Fairchild C-119 Flying Boxcar, doing a parachute drop from the rear
de Havilland Vampire T.11, whose booms keep the rear fuselage clear of the jet exhaust
Caproni Ca.3, whose booms provided clearance for a propeller - and a position for a gunner to fire to the rear

A twin-boom aircraft has two longitudinal auxiliary booms. These may contain ancillary items such as fuel tanks and/or provide a supporting structure for other items. Typically, twin tailbooms support the tail surfaces, although on some types such as the Rutan Model 72 Grizzly the booms run forward of the wing. The twin-boom configuration is distinct from twin-fuselage designs in that it retains a central fuselage.

Design

The twin-boom configuration is distinct from the twin fuselage type in having a separate, short fuselage housing the pilot and payload. It has been adopted to resolve various design problems with the conventional empennage for aircraft in different roles.

Engine mounting

For a single engine with a propeller in the pusher configuration or a jet engine, a conventional tail requires the propeller or exhaust to be moved far aft, requiring either a very long driveshaft or jet pipe and thus reducing propulsive efficiency. The twin-boom configuration allows a much shorter and more efficient installation.[1] The Saab 21 was originally built as a pusher type and was later adapted to jet power as the 21R.[2]

In these designs, the tailplane (horizontal stabilizer) is typically high-mounted on twin tail fins to keep it clear of the engine wake. The Scaled Composites SpaceShipOne and SpaceShipTwo sub-orbital spaceplanes adopted twin booms with outboard tails or outboard horizontal stabilizers (OHS) to keep the airframe clear of the more widely-spreading rocket engine exhaust.

Twin booms have also been adopted for twin-engined designs where the engine system includes bulky additional items such as turbochargers and heat exchangers, taking up a large volume of space. Examples include the Lockheed P-38 Lightning.

Field of view

For a rear observation or gunnery position to have an unobstructed field of view, placing it at the rear of a conventional tail moves it so far aft that problems arise with the centre of mass and balancing the aircraft. Getting rid of the conventional empennage allows the rear position to be located more forward, resolving the balance problem. An example is provided by the Focke-Wulf Fw 189.

However the twin booms and bridging tailplane still obstruct the field of view to some extent and guns in this position are especially restricted in firing to the side.

Transport access

Loading and unloading large freight or cargo items such as vehicles and containers requires large access doors. In conventional designs these doors must be located at the nose or side of the fuselage, necessitating heavy reinforcement of the main structure. Side doors limit the length of an item to the width of the door and access may also be obstructed by engines or undercarriage. The twin-boom configuration allows a large door to be placed at the rear of the fuselage, free from obstruction by the tail assembly, as on the Armstrong Whitworth AW.660 Argosy.

However access to the rear door remains limited, especially for trucks backing up to it, and a high-mounted conventional rear fuselage is often preferred.

Efficiency

Twin booms typically offer greater drag than a conventional arrangement. They are also typically shallower than the fuselage and thus inherently less stiff, requiring additional reinforcement to maintain a rigid tail position in pitch. On the other hand, tip effects on the tailplane are avoided and it is supported at both ends, allowing it to be made smaller and lighter. Moreover, span loading along the wing can reduce the structural forces between the booms and thus overall weight.

Some modern high-efficiency designs have twin booms which distribute the load along the wing span and/or stiffen the overall structure. Capable of flying non-stop round the world, the Rutan Voyager was a canard design with tractor propeller, in which the twin booms extended forwards to brace the foreplane as well as aft to support twin fins. The later Virgin Atlantic GlobalFlyer was jet propelled but with a similar range, still with large twin booms to accommodate the jet fuel in a lightweight span-loaded structure, but with a small conventional tail on each boom.

History

Twin boom designs can trace their history back to the lattices of booms used on many early boxkite aircraft. With the recognition of the tremendous drag these imposed, more compact structures covered in fabric were developed during the World War I. Prime examples include the Caproni series of trimotor bombers.

