Boeing Stearman Model 75 - Page 3
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Thread: Boeing Stearman Model 75

  1. #51
    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.

  2. #52
    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 didnīt seem to have these restrictions, and apparently
    were of the same type. Maybe thatīs why these are quoted as having 300 Hp power.


    One would think then, that the -13Bīs 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 werenīt?
    But then they wouldnīt 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?

    Thatīs 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 doesnīt make sense at all.


    Itīs 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 thatīs 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
    Last edited by aleatorylamp; August 16th, 2017 at 18:03.
    "Why make it simple if you can also make it complicated?"

  3. #53
    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.

  4. #54
    Hello Ivan,
    Thanks for your post. Iīll 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
    thatīs 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 75īs quoted by a large
    number of sources.

    I guess that RPM could be about 2200, because the AT-9 and 9-Aīs 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 75īs 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 couldnīt 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 didnīt 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 -13Bīs,
    and nowadays strangely only appears on -13Bīs 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...).

    Iīm 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. Donīt you find it rather exciting?
    Remember when Dr. Carter found Tutankhamonīs 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 hadnīt been looted in Egypt!

    Here we are looking at the evidence thatīs 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
    "Why make it simple if you can also make it complicated?"

  5. #55

    Tutankhamonīs 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 biplaneīs engine,
    where it says
    itīs 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 doesnīt 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 itīs an N2S5 and then goes on saying itīs an N2JS...

    P.S. Hereīs 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
    Last edited by aleatorylamp; August 17th, 2017 at 05:35.
    "Why make it simple if you can also make it complicated?"

  6. #56
    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.

  7. #57

    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 itīs 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 thatīs 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 itīs 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 itīs back to the 280 Hp mystery with the fixed or ground-adjustable propeller.
    Letīs 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
    "Why make it simple if you can also make it complicated?"

  8. #58
    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.

  9. #59
    Hello Ivan,
    Thanks for the info - I include myself in "folks who donīt simply know..."

    Iīve 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 Iīd 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
    "Why make it simple if you can also make it complicated?"

  10. #60
    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.

  11. #61
    Hello Aleatorylamp,

    Here are some general observations thus far:
    You seem to want to build a nice high powered (and fast?) biplane.
    You want to build a Boeing Stearman 75 Primary Trainer because of the article from Smilo's magazine.
    You want it to be equipped as it would have come from the factory.

    I do not believe that all of those features are possible.
    A lot of Stearmans are still flying today, but none of them are absolutely original.
    Those flying today have a different purpose. They are no longer military Primary Trainers.
    They are no longer Military and are now subject to civilian (FAA) regulations.
    Technology has advanced.
    Parts have worn out and are no longer being produced, so to stay flying, they cannot be 100% original.
    Engines have been rebuilt or replaced and often the replacements are better than the originals.
    Folks don't use unshielded ignitions any more because it interferes with electronics many of which did not exist at the time these aeroplanes originally left the factory.

    The Stearman 75 was a pretty good airframe, but had its problems as it came from the factory.
    It was quite low powered for the size of the aeroplane and it only had two ailerons.
    Folks who acquired them as military surplus have chosen to correct some of those issues because the airframe accepted those changes pretty easily.

    The point I am getting at is this:
    The Boeing Stearman 75 in its military configuration is quite a respectable project, but it is certainly no hotrod of a biplane.

    - Ivan.

  12. #62
    Hello Ivan,
    I am putting together a document with the different versions, their power and their speed indications, to have an overview of whatīs happening. As you pointed out, thereīs 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 Iīd 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, weīll 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, Iīd 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
    "Why make it simple if you can also make it complicated?"

  13. #63
    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.

  14. #64
    Hello Ivan,
    Hmmmmm... As Iīm still undecided as to the power/performance for the more powerful military version, I haventīgone into studying the details of the planned hotrod yet.

