There is a saying in general aviation regarding twin engine aircrafts: "The second engine will make sure you arrive at the scene of the accident" and that's truth of any redundant system.

Ask the designers of the shuttle Columbia if their quadruple redundant computer systems could have prevented their disaster. My point is that it doesn't matter what we do to prevent a catastrophic failure fate has its way in the end, but that doesn't prevent engineers from trying to increase the odds in our favor. Of course you must exercise an analytical decision making process when designing your system. That means evaluating every component and then deciding which options satisfy your mission requirements. In my opinion in the case of a 3D machine, which options will be the lightest, most reliable, easier to install, and least expensive.

In any case I don’t see how a 0.3 oz. optical kill switch is going to ruin your 30 lb. plus 110” wingspan, overpowered 2.5:1 3D machine wing loading. Or for that matter the cost of such unit is not going to drive you directly to bankruptcy court because you are going over budget on your $3,000 dollars project.

I personally use optical kill switches on all my big planes? Why? Because I like having the ability to immediately cut my engine at any time from my transmitter. I use the spring loaded trainer switch on my 9C--it's a big switch so I can hit it fast and yet it's spring loaded so it doesn't get hit accidentally.

I still have a 4*60 that I fly occasionally and for fun flys. Years ago my throttle linkage came off the carb arm. The plane flew around at 3/4 throttle until it ran out of fuel and then I deadsticked it--it's a 4*60 so there's no problem there. I don't use an optical cutoff on this plane.

One of my warbirds is a 1/4 scale ME109G (34lbs; 102" wingspan; 75cc engine). One time several years ago the fuel line slid forward through the firewall into the cowl because of engine vibration. I had some excess fuel line behind the firewall so that I could pull the tank back for inspection without removing the fuel lines from either the tank or the carb. I had full throttle down to about 3500rpm--it wouldn't go any lower because the fuel line was interfering with the movement of the throttle arm. I flew it around a while trying different throttle settings but couldn't fix the problem. I ended up bringing it in for a landing and once over the end of the runway cut the engine using the optical ignition cutoff. I was able to cut the engine at the exact point that I wanted and deadsticked the plane perfectly. If I did not have the optical kill switch I would have had to fly around up high until the plane ran out of fuel. I use a tank sized to give me a reasonable amount of flying time--say 15-20 minutes, so I was not in danger of my batteries getting too low. But, I would have had to do a deadstick from high altitude not knowing when the engine was going to stop. I don't think this necessarily would have been a problem, but this particular plane is difficult to deadstick. It is highly preferable to land under power! I was glad that I was able to kill the engine from the transmitter right when I wanted to. Throttle trim would not have worked in this situation, although a choke servo would have.

I have not had any other situations like this, but once was enough for me to keep using optical kill switches. I can still use the throttle trim, and on occasion do, but I like being able to cut the ignition from my transmitter.

-Ed B.

All the Gloom and Doom testimonials are fine. I use the throttle kill function in my radio to stop my engine whenever I need to. Again, maybe it's just me but I've never had a run away engine, had a linkage fall off an engine of any size, or used an optical kill switch. Sure I can afford one but why.........because of what could happen. Live life like that and you'll soon be living in a bubble. I think my money is better spent avoiding what is probable rather than what is possible. One in thousands of RC flights may end up with a throttle linkage coming off for the simple want of a pre flight check or routine maintenance on these MEGA BUCK aircraft. Lack of kill switches I can almost assure you is not the problem.

Mr G.

As you can see there are many opinions about what to use as a secondary method to shut down the engine (and whether even necessary). You can use either a choke servo or an electronic switch of some sort. I personally think an optical switch is not necessary and therefore use a solid state switch. The choke servo has the added advantage of not having to rig up a manual method, especially on the rear carbed DA.

To each his own.

I hope you got the answer you were looking for.

N7160F,

I have been monitoring this thread for all of the replys.

I would first like to thank everyone for their input, it has been a great help.

There were a few post brining up issues I had not thought of. For example: Choking to death could result in
excess fuel in the engine with a LIVE ignition!! Their are a few others also.


I have not yet made up my mind on what I will do, but the posts in this thread have really got me thinking. Thankyou

After I have reached a decision I will post my decision as well as the reasons for it.

Thanks again to the guys at RCU!!

MR G

Having almost lost a scale warbird when the cutoff switch failed off, I do not put a kill switch on my planes anymore. I set the throttle to kill the engine with low trim.


