View source for Lippisch DM-1

{{Short description|German single-seat research glider, 1944}}
{{Infobox aircraft
| name = DM-1
| image = File:Akaflieg DM 1.jpg
| caption = The DM-1 at Munich Prien airport after the war
| type = Full-scale [[Experimental aircraft|research glider]]
| national_origin = Germany
| manufacturer = [[Akaflieg Darmstadt]] & [[Akaflieg München]]
| designer = [[Alexander Lippisch]]
| first_flight = Not flown
| introduction = 
| retired = 
| status = 
| primary_user = 
| number_built = 1
| developed_from = 
| variants = 
| developed_into = [[Lippisch P.13a]]
}}

The '''Lippisch DM-1''' is a single-seat [[Experimental aircraft|research]] glider that was designed and built in Germany from 1944.<ref name="DM1">{{Cite web |url=http://www.akaflieg.vo.tum.de/index.php/en/old-prototypes/20-englische-artikel/aeltere-projekte-en/148-dm1-bis-dm4 |title=DM1 bis DM4 |access-date=2014-07-01 |archive-url=https://web.archive.org/web/20140714233908/http://www.akaflieg.vo.tum.de/index.php/en/old-prototypes/20-englische-artikel/aeltere-projekte-en/148-dm1-bis-dm4 |archive-date=2014-07-14 |url-status=dead }}</ref>

== Development ==
During [[World War II]], [[Alexander Lippisch|Dr. Alexander Lippisch]] proposed a [[ramjet]] propelled point defense fighter, the [[Lippisch P.13a|Lippisch P.12/13a]]. It was a sharply-swept delta [[flying wing]] with the engine buried in a thick, blunt-nosed wing. The pilot was accommodated in the forward section of the tail fin, which was as thick as the wings and almost as large. A scale model of the P.12/13a was successfully flown at Spitzerberg, near Vienna.<ref name="sharp">Dan Sharp; ''Luftwaffe: Secret Jets of the Third Reich'', Mortons, 2015, p.119.</ref><ref>{{cite web  | last =   | first =   | title = Experiments with delta wing models of small aspect ratios (circa 1944)  | work =   | publisher = youtube  | date =   | url = https://www.youtube.com/watch?v=-b2TvjL2lpo  | archive-url = https://web.archive.org/web/20160612092710/https://www.youtube.com/watch?v=-b2TvjL2lpo  | url-status = dead  | archive-date = June 12, 2016  | format = YouTube video  | doi =   }}</ref>

Lippisch himself lost interest in the design and began work on the [[Lippisch P.13b|P.13b]] with a different wing, but he was approached by students of [[Akaflieg Darmstadt]] and [[Akaflieg München]], who asked for vital war work so that they would not be drafted. By this time in 1944 Lippisch realised that the war was hopeless and was happy to oblige, arranging for them to build a full-scale aerodynamic test glider for the P.12/13a project.<ref name="sharp"/>

Construction was begun at the workshop of the [[Akaflieg Darmstadt]], as the Darmstadt D-33. The workshop was [[Bombing of Darmstadt in World War II|bombed in September 1944]], so the part-built airframe was moved to the [[Akaflieg München]] workshops at [[Prien am Chiemsee]], where it was redesignated the DM-1 (for Darmstadt-München 1). At Prien, [[Wolfgang Heinemann]] and Hans Zacher from Darmstadt, with [[Klaus Metzner]] and [[Hermann Nenninger]] from Munich, continued the work.

The DM-1 was a single-seat glider made from steel tubing, plywood and bakelite impregnated plywood. The cockpit canopy was integrated into the fin leading edge. Launching the DM-1 was to be by piggy-back or aero-tow.

After occupation by U.S. troops in May 1945, work continued at the DM-1 on behalf of the U.S. military government, with [[General Patton]] and [[Charles Lindbergh]] visiting Prien to see the project. Completed in early November 1945, the DM-1 was shipped in a wooden box to [[Langley Field]] in [[Virginia]] where the flow behaviour of the DM-1 was examined in the [[NACA]] (National Advisory Committee for Aeronautics, forerunner of today's [[NASA]]) full-size wind tunnel.

