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Aluminum foam composite construction

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cheeka

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Hello everyone, I was wondering if it was possible to use a building method for a wing where we can use aluminum as a "skeleton" for handling all the structural loads and foam blocks hot wired with the appropriate airfoil shape which would then be Fastened to the "skeleton". I envision upper and lower foam block halves that would be attached to the wing and then have the wing covered by Oratex or the like. What do y'all think?

I think that the hot wired foam block would conform to the airfoil profile way better than a riveted wing would. I don't think there has ever been a metal wing sailplane that comes close to the performance of a composite sailplane that seem like they literally stick to the sky.
 

BBerson

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Aluminum skin can be covered with fabric and sanded to any level of perfection desired.
The Schweizer 1-35 was fabric covered metal.
 

Vigilant1

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OP:
So the aerodynamic forces on the wing get passed through the foam to the aluminum structure? What's the plan for affixing the AL to the foam?
What's the advantage over a regular hotwired solid core wing? Oratex ain't cheap. What will we do when the service life of the Oratex is done--how to remove it from the foam.
 

cheeka

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Pictsidhe, bonding for the Oratex will be done on the metal ribs. The metal ribs would be spaced throughout the span and the space in between would be taken up by the foam blocks. Heat resistant foam is available, that might alleviate the issue.

BBerson, the Schweizer 1-35 wasn't fabric covered. It was metal skinned but after manufacture body filler was applied and template ground to help retain the airfoil profile. Even this level of preparation didn't help it in competing with the glass ships.

Vigilant1, having a solid core hot wired wing does not in my opinion give predictable structural performance which is why the VariEze was derated. Yes the loads would be transmitted through the foam blocks to the aluminum structure.

What I am trying to get at is if we have an accurate wing profile using foam blocks or whatever will it be possible to take on the glass ships?
 

Victor Bravo

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What I am trying to get at is if we have an accurate wing profile using foam blocks or whatever will it be possible to take on the glass ships?
NNNOOOooooooo....... :) I flew against one of the most well-prepped 1-35's that there was, and it was not even as good as my old Mini-Nimbus. The 1-35 pilot was more experienced than I at the time, so he would stay with me most of the time. But the 1-35, even sanded and filled and sealed and flying at aft CG, was just not quite there with the glass ships. It was a tremendous effort by the Schweizer brothers, and they were to be truly commended for even trying.

Dick Schreder did well with metal ships until the fiberglass ships got themselves sorted out, but the HP's were not competitive with glass. And Schreder came up with some pretty clever stuff, rivet-less skins bonded over contoured foam ribs, etc.
 

BBerson

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What is meant by metal skeleton? No metal skin?
Foam and Oratex cannot provide torsion like aluminum skin.

I meant the fully sheeted structural metal skin of the 1-35 was later covered with some smoothing fabric to provide a laminar surface. That's what I read, I never inspected one, so don't know the details. I suspect either a sanded fabric or sanded body filler surface could equal molded fiberglass surface with much work. Sanded fiberglass fabric is more crack durable than body filler.
Might have been other reasons for Schweizer performance (fuselage, airfoil etc.)I don't think Paul was interested in switching to composite.
 

cheapracer

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Bede 4 wing construction method is where you would go for this, aluminium, aluminium honeycomb and less rivets through bonding.

You might get to fiberglass levels but forget the newer carbon fibre craft.
 

litespeed

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The BD4 method is very similar as the new Belite Pipper design- honeycomb alloy and bonded with rivets where needed.
 

BBerson

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Alex Strojnic built his wings with aluminum spar and fiberglass skin. Details in his book.
 

Victor Bravo

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The original Monnett Monerai and Moni ALMOST got it right, but they failed to fully address the difference between homebuilders and Lockheed. They tried to bond the skins to aluminum ribs, and bond problems actually caused more than one crash.

A very good friend of mine has the technical and chemistry background to have advised me that there are indeed specific metal surface conversion treatments that will support structural aluminum bonding to an aircraft safety level. These are SIMILAR to the common Alodine process but are NOT the common variety of Alodine chemicals.

So using the CORRECT type of chemical conversion and the CORRECT type of adhesive... plus the "chicken rivets" in the areas that are less sensitive to laminar separation, would likely yield a safe and low-drag bonded wing skin without ten thousand flush rivets. The time and cost of using the correct conversion coating just has to be put into the project form the start.
 

Vigilant1

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The original Monnett Monerai and Moni ALMOST got it right, but they failed to fully address the difference between homebuilders and Lockheed. They tried to bond the skins to aluminum ribs, and bond problems actually caused more than one crash.

