Boeing Stearman Model 75

Hello Ivan,
Sorry to be such a pain, but before embarking on your proposed more thorough CV-prop tuning-check (post #139), and to avoid the fears you expressed in Post #133, I just checked some things on the RPM difference between full max. and normal max. power, and also did some preliminary checking for some possible improvements to be obtained by increasing or decreasing the torque/friction balance (still using the fixed pitch propeller).

First: Is the 2200-2100 RPM difference really correct for the 237-225 Hp difference?
100 RPM for only 12 Hp... Hmmm... I´m only getting a difference of 39 RPM here.
I checked, and saw that the Navy Stearman Manual mentions 2100 RPM with 220 Hp.

Doing my testing again, I found I got 58 RPM difference between 220 and 237 Hp:
237 Hp - 2202 RPM (2 RPM slightly too high for Full max. power)
220 Hp - 2144 RPM (44 RPM somewhat too high for Normal max. power)

Then, as you had proposed Vno at with 1900 RPM and 202 Hp, I checked:
202 Hp - 2078 RPM (178 RPM - very high).

Now, to try and increase the RPM difference between the 220 and 237 Hp, I tried out a few things:

First, I tested shifting the ZERO POINT on the graph tables from J=0.86 to J=0.8 (and adjusting the J=0.6 and J=0.7 positions accordingly), but this only reduced the difference by 1 RPM.

Then, I raised the balanced torque/friction settings from .64/15.9 to 0.725/27, but this only reduced the difference by 3 RPM, compared to my initial 58 RPM.

Next, I lowered the balanced torque/friction settings to 0.58/8.15, and this increased the difference, but only by 1 RPM, compared to my initial 58 RPM.

I am assuming that my initial 0.64 torque setting, as well as the increase to 0.72 and the decrease to 0.58 would still lie within the criteria for a reasonable torque setting. Lowering torque further would perhaps not be a reasonable setting, I suppose.

So, my question is whether it will be worth while to conduct the more thorough CV-prop engine tuning test to adjust torque and friction before putting in the fixed pitch propeller, if changing the torque/friction settings will hardly make any difference.

Of course, because I didn´t change the Zero Lift Drag settings, all this preliminary testing may not be accurate, and may not reflect what would happen with the more thorough CV prop engine tuning test, so my line of thought could be totally wrong and useless.

So, the next thing I´ll do is conduct your proposed CV-propeller test!
Cheers,
Aleatorylamp
 
Tuning with CV Prop

Hello Ivan,
Update: OK, I´ve tuned with the CV prop, (not on a bolted down aircraft), for the different settings: 237 Hp at 2200 RPM, 220 Hp at 2100 RPM and 202 Hp at 1900 RPM, all at full throttle, and I have noted down Thrust and Torque readings.
I needed a higher torque graph setting (.612) for full max. power, and the other two are at 0.628 and 0.610, with Friction at 14.7 for all three.

Then I put on the 16-degree fixed-pitch propeller, and on the bolted down aircraft, at full throttle the engine gives 1870 RPM and 232 Hp.
OK!! (FAA dictates: Not over 1950 RPM, not under 1725 RPM).

So, it seems like it´s going along the correct path, this more profound tuning procedure.

More later!
Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,

Go back and re-tune your Engine with the Constant Speed Propeller.
Your power curve is pretty messed up.

From what I am reading you are getting:
2200 RPM - 237 HP (Good!)
2100 RPM - 220 HP (OK, but just a touch low)
1900 RPM - 202 HP (Good!)
1870 RPM - 232 HP (What the Heck?!?!?)

Why does 30 RPM down give 30 MORE Horsepower?
This kind of abrupt jump is not good. Curves should be pretty smooth and look like the ones in the manual.
Something is wrong here.

Now assuming that your 232 HP is really 202 HP and that the 232 was just a typo, then I suggest you go back to the shop and get a new propeller.
The one you have is pretty worn out!

