Douglas A/B-26 Invader

On Mark Engineering Co. - Military














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The On Mark B-26K Counter Invader was the final chapter in the development of the Douglas A-26 Invader as a fighting machine.
More powerful engines, tougher wings, more capacity for firepower and ordnance and state of the art weapons and radar systems.
Apart form the continued problems with wing integrity, this aeroplane already with 20 years combat service was ready to partake in yet another conflict, along side newer and faster aircraft that could only sit back and watch the B-26K do the work they could not.

The On Mark B-26K Counter Invader was a major redesign of the Invader, produced in the mid 1960s for use in Vietnam. Work on the B-26K began in 1962, but was given more urgency after a series of wing failures in 1963 and early 1964 forced the Air Force to ground its fleet of elderly B-26s.

On Mark Engineers, of Van Nuys California, was chosen because it had developed some expertise in converted surplus B-26s into high speed commercial transport aircraft.

On Mark proposed an almost total rebuilt of the aircraft. The fuselage and tail would be remanufactured, the rudder replaced with a larger version and removable duel controls fitted as standard. The wing would be reinforced with steel straps running from tip to root, partly to solve the wing failure problem but more importantly to allow for the installation of eight hard points each capable of carrying 1,000lb of stores, bringing the total payload of the B-26 up to 12,000lb. More powerful 2,500hp Pratt & Whitney R-2800-103W engines with water injection were to be used, maintaining the aircrafts top speed even with all of the extra weight. The aircraft was also given 165 gallon fuel tanks at the wing tips and a full package of up-to-date airborne electronics.

The hard points allowed the B-26K to carry a wide range of armaments. They could carry XM75 grenade launchers, P-2 grenade dispensers, LAU-3A, MA3, Aero 6A and LAU-10A rockets, MA3 rocket adaptors, SUU12 .50-caliber machine gun pods and bombs of up to 1,000lb. The inboard pylons could also carry a 230 gallon drop tank.

The prototype YB-26K made its maiden flight on 28 January 1963. After a series of tests it was accepted by the Air Force, and in November 1963 On Mark were given a contract to convert 40 B-26s to the new standard (using -52W engines instead of the -103W of the prototype).

Only 30 of the original 40 airframes selected to be converted were actually modified using the new 64-xxxxx numbers, the remaining 10 were kept for spares.

 The last conversion for the Air Force was completed in April 1965, and the company also received orders for the same conversion from other operators of the B-26.

The B-26K entered combat with the 609th Special Operations Squadron, from bases in Thailand. This led to one final designation change. The Thai government was unwilling to let the Americans operate bomber aircraft from its air bases, so the B-26K became the A-26A, reusing the designation once allocated to the Invader night fighter.

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The On Mark A-26 Invader, an article taken for The IPMS/USA Quarterly magazine Vol 16 No 4 - Summer 1981 by Mike Byers

 
Specifications
On Mark B-26K ( A-26A ) Counter Invader

 
Crew: 2
  • Length: 51 feet 7 3/16 inches
  • Wingspan: 71 feet 6 inches (over wingtip tanks)
  • Height: 19 feet 0 inches
  • Wing area: 540 square feet.
  • Empty Weight: 25,130 pounds empty
  • Loaded Wieght: 37,000 pounds loaded
  • Max takeoff weight: 39,250 pounds maximum.
  • Powerplant: Two Pratt & Whitney R-2800-52W air-cooled radials, each rated at 2500 hp for takeoff and 1750 hp at 15,000 feet.

Note:

The A-26A R-2800-52W engine was the military version of the CB-17. The R-2800-52W had the bolted front case like that of the "C" series R-2800. The ignition was, quoting the "Dash -1"

The ignition system was a low tension, high altitude type, comprised essentially of one double tandem, low tension magneto, two distributors, thirty-six shielded ignition harnesses, eigthteen double high tension coils, shielded spark plugs, and one induction vibrator for each engine.

The system was completely independent of the aircraft electrical system, with exception of the induction vibrator."

The distributors were those shaped like an inverted tapered drinking cup. The coils were bolted to the baffle plate on top of each cylinder.

