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

Blown Glow Plug

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Old 07-11-2004, 03:23 AM
  #1  
KC-Lovespeed
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Default Blown Glow Plug

Took the trusty Shrike to the field today. Set up is a Jett 50, 9x6.5 APC narrow pylon prop, Wildcat 30 %. Tached at 17,000 launching and flight were fast and smooth till I heard pop and observed the prop to be windmilling. Inspection showed the glow plug had bben forced out with some minor thread damage. I was able to get a new plug on and richened the motor some. Made three more flights with out a problem. I have used 30 % before and not had this problem. Was I running to lean ? It was also very hot today in KC. Love the Jett 50 for speed !
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Old 07-11-2004, 09:47 AM
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Default RE: Blown Glow Plug

If the plug physically exited the head button, the plug was simply not tight.

Running in warmer weather, combined with higher head temperatures can cause the plug to come loose when the engine is running. A few temperature cycles like this, and it will back out in flight.

Check that the plug is secure prior to flight. No need to over-tighten it, but just make sure it is snug.

Also of note....... you may want to replace the head button somewhere along the line. Once a screw/plug comes loose in flight, the threads tend to become damaged.

As for the 30% fuel.... you can use it, just keep the engine a bit more rich before launch. But the way the engine is timed and with the standard head spacing, you are actually better off with just 15%.
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Old 07-11-2004, 01:36 PM
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Default RE: Blown Glow Plug

Send the head to LEE MFG, and they will repair it with a helicoil insert. 17,000 with a 9-6.5 isn't very good, maybe the plug was loose to begin with?
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Old 07-12-2004, 01:21 AM
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Default RE: Blown Glow Plug

Well for not very good the plane was like a bullet. What would be a "good " rpm to shoot for ?
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Old 07-12-2004, 01:32 AM
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Default RE: Blown Glow Plug

KC,

Which Jett 50 are you running? Side or rear exhaust. Bar Stock motor?
How much oil are you running in your fuel? The Jett 50 is a great motor, but if run lean, it overheats something fierce. The head Will go bye-bye in no time. I've killed a few head buttons on Jett 50's. They don't like lean runs. Dub says as a rule, "Back off of a high tach setting by 800-1000 rpm's to get a close setting, then observe your engine on the run to see how it peaks. Each motor is just a little different, but that should get you close without burning plugs or the motor.

Dan
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Old 07-12-2004, 07:48 AM
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Default RE: Blown Glow Plug

Its not worth repairing the head button. They are not expensive, and easy to replace.

The Jett SJ-50 (standard side exhaust and sport jett-stream muffler) should turn a 8.75x9W pylon or standard blade 9x8 APC prop over 17K rpm at peak........ launch 800 rpm down from peak.

The muffler is tuned to run between 16,000 and 18,000. You want to prop the engine to run in that range.

If it has gotten over heated a few times, it may have lost the hot seal. That would require a breif trip to Dub where he may simply re-fit a piston (if nothing else is wrong).

Bob Brassell
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Old 07-12-2004, 11:50 PM
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Default RE: Blown Glow Plug

Can you get a head button for use with a Nelson plug for this thing? Want to go fast, a Nelson plug will give you an instant few hundred RPM at least.
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Old 07-13-2004, 07:17 AM
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Default RE: Blown Glow Plug

As far as I know, Dub only has nelson plug head buttons for the QM and Q500 .40 engines. He may have made a custom one somewhere down the line for a .46 or .50. We run regular 1/4" thread plugs in everything except the racing engines.
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Old 07-13-2004, 03:02 PM
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Default RE: Blown Glow Plug

Well...

