Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Glow plugs... need some suggestions

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Old 10-21-2008, 12:01 AM
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Troy-RCU
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Default Glow plugs... need some suggestions

I'm burning up a plug per flight on my Tiger Demon and K&B 6.5. I am tuning so the motor is not lean and it lands with the head just barely warm. In fact, the motor is running super. Problem is I am popping a plug per flight on only 15%!!?? A flying buddy at the field gave me a good McCoy and it lasted 1 flight. I am flying 8oz of fuel per flight so the flights are about 6-7 minutes at full blast and around 20K+ RPM (in flight). Is this a compression thing needing shimming of head or do I just stock up on plugs. Pretty soon I am going to wish I threw an electric set up in there if I blow up a $5-6 plug per flight.

Do I go to a cooler plug, hotter plug, add a shim and if so how do I make one and thickness needed. Thanks.
http://www.youtube.com/watch?v=TPnXLDbEO9M
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Old 10-21-2008, 12:10 AM
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Default RE: Glow plugs... need some suggestions

The DF guys use cold plugs. They don't idle so well but they seem to last longer. Maybe try some lower nitro fuel.
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Old 10-21-2008, 12:26 AM
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Default RE: Glow plugs... need some suggestions

Could be several things. Most likely, overcompressed. Add .005 to .008 shim.

Secondly, the bearings sound a bit raspy. If one is breaking down, the small bits of metal spalling out will kill the plug.

Third, it sounded like it went lean on the launch. Also a sure fire way of killing a plug.
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Old 10-21-2008, 02:30 AM
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Default RE: Glow plugs... need some suggestions

Troy, go for plugs that are wound from the heavy wire. At this level of performance, plugs take a beating. I think 3 runs per plug is acceptable. Like HP says, lower the compression. Make sure your bubbleless tank has no trapped air when you refuel. Creep up on the killer setting from the rich end. Like ILJ says, it is best to rig up an in flight mixture adjustment from a remote needle valve.
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Old 10-21-2008, 06:09 AM
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Default RE: Glow plugs... need some suggestions

A plug per flight!!!
Ha , I know what you mean and understand how you feel dude.
I'm going through a similar situation. Infact I've gone through loads of plugs this season.
I've found that these high revving engines prefere cold plugs and I believe the platinum is thicker on these plugs but can vary with maufacture.
One time, due to excess heat the coil had gone and scored the barrel and piston. More expense. just unlucky it didn't spit it out of the exhaust which you hope it would do.
I think too much nitro can effect it too.
Also running your tank to empty will lean your engine and kill your plug at the end of the flight.

Now, I try and land with fuel, cut the engine in flight and examine the plug after and feel the engine temperature.
Maybe tune yr engine with half a tank of fuel.

Generally Im not happy if its not screemin from lift off. rich sucks for performance flight and the expense of a lean run.

Shim it up will help lower compression.

You could look at installing an arm attached the high speed needle on a servo that you use on a spare channel to richen or lean in flight.

At the end of the day its a pain in the ass when the plugs blow, which are about 1/4 price of a gallon of fuel.

Keep looking at your plugs. Richen the mix is going to help.Maybe also a lower oil content fuel will give you a colder engine
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Old 10-21-2008, 07:56 AM
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Default RE: Glow plugs... need some suggestions

What does the coil look like? When I started running my 6.5's I went through several plugs...until I shimmed it up a bit, and went to the K&B HP plug...that plug seems to be heavier duty than most. My plugs coils were pushed up into the cavity...a sign of too much compression.

Another thing....are you sure you have the pipe the right length? It could be over charging the cyl and perhaps acting similar to being over compressed? I'm no expert at tuned pipes, but recall reading something like that around here somewhere...

One more tidbit I learned about pipes from running r/c cars...is if the pipe and header are rubbing, that can blow plugs, because some of the alum. can get back into the cyl. and contaminate the plug.
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Old 10-21-2008, 09:06 AM
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Default RE: Glow plugs... need some suggestions

ORIGINAL: Troy-RCU

Problem is I am popping a plug per flight on only 15%!!??
That K&B 6.5 RIRE indeed sounds kinda restricted, maybe to much of exhaust gas restriction leading to overheating head temperatures...

Or there's simply too much prop load involved...



Please also check out this tread:

[link=http://www.rcuniverse.com/forum/m_8011495/tm.htm]No more lean runs?[/link]


An in-flight R/C mixture control is a must-have for all serious speed planes!

Too rich (i.e less powerful) take-offs as well as too lean speed dives will be avoided applying such a mixture control.






The extra-cold ROSSI #8 plug is the best regularly threaded glow plug (non-conical) for the speed folks.

As for technically sophisticated conical plugs, namely the so called "turbo" plugs providing better performance than NELSON HD or GloBEEs, the extra-cold NOVAROSSI / TOP / REX turbo 8Tf plug should be used.

