Focke Wulf Fw200-A Condor

Propellers and Such

Hello Aleatorylamp,

I am surprised that converting the Propeller Components to single blade caused those kinds of problems.
I do that all the time on my own projects.
The animation gets more difficult, The shading becomes different, and a few more Parts get used, but otherwise there has not been a difference.

A set of Two Pitch Propellers installed in the Condor is being shipped to you.
Note that there are a few side effects from the changes.
Some can be addressed via changes in the Torque Curve of your Engines.
I had to do something very similar for my Ki 61 for 2400 RPM versus 2500 RPM operation.
RPM is obviously much harder to control now.
Let me know if you like the changes as a whole.

When you look at the graphs, you will see that the concept is very simple, but to get there took a lot of calculations.

- Ivan.
 
Hello Ivan,
Thank you very much for the shipment! My mechanics have been mounting the propellers and taken the machine for a preliminary test flight.
It is very, very interesting indeed, what you have achieved, and everyone is completely amazed!

The Efficiency Table looks more realistic, by the way, and the Thrust Coefficient table is totally mind boggling, and I suppose that that is precisely where the secret lies.

Anyway, the first trials: At first I was waiting to discover where or when 18 deg. low pitch would change to 35 deg. high pitch, as I had expected this to happen automatically, but it stayed there even at almost 197 mph, and also, the plane didn´t get any faster, although I was already at 1000 ft.

So, I slewed up to 5000 ft and there it was at 35! I went down to 300 ft again and it was still at 35, and it was then I discovered the manual change would do it. I repeated the test with 18 deg. upto 197 mph and then gave 35 degrees, and it continued speeding up, this time to 215 mph. Of course, minor adjustments in Drag will put speed up to 226.8 mph. Hp is at 718, so a very small adjustment will get it to 720 Hp.

Although here I have some misgivings, because I saw on hand-pencilled graph for the performance of the BMW 132 engines, the real power curve for 1.2 ATA for 720 Hp went from about 685 Hp at S.L. to 760 Hp at 3280 ft... so I might even leave the torque graph as it is now, if it turns out to be more exact!

At 6000 ft speed went up to 235 mph, and I saw that pitch would stay stay at 35 deg. even though I changed the setting. So, obviously there must be a point where it changes by itself. Then I noticed it changes with RPM, and pulling back the throttle to slow down the engine, pitch drops to 18.

Anyway, I am still trying to decypher how exactly it works, but it does seem to be completely realistic. I still have to discover where if it changes automatically from 18 to 35, or if this is to be done manually only.

It´s absolutely great!
Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

I am glad your mechanics are having fun. My mechanics had lots of fun also but really don't know much about the Condor or even Propellers for that matter. One fellow had an idea how this could work and convinced the others to follow along for a while. If nothing else, it would have been a learning experience.

My suggestion regarding under speeding and over speeding is to use the torque graph to adjust things until they look right.
The under speed is about 100-150 RPM too slow, but with the right torque graph adjustments, the power loss will be minimal though it should still be higher at 2050 RPM.
The over speed seems to be around 100 RPM at worst and that can be adjusted by using the torque graph as a rev limiter. Imagine if the torque is 100% at 2050 RPM but drops to 50% at 2075 RPM....
There are of course other ways, but I suggest you do not mess with the Friction graph.

Note that in places where the aeroplane is now going faster, it is mostly because RPM and Engine Power are higher.
Also, if the speed gets stuck at 197 MPH at low level, you can probably adjust the efficiency on the 15 Degree graph to push it past the hump. If you tell me where this is happening:
Altitude,
Speed,
Power,
RPM,
then I can do it for you. My guess is that this is happening very low at Sea Level to 500 feet.

By the way, how do you manually adjust propeller pitch??? I actually never tried that.

Working on your propeller got my technicians thinking about what was wrong with the propeller on the Ki 61 and that aeroplane will get another edit soon.

- Ivan.
 
Hello Ivan,
This is getting more interesting every time.

Pitch can be forced into high by manually moving down the blue propeller pitch levers on the thrust quadrant, despite the CV-prop entry of 2 in record 330 "Propeller Type".