You can get his racing engines with standard plug heads... how hard is to make a head button for a standard engine that takes Nelson plugs...?
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Old 07-14-2004, 10:52 AM
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Default RE: Blown Glow Plug

Its not hard. But there is little call for them for production. Likely Dub has one laying around for a .50 somewhere. I seem to recall we tested them in the .50 ducted fan engine for a while.
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Old 07-15-2004, 01:13 AM
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Default RE: Blown Glow Plug

It does seem to me that this is one of the least used things that will actually give you a good boost in power without much effort. I'm surprised the ducted fan people haven't been using them, and I wonder if they've caught on with the boat crowd. All it takes is a different head button. So I am surprised Sport Jetts aren't offered with the option.

It's not like Nelson plugs cost a bundle, either - $3 a plug is a lot less than an OS #8 or Rossi R5. Not to mention Rossi turbo plugs (same idea, a lot more expensive). The Nelson plugs are used exclusively in F2D Combat motors, and they are great in 1/2-As (with the Galbreath head), where they're a LOT cheaper than Cox 1702 glow heads or even Norvel Freedom XL plugs.

Henry will sell you the drills and taps needed, as well as head blanks, if you have a lathe. John Booker (CL Speed flier) has drills and taps, as well, and his own line of compatible plugs.
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Old 07-15-2004, 07:43 AM
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Default RE: Blown Glow Plug

You are right on that account.....the nelson plugs are a pretty good value

As I noted..... if a nelson type head is desired, one can be obtained with little more than an email or phone call.

Of note, the Jett SS40 pylon engine is sold in two variets.... the SEMPRA version with the std 1/4" glow plug, and the CAPS version which uses the nelson plug. From my experience with the two, I have seen no signficant rpm difference between the setups, plug wise. I usually run K&B 1-L or -HP plugs, or the Merlin 'hot' plugs jett currently ships with the engines. (Merlin plugs are outstanding glow plugs btw.... lots of differnt types and heat ranges) Side by side, the CAPS engine and SEMPRA engine run pretty much the same, just swapping the head button. The plug does not make a differnce, other than the Nelson plug will run for pretty much an entire season, where as I usually changed a K&B plug after a weekend of racing (usually nothing wrong with it...... the plugs go in my 'sport' plug collection).

(for those about to correct me, yes...the sempra and CAPS engines also have different size carb bore too, but I always run the smaller SEMPRA carb anyway)

Glow plugs actually control the ignition timing of the engine. In that respect, you can get a power band shift from changing from plug to plug...sometimes this helps, sometimes it will make the engine run like crud. Often you can achieve a higher top end, at the sacrifice of the ability to idle or transition well. Nelson plugs tend to fall into that catagory. The have a somewhat large diameter wire forming the coil, and they cool off quickly if you attempt to idle. Not very useful for a sport engine.

One of the other reasons the sport engines are generally not sold with Nelson plug provisions, is that the nelson plug installation does not use a gasket. If you overtighten a Nelson plug, you can destroy the mating seal, and the plug installation will leak. Most of us using them for racing, CL, and other uses know this, and understand the installation technique. The 'sub-average' sport pilot who tends not to read instructions would ruin the head button in no time. ... resulting in poor performance, and a returned engine and dissatisfied owner.... and the eventual bashing of a 'crappy engine' here on the message boards
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Old 07-15-2004, 08:15 AM
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Default RE: Blown Glow Plug

Is the use of anti-seize lubricants as used with full size spark plugs in aluminum heads good with glow plugs?

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Old 07-15-2004, 11:41 AM
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Default RE: Blown Glow Plug

I would imagine they could be used.... they are used in aluminum head automobile and boat engines.

However, I have never found a reason to use anything like that on a glow plug.
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Old 07-15-2004, 07:42 PM
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Default RE: Blown Glow Plug

ORIGINAL: bob27s
I usually run K&B 1-L or -HP plugs, or the Merlin 'hot' plugs jett currently ships with the engines. (Merlin plugs are outstanding glow plugs btw.... lots of differnt types and heat ranges)
The Merlin that came with my Quickie Jett lasted about 1 minute... still looks like new, still glows, wire still intact, not distorted... engine just does not run on it anymore unless I put the glow power on... had me baffled for a moment.
I guess the platinum coating got wasted during the first few seconds I ran the engine... must be something like that...

