Personal Cruiser!

Discussion in 'General Experimental Aviation Questions' started by Nickathome, Apr 6, 2011.

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  1. Jul 11, 2011 #41

    bmcj

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    Or maybe he has changed his view, but there may have been no reprintings since (still working from a stockpile of initial release books?).
     
  2. Jul 11, 2011 #42

    orion

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    Keep in mind that that the books are about thirty years old and updates, if any, were pretty minimal. There were no actual rewrites.
     
  3. Jul 11, 2011 #43

    AVT

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    Copyright 1993 on my copy. If you would see how they are self published, (copy machine printed) changes could be made very quickly.
     
  4. Jul 11, 2011 #44

    AtomicZ

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    I could be wrong, but I believe that Advanced Composite Techniques by Zeke Smith (2005) also advocates the use of Last-A-Foam. Now if only we could get Steve Rahm (designer of the Vision and Personal Cruiser) on here, this would REALLY be interesting.
     
  5. Jul 14, 2011 #45

    BGStewart

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    Hello all,

    This is a great thread. For what it's worth, I am the builder of personal cruiser # 10. I wish I would have known this information two years ago. It's would have saved me alot of grief and money.

    My experience with last o foam totally supports Orion's findings. Several off the fold a plane panels I received from Pro-composites (the kit manufacturer) later developed major seperation between the glass and the foam core. In fact, I was able to peel the glass off the foam off the entire panel without damaging the foam at all.

    This along with other issues lead me to discontinue the project.

    If you are building a composite aircraft , you should do the research and listen to the advise from expert's in the field. Don't just blindly follow the designers recommendations. You might be sorry.

    Bryon Stewart
     
  6. Jul 15, 2011 #46

    AtomicZ

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    Before throwing Pro-Composites under the train, did you seek any sort of feedback from them to remedy the situation? I'm getting the feeling that if Pro-Composites would offer the Personal Cruiser and Vision kits in Divinycell (or other foam), they just might sell more. Who knows.
     
  7. Jul 15, 2011 #47

    BGStewart

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    I wasn't throwing them under the train. My intent was to point out that if a professional shop has problems with last o foam, us as homebuilders are going to have problems with it too.

    I agree that if the kits were made from Divinycell or simular pvc it's would probably be more apealing.

    Just to be clear, I have no ill will toward Scott V or his company. I just disagree with his choices of materials and components. My decision to part ways with him was in the best interest of both of us.

    As for the delaminated parts, his advise was to re-bond it.
     
  8. Jul 16, 2011 #48

    flyoz

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    I have done quite a bit of testing on foam cores and the attached PDF is an update of some previous testing i did ( i have done 64 samples ).

    I am trying to find some "rule of thumb " test that could be applied to most foam types to give the average home builder "a non manufacturers " perspective of the various strengths of foams .

    These tests are basic but surprisingly repeatable . They are a combination of peel and rupture . They are not defiative and will have to be modified but its a start - i gladly accept constuctive criticism .

    I did not test a lot of Urethane but the samples i tested seemed quite good . However the Divinicell and Corecell were miles ahead .

    Flyoz
     

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  9. Jul 16, 2011 #49

    brehmel62

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    To be honest, I'm a bit confused about this thread. I've seen post after post after post about foam core material, however, I don't recall seeing any mention of the resin. I've worked with both polyester and epoxy (I have not worked with vinylester) and I know that these two have very different properties. It seems to me that a given foam material might work well with one resin but not necessarily another. So, are we talking about known delaminations with polyester, epoxy, and vinylester or with just one of these and then generalizing to all resins?
     
  10. Jul 16, 2011 #50

    orion

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    Most of the work within the industry on many of these designs being discussed the resin is Vinylester however, several structures where evidence of this failure was detectable used epoxy also. The tests we did some years back used Hysol EA9412, which is one of the best and strongest resins applied to this industry. But when it comes to the properties being discussed, the resin is irrelevant. It is the characteristics of the foam that are the principal issue. And just FYI, Polyester resins are not (and should not be) used at all in aircraft primary structure. That however has been discussed at length in other threads herein.
     
  11. Jul 16, 2011 #51

    brehmel62

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    Like aluminum?

    You mean the most expensive foams?