Around the same time, the first wooden monocoque fuselages appeared, and it wasn't long before this technique was applied to provide twin booms. Possibly the first of these was the pre-war Nieuport pusher, which used paper impregnated with Bakelite however the most successful were the AGO C.I and C.II which used a more conventional wooden shell, built up from strips of wood glued over a form. With the development of aluminium stressed skin monocoques later in World War I, the same technique was extended to twin boom designs, beginning in the 1920s.

Most of the early designs used twin booms to clear a rear mounted propeller, however even in World War I, several larger aircraft used them to provide a gunner with the ability to cover the underside of the tail without having to have the weight at the very extreme end of the aircraft where it posed balance and control problems.

Only in World War II, with the increasing prevalence of transporting bulky items and vehicles by air was the utility of a rear door, in line with the cabin to ease loading realized, and with it, the utility of moving the rear fuselage structure to the sides to avoid excessive height in the rear fuselage as on the Gotha Go 242 glider.

With the beginning of the jet age, the need for clearance for the propeller was replaced with the need to provide a clear path for hot exhaust gases. Jet engine efficiency was hampered by long intake and exhaust trunks, as were used on many early designs, and one solution was to use twin booms to shorten the exhaust trunking to the minimum, such as de Havilland used on their successful Vampire and Venom jet fighters.

A small number of designs used twin booms for other reasons, most notable being the Lockheed P-38 Lightning, whose booms contained the overly lengthy engine turbo-superchargers, which would have made for an unusually long nacelle. The final use for a twin boom to be developed was in tying together very high aspect ratio wings and canards as on the Rutan Voyager, to reduce flexing, and the weight needed to otherwise constrain it. Also, by having the mass from most of the fuel mid-span, it reduces the forces on the wings considerably, much in the same manner mounting the engines mid-span on most jet transports does.

Despite these anticipated benefits, twin booms remain unusual. For most cases, the booms are less efficient structurally in providing pitch stiffness, and produce more drag. In the case of those using twin booms to improve the field of fire downwards, it severely reduces it laterally, and often directly astern. For transports, the booms may facilitate access to the fuselage, but trucks then have to be extremely careful to not hit parts of the aircraft that they are then getting closer to. As a result, the C-119 remained an anomaly, and most successful post-war transports, such as the C-130 Hercules, reverted to a single rear fuselage.

