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Old May 11, 2010, 08:33 PM
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rcmorrow's Avatar
Stamford, CT
Joined Jan 2005
415 Posts
First and most important: I am sorry to hear you had this happen, it is lousy when something like this happens, especially when you lose important electronics and components.

I have had unfortunate flights also, sometimes on the first flight, which really makes my day !

I have always found that I need to reinforce the firewall of any of the arf's I have had. I usually use a mixture of resin and microballoons to make a paste that will make a good fillet.

For the build I am working on with this one I am making a pair of cf motor mounts that will sandwich the existing firewall and then use resin and microballons to put it into place.

Because of the Hacker motor I have I am concerned about the firewall coming loose or fully coming out.
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Old May 11, 2010, 09:04 PM
You down with EPP?
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Houston, Tx
Joined May 2009
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Quote:
Originally Posted by rcmorrow View Post
First and most important: I am sorry to hear you had this happen, it is lousy when something like this happens, especially when you lose important electronics and components.

I have had unfortunate flights also, sometimes on the first flight, which really makes my day !

I have always found that I need to reinforce the firewall of any of the arf's I have had. I usually use a mixture of resin and microballoons to make a paste that will make a good fillet.

For the build I am working on with this one I am making a pair of cf motor mounts that will sandwich the existing firewal and then use resin and microballons to put it into place.

Because of the Hacker motor I have I am concerned about the firewall coming loose or fully coming out.
Yeah, it's a bummer. This was my first hotliner and I really was starting to like it. I never though I would need to reinforce the firewall unless I was turning a big prop and running a lot of power.

Next time I will do whatever I can to reinforce the firewall. The plane is under warranty so I am going to call Tower tomorrow. I was running a very weak setup in my opinion. It was a very wind day, but that should not have happened.
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Old May 11, 2010, 09:23 PM
The Kid
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Detroit, MI
Joined Dec 2007
2,586 Posts
Can you really blame it on the model when it wasn't being flown how it was intended to be flown? Not to mention, its been said many times to fix the motor mount, its a known problem...

Are you sure there wasn't a problem with the prop. What brand 8x5 were you running? You were certainly turning too many RPM for it regardless of manufacturer, as the highest rating out there is 16k, and you must have been past that. Theres a chance you threw a blade, or even just a miss balance could have shaken the motor loose.

Sucess comes from preparation

kid
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Old May 11, 2010, 09:46 PM
You down with EPP?
johnnyrocco123's Avatar
Houston, Tx
Joined May 2009
6,826 Posts
Quote:
Originally Posted by Thekid3418 View Post
Can you really blame it on the model when it wasn't being flown how it was intended to be flown? Not to mention, its been said many times to fix the motor mount, its a known problem...

Are you sure there wasn't a problem with the prop. What brand 8x5 were you running? You were certainly turning too many RPM for it regardless of manufacturer, as the highest rating out there is 16k, and you must have been past that. Theres a chance you threw a blade, or even just a miss balance could have shaken the motor loose.

Sucess comes from preparation

kid
Aero-naut CAM carbon 8"x5

Not being flown how it was intended to be flown? That's interesting, did you see the video? How would you say it is intended to be flown? I gave it 3-4 seconds of throttle at most. Wasn't doing any crazy G-Force moves.

There wasn't a problem until I put a folder on it. I should have stuck with the APC with the prop adaptor, but that's not how it was intended to be flown.
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Old May 11, 2010, 10:26 PM
The Kid
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Detroit, MI
Joined Dec 2007
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Quote:
Originally Posted by johnnyrocco123 View Post
Aero-naut CAM carbon 8"x5

Not being flown how it was intended to be flown? That's interesting, did you see the video? How would you say it is intended to be flown? I gave it 3-4 seconds of throttle at most. Wasn't doing any crazy G-Force moves.

There wasn't a problem until I put a folder on it. I should have stuck with the APC with the prop adaptor, but that's not how it was intended to be flown.
That prop is rated at 16k RPM. On 3s, you should be right at that RPM. On 4s, surely passed it. Personally, I would be very nervous of running a folding prop up to or past its suggested RPM.

The plane was not designed for full throttle blasting passes in level flight. It was ment to climb, then glide etc. etc. Im not saying that I fly the model exactly how it was designed to be flown. But if/when it fails (and I hope it doesn't!) I certainly won't be saying that it is Great Planes problem.

