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Old Oct 21, 2011, 08:16 PM
Captain Coolite
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Meringandan, QLD , Australia
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Originally Posted by Mtn_Commando View Post
Thanks for your detailed response, gnats. So you mean these are neither available, nor importable in the states? Ah, what a buzzkill! Guess we'll have to wait. At least that's good news for my wallet.
I know this is all just hypothetical, but, how would you protect the foam from the engine and exhaust heat?
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Old Oct 21, 2011, 08:21 PM
Ldm
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Kimey, great job , can you post a build thread on the system please
Thank you
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Old Oct 21, 2011, 09:26 PM
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Originally Posted by gnats82 View Post
Yeah, I threw that one out there and here is some general views I have about installing a glow ign. motor in one of these:

Since alcohol is the main fuel ingredient, the foam would be impervious to that but as to nitro content and oil, they may be a longer term hitch in the works and some testing would need to be done on an epo sample for unwanted reactions. In any case, a fuel proof coating would need to be applied in most areas around the motor and with epo, it's shown to not take coatings well at all.

Getting a mount system for the motor would require that the loads be spread out over as large an area as possible. Just a firewall mounting, say with epoxy, won't take the power pulses for long without breaking loose and a nose over would probably pop the whole thing loose. The mount system would by necessity need to extend forward from the actual firewall location, past the motor mounts and glued to the insides of the fuselage going to the nose. Material could be a composite of wood with rigid sheet fiber-glass spreading the loads.

An automotive silicone sealer may be usable the fix the whole thing together to the epo as it would spread out shock and loads. It would all be experimental. I've certainly not tried any of this but in practice I sort of know my way around the materials and what they can do.

As for weights and such, I'm sure that would be relatively straight forward to work out and there's probably plenty of room to work with for components.

Bear in mind Commando, I don't have one of these great looking P-40s as yet as they're not imported to the U.S. due to shipping regs.
just having a thought and think about it, once you've worked out where the firewall has to be located, fibreglass the engine mount to the firewall, the firewall to the inside of the nose/cowl, wrap the f'glass around the outside of the fuse & continue back externally at least past the main wings... then i'd do the same on the aft side of the firewall and through the inside of the fuse.
If you are going to go to that extreme, you may as well f'glass the wings & tail as well...
I'd reckon it would be do-able... but why would you?
Plenty of kits out there ready-built for nitro/gas, save an awful lot of grief
This P40 is no doubt a very nicely detailed bird, but IMHO electric only, it is a foamie... and perhaps add an awesome sound machine!

in the past with planes I've really taken a liking to, I've often thought to fibreglass foam wings, then remove the foam within... not difficult to do really
I'd love to 2x or 2.5x scale up a funjet & f'glass it, what a wild flight that'd be!

if you are after IC powered, I have an 81" T-28 I'm yet to get in the air (yeah, one fine day...) but with this I am tempted to splurge on a 4 stroke radial... gawd i lurve the sound of a radial!

oooops... sorry guys, a little off topic...
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Old Oct 21, 2011, 09:29 PM
Gentle 'Bella'
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Originally Posted by Rob Knox View Post
I know this is all just hypothetical, but, how would you protect the foam from the engine and exhaust heat?
Rob, if it were me I'd try making the lower cowl out of epoxy-glass or fiber-glass (polyester resin) which would stand up to the heat o.k. The engine I'd choose would be a four-cycle .91 - 1.0 cu. in. with no muffler and route the ex. out the bottom. Also, a 4-c tends to run cooler than a 2-c.

With a 2-c, there's need for a muffler and that's a tricky installation in an enclosed cowl but I've had a .60 size P-40 in the past with a custom, internal expansion muffler and it worked out fine. For the cowl top's inner protection, just a layer of 2 oz. fiber-glass cloth with epoxy resin might be enough to keep it from heat damage.

I think there could be several approaches to IC motor use but it would be out of the question for my uses unless I belonged to a club with a dedicated field. I wouldn't be bothered with a project like this these days but if this hypothetical opportunity had arisen maybe 20 years ago, I might have opted to try it.

