The forgotten X_-900 series...

Between 1918 and 1930, the U.S.A.A.S., and then the U.S.A.A.C, evaluated a number of aircraft at Wright Field that were usually modified by the Engineering division from existing designs. These were allocated a "P-" number ranging from P-1 (a Curtiss Jenny) to P-599 (a Curtiss A-3B). These were mostly military models, but there is a handful of cases where you get the odd civilian type such as the Driggs Dart (P-443) or the Waco 9 (P-447). This list of projects is pretty well documented (and in fact complete up to P-339). Gaps exist though (P-340/-350, P-401/-406, P-408/-420, and two dozen more in the latter part of the list) but these have not been found by the historians who worked on the subject.

Today I would like to start a topic on something that has never been dealt with anywhere before, at least to the best of my knowledge. In the first half of the 1930s, the U.S.A.A.C. evaluated a number of civilian projects for possible purchase. Instead of using the "P-" list from number 600 up, the Air Corps used a whole different and original system of temporary designations which incorporated the planned mission of each aircraft: (A) for attack, (B ) for bomber, (BT) for basic trainer, (C) for transport, (O) for observation, (P) for pursuit, and (PT) for primary trainer. The list started at number 900 and is known to have extended up to number 950. All type numbers were preceded with an "X", indicating their strict experimental status.

Now these designations were no longer simple airframe numbers as in the old system; here each designation corresponded to a different type (with sub-types in a few cases). Very often the manufacturers themselves would use the designations in their records, while the Air Corps would drop them and replace them with appropriate numbers in each of their respective series if purchased.

This designation system and the list of airplanes that are concerned have all but fallen into oblivion, largely because aviation historians and enthusiasts didn't know what to make of them, assuming wrongly that they were in-house designators from the manufacturers.

I would like to share my list with you, bearing in mind that seven numbers are still missing. Also quite a few of the others are devoid of any details and have only made it to the list thanks to the index of the Sarah Clark archives, which contain documents about them (how I wish I could browse through these!)

So here goes:

XP-900 Lockheed low-wing pursuit with monocoque fuselage, retractable gear. Purchased as YP-24 [32-320]
XB-901 Boeing Model 215 bomber with P&W engines. [NX10633; c/n 1459]. Purchased as YB-9 [32-301]
XP-902 Boeing pursuit, no details.SCA
XP-903 Boeing pursuit, no details.SCA
XP-904 Curtiss pursuit, most probably the XP-23.SCA

XB-906-1 Ford bomber conversion of Model 5-AT [X9652]; found unsatisfactory; crashed before delivery
XB-907/A Martin prototype bomber. Purchased as XB-10 [33-139; c/n 434].
XB-908 Keystone low-wing, all-metal bomber project with side-by-side arrangement and retractable wheels, mock-up only.
(also found as the "Travel Air Mono", a Curtiss XB-908A is also quoted)
XC-909 Northrop "Alpha 1" transport [NX127W]. Likely became YC-19.SCA
XC-910 Boeing Model 221 "Monomail" transport [X725W]. Evaluated as the C-18 but kept civil registration.
XO-911 Curtiss observation type. Mock-up built in 1930. SCA
XPT-912 Stearman Model 6-A "Cloudboy" [NC787H]. Not purchased but four procured as YPT-9. (SCA has an "XOP-912", likely a mistake)
XPT-913 Spartan C2-165 low-wing navigation trainer prototype [to NC993N].
XPT-914 Verville AT "Sportsman" primary trainer. Two prototypes [479Y, NC457M]. Purchased as YPT-10.
XBT-915 Stearman Model 6-D "Cloudboy" basic trainer [NC786H]. Not procured but one YPT-9 modified to similar BT-5.

XB-917 American Airplane bomber. No details.SCA
XC-918 Douglas "Dolphin" amphibian transport. [X145W] Likely became one of the Y1C-21 batch. Also found as plain "C-918" and "X-918".