If someone out there knows better, please correct me on this issue, but as I see it:
The FAA specification allows for a max diameter 98 inch propeller but will allow for repairs taking it down to 96 inches or so.
The FAA requirement specifies the resistance of a propeller as being such to limit it to between 1725 RPM and 1950 RPM with the Engine at FULL THROTTLE and Zero forward motion.
What does this mean?
I see this as a Brand new Propeller will be limit things to 1725 RPM.
As the Propeller is used and nicks get sanded down, the blades get smaller and thinner and re finishing the tips all reduce the Power Coefficient.
When the Power Coefficient is such that the Propeller winds up to 1950 RPM at FULL THROTTLE with Zero forward motion, it is time to replace it.
Your Propeller is used and worn.
Get a New One!

- Ivan.
 
Hello Ivan,
I put in 220 Hp for 2100 RPM because that´s what the Navy Stearman Handbook states for the N2S-2, although granted, the FAA DOES state 225 Hp for 2100 RPM, which however leaves very little RPM difference for the simulator.
100 RPM difference of only 12 Hp? A difference of 17 Hp would sound more realistic, I´d wager.

QUOTE:
1870 RPM - 232 HP (What the Heck?!?!?)
UNQUOTE

This is what I got for Full Throttle with the static bolted down plane after I installed my fixed-pitch propeller.(Altough it WAS dragging around the concrete block at 6.9 mph!!)
Mistake: I had transferred the old Torque graph! No wonder...

Well, first I´ll try and make a new propeller to get RPM down to 1725 RPM first, and lower the Hp.
Thanks for explaining what this means (and everything else, of course).

Now I´ll test for the rest of the points on the curve between J=0 and J=0.8 (where the curve drops to ZERO). ...without the concrete block!

OK, then. Let´s see what ELSE happens...

Update: OK, I´ve got the new propeller on, and it´s dragging the concrete slab at 1725 RPM.
After several trials Hp is now at 198 Hp, and the Torque Graph setting is slightly lower than what it was with the CV propeller tests for max. full power. I suppose I´ve finally understood.

Update 2: It really came out as I´d feared in my earlier post #141. I got basically the same performance results as after I tweaked my own fixed-prop tests prior to this one, although slow speed performance is now correct. Below 100 mph I had it far too high before! However, the full max. is now a bit on the low side.
So, it´s much of a muchness... sixpence of one and a half a shilling of the other.

I had to put in a bit of a "step" in the graph in table 512, between J=0.6 and J=0.7. Speeds and RPM for 220 and 237 Hp are so close together, that both J values affect the result, and I tried lowering J=0.7 some more without getting too close to ZERO, and raising J=0.6 a bit, to separate the speeds a bit more. Oh well...

NEW S.L. Testing: Torque Graph: 0.625 / Friction: 14.7 (Zero Lift Drag was better left unchanged).
100%: 235 Hp, 127.5 mph, 2195 RPM - quite close.
_94.5%: 220 Hp, 124.35 mph, 2143 RPM - instead of 2100 RPM
_90%: 202 Hp, 120.7 mph, 2081 RPM - instead of 1900 RPM

Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,

Be careful about combining specifications from different model engines unless that is really your intent.

You sure seem to run a LOT of quick test cycles!

In my prior experience with switching from a Constant Speed Propeller to a Fixed Pitch Propeller, there hasn't been any significant power change that could not be attributed to general noise from imprecise tests, so I am not sure what is going on with your situation.

It might be worthwhile to plot your Engine Horsepower versus RPM to compare against the ones from the manual.
The numbers might be a bit different, but the shape should be pretty close.

If you don't like having your concrete blocks hauled around too much, just create a garbage Propeller Efficiency Table (511) for testing with efficiency values all at Zero. That should work.
Or if you can't keep the aeroplane from moving, then adjust the initial couple steps of the Power Coefficient Table to be the same so the curve is flat and it does not matter if it is really stationary or not.
Basically you just need the number for Advance Ratio Zero.

There really should be no great "Steps" in Table 512, but do as you feel you need to do.
They sometimes cab be seen in actual Power Coefficient Graphs.
I would be concerned at this point that there are other indications if this step appears to be necessary to get the performance correct.

