Conspicuous by Their Absence

Shock in the Alps

Hi all,
Just breaking the silence of mourning and consternation to express condolences to the families of the victims of the unfortunate, sad, shocking and strange aircraft accident in the French Alps yesterday morning, that cost so many lives, with so many young ones included. May they rest in peace.
Aleatorylamp
 
Counter Rotating Propellers

Hello Aleatorylamp,

In regards to being able to adjust Directional and Lateral Static Trim, I have no working solution.
In regards to being able to compensate for a Counter Rotating propeller, we have a pretty good working solution to this in another thread on this forum:

The Lockheed P-38 Lightning - Design Study had a pretty similar problem to address.
My solution there which probably is technically incorrect but has no side bad effects that I have seen thus far is to move the opposite rotating propeller LEFT.
In the case of the P-38, it was moved outward by around 20 inches, but for your Giant, I doubt it will be exactly the same.

I decided to respond here because I believe the subject may be of general interest.

Hope this works for you.
- Ivan.
 
Left yearning was Human Error

Hi Ivan,

The Giant was yearning left because when I adjusted the Tank Locations, I had mistakenly only made the right tank in-fuselage, at 1.5 ft from the centerlilne, leaving the left one -5.1 ft away from the centerline. My fault again...

So, my initially suspected culprit "Yaw Moment Sideslip (Weathervane Stab)" proved not guilty, but then, the question still remains: Why did the left yearn disappear when I set this parameter to Zero?

Cheers,
Aleatorylamp
 
YAW Due to Sideslip

My guess is that the imbalance caused a roll to one side and when the roll caused a sideslip, this variable caused a yaw to the lower side. That would be part of it.
The rest would be probably due to the yaw effect from the propeller. If you shut off the engines and glide, it should tell you if engine torque is the cause.

As an experiment, you might try using the test panel I sent to you and dump the left main tank and see if the imbalance to the right causes a right yaw.

- Ivan.
 
Tank weight offset

Hi Ivan, and Hi all!

Testing with an empty left inboard tank (in its now correct position) only has a minimal -0.1 right yaw effect, so I moved the right tank out into the incorrect position, and it had the same noticeable effect to the right as it did before to the left.

Neutralizing the weatherplane stab parameter gave the plane a strange sideslip, without the expected tendency to go into a dive, so it´s just as well that it wasn´t that! The plane is stable now, and perhaps not the most convenient design to test for engine torque - probably too stable for that.

This issue has given me an idea though, because as per the documentation, when loaded, the giant had to be fuel-trimmed nose-down for level flight after take-off and climb, to balance out the CoG.
I´m now debating whether to place the tanks toward the rear a bit or not, so as to perhaps make the loaded plane require forward trim for level flight with full tanks.

Then, returning from a mission without payload and nearly empty tanks (there was no fuel left for fuel-trimming), they required constant forward pressure on the helm throughout approach and it was difficult to land, so if my reasoning is correct, bombs should be placed a little forward of the CoG in the Dp files, to make this more realistic. Maybe not so much as to need forward pressure on the joystic for an empty approach, but at least one more notch forward trim?

Added later: A slightly rear placing of the fuel weight and a forward placing of the bomb weight would be consistent with a) the fact that the 8-10 inboard cylindrical fuel tanks (forward pair empty on take-off) were centered between wing leading and trailing edges (the taildragger main undercarriage was also centered here), and b) bomb-bay reached considerably further forward. Hence a fully loaded plane would be a bit tail-heavy until trimmed for level flight, when fuel was pumped into the 2 forward tanks, and quite tail-heavy without bombs or fuel.

Cheers,
Aleatorylamp
 
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Attitude and balance

Hi Ivan, Hi all!
Technical corrections keep delaying the Giant, but that´s not really bad! Ivan fortunately pointed out an attitude and trimming issue on the Giant, which had a yearn to dive. I was over-correcting a simulated tail-heaviness with a self-sustaining tailplane, but studying this further, I may have come up with an improvement.
Below is an AF99 blueprint showing:
- AF99 centre of rotation (CoG).
- Location of the bomb-bay (3 racks x 6 bombs),
placed 1.2 m. forward in Dp files.
- Location of fuel tanks (2 rows x 4 tanks),
placed 3ft aft of CoG. The yellow one is empty.

Trimmed for take-off with standard bomb load and full tanks, (forward tanks empty for fuel-trimming later on), the aircraft could take off by itself to begin a shallow climb, but normal procedure was different: To get rudder-control as soon as possible during take-off, forward pressure on the helm lifted the tail just after 35 mph. Then, slight back pressure rotated the aircraft at about 55 mph, and the aircraft climb to 300 ft at no less than 53 mph, where it was then trimmed for climb.

