Boeing Stearman Model 75

Hello Ivan, Hello Smilo,
The exposed cylinder radials I made for the Udet Flamingo and the Klemm Monoplane
are rather simple ones with square cylinders and 2D pushrods and sometimes 2D exhaust rings, or also exhaust structures.
An improvement could possibly be achieved by making hexagonal or octogonal cross-section cylinders, at the cost of a large number of parts, of course - and bleeds, I imagine.

I made 5, 7 and 9-cylinder ones (I´d forgotten about the latter).

The quality is not spectacular, to say the least, but they do give ambience, I feel.
Here´s a screenshot of the 7 and 9 cylinder engines on the above mentioned planes.
> 7-Cylinder 110 or 125 Hp Siemens Halske SH12 or SH12a , for the brown and red Udet Flamingo respectively, and a
> 9-cylinder 45 Hp Salmson 9AD for the Klemm Monoplane.
There is some bleedthrough with cylinderheads.

Building details:

7-cyl engine: made of 3 components, 1 part and 3 structures.
>>Diameter: 42.3 inches for Stearman 75
-Star-engine component: 30 parts. Includes forward and rear star shapes, 3 cylinder panels (sides and top), and 1 tween-cylinder panel per cylinder.
-Pushrod component: 15 2D parts - one disc and 14 rods).
-1 forward 2D exhaust ring with hooked exhaust outlets.
-Two lower exhaust pipe structures below nose, slanting backwards.
-One prop-axel structure.

9-cyl engine: Made of 2 components, 27 individual parts, and 1 structure.
>>Diameter: 43.5 inches for Stearman 75.
-Star-engine component: 29 parts. Includes forward and rear star shapes, 3 panels per cylinder (sides and top).
-Pushrod component: 9 2D parts "V" shaped.
-Short on-cylinder exhaust ports: 3 parts per cylinder - 27 parts.
-One prop-axel structure.

Cheers,
Aleatorylamp
 
as i've said numerous times before,
the upper seventies is pushing my comfort level.
yes, i'm a temperature wimp.
i'll not deny it.
i like living in an area,
where the moist, cooling winds
come in off the Pacific.
that's my comfort zone.

about my model 75 interest...
i read the article in Aviation History magazine
and my interest was sparked
when i came to understand
that most WWII pilots
learned to fly in the beast.
therefore, i thought it might be
a good candidate for the Conspicuous thread.
other than that,
i know very little about the aircraft.
...and so, here we are.

as a side note,
i was the final graduate
of the Joint Ops cfs multi player flight school,
as they were switching over to il2.
in that course, we started in the T-6-50.
it was a lot of fun, but, looking back,
the model 75 might have been more appropriate.

as for the Curtiss P-6E,
with a few exceptions,
my main interest is in WWII era aircraft.
consequently, the Curtiss P-6E
does not fit into that time frame.
not that it isn't interesting,
just, not so much to me.
of course one could argue
that the L10 is not WWII era,
but, frankly, i don't care.
i've always been a sucker for the twins.
(pun intended)
 
ps...another interesting model 75 point
is that it incorporated the naca 2213 airfoil,
which earlier models did not have.
apparently, this is the same airfoil
used at the spitfire wing root.
 
Hello Aleatorylamp,

Send me a couple of your current projects with the exposed radials. I want to see where the bleeds are and where the bleeds are.
I believe I might be able to cut down on the resource (Component) usage but probably won't be able to improve the quality by much unless I go to the hexagonal cylinders that you were describing.
I suspect that in general concept I am thinking of the same ideas that you are already using.

I believe the Lycoming engine came in a B series and a E series engine. The B series was a low power version and was the version installed in the Model 75 so 220 HP was about all the originals were good for.
The Jacobs engine had about 5 HP more and was the distinguishing feature of the PT-18.
Perhaps the Model 73 and 76 "Fighter" versions had better engines but I haven't found much information on those yet.
Keep in mind that this beast was a docile, sturdy little primary trainer and not a hotrod by any means.

As retrofits, apparently, folks have even gone up to a Pratt & Whitney R-1340 which makes this into a seriously high powered cotton ball.


Hello Smilo,

Perhaps the P-6E isn't a good WW2 example, but it sure is an elegant looking aeroplane.
The F11C looks a lot like the Curtiss Hawk III which served in the Chinese Air Force as targets for the Japanese so that actually would be a WW2 type.

I am also starting to get attached to some of the twins but realise that I really have no idea how to handle them well.

- Ivan.
 
Hello Ivan,
Thanks for the different details regarding the engines. There definitely is some difficulty in pin-pointing the power of the different engines that were used on the model E75/PT-13-D motorizations because of the confusing information coming from so many different sources. Anyway, that can wait.

Before you fire up your Development machine and risk reducing its longevity, I´d like to say that perhaps only some question-and-answer type coaching will be necessary based on some screenshot viewing. I wouldn´t want to help ruin your machine!

