Boeing Stearman Model 75

[Ivan]

Hello Gentlemen,

It appears that my initial assessment of the flight model for the Red Stearman was not correct.

As manufactured, the Stearman 75 only had TWO Ailerons on the four wing tips and was known for a very leisurely roll rate.
Modern Stearman, especially airshow birds typically have been refitted with FOUR Ailerons and have a much faster roll rate.
Now keep in mind that in appearance, the Red Stearman DOES have FOUR Ailerons or at least has the appearance of four Ailerons.

Apparently one model of the Stearman 75 was equipped with a 450 HP Pratt & Whitney Engine and that is actually a pretty good amount of power for aeroplane that probably doesn't weigh over about 3500 pounds loaded and that would explain a pretty high rate of acceleration on the runway.
The Textures do show a 450 and a Pratt & Whitney symbol.....

The Yellow Stearman has a much nicer roll rate but behaves much worse from a handling standpoint.

- Ivan.

[smilo]

according to the article,
the model 75 originally
came off the line with, either,
a Continental R-670,
a Lycoming R-680,
or a Jacobs R-755.
the Pratt and Whitney R-985 wasp jr
was a post WWII swap out.

[smilo]

seems, you were posting as i was typing.

will get the scanner set up shortly.
...unless my son calls
for me to pick him up from work.
either way, i will have the drawings up by morning.

since we're talking two models,
how about a docile military trainer,
and the hotter, modified civilian?
i believe visually, they look the same.
except, for paint, of course.
the devil will be in the air files.

[aleatorylamp]

Hello Ivan, hello Smilo.
Thanks, Ivan I´ve also seen the information you are giving. That´s why I said it was a bit difficult to confirm the scarce date I found about the 300 Hp and/or 330 Hp P-13D versions.

Of course there is no doubt about a P-17 with 220 Hp, so that one´s solved.

However, there is a video of an authentic 1943 300 Hp Lycoming R-680 running on a trolley, comments in more than one site that the engine these were also used on our friend the AT-9 Jeep (R-680-9), and also a post in a forum of a guy that wants to use a vintage 300 Hp R-680-R on some build he´s making.

So, if they weren´t ex-factory, many of these birds must have been retrofitted WITHIN the production period, i.e. upto 1943, before the end of WWII, which is good enough for Smilo. So, even the 330 Hp version I found referred to could have been existed and may not be a typo, from the site I saw, but at least, with the video, and the comment on the contemporary AT-9 Jeep as having the same engine, we know that 300 Hp versions during the war did exist.

So, I´d propose one military version with 220 Hp and 7 cylinders, and another military version in different colour scheme with at least 300 Hp, but that´s just my suggestion.

Cheers,
Aleatorylamp

[smilo]

i say, do it your way, Stephan.
it may seem like i'm passing the buck,
because....i am.
as i see it, as long as you're the builder,
the choice is yours to make.
i'm sure, you'll do what's best.

as we are all well aware,
one can make one's self crazy
trying to make things gnat's ass perfect.
just remember, this project
is suppose to be a fun change for you.

that said,
may i direct you to your signature?
seems appropriate.

sorry, i am spent.
today's short trip,
giving my son a ride to work,
turned into a four hour production
of dealing with an ahole and my vehicle.
each unrelated, but a drag all the same.
i'm home safe and am in dire need of a nap.

[Ivan]

Hello Aleatorylamp,

You can of course build anything you like. That is the advantage of being the designer.

As we discussed earlier with the Baltimore, the engine variant (dash number) may make quite a difference and higher doesn't always mean better.
Consider that a B-26 Marauder, P-47N, F4U-1 Corsair, and F4U-4 Corsair all used a Pratt & Whitney R-2800 engine, but they did not all make the same amount of power.
Consider that the Curtiss-Wright CW-21 used the R-1820 with around 1000 HP while the General Motors FM-2 was getting 1350 HP also with a R-1820.
Look at the P-39 and P-63. Both used a Allison V-1710, but the power levels were quite different.

I have no doubt that a 330 HP Lycoming R-680 existed during this period. I do doubt that the military would have converted a significant number of PT-13s (if any at all) to use such an engine though. There was no point; this was a Primary Trainer. High performance was not necessary nor wanted in such an aeroplane.
After the war, many of these aeroplanes became surplus, but that would not have happened before the war ended.