With this in mind, I decided to take the trimmed-for-take-off setting as neutral trim, and place bomb and fuel tank weights as on the blueprint, balancing out other parameters accordingly.

-With neutral trim, the flight model can take off by itself, lifting the tail at 32-37 kt depending on the load, and rotates at about 44 kt to begin a shallow climb. Normal procedure is also possible.
-Trimming for climb involved either pumping fuel into the aft tanks if there was space, or using the elevator trim wheel when tanks were completely full. Climbing speeds were between 53 and 55 mph, and RoC between 295 and 330 fpm, depending on load. The flight model now requires one, two or three notches of nose-up trim here.
-Inversely, trimming for level-flight involved pumping fuel into the forward tanks. With nearly empty tanks, the trimming wheel was used. The flight model will need slight nose-down trim here.
-Maximum up-elevator trim will induce max. RoC at 53 mph, and with less trim, a more mormal 55 mph RoC. Fully loaded RoC will be just under 300 fpm, and with 80% fuel + 80% payload it will be somewhat above that.
-More nose-down trim will be required after bombs have been released.
-Trim will also need to be adjusted when fuel is low.

Details of other .air file entries to achieve this:

Primary Aerodynamics:
---------------------
Lift due to horizontal Stabilzer= -600
Pitch Moment Coeff at AoA=0 (CoG Offset) *2048 = -201

Main Wing:
----------
Dihedral = 2.58 (real: 1.5 degrees, lower wing only)
Agle of Incidence = 3.5 deg
Angle of twist = -0.747 deg (real: -1.5 on lower wing only)
Main Wing Centre of lift Fore+/Aft- of CoG (inches) = 42

Horizontal Stabilizer:
-----------------------
Angle of Incidence = 1.5 degrees

I expect (and hope) this is now more logical and desirable than before!
Cheers,
Aleatorylamp
 
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Early aircraft radio

Hello everyone!
I hope you will all enjoy some really nice and relaxing easter holidays with chocolate egg hunts included, possibly with the family and/or friends!
Meanwhile, I was wondering if anyone could let me know if a default gauge like the Schweizer.Com.Radio gauge would be of any use for the panel of a bomber of the Great War, which at that time was already equipped with air-to-ground voice radio. The panel for the aircraft will only have default gauges for the sake of simplicity.
Thanks in advance for any suggestions!
Cheers,
Aleatorylamp
 
Great War Giant Bomber uploaded

Hi all!
I´ve just uploaded the Zeppelin Staaken Giant Bomber in the CFS1 Warbirds library. It´s taken longer than I expected this time, but better late than never.
Many thanks to Ivan for a whole lot of assistance and support!
My now slightly more experienced troop of mechanics are now tuning the brand new, more powerful BMW aero-engines for a second Giant, a night-bomber. They are also checking the new central fin and brushing on some dark varnish to darken the colours. Then the test pilot to have a go, if they can get him out of the bar... I wonder when they will be ready, but as soon as they are, we will have another beast!

Here´s the link:
http://www.sim-outhouse.com/sohforum...id=19&id=19552

If anyone discovers any glitches or bugs, please tell me and I´ll put them right!
Happy Easter!
Aleatorylamp
 

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Propeller Tables Update

After a couple weeks of revising spreadsheets to generate Record 511 and 512 Propeller Tables,
I believe I have finally had some success.

The choice to use the Ki-61-I as a test subject was because it could not develop maximum engine RPM until reaching a speed of 150 MPH.
One flight report comments that the propeller was lugging and only reached maximum RPM at 120 MPH.

My first attempts at building my own tables produced some very nice looking curves in the spreadsheet, but when I translated them to the flight model, I suddenly had an aeroplane that would have tremendous acceleration up to 41 MPH and then not go any faster. 41-45 MPH appears to be the speed at which the Propeller Tables actually are used rather than relying on a static thrust calculation.

It took almost a week to find the error in my spreadsheet. It wasn't obvious because the stray value was several columns to the right of my visible spreadsheet.
AirEd didn't show it either because it was also past the visible portion. (For a 41 MPH Issue, I didn't think to look at the last columns of the record.)

Once that issue was fixed, the table combination worked, but the flight performance was drastically changed.
(Adjusting the efficiency will tend to do that regardless of how smooth the curves look.)
Surprisingly the biggest issues were with Record 511 - Propeller Efficiency Table rather than the Power Coefficients.
After trying to adjust a few points by hand, I figured it would make more sense to base my spreadsheet on the curves from the stock P-51D AND my earlier spreadsheet values.

My first flight tests there showed about 25 MPH less speed at Sea Level and Critical Altitude (15,000 feet).
The problem was that my curves were dropping in efficiency earlier than the stock curves which never drop to zero and the interpolation was getting a value that was about 10 to 15 % too low.