By the way, if you do not get an exact match, I don't think folks are going to ever call you on it.

- Ivan.
 
Hello Ivan
Thanks for your feedback!
It was actually more a matter of what I could make the sim come out with, rather than simply which engine specifications I was going for.
Given that the only Lycoming with reliable, complete information is the 225 Hp R-680-B4 on the Navy N2S-2, which is reported in the Handbook as giving 220 Hp at 2100 RPM, this is the engine I´m trying for.
One thing is what I want to get, and another thing is what the sim gives me!

I managed to even out the curve and get rid of the annoying step, and even improving it a bit by using a lower Torque/Friction balance level, just to make the curve prettier and ever so slightly more fitting!
Top performance is now also more correct.

The results with 0.58 at the end of the Torque graph and 8.15 on the friction graph, combined with the corrected below 100 mph performance for the low "J" factors, gave the following improved results:

Full-max: 2201 RPM, 237 Hp, 127.9 mph, 100% throttle. (105% rated power)
Nor-max: 2145 RPM, 221 Hp, 124.5 mph, _95% throttle. (100% rated power)
Nor-max+: 2165 RPM, 226 Hp, 125.6 mph, _96% throttle (100% the other rated power)
Vno.___: 2080 RPM, 202 Hp, 120.6 mph, _89%
VCr high: 1888 RPM, 154 Hp, 108.5 mph, _75%
VCr slow: 1756 RPM, 126 Hp, 100.3 mph, _65%

Ceiling with 50% fuel: 103 fpm at 18500 ft (Oh !!!)
Initial RoC, 50% fuel: 808 fpm at 1400 ft

It was only possible to get a 221 Hp reading for Normal max. at 95%, because the 94% one went to 218 Hp. The same applies to the 225 Hp reading, which had to be 226 Hp at 96%, because 95% went to 223 Hp.
Of course, if one expects that BOTH of these should be at 2100 RPM, it just can´t be done - not even just one of them, actually!

I´ve prepared a picture of propeller tables 511 and 512. The numbers in the box at the bottom of each table refer to the curve position marked by the red dot. AAM isn´t bad to use, is it?
Cheers,
Aleartorylamp
 
Hello Aleatorylamp,

You seemed to want to discuss how to calculate when the efficiency of a propeller drops to Zero.
It would have made sense to copy the two or three posts from the BV 141B thread over here so that THIS message does not seem to be such a non sequitur.

Aleatorylamp said:
It quotes 98AA66, 98AA64, and 98AA66 propellers for the 220-225 Hp Lycoming radial engine.
The first number is the propeller length in inches.
The second number is the pitch in inches, (theoretical advance, supposedly no-slip).

Looking at the Sensenich Propeller Certificate List, these propeller reference numbers are found preceded by the letter "W". I found a converter to convert pitch inches to degree-angles at 75% prop radius.

W98AA66 standard prop. 66 inches pitch = 15.95 degrees.
W98AA64 climbing prop. 64 inches pitch = 15.49 degrees.
W98AA68 cruising prop. 68 inches pitch = 16.41 degrees.
Click to expand...

Remember this post of yours? We will use the numbers from here for examples.
I will be using only the first example for discussion for simplicity.

The name of the W98AA66 propeller means that it is 98 inches in diameter and Advances (<--- Important Word!!!) 66 inches per revolution at zero slip. Yeah, you already knew that!

So what happens if we have the propeller on the front of our neat little aeroplane turning at 1 revolution per second? (slow!)
If the aeroplane is moving less than 66 inches per second, the propeller provides thrust.
If the aeroplane is moving MORE than 66 inches per second, the propeller does not provide thrust and is actually being driven by the airstream.
So in this case, the ADVANCE RATIO at which the aeroplane is moving 66 inches per second is where the EFFICIENCY DROPS TO ZERO.

Note that the angle of pitch is calculated by Trigonometry using the Tangent Function.
Y = 66 inches
X = 98 inches * 0.75 * Pi
Tan (Theta) = Y / X = 0.285829
Theta = ArcTan (0.285829) = 15.95 degrees.

