From: Joseph F Baugher <jfb@ihlpl.att.com>
Subject: Fifteenth in the series--The Boeing XP-15
Keywords: Parasol Wing Monoplane
Organization: AT&T Bell Laboratories -  Naperville, Illinois
Date: Fri, 11 Sep 1992 14:01:23 GMT


From Joseph F Baugher <jfb@ihlpl.att.com>


By the end of the 1920s, Boeing had realized that the biplane  fighter
was  soon  going  to reach the end of the line, and that the monoplane
held the key to the future.  Rather than start  with a  radically  new
design,  as had been attempted in the abortive XP-9, Boeing decided to
adapt an existing design for its next monoplane fighter project.  From
the  start,  the  project  was  a  company-financed  venture,  with no
promises of support from the military.

As first planned, the new Boeing design was merely the basic Model  89
(second  prototype  of  the F4B/P-12 series) redesigned as a monoplane
through deletion of the lower wing  and  the  addition  of  struts  to
support the upper wing which was moved slightly aft to keep the center
of lift in the correct position.  This design was known by  Boeing  as
the  Model  97, but was not built.  Following a decision to go to all-
metal construction with a new fuselage design based on the XP-9 (Model
96),  the  designation  was  changed to Model 202.  The reason for the
large gap in company designations was due to  the  fact  that  company
model  numbers  103  through 199 had been reserved for Boeing-designed
aerofoil sections.

The Model 202 that finally emerged was essentially a P-12/F4B with the
lower  wing  removed   and   with  a  newly-designed  parasol  wing of
increased wingspan attached to the fuselage by numerous  struts.   The
wing  was  similar  to that of the upper P-12 wing except for a 6-inch
increase in span, the substitution of built-up dural  spars  and  ribs
for  wood,  and  the use of dural skin for covering. The undercarriage
was of split-axle design, and a tail wheel replaced the tail  skid  of
the  P-12.   The  portion  of  fuselage  aft of the undercarriage rear
attachment point was a semi-monocoque all-metal structure  with  dural
formers,  longitudinal  stiffeners,  and  dural  skin.   The structure
forward of this point was welded steel tubing covered  with  removable
access  panels  and  cowling.   The  original  metal  skin of the tail
surfaces was smooth, but the second fin-rudder  combination  that  was
used  was  covered  with  corrugated metal.  External tail bracing was
similar to that of the biplanes.  The undercarriage was of  split-axle
design,  and  a  tail  wheel  replaced  the tail skid of the P-12. The
powerplant was the Pratt and Whitney SR-1340D Wasp air-cooled  radial,
rated at 450 hp at 8000 feet.

Since the Model 202 was a company  venture  rather  than  a  military-
financed project, it carried a civil registration (X-270V) rather than
a military serial number.

The Model 202 flew for the first time in January of 1930.   The  shape
of  the  vertical tail was changed to that eventually standardized for
the later  P-12E  and  a  ring  cowl  similar  to  that  installed  on
production P-12Cs was added before the XP-15 was sent to Wright Field.
The military designation of XP-15 was assigned unofficially  when  the
USAAC  accepted  the Model 202 at Wright Field for flight test under a
bailment contract on March 10, 1930.

During tests at Wright field, the XP-15 attained a  maximum  speed  of
163  mph at sea level and 190 mph at 8000 feet. The initial climb rate
was 1800 ft/min at 800 feet.  Service  ceiling  was  26,550  feet  and
range  was 421 miles.  Weights were 2052 lb empty, 2746 lb gross.  The
aircraft was to have been armed with two 0.30 cal  machine  guns,  but
these were never actually fitted.

The deletion of the lower wing increased the top speed  of  the  XP-15
over  that  of  the P-12B, but the rate of climb, the maneuverability,
and the landing speed all suffered from the  decrease  in  wing  area.
Consequently,  the  design  was  not  accepted  for  production by the
military, and the Army never actually purchased the  XP-15  prototype.
Therefore, it was never assigned a USAAC serial number.

The XF5B-1 was an almost identical duplicate of the Model 202 that had
been  ordered for the US Navy.  It differed mainly in being fitted for
operation from aircraft carriers as  a  fighter-bomber.   An  arrester
hook  was  fitted.    The  engine was a supercharged Pratt and Whitney
SR-1340C offering 480 hp at sea level.  The  company  designation  for
this  aircraft was Model 205.  The Model 205 was delivered to the Navy
in February 1930.  Like the Model 202, it was originally tested by the
Navy under a bailment contract and bore the civil registration X-271V.
By the time that test flights were  terminated  at  the  beginning  of
1932,  it  had  been decided that the monoplane still did not have the
reliability needed for a successful carrier-based airplane.   Although
the  Navy  did  not  accept  the  aircraft  as a production type, they
nevertheless purchased the airplane and the designation XF5B-1  became
official.   The  serial  number  was  A-8640.   After  three  years of
testing, the airframe was static tested to destruction.

After return to the factory from Wright Field, the XP-15 was used  for
further  test  and  development  work,  in the vain hope that it might
eventually be granted an Army contract.  However, all such hopes  were
dashed  on February 7, 1931, when the XP-15 crashed near Seattle after
a propeller blade failed during a  vertical  climb  following  a  high
speed  run.   The  resulting  vibration  shook  the  engine out of the
airframe.  The program was abandoned shortly thereafter.  Although the
aerodynamic  design  was  not  accepted  by  the  Army,  many  of  the
structural features of the XP-15 were incorporated into  later  models
of the P-12/F4B series then in production.

Sources:

  Boeing Aircraft since 1916, Peter M. Bowers, Naval Institute  Press,
  1989.

  "Boeing F4B-4", Peter M. Bowers, in "Aircraft in Profile", Doubleday,
  1969.

  United States Military Aircraft Since 1909,  Gordon Swanborough  and
  Peter Bowers, Smithsonian Institution Press, 1989.

  The American Fighter, Enzo Angellucci and Peter Bowers, Orion Books,
  1987.

Joe Baugher       AT&T Bell Laboratories    2000 North Naperville Road 
		  Naperville, Illinois 60566-7033.   (708) 713-4548



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