I thought the speed limitation at for low pitch was intentional, to make the pilot manually move pitch into high, but of course, if this is altitude-dependant, it can´t be intentional! It´s curious anyway, and can be left that way.

Here´s a little performance table for this.
I haven´t adjusted Torque or Drag to get correct specified performance yet.
I was looking for exactly where pitch went from low to high.
Of course, it not olnly depends on altitude, but also on speed.

18 Pitch:
_500 ft, 689 Hp, 1951 RPM, 194.5 mph, 1858 torque, 714 Thrust.
1000 ft, 708 hp, 1985 RPM, 197.4 mph, 1879 torque, 725 thrust.
1500 ft, 724 hp, 2003 RPM, 199.6 mph, 1899 torque, 733 thrust.
2000 ft, 733 Hp, 2022 RPM, 201.4 mph, 1904 torque, 737 thrust.

Note: Any millimetrical misalignment on even only one of the blue propeller pitch levers (this often happens on start-up if full power is given too soon), will facilitate the automatic change to 35 pitch if it can get above about 204 mph when at 2000 ft.

2000 ft, 736 Hp, 2026 RPM, 208.0 mph, 1906 torque, 899 thrust.

Even at 2800 ft, pitch will stay at 18 pitch, unless a certain speed is surpassed, but it is difficult to establish when.
At first I thought it was also about 204 mph, but later during another test the change already occurred below 200 mph.

At any rate, now I will try and adjust power and speeds as you suggested before doing any other tests.
Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

Last night, I was a bit bored, so I did a little testing with the FW 200.
You are right, it does get "Stuck" at about 197 MPH or so at the 500 feet altitude where I was testing.
On my test panel, I did not think of bringing up the engine controls panel, so I just used <Control>F2 to drop the RPM a bit and was able to switch to 34 degrees pitch.
To me, this seems to be pretty reasonable behaviour.

My problem here was that I did not have a way of telling where I had the RPMs set for (didn't think of the propeller control lever), so when I increased RPM to get closer to full power, it would drop the pitch back down to 18 degrees again.
(By the way, I suspect that the actual low pitch setting was a bit higher than 18 degrees.)

So far, I see that all your testing is done at low level.
I can tell you that for some reason, the Power Coefficient (Engine Power) is quite low below about 3000 feet.
Do some testing higher up and you may find a difference in behaviour.
I was figuring that for that era, the cruising altitude was 8,000 feet to about 10,000 feet (Probably closer to 8,000 feet) the pilots would want to get the aeroplane up higher to cruise faster in the less dense air but also have enough air not to need oxygen for crew or passengers.

Your table is interesting and would be useful data for a checklist, but I suspect you do not really have a feel for what is really happening here. (I know I didn't when I started messing with these tables and even now I find things that should be obvious if I really had a good feel for how things worked.)

The actual values as you can tell from the Table 512 labels are Cp and J.

The values you mentioned are all included in Cp and J:
Speed affects Advance Ratio
RPM affect Advance Ratio AND Power Coefficient
Horsepower affects Power Coefficient
Altitude affects Power Coefficient (but it also affects Engine Power.......)

Both are pretty easily defined, but the combination is not necessarily intuitive (at least not for me).
My suggestion is to build a spreadsheet for calculating these values and alter the inputs to see how Cp and J change.
You may be quite surprised by some of the effects of changing a single variable.

As I mentioned earlier, a couple ideas occurred to me while I was working on the FW 200 propellers and I need to think about how they affect the propeller tables I generated for the Ki 61.

- Ivan.
 
Hello Ivan,
Thank for your post. I still have to study it more closely, as well as your previous one.

I only had enough time to do the main testing at S.L. and critical altitude (5900 ft).
S.L. because it would be the basis for the rest, and Critical altitude because I was getting a power surge there, which I wanted to reduce without losing too much S.L. performance.

My initial trials increasing torque from 0.4995 to 0.51, 0.505 and 0.500, and reducing drag from 57 to 54 and eventually 52, gave an excessive power surge at 5900 ft. First, 836 Hp, then 815 Hp and 807 Hp, and I eventually managed to reduce that to 792 Hp by just going the the opposite way with the Torque graph, leaving it at 0.490.