==US modification==
===Vortex lift===
[[File:Naca Report L7F16 DM-1 Glider 8.jpg |thumb|The DM-1 modified for wind tunnel testing by NACA.]]
[[File:SAH-Lippish DM-1.jpg|thumb|Lippisch DM-1 in restoration at the Smithsonian]]
When tested at Langley, the DM-1 was found to perform poorly. It generated significantly less lift at low speeds than small-scale models had suggested. The cause proved to be vortex lift generated by the models which, due to its much higher [[Reynolds number]], the full-size aircraft did not produce.<ref name="hallion1979">Hallion (1979)</ref>

As a consequence it underwent a programme of modifications. Like all Lippisch deltas it had a thick wing with a blunt leading edge. A strip was fixed along the leading edge to simulate a sharp profile. This created the vortices seen on the model and greatly increased the lift. The origin of modern [[vortex lift]] theory (as seen most famously on [[Concorde]]) may thus be traced to the NACA study and the modified DM-1.<ref name="hallion1979"/>

===Drag reduction===
The large and even thicker vertical stabilizer was removed and replaced with one of much smaller size, along with a cockpit canopy from a [[Lockheed P-80 Shooting Star]] in a more conventional position. Together with improvements to the [[elevon]] hinges, this significantly reduced overall drag.<ref>[http://apps.dtic.mil/dtic/tr/fulltext/u2/a801410.pdf "Research Memorandum L7F16"], NACA, 5 August 1947. {{Webarchive|url=https://web.archive.org/web/20170503011249/http://www.dtic.mil/dtic/tr/fulltext/u2/a801410.pdf |date=3 May 2017 }}</ref><ref name="hallion1979"/>

===Preservation and restoration===
After completion of testing the DM-1 was retired to the [[National Air and Space Museum]], [[Smithsonian Institution]] in [[Washington, D.C.]] for storage at the [[Paul E. Garber Preservation, Restoration, and Storage Facility]].{{Citation needed|date=January 2021}}

===Controversy over its influence===
It has been suggested that the DM-1 influenced design of the [[Convair]] delta-wing jets, beginning with the [[Convair XF-92A|XF-92A]]. Convair engineers are known to have examined the DM-1 and interviewed Lippisch. This has led historians to assume his technical influence, however there is no direct evidence to support this assumption.<ref>Crellin and Lee, Part 4.</ref> On the contrary, Convair had independently discovered the thin delta wing, while the DM-1 had a thick wing and its aerodynamic behaviour is very different. They knew of Lippisch and at least one engineer met him, but his contribution was more in the nature of "moral support" than anything technical.<ref name="hallion1979"/>

==Variants==
Besides the NASA modifications, the Akafliege Darmstadt and München defined some powered designs for a development programme derived from the DM-1.<ref name="DM1"/>
:'''DM-1''' (Lippisch). Glider as originally built but never flown, with thick wings and large tail.
::(NACA). Glider as modified with leading-edge strip, small thin fin, conventional cockpit and sealed elevon hinges.
:'''DM-2'''. Larger, supersonic test plane with {{convert|8.5|m|ftin}} span, {{convert|8.94|m|ftin}} length  and prone pilot. Powered by a Walther liquid-fuelled rocket. All-up weight {{convert|11500|kg|lb}}.
:'''DM-3'''. Developed version of the DM-3 with pressure cabin and more powerful Walther C engine.
:'''DM-4'''. Engine flight testbed, initially fitted with a Walther C. Airframe weight (without engine) {{convert|2500|kg|lb}}

