Ripmax Harmony Twin

[RichB]

I'm afraid this is going to be a rather lengthy thread, as there are quite a lot of issues with this model, mostly documented in other forums.

I originally bought the Harmony over two years ago and decided that I would fit a pair of four-strokes instead of the recommended two-strokes.

On the initial build, I was a bit concerned about the quality of the materials used as the wing sheeting was a bit "crunchy" and the engine mounts didn't look too special, however I finished it off and gave the engines an initial run (they were run-in on the bench beforehand). The vibration had to be seen to be believed, both at tick-over and full throttle (yes - I had balanced the props and spinners).

After only a couple of minutes running, the engine mounting bolts had worked loose, so back at the bench I found that the vibration and the poor quality of the wood had resulted in the mounts being crushed allowing the bolts to loosen even though I'd used Nyloc nuts.

It was obvious that I had to add strength to the bearers, so epoxied carbon tape on all the joints and added thin alloy sheet either side of the bearers. The vibration was greatly reduced, but was still more than I thought acceptable, so in went a pair of Irvine 40's. Problem solved! All the strenghthening had made it a bit nose-heavy, but still within limits.

I'd read about the main retract unit pivot pins working their way out and causing major problems, so thought I would be clever and put fibreglass tape on the units to prevent this happening.

Out to the patch and after the usual engine run-ups and other checks I had what must be one of the best-ever first flights. This plane is one of the smoothest and nicest I've ever flown in over 30 years of model flying.

Six minutes later I called landing, which, I have to admit, was a little fast, but I didn't expect the nose leg collapse which ensued. Inspection showed that the ply(?) mounting plate had broken immediately behind the retract unit.

Back home, I found that there was very little glue on the mounting plate and the wood was very poor quality. I made a replacement out of good quality ply and epoxied fillets front and rear.

I also removed the wing retract units as one appeared to be loose. I found hardly any glue on the mounting plates, so epoxied fillets to these and added blocks to prevent the pivot pins from sliding out, as I found that the pivot pins had worn through the previously applied tape!

For the next session I added some weight to the tail and had another, even better flight. The subsequent  landing was slower this time, but the noseleg collapsed again. The mount held, but the servo had stripped a gear, I think this must have been due to the leg not locking down fully.

I've not had a chance to try a third flight, but I'm hoping that all the problems have now been fixed.

A fellow club-mate also has a Harmony and has experienced the same problems.

Summing up, I would recommend this model as a fantastic flyer, but only after attending to the engine and u/c mount weaknesses and using two-stroke engines.

[RichB]

I forgot to mention the leaky fuel tanks which need very careful assembly, sealing and pressure testing, and the rubbish spinners, which I replaced with nice shiny alloy ones.

[simon burch]

It was problems with the retracts which finally made me get rid of mine.

I'd read about the retract mounts, so beefed these up beforehand. It flew great, but always needed maintenance on the retracts, which spoilt a great model.

 

The one piece wing was a hassle as well. Replaced mine with a Seagull Dual Ace, which is still waiting for it's test flight. Not as cool with fixed undercarriage, but much easier to look after.

 

Cheers,

 

Simon

 

 

[Djay]

I have had mine for 2 years now, fitted with 2 ASP 52 four strokes.

Though not the fastest on these engines, i have had not one thing wrong with the plane, either at build or flying it.

The engine mounts were more then adequote for the engines, the tanks were fine, the gear has stood up to so much abuse with no failures of the gear or mounts, that the tyres have had to be replaced due to the first set wearing out.

 

All in all a very cheap fun twin, well on one engine, well worth getting.

 

Darryl

[Ronos]

I know this is a old thread, put can anyone of you guys remember what you set the C of G at.

[cymaz]

Try this link

[Ronos]

Cymaz, I have the pdf file, I got the Harmony second hand and is very nose heavy at 90-100mm, was wondering if this was the correct CogG. I have a seagull mosquito and in the book it says 150mm, but the best CofG is 130mm.

[cymaz]

All I can say is, and I bet you know, keep pushing the cg back on each flight until you feel it’s good. It’s a pita to do but it means to don’t go straight to tail heavy.