PRANDTL 4 onboard video

[@jimallen8186]

Should probably have the NASCAR neck collar for these events. Also, are you relying on the pull from the front for any stability concerns? Emergency quick release, stability concerns if quick release?

[@wingnutzster]

Congratulations! I have watched and read and understood everything in the Prandtl paper as well as A Bower's and his team's work and am amazed by this revolutionary understanding of aerodynamics which I really want to apply thoroughly in my own rigid wing foot launched project but I would love to know more about the build, construction and some of the numbers on your machine. I have sent an email so hoping to learn more.

[@wingnutzster]

That spoiler/speed brake is amazingly effective it seems. Is there any outside footage of the craft in flight or on the ground?

[@wingnutzster]

@Khari Jaxtyn thats brilliant how accurate you came to the truth in your opening remark about no one caring

[@Capnmax]

Beautiful Prototype. Any updates on this project?

[@darrylldodson6623]

Red, First of all congratulations to the group for thinking outside the box and on these outstanding achievements!!! This platform looks like it may be a good candidate for a self-launch glider. The related EAA article stated that improvements were going to be made and plans to conduct more testing. Was there more flying done this summer? Can you point me to additional info?

[@RedJensen]

Hi Darryll. Yes some improvements have been made, but unfortunately no further testing has been done at this point. We are trying to get together soon. The builder lives about 400 miles away, so it's not trivial. What other information would you like?

[@darrylldodson6623]

Thanks for responding! The video shows a low level tow, do you have any video or pics of the free flight? Was this wing load tested? Similar to Christian's inquiry: have you documented any performance specifications (empty/gross wt, g limits, glide ratio, Rate of sink, stall, wing area)?

[@RedJensen]

Hi Darryll, no video of the free flights yet, except where the tow line is released. This video is from the very first flight day. We are looking to do more flights soon however. The glider will be coming back down to SoCal so that we can fit some instrumentation (alt, airspeed, GPS, IMU, CPT's, A/B vane etc) where we will capture all of the performance data. We will be heading out for more flight test early in the new year.The aircraft as it sits now is very much just a proof of concept, there are plans to build another, refine some of the techniques and details. The builder (Erich Chase) would eventually like to offer it as a product. There are quite a few moving parts to this whole thing. The physical distance between all of the involved parties and their respective schedules has made it difficult to move forward on this spare time project.

[@justfly2525]

Hey Red... What is the current status of the PRANDTL 4? Could you give us a video update?

[@RedJensen]

Sorry no more video, but its currently being insturmented for test data and flights will resume in a couple months when it arms up.

[@justfly2525]

@@RedJensen Awesome... Keep us posted.

[@captarmour]

congrats great work. a question if i may, would a constant chord work? (or greater chord at wingtip). im thinking i could use shorter span Elevons with wider chord to give me more control authority

[@RedJensen]

Do you mean constant chord wing or aileron? Yes other shape ailerons will work, but the line about which they are hinged must remain straight. So not able to retrofit this, it has to be taken into account before it is built.

[@captarmour]

no, a constant chord wing, sorry i wasn't clear. the idea is with more chord at the wingtip i would have more space to fit larger elevons and also more area out board of the wing vortex may give more thrust. also with more wing area a lightly shorter wingspan may be possible. last of all easier build.

[@RedJensen]

Yep, the math says a constant chord wing will work, but we haven't done it yet.

[@captarmour]

wow thanks a mil...if i may i predict it may work better than expected.

[@RedJensen]

Yes the math says a constant chord wing would work as well, but we haven't done it yet.

[@scottbaxter2682]

Is that a Flintstone braking system ?

[@petegarnett7731]

I thought foot brakes were de rigeur these days.

[@captarmour]

With the bell shaped lift distribution may a constant chord wing with the same LE sweep work as tip losses are not a concern and more wing area at the tip may result in more thrust?

[@captarmour]

haha i forgot i wrote this 6 months ago!

[@Jack-ne8vm]

Curious about wing construction techniques...

[@RedJensen]

What, me worry? It’s hollow molded composite, what else would you like to know?

[@Jack-ne8vm]

@@RedJensen KZbin to the rescue, & beyond!

[@b7gwap]

Any progress on this project?

[@RedJensen]

Nothing more than talk at the moment.

[@b7gwap]

Looks like a really neat project. I’m building a Sandlin Goat 2 right now, maybe flying it later this summer if I stay at it. I’ve always thought it would be cool to have a wheeled ultralight sailplane that was a tailless design. You guys went one further and made it a Prandtl wing! Clearly know what you’re doing, and hopefully you guys can get the project up and flying again. Cheers.

[@ericoschmitt]

What is the glide ratio as it is? And what would it be if the pilot was prone in a blended body such as in the Horten gliders?

[@RedJensen]

We never got a chance to measure in either condition, suspect its over 20 though.

[@ericoschmitt]

That makes it a bit better than an ATOS with prone pilot, so looks like an improvement. Is it foldable somehow? Any idea if an actual sailplane would get better performance than current sailplanes? Like, getting well above 50:1 in the 15 meter class?

[@RedJensen]

@@ericoschmitt This one is a prototype, all composite not foldable. A faired pilot would help for sure, but it's not getting anywhere near 50:1.