List of twin-boom aircraft

TypeCountryClassRoleDateStatusNo.Notes
AAI RQ-7 ShadowUSUAVUAV1991
Abrams P-1 ExplorerUSPropellerSurvey1937Prototype1
AD Seaplane Type 1000UKPropellerBomber1916Prototype2
Adam A500USPropellerTransport2002Prototype7
Adam A700USJetTransport2003Prototype2
ADI CondorUSPropellerMotor glider1981Prototype1
AeroRIK DingoRussiaPropellerUtility1997Prototype1-5[3]
AGO C.IGermanyPropellerReconnaissance1915Production64
AGO C.IIGermanyPropellerReconnaissance1915Production15
AHRLAC Holdings AhrlacSouth AfricaPropellerAttack2014Prototype1
Air Utility AU-18USPropellerTransport1945Prototype1[4]
Airmaster Avalon 680USPropellerTransport1983Prototype1[5]
Airsport SongCzech RepublicPropellerUltralight2009Production
AISA GNSpainAutogyroUtility1982Prototype1
Akaflieg Stuttgart fs28 AvispaGermanyPropellerUtility1972Prototype1
Alaparma BaldoItalyPropellerUtility1949Production35 ca.
Alenia Aermacchi Sky-YItalyUAVUAV2007
American Gyro AG-4 CrusaderUSPropellerUtility1935Prototype1
Antonov LEM-2/OKA-33USSRPropellerTransport1937Prototype1[6]
Anderson Greenwood AG-14USPropellerUtility1947Prototype5
ANTEX-MPortugalUAVUAV2002
Antonov A-40USSRGliderTransport1942Prototype1
Arado E.340GermanyPropellerBombern/aProject0
Armstechno NITIBulgariaUAVUAV2006
Armstrong Whitworth AW.660 ArgosyUKPropellerTransport1959Production74
Arpin A-1UKPropellerUtility1938Prototype1
AVE MizarUSPropellerFlying car1973Prototype2
BAE Systems PhoenixUKUAVUAV1986
BAE Systems SkyEyeUKUAVUAV1973
BAT CrowUKPropellerUltralight1920Prototype1
Baykar Bayraktar TB2TurkeyUAVUAV2014
Baykar Bayraktar TB3TurkeyUAVUAV2022Project
Bell XP-52USPropellerFighter1940Project0
Belyayev EOIUSSRPropellerFighter1939Project0
Bendix 51 & 51AUSPropellerUtility1945Prototype2
Bestetti BN.1ItalyPropellerUtility1940Prototype1[7]
Blériot 125FrancePropellerTransport1931Prototype1
Blohm & Voss BV 138GermanyPropellerReconnaissance1937Production297
Boeing Insitu RQ-21 BlackjackUSUAVUAV2012
Bryan AutoplaneUSPropellerFlying car1953Prototype2
Bryant Dole Racer Angel of Los AngelesUSPropellerRacer1927Prototype1[8]
Burnelli CBY-3CanadaPropellerTransport1944Prototype1
Burnelli GX-3USPropellerExperimental1929Prototype1
Burnelli UB-14USPropellerTransport1934Prototype2
Burnelli UB-20USPropellerTransport1930Prototype1[9]
Buscaylet-de Monge 7-4FrancePropellerExperimental1923Prototype1
Buscaylet-de Monge 7-5FrancePropellerTransport1925Prototype1
Campbell Model FUSPropellerUtility1935Prototype1[10]
Canaero ToucanCanadaPropellerUltralight1983Production41+
Caproni Ca.1ItalyPropellerBomber1914Production162
Caproni Ca.2ItalyPropellerBomber1915Production9
Caproni Ca.3ItalyPropellerBomber1916Production269-383
Caproni Ca.4ItalyPropellerBomber1917Production44-53
Caproni Ca.5ItalyPropellerBomber1917Production662
Caproni Ca.37ItalyPropellerAttack1916Prototype1
Caproni Ca.61ItalyPropellerBomber1922Prototype1-2
CarterCopterUSAutogyroTransport1998Prototype1
Celier Xenon 2PolandAutogyroUtility2005Production100+
Cessna SkymasterUSPropellerTransport1961Production2,993
Cessna XMCUSPropellerExperimental1971Prototype1
Commuter Craft InnovatorUSPropellerTransport2015Prototype1
Conroy StolifterUSPropellerUtility1968Prototype1
Continental KB-1USPropellerReconnaissance1916Prototype1