The implausibility of a 330 HP PT-13 is my own opinion which is no more valuable than anyone else's.
I have not done any conclusive research to confirm my opinion.

Build what you want to build. You don't need anyone's agreement to do it.
Who knows, I may eventually try to build a "Stearman Special" myself at some point.

- Ivan.

[aleatorylamp]

Hello Ivan, hello Smilo,
Sorry, even at the risk of having me shot at dawn for being as persistent
as a bluebottle or a horsefly, I found another interesting article on a
Spanish site, albeit written in Spanish, of course:

http://avionypiloto.es/secciones/pruebas/stearman/

...by a guy called Dave Unwin who appears to be some kind of test pilot, flying what
seems to be a Navy N2S5 Stearman with yellow wings, grey body and blue tail.

Further down the text, there is a photo of the metal plaque on the biplane´s engine,
where it says it´s a Lycoming R-680-13, with Master Rod location at cylinder No. 7,
7:1 compression, engine spec number 1031-D, certified in 1941. It also said there was
a blower, giving the impeller diameter.

However, it doesn´t say anything about the RPM here, but at the bottom, the spec sheet
says 2200 RPM, for this 9-cylinder radial.

It also mentions under another large photo further below, that adjusting power to 25 inches
of mercury and 2000 RPM, you get an IAS of 100 mph and a fuel flow of 14.5 USG/H.

The second paragraph above the plaque, claims (in Spanish) it is an engine installed on the
N2JS, being the most powerful version, an R-680-13 of 300 hp, and that it had a 2-blade CV
Hamilton Standard propeller. It goes on to say that there was a single 46 USG tank mounted
in the centre of the top wing, and that the consumption was a voracious 20 USG per hour.

Well, I bet Smilo is happy because maybe it looks like he can have a nice and powerful wartime
stock Stearman! And maybe I am a bit less frustrated than yesterday!

What worries me is that it starts off saying it´s an N2S5 and then goes on saying it´s an N2JS...

P.S. Here´s an automatic online translation attached, from Spanish into English, for which I do
apologize, but frankly translating 10 pages (over 3000 words) properly would mean at least six
hours... so I did it with the Google translator in sections of about 3000 characters.

My Google browser only converts English into Spanish, not Spanish into anything else. But anyway,
it will save you from browser-translating it.
The style of the article is the typical Spanish flowery prose, which perhaps no Englsh-speaking
writer would express himself in!

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

Thanks for the translated article, obviously this N2S did not have its original engine.

Perhaps you are right. Perhaps you are not. You are the designer here. It is your choice of what to build.

I am only slightly curious from an academic point of view about the Lycoming R-680-11 that seems to be causing all the problems.
Otherwise, I have no great interest in the project which is a shame because this one has a tremendous amount of data available.
At this point, you certainly have done more research than I have, so go with what you believe; It is YOUR project!

- Ivan.

[aleatorylamp]

Hello again,
I´ve been downloading drawings and sketches with key measurements to double check, in order to discard inaccurate ones and fix the most usable one. A bit lengthy, but hopefully it will avoid later re-adjustments or corrections once building is underway.

The two places I´ve e-mailed about the possible 280Hp Stearmans haven´t answered, but I´ll discard the version completely - there´s little point. First of all, as Ivan says, performance would be limited by the propeller anyway. Secondly, I think I´ve discovered the reason for a possible incorporation of this engine, namely the severe engine shortage at the time, which forced the manufacturers to resort to the more powerful engine , of which there was more stock, but due to the wooden propeller, and perhaps even the gound-adjustable pitch one (which was also used), top performance had to be curtailed.

It is still strange, though, why so many sources state 135 mph instead of 124 mph for top speed for the same models. Even the 300 lb lighter version appears without weight reduction in other places.

Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,
Thanks for your post. I´ll e-mail the 2 links that I posted on this thread.
Perhaps they are not working for you.

Do you know what I think? The -13B did exist in the way I say, with a
280 Hp engine and a fixed prop or a ground-adjustable one, because
that´s mentioned somewhere as well. Maybe it had 6.7:1 compression, but
that is my own conjecture, and in this case must have used the strange
78 Octane gas I saw somewhere too, but it is also my conjecture.