This has the result that at 300 ft, with 18 pitch it goes to 195.3 mph with 657 Hp and 1923 RPM. Then, pulling the prop pitch levers to get 35 pitch, it goes up to 222.2 mph with 701 Hp and 2206 RPM.
Then, at 5900 ft critical altitude, I´m getting 244.5 mph with 791 Hp and 2208 RPM.

That´s the current position with the testing I´ve been able to do, and I´m looking through my documents to try and decide if this is OK.

The pencilled BMW 132 Graph table related to the BMW-132 L and H 800 and 830 Hp engines, is the only reference point I have, and I´m trying to imagine if the older 720 Hp BMW 132-G could have a 720 Hp line starting at S.L. and giving 791 Hp at 1800 meters altitude.

Note that for the engine on the pencilled graph, RPM for 720 Hp is 2250, and not 2050.
The older engine had 6:1 compression ratio, and these had 6.5:1. Presumably, with the lower compression, the 720 Hp max. power would have been a 5-minute affair, not a 30 minute thing by any means. Continuous power was 550 Hp though.
The newer engine on the graph has this at S.L. and going up to 625 Hp higher up.

Have to rush!

Update:
The graph must refer to the 132-Dc, that gave 850 Hp. At first I though of the 132-H1, but that one went up to 1000 Hp for 1 minute. Then, it could not have been the 132-L or -H, because those only went up to 800 and 830 Hp, not 850.
The -Dc gave 790 Hp for Take-off and 780 Hp at 9000 ft, and I don´t know about 1-minute power foir the -DC.

I was looking more closely at the graph, and the comment about the 720 Hp being a 30-minute thing, could confirm this.
The -H1 delivered 1000 Hp for 1 minute, and 800 Hp for 5 minutes. The Dc and H1 engines had a 0.62:1 reduction gear, hence a 3-bladed CV propeller, so it is hardly a good comparison for the 720 Hp engine. Also, the critical altitude was higher, between 7000 and 9000 ft, depending on throttle setting, and the supercharger supplied a maximum of 1.38 ATA. This engine seems to have had a "Vollgashöhe" i.e. a maximum throttle altitude as of 1100 meters, not below.

The 132-L engine was the one that was most similar to the engine I´m using, but the pencilled graph does not refer to it. It gave 800 Hp for 1 minute and 720 Hp for 5 min at 2150 RPM, had almost the same supercharger, no reduction gear and a 2-pitch-position, manual propeller.This engine also seems to have had a "Vollgashöhe", an altitude of 1400 meters, below which maximum throttle was not allowed.

What is clear, is that there is quite some confusion as regards Fw200 engines!!
So it is going to be even more difficult to try and extrapolate the behaviour of the 720 Hp 132-G from this graph!

What I have done, is drawn in the 1.2 ATA graph in red, corresponding to the 132-G engine that delivered 720 Hp at S.L., and maintained 1.2 ATA upto 1800 meters, 5900 ft. I wonder if this could be plausible.

Consequently, I would wager that the peak at critical altitude should be about 760 Hp, perhaps not 791, as I´m getting now, and that the 657 Hp at S.L. would be quite low.

Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,

You do realise that as soon as you significantly (and it does not take much to be significant) alter the power curve, the propeller tables need to be rebuilt again, right?
That is why I was waiting for you to be really sure about your power and performance numbers before even looking at anything.

- Ivan.
 
Hello Ivan,
OK, thanks. I understand. But perhaps the propeller tables are OK notwhithstanding, because I´m trying something that might work to get the curve better:

After getting the torque graph to give me about 720 Hp at 300 ft, I´ve lowered Boost gain a little so that the 800 Hp peak at critical altitude of 5900 ft critical goes down to 764 Hp. Drag is adjusted so that I´m getting about 225 mph at S.L. and about 243 mph at Critical Altitude. Then I´ll test some other altitudes further up and see what happens.

Of course, this slight reduction in Boost Gain has an adverse effect: Manifold Pressure is supposed to stay at the maximum 34.87 upto critical altitude, and it doesn´t anymore - it went down to 33.4 - so perhaps my idea is not so good after all.

Update:
I´ve started testing a bit further up, and it gets better.

