wind junkie

My Feedback: (1)

I'd like some help if this sounds familiar to anyone. I posted this on FG in the 2.4 section also but wanted to try here in the general forum.

I've been flying my TBM P40 with a DA 85 for a few months now. About 3 weeks ago, I had what I thought was an engine problem when the motor would cut out at some speeds usually downlines. It was consistient. Then the problem got worse and I noticed that it was not the motor's fault because I would watch the throttle servo go to idle when I'm just running up in the pits an obvious failsafe condition.

Range checks WITHOUT motor running are good. Today I switched to a new RX and even switched to a different TX, and all have the problem. I changed to a new throttle servo also. Range check with motor running is VERY BAD it goes to idle immediately and I can see the failsafe trying to activate at most throttle speeds when I'm standing right over the airplane (it pulses for a half second or so and makes the motor sound like it's hesitating, but really it's just the throttle commanding it). This will happen with me simply holding the RX in my hand (either RX) with only the throttle hooked up, and with either of two TX's I am using for test.

Perhaps I may have put some stress on the spark plug wire in fishing it through the hole in the cowl in the past month? Are the spark plug wires fragile? Someone told me that if there was arcing inside with a broken "carbon wire" in that area it could give interference. I think he was talking from automotive experince.

My question is I thought 2.4 would filter out such noise? I have seen threads where 2.4 users share a SINGLE battery for both RX and IGN, but I guess what I'm asking is it possible that the high voltage side of the circuit is more likely to cause proglems if it arcs?

If one can share a battery with IGN and RX, it seems obvious that position of the components near each other (which I understand was a big no-no with 72MHz gear) with 2.4 equipment wouldn't seem to matter. I do have the RX batter near the carb, and the ign module is also near the carb, about 5" away. The throttle and Ign switches are separated by only 3" and that's the closest their wires get to each other.

The thing that bugs me is I had beautiful performance since mid July and after Labor Day something changed drastically, so it seems to point to something other than equipment layout.

The spark plug cap is on all the way, but I did need to repair the red shrink tube which bridges where the braided shield enters the metal cap. When the plug floods I always need to pull the cap off with needle nose pliers through a small hole due to the cowl hiding everything. Sometimes I pull too hard and the cap gets jammed in the hole maybe kinking the wire?

I just thought of something else. I have both the sensor wire and the spark cable going through the same hole in the fiberglass fuselage from the ign to the motor. Both are wrapped separately in plastic coil protector, but maybe that has found a way to work loose and fray? I wonder if there would be a path for noise to enter into the RX back through the sensor wire.

Does anyone have experience in this area?

thanks,
Joe

Taildragger726

Try changing the spark plug.

Wingspam

I recently had a similar problem on my Peak models Yak, running an SPE 43 cc. I use the Futuba Fast reciever and my New 10c radio, I have digital servo's thru out the plane and everything has always worked great. No power expander . just a simple operation. One day at the field, I am a the starting station letting it warm up berfore I taxi out, checking all my controls and all of a sudden everything quits working and the motor dies. The same thing kept happening time after time, finally I noticed that the receiver light would switch from green to red and it would go thru the same routine.

Finally after about 30 mins or so one of the other members came over to check it out, his only suggestion was to put in a power expander , he told me no person flying a gas powered plane should be with out it. So off i go to the LHS tail between my legs and grab a power expander sport, I race back to the field where he offered to assist in the install of the module. A short time later it is ready to try again, again with the same results after dropping a $110.00 on what he was sure would fix the problem I headed home. I changed out everything , and the result was the same, if I had hair I would have been ripping it out by now.

