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Nickathome

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I recall reading posts here regarding the Personal Cruiser fiberglass homebuilt. I was on their website last night and this looks like a pretty simple aircraft to build. I doubt you can get any easier than Epoxy and glass sheets over foam. When the time comes for me to build I most likely will go with all metal, but I will still give fiberglass some thought. The process they used to create the fuselage looked very easy to perform.

What is the consensus on this aircraft?
 

orion

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You can use the search function herein to get more information but in short, no, this is a very poor choice of material. It's a Polyurethane that is very brittle and has a friable surface, meaning it's very susceptible to vibration and impact damage. A few companies are using it but this is really a foam best suited for making tools and maybe surfboards - not airplanes. The foam to use on aircraft is PVC as used in Klegecell, Airex, Divinycell, etc.
 

Nickathome

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Understand. Admittedly, I know nothing when it comes to fiberglass aircraft. I'm glad to know this in the event I were to ever decide to build an aircraft from fiberglass and foam. I would imagine this company is not selling many kits then using this last a foam....
 

orion

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The sad part is that most customers will most likely not know any better so they will purchase the kit or airplane regardless of company's material choices, assuming that the organization has done their due diligence in the design process. The reality of the situation though is that most companies make this foam choice more so based on cost than functionality, simply ignoring the drawbacks of the material and neglecting to recognize that the amount of foam in the airframe is small so the cost impact is relatively negligible.
 

NickH

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I am building a Vision, from the the same designer. The design is extremely clever in the way that it uses the foam, but has very little reliance on the strength of the foam or even on the glass attached to the foam. Anywhere that has any load and the foam is replaced with flox or micro. The firewall is made of plywood. I believe that last-a-foam is capable of being used safely in this design.

I am using divinycell.
 

orion

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Actually it has great reliance on the foam since it is the foam that provides the skin with sufficient stability in the sandwich form that allows the skin to carry the necessary flight loads, both axial and in shear. This is different from the type of load you describe, which is more in the form of a concentrated set of forces or localized pressures, where it is necessary to remove the foam and use a different, more structural filler. Since the Polyurethane foam can delaminate relatively easily, any such separation would allow the skin to lose its stability and stiffness, making it incapable of carrying the design loading.

And yes, Divinycell is a great choice.
 

AtomicZ

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As long as you can find the same foam density in the divinylcell, I don't see why the empty weight would be any different.
 

orion

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Orion.........ok if use the PVC as you have said will the empty weight still be same as using last a foam?
Like most foams, Divinycell comes in numerous densities and its structural properties I think I remember are better for a given weight than that of the Last a Foam. So yes, if you use the same density as the material the plans originally called for, your overall weight will not be affected. But keep in mind that the amount of foam n the plane is relatively small so any variation will be miniscule.
 

ScottV

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I have read with great interest the concerns around the use of Last-a-foam. As the owner of a small business that manufacturers composites parts I always want to keep abreast of concerns that builders or potential builders may have regarding the quality and safety of parts we supply or recommend or matters that affect the composite home building in general.

I agree with a previous statement " ... it must be pointed out that outside of the damaged firewalls I have not seen nor am aware of any other failures of the sandwich as a result of normal service. But I still hold the potential is there."

Regarding the "potential" Orion - do you recall what series of foam you tested? 3700, 7100, 6700, 4500, 4300?

The broad statement regarding LAF "It's a Polyurethane that is very brittle and has a friable surface, meaning it's very susceptible to vibration and impact damage." Is true "in a general sense." However, not all polyurethane based foams are alike and especially the foams with the trade name Last-a-foam.

Last-a-Foam produced by General Plastics is manufactured with different blends and differing structural properties. They supply a number foams - I'll discuss 3 of them which composite builders may have come in contact with in the last decade.

6700 - excellent strength properties and friability, though currently not available in less than 8 lbs density. The 4.5 density foam was available up to about 2006 and then discontinued. This foam was selected as the replacement for Clark foam in the late 1990's when Clark stopped selling to ACS/Wicks. This is still available from aircraft supply houses in heavier densities.