Note that the angle is the important part here.
If the propeller were twice the diameter and Advanced twice as far per revolution, the angle would be the same.

Advance Ration Formula

J = V / n * D

When the values for the W98AA66 propeller are substituted in this formula
ALONG WITH Propeller rotational speed, the result is the Advance Ratio at which Efficiency drops to Zero.

This is purely from a Geometry viewpoint.
Reality is not quite so simple which is why I keep giving an approximate range of values.
The Propeller is not a single Blade Element at 75% Radius.
The Blade Cross Section is an Airfoil and not completely flat so even at Zero degrees AoA, there is still some lift.

I have made some working assumptions there which probably would not stand close scrutiny, so you will need to make your own assumptions.

Hope this helps.
Let me know if you need some additional clarification.

- Ivan.
 
Formula for Advance Ratio

J = V / (n * D)

Left out the Parentheses on the last Post.
The Parentheses are not needed when writing on multiple lines.

- Ivan.
 
Hello Ivan,
OK.
Propeller Pitch in inches of Advance per propeller revolution,
translates into a speed for a given RPM, at which the propeller´s
work becomes useless, i.e. zero, at least in theory.

This theoretical speed is higher for any given practical operating
speed with its corresponding propeller RPM.

Theoretical speeds and practical speeds have their corresponding
"J" factors.

How big the difference is between theoretical and real speeds and
"J" factors is, depends on the aircraft.

As it happens, for the Stearman-75, I am getting consistent differences
of 10 mph and 0.05 in the "J" factors. You had calculated a recommended
"J" factor of 0.8 for the Stearman.

This would add another 0.13 to the "J" factor difference, making the
difference 0.18, i.e. 3.6 times larger, which would account for the
working assumptions you were making.

A correct propeller efficiency curve steeply goes down to zero,
as opposed to stock CFS propeller efficiency curves, whose angles
get much shallower as they approach zero. To improve these, it is
necessary to see where the curve reaches zero.

You were discussing improvements on the efficiency curves of the BV-141,
on the BV-141 thread, showing the improved curves of the Ki-61 and the
Condor, as well as illustrating the "before and after" BV-141 curves.

My query about how to go about these calculations met with your suggestion
I should go and look on the Internet. I wouldn´t have asked if I had found any
understandable information on the Iternet. My explanation that followed
as to why looking on the Internet had been useless for me led to your cutting
comment that the subject was off topic on the BV-141 thread.
Off topic? What was off topic?

Why is it on topic only for the Stearman thread? I already had the solution for
it here, the zero at J=0.8 you recommended - Mentioning the Stearman in this
context was only for comparison purposes, just like you mentioned the Ki-61
and the Condor.

Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

Aleatorylamp said:
My query about how to go about these calculations met with your suggestion
I should go and look on the Internet. I wouldn´t have asked if I had found any
understandable information on the Iternet. My explanation that followed
as to why looking on the Internet had been useless for me led to your cutting
comment that the subject was off topic on the BV-141 thread.
Off topic? What was off topic?
Click to expand...

We must have very different search methods on the Internet because that is actually the source of most of the information that I myself am using. I don't have any formal education in this field either; I have just spent a fair amount of time looking around for scholarly articles on the subject.
The data for this Stearman project was the same way. The performance information took about 15 minutes to find. The Lycoming R-680 manual that we recently discussed was found in well under 5 minutes (probably closer to 1 minute) after I started looking for the data and I am not even that interested in the aeroplane! This isn't a new phenomenon. It goes back at least as far as the P-3 Orion where there were lots of manuals and useful diagrams online but you just either were not finding them or were not looking.

Regarding just a general definition of Advance Ratio, Wikipedia gives an excellent explanation and is where I looked when I needed a quick reminder of what the formula was. It isn't hard to find!
The rest of the terms give a lot of hits on a search engine and I go typically to the sources that are organised the neatest and closest to the way I wand the data to be presented which tends to be documents from either NASA or University classes on Aeronautical Engineering.