Larry

Another vote for the optical kill---Whats another 60$ when Im spending $2500.00 or more in a plane...Worth the peace of mind for me.

I put a optical kill on my ignition because I get a single spark when I turn my ignition switch on. It gives me a extra measure of safety in case I forget. Bob

Sent post twice OOps.

I put my first optic kill switch in when I was invited to fly a demo at a local air show. I felt it added a extra measure of safety. I know after a good inspection of my plane the chance of a problem are remote. If there was a problem and the plane hurt someone I want to know I did every thing I could to be safe and yes it is a personnel choice. To say you do a good preflight inspection so I'm not likely to have a problem doesn't cut it for me. I didn't build the batteries, receivers, switches, transmitter, or servos. When guys in our club ask me if they should put one in there plane I tell them its not necessary but I feel more comfortable with one.

Not gloom and doom, but practical common sense.... if anyone has ever had bolts loosen, thus preventing throttle servo closure, or throtlle pushrod / link failure, or (and this happens more frequently than many probably admit) throttle servo failure..... I want to be SURE I can kill that sucker. As others have said, "to each their own", but I find a lot of PRACTICAL reasons to have a secondary kill that doesn't depend on mechanical integrity of the firewall, mounts, throttle servo, or linkage.

Worth thinking about.

Like I said in the beginning. This topic always ends up being a matter of personal choice. You can come up with all the scary stories anyone can imagine but in the end we all do what we think is best and necessary. If the AMA, IMAA, IMAC aren't concerned enough about it to make it mandatory then just maybe It really isn't necessary to spend that $60.00.

I agree with Surfer! I set up with throttle spring and Hi-torqe servo. I only have 15 years of exp and only 2 years of gas and I have never had a problem with linkage coming off or throttle servo problems (KNOCK, KNOCK). But I do check batteries before every flight to ensure I have safe flying voltage. Planes that go out of control from no rx voltage are much more dangerous than no ign cut off! I see countless people bring their planes out and say I charged it last night! And they fly 5-6 flights, after the 6th flight they are walking out to pick up the pieces. Then its bad rx, radio hit, someone shot me down. Its never OH my batteries were dead I f$#@@d up. I should have used an ESV before every flight. Any how, I heard another say do it right the first time and preventative maintenance is everything. Just my Nickle

3DAP

For those of you that believe an optical kill switch is a practical small device that will enhance the safety of your gas powered birds; 42 Percent Products is offering a very inexpensive [link=http://www.42-percent-products.com/gas-accessories.htm]OPTO Coupled Kill Switch [/link] designed for igniton fired engines.

They also manufacture a Kill Switch for magneto fired engines and other nifty devices like high voltage digital switches, servo testers and a very inexpensive voltage regulator.

I tried to check on the I4C Product line since I think they carry similar products but their web link is dead (400 Error). Does anyone knows if thery are still in bussisnes?

A few months back the I4C web site had a notice posted informing everyone they were getting out of the RC market.

Sure there will be some who think different on this... but I have heard atleast 5 times where that switch hasn't worked properly... in fact I know someone who had 3 of them shipped to them just to get one that worked properly.

The best option is the Smart-Fly Product... sure its a bit more money but it works.

Well that's good information to know. By the way was the failure related to not operating when turned off, or was it turning off the engine when not commanded to do so?

I have heard of problems with the Smart-Fly switch turning off the engine because of RMI generating a false signal from the transmitter. I believe Smart-Fly has taken care of that problem with some type of filter or delay circuit. Does anyone out there knows more about this issue?

We could only make this a more controversial topic by adding an Amsoil 100:1 vs Pennzoil 40:1 discussion

I am a big fan of redundant backups since I'm an engineer and understand that a plane is a system depending upon a lot of individual things to all work each time. Many of them won't be seen in a preflight inspection and honestly, almost nobody does a preflight before each and every flight. I've personally seen 3 instances where a ignition kill switch would have prevented a totaled aircraft.

I have one Smart Fly that worked ok for many, many flights. I did experience problems with it one time. Not in flight...just would not allow the engine to start on the ground. It tested fine when pulled from the aircraft. Most likely an end point setting sensitivity or perhaps the fiber optic cable might not have been seated properly in its socket. Nice, with a remote LED, but it is really overkill in my opinion.

The best success I've had is with the $25 RC100 by RCAT Systems. http://rcatsystems.com/electronics/rc100.php I have half a dozen of them and they work very reliably. They are lightweight and cheap. No need to spend $60.