For the moment it´s back to about where I was a short while ago:
S.L: Correct 720 Hp at 2023 RPM, and 224 mph (OK)
Critical altitude 5900 ft: quite high 811 Hp, with 2223 RPM, and 246 mph (OK).
and higher up at 9800 ft, much better 695 Hp, with 2210 RPM, and 245.2 mph (OK).

I have had no time to test cruise speeds yet, but tomorrow is another day!

You mentioned that pitches were not exactly 18 and 35, which is what I´m getting - probably because my beta-min and beta-max are defined as 18 and 35 in the air file. Should I define other values for this?

Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,

I was getting 719 HP @ 500 feet and 223 MPH or so before I quit testing.
I was only testing for the propeller pitch versus power, so that was sufficient.
I am not sure it was at full RPM at the time, but those values were pretty close at least for power.

The comment I made about Low Pitch and High Pitch angles is because I suspect that although 18 degrees seem pretty optimal when running a CS propeller, the actual aeroplane probably had a higher Minimum Pitch than 18 degrees because this model was coming off its minimum pitch just after the take-off run.
Then again, this kind of depends on the match of the original Power Coefficient Table.
Another indication that this number was too low is the huge dip in efficiency between 18 degrees and 35 degrees in the Efficiency Table.
The Efficiency drop between 18 and 35 was hidden earlier by use of a CS propeller.

You have quite a few variables here, so there may be more than one solution.
Obviously we CAN get 18 degrees Minimum Pitch to work.

By the way, here is an illustration of how things can get interesting:
I was originally working from your performance data sheet which says
5900 feet ---- 757 HP
I presume this was at 2050 RPM which with a Constant Speed Propeller is pretty much guaranteed.
Cp = 0.060919


Now you have 764 HP which probably is not significantly different if it is still at 2050 RPM.
Power Coefficient would be very slightly higher but not enough to make a difference.
Cp = 0.061482

Not VERY different at all, but you will notice a slightly earlier shift to High Pitch.


But for 811 HP at 2223 RPM, Life gets interesting. You remember I said earlier that things are not always intuitive....
Cp = 0.051183

Hmmmm..... My guess is that you might notice it NOT shifting to High Pitch until around 240 MPH to 245 MPH or so.
Perhaps it would even be past your maximum level speed?
This is by eyeball correlation of the version of Propeller Tables as I sent them to you.
This time around I did NOT do any very precise calculations other than for Cp which is pretty easy.
Bottom line is that the shift point WILL be higher and performance will be pretty awful until that shift happens because the Propeller Efficiency is dropping very fast at that speed with 18 degrees pitch.
At 245 MPH you would get around
40% Efficiency with 18 degrees Low Pitch
and
73% Efficiency with 35 degrees High Pitch

Life can get really messy really fast here.

- Ivan.
 
Let´s try a higher low pitch.

Hello Ivan,
Thanks for your post. Yes, it is a very interesting experiment!
A good side-effect is that you seem to be getting some information out of it for your Ki-61 as well.
All the better!

The 757 Hp at 5900 ft would be fine, better than 764 or 760, but then S.L. power would go even lower!
The thing was that due to the increased peak at 5900 ft, I was willing to accept 764 Hp, instead of 575, just so to get away from the >800 peak there.

I was basically just rounding it off to 760 Hp, which was only a decuction I had derived from the pencilled graphs of the CV-prop -DC or -H1 engine, whose power graphs "conveniently" included a graph for 720 Hp.
However, 757 Hp is of course better, because of the less efficient propeller.

I think it will be better to leave that part of the curve alone then.

So, you are saying that increasing low pitch will give us more S.L. power, which will be necessary.
I´ll go with that! An increase there will bring down the >800 peak at 5900.
As you say, the CV prop will have hidden the lower efficiency of the 18 degrees.

