A new way to control pitch

I had a idea several years ago. I totally forgot about it till I was searching for some old files. Here it is. I scanned the old drawings, so there are some texts in the scans. Don't try to read them. Waste of time. I placed the full text in this page.

My source of inspiration

In the Nurflugel mailinglist a member wrote that the airfoil of a unswept flying wing glider gets deformed when the glider is trimmed for a higher AoA (angle of attack). This does lead to less Cl.

The other part of my inspiration was the trim-tail of the Genesis.

How my idea got shaped

"Trimming a unswept glider gives it a lower Cl"

Trim-tails always give drag

Question: "Is a elevator always used?"

It was this last question that got me thinking. A elevator is used while maneuvering, but not on straight glides. So, at those glides a trim-tail gives unnecessary drag. Well, I thought.. why not make a disappearing tail?

The development

A disappearing tail.. hmmm.. how could I make it?

Step 1

I first thought about pulling the tail inside the fuselage. But that would lead to a very thick fuselage to hold the entire tail. And the technique would be hard to make.

Step 2

Rotating the tail away would be easier (no rail-system). I thought first about one rotating tail-part. It would turn behind the fuselage to one side and it would rotate as a fully moving tail. Both actions happen at the same time.

I thought to change the incidence to the maximum at the smallest movement of the stick. Small or high tail-forces would depend on the angle at which the tail appears from behind the fuselage.

I was rather happy with this development at first, because it made less drag during straight glides. But the technique did sound rather complex. A bit too complex to scale down for a proof-of-concept scale glider.

The single tail could also create a roll-moment. But due to the short distance between the tail lift-force and the roll-axis, the roll-moment will not be large.

Step 3

I wanted to make the second rotation (incidence control) disappear. This way the technique would be easier to make and to scale down. So I did split the single tail up into two tail-parts. One fitted with positive incidence and one with negative incidence. Pulling the flight stick makes the one with negative incidence appear while the other remains hidden. Pushing the stick would do the reverse.

If you look at the picture you will see that they fit nicely together.

I think that this system will weight a bit more, but it surely is less complex.

I did give the tail-parts a lot of incidence because they need to give the maximum needed lift when fully deployed. But they still can create a roll moment.

Step 4

To solve the roll problem, why not use a tail-part on both sides at once. To solve the complex needed technique I did use both necessary rotations (in-out & incidence-control) but I placed them far from each other.

I really like this variant. It would still be rather easy to construct and it gives control over the incidence and the used tail-surface.

One question I still ask myself: Should I give control at the same time to both rotations or could I fold the device till it is needed and then extend it fully and use the incidence control alone. The latter should be controlled by two levers (flight-stick fort incidence control and a separate lever to extend the tails). But would it be safe??

This variant looks a bit like a set of F-15 wings on a snake tail.

My thoughts about this design

  1. Wouldn't it give a too large gain in weight?
  2. It sure will create a weight further away from CG when compared to the elevators on any Fauvel or Marske design. So a new balance around the CH should be made.
  3. The tail-parts don't have fixed points like a normal tail. Those normal tails have a spar that runs through both sides. This tail-system is fixed to the fuselage only by its rotation-point. Could the tail be constructed (lightly enough) so it wouldn't snap when high forces work on the tail?

Possible variants on the idea.


I hope you can use the idea. If you can, please, tell me how your tests went.