Performance:

  • Maximum speed: 323 mph at 15,000 feet, 291 mph at sea level.
  • Cruising speed: 169 mph.
  • Stalling speed: 114 mph.
Airfoils
  • Wing Root Airfoil: NACA 65-215
  • Wing Tip Airfoil: NACA 65-215
The following items were some of the more significant and visible mods included in upgrading to the On Mark B-26K.
  • Higher powered Pratt & Whitney R-2800-52W Double Wasp.
  • New DC-6 props ( shortened ). With reversing capability
  • Wing tip fuel tanks
  • Improved and strengthened wings with more pylons re manufactured fuselages Updated avionics.
  • Landing Gear strengthened and KC-135 wheels/brakes used.
  • Larger rudder installed, Rudder was broadened some 8 inches
  • Dual controls and a standardized cockpit Provisions for JATO use Gun armament was standardized with an eight gun nose.
  • Turrets were deleted and paneled over
  • Larger rudder installed, the actual difference is in the chord of the rudder - it was widened 12 inches, in an attempt to lower the VMC (minimum single engine control speed with one engine operating at take-off power and the second engine is windmilling - rather critical on any twin engine aircraft on take off - on the early model A/B 26s it was 140 kts) as a single pilot facility.

Note: An air tanker company that operated 9 A-26 Bs and Cs for air tanker ops, looked into the possibility of swapping the K model rudder to their aircraft for single pilot operation, to emulate the B-26K's handling characteristics. 

For the most part, it was a straight forward swap. Simply remove the original B/C rudder, swap positions on the rudder attach brackets (Top bracket moved to the lower position and bottom moved to the top position) and bolt on the K rudder. However, the FAA insisted that we also had to install the two rows of vortex generators that had been installed vertically on the right side of the vertical stab in front of the rudder. Unfortunately the vortex generators were not available and the operator would have had to have them manufactured to match the original drawings so it didn't go forward with the modification.

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Above, Vortex generators on the fin of a B-26K, which directs dedicated airflow onto the rudder for more a responsive flying surface operation.
 
 

On Mark B-26K Flight and Maintenance Manuals

B-26K Flight manual

Maintenance Manual Part 1

Maintenance Manual Part 2

Maintenance Manual Part 3

Maintenance Manual Part 4

Douglas YB-26K Prototype
"Counter Invader"

 
The B-26B was used in Vietnam in the early 1960s in the armed reconnaissance role. The 4400th Combat Crew Training Squadron (CCTS) initial stated purpose was to provide advisors and training in support of counter insurgency operations. The aircraft began flying in 1961 in support of various operations including Ranch Hand and Farm Gate; however, with two losses due to structure failures, the B-26Bs were withdrawn in 1964.

The B-26Bs were suited to the counter insurgency role, so the USAF ordered an improved prototype aircraft built with the designation YB-26K. A B-26C (S/N 44-35684) was sent to On Mark Engineering Co. for conversion. The engines were updated to 250-hp Pratt & Whitney R-2800-103W radial engines, each equipped with a larger propeller. The wing was strengthened, 165-gallon wing tip fuel tanks were added, and four weapons pylons were installed on each wing. The vertical stabilizer and rudder were enlarged. The cockpit was adapted for dual controls and improved, updated avionics were installed. The nose retained the eight .50-cal. machine gun arrangement, and the wings each had three .50-cal. machine guns.

Testing began in January 1963 and showed the aircraft to be well suited for the planned counter insurgency mission over Southeast Asia. Based on the success of the YB-26K, a production contract for conversion of 40 more aircraft was signed later in the year.

Type

No. Built / Conv'd

     Remarks

YB-26K

1

    Counter insurgency mod.



Notes:
Prototype serial number: 44-35634 (B-26C-40-DT)
First flight was Jan. 28, 1963

SPECIFICATIONS:
Span: 71 ft. 6 in.
Length: 51 ft. 7 in.
Height: 19 ft.
Weight: 38,314 lbs. maximum
Armament: Eight .50 cal. nose machine guns, six .50-cal. machine guns in the wings, eight wing pylons capable of carrying 8,000 lbs. of mixed ordnance, and 4,000 lbs. of bombs internally
Engines: Two
Pratt & Whitney R-2800-103W.s of 2,500 hp (maximum with water injection)
Crew: Two
Cost: $577,000

PERFORMANCE:
Max. speed: 323 mph/281 knots
Cruising speed: 310 mph/270 knots
Range: 2,700 statute miles/2,346 nautical miles
Service ceiling: 30,000 ft
 
Armament
  • Eight forward-firing 0.50-inch machine guns in nose
  • Six forward-firing 0.50-inch machine guns in the wings.
Ordinance
  • 2 No - SUU-025 flare dispensers
  • 2 No - LAU-3A rocket pods
  • 4 No. CBU-14 cluster bomb units.