    However, I did notice that the 450 Hp 985 P&W is said to be rather heavy, and now that you mention it, perhaps the 360 Hp Lycoming series (is that the 4-cylinder Boxer aero engine?), or maybe the 415 Hp P&W R-1340 Wasp, would indeed be more appealing alternative. Because of its looks, the Wasp would probably be more fitting...

    Trials on the simulator could give a general feeling as to the different behaviours resulting from the added power and weight of the three engines, so I might experiment a bit with that at the weekend and see what comes out!

    Cheers,
    Aleatorylamp
    "Why make it simple if you can also make it complicated?"

  15. #65
    Hello Aleatorylamp,

    Please note that the Pratt & Whitney R-985 "450 HP" Engine was only good for 450 HP for ONE MINUTE pf Take-Off (WEP) Power.
    Normal maximum was only 310 HP @ 1950 RPM. (See Post #8)
    That puts it way above a purely stock Stearman Model 75 engine but not above the other hotter Lycoming R-680 engines AND the engine weighs about 150 pounds more.

    The 360 HP Lycoming would be a modern version of the same R-680 that we keep seeing on the PT-13 and the beautiful thing is that they give a lot more power but are in the same weight range as the stock engines.

    The R-1340 is the same engine as found on the AT-6 Texan / SNJ Harvard and would be giving about 600 HP in stock configuration and probably a bit more if tuned a bit.
    At that point, I suppose you would need to change the designation to AT-13, AT-17, AT-18, or AT-27????

    Need to go out again.
    - Ivan.

  16. #66
    Hello Ivan,

    Wow! - as I said, I hadnīt done much research on the P&W R-985, and then, upon seeing your last post I decided to discard the heavy P&W R-985 with its 450 Hp only for 1 minute. Then I had a quick glance at the info on the other two engines, but it seems that it wasnīt quite enough to obtain their correct power data to see what we really have afoot. Thanks for the clarification!

    Hello Smilo:
    Just out of curiosity, which of the two engines would you prefer? The modern 360 Hp Lycoming R-680, or the 600 Hp P&W 1340?

    Cheers,
    Aleatorylamp
    "Why make it simple if you can also make it complicated?"

  17. #67
    SOH Staff
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    to be completely honest,
    it doesn't really matter.
    my main interest
    is in the WWII era trainer.
    the post war crop duster
    or modified civilian hot rod,
    i'm sorry to say...not so much.
    (i hope that wasn't rude)

    i patiently await
    the visual model.
    sometimes the magic works.
    sometimes it doesn't.

  18. #68
    Hello Smilo,
    No, it wasnīt!
    OK then, then, Iīll put the 360 Hp Lycoming R-680 into the hotrod.
    I tried both out both ( with CV props), with correct displacement
    and compression settings (albeit with standard propeller tables...)
    and got exact power and RPM readings from the Lycoming, and quite
    reasonable approximations for the other one.

    The 600 Hp P&W 1340 with twice the cyl. diplacement seems a bit outlandish,
    also a bit more complicated to programme, because it is supercharged, but it
    was good enough to see what it feels like. Engine torque , accelleration and
    climb is much greater than on the other one, and top speed is 170 mph.

    However, I like the Lycoming one better, and got 150 mph top speed from that,
    with the same airframe that I had for the standard military version where I got
    exact 220 Hp/125 mph, and 280/136 mph for the mysterious, elusive, yet possible
    other one.

    The probabilities of this military, stock 280 Hp version having existed, with an
    official speed of 125 mph, limited to that by possible caution because of the
    fixed pitch prop, but extraofficially capable of achieving 136 mph, could be:

    1) It canīt have existed.
    2) It might have, but probably not.
    3) It may have, but the again it may not have.
    4) It may probably have existed, but it might not have.
    5) It may well have existed.
    6) It must have existed.

    If Ivan and yourself were to choose Options 5) or 6), it is reasonable enough
    to make the second military model a 280 Hp powered one.

    Opinions, please?

    Then, I donīt mind if we donīt have a cropduster - Iīm non-plussed about that.

    Iīll very soon start on the visual model. I only have to scale print out the plans.
    Cheers,
    Aleatorylamp
    "Why make it simple if you can also make it complicated?"