Aleatorylamp said:
Why is it on topic only for the Stearman thread? I already had the solution for
it here, the zero at J=0.8 you recommended - Mentioning the Stearman in this
context was only for comparison purposes, just like you mentioned the Ki-61
and the Condor.
Click to expand...

The reason I thought your posts were off-topic was because you were asking for an explanation of how I arrived at the Zero efficiency but in the context of the Stearman as an example. We have already spent literally weeks discussing the issues of the Stearman's Propeller here.
If you had wanted an explanation of how I arrived at that information for the Stearman, you should have asked about it in the thread about the Stearman.
Otherwise, there is no continuity in EITHER thread.
That is why I chose to post the response here: because it makes logical sense in the context of the last several weeks of discussing propeller efficiency numbers along with the various graphs that have been posted.

You may have had a solution (actually you are quoting out of context for J=0.8), but may not have understood WHY that was the solution which is why you were asking and why that question belonged here.

The examples of the Ki 61 and Condor are good illustrations because both are either released or in a "reasonable form".
The Stearman's Propeller Graphs are not because you are still trying to figure them out (and still misquoting by the way).
The BV 141B Propeller Graphs were also not a good example because they were also still being edited.
They were posted because they were the subject of the discussion.

The latest has not been posted because it isn't necessary for illustrating anything important in that discussion and also because they are still subject to edits as needed if I should encounter something I don't like while testing.

- Ivan.
 
Such is life...

Hello Ivan,
Oh well... such is life.
Some are better and/or quicker than others in finding the information needed at a given moment - obviously because some know more than others about the subjects in question, and can thus more easily identify useful from useless information within the quagmire of Internet.

Even Pilots´ Handbooks for similar aircraft supply different and/or inconsistent information, (did the Lycoming engines in question have 220 or 225 HP??) as in the case of Army Corps and Navy Stearmans, or information which is only similar to that required, as in the case of the Orion.

Also, Engine Manuals ommit certain details. For example, there isn´t a military designation for the 240 Hp Continental W670-M, but the Navy had quite a few, but neither do they say how many, nor on what planes. ...and not to mention the 280 Hp Lycoming-engined Stearmans, buried in oblivion largely due to the FAA, although 2 or 3 historical texts do mention 255 units as having them! So, to say I´m perhaps simply not looking is quite unjust, to say the least.

Anyway, turning back to propellers: After the more thorough method of testing and tuning that you proposed, which yielded almost the same results as I´d got before, now I am surprised to hear that the Stearman propeller tuning is still not good. Oh, well, such is life... I don´t know any more to do anything further, but I do know where the problem lies.

In real life, 2100 RPM on the Lycoming gave 220 or 225 Hp (we will never know the exact number, will we?), and 2200 RPM, gave 237 Hp. In the Sim, this seems impossible to achieve, at least for me. The positions on the curve are so close that a 100 RPM difference for 12 or 17 Hp is impossible without incorporating a stupid, big step - so again, ...such is life!

My question on how to calculate the point where the propeller curve reaches zero was meant in general.
I have already said that I mentioned the Stearman example only as a check-reference.
You suggested J=0.8 because your calculation results ranged from J=0.7 to J=0.9, and included some working assumptions - and, now why was the J=0.8 out of context? ...and I do apologize for misquoting something or other on the Stearman propeller curve.

Anyway, my aim behind getting this information (that you so generously supplied, thank you very much) is to use for the Lockheed Electra-10´s two-pitch position propeller, which is quite a lot smaller than the Condor´s one you so effectively made.

This business is tedious enough as it is, more so if one adds the CFS and AF99 limitations.

Anyway, it seems that all my questions have been causing you some degree of bother for quite some time already, and I am sorry to hear that. So, the solution is really very simple: I will just reduce the number of questions and interventions to the barest possible, absolute minimum. The last thing I want to do is to be a pain.

It´s a hobby, and it´s supposed to be fun, so why turn it into such a harsh discipline in so many aspects?