Note: Later, the rockets and flares were often replaced by 500-lb BLU-23 or 750-lb BLU-37 finned napalm bombs.

Additional inventory:
  • M31 and M32 incendiary clusters
  • M34 and M35 incendiary bombs
  • M1A4 fragmentation clusters
  • M47 white phosphorus bombs
  • CBU-24, -25, -29 and -49 cluster bomb units
Note: General-purpose bombs such as the 250-lb Mk. 81, the 500-lb Mk. 82 and 750-lb M117 could also be carried.

 
 
 
 
 
The YB-26K - Prototype for the B-26K
On Mark B-26K Counter Invaders (40 aircraft produced)

Note: The Pentagon paid On Mark $400,000 each to rebuild 40 A-26s, double what the planes cost when they were built initially during World War II by Douglas Aircraft Co.

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The above shot - YB-26K underwing pylon install prior to first flight.
 
Regarding the above shot
Hello,
I happened upon your site and wanted to tell you that the pictorial on On Mark Engineering was excellent. I do have a question though regarding the photos,  
My father worked at On Mark when I was a young girl...he is in one of your photos...and I was wondering how I could get a copy of the photograph
The photo is the one with the guys working on ladders installing the underwing pylon...it is labeled... (YB-26K underwing pylon install prior to first flight.)   I would really appreciate it ...thank you. 
And would you by chance know when On Mark closed its doors and why ?
Thank you
Robin Wright
 

The above eight photos of the YB-26K Prototype were sent in by Richard E. Fulwiler of Portland, Oregon. 
 
Reference: Richard grew up near the Van Nuys Airport, home of On Mark, and had access to their facility until Marksman C #7 and 8 were started, coinciding with the B26K modifications. He was present on the return of the prototype of the YB26K (#35634) from its first flight when he was 16.
 
Thank you Richard
 
 
 

Development

 

With the success of the YB-26K test program, the USAF ordered 40 B-26s converted to B-26K standards.

Only 30 of the original 40 airframes selected to be converted were actually modified using the new 64-xxxxx numbers, the remaining 10 were kept for spares.

The production B-26K differed from the prototype in a few areas. First, the Pratt & Whitney engines were changed to the R-2800-52W from the R-2800-103W of the YB-26K. The prop spinners installed on the YB-26K were deleted for the production K model. The six .50-cal. machine guns mounted in the wings were removed also. The B-26K still retained a considerable firepower with eight .50-cal. machine guns in the nose, 4,000 pounds of bombs carried in the bomb bay and up to 8,000 pounds of mixed ordnance carried externally on eight wing pylons.

A $12.6 million dollar contract was signed with On Mark Engineering Co. and the 30 aircraft were converted in 1963 and 1964. The aircraft were assigned 1964 serial numbers, although all were originally built in the early 1940s. 

The B-26K conversion program was completed in 1964 when the last of 30 B-26s rolled out of the On Mark Engineering hangars in California. The B-26K was designed for counter insurgency missions in Southeast Asia. The USAF needed an aircraft to seek and destroy supplies moving towards and into South Vietnam from the north. The B-26B had been used up until 1964 when structure problems forced the withdrawal of the aircraft from combat.

Because of the urgent need for counter insurgency and interdiction aircraft, the USAF began using A-1E Skyraiders for these missions and the B-26Ks were not used in combat until 1966. Between 1964 and 1966, the B-26Ks were assigned to special operations squadrons (SOS), air commando squadrons (ACS) and composite fighter squadrons. The K models were basically combat trainers during this period.

In 1966 the USAF decided to base a squadron of B-26Ks in Thailand for use in the panhandle area of Laos in support of operation Steel Tiger. Since the Thai government restricted USAF bombers from using its bases, the designation of the aircraft was changed to A-26A, even though no changes were made to the aircraft or its mission.

The B-26Ks were initially delivered in glossy Green over Grey paint scheme, but this quickly changed to the two Greens and Tan over light Grey or Black. National insignia was either totally eliminated for those operating in Thailand, or made very small and in Black.

