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MalcolmW

Well-Known Member
Hello, I’m a pilot working on an IFR rating and curious about the world of experimental aircraft. I’ve looked over some of the postings and may have some comments – hopefully helpful. As a child, I build several model aircraft and flew them until they crashed. I repaired them until they wouldn’t fly. It was fun!

I’ve had three careers (that dratted restructuring!), starting in research, then in banking and ended up running my own consulting business primarily as owner’s representative on construction projects. Along the way, I’ve had fun with fast cars, sailboats and lots of home repair. I guess I’m useful with my hands, which is one of the reasons experimental aircraft fascinate me.

However, I find that few experimental aircraft truly use leading edge technology, which puzzles me. I don’t understand why more usage is not made of contemporary aircraft design and construction practices. Yes, I understand why Lycoming and Continental engines rule the certified aircraft field, plus I understand the limitations of auto derived engines. Yet, there are other avenues – to me – that should have potential.

I fly Cessna aircraft (several types) and I know their design is dated. Even aircraft like the Cirrus does not embody contemporary aircraft technology. So, this is likely to be a learning experience for me. However, I’m willing to share whatever knowledge and technology I have that might prove useful to others in this field.

That's enough!

orion

Well-Known Member
There's really a simple answer to your inquiry and frustration (and that of many others too): 

It takes a substantial amount of investment to incorporate some of the new technologies you might be referring to, into a production aircraft, be it kit or certified. Some of these concepts also require specific knowledge or skill for their use - something that your average homebuilder wont have and probably shouldn't be trusted with.

Now, combine that with the economics of the kit plane business (very low volume production and usually underfunded developments) and you wind up in an economic environment that will not see sufficient return on investment to justify using the "modern" aerospace techniques and materials. Even composites are now getting to the point where the kit price often ends up being well above what might be a justifiable level. Yes, a part of that is due to the fact that many composite airplanes are being designed with metal thinking, resulting in high part counts and complex assembly procedures, but the labor and raw material costs associated with composites are contributing heavily to the rising prices.

For simple, light, and low cost airplane structures, it really is hard to beat tin bashing.

smenkhare

Well-Known Member
Hello, I’m a pilot working on an IFR rating and curious about the world of experimental aircraft. I’ve looked over some of the postings and may have some comments – hopefully helpful. As a child, I build several model aircraft and flew them until they crashed. I repaired them until they wouldn’t fly. It was fun!

I’ve had three careers (that dratted restructuring!), starting in research, then in banking and ended up running my own consulting business primarily as owner’s representative on construction projects. Along the way, I’ve had fun with fast cars, sailboats and lots of home repair. I guess I’m useful with my hands, which is one of the reasons experimental aircraft fascinate me.

However, I find that few experimental aircraft truly use leading edge technology, which puzzles me. I don’t understand why more usage is not made of contemporary aircraft design and construction practices. Yes, I understand why Lycoming and Continental engines rule the certified aircraft field, plus I understand the limitations of auto derived engines. Yet, there are other avenues – to me – that should have potential.

I fly Cessna aircraft (several types) and I know their design is dated. Even aircraft like the Cirrus does not embody contemporary aircraft technology. So, this is likely to be a learning experience for me. However, I’m willing to share whatever knowledge and technology I have that might prove useful to others in this field.

That's enough!
the reason why a lot of the newer tech is not used in existing designs like cessnas and pipers, is because every time the change something, it needs to be recertified which costs a lot.
homebuilt experimentals don't have to be certified the same way so the manufacturers can get away with a lot more.

MalcolmW

Well-Known Member
Hmm, so  are the answer? Gee, I see several areas where some fifty year old aerospace technology could be applied in experimental aircraft to improve performance. In addition, there is one very well documented aircraft that is a significant step forward in design (Facetmobile) that just seems to languish. Why?

In addition, the report prepared by Barnaby Wainfan on his PAVE version points the way to use more technology currently unemployed in the experimental field - see Barnaby Wainfan’s P.A.V.E report (NASA) http://members.aol.com/slicklynne/pavereport.pdf

Now I well understand why Cessna & Piper are slow to introduce new technology, and some of it is due to occupying an oligopolistic position (yes, I did study economics) and extracting economic rent from the marketplace.