I have used both the optical & choke servo route. Both kill the engine fast (one is no faster or any better then the other.) The statement
"Choking to death could result in excess fuel in the engine with a LIVE ignition!!" is simply not worth the worry. When you choke the engine you are choking of the AIR supply so no burn happens. When you kill the engine with the ignition there is no spark but you do have fuel & air in the cylinder. You can kill an engine by removing the heat (ignition-fast) removing the fuel (out of gas & low throttle cut- slow) or remove the air (choke - fast). I do agree that a second means (not a low idle cut) of killing an engine is worthwhile. I watched a GS war bird go through a crowd of people because of a stuck throttle.

Of the 4 RCAT RC100 switches that were being used at our field, 2 caused interference to the electronic ignition. The engines would run poorly and some servo glitching on other channels was noted. One was bad enough that the plane was almost lost. All 4 were removed, same day, and all the glitching and interference was gone. I did receive one of these that was dead on arrival. RCAT replaced it very quickly, but I am now afraid to try these inexpensive switches again. I would go optical instead. An interesting side note, I had one of these in a quarter scale Cub that was flown with a Spektrum 2.4ghz radio. No glitches what so ever. I switched this plane back to 72 mhz, to use the 2.4 in another plane, and immediately had glitching. I removed the RCAT switch and it was gone. The Spektrum masked the issue. RCAT did offer to inspect these and replace if anything was found.

Me too,, for another $.02

I put cutoff's to suit me and keep my 10 thumbs in place.

I use a cut off switch on the engine so I can insure the ignition is off when I turn the prop even if the battery for the flight pack is on the bench.

I also use a servo cut off in to make sure if my 10 dumb thumbs get to the plane on landing and I tow it back to the pits. (rules won't allow taxi into pits) then I can have the servo switch off.

The other reason I really like the servo cutoff is that it makes it so much fun to start the engine when I forget to turn it on.

Do you know what the battery setup was used in the planes that were glitching?

Not sure why you may have experienced problems with RFI, Vanguard. I have had success with both C&H and DA ignitions with no issue. All of my receivers for my gas planes are Futaba PCM, DP149's.

Some other tips for the RCATS:

END POINTS
On the RCATS switch, both end point settings are important. Otherwise, the contacts will chatter. You will see the LED light blipping on and off when this happens. On my Futaba 9C, I make the endpoint only 10 points or so higher than it takes to engage the switch. I do this in both directions. If it requires an endpoint of 30, let's say, to just barely close the switch (green LED turns ON), then I will set that end point to 40. Some folks automatically set them to +/- 100 for a switch. That's a bad idea in this case...the RCATS switch will not be happy.

LOCATION
Since the RCATS switch is switching over the ignition battery, at least one end of the switch potentially has RFI passing thru it. I locate my switch fairly far forward in the plane, not close to the receiver. It's probably closer to the ignition module than to the receiver.

I hope this helps.

Hi guys,

Thanks for the comments on the RCATS switches. In the history of the switches, we have had VERY few reports of issues with them. We do offer a fiberoptic version that allows one to totally isolate the TX/RX of the electronic switch.

To note, we do not advertise that the RC-100X,RC-100, or RC-110 are optically isolated. The small processor and the actual lines being switched are isolated in the fact that the system uses a relay. The trigger line does not connect to the relay lines.

As mentioned, the end points do matter on the current switches, as does the voltage to the switch. They are designed for 5V operation and not >6V packs.

Any time that one places high current and wires that have RF on them near another set of wires, there is a possibility of interference or coupling of noise. Signal strength falls off quickly with distance, so this is why people have said to separate radio equipment as far as possible from electronic ignition over the years. What is likely happening in your case is that your ignition is emitting some signal that is either close/on 72MHz or that causes interference with your receiver. It is then picked up by coupling to the lines on the switch, causing issues. The 2.4GHz obviously didn't see this because the noise wasn't anything that affects it.

Michael Luvara
RCATS

Thanks for jumping in, Michael. I've been using your stuff for several years, quite happily and have found you to be very supportive.

Suggestion - it would be awesome to have a version with in/out universal servo plugs. This would make connecting the switch inline between the battery and charge switch that much more plug and play. I've gotten quite good at making the connector myself, though

So... you are going to spend 2-7K on a typical giant scale plane and avoid spending $35-45 on a safety item that could save you or your plane? Your choice.

P.S. - Can you inform us of the ground check/routine maintenance that can predict throttle servo sudden death?