Type

No. Built / Conv'd

    Remarks

B-26K

30

   Counter insurgency aircraft


Armament: Eight .50 cal. nose machine guns, eight wing pylons capable of carrying 8,000 lbs. of mixed ordnance and 4,000 lbs. of bombs internally

Production

 
  • 18 No B-26B
  • 22 No B-26C

  • 64-17640 - ex A-26C 44-35896 To civil N267G then N2294B.
    Preserved at South Dakota Air and Space Museum, Ellsworth AFB, SD.
  • 64-17641 - ex A-26C 44-35322 Shot down 29/12/1967.
  • 64-17642 - ex A-26C 44-35435 MIA 27/08/1967, Northern Loas.
  • 64-17643 - ex A-26C 44-35392 w/o 24/07/1966.
  • 64-17644 - ex A-26C 44-35451 To Congo 1964-1967 as SF644, then FR-644. To SEA 1967 To South Vietnam 1969.
  • 64-17645 - ex A-26C 44-35546 To Congo 1964-1966 as RF-645, then FR-645. To SEA 1967. To South Vietnam 1969.
  • 64-17646 - ex A-26C 44-35375 To Congo 1964-1967 as RF-646, then FR-647. To Vietnam , crashed 08/07/1969.
  • 64-17647 - ex A-26C 44-35904 To Davis-Monthan 1972.
  • 64-17648 - ex A-26B 43-22732 Shot down 30/04/1968.
  • 64-17649 - ex A-26B 43-22720 To Congo 1965-1966 as FR-649. To SEA 1967. To Davis-Monthan 1969, reclaimed 1972.
  • 64-17650 - ex A-26C 44-35766 Shot down 28/06/1966.
  • 64-17651 - ex A-26B 44-34119 To SEA 1967. To Davis-Monthan 1969. Preserved at Seoul Museum, Korea.
  • 64-17652 - ex A-26B 44-34361 To SEA 1968. To South Vietnam 1969.
  • 64-17653 - ex A-26B 41-39378 To SEA 1968. To Davis-Monthan 1969. Preserved at Pima County Air Museum, Tucson, AZ.
  • 64-17654 - ex A-26B 41-39491 To SEA 1967. To South Vietnam 1969.
  • 64-17655 - ex A-26B 44-34184 To Davis-Monthan 1972.
  • 64-17656 - ex A-26C 44-35847 w/o 16/12/1964, Eglin Range.
  • 64-17657 - ex A-26C 43-22649 To civil N62104, then N99218.
  • 64-17658 - ex A-26C 44-35865 To Davis-Monthan 1972.
  • 64-17659 - ex A-26B 41-39564    w/o 18/08/1965.
  • 64-17660 - ex A-26C 44-35608 To SEA 1966. To Davis-Monthan 1969, reclaimed 1972.
  • 64-17661 - ex A-26C 44-35433 To SEA 1967. To Davis-Monthan 1969, reclaimed 1972.
  • 64-17662 - ex A-26C 44-35458 To Congo 1965-1967 as FR-662, then FM-662. To SEA 1967, MIA 22/08/1967, Northern Laos.
  • 64-17663 - ex A-26B 41-39462 w/o 23/04/1965.
  • 64-17664 - ex A-26C 43-22665  To SEA 1966. To 1 ACO WG England. To Davis-Monthan, reclaimed 1972.
  • 64-17665 - ex A-26B 44-34145 To SEA 1966. To Davis-Monthan 1969, reclaimed 1972.
  • 64-17666 - ex A-26C 44-35483 To SEA 1968. Preserved at Hurlburt Field Museum, FL.
  • 64-17667 - ex A-26C 44-35468 To SEA 1966, shot down 23/03/1969.
  • 64-17668 - ex A-26B 44-34652 To SEA 1966, shot down 22/02/1967.
  • 64-17669 - ex A-26B 44-34606 To SEA 1966, hit by 64-17668 when it was shot down.
    64-17670 - ex A-26C 44-35634 To SEA 1968. To Davis-Monthan 1969, reclaimed 1972.
  • 64-17671 - ex A-26C 44-35820 To SEA 1966. To Florence Space Museum, South Carolina, later scrapped for spare parts.
  • 64-17672 - ex A-26C 44-35251 To SEA 1966, shot down 14/12/1966 Thai-Laos border.
  • 64-17673 - ex A-26B 44-34135 To SEA 1966, crashed 11/03/1069.
  • 64-17674 - ex A-26B 41-39573    w/o 01/01/1969.
  • 64-17675 - ex A-26B 44-34173 To SEA 1966. To Davis-Monthan 1969.
  • 64-17676 - ex A-26B 41-39596 To SEA 1966. To 1ACO WG England. To Davis Monthan 1969. To civil N268G, G-GXTF, then N22939. Preserved at USAF Museum, Wright-Patterson AFB, OH.
  • 64-17677 - ex A-26B 44-34108 To SEA 1967. To South Vietnam.
  • 64-17678 - ex A-26C 44-35205 To SEA 1966. To Davis-Monthan 1969, reclaimed 1973.
  • 64-17679 - ex A-26B 44-34198 To civil N269G, C-GXTG, then N4988N.

