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  1. #1
    Kentli22's Avatar
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    Will aluminum fuselage interfere with electronics

    If the whole plane is built out of aluminum frames, with all the electronics being totally enclosed inside the fuselage which is covered by aluminmum sheet as the skin , will the electronics such as CDI, Rx, tachometer, kill switch and batteries, etc., be interfered by the aluminum?

  2. #2
    All Day Dan's Avatar
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    The aluminum skin will block the signal from you transmitter’s antenna from getting to the receiver’s antenna. When that happens, you won’t have to worry about those other things you mentioned. Dan.
    Dan

  3. #3
    Kentli22's Avatar
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    have the reveiver's antenna hanging outside the plane?

  4. #4
    All Day Dan's Avatar
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    That’s how the full size do it. Blockage would still be a problem but not as bad. I have read the modelers using aluminum tape skin get away with it. They may keep their antennas inside and hope for plenty of leakage at the tape’s adhesive joints. Sounds like high risk to me. Maybe someone with real experience on this matter can comment. Dan.
    Dan

  5. #5
    speedracerntrixie's Avatar
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    Aluminum will block signal but lots of variables. Aluminum thickness and signal frequency play major roles. Less of an issue for 72 MHz then 2.4 GHz. External antennas would be the only way to survive with 2.4

  6. #6
    soliex's Avatar
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    The Futaba 2.4 receivers I use have two 3" long antenna wire with the last 1/2" exposed being the receiving portion of the unit. I've been working on an aluminum design and have thought I would run the antenna in push rod tubes hanging out the bottom of the fuselage at 90.
    Wait for it.......

    AMA77397
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  7. #7
    speedracerntrixie's Avatar
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    Ideally you would want to have exposed antenna no matter what attitude the airplane may be in. This is where Spektrum may have an advantage.

  8. #8
    flyinwalenda's Avatar
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    I would say to treat it as a carbon fiber fuselage and install a receiver with long antenna leads. Several 2.4ghz systems have carbon fiber receivers for this . If using 7Xmhz the external antenna strung from the vertical stab and isolated should work with a good receiver.
    Brian Ray

  9. #9

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    There used to be a guy in Abilene Texas that built a giant scale plne out of aluminum, every thing was metal. flew it with FM radio on 72 mz. had an external whip antenna about 10" long. never had a problem. I'm sure 2,4 would work fine with the carbon receivers.

  10. #10
    Moderator BMatthews's Avatar
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    I'd suggest that you answer your own question with your own gear. Make up a small board with the Rx, pack and a servo on board. make it so that the installation can be capped off with a couple of aluminium pop cans to totally enclose the gear other than for the small holes for the antenna and the pushrod that exit the equipment area. Set up the servo so it waves a flag at you so you can see that the signal is still being received and you have control. Then with the setup sitting up on a 6 to 8 foot pole off the ground get a handle on the range. Then put the cans on and try again. Have an assistant rotate the setup so you can see if at some point the metal of the cans shields the signal from reaching the Rx.

    Carbon fiber fuselages are bad enough. But now you're upping the anty with an all aluminium setup. You're basically creating a shielded box which will most certainly make getting any sort of radio signal into the box a problem. And even with the stub wires sticking out the effects of the metal so close to the wires might just affect the range. So testing to find out is pretty much all you can do.

    If your Tx has a ground check setting be sure to use that so the power output is reduced and you don't need to walk as far.
    Witty saying to be plagarized shortly.....

  11. #11
    acerc's Avatar
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    I did this very test with an aluminum box made from rolled aluminum flashing. I took the get up and my son to a street where I placed the aluminum box on a corner post at the curve along with my son. Using our phones about every 20 feet I would say up-down and he'd reply yep. There was a pushrod pointing out of the top with a square piece of balsa on it. I did this for one mile, at which point I could not see the pole or him. I cover numerous planes with this same aluminum, wrapping the forward fuse totally encasing the equipment and have not had a single issue. This is with Futaba 2.4ghz.
    Robert
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  12. #12
    Kentli22's Avatar
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    I am using the Futaba 2.4ghz, the aluminum skin will be 0.2mm in thickness. I agree to make an actual experiment with all sorts of electronic items and receiver packed inside an aluminum enclusure to see what weird things they might do, of course with the antena sticking outside.