Convair 106 SkycoachUSPropellerUtility1946Prototype1
Convair Model 48 ChargerUSPropellerAttack1964Prototype1
Creative Flight AerocatCanadaPropellerTransport2001Prototype1
Cunliffe-Owen OA-1UKPropellerTransport1939Prototype1
Curtis Wright 21USPropellerUtility1947Prototype1[11]
Curtiss AutoplaneUSPropellerFlying car1917Project1
Curtiss CTUSPropellerBomber1921Prototype1
De Havilland Sea VixenUKJetFighter1951Production145
De Havilland VampireUKJetFighter1943Production3,268
De Havilland Venom & Sea VenomUKJetFighter1952Production1,431
De Schelde S.20NetherlandsPropellerTrainer1940Prototype1
De Schelde S.21NetherlandsPropellerFighter1940Project1
Difoga 421NetherlandsPropellerUtility1946Prototype1[12]
Dyle et Bacalan DB-70FrancePropellerTransport1929Prototype1
Doblhoff WNF 342GermanyHelicopterReconnaissance1943Prototype3
DRDO NishantIndiaUAVUAV1996
Edgley OpticaUKPropellerReconnaissance1979Production22
Eldred Flyer's DreamUSPropellerUtility1946Prototype1[13]
Emsco B-8 Flying WingUSPropellerRecord1930Prototype1
Fairchild C-82 PacketUSPropellerTransport1944Production223
Fairchild C-119 Flying BoxcarUSPropellerTransport1947Production1,183
Fairchild XC-120 PackplaneUSPropellerTransport1950Prototype1
Fieseler Fi 168GermanyPropellerAttack1938Project
Focke-Wulf Fw 189GermanyPropellerReconnaissance1938Production864
Focke-Wulf FlitzerGermanyJetFighter1944Project0
Focke-Wulf Project VIIIGermanyPropellerFightern/aProject0
Fokker D.XXIIINetherlandsPropellerFighter1939Prototype1
Fokker F.25NetherlandsPropellerUtility1946Production20
Fokker G.INetherlandsPropellerFighter1937Production63
Friedrichshafen FF.34GermanyPropellerBomber1916Prototype1
General Airborne XCG-16USGliderTransport1943Prototype2
General Aircraft CagnetUKPropellerTrainer1939Prototype1
General Aircraft GAL.47UKPropellerReconnaissance1940Prototype1
Ghods MohajerIranUAVUAV1981
Gotha Go 242GermanyGliderTransport1941Production1,528
Gotha Go 244GermanyPropellerTransport1942Production174
Gotha WD.3GermanyPropellerReconnaissance1915Prototype1
Grahame-White GanymedeUKPropellerBomber1918Prototype1
Groen Hawk 4USAutogyroUtility1997Prototype3
Grokhovsky G-37USSRPropellerTransport1934Prototype1[14]
Grokhovsky G-38USSRPropellerFighter-bomber1934Project0[15]
Grokhovsky G-39 CucarachaUSSRPropellerFighter1935Prototype1[16]
Häfeli DH-1SwitzerlandPropellerReconnaissance1916Production6
Hanriot H.110 & H.115FrancePropellerFighter1933Prototype1
Harbin BZK-005ChinaUAVUAV2006Production100+
Henderson H.S.F.1UKPropellerTransport1929Prototype1
Heston JC.6UKPropellerReconnaissance1947Prototype2
Hughes D-2USPropellerFighter-bomber1942Prototype1
Hughes XF-11USPropellerReconnaissance1946Prototype2
HWL PegazPolandPropellerMotor glider1949Prototype1
Hydra Technologies EhécatlMexicoUAVUAV2006
IAI AravaIsraelPropellerTransport1969Production103
IAI HeronIsraelUAVUAV1994
IAI ScoutIsraelUAVUAV1981
IAI SearcherIsraelUAVUAV1992
Ikarus 452MYugoslaviaJetExperimental1953Prototype2
Ion Aircraft IonUSPropellerUtility2007Prototype1
I.S.T. XL-15 TagakPhilippinesPropellerUtility1954Prototype1
Johns MultiplaneUSPropellerBomber1919Prototype1
Kalinin K-7USSRPropellerExperimental1933Prototype1
Kaman HH-43 HuskieUSHelicopterUtility1947Production193
Kamov Ka-26USSRHelicopterUtility1965Production816
