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Old Jul 11, 2011, 07:47 AM
Future Pilot
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I think that is quite light. I don't think it should exceed 25 grams. I will try to make the airframe and see how much it weighs. Maybe later today.

I will get into brushless very soon though.

Thanks again for your help, I will be back here later.
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Old Jul 11, 2011, 12:09 PM
Future Pilot
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Hey, so I'm in the process of cutting it out. Looks great so far!

Just wondering, it looks too big right now for the parkzone motors. Should I shrink the plane by a certain percentage?
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Old Jul 11, 2011, 12:11 PM
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yes. Try about 60% version
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Old Jul 11, 2011, 12:17 PM
Future Pilot
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Hmm okay, but then the issue is that the cutouts wont fit my 5mm foam. So won't I have to alter that somehow too?
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Old Jul 11, 2011, 12:38 PM
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i see. build a small hotwire to slice the foam to 2.5mm. I use a guitar "E" string as the hotwire.
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Old Jul 11, 2011, 12:51 PM
Future Pilot
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Hmm that isn't going to be too easy as I don't have a power supply...

Perhaps it would be easier to modify the plans. What do you think? I could just cut the slots out to 5 mm from the shrunken plans. 2.5mm foam may be too fragile too.
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Old Jul 11, 2011, 12:54 PM
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5mm will be too heavy for a reduced sized plan.

I use a power supply from a broken Energy Saving Lamp (CFL) as the power source. It has a nice transformer inside
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Old Jul 11, 2011, 12:55 PM
Future Pilot
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Okay, I will look for a power supply in some electronics I don't use.

But I still think 2.5mm will be to flimsy. You don't think so?
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Old Jul 11, 2011, 02:17 PM
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Sorry i missed this discussion Astronaut.

The paper covered Dollar Store foam board is very heavy with the paper on, particularly if you paint it. If your flying skills are high and you have a powerful motor, I guess you could fly it that way. Generally you're shooting for 9 oz in a combat type. For mrexcel's type the weight is MUCH less, but he is using thinner uncovered stock, small motors and batteries, dihedral, rudder instead of ailerons, cambered wings, etc for ultralight slow flyer (or possibly even indoor type) performance.

The difference between the two types is extreme. His planes are trainer-like, and the original topic type planes for this thread are the opposite: fast, high performance combat planes.

So it really depends on what you are interested in.

You can peel the paper off foam core (which is the usual procedure) and you will end up with foam of about 5mm in thickness. Soak the boards in the bathtub before peeling. There are quite a few threads on RCGroups on peeling Readi-board.

The only problem I see with it is that it is very flexible. So its best for curved or built up fuselages, cowls, etc. where curvature gives you form stiffness.

A flat wing with no camber would probably be too noodle-like with peeled Readi-board. Unless you stiffened it somehow. The fuselage wouldn't be very stiff either.

However, you could consider covering the wing with packing tape, and adding a fiberglass strapping tape spar underneath.

True, you are adding back a skin after taking one off. But this is a much higher tensile strength skin, and it doesn't absorb paint as much, so probably lighter and stronger. Also, paper is more brittle, once you ter/crease it you're done. The packing tape can probably give a little more, and just bounce in a crash. So you don't fold anything.

The Cellfoam 88 I use, and blue FFF foam are both stiffer than peeled Readi-board. Though I have now built a second P-40, and even with Cellfoam 88, still felt the need to cover the front of the fuselage and the inboard 2/3 of the wing with tapefor added stiffness and crash resistance. Based on what broke when I crashed the first one numerous times.

Again, we are comparing apples and oranges when talking about the combat type, and mrexcels super light nice slow flyers. So keep the differences in mind when making building choices.

The ailerons in the combat type are pretty extreme. I'm sure slow fly version with rudder and dihedral, as well as undercamber is MUCH slower to react and more forgiving.
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Old Jul 11, 2011, 02:35 PM
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Hmm, thinking about this --- I wonder if it would be possible to peel paper off of foam core type board on the fuselage aft of the canopy/cockpit, but leave it on the front of the fuselage?