I guess the attraction is that this would be a fairly inexpensive alternative to the built up models available and, of course, this bird really looks the part. Maintaining the light wing loading is another attraction that a foam model offers, assuming weight build up in the conversion process doesn't cancel that out.

Aussie, I hear ya'. I was just pipe dreaming. Love the sound of the four-cycles and championed them in the early '80s. I won a national scale contest (AMA) class in '82 using a four-cycle in a Stearman, a real highlight for my involvement in the hobby. Hence, my handle (g)nats82.
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Old Oct 22, 2011, 01:18 AM
Never fly an A model anything!
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Epoxy and EPO foam are just a bad match. If this model came in EPS foam I would consider it myself but Wally stick to EPO foammexcept CA and kicker which chemically bond it.
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Old Oct 22, 2011, 05:42 AM
Gentle 'Bella'
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Originally Posted by jayb1rdz View Post
Epoxy and EPO foam are just a bad match. If this model came in EPS foam I would consider it myself but Wally stick to EPO foammexcept CA and kicker which chemically bond it.
jayb1rdz -

Good to know, sounds loads better and easier to work with too; c.a. saturated f.g. cloth.
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Old Oct 22, 2011, 06:14 AM
Captain Coolite
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Meringandan, QLD , Australia
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OK, this discussion has led me to my next question....may be stupid, but I just don't know.
What are the differences between, or just the definitions of the different foam types.
EPP
EPO
EPS
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Old Oct 22, 2011, 06:34 AM
Ldm
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posted by "Frank" in Rc groups
Expanded polystyrene is the classic "peanut foam" that has been in use forever. In different densities, it can be found in products like the Teddy and the Wingo. This is basically the same stuff that you see in foam coffee cups.

Expanded PS is made by shoveling a scoop of "beads" into a mold and then hitting the mold with steam. The plastic expands and conforms to the mold. After it cools, the parts are ejected and the process repeats.

Expanded PS works well with epoxy and aliphatic resins for gluing. Beware any glue that contains acetone (CyA) or Toulene (Goop). These will eat any polystyrene foam.

Historically, wing cores cut of white bead foam and sheeted with balsa were the foundation of foam tech and go back to the 60s at the very least. The downside of using Expanded PS as a structural material is that it is fairly fragile and retains all dings.

Extruded polystyrene is best identified as the solid "board" type foam you can find in home improvement centers. It is made using a continuous extrusion process and has no beads. It does, however, have a grain that flows with the direction of the extrusion if you look carefully.

Extruded PS is often used for glider wing cores and in "cut" foamies. It is tougher and stronger than Expanded PS, but building planes from this material requires more effort (Kit building). The same gluing concerns exist for Extruded PS as for Expanded PS.

EPP stands for expanded polypropylene. It is made essentially the same way as Expanded polystyrene, except that the material is more resilent ("springy"). It has excellent compression recovery, but is quite weak in tension (due to the bead structure). That is why EPP foamies are taped or covered whenever possible.

EPP also has an unfortunate tendency to expand unpredictably when decanted from a mold. Because it's so difficult to account for this expansion, you generally won't find a molded EPP model. (Due to the expense of setting up the tooling.)

Elapor is a "blended" foam that combines polystyrene beads with polyethelene beads. Originally developed for automobile bumpers, this foam has found its way into the model market as a compromise between the fragility of the traditional Expanded-PS material and the unmoldability of the less controllable EPP material. Elapor is more glue tolerant than Expanded PS, but it will still melt if you leave an uncured puddle of CyA sitting on it. That's why you have to use accelerator when assembling Elapor kits. However, it shares the same lack of tensile strength common with both Expanded PS and EPP because of its bead structure.

Elapor models are usually easily identified by the a slightly "swollen" appearance, since they also expand when decanted from the mold, just not to the degree that EPP will.