XC-920 Sikorsky transport, likely the S-39C "Sport Amphibion" purchased as Y1C-28 [32-411].SCA
XB-921 American Airplane bomber. No details.SCA

XP-923 Command-Aire pursuit. No details.SCA
XO-924 Thomas-Morse observation type. Ordered as Y1O-42 but not produced.
XP-925/A Boeing Model 218 pursuit with all-metal fuselage and Model D & E Wasp engines [X66W]. Not procured and sold to China.
XO-926 Vought observation type, likely the V-70A demonstrator [X781N].SCA
XP-927 New Standard pursuit. No details.SCA
XC-928 Fairchild "Pilgrim 100-B". [NC754Y] Also found as "928XC" and plain "C-928". Procured as Y1C-24.
XP-929 Northrop pursuit type. No details.SCA
XPT-930 Inland Model T, also Great Lakes Model 41 [X11398]. Not purchased.
XPT-931 New Standard D-32 primary trainer [X747Y]. Not purchased.
XO-932 Thomas-Morse orbservation type [NR33Y]. Purchased as Y1O-41 [30-90]. Later modified as Consolidated Model 23 company hack.
XPT-933 Consolidated Model 21A Trainer [NR784N] with Franklin engine. Not purchased, but led to PT-11 order with Wright engine.
XPT-933A Consolidated Model 21C Trainer. Same aircraft modified with Wasp Junior engine, led to PT-12 order.
XP-934 Curtiss Model 66 "Swift" monoplane fighter. Purchased as the XP-31 [33-178].
XBT-935 Stearman basic trainer. No details.SCA
XP-936 Boeing Model 248. Purchased as XP-/Y1P-26 [32-412; c/n 1678].
XBT-937 Consolidated Model 21C Trainer. Apparently purchased as XBT-6, led to BT-6 order.
XA-938 Detroit (Lockheed) company-owned aircraft said evaluated as Y1A-9 but not purchased, which seems dubious.SCA
XO-939 Detroit (Lockheed) type. No details. "XP-939" also found.SCA
XP-940 Boeing Model 264 all-metal pursuit with retractable gear. Purchased as XP-29, later redesignated YP-29A [34-24; c/n 1942]
XC-941 Kreider-Reisner (Fairchild) "Pilgrim 95". Purchased as the XC-31 [34-26]
XC-942 Bellanca SP-200 Airbus transport [785W?, 10796?]. Likely purchased as Y1C-27 [32-399].
XPT-943 Stearman Model 70 [X571Y], ancestor of Kaydet line. Not purchased.
XP-944 Seversky SEV-3 [X2106], not purchased as pursuit but served as a demonstrator for the BT-8 basic trainer ("XA-944" also found).
XPT-945 Stearman Model 75 [NX/NC14407]. Purchased as XPT-13, prototype of PT-13/PT-17 "Kaydet" series.

XP-948 Vought V-141/-143, the former Northrop 3A (FT) fighter modified. Not purchased.

XB-950 Martin Model 123 bomber, a development of the XB-907. Became the YB-10 prototype.

NOTES:

• Designations with the blue SCA indicate a mention in the Sarah Clark Archives index.
• A Stearman XBT-/XPT-934 appears in the Sarah Clark Archives, probably a mistake for XPT-943.
• A Northrop "XP-938" is most likely a typo for the XP-948.
• Fairchild's Model 91 series were also designated as the XA-942, XA-942A and XA-942B, but it is nowhere near an attack type! Besides the number 942 was already used. Did Fairchild hope to get the type evaluated? Or was it at some point, and the number reused? They even had a second amphibian proposal designated the T-943...
• There is no evidence of this system existing beyond XB-950.
• Existence of the XPT-945 designation is now subject to doubt, as all documents found pertaining to the XPT-13 refer to XPT-943.

For years I've searched high and low to get more info and fill in the blanks, but this is the best I've come to so far. Has anyone found a strange X_-900 designator somewhere that they didn't know what to do with? Here's your chance!

Re: The forgotten X_-900 series... and BuAer design numbers

Thanks for this, it filled some gaps in my listing.
Two comments: I have the XO-939 as XP-939 and the XA-944 as XC-944.

With respect to the Wright Field Project numbers, I presume that you have seen my list at http://www.aerofiles.com/wright-field.html. Probably the best there is (but then I am biased )) With the passing away of KO Eckland earlier this year, I have no idea how long this website (and list) will remain available.

Finally, are you aware of the Bureau of Aeronautics design numbers.
The US Navy’s Bureau of Aeronautics was established on 10 August 1921. Its duties were defined as comprising "all that relates to designing, building, fitting out, and repairing Naval and Marine Corps aircraft".
As such the Bureau issued specifications for a number of aircraft which were built by contractors. In the late 1920s and early 1930 a number of these specifications were identified as BuAer designs. Numbers known to me are listed, along with the designations of the contractors’ aircraft.

