Boeing Stearman Model 75

Hello Ivan,
Thanks for your comments! The AV Magazine I mentioned is the September Issue of the Aviation Magazine 2017 that Smilo scanned and posted in Post #6, that shows a top speed of 186 mph, whereas normally it is stated elsewhere at 124-135 mph.

Actually, I was just going to ask you if this would perhaps be IAS, because it seemed to me to be a bit much to get an increase of about 60 mph for a difference of 60 hp. Perhaps more plausibly it would be about 140 mph TAS?

Update: This makes even less sense, because IAS on the Beckwith gauge stack is lower than TAS.
Maybe it´s not 186 mph because it´s difficult to read on the AV Magazine article, and it´s really 136 mph, as opposed to the 124 mph of the 220 hp SPT-17. If this difference is more plausible, then the AV Magazine is referring to the 280 Hp Stearman PT-13B. It would also account for the fact that top speed is quoted at 135 mph by some sources instead of 124.

The greater difficulty of the more powerful Stearman 75 for novice pilots was that the more powerful engine increased the problems on the ground - ground loops were mentioned.

I hope this helps.
Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,

Not everything in print is correct. I do not believe the information in that article is reliable.

I found the You-tube video about the 1943 era 300 HP Lycoming R-680 engine on a trailer.
It is a later series engine than the ones in the Stearman because it uses a Hamilton Constant Speed Propeller and the earlier series engines could not handle a propeller governor.
I found a copy of an operating manual for the R-680 and it show there were many models of the R-680 and it appears that most of the power gain was due to a higher compression (and higher octane fuel) used by the later versions. I just have not found what version corresponds to the R-680-11.

An easy way to prove what models of the R-680 would have been installed in the Stearman would be to find out what the compression ratio and octane requirement are for the R-680-11 and what standard of fuel was used for training in the United States. (The B series engines used 73 octane minimum and I believe the E series used 87 octane.)

The Wikipedia page lists Jane's in its bibliography and I actually own the book, but although the book entry has an excellent technical description, it does not have what I am looking for either.

- Ivan.
 
Hello Ivan,
Your expertise is definitely bearing fruits towards clarifying the enigma of some possibly more powerfully motorized military version. Thank you for your comments on the video with the 300 Hp version and the CV propeller, which further confirm that I can safely discard this one, as I did yesterday and as you had already pointed out before.

The most commonly quoted top speed for the Stearman 75 is 124 mph. I seem to remember you once saying that performance increases were about 5 Hp per Mph, so the speed difference between 220 Hp and 280 Hp (60 hp) would be about 12 mph, making it plausible that the more powerful units could have a top speed of 136 mph. If a biplane´s airframe were to further reduce this difference a bit, we would arrive at 134 mph or 135 mph, which is a figure quoted on several other sites.

OK, I agree that just because it´s printed, it doesn´t mean it´s correct... our literature teacher at high school often said that, but here there are quite a few discrepancies that have piqued my curiosity. Granted, initially, in my ignorance, I was misguided by more exaggerated mistakes in some sources, but now it seems to be narrowing down to more plausible results.

Update:
The most commonly quoted top speed for the Stearman 75 is 124 mph, like the Wikepedia in Spanish amongst others.
Other sites quote 135 or 136 mph, like the Wikipedia in English, amongst others.
Both refer to the 220 Hp Engine!
Obviously something is quite wrong: 124 mph and 135 mph for the same engine power?!
Then, the R-680-11 is quoted elsewhere as giving 225 Hp, but 5 Hp don´t account for 11 or 12 mph speed difference.
Wouldn´t it be more likely that 280 Hp would account for that?

It is interesting you mention Fuel Octane. I saw a rather unusual one, I thought: 78 Octane. If usually 73 was normally used for the 220 Hp engine, maybe the 78 Octane would coincide for the 280 Hp one.

I´ll get there in the end!
Thanks again, and cheers,
Aleatorylamp
 
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P.S.
There are even a couple of South American sites in Spanish, that go even further, claiming that the 220 Hp engines conferred 186 mph, which sounds even more mistaken.