I did some more altitude tests, and got very satisfying results:
12500 ft: 242.6 mph, 610 Hp, 2166 RPM
15000 ft: 242.0 mph, 546 Hp, 2174 RPM
19700 ft: 237.5 mph, 434 Hp, 2137 RPM

Then I did some 12500 ft Cruising tests, which were also good:
Fast cruise, at 0.8 ATA: 224.8 mph, 477 Hp, 2018 mph
Normal Cruise 0.76 ATA: 217.3 mph, 422 Hp
Eco-Cruise at 0.73 ATA: 208.0 mph, 370 Hp, 1870 RPM

OK, then. Would you think that the default setting of 20 degrees used for fixed pitch propellers would be best?
I remember trying out fixed propellers on the Condor and they seemed to work quite acceptably.

Another thing you mentioned, is the speed at which the propeller would come off low pitch.
On one hand, you say that it comes off low 18 pitch very soon after the take-off run, and on the other, low pitch seems to be maintained all the way up to 195 mph. Higher would of course make things messy, as you say.
If you are suggesting that this could be lowered, I expect it would be better, so we wouldn´t get the propeller staying at low pitch at 195 mph.

P.S. Still another thing you said: While testing, you were getting 719 Hp at 500 ft and 223 mph. That´s fine! I can readily accept that - it´s not really very different from 720 Hp at 300 ft with 226.8 mph.
This, combined with the 575 Hp at 5900 ft would be perfect! Strange that I am only getting either one or the other of these correct at any time, not both.

Question: Is it possible to have the same power of 719 Hp at 500ft both with low pitch and relatively low speed, and then ALSO with high pitch at higher speed? I would expect, technically yes...

Cheers,
Aleatorylamp
 
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Communications

Hello Aleatorylamp,

Actually the issue I noticed that will get me to revisit the Ki 61 Propeller is negative Power Coefficients.
The numbers I am using right now pretty much mimic the stock Propeller Tables in that respect, but with the radical edits to get your Propeller Power Coefficient Table, it occurred to me that this probably was not the right approach.
Free time over the last couple days has been spent reading up on Windmilling Propellers and their effects.
It IS related to the Ki 61 propeller table, but in reality has more to do with working on the twin engine stuff.
If your single engine fighter loses an engine, you WILL go down. It is just a matter of time and angle of how you meet local terrain.
With a twin (and less so with more engines) single engine performance simulation is fairly important and I knew very little about that area until recently.
The next step is to create an experiment that can give better insight into how CFS handles negative Power Coefficient values.
As usual, one "new" idea puts a whole lot more stuff on the task list.

Aleatorylamp said:
Another thing you mentioned, is the speed at which the propeller would come off low pitch.
On one hand, you say that it comes off low 18 pitch very soon after the take-off run, and on the other, low pitch seems to be maintained all the way up to 195 mph. Higher would of course make things messy, as you say.
Click to expand...

As often happens, we are seriously miscommunicating again:
When I described changing pitch from 18 degrees just after take-off, I was referring to the original CS propeller.
It would obviously be dependent on the stock Hurricane's Power Coefficient Table that you were using, but since it was matched to your engine by Power Coefficient value similarity, it would imply that 18 degrees allows your engine to reach full RPM just after take-off which is great for a CS propeller but suggests that 18 degrees is too fine of a low pitch value if you ONLY have two angles instead of a whole range in between.
Arriving at this conclusion is not exactly that simple because the advance ratio between the Hurricane and FW 200 are so different, but it is one piece of data that should not be ignored.

Please Review the attached Screenshot of the Propeller Efficiency Table (511) from the Condor.
Note that I have removed the graphs for 25 degrees and 30 degrees to reduce the clutter and because they were not really relevant to this discussion.

The two pitch values in use are Red Dash lines.

Note where they cross. That is where we would want a propeller pitch change for optimum performance.

Note the values just above the Advance Ratios. Those are the True Airspeed MPH for each Advance Ratio assuming 2000 RPM.

Note also that the rising slopes and peaks of these efficiency graphs (other than for 25 and 30) are unmodified from the original values used for the Constant Speed Propeller.
One of the big advantage of the CS propeller over the two-pitch is that it can maintain a full 2050 RPM pretty much at any speed above about 100-110 MPH while the two-pitch propeller tends to lug below its optimum airspeed.

Remember I stated that the rising slopes and peaks were unaltered.
Note from the screenshot that 18 degrees and 15 degrees pitch have VERY small advantages over 20 degrees but past J=0.6, their efficiency drops VERY badly and I even raised the efficiency of the 15 degree graph at J=0.8 so that the interpolation for 18 degrees would not be quite so bad.