A very good friend of mine has the technical and chemistry background to have advised me that there are indeed specific metal surface conversion treatments that will support structural aluminum bonding to an aircraft safety level. These are SIMILAR to the common Alodine process but are NOT the common variety of Alodine chemicals.

So using the CORRECT type of chemical conversion and the CORRECT type of adhesive... plus the "chicken rivets" in the areas that are less sensitive to laminar separation, would likely yield a safe and low-drag bonded wing skin without ten thousand flush rivets. The time and cost of using the correct conversion coating just has to be put into the project form the start.
There has also been some work with using plasma to improve the bonding of aluminum to various primers and adhesives. It's similar to the plasma treatment some composites builders are using to get improved bonds to already-cured epoxy matrices. From the abstract at the link:
Silica-like primers deposited in the RF and MW reactors onto acid etched, Ar plasma pre-treated aluminum were excellent primers forming strong, durable bonds to the aluminum substrate and the epoxy adhesive. The plasma pre-treatment of the aluminum coupons was found to be important for durability. Ar and Ar/Hsb2 plasma pre-treatments removed some hydrocarbon contamination and adsorbed water, hydroxyl and oxyhydroxide groups from the aluminum surface. An Ar post-treatment of the silica-like primer was found to be detrimental to durability. Lap joints prepared from acid etched aluminum pre-treated with an Ar plasma and primed with silica-like films performed exceptionally as primers, forming strong durable bonds the aluminum substrate and the adhesive.
It might be a bit much for a homebuilder in his garage, and I don't know how it compares to the "chemicals-only" AL prep process. But it's something to watch.
 

cheapracer

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there are indeed specific metal surface conversion treatments that will support structural aluminum bonding to an aircraft safety level.
Old news really, there are thousands of bonded Lotus cars driving around for many years taking higher forces than aircraft do. The rivets you see are there only to stop peeling while curing.

4214200314_bf7252b4bd_o.jpg

lotus-elise-15.jpg

it's not a stretch to say that had Colin Chapman been alive today that there would be Lotus bonded aluminium planes in the sky today.

http://stargazer2006.online.fr/aircraft/pages/microlight.htm
 

BBerson

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Bonding only removes rivet heads. Bonding thin skin doesn't provide a ripple free surface. It still requires post assembly filling and sanding to get a ripple free surface at rib bond and especially spar bond. Even molded composites have problems at spar bond.
 

BoKu

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Hello everyone, I was wondering if it was possible to use a building method for a wing where we can use aluminum as a "skeleton" for handling all the structural loads and foam blocks hot wired with the appropriate airfoil shape which would then be Fastened to the "skeleton". I envision upper and lower foam block halves that would be attached to the wing and then have the wing covered by Oratex or the like. What do y'all think?

I think that the hot wired foam block would conform to the airfoil profile way better than a riveted wing would. I don't think there has ever been a metal wing sailplane that comes close to the performance of a composite sailplane that seem like they literally stick to the sky.
First, apologies for my cryptic and facetious earlier reply. Taking the long way around while looking for a shortcut is a grrrrr arrrgh for me. Especially in territories so thoroughly explored and charted.

Some background and observations:

There have been several Akaflieg and personal experiments along the lines described. Typically, they'd construct a relatively wide-chord aluminum box spar that has enough chordwise size so that it has adequate torsional stiffness. Then they'd dress the spar out with styrofoam blocks, carve it to an airfoil shape, apply fiberglass or other surface treatments, and then add control surfaces. Probably the greatest advantage to this approach is that it allows a great degree of freedom in the aerodynamic shaping. The primary disadvantages are:

* Because you're generally hiding a rectangular or trapezoidal aluminum cross-section inside an airfoil, you generally get lower bending and torsional stiffness per unit mass than you might otherwise.
* A big box spar is a great place to put water ballast for strong conditions, or it might be a good place to tunnel your control circuits, airbrake box, etc. But it probably won't do both without a lot of finicky partitioning.
* As to the OP suggestion of using Oratex covering, that takes heat, and generates compressive forces, both of which will make a mess of common styrene foams.
* Time. Hours and hours doing rough metalwork, then massaging tender foam into shape, then doing final finish.

Probably the closest to the OP suggestion in a successful design is the bonded-aluminum construction used in HP-16 through HP-18 (and of course the RS-15). Basically, they have a big aluminum box spar, PVC foam ribs 4" OC and interstitials ~4" OC, and skinned with .025" aluminum. Built carefully, they'd be pretty smooth and last a long time. Plans for the HP-18 are available in every collection of Soaring Magazine that covers 1976. And of course they're on the web.