The simple box-cylindered radial engines I mentioned and sowed in my last post come from 2010 and 2011. At that time I was still afraid of exceeding 100% parts count by much - I didn´t know enough about AF99 to maximize its capacities.

The biplane with the 7-cylinder model still has one free component left, and only 103.7% parts count, and the monoplane is only at 67.5% parts count with 13 free components left. Both also still have a number of free structures left. The front flat disk pasted to the engine could well have been made into a conical structure. I had done it on a 5-cylinder engine for the monoplane too.

With this kind of parts count, most probably hexagonal cross-sectioned cylinders WILL be possible. From what you were saying, I could deduce that one could split up the main engine component ("star") into maybe two left/right halves. I´ll prepare some more precise screenshots of the existing engines to show the bleeds.

Cheers,
Aleatorylamp
 
...and so, off we go, again,
into the wild blue yonder.
so many choices,
with so much conflicting
or insufficient data.
what to do? what to do?
i'm sure it will all work out in the end.

mean while, back at the ranch,
there's, still, so much work to do.

~~~~~~~~~~~~~~~~~~~~~~~

thanks for reminding me
about computers being on their last legs.
i need to back up the data
on my xp development machine.
there are so many years worth
of irreplaceable stuff.
one never knows when
the steadfast old beast
might want to give up the ghost.
it's not like there haven't been warning signs.
 
smilo said:
...and so, off we go, again,
into the wild blue yonder.
so many choices,
with so much conflicting
or insufficient data.
Click to expand...

Hello Smilo,

The Boeing Stearman Model 75 is hardly a case of insufficient data.
In fact there is so much data that there isn't much you CAN'T find out about the machine.
You have one in your local area.
I have one in my local area as well.

Around 8,000 total aircraft were produced. Enough spare parts to assemble another 2,000 aircraft were also produced.
Of the 8,000-something total airframes, about half still exist today.
Several THOUSAND are still airworthy.
The FAA has a LOT of data in their Type Certificate which is more than you can typically find about WW2 types.
I have come across 3 or 4 sets of pretty good drawings and I wasn't even looking hard.
There is a pretty easy to find flight instruction guide available and at least two or three pretty good flight evaluations to give a good impression of flying characteristics.
Basically it was pretty well behaved except for a tendency to ground loop rather easily.

Regarding conflicting data, a very small amount of reading will give a pretty good idea of what the original aeroplane really was.
One has to have the sense to distinguish between period sources and current sources. Each is good in its own way and for different details.

The first of these aeroplanes flew in 1934, so one has to consider how much equipment would be original in an example that is still flying today.
The fabric probably would have been replaced at least once.
The engine probably would have seen several overhauls or replacements and here is where life gets interesting:
If you owned one and needed an overhauled or replacement engine, would you keep it at the original 220 HP for historical reasons or would you go for a rebuilt zero-time engine with some modern accessories and 50% more power that weighed the same and looked the same?

This is one of those cases where there is so much data and it is so good that I have to actively resist the urge to start gathering information and build my own version of this beast.
It would not be hard, but is yet another diversion from things that deserve to be completed.


Hello Aleatorylamp,

The distinction between PT-13, PT-17, and PT-18 is basically the engine that was installed. All engines were of pretty similar performance and weight.
I believe there was only about 20 pounds difference between the lightest and heaviest of the engines originally installed.
The PT-27 as stated earlier was a Lend-Lease designation for the PT-17. I don't know for certain, but I suspect the designation change was probably because of some different equipment installed for the Canadians.

Here is some data I found a few days ago that I believe is reliable. I just copied it directly from a site to a MS Word document but neglected to save the URL.

PT-13 with a Lycoming R-680 engine (9 Cylinder) – 2,141 built.
PT-13 Initial production, R-680-B4B engine, about 215 HP
PT-13A R-680-7 engine, about 220 HP.
PT-13B R-680-11 engine, about 225 HP
PT-13C The same as the PT-13B, but modified for instrument flying
PT-13D R-680-17 engine, around 225 HP

PT-17 with a Continental R-670-5 engine, about 220 HP – with 3,519 delivered.
PT-17A Modified for instrument flying
PT-17B Modified with agricultural spraying equipment

PT-18 with a Jacobs R-755 engine, about 225 HP- 150 built.
PT-18A Modified for instrument flying

This information may also be found on Wikipedia in almost exactly the same format.

- Ivan.
 
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
 
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.
 
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.
 
Hello Ivan,
Thank you for abiding so patiently with my insistence on the possible use of 300 Hp engine during wartime use.
By the way, I can´t find the site where I saw the 330 Hp anymore, which was one of the first I found. It´s only 300 Hp now...

Most sites that go into any detail, coincide exactly with what you say, primarily that the 300 Hp engined PT-13D versions were post-war conversions (mainly acrobatics).

