My own prone tests

Admit ...when you see a drawing like this, you really get the bird-feeling and dream about soaring over forests and mountains like a eagle. If not, i do get that feeling. This pilot-inside-airplane concept gives me that feeling.

And then i start wondering: "Why are there not so many airplanes like this?"

Many people talk about the prone pilot position and many have opinions, but ...nearly nobody tested the concept the last years. So ...i did it for my own satisfaction. Is prone really easy to do or it is a problem like many sceptics say.

During X-mas holidays in 2011, i used some furniture to test this prone position. At first i wanted to test the position like it is known from the drawing of the Horten HXc.

Before i begin the reports on the tests, i need to tell you that most info about the prone position of the Horten airplanes talk about a angle of 30° for the upper body.

My findings test with 30° upperbody and 20° upperlegs

even after 10 seconds i had pain in the lower part of my back (sensitive area for me). Imagining to feel the shocks during a landing in such a position does make me think it is not a good idea. If you could land on your feet, it might be ok, but ...first you need to "survive" the time in the air in that position. Again ...not good for me.

Please, note that here i still try to keep my head upright. Later i changed that point of view.

My findings test with 30° upperbody and 30° upperlegs

I noticed the following:
Without the support of your knees you slide down along the 30° plank. A hip-harness can prevent that.The elbows feel more at ease below the body than beside the body like in Horten IV. Reimar Horten probably did it to keep the cockpits as tiny as possible. But ...i wanted to know if this position is comfortable. I might be wrong with my findings as i didn't test the position toooo long and i recall that during long car rides i like to lean my arm on the armsupport of the door. Hmm ...maybe more tests will show better result.

The wrists rotate less upsteering than downsteering. And we all know that the rotation for pitch will triple (Reimar Horten used a pitch-roll mixer of 1:3). Might be a problem to just count on the wrists. But ...during the running it is better to wrist steer for less steering oscillations from the running.

The long duration test

I installed the test couch and placed a TV in front of it (counting on the thought that i needed to see forward in a horizontal line). My shin was resting on a cushion. I was planning to view a long movie in this position. Toughest question became ...which movie to see.  :)

Here are the notes i took during the tests in the test couch set at 30° angle for upperbody and upperlegs. Oh yes, the film was the newest Blueray of the first episode of Star Wars, the Phantom Menace.  :)

My findings test with 20° upperbody and 20° upperlegs

My findings were:The head has the same rotation freedom like in the 30°, except ...the upperview is totally gone this time. At 30° you had still some ...but not much.You clearly see that the frontal area gets reduced a lot. You feel more like racing in this position.

The more comfortable prone support

During my tests i came to the idea that maybe the reason for my pains during my tests was the bad support of my body and the position of my head.

Why did i try to force my head to a nice vertical position? Hanggliders don't use that kind of head position. They look half down most of the time.

Could i make a support that is better shaped to my body? Yes, i can. And the technique is not really hard to get that result. I just made a plastic sack of about 2m (6.5 feet) long and about 60 cm (2 feet) wide. I filled it with expanding foam (a mixture of two chemicals you can find in the online composite shops). I let it foam a bit, than placed it in a U-shaped wooden frame which had a support (plastic tube) to get my legs to the proper angle. I placed a few layers of insultaion on the plastic bag to shield my body from the heat of the chemical reaction in the bag (do not do this without that heat protection!!!) and ...i stayed in that position for nearly half a hour.

I took the foam home and installed it at a angle of 10°. Why 10°? Well, i wanted to see if it would be possible to reduce the frontal area of the pilot to the max. Why not 0°? To understand this you need to look at the drawing of the HXa. If i would place the pilot at 0° his legs would stick out the upperside of the wing. Using 10° would make it possible to get more under the top line of the airfoil of the mid section.

This is what i wrote after the test:

"me super happy.
Just made a test on my foam negative shape. You know ...the thing to lay under me while testing prone poisition. Well, i saw only a movie of 1.5 hours. So ...you would think it went wrong, but ...no no, after 1.5 hours all i could say is that the skin support needs to be removed. I felt nothing strange as cramps in my muscles or ackes in my back. After 1.5 hours i was even willing to do another movie. But ...that will not be needed. I am convinced. It works! All you need is a really good shape to lay onto.

10,20,30 degrees. I guess it does not matter. All that changes is the place on earth you see as your head points a bit downwards like the pilot of hanggliders know too. But if they can fly that way with mostly looking downwards, why would i not do it?"

I got hold of a few pictures by Manfred Poznanski, which he took during the presentation of the Horten HIV replica. It shows a good view on the pilot. Now ...look at his hands! I was right in my thinking that the wrists are hard to be upright. You need to use force to do that. Here you can see that Reimar Horten thought the same. He placed the hands at a certain angle inwards. That position feels more comfortable indeed.

Final conclussion

I am very optimistic about the prone pilot position. It really is not hard to get it right. Just the idea to get a pilot really IN a wing sounds like science-fiction to many, like history to Horten Flying Wing Believers and like fun to guys like me.

But if you ever want to use a prone position in your own designs, take care to test the rest of the ergonomics. The freedom to move, the force you can put into the steering, how to fix ("seat belts") and release yourself  into that position without help, how to get in this position without being a elastic person and ...how to get the spar in your design when the pilot is where the spar should be. Don't underestimate the latter!

Have fun with your experiments. And feel free to report to me.  :)