Adjust the zero values required reworking the Power Coefficient spreadsheet to prevent the "Perpetual Motion" thing from happening.
Unfortunately it also took out most of the negative Power Coefficient graph areas so the propeller overspeed effect in a dive is mostly gone as well.

I found at that point that the Engine would reach Maximum RPM at 95 MPH, so the Power Coefficient curves needed a slight adjustment.
The Engine then appeared to hit Maximum RPM at about 125 MPH. This appeared to be a bit high, but then I realised that the numbers were flashing by VERY fast on a take-off run at full power. Reducing the simulation rate to slowest showed that it was actually reaching maximum RPM at 118 MPH which is close enough for my purposes.

So how much did the performance change?
I am still testing that:
The original maximum speeds were
323 MPH at Sea Level (which I thought was a bit too high)
380 MPH at 12,500 feet
378 MPH at 15,000 feet

The new maximum speeds are
314 MPH at Sea Level
376 MPH at 12,500 feet
374 MPH at 15.000 feet

The actual maximum performance of the Ki-61 is pretty hard to determine.
The US tests give it
302 MPH at Sea Level
348 MPH at 15,000 feet

I suspect this was with an aircraft in much less than perfect condition.
The Japanese claimed it could reach 368 MPH at 16,400 feet but this was on Military Power.
On "Combat Power" it should go a bit faster.

There is a lot more detail to this, but I am tired of typing.
Good Night.
- Ivan.
 
Propeller generator

Hi Ivan,
Sounds quite impressive!
I have never used a spreadsheet in my life as I´ve never had to, but I´d like to get my bearings on the subject.
So, I take it that you have a formula which you put in, and the values are generated into the different columns corresponding to the advance angle (see picture of fixed pitch prop), and in your case, you are getting an overall general result which you then test on the plane and then go back and tweak manually in certain places, or perhaps adjust the formula for that specific line (advance angle) or column (pitch on a CV prop).
Now, supposing you want to generate a different propeller for a totally different airplane, I understand that you would enter the necessary values mass, diameter, rpm and horsepower, and you would get a new CV prop?

Cheers,
Aleatorylamp
 

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Hello Aleatorylamp,

You are presuming that I accomplished much more than I actually did.
The kind of information you described in the last post is much more than one can typically find on a propeller on a typical WW2 Aeroplane.
In fact, even simple overall dimensions are not so easy to find sometimes.

Folks tend to use lots of approximations when describing propellers. The blade angle for example is a single number typically of the section at 75% radius from the center.
The other sections would all differ depending on their location.
Another silly fact is that the same propeller would have different behaviour depending on the airframe that uses it.
The reason is because a larger cross section behind the propeller (perfect example being a Brewster Buffalo) would interfere with the airflow and reduce efficiency.

What I did on the first try for Propeller Efficiency was to draw some smooth curves (using AF99) and then scale them to a reasonable profile.
That didn't work all that well, so I ended up just using the curves from the stock P-51D and adjusting them where I thought the numbers were obviously incorrect.
I also extended the Advance Ratio to 3.00 instead of the stock 2.4. Even J=3.00 is still too low for high speed dives but it beats 2.2 or 2.4 which isn't even sufficient for level flight.

The Power Coefficient spreadsheet only relies on a single formula to generate a smooth curve for the positive side and a goofy series to generate the negative side.
I don't really like the way I am generating the curves there either, but just wanted to get some results quickly. They will get revised at some point.

The real accomplishment here is that I believe that I finally have a pretty good grasp of how these curves fit together and affect flight performance.
I needed this to be able to properly work out flight models for very different aircraft such as the Ki-43-I Hayabusa with its two blade propeller and the FW 190D with its very wide propeller blades or the late model Spitfire with a 5 blade propeller.

There are still a whole bunch of holes that I can see in how this would match real-world physics though.

Consider these posts to be pretty much like bragging about finally passing a mathematics test in school.

- Ivan.
 
Spreadsheet prop, and blipping rotary engines

Hi Ivan,
I see! Probably my question is too lengthy to answer here, as I would probably need to learn to use a spreadsheet first. The thing is, I was trying to understand exactly how you were using the spreadsheet, as opposed to manually adjusting all the values for a CV prop. In my case with my fixed-pitch props, I only have to adjust a few values in a single column - which is lucky!

At the moment I´m adjusting a 50 hp rotary Gnome Omega engine (1200 RPM), and I´ve found a way to bypass the throttle lever altogether. The rotary engine should go to full power immediately after start-up, and the pilot would be "blipping" it with the magnetos to keep it from rushing off unwantedly. ...and he would get lots of unburnt castor oil in the face unless he had a pusher engine!