That might also explain the comment on other radial-engine related sites, that the PT-13D had the same R-680 (-9 or -13) as the contemporary 1941-1943 Curtiss AT-9 Jeep (300 Hp). I agree that the numbers after dashes on the engine model numbers are not a sequential increase indication for engine power. The dash numbers possibly add to the confusion, and a given dash number perhaps didn´t always mean the same engine power.

What throws me off, and has done so from the very beginning, it the figure of 186 mph top speed and 46 USG fuel tank stated in the AV History magazine scanned by Smilo, instead of the usual 124 or 135 mph and 40-43 USG tanks quoted for the 220-240 Hp engines used on this aeroplane.

Another comment I´ve read that also throws me off, is that some military bases were a bit afraid of using the higher powered Stearman 75 trainers on novices because of their difficulty and danger, and preferred to keep beginners on the lower powered, more forgiving ones. Also it was stated, that the higher powered Strearmans were more demanding on trainees´
skills, and were built because the lower powered ones were too easy.


So, although the majority of the thousands of Stearman 75 trainers used during the war had 220-240 Hp engines, I don´t think that a 300 Hp wartime version can be completely discarded... but maybe you´re right, maybe there wasn´t a 300 Hp Stearman during the war.

Anyway, it won´t affect the model itself - the 9 cylinders are there anyway, so there´s time to decide yet!

Cheers,
Aleatorylamp
 
Success!

Hello Ivan, Hello Smilo!
I found something else! This time it is probably 100% reliable:

It´s an E-book titled: "American Military Training Aircraft: Fixed and Rotary-Wing trainers Since 1916", by E.R, Johnson, Lloyd S. Jones. It contains a long chapter on the Boeing-Stearman PT Series that was built starting in 1934.

The interesting line says there was a delivery of
"...255 PT-13Bs (280 hp R-680-11 engines) in 1940, making it the Army Corps´ most important type of military trainer." - the "most important type" comment obviously includes the numerous lower powered versions ordered on several occasions before 1940.

Attached is a screenshot of the first part of the text on the Stearman PT´s. The chapter has lots of photos and further details, but the main thing is here, in context. If you save the .jpg image it´s easier to read.

So, Ivan was totally right about there not being a 300 or 330 Hp powered model until after the war, but we do get a nice and powerful 280 hp powered Army one for Smilo!! Then we can do the Navy one with 220 Hp, and the Aerobatics one with 450.

That´s good...

This new information would account for the pieces of information I mentioned in my last post that didn´t seem coherent with there only being 220 Hp or so versions.

Smilo, sorry to hear about the car and the ahole...
Things seldom come alone. They come in three´s , so be careful about a ppossible third problem. Life seems to send what one hates. I often get aholes on the road, and the result is that now I hate driving, which I used to love. Now I love taking the tram, but I get aholes on pedestrian crossings walking to the tram. So it´s on the road too, but not in the car. Less stressing, but perhaps more dangerous...
I mean... Why can´t life be perfect?!

Cheers,
Aleatorylamp
 

Attachments

  • PT-13 main-.jpg
    PT-13 main-.jpg
    92.7 KB · Views: 0
Last edited:
it's very hard to read, but,
doesn't this page, basically, confirm
what was said in post #3?
okay, the engine - designations weren't there,
but.....oh, never mind, i've got pixels to go count.

it's interesting that only 150 units
were produced with the jacobs r-755,
because the engine was needed
to power the sherman tank.
priorities
 
Hello Smilo,
OK, I understand - but Post #3 didn´t contain Hp information.
Anyway: 3 models, 220, 280 and 450 Hp.
It´s nice to be able to confirm historically correct specs though.

So the 2 military ones would be: 280 Hp Army in blue-and-yellow, and 220 Hp Navy "Yellow Peril".

Unfortunately, even though the image I put together, taking out the photos, for upload is clearer, downloading it, it is not as clear. As the images come from an E-book available, it´s not possible to get them any clearer.

I noticed the comment on the Sherman tanks´ need for the engines too! Radial engines probably came in handy because they were shorter than the usual in-line ones.

Here´s the second part of the article, where I also took out all the photos. It talks about the Navy versions, and contrary to what I was expecting, they didn´t have any of the powerful ones.

By the way, I could split the first part of the article into two and sent it in two different posts. It may be a bit clearer to read. The second part in this post is smaller, and looks clearer. So, if you want, I can split the first part and re-post.

Cheers, and have a nice cup of tea!
Aleatorylamp
 
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
 
Hello Smilo,
Off topic? Naaaahh. Radial engines are on topic, so the Sherman is too!
I just found a diagram.
I was wondering how they´d done it too - horizontally? in the middle?...
Actually, they stood it up, and it was so short that it fit snuggly into the aft section. Cooling by water, it seems, because there´s a water pump and a radiator, so they must have put jackets or whatever you´d call something like that around the cylinders.

If we put some wings on it it will surely fly in CFS1 !!!:very_drunk: ...and we´ll ask Ivan to fine tune the FD!
Cheers,
Aleatorylamp
P.S. Thanks for the Ctrl + keystroke. Depending on the size of the image, it works quite well!
 
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.
 
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
 
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.
 
You must log in or register to reply here.
Back
Top