Tanaka 26CC reed and glow (nitro) conversion

Here we have the first run of the used, Tanaka 26cc gasser converted to glow (nitro) fuel. We are using the "nitro" designation here as that is the more popular term used these days for an engine that uses a glow plug. In this case, though, it's a mis-nomer because the fuel we are using here is a 30:1 mix of just pure methanol and Klotz Benol, castor based lubricant. Not a drop of nitromethane anywhere.

The stock cylinder had the head milled off and a new head button was made that is secured with long bolts that also holds the cylinder down.

The stock intake port has been plugged and a new, reed intake assembly has been installed to the bottom of the crankcase.

The carb is from a K&B .40 Sportster with a venturi bore of .34" as opposed to the stock bore of .45"

On the baseline, 18 X 6 Zinger wood prop, we are getting a solid, 7500 RPM. That translates into an extra .4 horsepower over the stock gasser on ignition.

We have shed nearly two pounds of ignition gear and gained power at the same time. Can't beat that.

However, we likely would gain that and more, if we could increase the compression ratio on the stock gasser. The real payoff with this conversion is the weight reduction.

Unfortunately, throttling didn't exist. Anything less than 3/4 throttle produced a flameout.

Flipping the engine to a sidemount configuration cured that, interestingly enough. We are speculating that at low throttle, engine suction was insufficient to draw fuel properly. Sidemounting provides for much easier fuel flow to the bypasses for delivery to the cylinder.

The plug is a P8, OS turbo plug. This is their cold plug and was tried in this case, simply because that's what we had on hand.

The head button was made to give us a compression ratio of 14:1 and this has proven to be about right. Decreasing the compression as an experiment will be tried but we don't anticipate any benefits. The runs today don't exhibit any overcompressed symptoms. More productive will be increasing compression to the point of getting some ping. Then we'll back off a bit and proceed to experiment with a bit of nitro (2-5%) along with various plug heat ranges and extra shims.

ADDENDUM:

Today, we took the head button out and shaved it down for increased compression. The result was a loss of 500 RPM. We added a shim to bring us back but only got back 200 RPM. The original head had very low squish band clearance. Mucking with what's working sometimes just gives you grief but we always learn something. If it isn't broken, don't fix it comes to mind.

As it turns out, we got it exactly right the first time. Should have left it alone.

During this session we made up a mix of 3% nitro, 5% oil (20:1) and the rest methanol. The result was a loss of another 300 RPM and starting became a bit harder. ??? Yes, the nitro advances the ignition timing so we added two and then four shims. Still not good and so it looks like any amount of nitro is too much for 14:1 compression. The original has 7.5:1 and I'm sure that nitro, in that case, would be beneficial. Less compression and more nitro has been found, in some cases, to promote better throttling. That still remains an issue with this highly modified engine. The original idles and throttles virtually perfectly so the fault seems to lie in the reed assembly itself or its location.

Category:

Howto & Style

Tags:

• Tanaka
• conversion
• glow
• nitro
• RC
• Airplane
• Engine
• Gasser

[hopeso]

Tony,

For the sake of maximizing the glow configuration, I made the head to take turbo plugs. They can be a bit expensive so I hadn't tried more than two heat ranges.

[Ron5oh]

Nice work! Did you have any plans of using a carb with a larger diameter or tuned pipe? The tuned pipe should give you a little more rpm. I'm unsure if the carb would help at the rpm's this engine is intended for. BTW, what was the rpm before the conversion?

[hopeso]

Thanks Ron,

A brand new, Tanaka conversion does 7000 RPM on the same 18 X 6.

So the glow covnesion is more powerful with a much lighter weight.

I have plans to try different carbs and the like. A tuned pipe would be interesting to try. May look for something appropriate.

[nitroairplane]

that is the biggest nitro engine i have seen apart from the top fuel drag racers

[soverato3]

gas would be a lot cheaper than nitro.... and gas will decrease carbon build up cuz it has less oil in it.

[Mcroostr]

I had a go-ped a while back (26cc gas scooter) that I ran on 20% nitro rc/car fuel, the cool thing was that it still used spark ignition and at wide open throttle the spark kill button would have no effect, it was running on a glowing-hot sparkplug.

[tpvalley]

I used to tune 2 strokes a lot, big uns.

we would select different thickness reed petals for different speed ranges, ie a slower engine can have softer/ thinner petals but at high rpm thin reeds flutter.

For good low down power try thinner reeds.

Maybe ur fuel mixture burns to fast so at low rpm it just detonates? like using low octane petrol in a high CR car.?

[GREVS2]

interesting read, btw whtat is a shim ?

[joaorp]

And can i uze the stock carb?....

[joaorp]

Can i uze this system of glow plug in a 50cc motorcycle? I had the idea of adapting a spark plug to take the glow plug but i don't know if the 9:1 compretion ratio of the motorcycle is good for runing with glow plug and nitro fuel....

[tonyppe]

have you tried a hotter plug? a hotter plug will advance ignition timing..

generally higher comp = more power.. but will also advance ignition timing

nice work on getting it running!

what about decreasing the air inlet diameter so that the mixture gets richer?