Cheers,
Aleatorylamp
 
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MisQuotes

Hello Aleatorylamp,

The misquote I mentioned is here:

Aleatorylamp said:
As it happens, for the Stearman-75, I am getting consistent differences
of 10 mph and 0.05 in the "J" factors. You had calculated a recommended
"J" factor of 0.8 for the Stearman.

This would add another 0.13 to the "J" factor difference, making the
difference 0.18, i.e. 3.6 times larger, which would account for the
working assumptions you were making.
Click to expand...

The recommendation of Efficiency dropping to Zero at J=0.8 was for a Propeller Pitch of 10 degrees.
If that is still what you are using, then Great!
If not, then this Quote is out of context and is not what I recommended.
I have not worked out the rest of the math, so I do not know what the 0.13 or 0.18 or 3.6 are referring to.
I do not have your flight model, so I really have no idea what might be causing your 10 MPH issue or even what the issue is for that matter.

Your comments about Engines on the Stearman would have made more sense to me a couple weeks ago than now because as I said before, I never was particularly interested in the aeroplane and after I found what either you or I was looking for, I didn't archive it for later use.
Normally I keep a Data Repository and Data Sheet on projects that I am working on but didn't see the point of doing that here.

That is why it is so difficult giving a diagnosis when you are describing that something is wrong.
Without gathering the data and either building the flight model myself or at least poking around with data in a spreadsheet, I can't really get a feel for the specifics of what your flight model may be doing.

I suppose directing YOU to try an Internet search was a lazy approach, but the alternative was that *I* would do the Internet search myself and just tell you what I found which seems a bit silly.

- Ivan.
 
Hello Ivan,
OK, thank you very much, and pardon my frustration, so it wasn´t irrelevant at all, but quite important!

I´ll have to repeat, for clarity but expounding as well:
Testing in most operative flying conditions, with a 16-degree pitch propeller, (66 inches pitch Advance in one revolution), i.e. Normal Vcr, High Vcr, Vno, 100% Power Vmax, and 105% Power Vmax.
There was a consistent +10 mph difference between what the pitch 66 Advance Speed calculation gave, and what the model´s actual speed in the sim was,
for the following RPM settings, (Hp are just a reference):

Hopefully these number will give a feel, like you mention you need, but without having the inconvenience of making a flight model or a spreadsheet run... sorry about putting you out.

1900 rpm, 156 Hp, actual speed: 190.4 mph, J= 0.620. Zero point calculation: 118.74 mph, J=0.673
2000 rpm, 181 Hp, actual speed: 115.7 mph, J= 0.623. Zero point calculation: 124.99 mph, J=0.673
2077 rpm, 202 Hp, actual speed: 120.4 mph, J= 0.625. Zero point calculation: 129.69 mph, J=0.673
2100 rpm, 207 Hp, actual speed: 121.9 mph, J= 0.625. Zero point calculation: 130.67 mph, J=0.673
2143 rpm, 220 Hp, actual speed: 124.5 mph, J= 0.626. Zero point calculation: 133.93 mph, J=0.673
2160 rpm, 225 Hp, actual speed: 125.4 mph, J= 0.627. Zero point calculation: 135.00 mph, J=0.674
2200 rpm, 237 Hp, actual speed: 127.9 mph, J= 0.627. Zero point calculation: 137.49 mph, J=0.673

A) 1900 RPM: desired for 202 Hp, but this power isn´t possible even at 2000 rpm.
B) 2100 RPM: desired for 220 and/or 225 Hp but impossible to achieve in the sim.

Summing up: Using the J factor formula, there was a consistent +0.50 J difference in all these flying conditions.
The J factors that came out in the calculation were all around 0.673, and the factors in actual flight ranged from 0.620 to 0.627, so the difference was averaging 0.05.

The rest was then a mistake. I was wrongly expecting the correct "zero efficiency value" to be at J=0.8,
and I thought that the difference would account for the working assumptions you had mentioned.
So, the whole paragraph on "the 0.13 or 0.18 or 3.6 times" I was referring to can safely be discarded as erroneous, obviously...

