From: Joseph F Baugher <jfb@ihlpl.att.com>
Subject: Number One in the Fighter Series--the Curtiss P-1 Hawk
Keywords: fighters, pursuits, P-1, PW-8
Organization: AT&T Bell Laboratories -  Naperville, Illinois
Date: Wed, 12 Aug 1992 20:35:57 GMT


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


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

This article is the first in a series which will discuss the  US  Army
and  US  Air Force fighter aircraft in the P (later F) series.  I will
discuss them in the order  in  which  they  appear  in  the  numerical
series.  This first article will deal with the Curtiss P-1 Hawk.

The Curtiss "Hawk" series of fighter aircraft was  developed  directly
from  a  line  of specialized racing planes that the Curtiss Aeroplane
and Motor Company of Buffalo and Garden City, New York had  built  for
the Army and Navy between the years 1921 and 1925.  The powerplant for
these racers was a Curtiss-developed  compact,  water-cooled,  direct-
drive V-12 design with a displacement of 1150 cubic inches and a power
of 435 hp.  This engine bore the manufacturer's designation  of  D-12,
but  in  the  middle 1920s the US military services adopted a type and
displacement designation for engines.  The D-12 engine was  given  the
designation  V-1150, V for the basic Vee design and 1150 for the cubic
inch displacement.

The first fighter  based  on  the  new  435  hp  Curtiss  D-12  engine
originated  in  1922  as a private venture by Curtiss.  The design was
given the company designation of  Model  33.   Three  prototypes  were
ordered  by  the  Army  Air  Service  on  April  27,  1923  under  the
designation PW-8.   Serial  numbers  were  23-1201,  1202,  and  1203.
Examples  of  a  basically  similar  competing Boeing design were also
ordered by the Army, and were given the designation PW-9.

The designation PW-8 stood for "Pursuit, Water-cooled, Model 8".  This
Army designation scheme had been introduced in 1920.  There were seven
separate Pursuit categories, chosen  according  to  the  role  of  the
aircraft  and  the  type of engine which powered it--PA (Pursuit, Air-
cooled),  PG  (Pursuit,  Ground  Attack),  PN  (Pursuit,  Night),   PS
(Pursuit,  Special  Alert), PW (Pursuit, Water-cooled), R (Racer), and
TP (Two-seat, Pursuit).  The PW-8 prototypes were  redesignated  XPW-8
in 1924 when the X-for-experimental prefix was adopted.

The first PW-8 prototype was delivered to the Army on  May  14,  1923.
The  fuselage  of  the PW-8 was of welded steel tube construction with
fabric covering.  The undercarriage was of a divided-axle design.  The
wings  were  entirely  of  wood  and were of a very thin section which
required two bays of interplane struts for  stiffening.   The  cooling
system  for  the  D-12  engine  consisted  of  a  set  of wing-surface
radiators that were  pioneered  on  Curtiss  racers  in  1922.   These
radiators  were mounted flush with the upper and lower surfaces of the
top wing, resulting in an extremely well-streamlined wing surface.

In the flyoff between the XPW-8 and the Boeing XPW-9 at McCook  Field,
the   PW-8   proved  faster,  but  the  PW-9  was  found  to  be  more
maneuverable, tougher, and more reliable. The primary problem that the
Army  found  with  the PW-8 was in its unique surface radiator cooling
system.  Although these radiators improved streamlining,  they  turned
out to be a maintenance headache and were prone to constant leaks.  In
addition, the Army concluded that  such  a  cooling  system  would  be
extremely  vulnerable to damage by gunfire were the Hawk to be used in
combat.

The second XPW-8 prototype (Ser No 23-1202) differed from the first in
having  a  divided  type  of  landing  gear  with  reduced  drag.  The
streamlining of the cowling  was  was  improved,  and  strut-connected
ailerons   and  unbalanced  elevators  were  provided.   Gross  weight
increased from 2768 lbs. to 3151 lb

Although the Army favored  the  Boeing  design,  the  Curtiss  company
nevertheless  did  get  an  order from the Army for 25 production PW-8
fighters.  This order was given to Curtiss in return for the company's
agreement  to  collaborate on a pet scheme originated by General Billy
Mitchell to attempt a coast-to-coast  flight  across  the  USA  to  be
completed between dawn and dusk on the same day.

The prototype XPW-8 23-1201 was stripped of all military equipment and
used  in  two  unsuccessful attempts piloted by Lt. Russell Maughan in
July of 1923 to cross the USA in a dawn-to-dusk flight.  This aircraft
was  later  fitted with a second cockpit, temporarily given a spurious
designation of CO-X (for Corps Observation, Experimental) and  entered
in  the  1923  Liberty  Engine  Builders Trophy race for military two-
seaters.  It was withdrawn before the race because of objections  from
the Navy.

