Lifting body discussion

[lr27]

Depends on what you mean by a smoothmobile. Lots of delta wing rc models out there. Don't know if anyone's done a performance analysis.

One of the features of the Facetmobile was the sharp leading edge to create vortex lift. Might want to keep that with the smoothmobile, although I'm sure that there would be a drag penalty at the higher speeds.

 

[rotax618]

G'day,
I have studied the flight characteristics of our faceted models for some time and agree that the sharp LE would give a drag penalty very high speed, but is necessary to make the wing stallproof. My interest is in building safe light sports 2-3 seat aircraft with the performance equivalent to, or exceeding that of a conventional aircraft in that class.
The plan shape of the wing is important in controlling the stall characteristics, the inboard sweep angle and the outer greater outboard sweep angle create vortices which appear to detach at varying angles of attack - this removes the requirement for a very round LE inboard as with the Horton designs.
A curvedmobile would have a reverse Zimmerman shape which would start shedding the vortex from the inboard LE as the angle of attack increases, Barnaby was well aware of this phenomenon when he designed the FMX4. The vortex lift caused by the very low AR and low wing (thing) loading seems to compensate to give an acceptable L/D for the entire platform.
The models we have flown are stallproof, stable and are a joy to fly, most model flying wings are very touchy and can demonstrate deep stalls with no recovery.

Cheers Tom C

 

[brusty36]

G'day,
I was only relating my experience with the quarter sacle model I made of the FMX4 - the model was built from scaled up plans that appear on the Facetmobile web site - either the plans are not as accurate as they should be or I made an error in some way, because the model flew very poorly. I was stable enough but literally fell from the sky when power was reduced.
Obviously Barnaby would not have been able to fly the FMX4 to Oshkosh if it handled like the model I built.
My subsequent faceted aircraft models had about the same wing loading but they had a much more acceptable glide and really outperformed more conventional models I have built.
I believe that a faceted aircraft similar to the FMX4 but with an improved L/D would make a very practical light (2-3 seat) aircraft with many advantages over the conventional layout.

Cheers Tom C

Hi, Tom, those are interesting comments and a great video of your model model. I went to Oshkosh in 1994 when Wainfan attended with the Facemobile and won the "Dead Grass Award'. I was so fascinated by his concept that I just had to build a model, and a few years ago just like you, I downloaded the small 3-view from his website and in 2000, built a 25% replica out of 1/4 inch ali tube and pop rivets and covered with Solatex. I emailed him for the CofG position, the neutral angle of the elevons and the engine thrustline, to which he kindly replied with the relevant information the following day which I replicated. Unlike your model, which I must say appeared somewhat over-powered scale wise, I used an OS 48 fourstroke, and the model flew just as I observed the original, with all the characteristics described by Wainfan. My initial settings were far over-controlled, but once this was sorted, it was very stable in the roll axis (I noticed in your video that yours was quite sensitive in the roll), it flew quite slowly, didn't stall, but just mushed with power off, and as Wainfan suggested would survive a fairly vertical so called stalled arrival. As you say, it certainly was not a glider! Application of power immediately restored level flight. A fascinating aircraft and concept which certainly taught me some new skills.

Regards, Barrie.

 

[rotax618]

G'day Barrie, I have seen pictures of your model previously, It is certainly a beautiful effort. Its great thar it flies so well.
The video of my model was made on the day of its maiden flights and the rates for the controls were still being worked out, it was also a very blustery day with the wind gusting and rotoring over mangrove trees upwind of the mud flat that we used for testing. Subsequent flights have shown it to be very stable in all axes.

Cheers Tom C

 

[rotax618]

G'day Barrie, Attached is an early concept sketch of my model. I always draw models as if they were full size aircraft - so the dimensions are life size. The craft is a bit larger than the Facetmobile, to carry 2 POB.

Cheers Tom C

 

[brusty36]

G'day Barrie, Attached is an early concept sketch of my model. I always draw models as if they were full size aircraft - so the dimensions are life size. The craft is a bit larger than the Facetmobile, to carry 2 POB.

Cheers Tom C

Thankyou for that Tom, most interesting and warrants some study. Your previous comment also interesting and how well you set up for a test flight, you got a lot closer that I did with my over control. I managed two successive axial rolls on my second circuit. It amazed me that the facetmobile could achieve that, especially with my power being somewhat marginal. We have a 400 metre runway at our club and the grass was a little long on the day of my test flight and after 200 metres and the fence looming I just had to pull it off. Having had no experience, I was expecting a dreaded tip stall, but no, it just held the nose up and trundled up over the fence and quietly climbed away.

I have to say, with my limited experience, and what I saw at Oshkosh in 1994, I am surprised that the concept hasn't attraced more interest.

Cheers, Barrie R.

 

[rotax618]

Another interesting machine which showed some promis but hasn't been pursued is shown in the first part of this video.

The same inventor Cheston Eshelman also built a number of very furl efficient motor vehicles.
Makes you wonder why we have to continually re-invent the wheel.

