"1/2 A" & "1/8 A" airplanes These are the small ones...more popular now than ever.

NV Big Mig 074 vs Thunder Tiger GP .07 ABC

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Old 04-04-2014, 06:37 AM
  #1
Ledet
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Default NV Big Mig 074 vs Thunder Tiger GP .07 ABC

Is Norvel much better?
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Old 04-04-2014, 07:16 AM
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The Norvel is so much better that it is not even a contest.
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Old 04-04-2014, 07:23 AM
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That is what I Thought I would here but I never owned a Norvel
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Old 04-04-2014, 11:38 AM
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Quote:
Originally Posted by dennis View Post
The Norvel is so much better that it is not even a contest.
Ditto --

However, the downside is replacement parts may become increasingly difficult to find. As an example, the P/C for the .061 Big Mig has been OOS at the NV Engines website for months now.
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Old 04-04-2014, 06:02 PM
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For the price of motors, I figure if it is worn out, you just get another one. I have got a couple of TT .07's to equal a Norvel .07 in power. Was it worth the trouble? No, but it is a hobby. The Norvel .07 is pretty good, as is the rest of the line.
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Old 04-04-2014, 09:32 PM
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I bought a TT GP07 years ago and it was a turd. Wouldn't idle and not much top-end, either. Bought a Norvel .074 shortly after and never looked back. HUGE difference. Damned shame the wrong engine stayed in production.
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Old 04-05-2014, 04:11 AM
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Does the Norvel use a standard glow plug or does it have a glow head? Would the .061 be better or does it just depend on what you put it in?

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Old 04-05-2014, 04:18 AM
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They come with their own head, which isn't available any more. They sell an adapter head for a regular plug. It will be a performance robber. I would look for something that adapts to a Turbo plug. The .06 is less powerful for sure, but it would depend on your plane app.
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Old 04-05-2014, 07:31 AM
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The NORVELs (.049, .061, .074) use a head clamp and a separate flanged plug insert. Neither the clamp or OEM insert for the .074 are available from NV Engines, but head gaskets are still listed. Head clamps and OEM plugs for the .061 remain available from NV. However, OEM style inserts for the .061 and .074 can be purchased from Mecoa.com --- these are not standard plugs, but are the flanged button plugs found on the original NORVELs. Merlin (merlinglowplugs.com) also offers a clamp ring and plug for the .061, but I don't know if the plug is a standard plug or a flanged body plug.

You can also get a head clamp and flanged style plug from Exmodelengines.com or COXEngines.CA for the COX .049, however, the .049 COX adapter will fit the NORVEL .049 and .061, as will the original COX glow head --- thread pitch and diameter are the same. I do not know if the flanged inserts are interchangeable between the COX and NORVEL clamp rings.

I believe the best choice of head and plug for the NORVEL .049 and .061 is the Galbreath head/NELSON plug combination. Unfortunately, this is not available for the NORVEL .074. I think that Valentine made some NELSON head clamps for the .074 at one time, but know of no source now.

As noted, the use of a standard plug will be costly in performance and top end.
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Old 04-05-2014, 08:20 AM
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Andrew, What do you think makes the difference in performance between the head plug and the adapter for the standard glow plug? Is it compression?

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Old 04-05-2014, 09:37 AM
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Quote:
Originally Posted by Ledet View Post
What do you think makes the difference in performance between the head plug and the adapter for the standard glow plug? Is it compression?
Boy, this discussion can really open a can of worms.

Compression certainly is a factor, but I believe the causes of performance differences are far more complex. The classic argument is tied to differences in compression and is based on how the plugs seal the combustion chamber. Three different sealing approaches are used. (1) The standard plug uses a compression washer located at the top of the plug thread to seal against a seat at the top of the head. (2) Turbo plug styles (Turbo and NELSON) seal at the bottom of the plug using a tapered plug face against a tapered seat in the head and (3) Flanged plug inserts seal using the head gasket (commonly a thin copper gasket) between the plug flange and a stepped shoulder on the cylinder.

Folks tend to point to the fact that standard plugs suffer compression loss due to the volume loss in the threads because the plug seals at the top. I don't think this is the cause of performance loss simply because if you coat the standard plug threads with pure castor before inserting the plug, any compressible volume due to thread mismatch is filled with a non-compressible oil, consequently, you won't lose compression due to differences in thread tolerances.

So, what causes the decreased performance? Compression probably does come into play, but it is more likely tied to filament hole size, the volume lost to combustion chamber shape and how far the standard plug threads into the adapter. I'm more inclined to believe the shape of the chamber is the primary contributing factor rather than compression. Turbo styles and flanged plugs have a very smooth internal head shape while standard plug adapters may or may not have a rough hole where the base of the standard plug terminates. The Galbreath head/NELSON plug combo probably runs well due to the design of the chamber rather than just compression differences. We also have more options in modifying compression with the turbo and flange designs -- if over compressed, we can add gaskets. For the standard plugs, if compression starts low, about the only means of raising it is to search for another plug vendor or to use a medium heat plug to reduce filament hole size.

Head design on larger engines is a science unto itself ---- for the 1cc engines, I believe a smoother chamber appears to be more important than compression in how well they run. That's ma story and ah'm stickin' to it. (Flame suit on, BTW )

Last edited by Andrew; 04-05-2014 at 09:42 AM.
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Old 04-05-2014, 10:13 AM
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I'm not sure the glow heads are not made anymore, I know from time to time they go out of stock. There is an issue with getting the platinum in Russia. I agree it would be nicer to see "Out of stock" but I don't belive the web site works that way. If it's out of stock it just doesn't show. This has happened a few times over the last few years.