The error may come from the fact that several Stearman PT-13 batches were exported to South America with 300 Hp R-680 radials, and one site actually cites 186 mph top speed for this model. Even this seems a bit optimistic, to say the least, and
at most I suppose it could have been 145 mph for 300 Hp, but we don´t need that anyway.

In conclusion, most probably the 186 mph come from a misinterpretation of the 186 mph Vne which is quoted for the Stearman 75, and Vne doesn´t care about Hp. Then, I said before, the Aviation History Magazine article´s top speed quote that I mistakenly took for being 186 mph, must be a blurry 136 mph, so that´s my own fault for being stupid.

Incidentally, I just discovered that the cowled red model I found on the simviation page does not really look like a PT-17 at all, but rather like Stearman Model 6 "Cloudboy".

This was the predecessor, or base model that led to the Stearman 75, of which several units were built, with a list of different YBT- designations and motorizations that anyone can get lost in. It is even difficult to see how many were built - 7? 15? Who knows? - with all those re-engined ones, it´s impossible to tell.

Two had 300 Hp P&W Wasp Junior and 300 Hp Wright R-975-1 engines, and some others had different 165 and 170 Hp engines of different makes (Lycoming, Continental, Wright, Kinner). From what I can deduce, it appears that the 300 Hp "Cloudboys" were the ones that were too difficult for novices to handle safely on the tarmac, not the PT-13´s. Then, the military YPT- designations of these models also had one with 200 Hp engine which was quoted to have had 200 mph top speed, which is incomprehensible as the Model 6 Series was basically the same as the Model 75.

All this just adds to the confusion. It seems to have been normal in that time for manufacturers to do short production runs as experimentation led to further innovation.

Anyway, Cheers,
Aleatorylamp
 
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The 280 Hp Stearman

Hello Guys:
Here is further proof of the existence of the 280 Hp powered versions.
On the following internet page:
http://all-aero.com/index.php/54-pla...-1--n2s--pt-18

...it says, just before the end of the first section between the first two photos:

"Then came 220 PT-13Bs with the 209-kW (280-hp) R-680-11s of which six became blind-flying PT-l3Cs, and 895 PT-13Ds with R-680-1 engines."

The other text had mentioned 255 of these, and here there are 220, but that wouldn´t be all that important.
So, in conclusion, there was a 280 Hp poered PT-13B, and my calculation for a top speed for this aeroplane would be 134-136 mph. Is this plausible?

Cheers,
Aleatorylamp
 
Aleatorylamp said:
The most commonly quoted top speed for the Stearman 75 is 124 mph. I seem to remember you once saying that performance increases were about 5 Hp per Mph, so the speed difference between 220 Hp and 280 Hp (60 hp) would be about 12 mph, making it plausible that the more powerful units could have a top speed of 136 mph. If a biplane´s airframe were to further reduce this difference a bit, we would arrive at 134 mph or 135 mph, which is a figure quoted on several other sites.
Click to expand...

Hello Aleatorylamp,

I don't know where you got that idea from, but it wasn't me because it simply makes no sense.
A Late model Spitfire Mk.IX had about 1000 HP more than a Spitfire Mk.I but it certainly didn't go 200 MPH faster!

The 124 MPH maximum speed is probably correct for a stock Stearman 75.
The 186 MPH is a maximum diving speed.

I haven't done any calculations to check what the 136 MPH maximum speed might be but I am guessing it might be a racing version of the Stearman 75 with more streamlining, more horsepower and probably a Constant Speed Propeller.

The actual minimum requirement is 65 octane for Lycoming R-680 B series engines and Continental W-670 engines.
Jacobs R-755 engines require minimum of 73 octane.
Lycoming R-680 E series engines require minimum of 87 octane.

Pratt & Whitney R-985 also requires minimum of 87 octane.

There is a LOT of data out there on the Internet and it is very easy to find with a search engine.

- Ivan.
 
Hello Ivan,
Thank you again for your counsel and your comments.
Yes, there IS a lot of data.... and sometimes in some particular aspect, it´s difficult to pinpoint.

