Tails on tips

This concept is, according to some people, not a true flying wing. Euh... I don't see a classic tail, or a canard, so I see it as a flying wing.

Tails on tips might not be the right name for it. I heard about "Outboard Horizontal Stabilizer" or "Scissor wingtip controls".

Blohm & Voss

What has happened in this concept? The wing has a great angle of sweep (a German design had 40°). The classic horizontal tail surfaces are placed on the tips of the wing. This way you have the necessary down force to compensate the turning moment of the wing (the force-arm (distance between center of gravity and elevators) is long enough) and you don't need to have a long fuselage to hold the tail. Most known designs have the vertical tail also placed on the tip. Here you can also combine the elevators with the roll-rudders (combination known as elevons).

The German company Blohm & Voss did some tail-on-tip-designs in WW II. The Luft '46-site (see links nurflugel-site) has many of the unfinished projects of the Luftwaffe. They have superb 3D-drawings of some of these designs.

A nice picture of the Blohm & Voss P212-3 made by Tor Pedersen (permission granted by Dan Johnson) Click here for link to Luft '46 site (www.luft46.com) to see more of the last German designs of WW II.

I got these pictures from Bjorn Rabben. They show his model of the Blohm & Voss P212. He did use elevons in the main wing instead of the original rudder configuration.

I received this mail from Antonio Fernández (MEWGULL@terra.es), he seems to have had some problems, but now has a good model: "Have been experimenting with "backyard Nurflugels", small flying wings. I first built a high dihedral, 212-01 model that has the fins over the wing, at two-thirds span. It was horrible! spin both sides, flat spins, the lot! The CG range was almost nil (interestingly you must add the weight in the extreme tail, the exhaust of jet!) and then I made a larger 212-03 that has the double winglet-fin assembly on the tips...Steady as a rock, like an arrow on its trail. The winglets act like this: if raised inner only, like ailerons coupled to rudder, gentle turns. If depressed outer, like normal aileron, but sharp response. The rudder makes pronounced almost flat turns, that if exceeded tend to crab and in the extreme, swings out. But stable flyer when all straight and no spins, good cg range and very responsive, proportional to inputs of command. Used reflex profile and no elevons in wing. I´m building larger one with electric fan unit... "

I found out that RBC makes a kit to built a Blohm & Voss P212-023 RC model (electric ducted fan). So you can test its behavior yourself. I asked about its building and flying. They reacted:

"The P212 flies super (it is my personal favorite jet). He is controlled by ailevons (ailerons and elevators mixed) and the small tipwings are controlled directly at once too. The steering is direct and very effective, but it has a bit too much stability. In other words ...he wants too turn horizontal (yaw) just like a trainer. Not really something you like in a jet, but not bad.

We used a bit less sweep and dihedral than the original design. Although he can fly slowly, it is hard to judge the landings when the wind is low. Due to its great glide ratio you might overfly the airstrip.

There are fences placed on de wings (look halfway the wing) to keep the airflow healthy. I didn't try the model without the fences because I found flying the TA183 without fences not so good. I just wanted to go for good flight behavior at once."

www.rbckits.com

BV215 was a later design in the same style.

Advantage of tails on tips:

Q: I don't know them yet. Any reaction is welcome.

A: (From Kenneth M. Dorsett (Specialist, LMTAS Aerodynamic Stability & Control)) "I have some experience with such surfaces on high performance tactical aircraft; however, my comments should apply to a low-speed glider as well. Advantage: A large moment arm with respect to the CG makes these surfaces ideal lateral-directional controls. A great deal of control power can be generated by a relatively small surface. By staggering the surface aft (like Blohm & Voss did), you can generate a good deal of longitudinal control as well. These surfaces typically remain effective to very high angles of attack (AoA)."

Disadvantages:

Q: I don't know them yet. Any reaction is welcome.

A: (From Kenneth M. Dorsett (Specialist, LMTAS Aerodynamic Stability & Control)) "The primary disadvantage comes from structural integration problems. Tip mounted surfaces such as these are hard to keep stiff -- particularly on a thin-winged, high speed aircraft."

Extra info about these designs from Blohm & Voss

I saw this comment of Guy Inchbald from England in my Facebookgroup Horten Flying Wing Believers:

"As a historian I have made special study of these B&V "bats". I also have a family connection, by marriage. First, the main wing. It is constant-section (aerofoil unknown), built back from a leading-edge main D-spar which doubles as an armoured fuel tank. The tips are known as outboard horizontal stabilizers (OHS) and the design as semi-tailless. These OHS created span loading of the wing and reduced stresses on the centre section, making possible a fast and low-cost constant-chord construction without twist or anything like that.

Much wind tunnel work went into the positive feedback between OHS positioning and wingtip aerodynamics, allowing high efficiency and smaller surfaces than the equivalent conventional design, as well as enhanced takeoff, landing and that Holy Grail of the jet fighter - controllability at high AoA. Typical of this sort of idea - simple in concept, but hard to get right because everything affects everything else.

The trailing-edge control surfaces were quite complex, with several acting in various degree as elevator, aileron and lift flap. Skoda-Kauba adapted one of their light aircraft to test it, but nobody seems to know what the system was or whether it ever flew.

The basic design evolved through several projects, from a pusher-prop fighter (no fins needed because the prop offered enough tail area) to a twin-jet night fighter (with fins because more nose clutter and no prop) - this last receiving an order for 3 prototypes just before the war ended.

Just to add, as a model which does not need combat performance, yes just a plain wing with adjustable OHS should work well. I'd probably make the OHS and fins a little oversize, to be safe."

Pay attention to the vortixes!

Ragflyer told the following in the Homebuiltairplanes forum:

"One thing to keep in mind is if the elevons are out board of the wing then they experience an upwash from the wing tip vortices rather than a downwash as is typical for a tail inboard of the wing. This means that at stall you could have a pitch up making things hairy. If the wing lift reduces due to stall then the wing tip vortices get weaker and decrease the upwash on the elevons creating a pitch up . Careful design would need to be made to prevent this.

IIRC (maybe misremembering) space ship 1 did uncover an issue during testing relating to this."

cblink.007 added to this post:

"Correct, SS1 went into a deep stall during aft CG stall testing and departed controlled flight. The ultimate fix was increasing the horizontal stab & elevon span, as well as incorporating boundary layer fences."

Skoda-Kauba SL6

Spaceship One

Yes, you want to keep those rudders away from the flames of the rocket.

Below you can see the angle of the elevators. Slighty at negative angle as expected.

My own ideas with this concept

in my point of view this can create a fun ultralight. Something that will catch the attention and still rather easy to build. If you go see my first Birdwing-idea in the Few of my thoughts section, you will see a low aspect ratio with a split V-tail. That idea is going through my head for years. I made a few rough drafts of that idea.

Here a few drafts of the idea.

Now the comment of Ragflyer, which i mention above made me doubting this project. I told that on the HBA-forum and Ragflyer answered:

"While you may have other issues, this configuration would not be affected by what I said. You want to stay away from the tail being outboard and behind a wing. Here you have it blended with the wing. Build an RC model and try it out."