frenchie79

To all Radio/Receiver Guru's: I have been reading many posts on Radio Interference on Gas powered planes. I have my first (Giant Super Sportster) with 32 Fuji EI. My first intention was to use my Futaba 7C and a Hitec Supreme 8 standard receiver which i use in all my planes (Glow) with no troubles at all. Now after reading many posts on PPM, PCM, 2.4 ect... and all the radio problems with gas, i'm not sure i want to try putting the gas plane up in the air or even venture into gas. Of coarse i will after many Radio checks. Can anyone ease my mind if using a standard Receiver like the Hitec Supreme FM and following the MFG suggestions on 12" from the engine ignition is going to be fine or do i need to go to a PPM or 2.4 to be safe.

BarracudaHockey

My Feedback: (11)

PPM and FM are the same thing.

Considering the cost of putting a larger gas powered plane into the air, decent servos and a PCM reciever should be considered part of the cost of doing business.

Much the same reason I won't put a helicopter in the air w/o pcm. If for no other reason than to have fail safe on the throttle.

frenchie79

Thanks for the reply, I'm using Hitek 645 servos all around, but i still would like to know if it is Fine to use the standard fm receiver?? Haven't modelers been using them for years with no problems? or is because their was NO choice. If it is not a go option to use, what are the problems that i will find right away? Thanks

A.T.

Recommend Gas planes be set up using a quality proven dual conversion RX, such as the Hitec Supreme series of RX, and only instal a PCM/QPCM receiver if the fail safe features are required, after model passes all tests, especially full range test with motor running. PCM receivers often mask simple problems which will bite hard later. FWIW, 3 fliers on different frequencies lost their PCM RX equipped models in one day at a local event and those with dual conversion simply glitched and landed safely - later discovered an unseen electric fence well out, but across the landing path, had been switched on by the farmer and the PCM lock out as models flew over the zone of interference was to long for recovery before crashes occurred. A simple Fail Safe (example) on throttle is a safe option.
Further information on my web page under "Giant Scale, Large RC models, Twins & Multi Engines" as well as "Radio Systems, Accessories, Alterations and FAQ" sub sections "Range check and Range problem solving" and "Receiver - FAQ, guides and aids to best reception".
Regards
Alan T.
Alan's Hobby, Model & RC FAQ Web Links

frenchie79

A.T. Thank-you. If i read you right then, the Standard PPM Hitec Supreme receiver is a good choice and that it won't hide any problems and if set-up proper will be just fine. It never was a issue with $$, i just have plenty of receivers that have given me no problems. Thanks again for your response.

XJet

Alan, failsafe is *always* required when you're dealing with models large enough to use a gas engine.

A model that gets hit by interference or for some other reason loses signal can cause fatal injuries (there are many documented cases).

Imagine (for instance) that you're taxiing to the flightline with an FM/PPM receiver and someone else accidentally turns on a transmitter using the same channel. Before you can say "look out" there's a very real chance that the engine may have reved up and the model shot off into some innocent bystander or fellow flier.

At least with a failsafe you can ensure that the engine cuts or goes to a low-idle in such cases. That could save a life.

I'm not going to take such a risk for the same of a few bucks (probably just a few percent of the total model price) -- are you?

A.T.

Hi Bruce, you will recall that the last few RC power model deaths occured despite the models having a PCM receiver and at least one would not have happened if a dual conversion RX and a throttle failsafe, which I did mention in my last post, had been used. However, one must check for and adhere to any local regulations that may exist as there is no international collective agreement on the issue. Having lost good models with both JR & Futaba PCM receivers which locked out without enough height to recover, I now stick to PPM with failsafe on the throttle.
Regards
Alan T.
Alan's Hobby, Model & RC FAQ Web Links

XJet

The problem is that we don't know how many times a PCM receiver and failsafe have *saved* lives -- we only hear of the bad things. I'd wager that a lot of lives or injuries would have been saved to date.

That's interesting -- because I've done some quite comprehensive testing and absolutely without exception, when exposed to a level of interference sufficient to cause a PCM to go into failsafe mode, a PPM receiver has already gone into fits of apoplexy that would make the model totally uncontrollable. In fact, PPM receivers become so glitchy as to be rendered ineffective while PCM units are still providing a sufficient level of response to allow at least a modicum of control to be maintained.

Indeed, the average PPM receiver needs a signal to noise ratio that is at least 6dB to 9dB (four to eight times higher) than a PCM one to provide the same level of control authority when reaching those limits.

The only up-side of PPM receivers is that they will "glitch" when encountering interference and thus alert the pilot to the presence of a problem. However, with the arrival of DSP/IPD-based PPM receivers, even that becomes a moot point.

Having said that -- we're lucky down this way insomuch as nobody in our club has ever lost a model to interference despite the fact we have fliers on 35, 36, 40 and 72MHz.