I suppose that the 5 Hp giving 1 mph increase in speed would apply only to slower speeds, not to fighter plane speeds like the Spitfire, where the power difference you mention would probably only mean about 100 mph - i.e.10 Hp for 1 mph.

I remember it only as a general rule of thumb, for more "normal" speeds, perhaps for speeds of the old bomber biplanes, well below 100 mph. I must have got it from somewhere else. And of course it would depend on the plane.

OK, I agree that 186 mph is Vne, so it is confirmed that we can discard that speed reference.

The airframe of the 280 Hp versions was identical to that of the 220 or 225 Hp powered ones. This means we can also discard streamlining, and as it was a basic trainer, not intended to complicate trainee´s lives, it had no flaps and props were of the fixed type. Thus, we can discard CV props too. There was only an intentionally created difficulty on the Model 75 to make it a less easy but still basic trainer, namely placing the tank in the wing - hence the ground loop risk.

The sim appears to give me roughly 20 mph difference between 220 and 280 Hp readings, depending on some of the drag settings, and I´m getting about 138 mph for 280 hp, and 219 for 220, but that still seems too fast. I´m trying not to meddle with the propeller tables, only with the different Drag types, and Torque + Friction.

Anyway, things seems to be falling into place slowly.

Thanks a lot! Cheers,
Aleatorylamp
 
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Hello Aleatorylamp,

Regarding Maximum diving speed, if I were you, I would keep it as a reference for tuning the AIR file instead of discarding.

Regarding a stock 280 HP version of the PT-13, the more I read, the less inclined I am to believe that such a thing actually existed.

You probably will have to tune propeller tables anyway because the pitch angles typically run from about 7 degrees to about 13degrees maximum thus the stock tables won't work all that well for you not to mention the power coefficients are unlikely to match up.
It is unlikely that your power / drag tests are meaningful currently because of other data mismatches.

I am a bit puzzled as to why you think a gravity feed fuel tank in the upper wing center section has anything to do with ground loops either as a risk or as a cause.

- Ivan.
 
Hello Ivan,
I meant 186 mph as a discard for a top speed reference, not to discard the Vne.

The Drag/Torque adjustments are actually working quite well, because the engine
is very similar to one we had some time ago. Possible data mismatches would not
necessarily have to be very large, as the difference in power is only 15 Hp.

I´ve moved the update from my previous post into this post, for context reasons:

The engine I´m using is a slightly down-toned version of your 295 Hp R-680-9 from
the AT-9 Fledgling. It has 75.55 cu. in. cyl. displacement, 7:1 compression,
(same as the AT-9), but with a fixed pitch propeller (same diameter, 8.5 ft),
at 22 degrees blade angle, but a little lower on the Torque - 64.1 instead of 65.0.
RPM are at 2200, whereas the At-9 Fledgling twins did 2300 RPM. < this line is corrected!

Adjusting Torque and Drag more conveniently, at the moment I´ve got S.L. top-speed
for 220 hp at 124.2 mph, and flooring it to 280 hp, gets me 134.5 mph. My uneducated
impression would tell me that the sim could be giving a reasonably good approximation.
A cook would say "If in doubt, throw it out", and I´d say, "When doubt sets in, try the sim."
However, I still suppose that you will say that a 10 mph increase for an increment of 60 Hp
is too high, even though we are talking about speeds of around ony 130 mph,
which is not terribly fast.

As regards the non-existence of the 280 Hp engine, I´m sorry, but I´m inclined to disagree
with you, as it´s already on two different sites that a couple of hundred wartime examples are
mentioned. Compared to the thousands of units produced, the small proportion in the number of
machines could be the reason they are not often mentioned.

According to one source, the central top wing main tank raised the centre of gravity and made the
plane intentionally top heavy. That´s what they said...

Anyway, sorry to be such a bother, but if there is a possibility of making the two military versions
have notably different performances, it would add to their appeal.
Let´s see what else happens...
Cheers,
Aleatorylamp
 
Bingo!