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64-17679 - ex A-26B 44-34198 To civil N269G, C-GXTG, then N4988N
 
 

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64-17653 - ex A-26B 41-39378 To SEA 1968. To Davis-Monthan 1969. Preserved at Pima County Air Museum, Tucson, AZ.

 

 

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64-17651 - ex A-26B 44-34119 To SEA 1967. To Davis-Monthan 1969. Preserved at Seoul Museum, Korea.

 

 

Don Vogler ( a-26 Legacy Foundation) kindly sent me the three shots above and wrote:

Hi Martin …Just received these photos from Roger Graham … thought you’d enjoy ‘em too.  There’s a great shot of IF679 “Special K” and TA651 “Mighty Mouse” in the boneyard at David Monthan.

 

As part of the attachment enclosed within Don's mail was also these notes:

Don,

"Lindsay Peacockan aviation enthusiast with Jane's All the World's Aircraft, just shared some incredible photographs with me and gave me permission to share them with you with his compliments.

One of the photos depicts "Mighty Mouse" (wonderful photo I had not seen before) at Davis Monthan AFB in 1969.

The other notable photo shows 679 ("Special K") at the Bone Yard in 1969.

These are priceless photos.  I intend to show them in the new book project, noting that Lindsay has a copyright to the 679 photo.

Lindsay is aware of the A-26 Legacy Foundation website."

Best regards, Roger 

Operational history

CIA and the On Mark Invader

The Blue Goose and the Steel Tiger, Air Americas B26 Night Drop Project By Frank Bonansinga

"Any Time Any Place"

The A-26 and the cold war

YB-26K

63-5634    ex A-26C 44-35634    Scrapped

 
 
 
Misc. Photos

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Above, YB-26K Sept 1963

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Above, 17672 sits on the ramp in all its demonstration glory. The scheme wouldn't last, and this airframe would be at NKP by August of 1967. It was subsequently lost in combat.
 
 
 

b-26k-eglin-1965.jpg

And its sister ship, 17643. This bird was photographed at Eglin AFB, presumably during armament trials. Note the glass nose; it wouldn't last long before being replaced with the far-more-useful gun nose. This aircraft was also lost in combat after deployment to SEA. 

64-17679a.jpg

64-17679 - ex A-26B 44-34198 To civil N269G, C-GXTG, then N4988N
 
 

64-17653a.jpg

64-17653 - ex A-26B 41-39378 To SEA 1968. To Davis-Monthan 1969. Preserved at Pima County Air Museum, Tucson, AZ.

 

 

64-17651a.jpg

64-17651 - ex A-26B 44-34119 To SEA 1967. To Davis-Monthan 1969. Preserved at Seoul Museum, Korea.

 

 

Don Vogler ( a-26 Legacy Foundation) kindly sent me the three shots above and wrote:

Hi Martin …Just received these photos from Roger Graham … thought you’d enjoy ‘em too.  There’s a great shot of IF679 “Special K” and TA651 “Mighty Mouse” in the boneyard at David Monthan.

 

As part of the attachment enclosed within Don's mail was also these notes:

Don,

"Lindsay Peacockan aviation enthusiast with Jane's All the World's Aircraft, just shared some incredible photographs with me and gave me permission to share them with you with his compliments.

One of the photos depicts "Mighty Mouse" (wonderful photo I had not seen before) at Davis Monthan AFB in 1969.

The other notable photo shows 679 ("Special K") at the Bone Yard in 1969.

These are priceless photos.  I intend to show them in the new book project, noting that Lindsay has a copyright to the 679 photo.

Lindsay is aware of the A-26 Legacy Foundation website."

Best regards, Roger 



 
















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