Aleatorylamp said:
OK, then. Would you think that the default setting of 20 degrees used for fixed pitch propellers would be best?
I remember trying out fixed propellers on the Condor and they seemed to work quite acceptably.
Click to expand...

So.... To make a short answer VERY LONG.... a low pitch value of 20 degrees makes a whole lot more sense from an efficiency and geometry standpoint than 18 degrees.

Aleatorylamp said:
P.S. Still another thing you said: While testing, you were getting 719 Hp at 500 ft and 223 mph. That´s fine! I can readily accept that - it´s not really very different from 720 Hp at 300 ft with 226.8 mph.
Click to expand...

I told you I was limiting changes to just the propeller tables. That was so we could discuss things from a known common point.
That didn't mean that there were no other problems.
If 719 HP instead of 720 bothers you, adjust it up a touch.... You actually have a lot of room at Sea Level to do this because the Power Coefficient is much much lower than elsewhere.
If the lower speed bothers you, adjust the Coefficient of Drag. If that not precise enough, increase the Oswald Efficiency number to bring it back down again because that number is a bit on the low side anyway.

Aleatorylamp said:
Question: Is it possible to have the same power of 719 Hp at 500ft both with low pitch and relatively low speed, and then ALSO with high pitch at higher speed? I would expect, technically yes...
Click to expand...

I don't see why you can't, but I believe the problem here is not so much the power as reaching a consistent RPM and that may be a lot more difficult. That is why I suggested using the torque curve to keep power very similar for the operating range you want (as I did for the Ki 61) and use differences in manifold pressure to control engine output.
This is not unrealistic when compared to the torque graphs from real engines though you have to remember that real engines don't factor out friction into yet another graph when they are being dyno-ed.

- Ivan.
 

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Hello Ivan,
Thanks for your explanatory post. I see that I have understood most of it, and other posts, except for where and how the 4 different variables all interact - that´s where I get lost, but I don´t think that´s the problem.

I´m fine with 20 degrees for low pitch. I limited minimum pitch to 20 instead of 18, and take-off was fine, so we´ll be fine with the new value. No problem. I don´t think there´s any problem with the pitch switch either, and there´s no problem at higher speeds. The prop always goes into 35 pitch there.

The headache is the 811 Hp peak at critical altitude instead of the expected or hoped 757 Hp.
I wouldn´t mind even 770 Hp, for that matter, and from what I can see, it has nothing to do with the change in low pitch.

Alternatively, looking at it from the opposite side, tuning the curve down to get the peak into manageable levels, i.e. 764 Hp or even 770 Hp, as near as possible to my 757 Hp), the headache is then the reduced 657 Hp at S.L.

The manouevering capacity offered by modifications in Drag, Oswald Factor or Torque Graph is too small to help here.

Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

You have me pretty confused by the last couple posts about your engine power issues.

From your performance document:
1) S.L. 300 ft: 226.6 mph
720hp - 34.9 MP (1,2 ATA)
Pitch 26.4, Thr: 1010
2) 5900 ft: 243.6 mph
757 Hp - 34.9 MP (1.2 ATA)
Pitch 29.0, Thr: 984
3) 8500 ft: 243.0 mph
689 Hp – 31.7 MP (1.1 ATA)
Pitch 28.9, Thr: 897

Are you telling me that you did not actually get these numbers in testing?
Or are you telling me that a change in the propeller tables radically changed the engine output?

- Ivan.
 
Hello Ivan,
The performance document dates from a date which is rather older than the new propeller tables.
Why would I want to do all that testing again? The older .air file. is tested, done and finished.

The first part of the document states the specifications of the real aircraft, and the second part
describes the actual model performance results - with the old .air file, of course.
Why would I write out a performance document stating test results that I didn´t get? I don´t
understand your comment.

When you sent me the new propeller tables, a couple of days ago, the first thing was to see how
they worked, and of course I started testing them. Once I saw how they were doing, the next
step was to try and adjust performances as closely as possible to the specifications and/or
performances described in the performance document.