Hello Guys,
I think I´ve decyphered what´s going on with the different speeds and hp for stock Stearmen:

Summarizing:
- Some sites say top speed for 220 hp powered units was 124 mph, others say 135 or 136 mph. WHY?
- Several sites state top speed for 220 hp (e.g. R-680-5) powered units, at 124 mph. OK!!
- Two sites mention 220 or 255 PT-13B aircraft as having 280 hp R-680-11 engines. OK!!
- One of these 2 states top speed for the 280 hp R-680-11 powered units was 124 mph. WHAT??
- The other site quotes no speeds. WELL...
- Several sites ignore the existence of the 280 Hp engine on military Stearmans altogether. FAIL!!
- Several sites and Wikipedia mention the Stearman-75 engine as being the same on the AT-9 Jeep. OH?

But, wait a minute... the AT-9 Jeep (or CW-25 Fledgling) had 295 or 300 hp R-680-9 radials. So what´s going on?

Well...The improvement of the AT-9 Jeep was the AT-9A Jeep, with better hydraulics and avionics,
and the engines had improved ignition. They were two 295 or 300 hp pòwered R-680-11 radials!

So what´s the difference between the 280 hp R-680-11 engine on the PT-13B Stearmans and the
295 or 300 hp R-680-11 engines on the AT-9 Jeep or Fledgling?

On the engine? ABSOLUTELY NONE!! It is THE SAME ENGINE!
It was the AT-9A´s CV propeller and the fixed pitch one on the Stearman that made the difference.

15 or 20 Hp less on the Stearman because of the more inefficient, fixed pitch prop.

So... How fast can a 280 hp Stearman-75 go in level flight?
I bet it could do 136 mph!!

Cheers,
Aleatorylamp.
 
Hello Aleatorylamp,

As I said before, you can obviously build whatever pleases you.

<sigh> Basic research is important. Some reference are reliable. Some are not as you already know.

As I stated in Post #8, The FAA Type Certificate for the Stearman 75 is A-743.
I believe the data there is about 98% reliable in the Military context and almost 100% reliable in the specifications context.
You should read it.
I wish I had this kind of data for projects I work on.

Your use of the AT-9 Jeep engine specifications for the Stearman 75 is mostly incorrect for the following reasons:
The Lycoming R-680 B series engines as used in the Stearman only had a 5.5:1 compression.
That is why they could get away with 65 octane fuel.
That series engine also had no ability to run a constant speed propeller, but they had adjustable pitch props at times probably as a modification.

The higher horsepower Lycoming R-680s had 7:1 compression and need 87 octane fuel.
The fact that your other engines use a constant speed propeller confirms that they are not the same series of engine regardless of designation.

The octane labelling is something the FAA seems to take pretty seriously.
I read an article about their requiring octane labelling even for a Fokker Eindecker replica that needed 60-something octane fuel.
The author thought it was pretty ridiculous because finding something that low is pretty much impossible, but the FAA makes the rules in this country.

The Type Certificate lists PT-13, PT-13A, PT-13B, PT-13C, and PT-14D as all requiring a minimum of 65 octane fuel....
Perhaps it is incomplete, but I am much more inclined to believe that it is correct with the information presented thus far.

The Type Certificate (and other places) also gives a lot of Propeller specifications for the various engine models INCLUDING some retrofits.
You AT-9 propeller has both an incorrect diameter AND incorrect pitch, and I know how those propeller tables were derived.

With that many data mismatches, one has to wonder how many conclusions from this testing are reliable.

My apologies.
- Ivan.
 
Hello Ivan,
I read the FAA A-743 certificate, and see your point. I find it quite bizarre.

The higher powered engines were then only retrofits, and even so, were limited to 125 mph!
Why are there so many references to a 135 or 136 mph top speed?
There are also two sites that say they had adjustable pitch propellers, probably confusing
post-war retrofits with wartime machines.

The exported versions of the -13B didn´t seem to have these restrictions, and apparently
were of the same type. Maybe that´s why these are quoted as having 300 Hp power.

One would think then, that the -13B´s were also retrofits, wartime retrofits.
Why would anyone otherwise bother to say they had 280 Hp in the first place,
or that they were the same engines as the AT-9 - actually the AT-9A in reality,
when they weren´t? But then they wouldn´t be called -13B I suppose.