Compression could have also been 7:1, using 87 Octane gas like on the
contemporary AT-9 and -9A Jeep, why not?

I have found no reference to compression, fuel octane or RPM for the supposed
fixed-prop 280 Hp R-680-11 engine. The correct top speed of this engine on a
Stearman 75 is not to be found anywhere, but can be inferred from the erroneous
indication of 135 or 136 mph top speed for all Stearman 75´s quoted by a large
number of sources.

I guess that RPM could be about 2200, because the AT-9 and 9-A´s R-680-11
ran at 2300 RPM with a CV propeller, delivering 295-300 Hp. So 2200 is also
my own conjecture.

The higher stresses on the airframe would not pose a problem because the
Stearman 75´s large airframe was extremely sturdy and the later use of much
larger engines proves this.

But, something made the FAA eliminate the 280 Hp engine for the -13B later,
most probably because they thought the engine was too strong for a fixed-pitch
prop, and hence unsafe, and possibly also because the likely 78 Octane gas
later ceased to exist.

However, they couldn´t stop the Brazilians, Cubans or Peruvians from using it.

What happened after the FAA Certificate was created, and when Internet appeared?
Most sites probably thought they were being smart or just careful, and simply
eliminated this engine from the list because of what they read on the FAA certificate.

Other sites didn´t eliminate it but lowered the performance specifications to match
FAA restrictions. Still others, strangely enough, show seemingly contradictory leftovers
of its performance i.e. the 135 or 136 mph, erroneously generalizing it for
all -75 Stearmans.

But, the fact remains: 2 sites show evidence of literature that refers to a
mysterious engine that in 1940 appeared on a large number of stock -13B´s,
and nowadays strangely only appears on -13B´s exported to South America!

I have posted the links to these two sites in previous posts.

Strangely enough, in the sim, the numbers fit in perfectly. I know you will argue
against it, saying stock propeller tables we used are not good enough, but I can
get interesting results using the same engine with the same Torque as for the
AT-9A Jeep, but with an 8.5 ft fixed-pitch propeller and 6:7 compression. I can
also use a slightly lower Torque, and have 7:1 compression as on the AT-9.

This gets me 134.5 mph at sea level at 281 Hp. If I decellerate to 220 Hp, I get
124.2 mph. I could further reduce Drag slightly, and manage to get 125 mph at 220 Hp
and 135.3 mph at full throttle. (Then, if I use a CV propeller, I get 145 mph...).

I´m sure you will say this is not a reliable way of testing, but in a general way,
it may be an indication that the incomprehensible specifications of the -13B model
might well be covering up something interesting!

This is like archeaology. Don´t you find it rather exciting?
Remember when Dr. Carter found Tutankhamon´s tomb, and Lord Carnavon went broke
financing him? Everybody else said the Valley of the Kings was dry, all dug up, and
they were literally standing on top of the only tomb that hadn´t been looted in Egypt!

Here we are looking at the evidence that´s staring us in the face, of a covered up,
stock Stearman 75 with a 280 Hp engine and a fixed propeller, of which 220 or 255 were
produced in 1940, and which the FAA decided was unsafe and simply scrubbed off the list,
putting in some haberdashery that makes no sense at all.

Time for a cup of tea!
Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,
Now I remember we made a wooden fixed pitch prop for the 1917
high-compression D.IVa Mercedes engine (max RPM 1400).
I´ll have a look at my notes on the angle entries upto 25 degrees.
Maybe I CAN do something!
Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,
OK, you said 3 days ago that I would need a graph for 10 degrees, but you also mentioned that the computer interpolates.

This means, as you also say, that the sim uses whatever values it finds in the 15 degree graph for a 10 degree pitch, which would be correct anyway, as shown by the results.

I doubt that performance will change by moving the present 15-degree graph to the 10-degree position, but of course, I could be mistaken.

That´s why I didn´t understand why you repeated that the test was meaningless. I knew it was meaningless, but for a different reason - it had all the old graphs. The point I was making, as I said, was that it was the first time I had managed to get a fixed pitch propeller reflected on the Beckwith gauge.