Cheers Tom C

 

[rotax618]

Another example of a successful low aspect ratio aircraft that went nowhere

These Arups were stable, could fly fast, land very slow (far better than any of today's so called STOL types) and carry a reasonable payload in proportion to their empty weight -
A modern version of something like this would be the ideal sports plane.

Cheers Tom C

 

[Loco]

There is a couple of guys I have been trying to contact for a while, the are creating a plane with help of the late R. Horten the model is called a PUL-10, here is the link:

http://www.nurflugel.com/Nurflugel/Horten_Nurflugels/PUL-10/body_pul-10.html

also there is a Horten Flying wing ( glider) flying in Argentina, restored after almost fifty years, looks good:
http://nl.youtube.com/watch?v=k8in4nEyiNA

http://nl.youtube.com/watch?v=QXdTMswP19Y&feature=related

 

[Loco]

here it goes another video of the first flights:

http://nl.youtube.com/watch?v=-ah_Oa-Dd1w&feature=related

That bird is something.

 

[Norman]

Yeah, it may have come up before:whistle: Not exactly a lifting body or deltoid though. I heard that they were short of funds and work space. I also heard that one of the principals recently moved into a new place with a lot of shop space so maybe after he gets settled in they can get back to it. There is a Horten Group web site but you can't get past the home page without a password but it looks abandnd.

[edit] http://www.horten-aircraft.com/ [edit]

 

[gtex09]

Hi,
I'm also developping a Facetmobile-like airplane, based on the experiments done on the same principle.
Till now, with the 1.5m and the 2.45m span model, it looks very stable and safe.
The flow over the wing is really sticked to the surface even at high angle of attack.
Now I'd like to investigate the vertical surfaces need (reduce the main central one, or only two winglet....). Any experience from your side already on this kind of design ?
Rgds.

 

[lr27]

Nice project. Would love to hear more about it. Do you have any numerical measurements of performance?

Seems like the pilot might have trouble seeing over the nose in the -07 version.

 

[gtex09]

Hi.
No measurement in a wind tunnel, if it's your question. I "just" have some simulation of the flow (FLz_Vortex) and self made drawing, for all versions of course, on ACAD. This is the reason why I would like to make a lot of experiments in real life, on large model, before validating a ultimate version for scale 1.
Scale 1 will have to respect the Ultralight specs, it means more or less 450kg for 2 persons and 90hp engine (will be a flat twin BMW motorcycle engine).
For information, and understanding of how it works, it attach one of my engineering drawing where you find the longitudinal cuts of the craft to see, with this arragement of plates, how this gives you a stable wing. Actually, the Cm of each profile, except outboard close to the tips, are all positive. The AOA of the tips are negative, in the way that the craft doesn't stall too from those tip first...This is what I've verified on an earlier flight video (see model -05 stall test)
I also checked, you certainly saw it, the airflow on the top of wing on model -07...
Any more questions feel free...
Regards.

 

[gtex09]

How...I forgot to answer on the second point.
As from the drawing, the "visibility" from pilot's head should be correct, for take off and landing.
Then again, next coming days, I'll modify the cockpit to make it transparent and install a camera to record the view of a pilot, from the head point of view location. Then we'll check it on real data.
Rgds.

 

[lr27]

On something like this, I'm not sure how relevant the 2D sections are. Better than nothing, I suppose, at least at the lower angles of attack.

Any interesting papers or sources that you looked at while doing this design? I find the two papers by Zimmerman, in the '30s, on low aspect ratio "airfoils" (one is called "....small aspect ratio......" very interesting. Can be found at ntrs.nasa.gov with a search.

 

[steveair2]

That is a very nice project! What type of construction do you intend to use on the full scale version?

 

[gtex09]

Dear All,
Yes you're right, 2D sections are not enough to take decision, but it's already something helping. Also for example, at high angle of attack, if you consider "only" the airfoil profile, you do not in our case see the Polhamus vortex effect, giving you more lift.
The fact is that I don't have enough simulation tools to check all details of design. So that also one of the reason's of this step by step development, with the means I can access at my own private level.
I would have liked to know somebody managing the Xplane tools, so that he could modelize the project and check the behaviour....
I think that the solution of realizing the machine at a large enough scale can be helpfull and easier. We are just talking of some depron and fiberglas fabric.
Regarding full scale, I intend to have a composite skin made of either PS foam or PVC foam plus fiberglas fabric, with epoxy. Like models, but larger...Engine, gear, sticks, pedals, all together linked on a frame which is included in the cockpit front cell. Well, this is the idea, up to now.
Rgds.

 

[lr27]

X-Plane won't help you. Not terribly applicable to low aspect ratio planes, because it's computations are overly simplified.

I think a better route would be to instrument your model, though there are still Reynolds number issues, of course.

 

[lr27]

AVL or XFLR might help, but only for low Cl, I think. Say, below 0.2

Is your construction going to be similar to that advocated in the PAV report on the Facetmobile site?