==Specifications (DM-1)==
{{Aircraft specs
|ref=DM1 bis DM4<ref name="DM1"/>
|prime units?=met
<!--
        General characteristics
-->
|crew=1
|length m=6.32
|length note=
|span m=6
|span note=
|height m=3.25
|height note=
|wing area sqm=19
|wing area note=ca
|aspect ratio=<!-- sailplanes -->
|airfoil=<!--'''root:''' [[NACA airfoil|NACA ]]; '''tip:''' [[NACA airfoil|NACA ]]<ref name="Selig">{{cite web |last1=Lednicer |first1=David |title=The Incomplete Guide to Airfoil Usage |url=https://m-selig.ae.illinois.edu/ads/aircraft.html |website=m-selig.ae.illinois.edu |accessdate=16 April 2019}}</ref>-->
|empty weight kg=375
|empty weight note=
|gross weight kg=460
|gross weight note=
|max takeoff weight kg=
|max takeoff weight note=
|fuel capacity=
|more general=
<!--
        Performance
-->
|max speed kmh=558<ref name="AvWeek">{{cite web |last1=Rogers |first1=James |title=Design of Supersonic DM-1|url=https://ww2aircraft.net/forum/threads/1946-av-week-article-on-the-dm-1.59980/ |accessdate=15 Jan 2023}}</ref>
|max speed note=Max speed in terminal velocity dive
|cruise speed kmh=
|cruise speed note=
|stall speed kmh=72<ref name="AvWeek">{{cite web |last1=Rogers |first1=James |title=Design of Supersonic DM-1|url=https://ww2aircraft.net/forum/threads/1946-av-week-article-on-the-dm-1.59980/ |accessdate=15 Jan 2023}}</ref>
|stall speed note=|never exceed speed kmh=
|never exceed speed mph=
|never exceed speed kts=
|never exceed speed note=<!--<br />-->
<!--*'''Max rough air speed:''' {{cvt||km/h|mph kn}}--><!--<br />-->
<!--*'''Max aerotow speed:''' {{cvt||km/h|mph kn}}--><!--<br />-->
<!--*'''Max winch launch speed:''' {{cvt||km/h|mph kn}}-->
|g limits=<!-- aerobatic -->
|roll rate=<!-- aerobatic -->
|glide ratio=7<!--at {{cvt||km/h|mph kn}}-->
|sink rate ms=<!-- sailplanes -->
|sink rate ftmin=<!-- sailplanes -->
|sink rate note=<!--at {{cvt||km/h|mph kn}}-->
|lift to drag=
|wing loading kg/m2=
|wing loading lb/sqft=
|wing loading note=
}}

==See also==
{{aircontent
<!-- include as many lines are appropriate. additional lines/entries with carriage return. -->
|see also=
|related=<!-- related developments -->
* [[Lippisch P.13a]]
* [[Lippisch P.13b]]
|similar aircraft=<!-- similar or comparable aircraft -->
* [[Convair XP-92]]
* [[Payen Pa 49]]
* [[Handley Page HP.115]]
|lists=<!-- related lists -->
}}

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

===Bibliography===
*Crellin, E. and Lee, R,; "Lippisch DM 1 Reconsidered", Parts 1–4, Smithsonian National Air and Space Museum, 2015. (Retrieved 26 September 2020). Parts; [https://airandspace.si.edu/stories/editorial/lippisch-dm-1-reconsidered-part-1 1],[https://airandspace.si.edu/stories/editorial/lippisch-dm-1-reconsidered-part-2 2],[https://airandspace.si.edu/stories/editorial/lippisch-dm-1-reconsidered-part-3 3],[https://airandspace.si.edu/stories/editorial/lippisch-dm-1-reconsidered-part-4 4].
*Richard P. Hallion; "Lippisch, Gluhareff, and Jones: The Emergence of the Delta Planform and Origins of the Sweptwing in the United States", ''Aerospace Historian'', Vol.26, No.1, Spring/March 1979. pp.&nbsp;1–10. [https://www.jstor.org/stable/44524912 JSTOR copy]

==External links==
{{commons category}}
*[http://www.akaflieg.tu-darmstadt.de/geschichte/d-33/ Akaflieg Darmstadt website]
*[http://blog.nasm.si.edu/aviation/lippisch-dm-1-part-1/ Lippisch DM 1 Reconsidered, Smithsonian NASM]
*[https://www.youtube.com/watch?v=s5y37mTx5Ts "Declassified UFO recovery Nov 3, 1945 Germany Operation Paperclip - Lippisch"] (YouTube video)
*[https://www.youtube.com/watch?v=_zsZxaVP4v0 "Investigation of the DM-1 Glider"], NACA Langley, 1 August 1946 (YouTube video)

{{Akaflieg Darmstadt aircraft}}
{{Akaflieg München aircraft}}
{{Lippisch aircraft}}

{{DEFAULTSORT:Lippisch DM-1}}
[[Category:1940s German sailplanes]]
[[Category:1940s German experimental aircraft]]
[[Category:Tailless delta-wing aircraft]]
[[Category:Akaflieg München aircraft|DM-1]]
[[Category:Lippisch aircraft]]
[[Category:Akaflieg Darmstadt aircraft]]
[[Category:Unflown aircraft]]