The first thing I noticed was how effectively the low and high pitch were working, the 18 or 20
degree issue for low pitch being a rather minor affair.

It was then that I encountered the problems I have been describing: Now I can either have
720 Hp at S.L. with an 811 Hp peak at CA, or I can have correct output at C.A. with by far
insufficient power at S.L., and I´m trying to correct this without much success.

So, I went back to the new .airfile you sent me a couple of days ago, with the new propeller
tables 511 and 512, and with NO other alterations. Just for the record, these are the maximum
speed, power and RPM readings for this new .air file, all speeds at 35 pitch:

__300 ft: 214.0 mph, 712 hp, 1985 RPM
_5900 ft: 235.8 mph, 808 hp, 2198 RPM
_8500 ft: 235.2 mph, 728 hp, 2182 RPM
_9800 ft: 234.5 mph, 689 hp, 2172 RPM
12500 ft: 232.8 mph, 608 hp, 2149 RPM
15000 ft: 231.0 mph, 542 hp, 2125 RPM
19700 ft: 224.1 mph, 431 hp, 2075 RPM

I hope this helps.
Cheers,
Aleatorylamp
 
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Sorry Aleatorylamp,

It didn't come out quite the way I had intended.
I was wondering if the test performance was of the AIR file you sent to me or an earlier version because I know that you tend to make a lot of little adjustments very quickly.
I had the same issue when looking at old test results for my Ki 61.
I was working on version 0.58 and the test sheet I was looking at was for version 0.55.
The new results I was getting obviously did not match all that well.
The changes were not great, but there were enough differences that I had to go back and redo a few things.
Luckily I make a habit of documenting the significant changes IN the AIR file and could trace things back to version 0.55 and see when things had changed.

I believe I know where the problem lies and how to go about correcting it.
The problem is that this is complicated enough that I can't just give you more than just general directions on where the changes need to be made because it is a matter of changing something and seeing if something else needs to be changed.

I believe that the windmilling propeller aspect will need to be removed to get the proper performance which means that the propeller tables need to get tuned again.
Basically what is happening is that the new Power Coefficient Table is pretty good for 18 degrees but for there not to be a possible stable angle between 18 degrees and 35 degrees, the graph for 35 degrees needs to be very very close to that for 18 degrees and is being brought down too fast and does not supply resistance to keep RPM from climbing.
The best way to do things is to bring the 18 degree curve up to the one for 35 degrees but then even when efficiency drops to zero, it will not windmill because the curve is still positive.

As I commented before, the interactions are complicate enough that it would be a whole lot quicker for you just to send me what you have (if you have changed anything you want to keep) and let me do the final performance tuning.
If you haven't changed anything you need to keep, I can tune to best match your performance sheet, but I will warn you in advance that I don't generally try to get as close as you do to the target number.
I tend to numbers slightly higher than the specification.
If there are some numbers you are trying to change from the performance document, please let me know that also.

My apologies again for doubting your test results.

- Ivan.
 
Pitch Angles

Hello again Aleatorylamp,

We have already discussed the preference for 20 degrees minimum pitch over 18 degrees pitch.
I was just looking over your performance document again and wondering why you chose 35 degrees as your maximum pitch angle.
From what I can tell, none of your maximum speed tests go above 30 degrees and neither do your cruise speed tests and if they don't, there is no way that a maximum climb will go there either.

- Ivan.
 
Hello Ivan,
OK. I´m glad there is no confusion anymore.

The .air file in use at the moment is the one you sent me with the new propeller tables, with minimum pitch increased to 20 degrees. The .air file with the trials I did to fix the excessive critical altitude power peak is no good and I´ve discarded it.

In other words: I don´t have to sent you another .air file!
From what you are saying then, it sounds like you have a solution for the CA power peak.
Please go ahead on the .air file you have.
Thank you very much!

The reason I chose 35 degrees for high pitch was that:
> quote from post #61: "The CV prop tests showed that at 6000-7000 ft, 39.2 degree pitch was being used, and then higher up, from 12500 to 19000 ft, pitch went from 38.5 to 37.5, so I think I´ll try something like 35 degrees now."
If you have a different value in mind, please let me know and I´ll put it into the .air file.
If you like, we can reduce it to 30.

