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Getting shot down

Old 10-24-2004, 11:38 PM
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Flyboy BigK
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Default Getting shot down

Hi,
I went out today to get a few flights in while the weather was still good.
I met a few of my friends there who are kinda my flying buddies and then I checked out my
plane, it was alright and I fueled it up.

I took off and went out to fly a right pattern and "boom" my plane stopped responding to my TX,
did a few rolls, and then went WOT straight into the ground. I had gotten shot down.

The weird thing that I found out later was the guy who shot me down was on Channel 50 and
I am on Channel 42, is this common for this kind of interference to occur between channels
that are 8 channels apart? This question has been bugging me all afternoon since my plane went
down, any information or comments\opinions would be very appreciated.



- Kristen
Old 10-24-2004, 11:51 PM
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loading
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Default RE: Getting shot down

You might want to check your RX or battery. Or maybe the other guys transmitter is having a problem. I fly channel 58 and another flyer at my field used 56. There hasn't been a single glitch. Everything being normal, there should be no interference between channels that far apart.
Old 10-25-2004, 05:59 AM
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MinnFlyer
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Default RE: Getting shot down

It sounds like you have a bad Rx, or your friend has a bad Tx. Check them both (With planes on the ground) and if there is a problem, have them looked at by a pro.
Old 10-25-2004, 06:59 AM
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Default RE: Getting shot down

Yeah, I agree. You're not saying you saw the guy on #50 move the servos in your plane with his Tx, after the fact, are you? If so, one of you has a mislabeled radio!

WOT tells me your TX went dead, or your RX antenna stopped working (like, out of range, or never unfurled), or possibly your RX lost power from the battery. (Unless you were at WOT to begin with...)

Either way, I sympathize! Helpless doesn't adequately describe the feeling of watching your plane at WOT heading for plowed ground.

Good luck,
Dave Olson
Old 10-25-2004, 07:46 AM
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KiteThreat
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Default RE: Getting shot down

I was reading an article the other day, which does a fair job of describing the possible interferences between two transmitters and a single-conversion receiver. In the example given, the interference is generated with one (positive shift) transmitter on channel 14 and a (negative shift) transmitter on channel 60. The key (in this case) is the distance between the two transmitter signals in relation to the "Intermediate Frequency" of the receiver so it's not just being on a near frequency that's a problem.

I'm not saying this caused your problem. I have no idea.

But this is a good article for beginners. It explains some of the technical differences between AM and FM, single-conversion and double-conversion, PPM and PCM. And it also explains why there isn't a single "best" radio setup- EVERY system has weaknesses relative to the other systems.

The article is titled:
"Everything You NEVER Wanted To Know About Radios" by Ian Hirschsohn

and can be found at:

http://www.airmedia.se/Receiverfacts.htm

Even if it doesn't solve your mystery I hope it answers some questions for you. It did for me.

Scott
Old 10-25-2004, 08:24 AM
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Default RE: Getting shot down

I doubt very much if you were "shot down". Narrow band R/C radios (the only legal ones around) can opperate on immediately adjacent channels without mutual interference. I suspect that you have a RX battery, Tx battery, Rx or TX function, antenna, or wiring problem. In other words the problem was probably self-generated. Either that, or there was interference from a non-flying TX somewhere in your area. Is there a communication tower, or a construction site nearby?
Old 10-25-2004, 09:19 AM
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Default RE: Getting shot down

ORIGINAL: Flyboy BigK
I went out today to get a few flights in while the weather was still good.
I met a few of my friends there who are kinda my flying buddies and then I checked out my
plane, it was alright and I fueled it up.
Did this checkout include testing the battery voltage?
Old 10-25-2004, 10:10 AM
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Default RE: Getting shot down

How do you determine that this other guy shot you down? It really doesn't sound like he did. Sounds like you lost battery, antenna, switch, or something came loose in the plane. Look for the real cause so you get it fixed. Don't just assume because he was the only one on that you were shot down by him. Could it be that you stalled and just lost it bad enough to not be able to recover? Could one of the above possibilities come in to play? Too many yell "I was shot down" when they crash, and they never find the real reason they crashed, and then they crash again for the same reason.