Altering the left "Y" value in the Engine Throttle Effectivity Table 506 controls idle power. Entering 0.98 here, so that it is the same as the "Y" value on the right, it´s still 80 RPM short if you don´t push the throttle forward, but entering 1.07 (on the left), you get full power without touching the throttle. I thought that was quite interesting!

Cheers,
Aleatorylamp
 
Spreadsheets

Hello Aleatorylamp,

Initially, the Propeller Efficiency Table was quite a lot more complicated in its generation.
There were separate multipliers for each pitch angle and also multipliers for each advance ratio.
The spreadsheet gave me good graphing capability and the ability to alter entire sets of numbers very quickly.
I found that although I could get fairly close, there were places that needed quite a lot of manual adjustment without which the level speed or acceleration were drastically changed.

So.... Rather than doing this for the general case which I concluded would not be much of a "General" case anyway, I decided to start with a known set of values (Stock P-51D) and see if the results were close.
The problem with starting with the P-51D Tables is that the Advance Ratios are incremented by 0.2. I needed to increment by 0.25 in order to go from 0.00 to 3.00 in the same number of columns. To do this, I used the spreadsheet to interpolate values where the advance ratios did not exactly match. This was easier to do via spreadsheet than with a calculator.
I suppose a lot of this is just a matter of using a familiar tool (spreadsheet) rather than a less familiar and less reliable (to me) tool such as AAM.

The Spreadsheet for the Propeller Power Coefficient still retains it original purpose which allows me to change entire series with a multiplier or alter the shape of the curve by changing an exponent.

- Ivan.
 
The first twin-tail in history

Hi all!
I´ve just uploaded a 1914 twin-tail pusher, the Porokhovschikov-II, an armed observation sesquiplane equipped with a 50 Hp Gnome Omega rotary pusher.

The link is:
http://www.sim-outhouse.com/sohforums/local_links.php?action=jump&catid=19&id=19566

It is an interesting aircraft for its innovative design, and also, because the inventor built it in his appartment on the 6th floor! Performance during trials at the Komendant´s Airfield near St. Petersburg in August 1914 exceeded all expectations. With a crew of 2, a machinegun, a few grenades, and fuel, the load was almost equal to its empty weight, and the aircraft reached 99 kph (62 mph) and a RoC of over 600 fpm, quite remarkable for such an engine. The "Dvukhvostka" (twin-tail) was manoueverable, and a nimble climber. Unfortunately however, it never saw series construction because no agreement could be reached with the military, but it was the basis for all subsequent twin-tail designs.

The model is an improvement over the previous version, as it now includes a CFS1 .air file, a textured machinegun and crew uniforms. Also, I´d initially built the plane using structures for the wings, given the convenience of the rectangular shapes, but as the lighting effects do not spread well on structures, they have been substituted by components, with visually much more pleasing results.

I hope you all enjoy the model!
Cheers,
Aleatorylamp
 

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Tools for propellers

Hi Ivan,
Hmm... the spreadsheet certainly looks like a practical and convenient tool to do propellers, so it´s on my "to learn to use" list (the only item for now!). The part on the interpolation with a formula will help too.
I had been trying to use AAM for this, but I was only able to use it to have a look at the graphs and to read the comprehensive related texts, which in itself is quite good, but I couldn´t alter any of the graphs.
Cheers,
Aleatorylamp
 
Using .bmp textures instead of .Xaf

Hi all,
To improve some textures on an AF99 model, I´m trying to make it use .bmp textures instead of .Xaf ones.

With Texture Converter I changed them all round to .bmp´s , but the model won´t accept them, even though I tried different ways of re-naming them.
Also, the .cfg files don´t seem to control the texture type, and I haven´t found a reference to textures in the CFS1 SDK either.

Of course, perhaps the model has to be built with a different programme that allows bitmaps during the building process... I don´t know.

I wonder if anyone could indicate if and how this can be done.

Thanks very much in advance,
Aleatorylamp
 
it's been a long time,
so, i very well could be wrong.
as i recall, the .mdl file is calling for the .Xaf textures.
if you open the .mdl with scasm,
the .Xaf calls can be hand edited to .bmp's

Ivan, most likely, has an easier solution.
 
.xaf to .bmp

Hi No Dice, Hi Smilo,
Thank you for your posts!
OK, so textures can be renamed to .bmp with scasm or a hex editor. I´ve just looked into the .mdl file with scasm and right at the beginning, there´s a texture index, and further down, each texture is mentioned every time a polygon uses it.
I´ll try it out then!
Thanks and Cheers,
Aleatorylamp
 
there should be a lot of entries to edit.
don't forget any.
let us know how it goes.

if it was me, i would do a few,
then compile and have a look,
just to make sure it works properly.
 
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