It seems unlikely that the motor mount would just "shoot-out". The failures in the past have come from the brake stopping to aggressively, in which case all that torque is transmitted to the firewall. To have it just pull out would indicate some other issue, one that hasn't been experienced by anyone else in this thread to my knowledge.
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Old May 11, 2010, 10:40 PM
The frigin Catalina wine mixer
flightmare's Avatar
USA, CA, Buena Park
Joined Oct 2006
599 Posts
I would think that hoggy Turnigy inrunner was putting out way too many RPMs for that folder..What happened was it probably threw a blade,after that..it usually rips the whole nose out,not just the firewall..Happens to everyone at least once..
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Old May 11, 2010, 10:45 PM
The Kid
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Detroit, MI
Joined Dec 2007
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Quote:
Originally Posted by flightmare View Post
I would think that hoggy Turnigy inrunner was putting out way too many RPMs for that folder..What happened was it probably threw a blade,after that..it usually rips the whole nose out,not just the firewall..Happens to everyone at least once..
This was my initial thought as well
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Old May 11, 2010, 11:15 PM
geek.
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Joined Jul 2006
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Quote:
Originally Posted by johnnyrocco123 View Post
Aero-naut CAM carbon 8"x5

Not being flown how it was intended to be flown? That's interesting, did you see the video? How would you say it is intended to be flown? I gave it 3-4 seconds of throttle at most. Wasn't doing any crazy G-Force moves.

There wasn't a problem until I put a folder on it. I should have stuck with the APC with the prop adaptor, but that's not how it was intended to be flown.
Johnny-

Did you remember to put the screw in the elevator servo arm? If not, that most likely caused this failure. I've learned that lesson the hard way.

Also, make sure you clip the antenna wires down so they fit inside the fuse. If they stick out, the drag can induce enough flutter to break that firewall clean off.

I bet next time you'll put a streamer or small parachute on your motor.

Cheers
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Old May 11, 2010, 11:24 PM
The frigin Catalina wine mixer
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USA, CA, Buena Park
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Old May 12, 2010, 04:44 AM
Registered User
United States, CA, Rocklin
Joined Jan 2006
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Johnnyrocco123, how did your airframe fare the rest of the flight after your cog drastically changed?
I've had it happen to me for just an instant when the noise alerted me to something horrible happening. Even after immediately shutting down the motor, the front end of my airframe was in shambles. Luckily the motor stayed hanging by the wires and I was able to keep control bringing into a decent landing. This was all due to throwing a blade.
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Old May 12, 2010, 05:40 AM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
43,312 Posts
Quote:
Originally Posted by johnnyrocco123 View Post
There wasn't a problem until I put a folder on it. I should have stuck with the APC with the prop adaptor, but that's not how it was intended to be flown.
Not quite sure I'm getting all of this, but if you were running a fixed prop instead of a folder, the mount was probably knocked loose on landing.
..a
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Old May 12, 2010, 07:45 AM
You down with EPP?
johnnyrocco123's Avatar
Houston, Tx
Joined May 2009
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When the motor shot out, the CG did drastically change!! It did a few flips, but I regained control and landed it smoothly. I was lucky the battery stayed in place and plugged in, as well as my ESC.

I didn't have a problem until I put the folder on. It lasted all of a minute before it happened.

I don't understand why these folding props are rated at such low RPM's. 12K, 16K??? Who would run a folder like that? GP Siren aside, all I have ever seen in hotliners is 1500 - 3000 Watts. These were spinning folders way past these RPM's.

Bottomline, the Siren is not for me. If I get into another, it will be better quality that can take some power. AND MORE ROOM IN THE FUSE!

Kittman: Thanks for the excellent advice as always.
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Old May 12, 2010, 08:09 AM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
43,312 Posts
The folding prop you were using is not a high performance part. It's designed for small sailplanes using moderate power systems.

The RFM folders used on hotliners are most definitely rated for high power use, although as they are much larger and higher pitch (17x18 for example) they don't typically spin much above 10k RPM. Takes about 3kW to get there, though!
..a
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Old May 12, 2010, 08:22 AM
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rcmorrow's Avatar
Stamford, CT
Joined Jan 2005
415 Posts
Aero-naut has a website with specs on all their products. The page for the props with recs for max rpm can be found here:

http://www.aero-naut.de/en/products/...ropellers.html

I thought this might be helpful for those considering a variety of motor/battery/prop combinations so the limits can be understood and hopefully avoid catastrophic failures of the power systems.
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Old May 12, 2010, 12:24 PM
The Kid
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Detroit, MI
Joined Dec 2007
2,586 Posts
Quote:
Originally Posted by johnnyrocco123 View Post

I don't understand why these folding props are rated at such low RPM's. 12K, 16K??? Who would run a folder like that? GP Siren aside, all I have ever seen in hotliners is 1500 - 3000 Watts. These were spinning folders way past these RPM's.
.
This is where you are mistaken. The true hotliners (2kW or more) run with geared inrunners, and are usually geared steeply (from 5.2:1 all the way up to 8:1 or slightly more). With the exception of a few props, very few turn over 10k RPM. One exception would be the RFM 16x17 Wide, which does its best work at just around 10k-10.5k RPM. Everything else is a much bigger prop in the 17-18" range turning at around 8-9k RPM, so as to not over-rev the motor.

For example, my model is at 1600W (or today in the cold 1520W) and turns just over 8k RPM. Much lower then the ratings by even Aeronaut. And RFM is certainly stronger then that, or so I suspect.

Kid
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