Were these sources all so incompetent that they made such obvious mistakes and left that
mistaken information on their sites?

Then, also, the R-680-11 was both a B rated engine with 5.5:1 compression,
AND a higher rated engine with 7:1 compression as well?
That´s all quite wierd, and all because of the FAA.

It could of course be, that the -13B models were throttled down to officially have
220 Hp and do 124 mph, because of the FAA certificate, because they had perhaps
run out of other engines, but why call them -13B versions if they were all going to
have the same power anyway? Why not just call them all -A versions?
It just doesn´t make sense at all.

It´s all quite off-putting, I must say. Nobody likes being led up the garden path.
Such all-round incongruence and incoherence is quite disconcerting.

One last thought: Perhaps the more powerful -13B versions did exist and were in effect built
before the FAA certificate was updated to the certificate we can read nowadays?
The certificate is dated October 1987, not 1940. The restrictions then apply to all the existing
planes as of 1987. Do we know what content of this certificate applied in 1940?

So it seems that things are as they are, not as one expects them to be.

Of course I can build whatever I like, but that´s not the point.

I do however suspect that the more powerful -13B versions really did exist, and were really
stock built, most probably with the strange 78 octane gas reference I found, and about 6.7:1 compression,
but were later outlawed by the FAA in 1987, being forced to comply with the restrictions mentioned.
However, there will NEVER be a way of finding out and it will ALWAYS only be a conjecture.

Anyway... thank you very much for your efforts.
Good night,
Aleatorylamp
 
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Hello Aleatorylamp,

I should probably re-state my confidence in the FAA Type Certificate:
Accuracy (intent) is about 98%. Useful data for our purposes in relation to military service is about 95%.
What I mean is that their data is 98% accurate for current civilian use but only about 95% reflective of military service configurations.

125 MPH is probably what a stock Stearman 75 with 220 HP or 225 HP would achieve.
186 MPH is the maximum IAS for diving speed for a stock aeroplane as determined by the manufacturer.

Consider that for a moment.....

With additional power, a modified aeroplane WILL be able to go faster.
The problem with going faster is that dynamic pressures and stresses will be higher.
The FAA probably (I would say certainly) would not second guess the manufacturer and certify an aeroplane as being safe to operate at higher stresses than it was originally designed for, thus the Vmax and Vne may get lower that the original but never higher.
This is one of the reasons I believe that not everything in the Type Certificate is useful information.

Regarding the R-680 B series and E series engines having different compression ratios, that has nothing to do with the FAA; It is actually from the engine manual and there were other less common variations.
The practice of different designations based on different installed equipment is pretty common as you must know from building military aircraft projects.
Many times the designation change involves very little equipment difference which we as Flight Simulator modelers pretty much ignore.
Military designations can be quite strange at times:
Sometimes things don't change when they should such as with the BMW 801D-2 engine or Bf 109G series.
Sometimes things change when there is essentially no differences such as with the P-51D and P-51K

Do you have any basis for assuming that there was a version of the R-680 engine with a 6.7:1 compression ratio installed in a PT-13 aircraft?
On these sites that you are referencing, is there any mention of the RPMs used for 280 HP output?
Please email links to the sites that describe a 280 HP PT-13B.

Perhaps export users of the PT-13B ignored the operating limits specified in the manual and ran the engines much harder than officially authorized?
Note that some Curtiss P-40 operators actually did that operationally as I have mentioned before in other threads.

Regarding the idea that the FAA is "outlawing" the PT-13B built in 1940 because it had too much power, that simply does not make sense when they include the Pratt & Whitney R-985 equipped aircraft in the Type Certification. I don't believe the FAA existed in 1940, they do not regulate military aircraft and even today one can fly custom or "experimental" aircraft that are not covered by a type certification....

Good Night.
- Ivan.
 
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
 
Tutankhamon´s tomb?

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
 
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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.
 
Tomb with false treasure!

Hello Ivan,
Thanks for your words of caution! I was already fearing it was too good to be true, still hoping it could be a wartime retrofit, which would have allowed building such a model... but it´s not.