This would however not altogether invalidate the results giving +10 mph and +0.05 J factor difference that I got in the calculations, compared to the actual in-flight aeroplane speeds.
I thought it seemed logical that pushing the plane 10 mph faster in all these conditions, would make the Advance Speed equal to the Aircraft Speed, thus reaching the (theoretical) zero efficiency point, but maybe I am wrong...

Sorry... So I am led to believe that the results of the calculation are actually the zero efficiency point, MINUS the necessary working assumptions, which have to be done as yet. So, if the curve dropping down to zero at 0.8 is completely wrong, obviously the aircraft´s real flight behaviour will change. ...or will it?

Now I have to add a working assumption to J factor 0.673 and test for results. As zero at J=0.8 is bad, I could try 0.9. I wouldn´t use 1.0 because that seems to be for a larger propeller. My working assumption would then be adding 0.23 to the J factor calculation result.

Update: OK, I just tried the propeller with the graph going down to zero at J=0.9, and unfortunately, there was no performance difference. The 220 and 225 Hp positions and corresponding RPM, as well as max 105% 237 Hp at 2200 RPM positions all remain unchanged.
I very much doubt that anything can be done to improve the propeller.
I don´t get a bad feeling out of it at all!

OK, that´s it! :pop4:I´ve decided the propeller and the engine are doing fine, and I´m stopping work on it.

I really must get to building the plane - the delay with the propeller has taken FAR too long and hasn´t made any tangible improvement for a long time. Thus, the job qualifies as "as good as it gets", which is excellent!

Anyway, full technical information on the propeller is available here on this post, and it works fine!
I don´t think I have to bother you with it any longer, Ivan, the torture has ended!
Possible improvements I´m afraid will only be very marginal, so there´s nothing to worry about.
Much more important now, is to get the visual model underway!

Cheers, and thanks for the support all the way along this very long propeller whittling process!

Hereby I declare that this is the END of my participation on this thread.

Three Cheers,

:icon29::icon29::icon29:
Aleatorylamp
 
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Hello Aleatorylamp,

Aleatorylamp said:
A) 1900 RPM: desired for 202 Hp, but this power isn´t possible even at 2000 rpm.
B) 2100 RPM: desired for 220 and/or 225 Hp but impossible to achieve in the sim.
Click to expand...

What have you tried to achieve the correct power levels?
I don't know why you are testing anything else if you haven't gotten the Engine power correct with a Constant Speed propeller yet.

I am not familiar with the program you are using to check Advance Ratio but I am guessing that you are not using it for its correct purpose.
You do realise that Advance Ratio for Zero Efficiency does not change unless the shape of the propeller changes.

Advance Ratio of 0.673 for Zero Efficiency sounds like a calculation based on a single blade element and a totally planar blade airfoil which is probably not how things really are.
My calculation gives an Advance Ratio of around 0.9 or so for a 16 degree Blade Angle.

The differences you are getting in your calculated Advance Ratio during testing and the Zero Efficiency Advance Ratio is actually not useful information.
You should use your calculated Advance Ratio to do a lookup into your Propeller Tables to see what the simulator is using for Propeller Efficiency.

Aleatorylamp said:
This would however not altogether invalidate the results giving +10 mph and +0.05 J factor difference that I got in the calculations, compared to the actual in-flight aeroplane speeds.
I thought it seemed logical that pushing the plane 10 mph faster in all these conditions, would make the Advance Speed equal to the Aircraft Speed, thus reaching the (theoretical) zero efficiency point, but maybe I am wrong...
Click to expand...


There is nothing to invalidate because the Data you have tried to collect is meaningless.
The only possible way for your Airspeed and Advance Ratio to match the values calculated by this Program you are using is if:
1. The Airframe / Wing has Zero Drag.
2. The Propeller Tables are in agreement with a Theoretical Zero Camber and single Blade Element Propeller.

I believe you are using a tool that is meant as a "Rule of Thumb" check and do not understand the numbers it is giving you.
I believe your tool is giving you the Geometric Zero Efficiency Advance Ratio without consideration for other "practical" aerodynamic factors which may alter that point of Zero Efficiency.

