{{short description|1930s British aircraft piston engine}} <!-- This article is a part of Wikipedia:WikiProject Aircraft. Please see Wikipedia:WikiProject Aircraft/page content for recommended layout. --> {{Use dmy dates|date=December 2017}} {{Use British English|date=December 2017}} {{infobox aero engine |name=Dagger |image=File:Napier Dagger NASM.jpg |caption=Napier Dagger at the National Air and Space Museum |engine_type=Piston aero-engine |manufacturer=Napier & Son |first_run=1934 |major_applications={{ubl | Handley Page Hereford | Hawker Hector }} }}

The '''Napier Dagger''' was a 24-cylinder H-pattern ''(or H-Block)'' air-cooled engine designed by Frank Halford and built by Napier before World War II. It was a development of the earlier Napier Rapier.

==Design and development== The H-Block has a compact layout, as it essentially consists of two vertically opposed, flat-twelve inline engines lying side-by-side and driving side-by-side crankshafts. Another advantage is that since the cylinders are opposed, the motion in one is balanced by the opposite motion in the one on the opposite side, leading to very smooth running. The Dagger was remarkable for its fast rotation, running at up to 4,000 rpm but unlike the later Napier Sabre, it had conventional poppet valves.

Although considered a masterpiece of engine design by Frank Halford, there were problems with cooling, maintenance, manufacturing and weight, which were not solved during the Dagger's lifetime and went unresolved well into the lifetime of the Napier Sabre, its successor. The Dagger powered the Hawker Hector army co-operation aircraft and the Handley Page Hereford, a variant of the Hampden bomber. The operational usefulness of the Hector was restricted by engine cooling problems, which made it unsuitable for operations in the tropics and the Hereford was found to be unsuitable for combat, because its Dagger VIII engines were noisy and unreliable. The Dagger was also used in the experimental Martin-Baker MB 2 fighter.

==Variants== ;Napier-Halford Dagger I 1934 – 650&nbsp;hp. ;Dagger II 1938 – 755&nbsp;hp ;Dagger IIIM 1938 – 725&nbsp;hp ;Dagger VIII 1938 – 1000&nbsp;hp, intermediate altitude supercharger, initially known as E.108<ref>Jane's all the world's aircraft 1942</ref>

==Applications== Some of these aircraft were test beds only. * Fairey Battle testbed only * Handley Page Hereford - a few aircraft used for training only<ref>{{cite book |last=Moyes |first=Philip J.R. |title=The Handley Page Hampden |series=Aircraft in Profile 58 |location= Leatherhead, Surrey, UK |publisher=Profile Publications |date=1965 | page=10}}</ref> * Hawker Hart * Hawker Hector * Martin-Baker MB 2 - single private venture prototype

==Engines on display== A preserved Napier Dagger is on display at the Royal Air Force Museum London.

==Specifications (Napier Dagger III MS)== [[File:NapierDagger.JPG|thumb|Napier Dagger at the Royal Air Force Museum, London]] {{pistonspecs |<!-- If you do not understand how to use this template, please ask at Wikipedia talk:WikiProject Aircraft --> <!-- Please include units where appropriate (main comes first, alt in parentheses). If data are missing, leave the parameter blank (do not delete it). For additional lines, end your alt units with </li> and start a new, fully-formatted line with <li> --> |ref=''Lumsden''<ref>Lumsden 2003, p.174.</ref> |type=Twenty-four-cylinder supercharged air-cooled H engine |bore=3.813 in (96.8 mm) |stroke=3.75 in (95.25 mm) |displacement=1,027 in³ (16.8 L) |length=80 in (2,032 mm) |width=22.5 in (584 mm) |height=45.125 in (1,146 mm) |weight=1,358 lb (616 kg) |valvetrain=One inlet and one exhaust valve per cylinder |supercharger=Single-speed centrifugal type supercharger, 5.04:1 reduction |turbocharger= |fuelsystem=Napier-Claudel-Hobson carburettor |fueltype=87 Octane petrol |oilsystem= |coolingsystem=Air-cooled |power= * 725 hp (541 kW) at 3,500 rpm for takeoff * 794 hp (592 kW) at 4,000 rpm at 5,000 ft (1,520 m) |compression=7.75:1 |specpower=0.77 hp/in³ (35.13 kW/L) |fuelcon= |specfuelcon=0.43 lb/(hp•h) (261 g/(kW•h)) |oilcon=0.18–0.35 oz/(hp•h) (7–13 g/(kW•h)) |power/weight=0.62 hp/lb (1.02 kW/kg) |reduction_gear=Spur, 2.69:1 }}

==See also== {{aircontent <!-- other related articles that have not already linked: --> |see also=

<!-- designs which were developed into or from this aircraft: --> |related= * Napier Rapier * Napier Sabre <!-- aircraft that are of similar role, era, and capability this design: --> |similar aircraft=

<!-- relevant lists that this aircraft appears in: --> |lists= * List of aircraft engines

<!-- For aircraft engine articles. Engines that are of similar to this design: --> |similar engines= * Fairey Monarch <!-- See WP:Air/PC for more explanation of these fields. --> }}

== References == * Jane's All the World's Aircraft 1942

===Notes=== {{reflist}}

===Bibliography=== * {{cite web |url=http://www.flightglobal.com/pdfarchive/view/1938/1938%20-%203053.html? |title=Britain's Aero Engines |work=archive at flightglobal.com |date=3 November 1938}} * Gunston, Bill. ''World Encyclopedia of Aero Engines: From the Pioneers to the Present Day''. 5th edition, Stroud, UK: Sutton, 2006. {{ISBN|0-7509-4479-X}} * Lumsden, Alec. ''British Piston Engines and Their Aircraft''. Marlborough, UK: Airlife Publishing, 2003. {{ISBN|1-85310-294-6}}. * White, Graham. ''Allied Aircraft Piston Engines of World War II: History and Development of Frontline Aircraft Piston Engines Produced by Great Britain and the United States During World War II''. Warrendale, Pennsylvania: SAE International, 1995. {{ISBN|1-56091-655-9}}

==External links== {{Commons category}} * [http://www.npht.org/ Napier Power Heritage Trust site] * [http://www.oldengine.org/members/diesel/Duxford/ukaero3.htm Napier Dagger at oldengine.org] {{Webarchive|url=https://web.archive.org/web/20070805183522/http://www.oldengine.org/members/diesel/Duxford/ukaero3.htm |date=5 August 2007 }}

{{Napierengines}}

Dagger Category:1930s aircraft piston engines Category:H engines Category:24-cylinder engines Category:Air-cooled aircraft piston engines