Put in a new Rossi 4... engine screamed again... BIG smile...
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Old 07-15-2004, 10:18 PM
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Default RE: Blown Glow Plug

ORIGINAL: bob27s

I would imagine they could be used.... they are used in aluminum head automobile and boat engines.

However, I have never found a reason to use anything like that on a glow plug.

I never had any particular reason either. The thought just crossed my mind as I was putting new plugs in my Harley. I hear of folks stripping threads and wondered if the stuff might help. (It might just make the problem worse if the plug went in easier and one didn't realize how much torque was being applied).

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Old 07-16-2004, 01:49 AM
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Default RE: Blown Glow Plug

If you put the plug in crooked or just strip out the threads by overtightening, then no lubricant is going to help you.
Put them in with your fingers (no wrenches please) and then grab the plug wrench and just tighten them moderately... you don't have to use force, they don't have a habit of coming loose.

I can see how an anti-seize lubricant would be of use on a motorcycle or something... they can get really tight over time...
That would be like greasing the wheel nuts of your car... nobody does that, but everybody should... it can save you a lot of headaches when you're standing at the side of the road in the rain with a flat tire... and you just bent your wheel wrench on those rusted nuts...
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Old 07-16-2004, 06:53 AM
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Default RE: Blown Glow Plug

Heh heh heh.. We've just been having a big discussion about anti-seize compounds on the Stuka Stunt BBS. There have been some interesting comments made about the use of copper-based anti-seize compounds on model engines:

http://www.clstunt.com/htdocs/dcforu...mID1/9661.html

CL Combat fliers use anti-seize on Nelson plugs. I've had one get stuck. Really stuck. Never a problem with ordinary glow plugs, but with the Nelson plugs.. well, I learned my lesson.

What is CAPS and what is SEMPRA? It's interesting there's no difference. The K&B 1L, incidentally, along with the McCoy MC-9, used to be the choice for Fast Combat back when everyone ran Foxes. Both are OEMed by Ohlsson, by the way.

Incidentally, Henry makes three different plugs - a Std., a Heavy Duty (which is somewhat colder), and a two piece plug with a flat element (like the old Glo-Bee plugs) that the pylon racers like to use. The one piece plugs (especially the Std) are more friendly to use when it comes to setting needles, etc., the two piece supposedly gives an extra thousand RPM or two over the one piece plugs with the right motor. John Booker makes a fourth plug (also a two piece), and then you can get the Russians and Ukrainians to re-element your blown out plugs with a choice of different diameter wire.

I've heard that Al Kelly (well known around CL racing circles) makes the Merlin plugs. But I've never seen any info about them, online or otherwise. Is the line described/sold on the Jett web site?

Iskandar
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Old 07-16-2004, 07:32 AM
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Default RE: Blown Glow Plug

Yep, Al makes the Merlins.

He has done some excellent work over the past few years developing plugs. Also "word is......" he is manufacturing plugs for a major 'name'.

Right now, Dub is not 'selling' the plugs per say, but he has them available.
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Old 07-19-2004, 11:28 PM
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Default RE: Blown Glow Plug

Al's interesting to talk to. Some years back, at a Combat meet, the subject turned to glow plugs. He's sectioned lots and lots of them over the years, and wanted to see what some cheap Chinese ones I'd just bought at Indy RC were like inside.

He started talking about plug elements - what metals go in them, and why, and plug construction, and why Fireball plugs blow seals. It turns out there are only a few companies making plugs in the U.S. - Cox, Fox, Ohlsson and Swanson (Fireball). There may be one or two more (not sure if Nelson makes his own, doesn't look like Ohlsson construction, but the seal method is the same, and now Al's making plugs too). Most of the plugs you see around - McCoy, K&B, Thunderbolt, etc. are OEMed by Ohlsson (yes, that Ohlsson which made the O&R engines, they're still around, but don't make engines any more). The K&Bs and McCoys look identical when sectioned.
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