franklin_m

Wonder if anyone can help.

I've read a lot of the discourse on the glow plug adapters for Norvel engines, and I understand that I may lose some power by using one. That said, scarce Norvel plugs and the undeniable convenience of using regular glow plugs is enough to make me want to try one.

That said, I'm looking at the two offered by Mecoa. The say one is for "standard long plug" and the other is for a "standard short plug." I generally use Tower Hobbies plugs, and my question is should I get the short plug head or the long plug head? If it turns out the Tower Plug is somehow in between (and I'd not be surprised), then my next choice would be the OS A3. Same question would apply.

Thanks,
Frank

Mr Cox

It is not that you may loose some power, you will definately loose power...

What you need is a head for turbo plugs, these are e.g. made by Valentine and are available at ebay.

flyinrog

My Feedback: (1)

Or the Galbreath (sp?)head with the Nelson plug..Larry Driskill may have these in stock, not sure...Rog

franklin_m

Guys. Thanks. I know that I'll lose power, but the convenience of using the same plugs I use in other engines is just too much to pass up. Do either of you know which head would be used with the A3 or the Tower Hobbies?

thanks,
Frank

flyinrog

My Feedback: (1)

The turbo and nelson plugs are almost closed end much like the glow heads....the regular plugs are gonna open up too much space and reduce power and compression, if you can order a few of the throw away cox product engines, those glow heads will fit the norvel .049 and I think the .061 too...Rog

TGC

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I don't doubt the verity or validity of your unequivocal statement for a moment; but, I can't seem to find any empirical basis for it.


I hear this same subjective opinion expressed every time this question is raised, so it must be true!


Has someone, somewhere ever taken the same engine, same day with the same fuel, same prop and switched out all these adapters and plugs and written down their findings?


I'm not competing for the World Title every time I fire up my Tee Dee .049, but I'd like to know how many RPM's I am missing by using the Mecoa Short adapter and a Fox Std. Short plug.


Thank you for your help, Tom


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Mr Cox

I have tried it once on a Babybee but didn't bother to tach it, it just didn't sound right...

(If I can find the head again I could tach it, but I might simply have thrown it away in discust )

On other engines the difference will be around 1500 rpms.

TGC

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You were comparing what to what?


Thank you for your help, Tom


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Mr Cox

Ok, I haven't tached any cox with and without the "adapter". I could tell the running was poor anyway...

Other small engines like the TT GP-07 shows a 1500 rpm improvement when going from standard plug to a turbo plug (a turbo plug is then similar, in terms of combustion chamber, to the original cox head as no threads are included in the combustion chamber).

TGC

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Well done, Mr. Cox. Thank you for your help.


Would anyone have any quantitative data?


Thank you very much for your help, Tom


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uliner

My Feedback: (2)

Here is some data no numbers.

1/2 a control line baby flite steak, TD 049, cox 5x3 rubber ducky prop, Norvel 1/2 fuel, 35foot 008lines

COX standard plug, easily do the stunt patern,

A standard plug adaptor, aircraft was 10-15 mph slower and would bareley loop, ran like it had a head leak or about 15 extra gaskets.

Same fuel, same plane, same prop, same day.

Nelson plugs last a long time. I have not worn out many flying 1/2a.


Get the galbreth head and 2 nelson plugs and you will be set for a long time.
Or fool around for a few weeks and be frustrated.

Digger-RCU

TGC,
I have not tested the Mecoa head for an 049 or an 061, but I did test the 074 head on my norvels. I compared the performance of this head button with a standard glow plug and compared it to the standard norvel glow-head button.

average performance for my three norvel 074's with the norvel glow head and a 7x3 prop was 16600 Rpm

average performance for the same engines and the same prop with the Mecoa head was 15900 Rpm

I hope this helps.

Digger

gcb

Frank,

The reason for the RPM loss is because of the increased head volume created by the area around the threads and the area inside the plug. Remember the standard plug seals up at the washer, whereas the Nelson or "turbo" plugs seal at the base.

Factors that you can change that affects performance (and firing timing) for a given engine include prop load (diameter and pitch), fuel, and compression ratio. This plug discussion is about compression ratio. Switching to a standard plug is not unlike adding head shims. If you go this route, you can change some of the other factors to somewhat compensate. I would suggest upping nitro a bit, but try different props also. Since you are not interested in maximum performance, things should be OK.

Using a short plug should have less affect than a long one (I think!). I believe the Tower plug is a 'tweener" so you should be OK with the short adapter.