    Let's see: aluminum dents and stress cracks, fiberglass can fracture, plastics break down in ultraviolet light, kevlar doesn't have good compressive strength, carbon fiber can be brittle and is expensive, fabric covering has to be protected from the weather, and wood is susceptible to water absorption and fungal attack. Hand layup composites can soften and creep if they get too hot while rivets can work loose if they get too much vibration (like from a two-stroke engine). I guess someday when we find the perfect materials and building methods we will be able to build aircraft.
     
  12. Jul 16, 2011 #52

    brehmel62

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    I have not found any thread here where it was discussed at length. I have seen threads where it was mentioned in passing something to the effect that polyester was less strong and less tough. Very vague. I'm kind of curious how all those British Mosquitos managed to fly during WWII with plywood skins and balsa cores (truly inferior materials).
     
  13. Jul 16, 2011 #53

    orion

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    While your argument may be a bit snide or overstated, in essence it does represent the situation - virtually all materials that we use in aircraft design do have limitations that we have to understand and design around. The problem however is that some materials are simply not applicable, no matter the design. And that's the point of this discussion - some materials simply should not be used due to their weaknesses and the fact that no matter what you do to them or with them, their serviceability will be far below that of other, maybe more expensive, products. For instance, yes, aluminum alloys have limitations so in some instances we use a structural alloy like 2024-T3 or even a weaker one like 6061-T6. But we avoid the lower grade alloys or those in "0" condition since their properties are unsuitable to serve within the aircraft product. This is one of the few instances in life where you really do get what you pay for so bluntly, yes, choose the proven and more expensive product.

    The bottom line question is simply how much is your life worth? Or more importantly, how much is your customers' life worth? If a few more dollars or a few additional hours of work is significant to your airframe to the point where you prefer to choose a material that much of the industry is recommending against, then maybe you've chosen the wrong business.
     
  14. Jul 16, 2011 #54

    orion

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    Nonsense. Wood is far from inferior, as is balsa core, especially when applied to larger structures where the larger cross sectional properties are not as penalized by the balsa's higher density. And of course wood bonds quite well so the argument is not even germane to this discussion.
     
  15. Jul 17, 2011 #55

    BGStewart

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    So if I were to continue to build my Personal Cruiser, it would be best if I built all the LAF parts over using Divinycell or similar PVC foam? My tail (I'm the person building the conventional tail version) was built using Polystyrene so that should be ok. However, the entire fuselage tub, seat and bulkheads are all LAF.

    Orion...What would you recommend?
     
  16. Jul 17, 2011 #56

    Jan Carlsson

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    The Vision builder here in Sweden use Divinycell.
     
  17. Jul 17, 2011 #57

    brehmel62

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    No, actually I was just exagerating to make a point. I know that aircraft have been built with many, many different materials and building methods. And, I also know that the situation for light aircraft is not getting any better. Piper and Cessna have abandoned light aircraft and this is only partly being picked up by manufacturers under LSA in the US.

    I'm going to assume that you are familiar with the Pietenpol Aircamper from 1927. That aircraft flew without modern aluminum or modern composites. It flew with an overweight, converted Model A Ford engine that only produced 40 HP. It was a true homebuilt. What I am saying is that if you cannot match the spirit of Bernard Pietenpol then perhaps you should remove the word "Homebuilt" from this forum.

    The choice of materials is always a balance of strength, weight, workability, durability, and cost. Polyester resin has specific properties. You can't insist that it shouldn't be used unless you can show that either its properties are so bad that it is not a suitable material or that there is another material that is similar but superior in one of the above aspects.

    That is much too vague. How much weaker? How much more expensive? Something that is twice as strong at 10% more cost is a bargain. Something that is 10% stronger at twice the cost is not. Proportionate strength increases can offset cost. Workability is easier to offset if it is a production or kit aircraft; it is not as easy to offset for a homebuilder. Durability is variable. If it increases the durability from ten years to twenty then it is completely offset however if it increased durablity from fifty to one hundred years it would not be. Weight decreases are only partly offset since passenger weight is fixed.

    This is a ridiculous comparison and you know it. Aluminum alloys date all the back to before WWII. We have a good 80 years or so of data on these materials. No one today should have difficulty selecting a suitable grade of aluminum. You don't have a point unless someone starts talking about using aluminum roof flashing as a building material.

    Again, absurd. A few dollars more or a few additional hours is quite reasonable and no one here should or would disagree with that. The argument is against an open-ended comparison where any gain is suggested to be worth any cost.

