Fuel Quantity Gauge <--- New!
Elevator Trim Gauge <--- New
Magnetos <--- Conspicuously absent from the stock FW 190A
Landing Gear control / indicator
Flap Control

I still need to create a background for this sub panel and make sure I did not leave anything out.

- Ivan.

[aleatorylamp]

Hello Ivan,
OK, I get the point about the complicated instrument layout.

I guess it is difficult to decide how to put in the other instruments that are not on the main, slim, overhead panel, and which of these to have together on the main panel, and which to put on a separate sub-panel.

I´m just musing, not telling you what to do. I´m sure you understand:
As you must have also seen, there was a shelf running along the left side of the glazed canopy, containing Thrust and Propeller-Pitch levers, also Flap and Trim, and strangely enough, also Starter and Ignition switches, RPM, Boost and Fuel gauges, amongst others... I can´t see the landing gear lever, except an emergency one in the middle behind the pilot.
Then, the compass was infront of the rudder pedals, rather low down, on a window strut, with the bomb-sight a little to the right, nearer to the pilot. Maybe all this to be put on the main panel.

The whole thing seems to be an exercise in perspective drawing!

Radio equipment was on the right, further back, so this would definitely be a candidate for a sub-panel.

I agree, a difficult and strange layout indeed. I hope you can get it to your liking!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

As with any other kind of project, it is a matter of staying with some established game standards while retaining some of the characteristic appearance of the particular aeroplane.
The BV 141B used the same BMW 801 engine as the FW 190A, but apparently had a Propeller control while the FW 190A did not.
That would imply that there was no Kommandogerat or that it operated in a different manner from that of the FW 190A.
Real aircraft controls sometimes are tucked into odd places, but it doesn't make sense to have a great number of sub panels each with only a single dial or lever.
It also doesn't make sense to put both a Compass on the Window Frame and a Directional Gyro above the Windscreen because for CFS purposes, they both do the same thing.
I was planning on programming a Bomb Sight eventually, but this panel won't have it until I actually do it.
There also won't be a Radio Panel on this release or even an Autopilot.

The problem I am trying to figure out is how to put the Trim Gauge on a sub panel at a reasonable size and yet make it possible to see it well enough to read the number of notches of Trim.

- Ivan.

[Ivan]

A few days ago, I thought the BV 141B AIR File was pretty close to done.
I just needed to do a bit of testing and documentation to confirm that there was no unexpected strange behaviour.

The testing went pretty well with numbers falling well within range of where I wanted them.
One somewhat odd thing I noticed was that the BV 141B was able to maintain very near its maximum speed (tested at 2550 RPM) at an unusually great altitude range.
It was able to reach 280 MPH at 15,000 feet but even at 22,500 feet, it was still able to hit 276 MPH.

At this point, I was thinking that since I had done all this work with Propeller Tables but have not yet released any of my own projects with non-stock Propeller Tables, the BV 141B would make a good subject.
After all, how bad could it be?

With that in mind, the next step was to go back and record Propeller Pitch Angles and Thrust values for maximum speed at Sea Level and 15,000 feet because all I was planning was to adjust the Efficiency curves down to Zero where the Geometry indicated either Zero or Negative Angles of Attack for the Propeller Blades. Simple!

I went back and recorded the Propeller Pitch Angles for maximum speeds at ALL altitudes so that I could confirm that changes I would be making did not otherwise affect performance.
After a few tests, I started noticing something REALLY strange: Blade Pitch was always 32-35 degrees.

When I dumped the Propeller Efficiency Table to a spreadsheet, graphing it showed that there would be a lot more work than I had expected.
Compare the BV 141B Table 511 to the Table 511 from the Ki 61 and FW 200 Condor.
I believe the general shape of the Ki 61 and Condor Tables are closer to correct.

- Ivan.

[aleatorylamp]

Hello ivan,
Very interesting indeed! ...and a lot more complicated than a fixed-pitch propeller!
I´m curious to see the final BV 141B propeller!
Cheers,
Aleatorylamp