Glow plug patents and design
 

I've been looking around online for glowplug patents. The main problem is that if you search for "glow plug", you get hundreds of hits on patents for car diesel glow plugs. Luckily, newer patents reference older ones.

It's been pretty interesting. Here's a list.

2482831 (1948) and 2500395 (1950) - Ray Arden's "ignition plugs". Show details of his early, rebuildable plugs. Refers to some even older patents - e.g. 2138301 (Howie, 1938), where a filament is strung between two posts inside the combustion chamber.

3911326 (1975) - Irwin Ohlsson's patent for a crimp-top plug. The crimp presses on a cupped washer, which acts as a spring and pushes down the center post. This traps an insulating washer (asbestos or similar) against the a lower surface of the plug body. Ohlsson (yes, they are still around, or at least, was around last I was told) OEMs plugs for many companies, e.g. K&B, McCoy and Thunderbolt, and all of those plugs are made this way. So too are Nelson plugs (someone sectioned a bunch of plugs and posted a photo on Stuka Stunt a while back). Ohlsson's two big competitors, Swanson (Fireball) and Fox use somewhat different construction.

4088105 (1975) and 4080944 (1976) - Twinn-K's patents (the second one is the idle bar version) for their flat-coil plugs, which are constructed very differently from Ohlsson's plugs, using a glass seal. These are real glass - they start out as powdered pellets (two per plug), which are melted in-situ to form the seals before the element is welded in place. Twinn-K has long been out of business - their plugs were popular with racers. Nelson used to make a plug with a flat coil which was very popular with pylon racers, and now Merlin makes flat coil plugs also (with glass seals). One wonders why the Russian plug rewinders weren't rebuilding these - should be easier to do than normal plugs. Maybe they were, but I didn't get to hear about it.

6342690 (2000), 6346688 (2000), 6696670 (2002), 7176414 (2004) and 7205506 (2007) are patents awarded to Steven O'Donnell. O'Donnell sells to the RC car market, and has (or had) a very large (and confusing) range of plugs for sale.

6342690 is for a screw-top plug (as far as I know, it's not used for any plugs he sells). 6346688 is for a crimp-top plug which seems superficially like Ohlsson's (it uses a dome-topped washer under the crimp). 6696670 and 7176414 are for a plug with uses "fructo-conical" washers as seals. The top is a taper crimp, rather than one that folds over. The second patent seems to be an elaboration on the first - it gives more details about the philosophy behind the design. The plug described in these two patents is supposed to have a stronger seal than previous plugs. I get the impression that O'Donnell was involved heavily with tethered car racing - he mentions tethered cars in his patents - where extremely strong seals were necessary. Increasing the crimp pressure would result in a stronger seal, but would also deform a plug at the base.

7205506 is, or has the potential to be, somewhat controversial. It is about color coding plugs according to heat range. Problem is, it has been done before this. Apparently, Taipan plugs were color coded even back when Gordon Burford was making them. Merlin makes color coded plugs at the present, too.

O'Donnell sells two distinctly different types of plug - the "sport plugs" are more normal in appearance and are color coded (red - hot, purple - medium, blue - cold) and the "competition plugs", which are very tall, and have the hexagonal section extending all the way to the top of the threaded section (other plugs are round near the threaded section). The competition plugs, I think, are the ones based on patents 6696670 and 7176414. They look like no other plugs on the market (other than one Super Tigre marine plug, which I suspect is OEM'ed by O'Donnell).

This subject of seals is interesting. I've only seen a two or three complaints of O'Donnell plugs online - the ones that have to do with short element life can probably be discounted, as they might be the result of using too hot a plug or might be engine-related. The most interesting complaint, though, came from some boat racers. These guys push their engines to extremes - 65-70% nitro, lots of RPMs. And the complaint was that the O'Donnell plugs they tried leaked. Supposedly came back red hot - visible in daylight. Not 100% sure but I think this was with the Sport plugs - the same thread had people recommending their competition plugs (#87, #88, #90). They also complained about Merlins (while Merlins have been universally praised elsewhere). Interestingly enough, the gold standard for these people seems to be the McCoy MC-9 (they use lots of and lots of these) - a plug using the old Ohlsson crimp seal. One wonders why they never did get around to using Nelson plugs, like other racers.

