Fun in the desert

[Red]

Hey Guys,

I'm slowly settling into the life down here in Palmdale. The job is fantastic and I couldn't be any happier.

I thought I would tell you a little about a flying wing project that I am working on called PRANDTL-D (Primary Research Aerodynamic Design To Lower Drag). As you know, all aircraft suffer to some extent from the effects of adverse yaw, that is opposite nose swing with aileron input. The Wright brothers were stumped by this, and it resulted in many crashes and late night brainstorming sessions until they figured out that a vertical tail was the answer. To this day, the overwhelming majority of aircraft follow this tradition to deal with the problem.

In the early part of the last century there was a bright German aerodynamic theorist named  Ludwig Prandtl. The long held notion is that a wing should be deigned so that the lift is distributed evenly along the span (greatest at the center and tapering off in an elliptical arc to the tip) for greatest efficiency. Prandtl wrote a very short paper detailing that elliptical lift distribution was not the most efficient in the strictest sense, and it was universally ignored by the engineering world. The paper is in German and has only been poorly translated. This is the same guy more famously known for the Prandtl-Glauert singularity, which describes the pretty cloud that forms around an aircraft just before it goes super sonic.

Later on, two brothers named Horten built a series of flying wing gliders in the WWII era that had no vertical surfaces, yet flew incredibly well and and were rumored to have demonstrated proverse yaw, or yaw with  the direction of roll, potentially  building on the aerodynamic theory Prandtl had spoken of in his paper. The brothers were very secretive and never shared any of there research or records with anyone. Reimar, the brains of the two, took the secret to his grave, largely never writing anything down. They had figured something out though, as their gliders flew better than anything else at the time.

The Chief Scientist here at NASA, Al Bowers, has been a flying wing aficionado and has studied the Horten brothers designs and Prandtl's theories for many years trying to figure out the secret. The math used to predict this non-linear lift distribution is so arcane, that only Al and two other aerodynamics professors on the planet have a handle on it. In the future a computer program will spit this out, but for now it's all by hand. If Prandtl's theory is correct, it would mean that there is actually induced thrust at the tip causing proverse yaw, instead of the normal drag. This is not so far fetched as you would think. Look at any modern airliner and notice the upswept tips. These we developed by Dr. Richard Whitcomb and provide an efficiency boost the same way, by creating induced thrust. The Horten's were apparently achieving the same result but with no upswept tip. 

As a research platform, a pure flying wing is the perfect test bed to fly if you are looking for adverse yaw effects. Al designed the planform according to Horton tradition. This new design dubbed H Xc uses Prandtl's theory to vary the local angle of attack to achieve non-linear distribution.  Up until this point, nobody has ever flown a Horten wing that exhibited these proverse yaw characteristics with instrumentation to prove that this condition exists and flies in the face of conventional aerodynamic wisdom. Al has been driven to get that data and prove that Prandtl was correct after all. In the R/C world, models of the Horten fly fine, because we have differential throw, split drag flaps, gyro's etc. same for real aircraft like the B-2, it has a computer flying it. Prandtl on the other hand demonstrates a purely aerodynamic solution to the problem, no mixing or differential etc.

When I came here to Dryden, PRANDTL-D s/n 001 was already flying. In fact it was sitting here in the shop broken and abused. It had seen a hard life, crashing more than once and breaking in half twice. Every summer a group of 15-20 interns from colleges around the country come to Dryden for the summer. Led by Al Bowers they had built the first one as a student project, and began construction of a second. I immediately offered my assistance in getting it back airworthy and began a test flight program in earnest.

P-1 is strictly an R/C aircraft, there was no data system at all on board & it weighs 14 lbs. It is bungee launched with a heavy duty high start, so flights are quite short. It was intended to be a concept demonstrator only. After I came here, I made quite a few changes and soon it was flying very well indeed. I had doubled the time aloft, and more than quadrupled the total number of flights. It was soon decided that an attempt should be made to try to collect data with P-1. Ironically enough, and iPhone was used with an accelerometer app that turned it into a stand alone data recorder. Additional flights were made with this system, and another flight computer. Once the data was reduced, the gyro plots showed conclusively that s/n 001 demonstrated proverse yaw! Al took the data to a center tech review board (which must give their approval before the data can released publically) and while they agreed with the findings, they also agreed that a finding this stunning and controversial would require more intensive instrumentation to prove this without a shadow of a doubt. This would require that ship s/n 002 would need to be built up in a very short amount of time. In spite of this word was sent out of our success and while no data was presented, the aerodynamic world has taken notice, albeit in a small way so far.

Al was a bit dejected thinking we were sunk until next summer (he's really doing this for the interns) but I set to work on s/n 002 immediately with the goal of flying it by Aug 2nd, 1 week before the interns went back to school giving them the slimmest chance to reduce the data before they left. s/n 002 was built up over a 10 day thrash session. This one would be a bit more complicated as it would have a flight computer to record additional data. The aircraft would have to remain R/C controlled so that nobody could argue that the flight computer (autopilot) was having any kind of effect on performance. In addition, I added CPT's (control position transducers) that report back actual control position, as opposed to commanded position for data integrity. A sophisticated air/data probe was fitted with integrated Alpha/Beta vanes. These vanes would allow independent verification of Alpha (pitch) and Beta (yaw) activity. The first flight of s/n 002 occurred last Thursday, August 2nd, right on schedule.  3 series of doublets being performed to collect data. A doublet is a maneuver designed to upset the aircraft and measure its stability response. It is very short in duration and thus revealing true handling qualities and negating and stability over time effects.

