My own prone tests

If i like something, i test it. :)

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.

Horten HXa, the first of the hanggliders of Reimar Horten. The pilot is nearly complete inside the wing.

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.

Horten HXc

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

I try to imitate the pilot position of the HXc. I used the mixed position of 30°upperbody and about 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

After newyear i was able to make some primitive test-couch to test the 30° angle position of the pilot and the placement of the hands.

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.  :)

  • 21:11 start
  • 21:22 shin feels like i will not be able to do this for three hours
  • 21:36 knees get soar
  • 21:37 without chin rest
  • 21:45 test couch too wide. Arms start to feel numb where couch touches arm
  • 21:53 pain middle of back
  • 22:05 hard to sit still. Moving a lot
  • 22:25 drinking is tough in this position(bottle of Lipton Ice-tea)(need straw next time)
  • 22:30 with hands under chin it goes well, without not
  • 22:50 knees hurt
  • 22:55 the fillings in my mouth even start to hurt (strange feeling)(chin was on cushion)
  • 23:00 No prone pilots in my next drafts any more!
  • 23:05 Anakin Skywalker gets in spaceship. I get in pain. Chin pain, knee pain. I quit the idea of a comfortable prone position! (giving my back a more upright position and placing hands under chin)
  • 23:20 I step off test couch. I feel more air getting inside my lungs. Star Wars rules!  :) "
At this point i was no longer convinced to keep the prone position as a good idea. Not many pilots will handle this pain just for a good flight. I start to think that Mr. Sheidbauer (Horten's test pilot) was a really tough guy.

My findings test with 20° upperbody and 20° upperlegs

After looking again and again and again at the sideview of the Hxc by Reimar Horten, i still believe that Reimar didn't plan to use the 30° angle for this one. Maybe just for the upperbody, but those upper legs are not at 30° my honest opinion. That is 20°. Out of curiosity i tried to use a 20° over upperbody and upperlegs using my wooden test couch.

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.

Me getting cooked at a certain angle. :)

Here you can see that under my shoulders there is no foam shaping. I needed to do another session to get a pair of shoulder supports to get a proper body support.

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.

Testing the foamed body support with the extra shoulder parts. I cut out the part in front of my head.

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 would think it went wrong, but 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.

Sascha Hauser in the Horten HIV replica. Look at his hands. Surely NOT upright position. This way it feels neutral in muscle force. Permission to use picture by Manfred Poznanski.

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 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.  :)