I think performance document can stay valid as it is. There´s nothing that I can see that needs changing.

Well, let´s see what happens now!
Cheers,
Aleatorylamp
 
Optimal Propeller Pitch

Hello Aleatorylamp,

I guess it is time to put on our Aircraft Designer Hats again.

Please take a look at the attached screenshot.
It is basically the same as the last one but with the following changes:
18 degree graph removed
20 degree graph changed to Red Dotted Line
30 degree graph restored and displayed in Red

Note that there are now TWO lines of numbers above the Advance Ratio.
The first line is for 2050 RPM ------- Advance Ratio 1.0 would be 226 MPH
The second line is for 1900 RPM ---- Advance Ratio 1.0 would be 209 MPH
Note that even at 1950 RPM -------- Advance Ratio 1.0 would only be 215 MPH

So what can we tell from this graph?
With a Cruising Speed of around 205 MPH at 1900 RPM, we would be just below Advance Ratio 1.0.
At a Maximum Speed of 245 MPH at 2050 RPM, we would be pretty near Advance Ratio 1.1.
Now compare the Efficiency graphs for 30 degrees and 35 degrees at Advance Ratio 0.9 to 1.1.
It is pretty obvious which angle would give better results here.

By Eyeball, 35 degrees does not become better until about J=1.25 which would be around 290 MPH.
That speed range is basically in an area that we don't really need to worry about and would be a transient condition in any case.

Note also that the cross over between 20 and 30 is not that much of a drop compared to 18 and 35 that we were using earlier, so the shift would be better.

Basically we are going for a close-ratio transmission in drag racing terms!

Hope that all makes sense.

- Ivan.
 

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Aleatorylamp said:
The reason I chose 35 degrees for high pitch was that:
Click to expand...
Aleatorylamp said:
> quote from post #61: "The CV prop tests showed that at 6000-7000 ft, 39.2 degree pitch was being used, and then higher up, from 12500 to 19000 ft, pitch went from 38.5 to 37.5, so I think I´ll try something like 35 degrees now."
If you have a different value in mind, please let me know and I´ll put it into the .air file.
Click to expand...


Hello Aleatorylamp,

Back when you made that post, I was just giving advice and not really getting into the details of your AIR file.
I actually have no idea what you were testing back then though I suspect it might have been the 7 foot propeller.
Remember that back then, I had no idea how to build a set of Propeller Tables either.

I figure this thread is a learning exercise for me as well since I have no real experience with propellers either (which makes me wonder why anyone would consider following MY advice).
I consider this tuning exercise an open book Midterm Exam.

Go ahead and change the Maximum Pitch to 30 degrees if you want to see what difference it makes.
I suspect it will actually improve things by a fair amount.

As before, I need to spend some time to gather the data that I will need and do a few calculations.

- Ivan.
 
Hello Aleatorylamp,

Here is what my Technicians were able to get before I had them quit for the evening.
Flying in the dark can get a bit dangerous at times.

Original / Re Tuned
Constant Speed / Two Pitch
300 feet.......227 MPH....720 HP / 229 MPH....727 HP @ 2077 RPM
5900 feet.....245 MPH....757 HP / 246 MPH....766 HP @ 2231 RPM
8500 feet.....243 MPH....689 HP / 244 MPH....686 HP @ 2210 RPM
9800 feet.....242 MPH....655 HP / 243 MPH....650 HP @ 2196 RPM
12500 feet...241 MPH....584 HP / 242 MPH....572 HP @ 2172 RPM
15000 feet...240 MPH....525 HP / 238 MPH....510 HP @ 2146 RPM
19700 feet...236 MPH....425 HP / 234 MPH....416 HP @ 2111 RPM

It isn't exact, but I believe it is pretty close.
I used most of the methods I described in this thread.
The RPMs can be tuned down a bit by adjust

The shift points are a bit off now because of the different power levels, but that can be tuned without affecting anything else.
The problem is that it is a bit too high at Sea Level (207 MPH) but a bit too LOW (155 MPH) at altitude so one has to choose where to tune it for. This aeroplane is not mine, so it isn't my choice.

Good Night
- Ivan.
 
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