In any event the K&B ones from Mecoa work just fine. As Andy stated for the 061 the Galbreath/Nelson is the way to go. I recently had Doug make me a head for a TD 020 and it works just as well.
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Old 04-05-2014, 11:25 AM
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I just bought a few Merlin plugs for the .049 - .06. They work in the Cox .049, .051, Norvel .049 and .06. They work fine, likely as good as the Mecoa turbo style (which I have not tried) 3 for $10 at the Toledo show with one clamp ring included. You need his for his plugs. I think they are normally $5 each plus shipping. Al is a pretty knowledgeable guy and believes even the hole surrounding the plug element affects performance. Bigger being bad. When a Norvel .07 plug goes, I would likely get a turbo conversion head if I had no lathe. I would try to convert one myself if there is enough meat on it, as I do have a lathe. Anything under a .21 needs something better than a 1/4 - 32 plug IMHO. As an extreme example, I have a GZ .049 with a Nelson conversion head that picked up from 17,000 to 21,000 rpm with a turbo head that must have been shaped better or something. A CS turned up to 27,000 with a turbo conversion head. This is to compare to a Norvel .049 at 22,500 fuel and prop all being equal. 10% and APC 4 1/4 - 4.
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Old 04-05-2014, 12:52 PM
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Sorry about the complex questions. I am new to 1/2 a but have lots of experience with .25 and up. I have been thinking about building a pacer and trying to decide on an engine. Norvel seems like the way to go, I like good engines. I do have a ok cub that was given to me years ago that I have recently ran for the first time a few days ago (it runs good) but I want an rc engine.

Aspeed, If you have a lathe have you ever thought about make an adapter for a standard plug that works better than the adapter you can buy? (i also have a lathe)
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Old 04-05-2014, 01:37 PM
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With the standard plug adapters, the problem is not how the adapter is made, but the standard plug itself. The ones using turbo plugs made by Galbreath are great, but the ones using a standard RC plug lose about 1500 rpm on a standard 1/2a motor. The K&B buttons for the NV 061 and 074 seem to perform just as well as the factory ones. So unless you mess up the ring there is little need to go to an adapter. In the case of running an 061 in the higher rpms, say 23k to 30k, the turbo plug is a must as you will go through a lot of button types before you burn out a nelson.
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Old 04-05-2014, 02:46 PM
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Quote:
Originally Posted by hllywdb View Post
With the standard plug adapters, the problem is not how the adapter is made, but the standard plug itself. The ones using turbo plugs made by Galbreath are great, but the ones using a standard RC plug lose about 1500 rpm on a standard 1/2a motor. The K&B buttons for the NV 061 and 074 seem to perform just as well as the factory ones. So unless you mess up the ring there is little need to go to an adapter. In the case of running an 061 in the higher rpms, say 23k to 30k, the turbo plug is a must as you will go through a lot of button types before you burn out a nelson.
Point of order-gents-and to prevent further confusion to our 1/2A newbie who initially started the thread-Galbreath heads use NELSON plugs (or their clones-such as Merlin) TURBO plugs are similar in appearance-but not in size-being an 8mm thread. What they both have in common is sealing on a tapered conical seat in the head (or adaptor) and not on the threads and plug gasket. Can we PLEASE stop referring to 'Nelson' and 'turbo' as if they were synonomous because people will get the impression they're interchangable-they're not! (...more's the pity!)

Aspeed and Andrew have pretty well summarised the reasons why 1/2A heads are so fussy-and there's the additional simple factor of scale effect-a thousandth variation either way in a bigger engine may well not have any noticeable effect, in the small ones it may well be a significant variation-and impact on power or running characteristics. In the days before Nelson plug head conversions became standard in F1C, for example-it was common practice to have to mike the plug inserts for Rossi 15s and Cox Conquests as they varied enough in spigot depth to significantly affect running-and I'm talking to the tune of quite a few thousanths variation-which DID impact on head clearance.

ChrisM
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Old 04-08-2014, 05:38 AM
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[QUOTE=Ledet;11776291

Aspeed, If you have a lathe have you ever thought about make an adapter for a standard plug that works better than the adapter you can buy? (i also have a lathe)[/QUOTE] - I made a bunch of heads with the Turbo plugs. The taper is 60 degrees. The Nelson plugs aredifferent, maybe 30 degrees, and have an oddball thread. The Turbo plug is 8mm x .75 which was on the shelf at my supplier. I just used a 60 degree centre drill and backed it up to give the .28" dia. and a 3/16" hole. The plug will push through a bit if over tightened, so it can be below flush maybe .010". After some use it may be just right. I made a few for the TT .07, OS LA .10 and .15, the CS .049, and ASP .15. They all responded quite well. Mostly 1,000 to 2,500 rpm better, with the CS about 9,000 better!!! I think the original plug was way off. I made a 7/32 rad cutter up from a broken center drill for the dome shape. It was similar to a couple existing ones that I was copying. The .049 ones I made a 90 degree countersink after some guidance by a speed guy, and the Picco P0 was like that, as well as the Merlin 1/2A plug insert.
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Last edited by aspeed; 04-08-2014 at 05:46 AM.
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Old 04-08-2014, 06:55 AM
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For the TT07 I more or less copied the stock head but put a Turbo plug in it instead (see picture below with stock head to the right). The power is then somewhere in between a Norvel .061 and a Norvel .074.

The later TT07 engines are a little better than the old ones. They have fixed the hollow alignment pin, and the transfer ports are better matched between case and liner, etc.

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Old 04-08-2014, 02:16 PM
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Making an adapter or the turbo plug seems like the way to go.

Thanks
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Old 04-10-2014, 07:33 AM
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using the flat wound element glowbee style plugs are always a good bet if you don't have a turbo style or insert style glowhead engine...the 2016 is the one
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