Kamov Ka-126USSRHelicopterUtility1988Production17
Kamov Ka-226RussiaHelicopterUtility1997Production69
Kingsford Smith PL.7AustraliaPropellerAgricultural1956Prototype1
Kokusai Ki-105 OtoriJapanPropellerTransport1945Prototype9
Kokusai Ku-7JapanGliderTransport1942Prototype2
Kortenbach & Rauh Kora 1GermanyPropellerMotor glider1973Prototype2
Larkin SkylarkUSPropellerUtility1973Prototype1
Lawrence SpecialUSPropellerRacer1949Prototype1[17]
Levasseur PL.200/201FrancePropellerReconnaissance1935Prototype1
Lockheed P-38 LightningUSPropellerFighter1939Production10,037
Lockheed XP-49USPropellerFighter1942Prototype1
Lockheed XP-58 Chain LightningUSPropellerFighter1944Prototype1
Lloyd 40.08 LuftkreuzerGermanyPropellerBomber1916Prototype1
LWF model H OwlUSPropellerTransport1919Prototype1[18]
Maeda Ku-1JapanGliderTrainer1941Production100
Macchi M.12ItalyPropellerBomber1918Production10 ca.
Mansyū Ki-98JapanPropellerAttack1945Prototype1[19]
McCulloch J-2USAutogyroUtility1962Production83+
McDonnell XV-1USAutogyroExperimental1954Prototype2
McGaffey AviateUSPropellerUtility1935Prototype1[20]
Millet Lagarde ML-10FrancePropellerUtility1949Prototype2
Mikoyan MiG-110RussiaPropellerTransport1995Project0
Mirach 26ItalyUAVUAV1992
Mitsubishi J4MJapanPropellerFightern/aProject0
Moskalyev SAM-13USSRPropellerFighter1940Prototype1
Moskalyev SAM-23USSRPropellerFighter1943Project0
Myasishchev M-17 and M-55USSRJetReconnaissance1978Production8+
NASA Mini-Sniffer (II and III)USPropellerUAVn/aPrototype2
Nieuport seaplane pusherFrancePropellerReconnaissance1913Prototype1[21]
Nord NoratlasFrancePropellerTransport1949Production425
North American OV-10 BroncoUSPropellerAttack1965Production360
Northrop F-15 ReporterUSPropellerReconnaissance1945Production36
Northrop Flying WingUSPropellerExperimental1929Prototype1[22]
Northrop Grumman FirebirdUSPropellerReconnaissance2010Prototype1
Northrop P-61 Black WidowUSPropellerFighter1942Production706
NPO Molniya Molniya-1RussiaPropellerUtility1992Prototype2
OMA SUD SkycarItalyPropellerUtility2007Prototype1
Otto C.IGermanyPropellerReconnaissance1915Production25
PAL-VNetherlandsHelicopterFlying car2012Prototype1
Piper PA-7 SkycoupeUSPropellerUtility1944Prototype1
Pitcairn XO-61USAutogyroReconnaissance1943Prototype2
Pocino PJ.1AFrancePropellerUltralight1989Prototype1
Portsmouth AerocarUKPropellerUtility1947Prototype1
Potez 75FrancePropellerAttack1953Prototype1
Praga E-51CzechoslovakiaPropellerReconnaissance1938Prototype1[23]
Puget Pacific Wheelair III-AUSPropellerUtility1947Prototype1[24]
PZL M-15 BelphegorPolandJetAgricultural1973Production175
PZL M-17PolandPropellerTrainer1973Prototype1
Raybird-3UkraineUAVUAV2014In service
Rice Knowlton VolanteUSPropellerFlying Car1981Prototype1[25]
Rutan GrizzlyUSPropellerExperimental1982Prototype1
Rocheville Arctic TernUSPropellerRecord1932Prototype1[26]
Rotor Flight Dynamics LFINOUSAutogyroExperimental2006Prototype1
RTAF-5ThailandPropellerTrainer1984Prototype1
RUAG RangerSwitzerland / IsraelUAVUAV1999
Rutan VoyagerUSPropellerRecord1984Production1
S-TEC SentryUSUAVUAV1986
Saab 21SwedenPropellerFighter1943Production298
Saab 21RSwedenJetFighter1947Production64
SAB AB-20 & 21FrancePropellerBomber1932Prototype2