The 25 production PW-8s (Ser Nos 24-201/225) that had been ordered  in
September  1923 began to be delivered to the Army in June 1924.  These
aircraft were in the configuration of the second  XPW-8  (Ser  No  23-
1202),   which   differed   from   23-1201   by   having  a  different
undercarriage. Most of the  production  PW-8s  served  with  the  17th
Pursuit  Squadron,  although  several  production  PW-8s  were sent to
McCook Field for experimental work. On June 23, 1924,  PW-8  Ser.  No.
24-204  was finally able to complete the first successful dawn-to-dusk
crossing of the USA.  The aircraft, piloted by  Lt.  Russell  Maughan,
took  off from Mitchell Field on Long Island, with refuelling stops at
Dayton, Ohio, St. Joseph, Missouri, Cheyenne,  Wyoming,  and  Saldura,
Utah.

The PW-8 was powered by a 435 hp Curtiss D-12  engine.  Maximum  speed
was  171 mph at sea level.  Cruising speed was 136 mph.  Initial climb
rate was 1830 ft/min.  Service ceiling was 20,350 ft.  Range  was  544
miles.   Armament consisted of a pair of 0.30 cal machine guns mounted
above the engine synchronized  to  fire  through  the  propeller  arc.
Weights were 2185 lbs. empty, 3155 lb. gross.

The third prototype XPW-8 (23-1203) from the original order  had  been
held  back  at  the  factory  for  installation of a set of single-bay
wings.  These new wings had heavier spars  which  produced  a  stiffer
structure, permitting the installation of only a single bay of struts.
The new aircraft was assigned the company designation of Model 34.  It
was  delivered  in  this  form  to the Army in September 1924, and was
later redesignated XPW-8A.  The troublesome surface radiators  of  the
first  two prototypes were replaced by a core-type radiator built flat
into the center section of the upper wing panel.   A  modified  rudder
without  balance  area  was fitted.  XPW-8A Ser No 23-1203 was entered
into the 1924 Pulitzer Trophy race.  When modified for the  race,  the
radiator was installed in a "tunnel" underneath the engine, similar to
the installation on the Boeing PW-9.  In this guise, 23-1203 was known
as XPW-8AA.  It came in third in the race.

The new core-type radiator of the XPW-8A proved to  be  somewhat  less
temperamental  than the surface radiators of the first two XPW-8s, but
it was still considered inadequate by the Army.  In the meantime,  the
Army  Air  Service  had  been  impressed  by  the  performance  of the
competing Boeing XPW-9 at  McCook  Field.   The  XPW-9  was  basically
similar to the XPW-8, but it had tapered wings and was provided with a
tunnel radiator underneath the engine.  The Army  was  impressed  with
both  of  these features.  Consequently, the Army asked Curtiss to fit
tapered wings and a tunnel radiator to its  XPW-8A  and  resubmit  the
aircraft  for  consideration.  Curtiss  agreed to the changes, and the
modified 23-1203 was delivered to the Army in March 1925.  The changes
resulted in a change of designation to XPW-8B.

The Army was satisfied with the improved XPW-8B, and decided on  March
7,  1925  to  give Curtiss a contract for a production series based on
this design.  In the meantime, in May 1924 the Army had  combined  its
seven   separate   pursuit   category  designations  into  one  single
category--P for pursuit. The first pursuit  aircraft  ordered  by  the
Army under this new designation scheme were the production versions of
the XPW-8B, 15 of which were ordered  as  serial  numbers  25-410/424.
These  were  given  the  designation  P-1,  the first entry in the new
series.

The P-1 (company designation Model 34A) was the first of  the  Curtiss
biplane  fighters  to  carry  the  name  "Hawk", a name which stuck to
Curtiss-designed fighters up to and including the P-40 of World War 2.
The  only  external  difference between the XPW-8B and the P-1 was the
addition of an aerodynamic balance to the rudder of the P-1, plus some
minor  changes  to the single-bay struts.  These airframes were fitted
with the 435 hp Curtiss V-1150-1 (D-12C)  engine,  but  were  provided
with  engine  mounts  that would permit the installation of the larger
500 hp Curtiss V-1400 engine.  Original plans were for the  last  five
aircraft  of the P-1 order to have this V-1400 engine installed at the
factory.  Wings were again of wooden construction, but  were  tapered.
Fuselage  was  of  metal tube construction with fabric covering.  A 55
gallon auxiliary fuel tank could be fitted underneath the belly.

The first P-1s were delivered to the Army in August 1925. Weights were
2058  lb.  empty,  2846  lb.  gross.  Maximum speed was 163 mph at sea
level. Cruising speed was 136 mph.  The P-1 could climb to  5000  feet
in  3.1  minutes.   Service  ceiling  was  22,500 feet.  Range was 325
miles.  The P-1 was armed with one 0.50-cal and one  0.30-cal  machine
gun  mounted  in  the  upper  fuselage  deck  and  firing  through the
propeller arc.

