View source for Häfeli DH-3

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{{Infobox aircraft
  |name = DH-3
  |image = Der Doppeldecker wird in Position geschoben - CH-BAR - 3239658.tif
  |caption = 
  |type = Reconnaissance biplane
  |manufacturer = [[K+W]]
  |designer = August Häfeli
  |first_flight = 
  |introduction = [[1917 in aviation|1917]]
  |retired = [[1939 in aviation|1939]] 
  |status = 
  |primary_user = [[Swiss Air Force]]
  |more_users = 
  |produced = 
  |number_built = DH-3 24<br>DH-3a 83<br>DH-3b 3
  |unit cost = 
  |developed_from = [[Hafeli DH-2]]
  |variants = 
}}
The '''Häfeli DH-3''' was a 1910 [[Switzerland|Swiss]] two-seat reconnaissance aircraft, built by the aircraft department of the Federal Construction Works (''[[Eidgenoessische Konstruktionswerkstaette]]'', (K+W)) at Thun, Switzerland.

==Development and design==
Following the poor performance of the [[Hafeli DH-2|DH-2]], August Häfeli designed an improved version the '''Häfeli DH-3'''. It was basically the same airframe as the DH-2, the upper wing had a cutout to give a greater field of fire for the pivoting machine gun. 
It was a two-bay aircraft of wood and fabric construction, powered by a 120&nbsp;hp (89&nbsp;kW) [[Argus As II]] water-cooled inline engine. Initial problems with the landing gear and the engine cooling system led to modifications. Further developments were the re-engined and improved '''DH-3a''', and the '''DH-3b''' used for engine trials. Following successful trials with an installation of the [[Handley Page]] slats all surviving DH-3as were modified in 1932.

==Operational history==
On 8 January 1919 a DH-3 inaugurated the first Swiss air mail service between Zurich and Berne. A DH-3 aircraft failed a structural test in 1923 which caused the DH-3 to be withdrawn from service. The DH-3a, following modification, remained in service until 1939.

==Variants==
;DH-3
:Initial production version with [[Argus As II]] engine, 24 built.
;DH-3a
:Improved version with [[Hispano-Suiza HS-41 8Aa]] engines, four aircraft ordered in 1919. A second order for 30 aircraft was placed in 1919 with license-built engines, a third order for 49 aircraft being placed in 1925. Survivors were modified at Thun in 1932 with Handley Page slats and changes to allow crew to wear parachutes.
;DH-3b
:Three aircraft powered by the indigenous 150 hp (112 kW) LFW 0 engine developed by the Swiss Locomotive and Machine Works were built in 1918.

==Operators==
[[File:Häfeli DH-3 cutaway.jpg|thumb|Cutaway replica of a Häfeli DH-3]]
;{{SUI}}
*[[Swiss Air Force]]

==Specifications (DH-3a) ==
{{Aircraft specs
|ref=The Illustrated Encyclopedia of Aircraft (Part Work 1982–1985)<ref name=Orbis>{{cite book |title= The Illustrated Encyclopedia of Aircraft (Part Work 1982–1985)|publisher= Orbis Publishing}}</ref>
|prime units?=met
<!--
        General characteristics
-->
|crew=2
|length m=7.95
|span m=12.5
|upper span m=
|mid span m=
|lower span m=
|width m=
|height m=3.1
|wing area sqm=38
|aspect ratio=<!-- sailplanes -->
|airfoil=
|empty weight kg=1587
|gross weight kg=1110
|max takeoff weight kg=
|fuel capacity=
|more general=
<!--
        Powerplant
-->
|eng1 number=1
|eng1 name=[[Hispano-Suiza 8Aa]] (HS-41)
|eng1 type=V-8 water-cooled piston engine
|eng1 hp=150

|prop blade number=2
|prop name=fixed-pitch propeller
|prop dia m=<!-- propeller aircraft -->
|prop dia ft=<!-- propeller aircraft -->
|prop dia in=<!-- propeller aircraft -->
|prop dia note=
<!--
        Performance
-->
|max speed kmh=145
|max speed mach=<!-- supersonic aircraft -->
|cruise speed kmh=
|stall speed kmh=
|never exceed speed kmh=
|minimum control speed kmh=
|range km=400
|combat range km=
|ferry range km=
|endurance=<!-- if range unknown -->
|ceiling m=4500
|g limits=<!-- aerobatic -->
|roll rate=<!-- aerobatic -->
|climb rate ms=
|time to altitude=
|wing loading kg/m2=
|fuel consumption kg/km=
|power/mass=
|more performance=
<!--
        Armament
-->
|guns= 1x flexible machine gun in the rear cockpit
|bombs= 
}}

==References==
{{reflist}}

==External links==
{{commons category|Häfeli DH-3}}

* ETH-Bibliothek Zürich, Bildarchiv. [http://doi.org/10.3932/ethz-a-000021315 Häfeli DH-3 (M III) No 530, Argus As II engine], [http://viewer.e-pics.ethz.ch/ETHBIB.Bildarchiv/index2.php?id=ETHBIB.Bildarchiv_Ans_03716-FL viewer]
* ETH-Bibliothek Zürich, Bildarchiv. [http://doi.org/10.3932/ethz-a-000031687 Häfeli DH-3 M IIIb, Argus As II engine], [http://viewer.e-pics.ethz.ch/ETHBIB.Bildarchiv/index2.php?id=ETHBIB.Bildarchiv_Ans_05035-090 viewer]
* ETH-Bibliothek Zürich, Bildarchiv. [http://doi.org/10.3932/ethz-a-000031857 Häfeli DH-3 aircraft, Argus As II engine], [http://viewer.e-pics.ethz.ch/ETHBIB.Bildarchiv/index2.php?id=ETHBIB.Bildarchiv_Ans_05035-163 viewer]
* [https://web.archive.org/web/20110706222659/http://thunensis.braindesign.ch/index.php?option=com_ponygallery&Itemid=26&func=viewcategory&catid=33 Konstruktion Häfeli DH-3 in Thun]

{{DEFAULTSORT:Hafeli Dh-3}}
[[Category:1910s Swiss military reconnaissance aircraft]]
[[Category:Biplanes]]
[[Category:Single-engined tractor aircraft]]
[[Category:Aircraft first flown in 1917]]