2011/0146608A1 (application, 2011) is also very interesting - a way to use glow plugs in engines that burn fuels other than methanol or ethanol. They tested their invention using gasoline, kerosene and LP gas. You might be seeing this in a drone near you in the near future.

http://www.freepatentsonline.com/2482831.pdf
http://www.freepatentsonline.com/2500395.pdf
http://www.freepatentsonline.com/3911326.pdf
http://www.freepatentsonline.com/4088105.pdf
http://www.freepatentsonline.com/4080944.pdf
http://www.freepatentsonline.com/6342690.pdf
http://www.freepatentsonline.com/6346688.pdf
http://www.freepatentsonline.com/6696670.pdf
http://www.freepatentsonline.com/7176414.pdf
http://www.freepatentsonline.com/7205506.pdf
http://www.freepatentsonline.com/20110146608.pdf

Iskandar

RE: Glow plug patents and design
 

You do understand that all of the patents except the O'Donnell patents have expired, don't you?

RE: Glow plug patents and design
 

Of course. In the US you're only allowed exclusive use for 17 years (or 20 years from the filing date). Which is why Merlin can now make glass-sealed flat element plugs without any worries on that count. But they're still "valid" in terms of proof of prior art - someone can't file for another patent on the same thing. And since one of the reasons for patents is to disseminate information about inventions, they are very informative, and make VERY interesting reading.

Note, though, they don't reveal ALL of the secrets. None, for instance, tell you exactly what is used for the seal material. Or dimensions, or alloys used, in the elements.

Iskandar

RE: Glow plug patents and design
 

Veeeeeeery interesting Iskandar! Thanks for taking the time to research and post it. :)

RE: Glow plug patents and design
 

There are probably more I haven't found yet. And there are also foreign (i.e. European and Japanese) patents - some of the patents here refer to them.

Iskandar

RE: Glow plug patents and design
 

Incidentally, is there any reason why car plugs won't work in airplanes? McCoy plugs apparently work (and are popular) for both.

And are there any airplane engines (other than Profis) that take turbo plugs? Merlin makes turbo plugs for airplanes and another set of "heavy duty" turbo plugs for cars. Wonder who uses the airplane ones.

Iskandar

RE: Glow plug patents and design
 

The glow plugs are all compatible with each other. The limitations are with the heat range and the length. You have cold plugs to very hot heat range plugs. Then there is the length of a glow plug, you have a short, medium and long glow plugs. There are some special glow plugs such as the turbo plugs that may be a little longer. Plus the special 4 stroke glow plugs with the special recessed tip on them.
You just need to choose the correct plug for your application. You can usually get a different heat range glow plug to provide a little more RPMs from a particular engine. it is just the expense of buying and trying a number of glow plugs to find the optimum performance one for your application. But if you changed props or type of glow fuel, you may have to repeat the process of finding a optimum glow pug again.

RE: Glow plug patents and design
 

That's the thing.. One wonders if heat ranges for cars are the same as for airplanes. I'm encouraged by the fact that O'Donnell cross-references their plugs with McCoy plugs (which I know work in airplanes). Reach, I'm not worried about.

Interesting thing is you never see anyone posting about using car plugs in airplanes, despite the fact that 90% of the plugs on ebay seem to be car plugs. I'm about to try it myself, I'll post the results. Hope it works, I have over $300 worth of O'Donnell plugs from Tower coming! Of course, for my purposes, lots of plugs (from hot to cold) work - I run my engines flat out, no need to worry about idle.

Turbo plugs are an interesting thing, too. So far I've only seen car engines that use them - all the racing airplane motors use Nelson plugs instead (turbo and Nelson plugs are completely different from the usual 1/4-32 plugs). The only exceptions are some Cyclon engines (these come from Siberia), where turbo head buttons are an option (they usually come with Nelson heads). My current project is making turbo head buttons for my Foras.

Iskandar

RE: Glow plug patents and design
 

My guess would be that there's no real difference because they're both just glow engines and a plug that suits a high performance plane engine will be the same as for a car engine where both use the same nitro content.

RE: Glow plug patents and design
 

The car guys tend to use very high nitro compared to us airplane dudes. Also they use very low oil and produce a lot of power and rpms. Isee them using a lot colder plugs than airplanes since planes have a nice big air mover cooling the engine when it is running. Iuse a Merlin 2002 in my RC car with the SH 18 engine and it works fine. But Ionly run SIG Champion 15% airplane fuel in it since Iplan to keep it a very long time and it is still breaking in.

RE: Glow plug patents and design
 

True.

OS offer their [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXSBW9&P=ML]LC4 plug[/link], which has the same heat-range as does their [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCB27&P=ML]OS #8 plug[/link].

It is cheaper than the #8, but seems to be the same quality and have about the same life expectancy.


The LC4 is more suitable for OS' medium size engines, because it has a long reach and does not locate itself recessed in the combustion chamber, like the #8.

