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#337286
Last flight with my mosquito ended quite abruptly: after 10mn, the motor stopped running, after some strange noise and vibrations.
Back at home, the first thing that I noticed, was a missing screw on the air box bracket (the one that connect to the cylinder cover).

The screw was still inside the air box...but when I opened the motor, I found half a washer inside the crankshaft chamber, and lots of iron chips. Bummer.
So now I wait for a new piston and a new cylinder. Hopefully nothing else has been damaged in the process.

The fact is, before the flight, at home, I had time to check all screws and made sure every of them were tight enough. I just found that "this" one was
somehow not any more fixed to the air box body, so was turning when I tried to tighten it.
Anyway, I was confident, because the Nyloc nut was correctly screwed on it.
I was wrong, mainly because this screw was too short.

So it loosen while in the air, the screw fell inside, and the washer was suck into the carburettor all the way to the motor chamber.

If I think of a solution, it would be to have a bigger screw, on which you could have an additional nut between air box and bracket. Just now, I have to
figure out, how to place this screw back into its hole.

The positive side is, now I know exactly how is assembled my motor, and it is way simpler than I thought.
Attachments
the damage.bmp
the damage.bmp (764.91 KiB) Viewed 1042 times
the washer.bmp
the washer.bmp (646.37 KiB) Viewed 1042 times
missing screw.bmp
missing screw.bmp (776.82 KiB) Viewed 1042 times
User avatar
By mark selner
#337298
that sucks.i would like to try one of those
User avatar
By lafe.williams
#338127
bummer man,
something similar had happened to my mozzie before i got it,
the solution they came up with is to cut the plastic silencer directly opposite of the hole in an U shaped incision, big enough for tools/hands, so could bend the plastic insert the fastener and then it was covered with black duct tape.

mine revs a little low in rpm (8200 static test) following all this, i'm told a stock mozzie is around 9000rpm static, how was yours?

do you mind posting back with your rpm pre/post fix?
good luck.
User avatar
By Flyingseb
#338158
The engine is now fixed, and I need to make the first test as soon as I can.
I've made sure it can never happen again, of course, by using a way longer screw, and one extra nut, that still left some thread left.
Inserting the screw by the inside was really easier than I thought, no hassle here.

Before this incident, the max RPM was also 8200, more or less 50. I bought it used also, and don't know about his past service.
But I think anyway that it is also highly dependant on the propeller, said pitch.
Mine is the original folding one, a little bit modified. It has been repaired and reinforced, since it was damaged during a restart in flight, with too
much gas on the throttle. So I guess not as effective a a new one.

Considering this, if I could get 9000 RPM with the new cylinder and piston, I would very happy.

I keep you informed :wink:
User avatar
By lafe.williams
#338161
pitch, drag factor, for comparison, mine also is with a stock folding prop 8200,
i also have a fixed wood prop and it is around 7900/8000. (much more drag)
User avatar
By Tasi
#338258
Although quite common, the revs seem to be on the low side.
Don't have a mosquito but do have a Radne; mine revs at 9200-400 with fixed carbon stock prop depending on the quality of the fuel and the day I guess, all at sea level. Also a folding prop will give less thrust.

Is your carb tuned alright?what oil do you use?
User avatar
By Flyingseb
#338362
first 10 mn run gives me 8000 RPM. The mix is one month old, and 6% oil for a soft start.
I hope to get the additional 200 to 400 RPM that would signify back to normal.
Interestingly, it was running smoother as it never did (I bought it used).

Tasi: you have a Radne, but possibly not the same carb, and the stock propeller is not carbon for the mosquito...the comparison is not significant.
The Radne is engineered to go up to 13000 RPM: it certainly depends on the carb also.

I'm confident to test fly it in mild conditions now :wink:
User avatar
By Tasi
#338379
Flyingseb wrote:first 10 mn run gives me 8000 RPM. The mix is one month old, and 6% oil for a soft start.
I hope to get the additional 200 to 400 RPM that would signify back to normal.
Interestingly, it was running smoother as it never did (I bought it used).

Tasi: you have a Radne, but possibly not the same carb, and the stock propeller is not carbon for the mosquito...the comparison is not significant.
The Radne is engineered to go up to 13000 RPM: it certainly depends on the carb also.

I'm confident to test fly it in mild conditions now :wink:
Seb,

Some constructive criticism if I may :)

I'm pretty confident that 6% is overkill; the manufacturer recommends 3% for the first 10hrs if your unit is new and then 2% after the "break in", with the best oil you can find. There was a trend and manufacturer recommendation to use the Castrol TTS, but I'm not sure if its discontinued now. A higher % of fuel/oil mix can create muck and residue in your cylinder and piston and further down to your exhaust outlet. My carb is a Walbro WG8 by the way with a fixed high speed needle.

For the prop I'm also pretty certain that the stock prop is carbon with a folding one as an option...Using a wooden will certainly take your revs down somewhere aroubd the 8000-9000revs range if I recall well from my buddies. Mine went down 1000 with a wooden.

For the fuel, it would be good to consider replacing it if it sits for more than a week and it's good practice to use 100octane. You'll see a difference, both in engine response and in flight economy.

I had an event with the motor revs in the past, which back then I traced it in the quality of the fuel. It has been sitting for over a month and when I went flying I just couldn't bring the revs up to normal. Refreshed the fuel and problem was gone. Fuel can also "break up" your oil if sitting for too long. Since then I don't use more than a week old fuel.

Check the http://www.wind-drifter.com/ site which has a ton of info on these units, as well as the flphg group in facebook https://www.facebook.com/groups/FLPHG/
User avatar
By Flyingseb
#338382
I'm pretty sure 6% was overkill, too, but it represent only the first 2 litres that will be burned. Little risk of muck and residue, I agree.

Still I can get 8000 RPM of a one month 6% mixture.

As for the wood propeller, I talk about the Mosquito A10, the old one. Don't know about the NRG.
#400793
What I have always done ,providing I know my engine system is ok, is to trim the prop if wooden until desired static peak rpm is obtained .
1 cm from the tips and some fanning with a sander can do wonders to get the power band working .

Caution though, if the prop is not the problem you will be destroying a good prop and possibly a good engine .
8700 to 9300 can be achieved and is after all where the real kick starts .
Has any body gone further?
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