  19. #69
    SOH Staff
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    please, correct me if i'm wrong.
    you like the "mysterious"
    280/136 lycoming, right?
    if so...then, use it.
    make a note in the readme file
    explaining (as best you can)
    why you're using it and call it good.

    heck, you can even note it
    in a 280/135 mph air file description,
    so it shows when selecting aircraft.
    if others don't like it,
    they can choose another model
    with a different air file.

    when you're ready (and if you want),
    i can help you put together a package
    where texture, engine configuration,
    and three model options are available,
    all, in one model 75 folder.
    basically, allowing pilots to choose
    which ever variant they want to fly.
    ...but, that's way down the road.
    sometimes the magic works.
    sometimes it doesn't.

  20. #70
    Hello Smilo,
    Great! A 3-aircraft package sounds like a good idea: One standard Navy version, one Army model with a choice of two motorizations, and a third model, the civil aerobatic hotrod, all with 9-cyl Lycoming R-680 engines of different Horsepower.

    Your help, when the time comes, will be necessary to put the package together. Iīve done it very often, but very rarely because I found it rather tricky.

    Cheers,
    Aleatorylamp
    "Why make it simple if you can also make it complicated?"

  21. #71
    SOH Staff
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    it's been a while, but,
    when the time comes,
    it's very doable.

    i was thinking, maybe,
    two navy versions,
    two air corps versions,
    and the civilian hotrod.
    heck, while we're at it,
    we could even add,
    high powered,
    fantasy military versions,
    but, that might be pushing it.

    so, no seven cylinder choice?
    don't get me wrong,
    i'm not complaining,
    just askin'
    sometimes the magic works.
    sometimes it doesn't.

  22. #72
    Hello Smilo,

    Once I saw that the standard 220 Hp powered PT-13/17 could also have 9-cyl Lycomings, and I was more concentrated on power than on cyl-number, I automatically discarded the 7-cyl Continentals, but Iīll gladly supply one if you like. No Prob!

    I already have bleedwise half-way acceptable 5, 7 and 9 engines, with box-shaped cylinders, engine-block cones and pushrods on the front. Exhausts are either individual parts for each cylinder, or an exhaust ring with two pipes below the nose. These were the Siemens-Halske and BMW-X for the German Klemm and the Flamingo, so a Continental and a Lycoming reconversion wonīt be much ado.

    The 7-cyl. version works better that the 9-cyl one, so thereīs no problem in having two different builds depending on the engine. The more bleedless one will be the 7-cyl one.

    What Iīll try is make hexagonal shaped cylinders, if it doesnīt increase the bleeds, but the basically "v" shaped cylinderheads will probably be impossible and only cause extra bleeds.

    Iīll start with the 9-cyl engine, and once Iīve got it done, Iīll make a description with screenshots and see if Ivan can suggest ways of improvement, which Iīll try out. I donīt want to make Ivan fire up his development computer and reduce its longevity!!

    Interesting also is the tailwheel, steerable for the Army Corps and swivelling for the Navy one, I believe.

    If there are 5 or 6 versions, I donīt mind. We can have as many as we want! No prob either!

    Update: I have never been a fan of "what if" versions, either for download or for upload, and a fantasy high powered military version I find, would fit into this category. For the moment, the 280 Hp engine with such low performance is a contradiction and is totally ridiculous. Why would anyone build a -13B series with 280Hp engines to get the performance of more normal 220 Hp ones? The only way it could have existed is its the performance was officially disguised, and I need a bit more information to make it less of a fantasy, so I donīt think Iīll do one or worry about it any longer!
    Then, Iīm trying to figure out if it is reliable enough to say there was a 300 lb lighter edition of the P-17 to justify the 135 mph performance mentioned on some sources but not on others for the same model.

    Cheers,

    Aleatorylamp
    Last edited by aleatorylamp; August 20th, 2017 at 03:56.
    "Why make it simple if you can also make it complicated?"