I wonder why OS does not promote it instead...

RE: Glow plug patents and design
 

On the other hand I saw a post (in the RC Fuel FAQ) that said that car engines (especially the smaller ones) are over-cooled. They run very high RPMs because they're lightly loaded. They spend a lot of time in idle. They need instantaneous reaction to the throttle (if you've ever watched a on-road car race, they're always blipping the throttle on and off, which does look somewhat comical, because it looks so jerky), which is why they use so little oil (and can get away with it because they are lightly loaded).

Which means they need fairly hot plugs. Especially the smaller ones, and the ones that spend more time in idle (for courses with lots of corners and no long straights).

I guess I'll find out.

Iskandar

RE: Glow plug patents and design
 

Aha!!! I knew it.. Steve O'Donnell DID do tethered cars. He mentions them (and the 200 mph speeds they achieve) in some of the patents.

http://engine-analysis-software.com/heads.htm

Another page on the same site:

http://engine-analysis-software.com/chambers.htm

Interesting because it discusses alternate combustion chamber shapes, including an offset chamber (with a very wide squish band towards the exhaust), and oval chambers (with multiple plugs - for large engines). And the reason behind double bubble heads. No mention whatsoever of the old trumpet head, though (most commonly seen in the Cox 1702 high compression glow head). Probably an idea since passed over - don't know how popular it was among the racing/speed crowd in the early days.

Iskandar

RE: Glow plug patents and design
 

I have been using the O'Donnell 100 plug in an MVVS .49 powered aircraft.

It runs very well on nil nitromethane fuel.

The MVVS is set up with high compression. The O'Donnell plug runs as well as the recommended Nova-Rossi C6S, as supplied by MVVS for these engines.

Can anyone answer why the O'Donnell plugs have been discontinued? A rumour was that the parent company was bought out by Hobbico, who have quietly put the plug manufacturing side to sleep.

RE: Glow plug patents and design
 

Cool to know they work in RC engines - I have a huge stack of them I bought off Tower when they were discontinued. The 100 is specifically for monster trucks - and I wonder why monster trucks need their own plugs! They are tall, I suppose there's a chance they might get knocked off or break a head in an engine-to-engine collision.

Here's one of the several cards of the things I ended up with:

http://jerong.no-ip.org/ntaibpublic/...100%20card.jpg

I've also got a number of their turbo plugs - I'm going to try them in my F2D engines - I've made some head buttons for my Foras and have some factory heads for my Profis.

I spent the last two days analyzing plug elements - very interesting results. Haven't heard anything about why they went out of business - I suppose they'd be discussing it over in the car forums more than anywhere else.

Iskandar

RE: Glow plug patents and design
 

I've been using McCoy 59 plugs in my .26/.28 monster trucks and .20 Traxxas engines all on 20% nitro with no problems. I think the 59 is technically an airplane plug but I use the in nearly all of my engines both surface and aero. I use Enya 3's also in my Enyas.

RE: Glow plug patents and design
 

thanks for all the info you posted!

after looking at the patents i now know why the o'donnells are so long....but i still can't understand why they didn't turn the hex off the lower part of the body so they could be used with a twist on plug clip.

if you section one it would be interesting to see what they use for the insulators. the patent says hard anodized alum could possibly be used but doesn't say that's what they actually used. i would think thermal expansion would be a problem with that.

RE: Glow plug patents and design
 

Speaking of old looking plugs, my Enya .09 E-Bay buy came with an old looking plug. Amazing though, it lit off the venerable engine without any problems. Some old things are still good. [8D]

RE: Glow plug patents and design
 

That's an Enya glow plug. They can be refitted with new elements.

RE: Glow plug patents and design
 

If I read the patents correctly, the competition plugs are left unturned at the base because this allows one to exert greater pressure on the crimp. Too much pressure and the bottom of the body bulges out (that's how much pressure he puts on the crimp!). The bodies come out of a screw machine, so they have to be fully made and it wouldn't be economical to turn the bases down after assembly.

While analyzing elements last week I turned one of the color coded plugs upside down and zapped the colored washer - it is indeed aluminum. With copper, which (I have to look it up) makes it a 2000-series alloy (like Duralumin or 2024). Which, by the way, is the same alloy used in Cox 049 glow heads.