BuAer 35 Boeing TB
BuAer 77 NAF T2N, Martin T5M
BuAer 86 Berliner Joyce OJ
BuAer 96 Atlantic FA, Curtiss F9C, Berliner Joyce FJ
BuAer 106 Great Lakes SG, Loening S2L, Sikorsky SS
BuAer 107 Martin FM
BuAer 110 Great Lakes BG, Consolidated B2Y
BuAer 111 Two seat bi-plane fighter (F12C)
BuAer 113 Vought F3U, Douglas FD
BuAer 120 Berliner Joyce F3J, Loening FL, Grumman F2F
BuAer 124 ‘Hook-up’ fighter for airships, to replace F9C (not built)
BuAer 145 Replacement of Douglas TBD (not built)

Jos Heyman

Hi Jos, and thanks.

Of course I know your wonderful Aerofiles website. You may recall I once sent you a mail for help with the Bell designations... my name still appears on the page I think... Though it's not devoid of mistakes here and there, your site represents one of the best sources available anywhere and I've often refered to it for help! It would be sad to hear no-one can make it live on... If you need some help of any kind, please let me know.

XP-939 and XC-944 seem correct to me too. I never really believed they could be other than a pursuit and a transport type, but my initial source had them written this way...

As for the BuAer numbers, I had exactly the same list, once copied from this forum, hence from your site... We'll have to keep searching! Thanks again.

Just found another element to add to the list of mysteries here: the Northrop XP-938... Appears on the web in a photo archive from the war era that seems pretty accurate:



This aircraft, of course, is known elsewhere as the Vought XP-948...

Source: http://www.historicaircraft.org/Army-Air-Corps/index_4.html

That's a great contribution!

Thanks Stargazer and Jos Heyman

Hi,

also the Fairchild T-943 was twin engined amphibain aircraft,I think
it was only a project.

hesham said:

Hi,

also the Fairchild T-943 was twin engined amphibain aircraft,I think
it was onlu a project.

Click to expand...

Okay, thanks for the details! But as I said earlier on, the Fairchild designations A-941/942 and T-943 are inhouse designations and not actually part of this USAAC list. "A" was for Attack, not Amphibian, and the 941 to 943 slots are already clearly identified.

Hi all,

P.377 for Cox-Klemin C.K.2 (CO.1)
P.379 for Cox-Klemin C.K.2 (CO.2)

Servus Maveric

A single CO-1 was tested at US Army’s McCook Field with serial P-377, whilst a CO-2, fitted with a Liberty 400 engine, was tested with serial P-379.
Based on the German Heinkel HD17, the aircraft, which have also been referred to as the Cox Heinkel, must not be confused with the Engineering Division’s CO-1 and CO-2 design, ie the Cox Klemin CO's are not military serials.
Both aircaft were returned to Cox Klemin after testing was completed.

Maveric said:

Hi all,

P.377 for Cox-Klemin C.K.2 (CO.1)
P.379 for Cox-Klemin C.K.2 (CO.2)

Servus Maveric

Click to expand...

Jos Heyman said:

A single CO-1 was tested at US Army’s McCook Field with serial P-377, whilst a CO-2, fitted with a Liberty 400 engine, was tested with serial P-379.
Based on the German Heinkel HD17, the aircraft, which have also been referred to as the Cox Heinkel, must not be confused with the Engineering Division’s CO-1 and CO-2 design, ie the Cox Klemin CO's are not military serials.
Both aircaft were returned to Cox Klemin after testing was completed.

Click to expand...

Sorry guys, but you are NOT refering to the special X_-9xx series! This is the P-xxx series which is pretty well documented already... If you don't find a post around here on the subject, I'll get one started so you can contribute there.

Ever wondered what the U.S. Army Air Corps's Wright Field base looked like?

Here is a wonderful pin-up found in Popular Mechanics dated February 1928.

New about the X_-900 series:

• Photos of the Spartan XPT-913 have surfaced, and it was a 1931 low-wing monoplane primary trainer prototype with Wright R-540 engine, unlike any of the company's commercial models of the time. I'm enclosing one with also the cover of the Wright Field report.