Of course these extra cold plugs aren't well suited for engines operated with R/C carbs - but who intends to use a R/C carb instead of the mandatory and much more powerful speed venturi carb?





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Old 10-21-2008, 11:03 AM
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Default RE: Glow plugs... need some suggestions

is the glow plug distorting because of the run, or is it actually burning to "open".

Over 90% of the time blown glow plugs are due to one thing - a lean run. Does not matter what your mixture setting is or how cool/hot the head is when you land.

Someone described that the plane went lean after launch. If the needle is critical to set on the ground, the pipe may be set too short (you are seeing a false peak) On a piped engine, you always have to back down off of peak rpm several hundred rpm. Once in flight, the engine will "request" the extra fuel it needs to support the rpm gain - if its not there, the engine will go lean.

Distorted plugs come from being over/under compressed. The coil will be pulled out, pushed in, or slide to a side. That sort of plug failure is "good" because it tells you something about how the engine is running. Except for when the coil departs the plug and the engine eats it.

You may have a fuel foam condition occuring when the prop/engine/pipe unloads. You may not even see this condition on the ground, but in flight it manifests itself. Double check your fuel system. Unfortinately, the Tiger Demon and similar planes do not permit a "correct" fuel system install fuel foam is frequently an issue with higher performance engines.
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Old 10-21-2008, 11:30 AM
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Default RE: Glow plugs... need some suggestions

Yeah, what Bob said.

My K90 boat motors were running 60% nitro, short pipes, high timing and high compression. If I leaned on them too hard they would not only blow a plug they would burn a hole throught the piston in one run.

The simple solution is to back off the needle. Fuel is the coolant for the motor. Lean it down too much and the motor begins a thermal runaway.

The K&B HP and McCoy 9 plugs should be fine for this motor and will last several runs as long as you keep the needle on the rich side. Lengthen the pipe a bit to make the motor easier to tune until you get it down.

Post a picture of a plug if you can. Use a macro setting or crop the picture to just the face of the plug and the coils. You can learn alot by looking at the plug.



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Old 10-21-2008, 11:57 AM
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Default RE: Glow plugs... need some suggestions

Troy, in your place i would try, a richer setting, one or two more gaskets under the head and/or reduced nitro content . also a colder plug like a OS A5 or other would be in order. good luck
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Old 10-21-2008, 10:58 PM
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Default RE: Glow plugs... need some suggestions

That video is from the 2nd flight and I have adjusted the pipe since then. It wasn't really suppose to demonstrate the current issue, that run was actually very rich and the pipe was an inch too long. The pipe length has shortened and I have gained up to 2000 RPM. I needle the setting down about 500 RPM from max before launching. The hesitation on launch in the video was a very rich low end, it transitions much better now.

Any way, I have noticed distorted plugs. I found that odd since the plug may run one or two flights but the coil was distorted a bit. I have been checking the piston for any scorched marks or signs of a lean run period but it really is not sensitive on the needle one bit and runs great the whole flight. I just took the whole motor apart and it looks good all around.

Here are some pics of a couple plugs. These are just some regular LHS cheapo plugs but the wire is thin and the coils are definitely distorted. I should mention I burned plugs at richer needle settings too.

ps: anyone have a Perry Carb that would fit this motor? I am having some mechanical issues with my current carb. Looking for a .437" OD throat diameter or Perry #2100
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Old 10-22-2008, 12:08 AM
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Default RE: Glow plugs... need some suggestions

Plug on right has dry surface. LEAN LEAN LEAN
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Old 10-22-2008, 01:04 AM
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Default RE: Glow plugs... need some suggestions

Are you running a bladder tank? If not isolate the tank on foam rubber. You could be foaming. Don't let it run out of fuel, shut it down. I you were using a fuel cut off, that would be sudden, but you are getting a lean run for a bit before it dies. Try the K&B HP plug, my OS DF engines are getting at least 25 flights on 30% before I replace it due to the performance drop (the wire looks dull & frosted).

Food for thought, my 8oz. tank last only 3 minutes, you are getting 6 or 7? True you are useing 15% but thats still a lot of run time. Too lean???
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Old 10-22-2008, 10:09 AM
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Default RE: Glow plugs... need some suggestions


ORIGINAL: HighPlains

Plug on right has dry surface. LEAN LEAN LEAN
Yep.... lean run on that.
The other looks cooked too. Distorted a little, but mainly cooked.

500 rpm off peak is not enough. If you cant needle back down at least 1000 rpm before it falls off of the pipe, pipe is too short or the prop is too big.

Suggestion here is add a few head shims (.010 at least). And back down off the peak a bit more for launch.

As noted, 8oz of fuel should give you no more than 4-5 minutes of full throttle flying time with your setup. Consider at least the last 2oz "unusable fuel". Running the tank dry is a sure-fire blown plug.
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Old 10-22-2008, 10:33 AM
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Default RE: Glow plugs... need some suggestions

Troy,

When I raced boats it was common for guys to buy 100 plugs before the season started and end up with a handful by the end of the year.