So what does this all mean? For starters this theory could account for up to 13% reduction in induced drag. Beyond that, any aerodynamic shape can benefit; props, sails, parachutes etc. For me the implications are more personal, I'm sure my racers will get some attention here shortly. :-)

In the meantime, the data will be presented again, & hopefully cleared for public release. When that happens there will be press releases, interviews and articles in the major publications. NASA is applying for a patent so the data will be available to all. For now, the Smithsonian National Air and Space Museum in DC has requested that NASA donate PRANDTL- s/n 001 for public display.

Cheers
Red

[amackles]

Thanks Red, that's a great story (and glad to hear you are doing well).  Coincidentally we watched this documentary on how some of your NASA compatriots recreated the Horten brother's design to see it's stealth. Definitely worth a view - http://www.youtube.com/watch?v=NaJzKjtjZnY

[Red]

Oh man don't get me started on that 

The Horten brothers knew nothing of stealth and insinuating that they did is just disingenuous and fodder for TV I guess. Whole premise that Hitler had stealth in mind is ridiculous. The plane, being all wood naturally has a lower radar cross section (RCS). The shape is derived from many years of aero research, again nothing to do with stealth. They used wood because: a. They were familiar with it & b. There was a war on! Hitler ordered that no metal could be used, not for stealth reasons, but because it was in short supply and badly needed by those folks who were building production aircraft, not one off flying wings! The whole thing makes me throw up in my mouth a little haha 

Could it have had a low radar signature? Of course, but purely by coincidence however. Interesting revisionist history though.

[Jon_Stychno]

Awesome report Red, its cool to hear what's going on behind the scenes at an agency I think we'd all love to be a part of to some degree. Keep em coming.

[amackles]

Very interesting, hadn't thought of that but it makes great sense. Looking forward to the next update.

[poh]

I love the canopy on version 2, only a modeler would add that touch!

I guess I also assumed from that documentary that the radar cross section was being considered back then. I was wondering while watching why these guys from Northrop could spend so much time working on a mock-up not related to a real product, plus you'd imagine you could model/simulate it in CAD (but there would be a lot less drama).




 

 

[Red]

I love the canopy on version 2, only a modeler would add that touch!

I guess I also assumed from that documentary that the radar cross section was being considered back then. I was wondering while watching why these guys from Northrop could spend so much time working on a mock-up not related to a real product, plus you'd imagine you could model/simulate it in CAD (but there would be a lot less drama).
 

The NG guys worked on it because they were paid to lol

[Red]

Some more action: http://www.nasa.gov/content/nasa-drydens-droid-mini-uav-reaches-new-heights/#.UgA2dLaXPvY

[McDRacing]

Looks like you are having to much fun!!!

[Red]

More cool stuff...

You know, some days are better than others. My office seems to be a gathering point of sorts, you never know who or what will wander in here. Such was the case this morning when Al Bowers pops in with an unassuming tin can. He pops it open and produces the actual acetate film trace showing the precise moment in history where Chuck Yeager broke the sound barrier in the X-1. I held it in my hand, not a copy, nor a replica, the actual film, the Smithsonian has a copy! I have goose bumps.....soooo cool.

[PTKohlmann]

Heya, Red

Sounds like you've hit nerd nirvana down there! 

Glad to hear that you are settling right in.  That is an amazing piece of history.

Koh

[Red]

Guys,

The PRANDTL video has just been cleared for public release. It offers a bit more insight into the research effort ahead of the full data release while the patent lawyers do their thing.
https://www.youtube.com/watch?v=y8QWnvxwdHA

Also I had the pleasure of hosting the Mackles family last week for a tour of the NASA/Dryden facility. My offer still stands if anyone wants to come down for a visit.

Happy Holidays
Red

[amackles]

Speaking for the Mackles family, it was an amazing and inspiring day - seeing the history of Edwards, meeting with the other NASA scientists/engineers, seeing Red's shop and some of the really ground breaking work that can only be done through scale models. We highly recommend taking Red up on this offer, it's worth the trip down even if just for the tour. Thanks again Red. PS - some of our pictures are posted here: https://www.facebook.com/media/set/?set=a.10151933070664681.1073741831.660109680&type=1&l=c7e0ef3091
 

[Red]

Hey Guys,

I hope you are all doing well. I think of all of the good times I had at WCF often. It's good to see the website still active!

Thought you might like to see some of the stuff I've been up to. I'm still loving it down here! P1 is all crated up and may be heading out for display at a few select locations prior to the NASM. I've attached some other links as well.

https://www.youtube.com/watch?v=7sALW8qa8_o&list=PLiuUQ9asub3T6ehGBhTu-I10jfA8yMsrc
http://www.nasa.gov/centers/armstrong/Features/TGALS_first_flight.html#.VO300vnF-Ag
http://www.nasa.gov/centers/dryden/Features/usa_to_uas_air_tow.html#.VO31MvnF-Ag
http://www.nasa.gov/centers/armstrong/Features/fiber_optics_improve_efficiency.html#.VO31WPnF-Ag

C-ya
Red

[tall n skinny]

  Hey Red, Yep you hit the lotto with that job. AND I think you deserve it 100 percent.
John