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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Webra 91 P-5 motor issue in Robbe Nova Cuatro
07-24-2020 06:48 AM  9 months ago
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Hendry Hellerle

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Gauteng, South Africa

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Webra 91 P-5 motor issue in Robbe Nova Cuatro
This Robbe Nova Cuatro has been in storage for 11 years! I serviced EVERYTHING on this heli, and must say despite its years its still an absolutely beautiful machine!
The Webra motor I'd like to keep because of its historical value. Needless to say the bearings had it, as the ring was stuck inside the piston. I replaced the bearings, and managed to free the ring. Unfortunately the rind bended a bit. I worked on it for a few days to get it as perfect as possible and reassembled everything.
This old motor idles beautifully, and is very responsive, but it has one gremlin I cannot get rid of.
The motor keeps high operating RPM for a few seconds, and dies instantly all of a sudden. Tuning the low and high needle has got little to no effect on this problem. I'm running it with OS no 8 glow....
Please help me to save this piece of Austrian history. I've added a YouTube link that demonstrates the issue at hand.

Video:

Watch at YouTube

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07-24-2020 07:02 AM  9 months ago
TMoore

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Cookeville, TN

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Put blades on it dude. It's meant to be loaded up.Part 107.
The only ZERO flight hour certificate in the world.
It's like getting a driver's license without the driver's test.
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07-24-2020 07:54 AM  9 months ago
Rojoalfa

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Punta de Mata, Monagas-Venezuela

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/
/

Yes... Don't accelerate your motor without blades... It needs a load to work properly.

Ok...
Did you check silicon tubing layout?
Every fitting is in place and not clogged ?

/
Saludos cordiales,
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07-24-2020 02:13 PM  9 months ago
wjvail

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Meridian, Mississippi

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How old is your fuel and has it been stored tightly capped? If fuel has been properly stored will last 20 or more years. Fuel that has been stored such that it isn't airtight it will absorb moisture. Moisture in your fuel will do what you are seeing. I tell everyone that is having engine trouble: "Try a new OS #8 plug and fresh fuel."

Another question... This may be impolite but your equipment looks pretty old. That in itself isn't a problem but if it hasn't been stored well there is a possibility the ring is stuck or there are issues with the fuel lines and or filters. Are they healthy? Have you looked inside the tank and checked the clunk line?

Does your fuel foam as it spools up? It looks like your tanks is pretty empty and vibration may be causing the fuel to foam causing it to go lean. It looks like you are using a header tank. Is it full?

Your model should spool up without the blades. I've done it many time over the years. Just be careful. It will overspeed if you let it.

Keep us posted. I like a good mystery.
"Well, nothing bad can happen now."
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07-24-2020 03:03 PM  9 months ago
JLF92677

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Southern California

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How old is the fuel you are using?
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07-24-2020 03:22 PM  9 months ago
JLF92677

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Southern California

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Sorry to have posted the same question as wjvail, I watched the video and responded without reading the rest of the posts. I do think that most likely the problem is old “wet” fuel.
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07-24-2020 11:28 PM  9 months ago
wjvail

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Meridian, Mississippi

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JLF92677 How old is the fuel you are using?
Great minds think alike .
"Well, nothing bad can happen now."
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07-24-2020 11:53 PM  9 months ago
JLF92677

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Southern California

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It's funny how we both had the same initial response. This exact thing happened to me back in the mid 90's. I had been away from the hobby for a few years, so when I returned to the hobby, I used a half empty old metal can of fuel to start an airplane engine. Engine started and idled just fine with no issues, but once I raised the RPMs it flamed out. I could not figure out what was causing it. So I tried a number of things and wasted a bunch of time before I reached out for a new can of fuel. BINGO, all else was fine. Back then we did not have forums like RunRyder to ask questions and get answers... it was trial and error back then. GREAT to have the internet and RunRyder around these days!!!
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07-25-2020 02:58 PM  9 months ago
douflytoo

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Valparaiso, IN. USA

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Also, check out post #30 from this thread, is specific to Webras, may help in tuning.
https://rc.runryder.com/t80175p2/
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08-02-2020 02:12 PM  8 months ago
wjvail

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Meridian, Mississippi

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Any progress on this mystery?"Well, nothing bad can happen now."
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01-29-2021 09:56 AM  83 days ago
Hendry Hellerle

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Gauteng, South Africa

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wjvail Any progress on this mystery?
OK update:

The ring has got high and low points. I removed it from the piston, and inserted it again in the barrel. Looking towards a light source, one can clearly see some thin lines between the barrel and the ring. Obviously this implies that the ring doesn't seat as it should, and I may have tried tunig the problem away. I found someone that is busy manifacturing a new ring (let's see how it goes), but in the mean time I fitted an OS 91 SX to get the heli going.
Thank you for all the suggestions guys!

Watch at YouTube

Cheers!
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01-29-2021 11:08 AM  83 days ago
Craig G.

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Central NC

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I've always liked Webra engines but OS is hard to beat. Your Cuatro looks great, nice upgrades.

Word of advice if you're going to keep flying it... install Miniature Aircraft Tuff Strut landing gear:

https://www.miniatureaircraft.de/sh...&search=2500-02

to avoid using the brittle (and irreplaceable) stock landing gear struts which WILL break if you have a hard landing. The Tuff Struts will survive most crashes let alone hard landings.

Another fragile item (and also irreplaceable) is the crown gear driving the tail. Any contact with the ground will strip the gear. I use spacers between the rear struts and mechanics on my Milli, Nova and SE to get the tail rotors a bit higher to avoid contact. I've also replaced the rubbery stock tail fins with carbon to protect the rotors.
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