I was at the point of taking the motor off the plane and going to a larger glow motor when, I ran across a post telling me to check the plug wire cap and make sure it was on good, the cap on mine is metal with a rubber on the inside. It takes 2 people to take the cap off and on, one to hold the plane and the other to pull it off. I thought there was no way this was the problem it is too tight. After many attempts to get this thing running the way it always had (all this in my driveway) I noticed that the plug wire cap would actually move while the motor was running, when it did this the motor would slow down and die. I ran to the hardware store and bought a hose clamp for $1.39 put it on the spark plug at the base of the motor fired it up again. After spending almost $120.00 trying to fix the problem, it was solved for a $1.39 hose clamp..

CK1

My Feedback: (60)

The 3w and DA metal spark plug caps are prone to fail if not removed correctly ,don"t twist them or pry them sideways, always pry them straight up to get them off . It sounds like you may have stressed the cap by the way you have had to remove it because of the cowling restrictions. I would order a replacement cap and thoroughly inspect the ignition cable while replacing the cap . You may need to modify your cowling to prevent a repeat failure as well . The caps are a little pricey but not as much as a new aircraft .

bubbagates

My Feedback: (32)

Joe,

Even 2.4 can get swamped if the signal is strong enough. Since you have been pulling on the plug cap improperly with pliers and most likely from the side and also had to repair the cap at the joint in the wire, that would be my first bet. Vibrations, especially from a big single cylinder engine will eventually show you the weak points on any plane.

To give you an idea, I installed a DA170 into my 42% Extra, 45 flights later I was taking hits and the engine was roughing rough. I got the plane down and found both plugs a bit loose. I tightened them and have not had a problem since. I t was my own fault for not checking them when installing the engine.

Yes, carbon wires can be a bit of an issue, especially when treated roughly. Also, if any of the protective braiding around the wire is damaged, which is also the ground for the plug/ignition connection, you will also get interference even on a 2.4 if the damage is severe enough

If you are flooding enough to have to do pull the plug every so often, then you are way too rich as well on the low end. Remember, you never ever have to run a gas engine rich, you do need to properly tune it and if cooling is an issue and you are running it rich to get it to run cooler, I'd be looking at airflow as well as oil mixture. Oil mix and airflow are what keeps a gas engine cool. Running one rich robs it of power and fouls the plug and causes flooding.

The low end needle on a DA85 is very sensitive, so start out with no more than a 1/16th of a turn at a time until it can idle for a long time without the idle speed changing. Then do the high speed needle to get max rpm and drop it back around 100 rpm. You are looking to get instantaneous response to the throttle. Fly it and go vertical for all it's worth and listen to make sure the engine is not sagging on the upline, if it is, then it's too lean. Do all the adjustments with the cowl on.

wind junkie

My Feedback: (1)

Thanks for the tips guys. To clarify, the only reason I need pliers to get the cap off is because the hole in the cowl is very small and I can reach the cap by just gripping the "flange" which is an artifact of how the plug cap is made. I just put the tips of needle nose pliers through the hole, grip the flange, and pull (no harder than you would just using fingers, and the pull goes straight down. After the cap pops off I just push it out of the way and then put the socket in there. The hole is just barely bigger than the socket which I use to start the plug also when putting it back with my fingers.

A couple times I pulled too hard and part of the cap came through the small hole in the cowl and got jammed also putting stress on the rear part of the cap/shield so that is where I think the damage may be. I doubt very much that pulling the cap straight down it hurts the cap itself (unless it gets jammed in the hole again!).

Since I started draining the fuel tank at the end of a session, I haven't had any flooding, so I don't think I'll be removing the plug as often.

It makes sense that the damage could have gotten worse if vibration makes this come loose or frayed. I will look into this next chance I get.

Does anyone know if the ign from a DA 50 is the same as the DA 85 ign? I have a 50 sitting on the shelf now and could swap that out quickly to test this theory.

But in any case it is good to know that the spark plug end can cause 2.4 issues. Thanks again for your replies.

Joe

wind junkie

My Feedback: (1)

Wingspam, How did you get a hose clamp to fit around the cap and still clear the fins?

Wingspam

Sorry for the crappy picture but you can get the idea.