NALON VIPER 2.5 CC DIESEL

I don't recommend the integral finned version. I made one for a derivative design I'm working on at the moment and it weighs about an ounce and a half! OK in a display case but I like to fly mine.

The piston fit on my original Viper, made with the conical piston, was a bit iffy so I made a new one but with a flat top. The edge of the piston governs the timing so it's OK to just chop the cone off, no mods are needed to the liner. This has several advantages including lower reciprocating mass and easier manufacture. The contrapiston can be made thin-walled which is a boon for fitting.

Roy

Just to deviate a bit I took a trip to the local model shop for some glow fuel for a Humbug I have just finished, hoping to get some advice on a suitable fuel for the above and was met with "Dunno mate". all I was asking if they did a run of the mil fuel or a sport version and we wonder why people don't do anything!

Thanks Roy

Yes I did realise that the edge of the cone defines the timing but was thinking that if flat topped at that point the contra piston would need to be quite long to compensate for the loss - I assume lengthening the CP is how you dealt with the change?

I could never quite understand the thinking behind the second CI cylinder head version, from any aspect, though there are one or two commercial engines that have steel integral liners and fins, the ED 3.46 for one.

Bernard - I guess that sums up the 'current' situation with electric power overtaking IC power

Usually, small capacity glow motors run best on fuel with a Nitromethane content - (5 - 10%) if you didn't get any and can wait I can let you have some at LowMex, just let me know beforehand.

Tug

Thanks Tug will do.

Hi Tug. The contrapiston can sit anywhere in the bore so all that's needed is a longer comp screw, it wasn't an issue on my motor.

Re glow fuel, I'd be wary with the stuff in model shops nowadays, there are a lot of low/synthetic oil blends about which probably don't suit older motors. It's difficult to find out what's in them and how much of each ingredient.

Roy

Hah! Now why didn't that occur to me!

I'd say that's a great case of lateral thinking Roy

I can't recall the last time I visited a model shop the local ones long gone. For many years I've only used fuel from the husband and wife team of 'Southern Modelcraft' in Kent. Unfortunately only available from them at shows they attend or at their premises they do not supply shops nor will send it by courier but the quality is superb with consistent performance.

Though they do do synthetic based (glow) fuel I only use their castor based 5% nitro for glow and their Sport and Hi-performance diesel. As previously mentioned elsewhere the diesel will keep for years in a tightly capped tin but the castor in glow fuel for some reason can degrade if allowed to get cold in storage. Apparently that can be put right by heating the fuel but I've not tried it to say positively.

My days of visiting shows have come to and end but fortunately I have squirrelled enough of both to see the rest of my (control line) flying days out - I hope!

What do you fly BTW

Best - Tug

Tug, going a bit off topic, I'll PM you, Roy

Though I'm sure Keith wouldn't mind Roy I agree - will reply later, painting the shed at the mo

Tug

A hard chromed liner can handle the oil content down to 12% castor with a cast iron piston. But the cast iron piston and steel sleeve, like the materials used in a PAW engine, the synthetic oil fuel will ruin the piston liner fit after about 6 or so flights. Castor oil is one of the few oils, that will allow oversized parts to assemble. It is also very good when assembling the contra pistons to liners or heads depending on the configuration. After running the engines, I recommend that the engines get flushed out with some kero or other similar solvent , and then oil with AFT oil or after run oil. The washing out is to get rid of the castor oil, as it is hydroscopic, and can cause the bearings to rust. Some never have issues with bearings, and others do.

I think the main reason for going to the smaller front bearing was to get the weight down, and to also make the front of the engine narrower for aircraft designs. I don't think there is a problem with the cars for the front bearing diameter, but I do like the different sized bearings, as it makes it easy to control the spacing. I once made some changes to a diesel F2C team race engine, and made a special shaft spacer, that locked the rear race inner to the flywheel and the spacer, and it locked the front inner race at the same time. It worked really well for what it was intended to do. The front bearing outer was retained with a small threaded ring.

It is always satisfying running an engine that you have made, and the more of it you make, the better it is.