Cox had a standard plug adapter on their throttled .074...perhaps that's why it was dubbed a dog for performance. []

If it doesn't work for you you can still get a Nelson or Turbo adapter.

George

KidEpoxy

I have no idea if this will fit, it might hit the piston for all I know...

When using a standard plug, it seats on the shoulder up top. I cant help but think that the Long plug would have more material (more threaded plug body) inside the head than a short. More material in the head would have to give higher compression than having that space empty.

I dont know, it is just concept level.
Like I said, heck, a long plug might poke thru the piston.... and that will clearly lower your compression [:@]

franklin_m

Everyone, thanks for the input. I guess I'll risk the $10 and give it a shot. I do think the best long term solution is the Nelson head.

Frank

Walther

My Feedback: (1)

Go with the turbo head and you can't go wrong.

propjobbill

I have converted several .049 cox heads to glow plug. I haven't noticed more than about 300 rpm difference between heat ranges. I have found the the top rpm can be as much as 1,000 rpm or even more if you don't get a good leak free fit. I always take a little high temperature gasket maker and put it around the threads before screwing it in. My average rpm loss is about 500-600 rpm. With the nelson head I get just as good as new head and maybe 100=200rpm more.

The cox head will fit .049 and .061 Norvel. But I have never tried one on a Norvel engine. When I convert the Cox head I extend it about 1/64" into the chamber. I think the real problem is the standard glow plug allows for lower compression. The nelson glow plug adapter is made more like the high compression head by Cox. I think a plug with a small chamber for the heat element works better.

Nelson clams to work better because they seal at the bottom. And standard glow plugs seal at the top, which looses compression in the thread area. But if you look closely you will see the nelson head is shaved for higher compression, but the tread is longer raising the compression ratio. The problem with threading the conversion glow head in further is it alters the flow of air though the firing chamber. It is not possible to get the same compression with a converted Cox head. But because the compression ratio is lower you can raise the nitro content and get back the lost rpm from the conversion head.

I grind the top off the old head until flush with the aluminum, turn the head upside down use a punch to tap out the glow element from the inside of the head and it falls out easy.
to insure a good seal I fix the head at home and let the gasket material set up good. If a plug burns out I put a new conversion head assembly on. Take the old one home pull the glow plug coat the new plug with gasket material and let it dry until the old plug burns out.

To me at big loser is if you leak compression. The conversion head doesn't work as well but you may be satisfied with the slight lose if you increase the nitro a little it may even run better than the original set up on lower nitro.

One thing I do is use a flat head tool to square up the bottom of the seat. the picture is left to right; Cox standard head, Nelson head (notice it has a wider shallower base for higher compression), Inside view of conversion head, top view of a conversion head. Flat tool bit for squaring thread bottom from larger drill bit.

What I like about my conversion is there will be standard glow plugs as long as there is glow engines makers, and you are not locked into one supplier.

franklin_m

Propjob,

Thanks...that's an interesting approach! It's nice to have options.

Frank

Mr Cox

There are also several threads here on how to fit a turbo plug into a burnt out cox head. It is a little bit trickier with the seated part for the plug but not that hard once you get the hang of it and have the right tools.

I haven't tried sealing the threads of the regular plugs, does anyone have tach numbers with and without the sealant?

propjobbill

On the plugs that I converted I gain about 500 or more rpm by using sealant. Now if that was because I was not getting a good seal job or for what ever reason I can't say. But I know for a fact that I gained 500 or more rpm by sealing the plug threads with gasket compound because I tried 3 different plugs with the same basic results.

Mr Cox

Ok, thanks. That's a fairly easy way to get more power then!

lildiesel

I learned a couple of tricks in the late 80s messing around with a glow plug heads for the Cox .049 I got from Charlie's RC Goodies that tie in to some of the discussion above. I wound up using Indian Head gasket shellac to seal the threads of the plugs in the head. I also learned that it helped to thin (polish) the plug gasket a wee bit by sanding it on both sides on wet siliconcarbide paper on a piece of glass to get the plug to seat properly all the way down to the top of the combustion chamber. Not great or ingenious fixes, but they helped when trying various heat range short plugs on an RC Golden Bee.

I've been doing the same things for both the long plug and short plug MECOA heads for the Cox and now with short plugs and the heads on OK Cubs. BTW, the long plug MECOA head has 4 fins and the short plug head only 3 fins, so you should get a bit more cooling with the long plug head if you need it in some applications.