Changing the graph is easily done, so I´ll try it anyway, just in case I´m wrong and something does change.

Whoa!
Changing the graph to a 10 degree position is more easily said than done.
For the moment, it won´t budge, even exporting the table as a txt file, changing it and importing it again.
There is a decimal comma error - I use decimal points. I´ll have to change the computer settings and see if it works.

Whoa-2!
Changing the decimal point to a comma in the exported text file won´t work either.
Editing the label from 15 degrees to 10, is not allowed, neither in AAM nor in AirEd, and FDE won´t show the graphs, as you know.
We seem to be landed with the 15 degree graph that gives the sim the reading for its virtual 10-degree graph.
So then, if the values for 10 degrees are entered in the 15-degree column, so what? It works anyway.
If it works, why fix it?

Now, seriously... do you know of a way to move the graph, or make an extra one?
I remember you were using a binary or Hexadecimal editor to make alterations to these tables. Maybe that will be the only way - even if only to make sure that performance will or won´t get better...

Cheers,
Aleatorylamp

[aleatorylamp]

Hello Smilo, Hello Ivan,
Well... thanks Smilo, for setting up the thread. I thought it should be "yours"
because you sparked the idea for this new project.

And again thanks, Ivan, for your additional research, this time on the even more
powerful 450 Hp Pratt & Whitney R-985 engine option.

So, there are basically now 3 different motorizations:

A) A 225 Hp Continental 670-5 or -K engine, which would be
the "slow and easy" Army trainer (PT-17).

B) The 330 Hp 9-cylinder Lycoming powered version in the PT-13D scan.
This could also be a Jacobs R-755A1 base line 7-cylinder engine,
or its R-755A2 300 Hp variant,
or an R-755E even more uprated with reduction gearing. (PT18 or PT13)
Any of these would make for a more fun military trainer model with a bit
more of a bite, possibly the Navy version.

C) The 450 Hp Pratt & Whitney R-985 Ivan mentioned.

As the most powerful engine was also frequently fitted to post-war machines,
perhaps Option "C" would be for the civil souped-up version, which would leave
the military one maybe with the specs in the scan you supplied, or maybe we
could have two military ones, Army and Navy with 220 and 330 Hp, respectively,
and the civil one with 450 Hp would be a third variant?

I mean this just as suggestions to provide differences between the versions, that
would all have the same build. It will not affect the model build itself, so we can
do it whatever way you like!

Cheers,
Aleatorylamp

[smilo]

so many choices,
so many decisions,
so little time.
and it's up to me?
gosh...and we haven't even talked about
the crop dusters that saved the beast from extinction.
what was that "can of worms" comment?

seriously, as i see it,
make her too docile
and no one will want to fly it.
(well, maybe once or twice)
but, then again....
it would be nice to show the progression.

a more powerful, challenging
military trainer is in order.
yes, the Lycoming version.

and, of course, the civilian Pratt & Whitney.

in a dream world, three versions.

this is all contingent on you,
the builder and how much do you want
to mess around with visual accuracy,
building 6, 7, or 9 cylinder versions.
then, there's the air file work.

as you should know by now,
none of these tasks are in my department.
all i can be is a cheerleader
beta tester and critic.
that is, unless, you want to send me the afx files
and i could sequence the parts in ad2k.
in that case, build her as complex as you want.
BUT, then again, you know how speedy i am.

[aleatorylamp]

Hello again,
Perhaps it is best I post the link to the E-Book in question. There are also lots of other interesting trainers described!

The content available is given with permission, so I expect there is no Copyright infringement.

https://books.google.es/books?id=kIy...engine&f=false

If this link works, I could delete the images in the attachments, so as to save megas on my posts...

Cheers,
Aleatorylamp

[smilo]

no need to split the first and re post.
i forgot about the Ctrl + keystroke
to enlarge the screen view. works fine.
also, the link works.
i might suggest leaving the images,
until you get a upload ceiling warning,
then, delete them.
anyway, thanks for your efforts.

side note;
the jacobs being used in the sherman tank
is interesting, along with how it was done,
(how did they cool the thing, etc?)
but, it would take us way off topic,
so, i'll leave it at that.

stay cool

[Ivan]

Hello Aleatorylamp,

I would not be so certain that ANY data is 100% reliable.
This book is certainly more reliable than my unresearched conjecture, but if it is important to you, do some additional research.