Roy,

I am interested to know why you would want the piston to have a flat top.? With the 4 inlets angled up at 25 degrees,the piston top is the same angle,the purpose of which is to make sure that maximum fuel is forced to the top of the cylinder. The Mills 1.3 engine was advertised as having a notch in the piston top, adjacent to the inlet. to atomise the incoming fuel. This was claimed to be the reason for their famed easy starting.

Also, if you cut the top off the Vipers piston,as drawn, you end up with a big hole in it, as the inside shape follows the outside.

Keith.

Re the Mills comment Keith,

I always thought that the piston was stepped to give the desired inlet  transfer timing as opposed to a technical improvement reason. Did they advertise that as a feature at the time? There were those series of adverts in Aeromodeller that consecutively described the Mills attributes but that doesn't ring a bell. Besides - if a Mills piston is fitted in the wrong way round it will fire on a prime but will not run.

Re Neil's comment on old castor in bearings - this was the inside of a Merco 61 I rebuilt a while back

Edited By Ramon Wilson on 06/09/2023 13:50:03 Inlet should have been transfer

Edited By Ramon Wilson on 06/09/2023 13:51:20

Hi Ramon,

Yes I have the Mills advert series. Attached is the one I mentioned.

Keith

Well how about that Keith

I can't say I can remember that as I wouldn't see an Aeromodeller magazine until 1958 (age 13) but I did collect them back as far as 1944 and do remember the adverts generally.

I've looked at some other side port drawings some have a step in the piston on the transfer side others don't but as said if it isn't there by the piston being wrongly installed the timing is affected quite badly so was Mills making a thing of it as a sales pitch - after all why not do the same on all pistons at the point of transfer if it's that effective - who knows?

I've had quite a few Mills through my hands over the years all of which were accompanied by a 'Can't get it to run' comment. Some were simply worn and required new pistons but a high percentage of them all had the pistons in back to front.

Best - Tug

Tug,

I think at the time most people believed it. I made Ron Chernichs version a few years ago and did try out the test, as suggested and there was a deffinate look of fine atomisation.I did not reverse the piston to see if there was a difference tho. Why were so many with the piston wrong way round? As a teenager, I would take one to work and start it by holding it in one hand and flicking with the other, to demonstrate it's easy starting !

Keith.

It was a new flat top piston Keith, sorry I didn't make that clear. I can't remember exactly the thinking, maybe along the lines of, well, my PAW 2.5 Goodyear engines are very powerful and they've got flat topped pistons. Also, they are easier to make!

Neil, interesting observations about oil in PAWs. My experience is a little different. We went through a period of using 12% ML70 with satisfactory results until Tony Eifflaender advised that castor was quicker. I tried our Nelson fuel with 10% castor and he was indeed right. We carried on with this percentage with some success! All the piston-liner fits were pretty loose so that may have helped.

Roy

Tug,

Re- reading the Mills advert, it claims the "Mills Transfer System " is Patented, so perhaps this is why others did not use it. It might have been a bluff of course. If Michael ,our Patent expert is out there, perhaps he will know more of it?

Keith

Hi Keith, it certainly features in the odd side port design of the times so who knows? Mills engines did start well for the best part so maybe it has some effect - very few diesels have stepped or baffled pistons though.

I'm going to be offline for a few days - back later though

Best Tug

I hope it's ok to continue this thread, albeit it is not (yet) about building a Viper. But my problem is that I could not find out how to get the plans. I somewhere saw that they are available at modelenginenews.org, and emailed [email protected]. But I think now that's a dead site, as I did not get a response. Directly on that site, there is only stuff from 2002 to 2013. Now I' at a loss. Can someone here tell me where these plans can be bought?

Regards,
Hans

There was a link on Adrian Duncan's page of engines for home construction but it no longer works for me. Maybe it will for you. If that fails, pm me and I'll forward my copy. Roy

https://adriansmodelaeroengines.com/catalog/main.php?cat_id=214

Hans, as you have found the 'Model Engine News' site is no longer functional.

The plans are available somewhere as is the collection of plans from the 'Motor Boys'. I believe Ken Croft made these available from a free download but as to where to find them I cannot recall. Ken does visit on here so maybe he can re enlighten us if he reads this.

Like Roy I have the Viper plans and the others from the Motor Boys e book on file so happy to help if wanted

Best - Tug