My next bird - powered by Simonini

[twistair]

Well, today our next gyro made its initial patterns over Twist nest.
This is a tandem with Simonini Victor II Plus 102 hp 2-stroker.
I had some minor problems during first engine runs but we solved them.
The most unpleasant was that at engine rpm below 3200-3300 it thrown a lot of fuel out from carbs. I have close to zero experience with 2-strokers and cannot imagine that this may be caused by air filters but when I replaced it's original double filter with two singles the problem disappeared.
Engine runs well though I feel it needs slightly other prop for it - will see.
Very low vibrations and noise. I'd said it sounds even less noisy than Rotax-912 - surprisingly.
On the other hand there is still too little information from other owners about these engines habits so it won't fly any cross-countries before we get enough experience with it.
This gyro is based on the first stainless airframe I built so it still has some things I changed on the later airframes. I have one more such Simon engine on shelf and a new airframe for it which should fly early this summer.

Cheers,

[Brent_Brown]

Give reports as you fly it.
I hope it works for you.

[twistair]

hey now Alex is this the same motor or a new one? Give reports as you fly it.
I hope it works for you.

I knew, I knew: Brent will be first when one says "Simonini" :whoo:

Yes, it has that same engine and I'm really curious what will be second one.
I will sure report about it when we get more experience. Next flights - tomorrow :flame:

[C. Beaty]

Alex, Italian 2-strokes must be lubricated with extra virgin olive oil.

Do you ever have blue skies over Russia?

[Cobra Doc]

Alex, it looks like you are really staying busy. Good looking machine.

[JRB549]

Why two mufflers?

[twistair]

Why two mufflers?

That's simple - there were no space to install more :D

Alex, Italian 2-strokes must be lubricated with extra virgin olive oil.

Aha, now I got it! I thought that 10-litre can which came with engine was just a gift from manufacturer... It made an excellent add-on to our dinner salad :party:


Do you ever have blue skies over Russia?

I don't remember exactly but my grandpa told once that his grandpa told him he saw them once :)
Chuck, does any of these pass for blue skies?

[Brent_Brown]

Nice seat tank on the new gyro what will it hold?

[twistair]

Nice seat tank on the new gyro what will it hold?

These tanks are being built in St.Petersburg, made of glassfibre+epoxy and are extremely strong as well as suitable for wide enough stern. But they are 30 litres only ( 8.5 gal), hard to get one and cost ca. 300 euro. Weight is 7 kg.

Available both as a seat-tank or just a seat of the same shape.

Oops, 2 hours to sunset here, will do some more flying ;)

[C. Beaty]

Alex, I admire the dedication of gyro enthusiasts who fly open frame gyros in sub-freezing weather. But not for me.

We had a freak snowfall in Florida in the 1970s. My mother, then in her 60s, had never seen snow and traumatized by all the press hype about fallout from atmospheric nuclear testing, at first believed she was seeing ash from an atomic bomb.

It is characteristic for 2-stroke engines with induction controlled by piston ports to blow fuel out the carburetor at low speeds. The MZ 202 engine used on the Mosquito UL helicopter has reed valves which eliminate reverse flow. The Italian Arrow engines also used reed valves for induction.

Reed valve engines also have a smoother and flatter torque curve, a desirable feature for helicopters but not a necessity for driving a propeller.

[Brent_Brown]

This engine is reed valved.

[C. Beaty]

Yes, Brent, I see the Simonini has reed valves.

I suppose spitting back through the carbs would be a case of reed resonance/seating bounce.

[twistair]

My guess about fuel backflow was that it was some kind of pulse resonance between two carbs - at least when I replaced double filter by two singles it disappeared. I've also heard that sometimes this fuel backflow may be solved with different length of intake hose.
Today we flew more and with no surprises less EGT temps are higher than normal between ca.4500 and 5500 rpm. Tomorrow I'll try bigger main jets to see if this works.
A couple more photos from today:

[scandtours]

Can this be an altern. engine for gyros Alex?
Its a four stroke made in Czech and its 85hp engine.The prise is roughly 7000 USD comp. A little bit too high comparing it with Rotax but.......
I am sure youve heart about them.
Their rotary engines must be of interest too.
Their web http://www.vernermotor.com/
Giorgos

[Ron Marlett]

My guess about fuel backflow was that it was some kind of pulse resonance between two carbs - at least when I replaced doubled filter by two singles it disappeared. I've also heard that sometimes this fuel backflow may be solved with different length of intake hose.
Today we flew more and with no surprises less EGT temps are higher than normal between ca.4500 and 5500 rpm. Tomorrow I'll try bigger main jets to see if this works.

