Chip Shop

[Danny Fenton]

Thanks CS, as Colin states, Simon Delaney fitted an 70 four stroke and was happy with the scale performance. So thats probably a good place to start. Also be aware that with an 70 Simon had to shift the receiver pack to the under the rear seat so you may end up nose heavy. So may I suggest we try and keep the power plant to a similar weight to the original Merco 61 specified?

The problem with increasing the engine size, you increase the loads, and the weight, increase the weight and loads and you start adding strengthening pieces, change the spars to hardwood, this increases the weight and loading. Its a vicuous circle. So the plan as far as I am concerned is to try and build as per the drawing. There are a few things I don't agree with and I will change, specifically the tailwheel, I consider a steerable tailwheel a must. I cannot walk out to the end of the runway to take off and will have to taxi.

Simon also used Glosstex to cover the model, I think if we use glass cloth for the fuselage and wing leading edges tailplane and fin, and perhaps solartex for the wing trailing section and elevator and rudder we may be able to keep the weight down. I don't foresee anybody keen on trying silk pasted over tissue and dope, perhaps a step too far?

Cheers

Danny

[Colin Leighfield]

John, I understand from Bob that the Evo petrol motor depends on exhaust pressure to the tank because unlike the bigger petrols, it isn't fitted with a pump. Using a custom built silencer ought to be ok, because fitting it with a nipple for pressure take-off is simple enough, but I don't know how critical the motor is to silencer design. I also understand that the exhaust on a petrol runs hotter than on a glow, so need to know if that might be a problem for a fully enclosed silencer. I'm attracted to the idea because I've never tried a petrol motor, the fuel is a fraction of the price we pay for glow, the consumption is also very low, so the tank is much smaller and saves weight as well as further reducing the cost of running it. Because it's a two stroke, even with the ignition set-up and small battery, the weight should be advantageous compared to a four stroke and much as I like electric, on the larger sizes of model batteries are expensive and I reckon I'd need three to alllow for charging on the field. Also because of the small amount of oil needed in the fuel, there is a lot less of it coming out of the exhaust and getting everywhere, and extending the silencer to get the oil away in flight is unsightly. I find it a particular problem on my Fw190. I haven't committed yet and could go in any direction, but to me there could be real advantages from petrol for this model, which doesn't seem to need a lot of power.

Danny's point about the advantages of keeping weight down are spot on and I'm not always good at it. However, there's an opportunity here to take an overall view of the project and optimise the power choice as an integrated part of managing the finished weight, minimising running cost and sounding realistic.

I'm listening carefully also to opinions on the best approach on covering and finishing. I confess I've never used glass-cloth for this, so there's always a first time. At one time I'd have been very happy with nylon and dope for the "fabric covered" parts of the airframe, perhaps silk over tissue and dope isn't such a difficult thing to do? The silk is still easily available from I think Free Flight Model Supplies, I boight a load of it a while ago and haven't used it yet.

[Kevin Fairgrieve]

Thanks for the info regarding price Colin.

I intend to purchase mine around July time as I have a small windfall coming my way then.

For those still undecided on colour scheme`s take a look on fLickr for some really interesting one`s.

You could also check out my RC model pictures as well. Shameless plug!

Kev

[David Rothwell]

Decided I`m up for taking part

as I was born in Trincomalee Ceylon ( now Sri Lanka ) in the 50`s ( one of the last outposts of the empire) thought I do do it in the Sri Lankan colours of that time.

David

Edited By Davwik on 09/04/2014 08:49:38

Edited By Davwik on 09/04/2014 08:50:10

[Glenn Stratton]

Does anyone know the weight of a Merco 61, or has one that they can weigh so we have an idea to compare it too please.

Just found a Peter Chinn review on the mkIV in which he says it is 13.7ozs, without silencer & baffle! 

Edited By Glenn Stratton on 09/04/2014 09:34:56

[Kevin Fairgrieve]

Merco.

Kev

[Glenn Stratton]

Thanks Kev , hadn't found that article! So the original was a tad over 12oz's.

[Martyn K]

A Merco 61 weighs just under 12.75oz - but that is without a silencer fitted as far as I can see.

Martyn

[Bob Cotsford]

Peter Chinn reported the Merco as weighing 12.7oz which is 360gms (probably without silencer), while a 46-53 with silencer will be around 500gms, a 70 4 stroke around 620gms, while the Evo 10GX is 436gms + 93gms for the silencer + 98 gms for the ignition + battery.