3700 - Was the chosen as a replacement by Wicks for the 6704.5 foam around 2006. It is more brittle and friable than 6700 and 4300, though has acceptable strength properties. This is most likely the foam recent builders are familiar with and why there are problems associated with being too brittle or friable resulting in delaminated parts.

4300 - More flexible than 6700, and available in 5lb density, excellent structural properties if used below 160F continuous. It is used in the Personal Cruiser and composite kit parts supplied Pro-Composites. Many Vision builders switched to this foam after having problems with 3700 series foam. A recent batch of foam from ACS had 4305 stamped on it, not sure if this what they have supplied all along or not.

This may be the reason why builders are getting varying results from "Last-a-Foam." It is most likely a different series of foam. Look at what is stamped on the foam and you should be able to compare like materials. It would be beneficial to all concerned to preface the series number regarding Last-a-Foam when making comments.


Happy building,
Scott VanderVeen
Pro-Composites, Inc.
www.Pro-Composites.com
 

orion

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The basic formulation of Polyurethane foams has stayed pretty much constant throughout this company's product lines. True, there have been modifications and additives introduced to meet certain certifications specs but the baseline structure of the product, and thus its behavior, is consistent from one formulation to the next. A look at the structural foam market by one of our associates recently concluded that the use of this line of products should be limited to products that have only moderate loads (surfboards, boat decks, non-critical bulkheads or decorative panels, etc.), are not subject to acoustic, vibratory or shock loads, or ones that do not need a long service life.

The Polyurethane products are excellent for application to tooling and mockup uses, decorative structures, and so on. However, for application to aircraft structures, the only reason that most manufacturers decide on this product is cost. With proper care and preparation it is possible that a serviceable structure could be designed and fabricated however knowing the fabrication practices of many small companies and homebuilders, my recommendation would be to spend a bit more cash for a superior product in order to reduce the possibility of problems down the road.

This particular formulation of foam has two forms of failure that stem from its brittleness and and poor surface quality. Despite the foams physical strength, its inherent brittleness (shock sensitivity) may cause internal fracture even though there is no evidence of said failure, nor the impact that caused it, on the outside skin. This failure can take two forms. The first is a typical core failure where the core itself develops cracks in the region of, and/or radiating from, the point of impact. This is core failure where the cracks are perpendicular to the skin surface. The cracks, once formed, will spread throughout the core if the problem is not detected early. This of course causes total failure of the sandwich and thus any structure depending on the stable properties of the sandwich assembly.

The second form of failure is where the shock load is transmitted through the core to the inner skin. The energy of the impact will have little visible evidence of its occurrence at the point of contact however, since the energy has to go somewhere it does - it goes to the inner skin where it causes a delamination of said skin from the core. The interesting thing here is that it does not take much of an impact force to cause this to happen when one uses a foam with a friable surface. A dropped hammer is more than sufficient to initiate the debond. And of course the problem then is that since the damage is on the inside there is no way to inspect or test for it so it will not be evident until too late.

This failure form is actually common throughout the range of foam products, including PVCs, with the exception of the non-cross-linked Airex foams. But the difference between the products is the magnitude of damage and the energy that can initiate the failure. There have been several studies of this phenomenon conducted throughout the marine and aerospace industries - one I recall seeing while at HITCO years ago suggested that for a given density of core and dropped energy, the Polyurethane was about three to five times as likely to have damage, and if said damage does occur, it would spread out over five to ten times as much area as the competing products would see.

As far as the friability of the surfaces is concerned, so far I have not seen any Polyurethane foam, regardless of formulation, that did not exhibit a friable surface. True, the 6700 series is better however its improvement seems to come from the fact that even the lightest product is almost twice as dense as that which we normally use in aircraft.

As such, personally, I would not recommend the use of any Polyurethane foam in a flight product unless it's used in non-critical components.
 