Yep, a carb venturi works both ways and there is just a slight reverse pulse of air as the reeds are sealed by the case pressure. A longer intake pipe can help with this by giving a larger volume of air to absorb the reverse pulse. A crossover tube between the manifolds will also give the reverse pulse somewhere to go. This works well as one reed is closing, the other is open and that manifold is under vacume to help draw in the pressure buildup. The crossover helps to keep the airflow generally forward thru both carbs on a 2 cylinder. This was a standard feature on the last street 2 stroke that Yamaha produced for the US market, the RZ350. There is also been some work on a device called a "Boost Bottle"(google it) that is a resonant cavity that can help absorb the reverse pulse. At certain power settings, usually around low-mid throttle, this reverse would over enrichen the air as it picked up fuel passing thru the carb 3 times. Air filters clamped directly onto the carb mouth seemed to make this situation worse, particularly the type with a hard end cap. A longer smooth pipe or airbox between carb inlet and filter mostly eliminated the midrange rich spots.

A filter clamped to the carb mouth can also lead to low-mid range mix issues. The pilot air circuit(0-1/4 throttle) on most carbs draws it's air from a port usually located just inside the carb mouth. A filter clamped over the mouth results in that port being fed with turbulent air. Setting the filter farther away from the carb at the end of a smooth tube gives the airflow time to smooth out before it hits this port. Even race bikes that don't use filters, usually have smooth feed pipes installed onto the carb mouth or between carb and airbox called velocity stacks to provide smooth air to the carb.

Ron

[scottessex]

Ron, My hirth 2706 uses exactly as you described a balance tube between the carb manifolds, and uses a straight section of tubing between the carb and filter, they call it a velocity tube. But it is a piston port engine with no reed valves.

[scandtours]

The most unpleasant was that at engine rpm below 3200-3300 it thrown a lot of fuel out from carbs. I have close to zero experience with 2-strokers and cannot imagine that this may be caused by air filters but when I replaced it's original double filter with two singles the problem disappeared.
Engine runs well though I feel it needs slightly other prop for it - will see.

Alex.
This reminds me same problem I encounter with a Rotax 503 for many years ago (when they just appeared)
You are right I believe. Wrong prop and wrong torque.
Giorgos

[twistair]

Very interesting inputs on carbs and their tricks, thanks to all! I was often told that 2-stroker needs more attention to it's adjustments and I'm glad I have a chance to get some experience in them. Though... anyway I'd thought twice or more to fly 2-stroker a 500-mile cross country which we do regularly with 912 Rotax.

Can this be an altern. engine for gyros Alex?
Its a four stroke made in Czech and its 85hp engine.The prise is roughly 7000 USD comp. A little bit too high comparing it with Rotax but.......
I am sure youve heart about them.
Their rotary engines must be of interest too.
Their web http://www.vernermotor.com/
Giorgos

Yes, Giorgos, I've heard about them and considered them as possible powerplant. There is their dealer in Moscow and I talked to him. There is also a guy in Moscow who likely is building a single-seat gyro with this engine.
I think that this engine has some disadvantages for a gyro and first is that it's gearbox cannot be inverted and the engine itself cannot be inverted too so we have at least CLT question since engine CoM is below prop thrust line ( in a 912 Rotax this vertical offset is significantly smaller - I don't remember exact numbers).
Surprisingly it uses a chain for the camshaft drive.
And it's price is likely close to 7K euro, not dollars which makes it likely uninteresting.

As for Simonini - I hope this engine is good but there is still too little information about these engines and most of what I have is questionable.
I know some guys here who installed them on FWs, trikes and ... ehrr... these armchairs with paraglider above it :)
And there is a guy here who designed and built a 2-seat cabin gyro with folding mast and jump take-off (stop, stop, guys, wait a bit to laugh :D powered with such Simonini engine. I saw this gyro photos and talked to this guy once - he is a good guy but I felt he knows, say, not all the bits about gyros. He never flew one and recently he tried to test his creation. I don't know details to the moment but will have a videotape soon - will post details when ready.

[twistair]

Yesterday we flew this Twist with Simonini under gross weight for the first time and - nothing special.
Changed needle jets and EGT are OK now.
I'm still waiting for another prop which should add performance but even with current it flies good enough for it's price :)
Sure it cannot eat 8 liter per hour at 5200 rpm as it's stated at Simonini website - but that's no wonder since there are no wonders in fuel consumption at all. Today we flew it under gross weight for 30 min, fuel consumption at 5500-5600 rpm (which should be 80-85 hp) is ca. 23-24 litres per hour.
Also I must take back my previous statement that it's less noisy than R912 - no, it's slightly higher though not that much.

I'll continue reporting when we get new prop(s) for testing.

Cheers,

[Brent_Brown]

Looking good two up.