I am glad you found what you were looking for.

I actually have been debating on revising the flight model for my Kawasaki Ki-61-I-Tei because a source I had used for reference for fuel tank arrangements is probably not as accurate as I had first thought. The book has pretty good data otherwise.

- Ivan.

[aleatorylamp]

Hello Ivan,
I am putting together a document with the different versions, their power and their speed indications, to have an overview of what´s happening. As you pointed out, there´s only one PT-17 version with 135 mph, and the engine is a normal one. The empty weight, has a typo stating 1036 lb, and should be 1936 lb - but typos are more easily identified than hidden things.

I had been hoping to find the higher speed related to a -13B (or even a -13C) version...

The more I think about it, the more it seems that the -13B with 280 Hp was officially throttled or limited to the standard 124 mph, for bureaucratic certification reasons on the grounds of the fixed pitch prop, to keep everything within limits, but thatextraofficially, the -13B was capable of a much higher speed thanks to its power.

Otherwise there would be no reason to name this batch -13B. The naming always seems to have depended on the motorization. So, the R-680-13 engine on these units may well have been the higher compression type with a 7:1 compression ratio, and the top speed then may have been higher even than the 135 mph I´d thought would be applicable here.

Incidentally, the blower indication on the plaque of the atmospheric 1941 300 Hp R-680-13 on the "false treasure" 1996 Stearman is stated as being a direct drive blower. If I am not mistaken, this would then just be a fan on the crankshaft, blowing a bit more air into the carburettor to get a bit more oxygen, which would then not be a supercharger with any critical altitude.

Anyway, before deciding on something definite for the 2 planned military versions, we´ll have to study the matter a bit more.

I have just seen your second post, thanks, and shall we say, I am trying to find the fastest and most powerful factory-original military version possible.

Because of the 2 or 3 different and colourful attractive military colour schemes, there are 2 military versions planned. To make these more attractive, the first one would be the normal 220 or 225 Hp version with 124 or 125 mph. For the second one, I´d like a faster and/or more powerful one, IF this were to have existed, and there seem to be certain indications that this MAY be possible.

However, should this only be a chimera, I will settle for a difference of only 5 Hp and a couple of mph, because anyhow, there will be a third model, a 450 Hp P&W powered civil aerobatic super hot-rod, so the apetite for more speed and power will be satified anyway.

OK, then,
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

If you are really going for the hotrod version, there was at least one with a Pratt & Whitney R-1340 installed.
I don't think it would be all that fast, but it should climb REALLY well with such a high power to weight ratio.
My impression is that if you really look at the operating limits, the 450 HP Pratt & Whitney R-985 wasn't noticeably better than the current 360 HP Lycoming engines.
The 450 HP was just a Take-Off / 1 Minute Rating and normal maximum RPM was only 1950 which is really low.
Not only that, but the R-985 is a substantially heavier engine.

- Ivan.

[aleatorylamp]

Hello Ivan,
So here I was trying to keep things simple... wishfull thinking.

Anyway, I remembered the 2-position 2-blade prop you made for the FW-200 Condor, and transferred the prop efficiency table (whose graphs drop to zero) over to the Stearman .air file, and entered 10 degrees for the fixed pitch setting. I suppose the max. and min. pitch setting are ignored by the sim´s .exe file.

This efficiency table is of course for an 11 ft propeller on a 720 Hp engine, and good for 247 mph, so I suppose the propeller efficiency tables have yet to be adjusted.

For the moment, strangely enough, the Beckwith gauge still always shows 20 or 21.4 degrees pitch after take-off. Perhaps what it is doing is reading the angles used along the blade, even if the blade itself is at 10 deg. setting? Or, it isn´t ignoring the max. and min. pitch settings I thought it would override. I´ll try putting both of them at 10 too.

I´ve printed out your post and graph, and will see which way I have to alter the efficiency graphs for the indicated j-factors. The concept then is, that the graphs indicates the engine power needed by the propeller to get a move on. So, to make the propeller more efficient, I´d have to reduce the height of the graphs, I suppose.