The first P-1 (Ser No 25-410) was used primarily for test work. It was
briefly  fitted  with  an inverted air-cooled "Liberty" engine and was
entered in the 1926 National Air Races.  Later, it was fitted with  an
experimental Curtiss V-1460 engine and was redesignated XP-17.

The last 5 P-1s which were destined  for  the  larger  Curtiss  V-1400
engine   were   considered   sufficiently  different  that  they  were
redesignated P-2 when they were delivered to the  Army.  However,  the
V-1400  engine  proved to be completely unsatisfactory in service, and
three of these P-2s (25-421, 422, and 424) were converted back to P-1A
standards after less than a year of service.

The P-1A (Model 34G) was an improved P-1.  It was  the  first  of  the
Hawks  to  serve in quantity with the Army Air Corps.  25 were ordered
in Sept 1925, with deliveries beginning in April 1926.  Serial numbers
were  26-276/300.   Power  was  provided  by  the improved D-12C.  The
fuselage was 3 inches longer than the  P-1,  the  cowling  lines  were
revised,  the fuel system was changed, and the bomb-release system was
improved.  In addition, some additional service equipment was provided
which  increased  the  weight  by some 20 pounds and decreased the top
speed slightly.  Weights were 2041 lb. empty, 2866 lb. gross.  Maximum
speed was 160 mph at sea level.  Cruising speed was 128 mph.  The P-1A
could climb to 5000 feet in 2.6 minutes.  Initial climb rate was  2170
ft/min.   Service  ceiling  was 21,000 feet and range was 342 mi.  The
P-1A had the same armament as did the  P-1.   Three  additional  P-1As
resulted  from  installation  of D-12 engines in P-2 airframes 25-421,
422, and 424, as described earlier.  Only  23  out  of  the  25  P-1As
originally  ordered  were delivered as such. 26-296 was later modified
as the prototype for the XAT-4 trainer,  and  26-300  was  transformed
first into XP-3, then to XP-21 and XP-21A.

P-1A Ser. No.  26-295 was modified into an Army racer known  as  XP-6A
No.  1.  The old XPW-8A wings were installed on 26-295, along with the
PW-8-type surface radiators.  The  new  V-1570  Conqueror  engine  was
installed  in  a  PW-8-type  nose  cowling,  and  various  other minor
refinements were made.  A really fast aircraft was  the  result.   The
XP-6A  No.  1  won  the  1927 National Air Race at a speed of 201 mph.
However, the aircraft was destroyed shortly before the  1928  National
Air Race.

The designation XP-1A was applied to a stock P-1A (26-280) diverted to
test work.  Despite the X-prefix, the aircraft was NOT a prototype.

The P-1B was an improved model ordered in August 1926.   Serials  were
27-63/87.  Deliveries to the Air Corps began on October 28, 1926.  The
radiator was slightly more rounded and the wheels were slightly larger
in diameter.  The cowling was redesigned.  Flares were added for night
landings and controls were improved.  Equipment changes increased  the
weight  still  further, and reduced the performance still more.  First
deliveries to the Army began in December 1926.  Power was provided  by
the  435  hp  Curtiss  V-1150-3 (D-12D) engine.  Weights were 2105 lb.
empty, 2932 lb. gross.  Maximum  speed  was  160  mph  at  sea  level.
Cruising  speed  was  127  mph.   Initial climb rate was 1540 ft/min.,
service ceiling was 21,400 feet, and  maximum  range  was  600  miles.
Armament  was identical to that of the P-1 and P-1A.  The P-1Bs served
with squadrons already flying the earlier Hawks.

The designation XP-1B was applied to a couple  of  stock  P-1Bs  (Ser.
Nos.  27-71  and 27-73) which were used for test work at Wright Field.
27-73 had machine guns mounted in the wings.

33 improved versions known as P-1C (Model 34O) were ordered in October
1928.   This  was the largest Army Hawk order to date.  Serial numbers
were 29-227/259. First deliveries to the Army began in April 1929. The
P-1C  had  larger  wheels which were fitted with brakes.  The last two
P-1Cs  were  fitted  with  hydraulic  instead  of  rubber-block  shock
absorbers.   Once  again,  the  weight  increased  and the performance
decreased.  The P-1C was powered by the 435 hp  Curtiss  V-1150-5  (D-
12E).   Maximum  speed was 154.4 mph at sea level.  Cruising speed was
124 mph.  Service ceiling was 20,800 feet.  Empty weight was 2136  lb.
and  gross  weight was 2973 lbs.  The P-1C could climb to 5000 feet in
3.9 minutes.  Initial climb rate was 1460 ft/min.  Service ceiling was
20,800  feet.   The normal range was 328 miles, with the maximum range
being 554 miles.

