Super Chipmunk Engine Upgrade

Here is the story.

On Sunday I went up to Cashmoor with the Super Chipmunk which was fitted with an ASP180 FS. I have had this model for a number years and tried numerous props. Prior to Sundays outing (there was only three of us there ) I had tried a Menz wood 17x10. It did not like it at all, started to overheat. Rummaged in the prop store and found a "club" of a prop. MS Classic 18x6. Go for it! I raised the compression ratio a little by removing one head shim and did a quick home test. Well it swings it okay and a lot of air moving. Really need to WOT it up at Cashmoor with the tacho on it.

Before it never went above 7900 with a lighter loading prop. Now it was giving 8500 peak with the lawn mower blade from MS. As Chris H said fly it and see. Sounds like a real plane, slightly faster but above 2/3 throttle a real bark begins but not much more agility. Back on the ground tweaked it again with a slightly richer mixture and played with the throttle curve. Fly it again, slightly better. But not much! Flys around at half throttle easily and relatively quiet. An afternoon of p***ing about and covered in oil plus little time with the Angel which was getting bounced around a bit in the gusty NWesterly, then came the rain.

Driving home I thought, b*gger it, i have had this model for at least 3 years and never been happy with the performance even for a 13 pound scale model. It's gonna get a 30cc/35cc gasser. So today Monday pulled the ASP out, re-plumbing 600cc tank for petrol, removing the anti-vibration mounting. Test fitting a DLE 35 RA as a dummy engine on to the firewall looks like I will have to fill in some of those original mounting holes.

Finally plumped for a OS GT33 and ordered it today. Going to use DLE30 stand-offs (ex Ebay) Chippy looks rather forlorn now but while it is at this stage I will tidy up the covering and work on the new cowl locating screws positions.

Nice one.Phil, can't beat a gasser

flyingpete wrote: Nice one.Phil, can't beat a gasser

A sort of "trial run" for the Pepsi too .......

Due to rain and some DIY to undertake was unable to work on the Chippy's firewall. However, have replumbed the original 600cc tank for petrol. TNT delivered the OS GT33 this afternoon. Had to take a good look over the motor. Machined surfaces are superb nearing a mirror finish unlike DLE although I am knocking DLE as such.

As the future days (weeks) look like mini hurricanes mingled with wet stuff, which will put flying out of the question, I will share the DIY time :lol: with sorting out the firewall so I can mount the engine. Rummaging through my parts stores I have found an Opto Kill switch, breather outlet and heavy duty switch. Planning on using LiFe direct power for all electronics.

As the OS GT33 is a little lighter than the ASP 180 FS I may be able to bring hardware forward. We will see.

A question although I cannot see any reason why not. Is there any issue with mounting a Dubro tank inverted? It's the type with the recessed front. To me it just means that the outlets are at the bottom. I really would prefer it that way so access to the plumbing is easier to work on and maintain.

Plus when the tank is low in fuel the clunk would be in the small area therefore more depth of fuel.

PhilF51 wrote: A question although I cannot see any reason why not. Is there any issue with mounting a Dubro tank inverted? It's the type with the recessed front. To me it just means that the outlets are at the bottom. I really would prefer it that way so access to the plumbing is easier to work on and maintain.

Plus when the tank is low in fuel the clunk would be in the small area therefore more depth of fuel.

p

Phil - I used a Dubro tank in a Galaxy " Mystic" powered by a Laser 150, as long as the filler & breather pipes are angled
to the top of the tank ( in fitted position ) cannot see any problem, Never had any fuel problems when flying inverted
Colin

The OS engine is now fitted using ex Wots Wot stand-offs. DLE stand-offs were10 mm too long. I had to beef up the firewall on the backside with 6mm ply, this would blank off the original grommit holes, plus give plenty of wood for the new captured nuts to bite into. Also bored some 25mm holes to allow for plumbing and electrical leads in F2.

Was hoping to re-use the original throttle servo but alas to far out of line. So, with just a Stanley knife I had to create a new servo tray and use a mini servo to ensure clearance for the servo arm when the tank is installed. Now the servo is directly in line, the servo on this set up has to push the throttle lever rather than pulling back. Throttle arm is spring loaded to close throttle if it becomes disconnected. There is no idle stop on this Walbro carb. Here are some images of progress so far.

I have also stripped off the oil soaked Monokote at the front end. Awful stuff - leaves most of the pigment behind. Replacing white no problem but the Red is not Oracover/Profilm so the replacement Red (no.22) will be a bit different to the rest of the plane. I don;t really care.

As of time of posting waiting for delivery of an AR9020 RX and some 3/32Tygon.

Engine permanently installed now. Tank and plumbing installed. New 9 channel RX. Why? (Because JR will only let me assign Aux 4 to the trainer switch, which is now my ignition cut off) Had lots of fun getting the new cowl to sit right and to make several cut-outs for cooling. On the other hand the GT33 sits neatly inside the wide cowl. Cowl painting in progress which may take some time as there are two colours and RC Colours takes at least 24 hrs to dry. If hard enough then I can mask on to it for the next colour.

Just got to decide on a battery pack for the ignition module and where it will be installed. OS ignition module Ver 2 now supports 7.4v, 6.6, etc.

Meantime I hope to start the engine up over the weekend swinging a 18x8 Menz.

Upgrading has not been that easy. Especially when the builder had designed it for a 180 four stroke glow. You can guarantee holes and servos are all in the wrong place for the next engine..........

What breezy day Sunday is! Glad I am indoors.

Saturday finally got the engine to running but needs some fuel through it to get it to settle down. After the little episode I put th ewing back on to see where she balances. On the engine bearers needed 450 gms! :huh: The new engine is only a few grams lighter. Ah! Had not allowed for the fact that the original lump was mounted on a insulated secondary firewall along with mountings and bolts, etc.

So, I had to make up a battery tray which is fitted up to the tank wall, F2, with two life packs (RX) and a NiMh pack (ignition). A bit windy in the drive when testing again but I think that balances it.

Sunday afternoon, did not want to watch Wimbledon so painted the top half of the cowl in Red now that the white is dry and hardened. Then checked out the wing for maintenance. Why has the gear got toe-out? Ah! some numbnut must have put them back in the wrong sockets. :whistle: That's done now with toe-in.

Images to follow when I get round to it.

Unfortunately when I pulled the masking tape off it took some of the previously painted white too. Now I'll have to wait a few days for the enamel to harden before flatting down and redo the white. Um! I think I will use this time to do other stuff and not DIY as that has stalled at present.

When are these high winds going to subside?