    Again, if the properties of a specific material are substandard then that should be an easy point to make. For example: I would not reccomend using luan as an aircraft building material because this type of ply is ungraded and has inconsistent strength properties which cannot be determined by looking at the outside of the paneling. What specific property of polyester resin makes it unsuitable as an aircraft building material? Or what material is available with superior properties at a similar cost?
     
  18. Jul 17, 2011 #58

    orion

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    If it were my project I would definitely switch over to a more durable material and as such, would definitely go with the Divinycell, Airex or other, similar PVC type foam core. But in doing so I would also make sure that I was prepared to do this in a way that will assure me of the greatest chance of success. This simply means not only getting the right foams and epoxies but also the right materials that will enable me to build the proper laminates and bonds. The chief amongst these requirements will be the ability to make your parts with the aid of a vacuum system that will enable you to suck down the laminates and the core bonds. A small laboratory vacuum pump will do, as will a converted air compressor (reed valve heads). For most of this work you should be able to suck down about 15" to 20". At the lowest range that means you'll generate about 7.5 pounds per square inch, which equates to just over 1,000 pounds per square foot. (Don't try to do this with distributed weights - it really is not enough of a clamping force to get reliable results).

    You may also want some form of regulator since too much vacuum could cause you to squeeze out all the epoxy if it is too liquid. For foam bonds it's a good idea to use some form of filled epoxy - this allows you to maintain a finite bond thickness even if you pull a few more inches.
     
  19. Jul 17, 2011 #59

    BGStewart

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    Thanks for the advise. If I ever decide to continue the project (and I probably will at some point), I will take your advise.
     
    Last edited: Jul 17, 2011
  20. Jul 17, 2011 #60

    orion

    orion

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    Well, you have to remember that in all these discussions this is simply a public forum for advice based on what others have encountered. We all have favorite materials and processes, most of which can be safely used in aircraft construction. But some cannot and/or should not be used and when someone here has experience with the negative aspects, that should be so expressed. But this is not a scientific or engineering dissertation, nor can it be. If we have direct documented proof than it is presented if available. But as I have pointed out previously, most of the workability data is developed by companies internally and so usually not published in any way. Yes, that is too bad but companies must run their business, not spend time disseminating their own work to potential competitors.

    In offering advice, I can do this since I've worked with most of these materials and have seen and/or experienced many of these issues first hand. Yes, some of my answers may be a bit vague but that's the nature of this medium. If you want more succinct answers then do your own research and/or testing. I have a company to run and airplanes to build and I cannot take the time to document every piece of experience that I've gained. At that point you have the option of taking the advice or not. But that's your choice and risk.

    As an example, the issue of polyester resin and aircraft structures has been known about since the late sixties - about the time when the Windecker Eagle became the first composite airplane ever certified. I recall reading articles of that era that documented the brittle nature of the resin/glass combinations when subjected to the types of loadings that the structure would see in typically loaded structures such as wings. The fatigue properties were poor to the point where tests revealed crack initiation at less than 100 hours. But again, I understand why this may be too vague for some but since I read this in the late seventies, it's not likely that I can point you to the specific article. But I can tell you about it and you can make your own choices. Polyester has also been tested in conjunction with graphite fabrics and while the laminates were sound from the standpoint of strength, impact tests showed a tendency for brittle type failure. That, taken with the Polyester resins relatively poor performance in secondary bonding makes it a pretty unsuitable material for aircraft applications.

    The bottom line of much of this is simply that materials that are suitable and safe for aircraft structures will usually be more expensive, regardless of whether we're talking aluminum, graded wood or composites. But if we keep the discussion limited to relatively affordable materials (glass, graphite, structural foams, aluminum wood, etc.) usually the cost differences are relatively small so in most applications, picking an optimum material based on properties rather than cost only makes sense.

    But most of this information is out there - all one has to do is a bit of digging and maybe a bit of in-house testing. One of the sad parts of our work is that we also have to consider the legal ramifications in much of this and as such, we have to be able to fully defend our choices. And of course some choices are more defendable than others. True, this probably should not be the key consideration but unfortunately that's the reality of our social economy. It does not mean we have to be paranoid (the number of aviation lawsuits is actually pretty small, especially for small companies with shallow pockets) but a certain amount of due diligence is always to ones best interest.
     

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