    I had once had the power switch, kill switch, tachometer, throttle servo and the CDI battery all mounted tightly on a sheet of aluminum which sit in front of the plane right below the engine and CDI, the receiver was mounted very close too. Everything ran normally for a few flights, then the engine started to quit regularly while the tachometer would show "91" intead of the "0" rpm when the engine was off. I couldn't figure out the problem. I suspected the alunumum sheet might be producing interference or the electronic items were packed too closely together. After I got rid of the aluminmum sheet and mounted all the things a little bit apart, then everything runs normally again.

  13. #13
    Moderator BMatthews's Avatar
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    The issue with the CDI might have been a little different from the radio shielding issue you're looking at for the antenna. A CDI box generates a lot of RF level noise due to the switching and high voltage. The big plate of metal might have caused some feedback of an interference signal from one part to another.

    But then again the ESC's on electric models generate some pretty sharp high frequency signals and the harmonics from that are quite likely up where it could produce some issues. So all in all enclosing much of the gear in a similar configuration of metal is not a bad idea.

    The thing with metal and RF is that it doesn't matter how thick it is. There is either metal or there isn't. What might save the day is if the various plates are not in electrical contact with each other. Or openings for such things as landing gear or wood wings or even the cockpit. All those leaks can add up to a metal fuselage that might not cause any signal degradation. But without testing it's tough to say for sure.

    Acerc, any chance of some pictures of how you arranged your antenna on these models? I'm sure Kent and others would like to see what worked out well for you.
    Last edited by BMatthews; 03-02-2014 at 02:08 AM.
    Witty saying to be plagarized shortly.....

  14. #14
    Neverlost1's Avatar
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    I have to agree with BMathews, CDIs can cause a lot of radio frequency interference, and receivers have to be placed as far away from the CDI as possible. 2.4 GHZ receivers are "less" likely to have problems than 72 MHZ, but can still be interfered with. It is definitely possible that the aluminum plate was "transmitting" the RFI to the components mounted to it. From personal lessons learned, always range test while running your engine at full throttle.
    When everything seems to be going against you, remember that the airplane takes off against the wind, not with it.
    - Henry Ford

  15. #15
    acerc's Avatar
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    Quote Originally Posted by BMatthews View Post

    Acerc, any chance of some pictures of how you arranged your antenna on these models? I'm sure Kent and others would like to see what worked out well for you.
    I am assuming you are asking if the antenna was external of the airframe. No, it was not, it is totally encased within the airframe dead center of all that aluminum. I have enclosed a pic of my small Pitts, from the rear of the cockpit forward is aluminum sheeted and the Rx is center of the cabanes. I am currently building a $8500 Pitts and it will be the same. I personally have no doubt the signal has no issue with aluminum. Carbon fiber is a different story!!!
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Robert
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  16. #16
    speedracerntrixie's Avatar
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    Bmatt is corrects that it dosent matter the thickeners of aluminum. One thing that has not been touched on yet is internal interference. All the components within the airplane give off RF emissions. That includes servos, CDI, regulators and the RX it's self. An aluminum airframe can trap these emissions in and reflect them to different areas of the airplane. If anyone is familiar with Wavegiude it's the same principal. If a signal is going through the the fus front to back, the signal frequency could actually increase. This is all theory of course and as we all know in practice things can work out differently.

  17. #17
    acerc's Avatar
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    Post #11 was a test of all those theories, the theories gave way to the facts!!!
    If it would calm some nerves, tomorrow I could do another test. I have that little Pitts in an aluminum trailer so I could video me sitting in the house operating the radio while one of my sons will be in the trailer telling what is going on via the phone while I show the stick movements. That would be the signal going through two exterior walls, two interior walls, and at least two layers of aluminum. How's that sound?
    Last edited by acerc; 03-02-2014 at 10:35 AM.
    Robert
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  18. #18
    speedracerntrixie's Avatar
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    Much easier test to do. Turn on yout TX and RX, place TX in your aluminum carry case and see how far you can get the TX away before the RX goes into fail safe. I can't give a lot of details but on antennas we build at work always have aluminum housings. This prevents signal spillage out the back and sides of the antenna.