Sadler VampireUSPropellerUltralight1982Production
SAIMAN LB.2ItalyPropellerUtility1937Prototype1
Savoia-Marchetti S.64ItalyPropellerRecord1928Prototype2
Savoia-Marchetti S.65ItalyPropellerRacer1929Prototype1
Savoia-Marchetti SM.88ItalyPropellerFighter1939Prototype1
Savoia-Marchetti SM.91ItalyPropellerFighter-bomber1943Prototype1
Scaled Composites ARESUSJetAttack1990Prototype1
Scaled Composites ATTTUSPropellerTransport1986Prototype1
Scaled Composites Pond RacerUSPropellerRacer1991Prototype1
Scaled Composites ProteusUSJetExperimental1991Prototype1
Scaled Composites SpaceShipOneUSRocketSpaceplane2003Prototype1
Scaled Composites SpaceShipTwoUSRocketSpaceplane2010Prototype2
Scaled Composites White KnightUSJetTransport2002Prototype1
Schneider Sch-10MFrancePropellerBomber1925Prototype1
Schwade Kampfeinsitzer Nr 2GermanyPropellerFighter1916Prototype1[27]
Schweizer RU-38 Twin CondorUSPropellerReconnaissance1995Prototype5
SECAN CourlisFrancePropellerUtility1946Production144
Selex ES FalcoItalyUAVUAV2003
SIAI-Marchetti FN.333 RivieraItalyPropellerUtility1952Production29
Siemens-Schuckert L.IGermanyPropellerBomber1918Prototype3
Siemens-Schuckert R.IGermanyPropellerBomber1915Prototype1
Sikorsky S-38USPropellerTransport1928Production101
Sikorsky S-39USPropellerTransport1929Production23+
Sikorsky S-40USPropellerTransport1931Production3
Sikorsky S-41USPropellerTransport1930Production7
SIPA S.200 MinijetFranceJetTrainer1952Prototype7
Škoda Kauba Sk V6CzechoslovakiaPropellerExperimental1944Prototype1[28]
SNCAC NC.1070FrancePropellerAttack1947Prototype1
SNCAC NC.1071FranceJetAttack1948Prototype1
SNCASO SO.8000 NarvalFrancePropellerFighter1949Prototype2
SPCA 30FrancePropellerBomber1931Prototype2
Spectrum SA-550USPropellerUtility1983Prototype2+
Stearman-Hammond Y-1USPropellerUtility1931Production20 ca.
Stout SkycarUSPropellerTransport1941Prototype4
Sukhoi Su-12USSRPropellerReconnaissance1947Prototype1
Sukhoi Su-80RussiaPropellerTransport2001Prototype8
Tachikawa Ki-94-IJapanPropellerFightern/aProject0
TAI BaykuşTurkeyUAVUAV2003
Teledyne Ryan Model 410USUAVUAV1988
Tengden TB-001ChinaUAVUAV2017Production
Terrafugia TransitionUSPropellerFlying car2009Prototype2
THK-11TurkeyPropellerUtility1947Prototype1
Thomas-Morse MB-4USPropellerTransport1920Prototype4
Transavia PL-12 AirtrukAustraliaPropellerAgricultural1965Production118
Trella T-106USPropellerUtility1949Prototype1[29]
Trella T-107USPropellerTransport1954Project0[30]
Tupolev I-12/ANT-23USSRPropellerFighter1931Prototype1
Vance VikingUSPropellerRacer1932Prototype1
Virgin Atlantic GlobalFlyerUSJetRecord2005Production1
Voisin E.28FrancePropellerBomber1919Prototype1
Voisin TriplaneFrancePropellerBomber1915Prototype1
Vultee XP-54USPropellerFighter1943Prototype2
Vultee XP-68 TornadoUSPropellerFightern/aProject0
Wagner AerocarGermanyHelicopterFlying car1965Prototype1
Weick W-1USPropellerExperimental1934Prototype1
Weymann 66FrancePropellerTransport1933Prototype1
Willoughby Delta 8UKPropellerExperimental1939Prototype1
Willoughby Delta 9UKPropellerTransport1939Project0
WLT SparrowCzech RepublicPropellerUltralight2010Production13
WNF Wn 16AustriaPropellerExperimental1939Prototype1
Yakovlev Yak-58RussiaPropellerUtility1993Prototype7
Yakovlev Yak-141RussiaJetFighter1987Prototype4