Aleatorylamp said:
Update: OK, I just tried the propeller with the graph going down to zero at J=0.9, and unfortunately, there was no performance difference. The 220 and 225 Hp positions and corresponding RPM, as well as max 105% 237 Hp at 2200 RPM positions all remain unchanged.
I very much doubt that anything can be done to improve the propeller.
I don´t get a bad feeling out of it at all!
Click to expand...


Your Aeroplane is getting stuck at an Advance Ratio of around 0.625 or so by your own account.
What did your alteration to the Tail End of the Graph to extend it to 0.9 actually do to the place you actually happen to be?
(Probably Nothing which is why nothing changed!)

The Technicians in my Workshop actually have also been working on a Propeller for the BV 141B.
Actually, They are working on the Constant Speed Unit and if you think you have it bad with just one Blade Pitch.....
They finished up the CSU just before I started this post, so it is time to install and test.
(Can't Ground Test this one because it needs some altitude for a proper test.)
I suspect Zero Lift Drag will change again as a result, but such are the problems when things are done in the wrong order.

- Ivan.
 
Success at last.

Hello Ivan,
It was getting too hard and taxing on my mind, and I had to disconnect from the Lycoming engine/propeller tuning for a while. A change is as good as a rest.

Meanwhile, I´ve managed to build most of the Stearman-75 Model, with reasonably satisfying results, in 2 versions: One blue/yellow Army Corps version and one yellow Navy one.

I still wanted a better engine though, as the 9-cyl. Lycoming R-680-? was only possible as a usable approximation. Thus, I switched to the 7-cyl. Continental R-670-4, applied all the necessary propeller and engine adjustments, and tested it.

Lo and behold! I expect you will be pleased to hear that after a few tries and slight further adjustments, it worked out perfectly! Performance is almost exactly as per specification!

So, why did it work so easily with the Continental engine?
What was amiss with the other engine? Conflicting information from the two Lycoming engine certificates regarding rated horsepower and RPM that just couldn´t tally. So, this engine can´t be used until these contradictions are cleared, which I doesn´t worry me, though!

Anyway, I just thought you´d be interested to know.
Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

Sorry about not getting back to you for a while.
I wanted to concentrate on the BV 141B until it could go into production (Uploaded).
My Son also has been sick and out of school for the entire week with a fever, so online time has been somewhat limited.

I am somewhat surprised that the Continental and Lycoming Engines are so different in the Flight Model.
In theory, there should be very little difference as far as representations of the 220-225 HP military engines are concerned.
RPM, Displacement, Power, Compression are all very similar, so I wonder where the difference would be?
I have done no research on the Continental R-670, so can offer no specific information.
Glad you are happy with the results.

Please note though that the flight performance and correct engine simulation are really not the same thing so I would suggest not letting that be the sole determination of the correctness of the flight model.
On my BV 141B for example, the straight line performance was probably closer to the book when I started than it is now but the engine and propeller models had serious errors.
Other than straight line performance, there were other performance and handling issues that were not so obvious but could be found with some specific testing.

- Ivan.
 
Lycoming problem mystery solved.

Hello Ivan,
I have also commented on this on the other Stearman thread,
but in less detail.

The problem appears to lie in the specified RPM for 105% power:
An increase of 12 Hp for a 100 RPM increase won´t tally - at least in the sim.

Specs: 100% = 220 Hp at 2100 RPM, and 105% = 237 Hp at 2200 RPM.
The best difference I obtained was 45 RPM, and it was making me ill, so I gave up.

The Continental engine didn´t have an RPM specification for 105% power,
and with 100% at a close 2080 (instead of 2075), and 105% at 2020 RPM,
it all seemed more correct. Even more so when I eliminated the extra 5% altogether.

Later, comparing the normal 100% performance for both engines, the
7 x 95.4 cubic inches with 5.4:1 compression ratio of the Continental, and the
9 x 75.55 cubic inches with 5.5:1 compression ratio of the Lycoming, there was
virtually no difference at all in the 100% power performances of both engines!

So, you are right in that the engines are virtually the same,
even in the simulator, of course!

Cheers,
Aleatorylamp
 
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