  19. #19
    Moderator BMatthews's Avatar
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    Acerc, since you're working with an open ended tube I'd suggest that is why it works for you. You've got a relatively open end at the nose with the, presumably, fiberglass cowl and plywood firewall. And at the rear the sheathing is open ended with the wood rear section. So that's why you're not having an issue. Not to mention the open top of the cockpit and the opening on the belly for the lower wing. So you've got SOME aluminium but it's got more holes in it than a colander.....

    It would quite possibly be a whole other story if the model in question were an aluminium foil sheathed B-52 model with the receiver in the middle of all that metal with no similar openings.
    Witty saying to be plagarized shortly.....

  20. #20
    acerc's Avatar
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    I guess no one read my very first test that I posted ( #11) which was done just to reassure myself that there would be no issue. A fully encased Rx system did not have any ill affects. But it would appear there is something being sought here that I do not see. Enjoy.
    Robert
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  21. #21

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    Anyone remember when receivers were aluminum boxes with all the electronics inside with only the anetna wire sticking out. No problem with a properly tuned radio. Old Kraft radios made in the USA.

  22. #22
    All Day Dan's Avatar
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    ace, I read it. Take a look at your Direct TV antenna. That concave surface is called a reflector. Under the gray paint is a very thin coating of copper. All it needs to be is an electron thick in order to work. That copper coating reflects the electromagnetic wave coming from a satellite into the pipe looking thing in front of it called the feed. The antenna works because the signal coming from the satellite is reflected from a metallic surface. The same thing happens with the metallic coated RC models whether they are coated with metallic paint, tape or are all aluminum. No body doubts that the metallically enclosed antennas work. They are working because of leakage. Nothing is a perfect seal. The problem is that the margin of operating the manufacturer puts in to his system is considerably reduced. Just because it happens to work in one type of test does not mean it is safe to fly with. Just make sure you don’t fly near the pits. Dan.
    Dan

  23. #23
    acerc's Avatar
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    Ok, fine, here! The aluminum (partially) covered plane in the aluminum trailer and then with three aluminum sheds in between. A bit generic in videography but shows the results just the same!
    ( Whoops! )
    If this isn't enough then you'all are on your own....
    Last edited by acerc; 03-02-2014 at 04:23 PM.
    Robert
    Cub Brotherhood #3\\ Ryan STA Brotherhood #4
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  24. #24

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    Quote Originally Posted by Kentli22 View Post
    If the whole plane is built out of aluminum frames, with all the electronics being totally enclosed inside the fuselage which is covered by aluminum sheet as the skin , will the electronics such as CDI, Rx, tachometer, kill switch and batteries, etc., be interfered by the aluminum?
    Respectfully, many here talk based upon assumptions without Facts....Real airplanes have tons of aluminum, steel, magnetic components, lots of very thick hardware surrounding those diminutive antennas which ARE CRITICAL for their navigational equipment .

    This being said, I have many years of experience building all aluminum large scale airplanes and radio signals ARE NOT affected if you use the proper radio set up. I HAVE Lost airplanes due to dump thumb but NEVER for radio reasons. Before radios were reliable, we built a 45% scale Cessna flown with a EK FM radio and a go-kart engine which we flew very successfully for years.

    With 2.4 , You will better off if you use a radio based on receivers with remotes to insure flawless performance..

  25. #25
    speedracerntrixie's Avatar
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    Quote Originally Posted by allmetal plane View Post
    Respectfully, many here talk based upon assumptions without Facts....Real airplanes have tons of aluminum, steel, magnetic components, lots of very thick hardware surrounding those diminutive antennas which ARE CRITICAL for their navigational equipment .
    ..

    While you are correct about the construction of full scale airplanes, I can assure you that the antennas design and location are key factors to them functioning correctly in this environment. The antennas are not mounted inside the aircraft. I wish I could give more details then this but this is a case of better safe then sorry. The reason that your airplanes fly with metal construction is that there is enough signal leakage into the structure and 72 MHz would be much more reliable in this environment then 2.4 ghz.


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