Then, same with the wings, leave the paper on for the middle half of the wing, but peel the tips?

Then hit the paper covered parts with water based polyurethane (WBPU) or Minwax clear acrylic?

You'd have to somehow be able to wet part of each foam piece with water without wetting the part you want to leave intact. I suppose you could cut off a thin strip between the two with a knife and peel it off before wetting the part you want to remove.
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Old Jul 11, 2011, 02:51 PM
Future Pilot
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Thanks a lot my friend!

A very in-depth post!

The thing is, I don't have a battery or charger to create the normal sized version, so right now I am opting for one 60% of the size. I have a 1S battery and charger, plus those parkzone ultra micro electronics.

60% of the size should be a good size for those electronics. Leaving the paper on some parts is very doable, but how will I paint those parts? The paper will just peel right off. I am trying to think of some other solution for stiffening the wings, but the micro version will have a wingspan about 12" shorter, so they won't be as floppy anyways.

I'm working on putting the micro version together right now, and will see how it goes.

The ailerons are also another problem altogether. I am using the AR6400 RX, and it comes with the AS2000 aileron servo which is too weak in my opinion for good ailerons. I want to use a 9g servo on this micro version, but I'm afraid that may be too heavy.

A lot of obstacles for me to pass right now, as I have to make do best I can with the resources at my disposal. I hope to buy a battery/charger someday soon, but as a student can't fund those right now.

Thanks! I'll report back soon!
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Old Jul 11, 2011, 03:07 PM
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Okay Astronaut, I have a better picture of what you have and what you want.

Definitely NOT the combat version. You need ultralight and 18" span with AUW of about what the Hobbyzone RTF's are.

Let me think about this a little. I'm sure you can do it with inexpensive materials, but foam core with any paper on will be too heavy.

I'm thinking that with your small size plane, light weight and low power, the peeled foam core 5mm might be stiff enough as is. We'd have to figure the weight out. Do you know the weight of your motor+receiver+servo+battery?

Then subtract that from the weight of your old RTF, and you will get the weight of the bare plane you have to shoot for.

We can figure out the weight of the foam core minus the paper pretty easily -- I happen to have some peeled readiboard and a gram scale.
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Old Jul 11, 2011, 03:18 PM
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I think you should use the aileron servo you have and make the ailerons out of foam from a disposable foam dinner plate, or a foam take-out container.

Area of the ailerons should be reduced down to the same area as on your old (guessing, RTF Texan?)

Wing should be sanded down aft with a sanding block and then bent into a slight undercamber. Forward edge rounded.

Tail pieces should also be made out of dinnerplate or take-out box material.

I'd use 5 minute epoxy applied with a toothpick in preference to hot glue, which would add too much weight. Alternatively, use wallpaper "seam repair adhesive" in a tube (NOT wallpaper paste), although this is slower to dry -- only on thin seams. Not on laminations (like the wing to flat shoulder joint).

Or you could use elmer's Pro-bond polyurethane glue (gorilla glue type). Apply this VERY sparingly with a toothpick (it expands as it cures) to one suface only. Mist or dampen the other edge -- this stuff cures with water.
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Old Jul 11, 2011, 03:22 PM
Future Pilot
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Awesome, you are so helpful!!

I just finished cutting out the paper templates, am now in the process of tracing out on foam. Got to get the paper out, so will give the foam a sponge bath. I think for this small size, it will be stiff enough. The combat version will be put on hold until I get the power sources.

My WS is about 17-18" I believe - which is perfect.

I will find out the weight of all the good stuff soon. But first I need to decide what I will be using.

The AR6400 has the rudder and elevator on one board, so the question also arises if I should use the rudder servo for ailerons, and save a lot of weight by not attaching another servo. The only issue then would be that aileron would be on left stick with throttle...

Funny situation I am in, but thanks for trying to help me out.

I think I may add some camber to the wing too since a combat version is kind of out of the question.
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Old Jul 11, 2011, 03:23 PM
Future Pilot
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Thanks for the suggestions! I am going to put together what I have right now, and modify the parts with the foam plates as needed.

Will be back soon, this is fun!
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