Maurice Delanne (Duo-Mono)

No no ...not a bi-plane!


I got several mails telling that I still miss a page about the Delanne airplanes in my tandemwing section. They were right.

After I received more info about the Delanne concept (Magazine: Air trails, october 1950 and Le fana de l' aviation, Dec. 1988) (thank you, Paul Deweer and Brian Ward), I noticed that this concept is nearly forgotten, while it has the potential to solve some current problems in light and passengers aviation. Later more about that. Let me first explain how the concept works, its advantages and disadvantages and how it was tested.

Modern looking four-seater, isn't it.Wrong, I found this Delanne design in a magazine of 1950!

Maurice Delanne had his own idea about airplanes. He thought that the airplanes were too heavy and they needed a huge engine (adding more weight) to get them in the air. His first own design (a three seater low wing monoplane) which was to be build in his own factory was as good the structural patents were acquired by the French Air Ministry! Due to the lighter weight the performance was better.

Now it was time for Maurice Delanne to learn to fly himself. He notes that he was not such a bright pupil. The airplanes at that time needed to be flown at a regular rate to be able to steer them correctly. You needed experience! That was the reason why so little people flew. Not everybody had the time or money to fly each day. Delanne's idea was to simplify flying so it would attract more people. Attracting more people would lead to more airplanes and ... to a large airplane industry. So, he needed to built a airplane for the Sunday-flier. Delanne wanted:

  • stability
  • quick take off and landing (only needing short airstrips)
  • no stall
  • no complex devices (to increase lift) and the resulting low cost
  • high cruise speed

He knew about the shortcomings of the conventional airplane and heard about the promising possibilities of tandemwings. Even though it has a lower performance due to the interference between both wings, Delanne was convinced that the solution for his problem was to be found in that configuration. He started his tests in 1932.

Quickly he noticed the advantages of this concept in a wind tunnel. Go see the part I wrote about the slotted wing in the page of Nenadovitch to better understand it.

But here Delanne did not use a horizontal tail like Nenadovitch did. He used the rear wing as elevator and ailerons. Also he place endplates on the rear wing. Doing that he created another advantage: the air over the rear wing (captured between the two endplates) was in a delayed stall effect due to the slotted wing effect. As long as the stall was delayed, the good air flow over the elevators and ailerons made control at low speeds possible.

Place your elevator (pitch control) and ailerons (roll control) on the rear wing.The front wing "forces" the air over the rear wing and is captured between the endplates.The control surfaces have their control as long as stall is delayed.The Delanne could not be stalled, so ... you always have control! Safety at low speeds!

OK, you say, hey, Henri Mignet has a similar advantage. Yep, but here there is even another advantage: The CG (Center of Gravity) range is enourmous. Tests showed that it could be placed to 67% of the mean aerodynamical chord. With other words ... no tricky centering. Mignets designs are still touchy to that part. The CG should be at 25% of the total chord. Further backwards ... DEATHLY.

Delanne got funds from the Air Ministry to built a prototype. The goal was a flying command post. French tactical experts wanted to have a commander in the air above his fighting squadron. They needed a two-seater fighter where the rear of the fighter was protected by a set of guns. That way the pilot-commander could turn all his attention on his task. Another thing that the French high placed wanted were braced gull wings. Delanne asked to use a straight wing. But he could not change their minds.

A drawing I made based on a artist impression of the French Arsenal Delanne 10.

In the book "The design of the aeroplane" by Darrol Stinton I found out that they designed eight versions, but only two were built and flown. The front wing was slightly larger than the rear wing. In top view the wings leading edges were separated by a distance of about two times the front wing chord. The vertical distance was about once the chord of the front wing.

A dihidral of 3° and aspect ratio of 6,78 are typical for both wings (Quote article in "le Fana de l' Aviation", Dec. 1988).

Darrol Stinton mentions also that the Arsenal Delanne 10C-2 tandem-wing two-seater fighter with retracting gear had a maximum level speed ratio (Vc/Vso) of about 7,5. Conventional airplanes with piston engines and tails normally had 3 to 3,5. So ... there was a big advantage in speed range. Another advantage was that a rear turret could be placed too. The British would experiment with last last advantage with their Westland Lysander.

To several people the Arsenal Delanne was a proof that a tandemwing could be beautiful too.