Also see: http://www.flyingfoam.com/FoamTypes.html
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Old Oct 22, 2011, 06:39 AM
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Quote:
Originally Posted by Ldm View Post
Kimey, great job , can you post a build thread on the system please
Thank you
Look here:
http://www.rcgroups.com/forums/showp...0&postcount=94

By the way, one of my RcLander retract unit have had it´s first snag..... did not retract completely today. Seems like the gears are worn

Considering the .60-1.20 retracts from E-flite.....
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Old Oct 22, 2011, 06:59 AM
Captain Coolite
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Meringandan, QLD , Australia
Joined Jan 2011
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Thanks Lou.
That actually helps with my understanding of the materials and their properties
WRT model selection and the reasons why my HK Giant P51 retains dings, where as the FMS P40 and the 109 don't.
Rob
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Old Oct 22, 2011, 01:20 PM
Never fly an A model anything!
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There a different grades of EPO foam as well and that depends on the bead mix. The bead mix will determine how much deatl can be molded. This is whe the compromises come in. The more damage resistance you want, the less detail you can mold in.

If you look at the 50mm Edfs, they carry a fair amount of detail for their size. Their ability to absorb damage is as much about being light it is about the material. J
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Old Oct 22, 2011, 04:50 PM
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Always possible to make a mold out of this plane and do a copy in epoxy?

Think a gas engine whould give a less oily plane. Latex paints would do. Heat? A new cowl is indeed needed.
The Top Flite ARF could fit? Or made to fit.
Fire wall could be attatched to a lengty box construction locked in the plane over a larger area. Lot's of work... Scratch build possibly cheaper?
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Old Oct 22, 2011, 07:31 PM
Gentle 'Bella'
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Originally Posted by RC-Powerbus View Post
Always possible to make a mold out of this plane and do a copy in epoxy?

Think a gas engine whould give a less oily plane. Latex paints would do. Heat? A new cowl is indeed needed.
The Top Flite ARF could fit? Or made to fit.
Fire wall could be attatched to a lengty box construction locked in the plane over a larger area. Lot's of work... Scratch build possibly cheaper?
Most of the incentive to even consider doing an IC conversion was that this plane would come with good retracts - ones that lived up to the promise of dependability and value. That made economic sense to me at the time.

Since that hasn't panned out to be true, it pretty much negates the hopes of a worthwhile conversion, which was just whimsical speculation anyway. With the cost of a set of retracts one would have to buy in any case, a scratch build would be o.k. for one who wants to take up such a project but I, for one, wouldn't be up to it. If I did, though, it too would be largely of foam. Also, other arfs in conventional built up construction just wouldn't have the qualities that I'd be looking for such as a lower wing loading.

Watching folks work out trying to choose alternative retracts for this plane has been a real education. To me, H-K would have a really good market for oem units for this plane for sale in other applications were they dependable and available. These 1700 mm span planes that are appearing on the market are producing a demand for factory installed retracts that is a step into territory that is usually covered by expensive alternatives.
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Old Oct 22, 2011, 09:43 PM
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Originally Posted by gnats82 View Post
Most of the incentive to even consider doing an IC conversion was that this plane came with retracts - ones that suggested the promise of dependability and value. That made economic sense to me at the time.

Since that hasn't panned out to be true, it pretty much negates the hopes of a worthwhile conversion, which was just whimsical speculation anyway. With the cost of a set of retracts one would have to buy in any case, a scratch build would be o.k. for one who wants to take up such a project but I, for one, wouldn't be up to it. If I did, though, it too would be largely of foam. Also, other arfs in conventional built up construction just wouldn't have the qualities that I'd be looking for such as a lower wing loading.

Watching folks work out trying to choose retracts for this plane has been a real education. To me, H-K would have a really good market for oem units for this plane for sale in other applications were they dependable and available. These 1700 mm span planes that are appearing on the market are producing a demand for factory installed retracts that is a step into territory that is usually covered by expensive alternatives.
So not only is this not available in the states, but it doesn't really come with retracts either?
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Old Oct 22, 2011, 10:35 PM
Gentle 'Bella'
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Originally Posted by Mtn_Commando View Post
So not only is this not available in the states, but it doesn't really come with retracts either?
I didn't make that clear enough and I edited post #1528 with better language. It does come with retracts which have nice, shock absorbing struts but experiences with them have been unsatisfactory for several users as the internal mechanism has plastic parts that aren't up to much stress. All but the most gentle landings have broken several. Plus, H-K has not put them on the parts list so one has to shop for alternatives when they fail.
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