I was going to ask about when you think it was re-engined, and what the N2JS meant, but I found out myself:

-It seems that the Navy N2S-5 models were all delivered with 225 Hp R-680-17 engines.
-It looks like the N2JS is a registration number of a 1996 Boeing Stearman Model B75N1 which had an authentic, 300 Hp, 1941, original R-680-13 300 Hp put in!

The wording in the text is very trickily expressed, because it just drops in the "N2S5" and then the "N2JS", and the fact that the airframe is not an original A2S-5 one from 1940 really goes unnoticed! ...1996 Jeez!

It is not a case of wartime retrofitting either, so for my use it is absolutely useless, even if it was lovely to fly like the author said... Anyway, the translation does give an idea of what this plane behaves and feels like. At least that´s something.

Automatic translation has got much better over the years, and even recognized context. In this case it is not too bad, other mistaking the use of personal pronouns - Spanish omits them because the verb is conjugated - so it´s a bit funny when the English translation tries to point out who did something! Also, "reactor" instead of "jet" or "jet turbine", "auger" instead of "stall", and some other quaint ways of expressing itself.

Well, that was a false find then. So it´s back to the 280 Hp mystery with the fixed or ground-adjustable propeller.
Let´s see if I can find something else, something additional, without a scorpion stinging me or suffering the curse of the virtual sands it is buried in.

Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

If written properly, it is pretty easy to tell one "code" from another.
Naval Designations always end with a manufacturer letter or dash and digit if they are complete with subtype thus:
NS = Trainer from Stearman (I presume)
NS-1 = First Variant of the NS Trainer
N2S = Second Trainer from Stearman
N2S-1 = First Variant of the N2S
N2S-5 = Fifth Variant of the N2S
F6F-3 = Third Variant of the Sixth Fighter design from Grumman.
F4U-4 = Fourth Variant of the Four Fighter design from United Aircraft (Chance-Vought)

The problem is that folks are not always so careful or simply do not know.

Sounds like the R-680-13 also came in a low power and a high power version.
It might be worthwhile to read up on the Lycoming R-680 engine's history and evolution.
There is also the possibility that a low power -13 engine was rebuilt to later standards.

The specifications for compression ratio actually came from Jane's and not from the FAA.

- Ivan.
 
Hello Ivan,
Thanks for the info - I include myself in "folks who don´t simply know..."

I´ve also finally tracked down the information on the 2 different compression versions of the Lycoming R-680-13 that you say, in fact, the all-aero page also has a page on it!

Then, the 220 Hp Continental on an approx. 300 lb lighter airfraime you pointed out (and I´d missed on the all-aero containing information on the 280 Hp engine, PT-17), taking into account that so many aircraft of these were built, would well justify the 135 mph quoted by several different other sites.

So then, if we were to use only the 220 or 225 Hp powered Stearman versions for the 2 military models, at least we would have two military versions with different performances: 124 and 135 mph! That would be very satisfactory.

Thanks a lot again!
Cheers,
Aleatorylamp
 
Hello Aleatorylamp,

I will have to go look for the page on the different compression ratio R-680-13 then.
I hope they list the company designations for the engines because that is all I have in the manual and I believe that is also what the FAA document is listing.

By the way, be VERY careful about the 135 MPH maximum speed.
Note that it is ONLY on the PT-17, not the PT-17A or later versions of the PT-17.
I am guessing that there is something else besides the 300 pound weight difference that is accounting for the difference in performance.
With what we know about the aeroplane, we can do a LOT of calculations to figure out if that makes sense though.
You know the aircraft weight.
You know the stall speed.
You know the NACA 2213 Airfoil used and can probably find its CL graph.

You also have a pretty good amount of propeller data from the FAA Type Certificate so building a propeller table from it should not be too difficult and you are almost certainly going to need one because of the low pitch angles.

As long as we are having fun with designations:
McDonnell Aircraft built a jet fighter for the US Navy called the Phantom II.
The F4H-1 was the first version.
The F-4E was a much later version as was the F-4G.....

How is that for making a lot of sense?
(Observe where the dashes are!)

- Ivan.
 
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