• A photo of the Seversky SEV-3 on floats appears on a site as the XP-944. Now that's interesting because if confirmed, it's sort of the missing link in the P-35 story, a Seversky aircraft of earlier configuration tested by the Air Corps prior to the XP-35 (but why the float version?) Only trouble is the doubling of the "944" slot, already said to have been used by a Sikorsky transport...

The Great Lakes Model 41 started life as the Inland Model T.
It was evaluated as the XPT-930, which variously appears under both identities.

This makes the XPT-913 the Spartan C2-60, details of which can be found in Aerofiles.
As far as the Great Lakes XPT-931 is concerned, I have this one also listed as XO-931. A bit confusing.....
As far as the Seversky XP-944 is concerned, I believe we need more evidence that is solidly reliable. Unless such evidence is available we might end up with another designation that has been invented at a later date.
For the time being I stick with the Sikorsky XC-944 Amphibian. If the latter would have been designated as XP-944, we could have interpreted Sikorsky as a 'typo' for 'Seversky', but the P/C difference does not justify that interpretation.

Thanks, Jos. At least there is one source I have found to justify the XP-944 designation, and it's the Polish Monografie Lotnicze #25 on the P-47 Thunderbolt.

As for the duplicated numbers, there seems to be a pattern of this (likely du to some typos along the way for some of them):

• "938" was used for the Detroit-Lockheed attack prototype that became the Y1A-9 (XA-938) , but may also have been used for the Northrop 3A (XP-938) — unless it is a typo for the Vought XP-948, which was in fact the same aircraft modified.
• "942"was used for the Fairchild Model 91 amphibian (XA-942) but also for the Bellanca SP-200 Airbus (XC-942).
• "943" was used for the Stearman Model X70 (XPT-943) but is also quoted for a second Fairchild amphibian proposal (T-943).
• "944" was used for the Seversky SEV-3 floatplane (XP-944) but is also found as a Sikorsky (XC-944). The designation XA-944 was also found.

The Fairchild designations are especially confusing. Why use the "A" for "amphibian" since that letter was clearly used for attacks (which the Model 91 assuredly was not)? Why the use of the "T-" prefix on the second amphibian proposal, which doesn't appear on any other evaluation in the series, and why no "X" attached to it?

Now if the "A- for amphibian" was genuine (which remains to be seen), I guess this would simplify in part the "944" question. Indeed, the book Long Island Aircraft Manufacturers (Arcadia Publishing, 2010) has the following caption for a SEV-3 picture: « The aircraft set numerous speed and distance records for amphibians in 1934 and 1935, which attracted the interest of the U.S. Army Air Corps. » So the quoted "XA-944" may have been genuine and therefore "XP-944" a typo (after all, the SEV-3 doesn't look anywhere near a pursuit!). Questions, questions...

More on the U.S. Army Air Corps evaluation of the SEV-3:

Contrary to what's said above about it's evaluation as an amphibian, here is a photo of the SEV-3 on wheels with spats with the following caption: « The record breaking SEV-3 amphibian as it appeared at Wright Field in the summer of 1934. »

It would seem therefore that along the way, the SEV-3 was changed to standard configuration for Army testing — which is logical since the SEV-3 is said to have served as a basis for BT-8 procurement.

Source: Air Racing History website

Jos Heyman said:

This makes the XPT-913 the Spartan C2-60, details of which can be found in Aerofiles.

Click to expand...

I'll have to disagree on that. If you compare the two aircraft, you'll notice significant differences, notably the tail's shape, overall size and absence of wiring between the main wheels. This is definitely NOT a C2.

I seem to be doing all the posting on this page, but anyway... another scan, this time from Republic P-47 Thunderbolt (MBI). And although it doesn't state a Wright Field designation, it definitely says that "in Dayton, the SEV-3L participated in a training aircraft contest" and "displayed a performance superior to the existing fighters."

This makes the "XP-" prefix for the "944" very unlikely, therefore. "XBT-" would be logical; "XA-" for the original amphibian configuration, maybe. But not "XP-"...

The New Standard D-32 prototype [X747Y, c/n 3000] was evaluated as the XPT-931 but not procured:

Thanks, that is another one further identified.
If I am right the following X numbers are still to be discovered: 905, 916, 919, 922, 946, 947, 949 and anything above 950.