[@ericoschmitt]

@@RedJensen that puzzles me... Wasn't the whole idea of the Prandtl project to achieve a lower drag shape than aircraft with empenage? And doesn't lower drag mean it would have a better glide ratio? The builders of the new Horten HX-2 say it is more efficient, so I would expect that a well developed flying wing sailplane would beat a traditional competition sailplane in performance, meaning going above 50:1 in 15 meter class and above 70:1 in open class. Could flying wings possibly do that one day?

[@RedJensen]

Érico Schmitt yes of course. But this particular design is not for that, it eventually will be a foot launched sailplane, not an Open class racer.

[@swiftdereve]

Hello Red Jensen, congratulations for your project. I'm a Swift light PAS pilot and I'm very interested about the technical characteristics (weight, MTOW, glide ratio, speed,...) and your project for the future. Thanks. Christian

[@RedJensen]

Hi Christian, The glider weighs about 140 lbs I believe, 50' span. L/D is somewhere north of the 20:1 range (based on very limited data). Cruise speed seems to be in the low 30's, we'll know more when it flies with an instrumentation package soon. Cheers Red

[@swiftdereve]

Thanks very much. I thought that the glide ratio would be more....28:1 or 30:1 I'm waiting for the good calculations

[@RedJensen]

Christian, we expect that the L/D is actually much better, but we don't want to overstate anything until we have accurate data. :-)

[@swiftdereve]

I understand Red. Good luck in this fantastic project. An with a protection around the pilot, it will be much better. It is the same for the Swift light or Millenium with or without protection fairing.

[@tessemi]

pretty sure thats the first manned test aircraft in quite a while.

[@LunaRendezvous]

Are you working towards wing warping for yaw control as well as roll?

[@RedJensen]

No warping at all, it a very stiff molded carbon fiber wing. In the future maybe split elevons for yaw.

[@Thegillmor2010]

I want one! Thanks for sharing

[@gregripp]

Wouldn't a trike landing gear help?

[@doultonduck6534]

does it have red lights on the bottom

[@wingnutzster]

hahahah - that would explain a lot no?

[@antoni973]

It’s a wonderful invention, can please set me the size mesure of the glider, wont to make one

[@jazldazl9193]

Want gold bars with that?

[@gunnarerdmann7104]

Braking like the Flintstones.

[@thomasrobson6370]

Wow, is the 50' span a requirement for the PRANDTL wing configuration to carry one person?

[@RedJensen]

The plan form of the airplane is Horten Xc, which was a 50' span, foot launched glider. When Al (Bowers) started the research, that's where the span came from.

[@thomasrobson6370]

I thought he was building based on the albatross, my bad..:-(

[@thegreen4me]

prandtl does require a slightly larger span than a similar wing with an elliptic loading if you think about it, since the load starts to decrease closer to the body of the aircraft

[@mavigogun]

thegreen4me , what “body”?!

[@lucywucyyy]

i wanna see a prandtl wing slope soaring, they should take the rc one up a hill or make a hang glider from one

[@petegarnett7731]

They have been doing it for years.

[@1967250s]

You have recreated the Swift ultralight hang glider. Except for their highly aerodynamic pilot enclosure. What was the point of dragging this with a car for several miles? With all that drag underneath? If you wanted to reduce at least a little drag, at least get the passenger legs straight.

[@RedJensen]

If you'd care to read the paper ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160003578.pdf you may have a better understanding of why your comment is off base, or maybe not. The research is stability and control & minimum induced drag with no vertical tails, nothing like Swift actually. There wasn't much consideration for pilot streamlining at all, this was just initial flights and functional testing. Streamlining will be addressed in future iterations. Thanks for taking the time to make a pointless comment anyway though....

[@bipolatelly9806]

That didn't look much fun.... much.... and was that the best place you could find? 😋

[@thomaspiepenbring7132]

Attaching an aircraft to the ground - or to a car - generates stability. So this was not free flight because yaw-axis was completely stabilized by the car !!!

[@Appletank8]

They did let go halfway in other flights.

[@d3xterown]

nice I dream of doing the same

[@RedJensen]

No lights at all. Day VFR only :-)

[@doultonduck6534]

Only day ? So they don't fly them at night at all?

[@RedJensen]

No, gliders don't fly at night.

[@doultonduck6534]

Ok Thanks

[@williamhuang2780]

THIS IS AWESOME!!

[@liefbrunhilda926]

Love the seat belt.... lmao

[@RedJensen]

Lol, except for when it wasn't.

[@charlesbecker6305]

4 minutes

[@alexanderfoelkel8316]

So, a highly aerodynamic wing with an undercarriage totally not streamlined...way to go gents...really...

[@RedJensen]

This video is from the first flight day. Streamlining wasn't considered at this point for a few reasons. 1. The pilot needs to get out as quickly as possible in an emergency. 2. The cage is adjustable fore and aft for CG purposes, which we did. Next time though we'll consult your far superior aerodynamic background for advice before we share.....is that ok?

[@seriousaf8020]

The pilot wants to enjoy the wind dude. Well, I like the sense of having the wind blowing on my face while flying or driving a car, I don't know about other people though.

[@ddegn]

@@RedJensen "we'll consult your far superior aerodynamic background" You might want to check with the people commenting under many of NASA's videos. They've got all the answers. Thanks for sharing your progress with us.