One thing I wonder about though.. he mentions in the "color code" patent that some lines of plug have a range of a DOZEN types, each with a different heat rating. The color coding was meant to avoid confusion in the pits - using the wrong plug would result in something bad happening. I've NEVER come across such a range of plugs. The biggest range I've seen (from extra hot to ultra cold) is in the Rossi (now AXE) plugs, where you have eight (R1 to R8) - and amusingly enough, once you take one out of its packet, you've got no quick way to tell what you have in your hand, they're not marked in any way and all have the same black oxide finish! Then again, there are many I have not seen - Taipan plugs from Australia, or Taylor from the UK, for instance.

So there are a couple of things about the O'Donnell line of plugs that puzzles me. The first is that he didn't color code the tall competition plugs. Second, and related to the first, he never did sell a coherent range of plugs to be used by competitors as needed under different climatic conditions, as he mentions in the patent. Instead, he made one or two specific plugs for 1/10 scale cars, another pair for 1/8 scale cars, and another pair for Monster Trucks (why????). Add to that three turbo plugs (two for 1/8 scale, one for 1/10), one airplane plug, and "OS" (i.e. medium reach) versions of some of these and you have.. what? I suppose those in the know could assemble a range of plugs to compensate for the weather and such not, but..

Before I forget - there's a (just one!) "FAI Tether Car" plug mentioned in the range (ODO67). I'll bet they're exceedingly rare, I'd love to have one to analyze. It just occurred to me that "FAI Tether Car" is an oxymoron - FAI is the governing body for AERIAL competition and records, not for cars! The "FAI" probably refers to the fuel (80/20 methanol/castor is known as FAI fuel).

Iskandar

RE: Glow plug patents and design
 

The old Arden plugs (of which I have a couple) could be rebuilt, these look like Ardens, but don't have the little circlip at the bottom to which the replaceable elements are attached. To re-element a Enya plug you'd need a spot welder. I'm not sure how much of it comes apart, I suppose it'd be easier to re-element than other sorts if you could remove the center post. All plugs can be re-elemented, there's a cottage industry for re-elementing Nelson plugs. Most of this is done in Eastern Europe with the vertical-coil plugs, but there's someone in Italy who makes a specialty of the flat-coil ones - he sells them to F3D fliers (who it seems go through them like hot cakes). He puts really heavy elements in them, too, to make them last longer, but your regular plug drivers won't work with them since they draw a lot more than the usual 3 amps.

Here's the little manual that comes with the replacement Arden elements (I have a pack of those):

http://jerong.no-ip.org/ntaibpublic/...0004_small.jpghttp://jerong.no-ip.org/ntaibpublic/...0003_small.jpg

Yes, these will also go under the beam. A good example of what people used at the beginning, though I don't really have a date of manufacture for these. I wonder when they stopped making them, might have been quite late.

I suppose this makes the Enya plug a throwback to the 1950s!

Iskandar

RE: Glow plug patents and design
 

i have a couple of enya #3 plugs with the screw-on center post but the filament is welded to the body so no replacing it. i'm guessing that's the difference in the #30 plug?

and on o'donnells: i once got a dozen of the tall competition plugs from tower due to a screw up in ordering and being that they're "car" plugs and looked kinda wonky i dismissed them as yet another piece of "nitro car" marketing where some guy's name gets slapped on the same old junk with a "special" body added for bling factor. gave them all away except for two that i can't currently find...

RE: Glow plug patents and design
 

thanks for the explanation on the hex body, guess i just skimmed over it a bit too fast.

and the insulators, are both the top and bottom the same material? and 2024 is a strange choice IMO, for the cox head i can understand it because of the threads but as plug insulator? more difficult to anodize as well. maybe just easier to crank them out on screw machines than it would with something gummy like 6061...

RE: Glow plug patents and design
 

I don't know if I can get to the lower insulator (until I burn out a plug and remove the element). Even then it's recessed inside, even if I can hit it with the xray probe the xrays given off might not make it to the detector. I suppose I could section one at some later time and analyze it then.

Yeah, I don't know why they used 2024 - it definitely has a bunch of copper in it, so I'm pretty sure it's that or something similar. Maybe it has to be strong enough to withstand the crimping forces.

Kinda wondering what the other plugs use for insulation - Al Kelly mentioned some sort of fiber material. What they use in Fireball plugs apparently has a tendency to burn through due to the way the plugs are constructed, according to him.

Next week I'll analyze some old Glo-Bee plugs - maybe I can get the chemical composition of the glass seals.

Iskandar

RE: Glow plug patents and design
 

I assume the Enya plugs have the center post and element installed first and the element welded to the body afterward. The plug GG posted doesn't look like an Arden to me. Similar, but not quite the same. I mean... Doesn't it make sense to use an Enya plug in an Enya engine?

Did the Arden plugs have long, medium or short reaches?