After flying a spectrum analyser to 300 feet, I'm not so optimistic about 2.4GHz around here though, especially the Spektrum with its fixed (albeit dual) frequency operation.

frenchie79

Great points by both of you, anyone else like to give their expert opinion. Thanks

BarracudaHockey

My Feedback: (11)

This is exactly my experiance.

Lockout isnt a one and done affair. For a pcm lockout to persist the intererence would have most definatly caused a ppm reciever to crash.

Again I dont understand the thinking of going cheap on a large gas powered airplane.

A.T.

[quote]ORIGINAL: BarracudaHockey With respect, I must disagree. As mentioned earlier, models flying with a Dual conversion RX over a line of interference (e.g. electric fence) simply glitched whilst keeping control inputs and passed through to land safely. Those with PCM locked out and control was not regained before the models crashed. Once a PCM RX locks out, the time for RX recover may be only half a second or so but on take off and landing that delay costs $ and the model could shift course, depending upon how the control positions are set for failsafe activation, and even if control is regained it is a matter of further time to correct the changed attitude of the model.
First bad PCM occurence was with JR PCM equipped .60 Trainer with which all appeared fine until one landing sequence when a very good student "lost it" on approach in from the harbour. On taking over the control, there was a delay before the model started to correct but to late as it disppeared out of sight/control below the coastline and crashed into the beach below - fortunately no damage to limbs or property. There was a distinct third to almost one second lock out period with the PCM which does not occur with PPM.
Again, each to their own or the dictates of their sport's ruling body but do suggest perusal of the information provided on my web page under:
"Giant Scale, Large RC models, Twins & Multi Engines"
"Radio Systems, Accessories, Alterations and FAQ" which includes:
AM, FM, PCM & Spread Spectrum radios - FAQ re differences
PCM vs PPM Evolution and uses
PCM vs PPM. AM vs FM - everything about 72 MHz radios
PCM - how & why = SE Modeler
as well as the sub sections which include:
"Receiver - FAQ, guides and aids to best reception"
"Glitches & Jitter in RX & Servo - causes and cures "
Over and Out.
Regards
Alan T.
[link=http://homepages.ihug.co.nz/~atong/]Alan's Hobby, Model & RC FAQ Web Links[/link]

frenchie79

B.H. I wasn't implying going cheap by using a Hitec Supreme receiver, this receiver has been serving my glow planes with no problems what so ever and they are in expensive planes with actually more power than a 32 Gas. If everyone out their says i need to go to PCM and have solid reasons-I'm there no matter the cost of the receiver. Thanks again for your input.

Darkbird

My Feedback: (7)

Have used ppm for years in large gas models without any serious problems. Have a 33% extra and a 1/4 scale Corsair both on ppm. As long as your setup is ok you should be fine. JMO

BarracudaHockey

My Feedback: (11)

A proper radio installation and range check with the engine off and running with the plane secured will go a long way to problem free operation but ignition engines are inherently electrically noisier environments than glow engine powered planes. Just like helicopters with moving parts and bearings etc are noisier than our fixed wing counter parts.

At the very least I would add a throttle fail safe even on your large nitro powered models.

frenchie79

Thanks for the replys everone-B.H. thanks for your views and i will look into throttle Fail safe. This does make you wonder if all planes should have their throttle on a fail safe system at a minimum, even a 40 size plane that can travel 70+mph at five + pds spinning a 12x4 prop at 12K + RPM's-that is probably just as deadly as a 14LB Gasser???

BobH

My Feedback: (2)

Twenty six years ago we had a guy killed at our field by a 60 size plane. It was due to the air craft hitting him in his back/side and rupturing his liver. So yes.. lethal isn't always bigger.

I use PCM and prefer it for gas planes and my WWI plane (lots of flying wires). I'm familar with the debate of PPM vs PCM, lock out vs no-lock out etc. I believe lock out is pretty rare on the newer PCM equip. At least that's been my, and many others, experience. I also think that some PCM crashes are a product of improper "fail safe" settings. In reality you can't have a "fail safe" setting other than throttle. No one knows the attitude the plane will be in when fail safe is engaged so any attempt to make one's servos, other than throttle, go to some pre-set condition means?

Now that 2.4 ghz is here I suspect that this entire subject will be come academic in a few years.. and that's a good thing!

mapnet

Resistor type spark plugs must be used to cut down RF interference.

frenchie79

Thanks Bob, I might be best served looking into the 2.4 for gas and converting my planes as i go. I'm new to the Sport and only own two Radios at this time. Thanks again to all for your opinions.

The_Other_Dave

Do any of the 2.4 GHz systems have fail safe.....? I am less worried about interference problems than I am about plain old radio failure.

A.T.

Spectrum & XPS failsafe query answered
Regards
Alan T.
Alan's Hobby, Model & RC FAQ Web Links