See also

References

Citations

  1. Martyn Chorlton and Tony Buttler; "De Havilland's First-Generation Interceptor", Vampire, Aeroplane Icons, 2014. Page 6.
  2. Green & Swanborough (1994), pp.512-3.
  3. Savine, Alexandre (13 November 2000). "'Dingo' amphibian by NPP "AeroRIK" (Designer General Viktor Morozov)". Russian Aviation Museum. Retrieved 16 December 2019.
  4. Various (2 May 2009). "American Airplanes: Ab-Ak". Aerofiles.com. Retrieved 16 December 2019.
  5. Various (2 May 2009). "American Airplanes: Ab-Ak". Aerofiles.com. Retrieved 16 December 2019.
  6. Savine, Alexandre (27 July 1998). "LEM-2, OKA-33 by O.K.Antonov, L.P.Malinovskij". Russian Aviation Museum. Retrieved 16 December 2019.
  7. Brotzu, Emilio; Caso, Michele; Garello, Giancarlo (1977). Scuola-Collegamento Volume 2. Dimensione Cielo, Aerei Italiani nella 2ª Guerra Mondiale Vol.11 (in Italian). Rome: Edizioni dell'Ateneo & Bizzarri. pp. 87–92.
  8. Various (2 May 2009). "American Airplanes: Bo-Bu". Aerofiles.com. Retrieved 16 December 2019.
  9. Various (13 October 2009). "Burnelli". Aerofiles.com. Retrieved 16 December 2019.
  10. Various (15 August 2008). "American airplanes: Ca - Ci". Aerofiles.com. Retrieved 16 December 2019.
  11. Various (3 August 2008). "American airplanes: Cu - Cy". Aerofiles.com. Retrieved 16 December 2019.
  12. Wesselink, Theo (2019). Difoga 421 en Fokker F.25 Promotor (in Dutch). Netherlands: Wesselink. ISBN 978-9491993145.
  13. Various (16 October 2008). "American airplanes: Ea - Ew". Aerofiles.com. Retrieved 16 December 2019.
  14. Maslov, B.; Kapustyan, A.; Komsomolsk on Amure, G. (2003). "Гроховский Г-37 "УЛК" (Grokhovsky G-37 "ULK")". Avia Museum Narod. Retrieved 16 December 2019.
  15. Savine, Alexandre (2 January 2001). "G-38, LK-2 (Light Cruiser) multirole aircraft project by P.L.Grokhovskij, P.A.Ivensen". Russian Aviation Museum. Retrieved 16 December 2019.
  16. Savine, Alexandre (21 October 2000). "G-39 Cucaracha by P.I.Grokhovskij, V.F.Bolkhovitinov, S.G.Kozlov, A.E.Kaminov". Russian Aviation Museum. Retrieved 16 December 2019.
  17. Various (16 April 2008). "American airplanes: La - Li". Aerofiles.com. Retrieved 16 December 2019.
  18. Various (2 September 2008). "American airplanes: Lo - Lu". Aerofiles.com. Retrieved 16 December 2019.
  19. Francillon, René J. (1979). Japanese Aircraft of the Pacific War. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-313-X.
  20. Various (2 April 2009). "American airplanes: Ma - Me". Aerofiles.com. Retrieved 16 December 2019.
  21. Sanger, Ray (2002). Nieuport Aircraft of World War I. Wiltshire: Crowood Press. pp. 28–29. ISBN 978-1861264473.
  22. Various (8 August 2008). "Northrop". Aerofiles.com. Retrieved 16 December 2019.
  23. Němeček, V. (1983). Československá letadla 1918-1945 (Czechoslovak aircraft 1918-1945) (in Czech). Prague: Naše Vojsko (Our Troops).
  24. Various (18 November 2008). "American airplanes: Wh - Wy". Aerofiles.com. Retrieved 16 December 2019.
  25. Various (17 April 2009). "American airplanes: U - V". Aerofiles.com. Retrieved 16 December 2019.
  26. Various (12 October 2008). "American airplanes: Ro - Ry". Aerofiles.com. Retrieved 16 December 2019.
  27. Green & Swanborough (1994), Page 521.
  28. Němeček, Václav (1983). Československá letadla 1918-1945. Československá letadla (Czechoslovakian airplanes) (in Czech). Prague. {{cite book}}: |work= ignored (help)CS1 maint: location missing publisher (link)
  29. Various (2 May 2009). "American airplanes: Ti - Ty". Aerofiles.com. Retrieved 16 December 2019.
  30. Various (2 May 2009). "American airplanes: Ti - Ty". Aerofiles.com. Retrieved 16 December 2019.

Bibliography

  • Green, W. and Swanborough, G.; The complete book of fighters, Salamander, 1994.
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