I wonder about PC's statement of the Merco weight as an Enya 60-II BB of the same period is listed around 480gms without silencer.

[John Timmis]

Hi,

just weighed my Merco. 400 grams.

John

[Martyn K]

Hi John - was that with a Silencer?

M

[Colin Leighfield]

Nice one Kevin, loads of stuff there. Davwik's Sri-Lankan scheme is a good unusual choice, I've not seen that one before. It's amazing how much information we find when we share through the forum, it just shows the power of talking to each other.

Bob's, Martyn's posts etc. show that the lightest option is still a straightforward two stroke glow, but I wonder if anyone will do that now? It also looks as if the weight of the Evo petrol motor wouldn't be a problem, Bob, are you still happy with it in the Mustfire? (Excepting the pong in the car)!

This has all the makings of a great project. I enjoyed poring over the plan last night and there's plenty of time to get all of the ducks in a row before starting the build process. Thanks to Danny and Chris for kicking this one off.

Edited By Colin Leighfield on 09/04/2014 10:19:24

[john stones 1 - Moderator]

Colin

I am mostly petrol now, fuel cost is nothing compared to glow. I find cooling just the same as with glow.

I can't see why custom exhaust would not work, it works for glow

I am wavering a bit myself I may end up with an O.S fitted.

[Colin Leighfield]

Thanks John, sounds as if exhaust heat wouldn't be a big issue then.

[Graeme Poke]

Gee Kev, That's a lot of Chipmunks. Too many to choose from. Some pictures show good detail of the tail wheel and the majority of the spinners are very shallow. may be difficult.

Cheers Graeme

[Bob Cotsford]

Posted by Colin Leighfield on 09/04/2014 10:18:45:

Bob, are you still happy with it in the Mustfire? (Excepting the pong in the car)!

Colin, it's a bit of a mixed message from me on the Evo 10. It's just different to the reliable, powerful but mucky glows. It starts very easily and runs well but it has the power of a good 4 stroke with the noise of a 2 stroke, and it's not as clean running as the larger petrols (20:1 mix rather than 33:1 or 50:1). Fuel is cheaper, but for the amounts used it's not significant and don't forget you need to factor in the price of high quality 2 stroke oil with the cost of the petrol. I would say it's 1 or 2 dBa louder than an equivalent glow but I haven't tried different exhausts yet, though I do have JE super-quiet exhausts and a Genesis short pipe that would fit.

Would I recommend it to someone who wants to play with a petrol motor - yes. Would I recommend it as an everyday alternative to a glow? Not really.

[ZK BAP]

I have built a chippy and most happy with it. They fly superb. Mine is an Airsail 1/6th. My mate just bought a kit. They are a true 'builders' kit. The plane is very agile, yet dose as its told. In some respect, the 'chippy' flies better than the average trainer. Not bad for a low wing.

[Glenn Stratton]

Hi ZK BAP, good to hear about your Chippie, what did you power yours with and where's the piccy!

[ZK BAP]

I put an ASP61FS in mine. Goes perfect! After 3 weeks no run, second flip, off she goes.

More pics in my album.

[Glenn Stratton]

Nice one ZK . I have a Saito 65 (550g) so I think that's going to find its home in mine!

Edited By Glenn Stratton on 09/04/2014 11:27:01

[David P Williams]

Yes I was thinking of the ASP 61FS - it appears to be lighter than the 52 (444g vs 455g) and 0.83kW vs the 1.1 of the 70.

David

[ZK BAP]

The ASP61 is the same as the OS. I believe even parts fit.?

[Glenn Stratton]

ZK, sorry n'other question, and I know you shouldn't ask a lady , but do you know off hand what she weighs in at?

[ZK BAP]

I was sneeky at placing weight, and added engine weight, ended up balance with 2 4 nimih packs behind tank(600mls) perfect. 2.7kg all up. fully laden. Purrs for 25mins, and glides forever. What can i say. Even flies upside down lol.

[ZK BAP]

One thing I would recommend is a bit of beefing up here and there. The tail wheel arrangement and back end need strengthening and the front cowling, due to nose overs. One can over come the nose overs by simply placing the undercarridge mounts about 15-25mm backwards. The origonal is too close to the c of g. I laminated 2 6mm ply blocks and recessed my uc wires into the new holes and since, never had a nose over.