Use the scientific method, don't change more than one thing at a time. I'd start by fattening it up about 1k from peak as Bob noted. Then switch to the K&B HP or McCoy plug. If those plugs are still blowing or turning dark brown like the one on the right then add .003" shims one at a time until the motor settles down. BTW: I always liked the McCoys better for testing because you can see the color change easier on silver plugs than black ones. They both run about the same in testing.

Now go off and tweak away then report your findings.

Good luck,


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Old 10-22-2008, 10:34 AM
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Default RE: Glow plugs... need some suggestions

I was about to chime in and suggest (a) compression may be a bit high and/or (b) the pipe too short/prop too much load - but then I saw folks got those covered already. And the part about running bladder tanks.

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Old 10-22-2008, 02:33 PM
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Default RE: Glow plugs... need some suggestions

When I was racing Formula One, I usually used up 15 to 20 cards of K&B's each season. Good thing was that they were only 50 cents a plug back then. Even less when Bill W. showed up at a race. What you want is a wet shiny dark surface on the face of the plug. The dull dry surface is oh so hard on the piston and liner. Another thing that can kill the plug is jerky flying, stay smooth. And if the tank height is too low, the engine will lean out in turns and kill the plug.
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Old 10-22-2008, 03:47 PM
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Default RE: Glow plugs... need some suggestions


ORIGINAL: HighPlains

Another thing that can kill the plug is jerky flying, stay smooth.
Is a high G pylon turn considered jerky? Abrupt direction changes fun.
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Old 10-22-2008, 05:22 PM
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Default RE: Glow plugs... need some suggestions

In engineering terms:

Velocity is the change of position per unit time
V=m/s

Acceleration is the change of velocity per unit time squared
A=m/s^2

Jerk is the change of acceleration per unit time cubed
J=m/s^3

Early astronauts were really aware of jerk. Those rockets were quite rough riding in addition to the high g loads.

We pulled a lot of g's with the old Formula One pylon model on 65% nitro, but the pilot needed to fly smoothly to avoid blowing the plug. One whoopy and your heat was over.
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Old 10-22-2008, 10:17 PM
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Default RE: Glow plugs... need some suggestions

I wiped off the plugs pretty good to get a good photo shot. The last one I ran was pretty oily. Still, you guys are giving sound advice and I am taking notes. I am not running a bubble-less tank but it is wrapped in soft foam. I don't pylon turn this thing since it skids off speed anyway so it's big swooping runs. I have run the tank empty a few times. My last flight I had a stuck throttle so no choice. Was fun while it lasted. Actual run time is guessed so I will set timer in the future so I don't deadstick.

I did notice that I was down on peak RPM on my last flight. I checked the plug prior to flight and it was slightly distorted and not glowing super bright. I figured it would go one more flight and have to switch out. I was down about 700 RPM. I am able to peak at 21,400 but only able to get 19,700 last flight. I needled to 19,200 and it still seemed to get on the pipe a decent amount.

Learning lots from you guys! Wish I had some more 'tuners' in my neck of the woods. What would we do without the Net? So anyone have a spare Carb they want to part with!?
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Old 10-23-2008, 04:22 AM
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Default RE: Glow plugs... need some suggestions

I found if the plug is going or bad from a previous run it will show poor performance in your flight. Land, save fuel and bin it. Fit new one for your next blistering flight. Happy days.
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Old 10-23-2008, 10:08 AM
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Default RE: Glow plugs... need some suggestions

Hi!
Try a Rossi 6,7 or (coldest) an 8 plug! The Rossi 8 plug was the plug we used in F3D pylon before the Nelson engines/plugs came along 15-16 years ago.
What propellers are you using? Fuel?
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Old 10-23-2008, 02:28 PM
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Default RE: Glow plugs... need some suggestions

Troy what prop are you spinning?
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Old 10-23-2008, 11:31 PM
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Default RE: Glow plugs... need some suggestions

It's an APC 7.5X8 carbon Q40 prop. I have some other Q40 props to play with... 7.2X7.7 and 7.2X8 I also have a thinner blade 8X8 I can eventually trim down to 7.5 or something.

I will be looking for some shim stock and make a set of shims to play with. I am also on the hunt for a Perry Carb since my current carb has broken two bolts on the barrel set screw. I have some time to find good plugs and build shims. When I can get the motor combo dialed in I want to build a cowl to add some mph's but as it is it flies well and is quick.
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Old 10-27-2008, 11:26 PM
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Default RE: Glow plugs... need some suggestions

OK, looking for brass shim stock for the head. How does this look to start:
9011K5
http://www.mcmaster.com/ctlg/DisplCt...21982858575944
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