Getting further into the weeds, the Europeans have absolutely dominated sailplane construction because they studied the problem, did the math, experimented, and drew their conclusions. And then, by and large, they invested in the tooling and infrastructure required to make sailplanes that were worth owning at prices that comfortably covered the costs. Contrary to what you might think, they're not getting rich; by and large the Big Three are just getting by.

You can make something just as good, and even better, without all the molds and tooling, and many have done so. But, and this a monstrously huge but that oughta be in flashing electric blue neon, it takes a lot more time, as in two or five times what it takes for Friedel's or Tilo's or Kremer's guys to squirt out a top-of-the-line 18m ship. And, take it from me, unless you're bringing some pretty special innovations to the table (like turbines or electric propulsion), the hero cred you get for doing that is kinda meager compared to all the spiritual or financial wealth you could have been creating with all that time.

BBerson, the Schweizer 1-35 wasn't fabric covered...
Been there, done that, got the iron. Some, but not all, 1-35s had fabric-covered wings as BBerson describes. I think the idea was that the fabric would help consolidate the filler applied at the wing skin seams to prevent it and the overlying paint from cracking along those boundaries. It kind of worked, but in general caused more problems than it solved.

My recommendation to the OP is to hit the 152 and come up to the HP shop one of the next couple weekends. We'll be glad to show you our set of solutions to this set of problems. In a nutshell, we concluded that prototyping methods are great for making prototypes--things that are likely to fail, or things that are so laser-focused that the world only needs one or two of them. For anything else, you might as well tool up and make lots. We're taking our standard set of molded parts and stretching and shrinking them to suit a wide variety of needs and desires.

Thanks, Bob K.
 

BoKu

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The original Monnett Monerai and Moni ALMOST got it right, but...
WARNING: Off-topic screed. You have been warnded.

I really liked the Monerai back when I was a kid. It was the perfect glider for someone 5'7, 110 lbs, and immortal. For larger and less impervious (More pervious? Is that even a word? It doesn't sound like something I want to be) folks, it left and leaves much to be desired. It kind of got away with having such a small wing by having low empty weight, and it achieved that by leaving behind anything not directly related to normal operations. Instead of a seat, it has a canvas hammock almost guaranteed to cause lower back pain in an hour. Instead of a crumple zone, it has a single steel tube out front where the rudder pedals are, which puts your feet and ankles at the unhappy end of the energy absorption column. The constant-chord wing limited performance, and by most accounts the somewhat hokey control systems gave it mediocre handling and feel.

Basically, what the Monerai did was reduce the idea of a sailplane to a very affordable level, but one that resulted in a sub-functional machine. Hundreds of kits were made and delivered, but I have never seen one fly, despite having spent several years worth of days at various gliderports. There seems to be a robust market for kits and parts and the few finished aircraft, but it seems more like Pogs or Beanie Babies or Black Diamond Disney VHS tapes--an economy based on myth. And that's all fine if you're into the dream of flight and you enjoy collecting its artifacts and trading them with friends. But if you really want to soar, it seems to me to be the sort of thing you'd fly maybe once or twice and then quietly move on from.
 

lr27

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snip

Vigilant1, having a solid core hot wired wing does not in my opinion give predictable structural performance which is why the VariEze was derated. Yes the loads would be transmitted through the foam blocks to the aluminum structure.
I'm sure that with an appropriate level of care, and maybe the use of pultrusions, a foam core wing with composites can be consistent, predictable and reliable. Much as bonds to aluminum can be reliable if careful attention is paid to cleanliness, process control, etc. I've read more than one article about how to reattach delam areas in Schreder sailplanes.
 

Victor Bravo

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but I have never seen one fly,
You didn't miss much Bob. I saw one of the earliest Monerai P (R/C model style "power pod" on top of the fuselage) fly back in 1983 at California City. The guy's name was Lenny Padios. Nice enough guy, but very much in over his head. The 20-23HP Xenoah powered Monerai made approximately the same amount of noise as a DC-8 (before the bypass engines). It also took approximately the same distance to get airborne. It used ALL of the Cal City runway (6300 ft.+ for those of you unfamiliar) to get into ground effect, and made two or three laps around the pattern at just above sagebrush height. Regrettably, myself and the other snot-nosed sailplane guys were joking whether he was going to live or not. Never saw the guy again. I wish I could go back in time and see if I could help the guy instead of looking down my nose at him.
 

BBerson

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I saw a Moni land once. Very fast and flat angle.
Then I saw it in the rafters of a mechanic school where derelicts go to live.
 
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