Ultra-Light Aircraft with ETFE Skin

I would start by getting the material data, try www.matweb.com. Next you would have to run a series of calculations based on your actual/proposed dimensions, weight, speed etc. (allowing a rather large safety factor) Possibly someone on here will be brave enough to throw out the equations, and numbers. Unfortunately for a project that has fatal consequences in the event of a failure, I am reluctant to disclose any specific data, sorry.

You might try finding an engineer who can do some consulting work for you, and put his signature/stamp on things.

What is your background in aeronautical design?

It is a dangerous project if you do not enjoy the support of some skilled engineer. have you support from IAA? If yes then they can give you a lot of input.

Before others offer further answers, could you please indicate what size of aircraft you are talking about. Are you talking about small scale models or UAV's (unmanned aircraft) or are you talking about a full-size person-carrying plane?

I am thinking about a 2 seats aircraft.

I have the support of an aerdynamic professor,but since at the moment he is very busy [otherwise I would ask for his help...],I try to promote my plan.

azi

You should take these requests directly to your ethylene trifluoroethylene supplier. Do I have the name right?

He'll share the liability when you crash, so he will want it right.

Fly on.............................

The covering must take into account the structure to which it is attached, so, for instance, with a thin stretchy cover the wing rib spacing has to be closer than for a stiffer, stronger covering. The structure in turn must be designed with the covering in mind. Therefore, the design process is iterative.

This process is time consuming, and must be done quite carefully, for obvious reasons. Most engineers will advise against using an untried covering material, and in many countries you could not fly the plane until someone signs off on it, and no one will sign of on a structure and covering with which they have no experience.

I would not recommend etfe as a covering, partly because it is not puncture resistant, and can rip when punctured. But you should talk to someone locally who has experience in building experimental aircraft.

I have the same doubts on ETFE.

ETFE is known as a good insulator due its material properties: low E-modus and high deformation limits. (it will follow the bending of the cables, allowing short bending radi)

The wing will simply not keep its form, which is the last thing you want as a wing designer.

But it is an iteration process: design a wing which will do it's task and try different materials on it (first theoretical then practical) but always keep in tune with the supplier of the material. And only use it when he supports the usage. (We simply refuse the usage of our products in any commerical aircraft)

Hi AZ Native,

you have a very well developed and equipped company nearby, you should search for support there.

IAI is working in many aspects of planes, try.

Your approach is a good one, the foil will not be the biggest problem but the attachment of foil to ribs.

Look at dragonflies and bats and their wing-structures.

I would try to start with an UAV as with this you will have much more testing capability and any loss will be accepted. UAV may be same size as you plan or at some scaling down for cost.

Have success!

RHABE

I had Falcon Ulralight. A plane many consider to have been the most advanced design of its type.

The main wings were covered in a transparent film manufactured by Dupont for covering greenhouses. It was perfect for the application. UV stable and with excellent tensile properties, it was easy to install.

However, Dupont suddenly changed the material sheet size in what we were told was a deliberate attempt to frustrate its use as an aircraft covering material. Although I never saw the correspondence myself, Dupont is said to have written the manufacturer of the Falcon and threatened action if they continued to use the film.

My whole point in telling you this is that virtually everyone in manufacturing is fearful of having to defend themselves againt product liability suits and nothing attracts sharks with law degrees faster than an aircraft related accident.

There are many materials suited for use in covering ultralights and approved by government agancies like the FAA for use on certificated aircraft. Dacron is but one and, ironically, it's made by Dupont!

L.J.

I'm puzzled by your statement, "It should be faster than the common types...". I don't know about Israel, but I do know that in the United States an ultralight by definition cannot exceed 55 knots (102 km/hr, or 28.3 m/s) top speed in level flight: see http://en.wikipedia.org/wiki/Ultralight_aircraft_(United_States). Other countries call this category "Microlight". In still others, an "ultralight" is vaguely equivalent to what we call a Light Sport Aircraft in the US. Can you tell us what rules you must play by in Israel?

Probably the largest amount of information for design of such aircraft is through the EAA (Experimental Aircraft Association: www.eaa.org). The entire content of the magazine Sport Aviation, going back over 50 years, is archived, indexed, and available on CD (see http://www.eaa.org/sacd/). Their description is "The Ultimate Aviation Reference Library: EAA proudly presents to members The Complete Collection of EAA Sport Aviation Magazine on CD. That's roughly 600 issues, or 50,000 pages of every article, photograph, drawing, letter, and advertisement ever placed in EAA's flagship publication." If anyone has used this specific material, you can likely look up an article on their work. Membership is not very expensive, and would give you access to enormous resources. You DEFINITELY ought to subscribe to The Experimenter online - there's even a free trial period for non-members - ( go to http://www.magnetmail.net/actions/subscription_form_ExAA.cfm) and download the free book! [full disclosure: I've been a member since 1978]

Clear coverings are also available in Mylar (see the Lazair at http://en.wikipedia.org/wiki/Ultralight_aviation, or a Sisler Cygnet SF-2A).

Another thing you will find out as you become involved in the experimental aircraft community: Never use an experimental engine and an experimental airframe together. One or the other, never both. By experimental regarding engines, that means any engine that is not either certified for aircraft use or which has a very long history of use in ultralights.

Even otherwise successful designers (notably Jim Bede) have failed to follow this rule, and people were killed as a result.

From what I know the best way to proceed with building an aircraft, is to pick the engine first, and design according to its potential.

An ETFE skin? I'd be worried also, with its low puncture and tear resistance. If you are making a skin out of this I would GREATLY suggest using a ETFE matrix composite with some sort of fibers. Glass or Carbon fibers, anything that bonds well to a ETFE matrix. Using ETFE alone and being safe means you'll have to make the skin soo thick (to prevent catastropic failure) that you'll probably lose any advantages ETFE can offer. TECAFLON ETFE is offered by a company called Ensinger. You should consider making a normal takeoff UAV (model craft) or single seat aircraft because while experimenting with a different skin material unforseeable risks are apparent. You should do this especially before you make a two-seater STOL craft.

Your question prompted me to ask about engines. You may find that thread of interest. Frankly, I do think if you are going to build an aircraft, pick an engine and build from that. Could be that it could be covered in silk and just painted with the right stuff to smooth it out and keep bugs from punching through. What do you really want to do? Cirrus success is interesting. Once when I was working on a commercial about toothpaste the grip got married to a rig, and I suggested he get a divorce from his idea. He immediately came up with a better rig that worked in short order.