  23. #73
    SOH Staff
    Join Date
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    i'm not much for fantasy aircraft, either.
    i was just saying,
    putting one together could be easily done
    with a few lines added to the the aircraft.cfg.

    my mention of no seven cylinder version
    was just a query, not a request.
    i'm good without it, but,
    if you want to do it,
    i'm okay with that, too.

    visual engine details would be very cool,
    but, for the most part,
    i understand the limitations of af99.
    all i can really do, is sit back,
    watch and say, good luck.
    sorry, i can't be of more assistance.
    sometimes the magic works.
    sometimes it doesn't.

  24. #74
    Hello Smilo, Hello Ivan,
    I hope youīve had a nice weekend. Here it was sweltering again, and the brain gets mushy with
    temperatures that donīt fall
    below 26.5 C at night... but we get by.

    Thereīs an excellent Stearman PT-17 Pilotīs report here:
    http://www.airbum.com/pireps/PirepStearmanPT17.html
    It describes a lot of the sensations, and makes a very good read.
    Talking of sensations... Iīve seen a couple of videos with these planes flying SIDEWAYS, at 1 yard above the ground.
    Quite spectacular, to say the least. These planes must really be absolutely fantastic to fly - even the normal 220 Hp ones!

    Anyway, I got the link to the article from an ad where a 280 Hp Stearman is being sold in the Czech
    Republic. Curious is, that it has a wooden propeller. Unfortunately there are no performance details.


    This is the link to the ad:

    http://www.planecheck.com/index.asp?...id=34151&cor=y
    The ad says:
    Boeing Stearman N2S Kaydet For Sale in Czech Rep.
    Year of construction: 1943 - Country Czech Rep. - City/Aerodrome: LKOT
    Description:
    TTSN 5293 hrs
    NORMAL Category plane
    Radio + transponder
    Lycoming R-680-11 Engine 280 HP
    SOH 0 hrs
    Wood Sensenich Propeller

    I have sent them an e-mail asking about the engine installation date and aircraft top-speed. Letīs see if they answer.

    Now, to make this whole 280 Hp tease even worse, there is yet a third place where it is mentioned:
    Aerofiles.com also mention the stock 280 Hp Stearman, but donīt give any performance details.

    http://www.aerofiles.com/_stear.html

    They present a photo of a Boeing-Stearman PT-13B Final assembly (Boeing)
    and also give unit numbers. Note the 255 factory -13Bīs from 1940 and the 6 -13C refits from 1941.

    PT-13B 1940 = 280hp R-680-11. POP: 255 [40-1562/1741, 41-787/861].
    PT-13C 1941 = PT-13A repowered with 280hp R-680-11. POP: 6 modifications.

    Thatīs why I think a stock 280 Hp Stearman canīt be a fictitious thing, but something that must have existed.

    Cheers,

    Aleatorylamp.
    "Why make it simple if you can also make it complicated?"

  25. #75
    Hello Gentlemen,

    We dropped off my Daughter down in Charlottesville on Saturday.
    Yes, the same Charlottesville where all the disturbances are!
    Just got back from another supply run today for some essentials.
    Just finished watching the eclipse.
    The peak was during a storm and hidden by clouds but we do have some good pictures.
    It was clear about 3 minutes before the peak though.

    Now back to the Stearman.
    Assuming that there WAS a 280 HP R-680-11 installed in a few PT-13B's and PT-13C's (and I am still not entirely convinced that there were), there is the possibility that the level speed performance did not change at all.

    How can this be? More power and it should go faster, right?

    What happens if the extra power is gained by increased engine torque without an increase in maximum RPM limits?
    In that case, with a fixed pitch wooden propeller, you pretty much would not see anything unless you changed the propeller pitch which you cannot do.
    The aeroplane would accelerate better and climb better, but would not necessarily go significantly faster because if engine RPM and propeller pitch were matched well for the standard power engine, you would overspeed the engine to go any faster.
    That is the way it appears to me, but I have not thought about it a lot.

    - Ivan.

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