ScottV

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If you can not show your data (what, when and how a product was tested) then there is no validity to your claims and you are doing a great disservice by singling out Last-a-foam with broad sweeping statements. It is a disservice to the home builders who have used it successfully for years and misinforms many potential builders.

Your statement that "the formulations are basically the same" is false.
It's like saying 3003 aluminum is that same as 2024. 4300 series foam was formulated to compete with Divinycell. It is used extensively in race car bodies, (cost is not a factor) and for than matter if it had a propensity for delaminating and cracking internally - that industry would cease to use it.

Last-a-foam is used in the aircraft industry as edge closing material for honey comb core composite panels. It is no coincidence the Boeing and General Plastics in the same general vicinity.

You are making a claim that Last-a-foam is selected based on cost alone. Workability can also be a selection criteria - PVC based foams do not shape nearly as well.

Delamination of a skin from a core can occur in any composite structure when it is not designed to meet the requirements of the load. That said, the use of edge closeouts, hard-points and additional reinforcements or different core densities and thicknesses allow a designer to tailor the design to meet the loads required.

Building and flying is nerve racking enough. Claiming a product is not safe without any supporting data is irresponsible and invokes unnecessary fear.

Happy Building,

Scott VanderVeen
Pro-Composites, Inc.
Pro-Composites Home of the Personal Cruiser Kit Aircraft
 

autoreply

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First of all, I highly appreciate your response here Scott. It's so much better to have the companies that are discussed replying in a grown up manner vs the complete ignorance or the name-calling that you see too many times, so thanks for your replies :)
It is a disservice to the home builders who have used it successfully for years and misinforms many potential builders.
Maybe that's a personal sensitivity, but I've heard that just too many times.
Something that "has been succesfully for years" might work for ships, cars or oilrigs. It doesn't for aircraft. The Nimbus 4 has been built for 20 years and only a few years ago, it was discovered that it was 40% under strength in certain conditions. Most of those aircraft flew thousands of hours without finding out. The Comet did fine for many, many flights. Zenair has hundreds flying for years before they found out some major issues. And so on.
While "proven history" certainly has some value, I don't buy it as a "major" argument. Proof, design, engineering and/or certification are important. History... not so much, unless it's "bad history" like the Comet.
Claiming a product is not safe without any supporting data is irresponsible and invokes unnecessary fear.
Here I disagree. Orion has mentioned several cases (admittedly, you have to use the search as he advised) where he actually found out problems.

Back to my line of thought; you being the manufacturer of the kits would be the one to "prove" your product to be safe, not somebody who has had real experience (with a different variant of the same product) and has reason to caution. Of course that's a whole lot easier said then done, but I'm afraid that's just how it works.

If I look at my own design decisions I also go for the materials and techniques that are proven in certified and thoroughly tested products and I stay far away from anything that is not, even though it might be superior in many ways. It was interesting to hear that Last-a-foam is used in "professional" aviation too, would you be willing to share a bit more about that? Might turn my own choices around too ;)
 

NickH

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Portland, OR
There is a foam core comparison chart which a member here created. It lists 6700 Last-A-Foam, but not 4300. According to the general plastics website 4300 has numbers that are around 10% better. Divinycell is typically over 90% improvement in all numbers, some significantly more.

The only downside (apart from cost) is the lower temperature requirement of 158 degrees. Requires care when post curing parts.
 

mjte43

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Jul 7, 2011
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Fort Collins, Colorado
ScottV, Have there been any more Personal Cruiser completions? It looks like your web-site has not been updated since Oct 2010. I see links to several builders, but nothing recent. I see in one of the builder photos, that they have gone with a conventional Vertical/horizantal stab vs the "V" tail. Will this option become available? I look forward to an update on your flight testing when you get a few minutes. Thanks, Mike
 

NickH

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Divinycell allows 85C as a maximum skin temperature, with 70C as the maximum core temperature. This compares to Diamond and Jabiru with max core temperatures around 55C.
 
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