I have discussed adhesive bonding elsewhere, and will start on structural and design issues soon.

If I ever build an aircraft, I want it to embody current technology, and this forum will be an excellent place to learn a lot from people who know far more than I about aircraft.

orion

Well-Known Member
The Facetmobile was an interesting airplane and as the PAVE report suggests, could have been very well adapted to the sandwich panel based manufacturing. The problem though was that the design was not really well optimized and according to one of my sources, might have had a few handling quirks that could have made it unsafe for pilots not well prepared for that type of airplane.

The other reason that it didn't rally go anywhere (yet?) is probably simply due to the conservative nature of the aviation marketplace. Airplanes like the Facetmobile get a lot of press (as they should) but there is a big difference between being something that draws a crowd and being truly marketable.

MalcolmW

Well-Known Member
Hmm, very interesting. I did read Barnaby Wainfan's account of the FMX-4, and not being a test pilot, I could only surmise that the design worked well.

However, from your comments (Orion), I deduce that there were some 'deficiencies' or 'quirks' that frightened people away. I'd surely love to hear more about this, for the PAVE report suggested that this lifting body aircraft was a significant advance in aircraft efficiency, and thus, and advance in technology for general aviation.

Does anyone else have insight or special knowledge about the 'Facetmobile' class of aircraft?

orion

Well-Known Member
Well, as they say, there are efficiencies and then there are efficiencies. The Facetmobile did prove a number of ideas that most of us (in the design end of things) knew about but that weren't really generally publicized. The primary two of these were structural and partly aerodynamic. On the latter, it wasn't so much that it was a clean and aerodynamically efficient design (the faceted shape is anything but) - it was more of a practical application of a concept that simply indicated that when addressing wing efficiency, sometimes area is a good compromise to high aspect ratio. This addresses primarily the issue of induced drag and concentrates on the lift coefficient squared part of the equation (numerator) rather than on the aspect ratio (in the denominator). By increasing area you reduce the lift coefficient for any particular aspect of the flight, thus reducing the induced drag. Sometimes the added wetted area is less of a penalty than trying for the long and skinny wing.

One practical example of this was demonstrated back in college where it was shown that when you normalize all the numbers, the Avro Vulcan is just a hair more efficient in cruise that a B-52. This goes counter to the vast majority of publications but if you follow the math and take into account all the configurational details that a high AR wing forces you into, then the blended wing/body comes out well ahead.

But there are several aerodynamic drawbacks to the low aspect ratio configuration also. The major one of these is simply that the pilot had better understand the limitations of such a shape, namely in climb and in maneuvering in the pattern (this also applied to the other airplane of this type, the Dyke Delta). The primary form of glide path control in this airplane is angle of attack. Given the shape of the airframe, this is where the low AR can bite you since if you increase the aoa too much, the drag rise is nearly exponential. Pitch up too much after take-off and you can find yourself in a steep descent before you have a chance to properly react. In landing, put the nose down too much on approach and the lack of any drag devices will have you overshooting the runway. The airplane has to be flown within a precisely controlled narrow band, something a pilot would need quite a bit of training for before jumping in.

The other efficiency that the Facetmobile well demonstrated is in its structural makeup. If I recall the construction right, there were no concentrated masses in the space frame (no spars). It was a simple and light tubular frame that allowed the loads to be easily distributed over the large area and carried by a relatively light structure. If made of composites, the upper and lower skins could be molded as a single piece, then simply reinforced internally with the sandwich bulkheads. Again no concentrated masses - it would be the ideal stressed skin structure.

Expanded to a slightly larger size, the shape provides a lot of volume so issues of baggage and range could be tailored to meet just about any need.

In short, the Facetmobile was an interesting idea but I think it would need quite a bit of refinement before it would have made a good product. Couple that with the conservative nature of the airplane buyer and you find pretty quickly that the success of this airplane would have been pretty questionable.

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