Don't let it happen to you.
Old 10-25-2004, 04:48 PM
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Default RE: Getting shot down

are you anywhere near a military site?i got shot down by the royal air force!i was flying at my parents hill top farm when i saw 2 tornados approaching at low level which they do all the time as they use the area for low level practise.when they got level with me my aircraft went full throttle and full up elevator,there wasn't a lot left of it!,i reckon their radar or something else screwed up my rx or tx,guess i was lucky they didn't get weapons lock on me!
Old 10-25-2004, 05:15 PM
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Default RE: Getting shot down

Um, are you running PCM? One year when I was flying at the nats in washington state, the only guys getting hit were those of us on PCM systems. The rumor was that it was caused by a sattelite doing something by the base near us, but who really knows. Stranger things have happened.
Old 10-25-2004, 05:26 PM
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Default RE: Getting shot down

yup.i'm using pcm.
Old 10-25-2004, 05:58 PM
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Default RE: Getting shot down

FlyBoy Big K,

Did you have Fail/Safe programmed? Might be worth doing, and it may save another aircraft.

I`m no expert on RC equipment, but I think that inter channel interference is unlikely also. I have a background in electronics, 9 years as an Air Force technician, and it just doesn`t seem possible that if both Tx`s and Rx`s are on the nominated frequencies that there could possibly be interference. As suggested above, I`d be having the Tx`s checked for output frequency, and you could start with the crystals.

The article for which KiteThreat supplied the link mentions PPM vs PCM, and says that PPM is preferable........

"Unless you want an edge for close-in precision aerobatics or racing, avoid PCM. You will save money and your hair.
PCM may not be a good idea for thermal duration, where distance invites signal corruption (fail-safe may, however, be a help
for polyhedral ships).
Absolutely precise servo positioning is a debatable benefit for most gliders."[/b]

I run PCM, but after reading this think that PPM might be better for me. Oh well. Does that mean my wife will go along with a complete change of radio gear?
Old 10-25-2004, 11:23 PM
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Flyboy BigK
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Default RE: Getting shot down

Thanks for the information everyone,
the reason I say I was shot down, was once I recovered what was left of the plane I did
a range check, range was good, approx 150ft. with TX antenna down, and all servos
and clevises were still connected. Also as soon as the guy on channel 50 turned back
on his TX my plane servos went crazy! They jittered and moved back and forth on
their own. Perhaps his TX has a problem, I often fly with guys on channels 40 and 46
and have never even experienced any type of servo jittering.

As for the interference from an airport or construction site, the place I fly at is approx.
30-35 minutes doing 60mph away from an airport, also no construction sites around.
Closest thing that could have cost that is an telephone tower a few miles away but that
had been mostly disassembled because of damage done to it courtesy of Hurricane Jean.
I am flying on FM PPM I think, I am using a Futaba 6EXA TX. As for the RX batteries were
fresh, made sure they were charged and topped off before I went to the field, and this
was supposed to be my first flight of the day.


With that said I thank you for the information, and if anything else comes to mind I would
appreciate any more information available.

- Kristen
Old 10-25-2004, 11:39 PM
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Default RE: Getting shot down

Flyboy BigK,

Here's a thought. Was your transmitter in close proximity to the other pilot who may have shot you down? If you were too close, you may have been the victim of 3rd order intermodulation:

[link=http://www.electrodynam.com/cgi-local/SoftCart.exe/ttip.htm?L+scstore+ymdz2804ff176817+1107744098]Electrodynamics[/link]

Marl
Old 10-26-2004, 12:04 AM
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Flyboy BigK
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Default RE: Getting shot down

Wing- Ding,
That actually could be the answer I was looking for, it so happens that I was standing
almost in front of the guy who shot me down while I was flying, and he was checking
out his plane. We were probably no more than a few feet apart.

Thanks very much for the information, and the quick response.

- Kristen
Old 10-26-2004, 07:33 PM
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Default RE: Getting shot down

Just a thought, but check with the other guy and see if he changed the crystal in his Tx to a different channel without getting it re-tuned. Same goes for your Tx. Was the crystal in your Rx changed? Futaba has low band and high band Rx's. Changing the Rx crystal to a channel in the wrong band can open the door for interference from another Tx on a different channel. Just a few possibilities. Something is definitely askew if another channel is causing your servos to go nuts.
Old 10-27-2004, 09:57 AM
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Default RE: Getting shot down

If he was right beside you and you were checking it after the crash, he could have been swamping you causing the problem. Was your transmitter on when the servos were jittering?

It is highly likely you had a problem unrelated in the air that didn't show up on the ground.

If he is in fact causing your radio to glitch when he turns on, I would send both sets in for tuning. That would be a huge problem.

You need 3 radios for 3rd order problems. I don't think its possible with just 2, but someone may know more about that than me.

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