My pal has been having problems from noise wiping out his radio reception in his turbine powered helicopter. He has switched off all instruments but at over 50% power the radio is still awash with noise. I can only think the metal blades are generating static which the AM radio picks up. Is this a normal problem and how can it be rectified?
Yes, your suspicion is correct. Helicopter rotors generate huge amounts of static.
The static builds up all the time, it’s just much worse when operating in dust, clouds, or precipitation. It can be a real problem while sling loading, as the entire charge unloads on whomever or whatever the hook first touches on the ground. I had a friend who was ground crew for a heli-logging operation; apparently it was great fun to watch the new guy unknowingly grab the hook the first time and get the shock of his life.
Here’s a better explanation than I could hope to give you.
With all that said, you bring up a great question with how to isolate the radios and antennas from all of the static buildup. I’ll be watching to see what the solution ends up being.
Just wanted to add that airplanes also build up static, especially while flying through precipitation. It is dissipated by making sure all of the exterior surfaces are electrically bonded to the airframe and placing static wicks at the tips of the wings and tail. I once flew an airplane that had improperly bonded fuselage skins. The static just sat on the skin and antennas, and rendered the radios useless while flying through precip. It was a very serious problem.
I have no idea how realistic this is, but here’s the helicopter scene from The Hunt For Red October, which is actually what I figured the thread was going to be about when I saw the subject.
It is a great pity that the aircraft industry never changed over to FM, which of course would not have the same problem with the static, apart from attenuating the incoming signal somewhat. I would imagine that ll military use FM on special channels.
I just cannot think how to dissipate the static buildup on the rotors whilst in motion. They are already grounded to the airframe.
Actually, the comm and nav radios commonly in use on civilian aircraft are in the FM band. With the exception of ADFs (which do use AM but are falling out of use except in remote locations), navigational radios operate from 108.0-117.9 MHz, and communications radios are 118.0 to 136.9 MHz. The military (aviation, at least) tends to use UHF frequencies up in the 300-400 MHz range.
cite please.
You have the correct frequencies, but the communications are most definitely AM, confirmed by both Wikipedia as well as my air-band scanner.
[QUOTE=Wikipedia]
As of 2012 there were 760 channels available in most countries for amplitude modulation voice transmissions, in the 118 - 136.975MHz section of the band, in steps of 25 kHz.
[/QUOTE]
Given that helicopters are designed with radio use in mind, the solution is already built into your friend’s helicopter. It sounds like something is wrong with it. Are we talking about voice radio, ie a commercial radio station, or a navigation radio?
Don’t mistake the frequency band for the modulation technique. The airband voice frequencies are amplitude modulated even though they’re in a similar band to FM commercial radio. NDBs* are AM as you noted and VORs use a combination of FM and AM.
*An ADF is the instrument fitted to the aircraft, the navigation aid on the ground is an NDB.
I don’t understand posts like these. If your friend has the money to operate a turbine-powered helicopter, doesn’t he have the money to pay an avionics shop to solve this for him?
Thank you for the correction.
Unfortunately, living in Africa you are very limited to expertise in this type of interference. He has been the route of the so called experts and they have thrown in the towel and cannot find the problem. I actually diagnosed the problem as static after ruling out all other sources of interference. The noise comes in very gradually at half rotor speed and at full speed the AM coms radio is virtually unusable. I know on fixed wing aircraft we have small braided wires on the wing tips to dissipate the static, known as St. Elmo’s Fire.
This static is not the same as in Hunt for Red October as this phenomenon is also prevalent when the helicopter is still on the ground.
I will post the solution, if we can find it, later.
Seems like you might have better luck asking in an actualhelicopter forum
Is the noise masking comms or are the comms ok but with a lot of noise when it’s not transmitting/receiving? If it’s background noise has the internal squelch been set properly on the comms boxes? Unless there are static wicks missing, I wouldn’t be trying to solve a static buildup problem but would be looking at the shielding of the electrics. In other words, don’t try and fix something the manufacturer has already fixed, look for where the manufacturers fix has failed.
The helicopter came out of the factory with working radios and electrics designed for the machine. The helicopter itself is unlikely to be much different since then but radios, wire looms, etc get worn out and/or replaced.
Is the problem something has just started happening? What has been changed in the radios/electrics recently? What’s the most recent work done?
Yes, he has modified the helicopter from a petrol engine to a turbine, so it is now using a computer for engine management. This of course we cannot switch off.
The hash is incredible and no setting of the squelch removes it and it blocks out communications on the radio. The only other modification that has been done is that the comms antenna has been moved from the tail to underneath the cockpit. We are going to move it back this weekend and try again.
Strange thing is that with the original petrol engine and the blades turning at the same or similar speed there was not a problem.
computers make noise that can wipe out signals on nearby AM radios. keeping antennas away from interference sources is a good thing.