Jos Heyman said:

Thanks, that is another one further identified.
If I am right the following X numbers are still to be discovered: 905, 916, 919, 922, 946, 947, 949 and anything above 950.

Click to expand...

Absolutely correct. The question of possible duplicates on 908, 912, 930, 934, 938, 939, 942 and 944 also needs to be solved...

Coming to think of it, there are quite a few mysteries left in the other designations too... A few updates from my research:

• The Boeing XP-902 and XP-903 pursuits: possible candidates are the P-12F prototype and the Model 100E and 100F.
• I am pretty certain that the Curtiss XP-904 must have been the XP-23 but I have no document to back it up... yet.
• Since Keystone became a part of Curtiss, the Curtiss XB-908A was probably a modification of the Keystone XB-908 proposal.
• The Curtiss XO-911 could be the YO-40 Raven.
• The Sikorsky XC-920 can only be the Y1C-28, a single S-39C Sport Amphibian and the only Sikorsky transport purchased at the time.
• The Command-Aire XP-923 pursuit is quite a strange entry. Possibly a pursuit proposal based on the MR-1 "Little Rocket"? Perhaps even the same aircraft modified? Apart from this monoplane type, all known aircraft from that company are biplanes and they're older. Incompatible for a 1932-33 evaluation.
• The New Standard XP-927 is most likely the one D-29A that was modified as a D-31 after the 100 hp Kinner K-5 was replaced by the 125 hp Kinner B-5. Indeed, that aircraft (registered NC154M) appears on a photo with USAAC markings applied over the civilian registration (see attachment).
• The Northrop XP-929 pursuit makes me wonder if the USAAC may not have evaluated the Beta 3D. Just a guess here.
• The Detroit-Lockheed XP-938 is supposed to have been the Y1A-9 attack proposal derived from the YP-24 (itself the XP-900). Many sources however indicate that there never was an A-9. Could they be wrong?
• The more I consider the '944' slot, the more I'm convinced that "Sikorsky" is just a typo for Seversky. There is still the question of the prefix — XA- for attack? Not much of an attack... For amphibian? Unlikely, the SEV-3 was a floatplane. XP- for pursuit? Not in that configuration. XC- for transport? A little better but not ideal if we consider that the aircraft served as a demonstrator for the BT-8 trainer.

Possible candidates for the unidentified slots:

• The Atlantic (Fokker) Y1C-16, a commercial F-11A Sky Yacht purchased and registered 32-398.
• The General Aviation (Atlantic/Fokker) YC-20, a single commercial F-32 transport evaluated but not procured.
• The single Detroit-Lockheed DL-2A Altair purchased as Y1C-23 and registered 32-232.
• The quite similar Lockheed 8D Altair purchased as Y1C-25 and registered 32-393.
• A Martin Model 139 (B-10 conversion) evaluated as the YO-45 but not procured.
• The Douglas YB-11 became the YO-44 and then the YOA-5.

Stargazer2006 said:

Jos Heyman said:

This makes the XPT-913 the Spartan C2-60, details of which can be found in Aerofiles.

Click to expand...

I'll have to disagree on that. If you compare the two aircraft, you'll notice significant differences, notably the tail's shape, overall size and absence of wiring between the main wheels. This is definitely NOT a C2.

Click to expand...

Jos, we were both right AND wrong about this one! The XPT-913 was the sole Model C2-165, a navigational trainer prototype that owed more structurally speaking to the C3 biplane than the C2 (Spartan designations are definitely confusing). See topic here:
http://www.secretprojects.co.uk/forum/index.php/topic,16699.0.html

The Seversky SEV-3 was an amphibian, the wheels retracted into the floats.
A for Amphibian would fit if the SEV-3 was the XA-944.

Digging out this old thread

In "The 1934 Aircraft Year Book" which can be downloaded here (more than 500 pages!) I found a photo of the Great Lakes XPT-930

Great find Fabulousfour,many thanks.

fabulousfour said:

In "The 1934 Aircraft Year Book" (...) I found a photo of the Great Lakes XPT-930

Click to expand...

Yeah, the Aircraft Year Books are great. I have downloaded them all and keep discovering stuff in them!
Here's another photo of the Great Lakes XPT-930, by the way, along with a three-view arrangement:

The Seversky SEV-3L (X2106) in its amphibian form can be found in this old Kendall advert from Aviation magazine (December 1933). The ad also gives some specification data.