I´ve also now (for the first time) understood the intricacies of what the FAA document mentions regarding propellers. A 10-deg. setting for the 9-11.7 deg. range given would then in principle sound quite sound.

Thanks a lot for the calculated data! I should have mentioned that before.
Well, let´s see what happens.

Update: Yes indeed, now the fixed 10 degree pitch remains fixed!
All prop pitch entries in the FD have to be entered at 10 degrees, meaning that the sim.exe doesn´t override anything!
Now the Beckwith gauge reports a constant 10 deg., and Hp has rocketed from 225 to 312 Hp. RPM have gone up to well over 2900 RPM instead of staying at 2000 or so, and speed is rather fast, to say the least.
So, at least it´s a starting point for adjustments, I´m glad to say, and I won´t as yet alter the FW-200 efficiency graph then.
Fine, fine. Maybe it´s getting easier now.

Thanks again,
Cheers,
Aleatorylamp

[aleatorylamp]

Hello Smilo,
Not to worry, it´s no problem!
There´s enough time, and the can of worms only referred to Ivan´s comment about some SCASM-improvable shapes on the existing red version which he hinted at, were one to try and SCASM improve the red one to have exposed cylinders.

Thus, I´d personally prefer to build a new one, as you also voiced.
So, as I am going to be the AF99 builder, and I also like the Stearman very much, I would want to make it as per your preferences, because you had started off the idea.

We have already coincided that it would have exposed cylinders, so a cowled version is discarded.
Also, I´ll gladly abide by your choice of which model to supply, because it was your idea to have a good model with exposed cylinders, - a more modern build than FS5 model, and an exposed cylinder model in the quality of the red version.

Must rush, I´ll continue later.
Cheers,
Aleatorylamp

[Ivan]

Hello Again, Gentlemen,

From what I have been able to find, there was yet another version: the PT-27 which was the designation given to Lend-Lease versions to Canada.
Also, if you intend to build them as they left the factory, the 330 HP version appears to be a re-fit and not a factory produced version.

I found a pretty good site (actually a bunch of sites) that describe the different models and also looked through the entry in my copy of Jane's and there was no mention of a 330 HP PT-13.
That isn't absolutely conclusive, but it does seem odd to build many similarly powered aircraft models and then build one primary trainer with 100 more HP.

If you intend to stay with AF99, I have an idea for designing the exposed cylinder Radial Engine as a single Component.
I do believe however that you will end up with a much better model with AD2000 instead of AF99 because of the ability to face Polygons the direction you want them, so that would allow a properly shaped engine instead of the minor distortion that would be required in AF99.
I would build a demonstration model of the engine if I had a working Development Computer at the moment.

- Ivan.

[smilo]

funny you should mention the pt-27.
according to the article,
about 300 were build
with several modifications.
the most prominent being a canopy.
BUT, the navy intercepted the canopies
for their own cold weather use.
the Canadian planes were shipped
back in short order.

to be honest, which model(s) are built
doesn't really matter to me,
as long as there is a less powerful
military version and the civilian hot rod.
heck, i would be more than satisfied
with just the military Lycoming version.

Stephan, just for fun,
build the engine block
and the number one cylinder.
then, ship me all the parts.
i think i might be able
to put an engine together.
who knows, it might be fun.

[aleatorylamp]

Hello Ivan,
Well, OK, then maybe 95%...

Another possibility would be to e-mail some flying clubs that participate in Stearman Fly-ins, that could possibly have members who would remember actually flying these aeroplanes, but I´m satisfied enough as it is.

The 186 mph top speed in the AV History magazine, as opposed to the usual 124 or 135 mph, is accounted for, and so are the other comments elsewhere, relative to the greater difficulty of higher powered Stearman trainers.

It´s rather fortunate that the data on this biplane is contained in the first 89 freeware pages of the 471-page E-book!

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

Since I don't have the Aviation History article to reference, I will not comment on its contents.

Not sure what you mean about a 186 MPH top speed.
If this is maximum diving speed / indicate air speed, it makes sense.
If this is maximum level speed, it makes no sense whatsoever unless the airframe has been heavily modified.

I don't know what you mean about the greater difficulty of higher powered Stearman trainers.

- Ivan.