The P-1C Ser. No.   29-259  was  completed  as  the  XP-6B,  with  the
Conqueror  engine  in  place of the D-12.  It was intended for a long-
range flight from New York to  Alaska.   However,  the  XP-6B  crashed
short  of  its  goal  and  was  shipped back to the USA for repair and
subsequent test work.

XP-1C was the designation applied to P-1C Ser. No. 29-238 diverted  to
test  work.   It was fitted with an experimental Heinrich radiator and
Prestone cooling system.  Despite its X-prefix, the XP-1C  was  not  a
prototype.

In 1924, The US Army decided that it might be a  good  idea  to  equip
up-to-date pursuit designs with lower- powered engines and use them as
advanced  trainers.   These  advanced  trainers  were   all   unarmed.
However,  the concept was not successful.  Since the trainers used the
same airframes as did the fighters, the lower- powered  trainers  were
vastly  over-stressed  for  their  missions  and were over- weight for
their power and had very poor performances.  After  a  short  service,
these  advanced trainers were converted to full fighter configuration,
provided with armament, and were retrofitted with D-12 engines.  These
converted  trainers  were  then  given  pursuit designations, and were
designated P-1D through P-1F.

The first Curtiss advanced  trainer  prototype  had  been  created  by
fitting  P-1A  Ser  No 26-296 with the 180 hp Wright-Hispano E liquid-
cooled engine.   It was delivered to the Army in July 1926  under  the
designation XAT-4, where "AT" stood for "Advanced Trainer".

The AT-4 was the  production  version  of  XAT-4.   Forty  AT-4s  were
ordered  in October 1926 under Ser Nos 27-88/97 and 27-213/242. All of
these were powered by the Wright-Hispano  E  (V-720)  engine.  Maximum
speed  was 133 mph at sea level.  Cruising speed was 107 mph.  Initial
climb was 950 ft/min. Range was 535  miles.   Weights  were  1847  lb.
empty,  2484  lbs.  gross.  35 AT-4s were eventually converted back to
fighter configuration by the fitting of the Curtiss  V-1150-3  (D-12D)
engine  and  the  mounting  of  a  single 0.30-cal machine gun.  These
converted aircraft were assigned the designation P-1D.

The last five airframes of the AT-4 order (Ser. Nos. 27-238/242)  were
completed  as  AT-5s,  with  the 220 hp Wright J-5 (R-970-1) Whirlwind
radial engine in place of  the  Wright-Hispano  liquid-cooled  engine.
This  engine was considerably lighter than the Wright-Hispano, but the
disadvantage of lower power was still there.  Maximum speed was  125.4
mph at sea level.  Cruising speed was 100 mph.  Initial climb was 1096
ft/min.  Range was 488 miles.  Weights were 1802 lbs. empty, 2445 lbs.
gross.   These  AT-5s  were later redesignated P-1E when they were re-
engined with D-12D engines of 435 hp and fitted with a single 0.30-cal
machine  gun.   Both the P-1D and the P-1E served with the 43rd School
Squadron at Kelly Field.

The AT-5A (Model 34M) was an improved AT-5, with the  longer  fuselage
and  other  structural  improvements  of  the  P-1A.  31 examples were
ordered by the Army on July 30, 1927.  Serial numbers  were  28-42/72.
In 1929, these AT-5As were all converted to fighter configuration with
the switch to the 435 hp D-12D engine and the  addition  of  armament.
These  aircraft  were  then  redesignated P-1F. One other P-1F (Ser No
28-189) was obtained by converting an XP-21, which in turn had earlier
been converted from a P-3A.

There were only a few export sales of the P-1 Hawk.   Four  P-1s  were
sold  to  Bolivia.  Eight export models of the P-1A were sold to Chile
in 1926.  One example was sold to Japan in 1927. Eight  export  models
of the P-1B were sent to Chile in 1927.  Some examples are believed to
have been built in Chile.

With each successive variant of the P-1, the  weight  of  the  fighter
increased,  leading  to  a gradual falloff in the top speed and in the
climbing performance.  P-1s  were  flown  by  27th  and  94th  Pursuit
Squadrons  of  the  1st  Pursuit  Group  based  at  Selfridge Field in
Michigan and later by the 17th Squadron which  kept  them  in  service
until 1930 until they were replaced by later types.  I don't they ever
fired a shot in the defense of American territory.

Sources:

  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.

  Curtiss Aircraft: 1907-1947, Peter M. Bowers, Naval Institute Press,
  1987.

  "The Curtiss Army  Hawks", Peter  M.  Bowers,  Aircraft in  Profile,
  Doubleday, 1969.

Joe Baugher       AT&T Bell Laboratories   Naperville, Illinois

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