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GrandRC . CanoMod . Futaba-RC

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Audacity Models Pantera 50 - Tiger 50 > This could have been scary.
 
 
Mr.HillBilly
Senior Heliman
Location: Salesville, OH - USA

It finally stopped raining so I got to take the Pantera out tonight. A little windy but good night until this....

I just put a new motor, (used) Thunder Tiger 70, in the Pantera and I was getting the needles set up. I got her running good, into my 3rd. tank just running high speed figure 8's. About 3/4 through the tank I came out of a hard banked turn and leveled out. Throttle dipped so I put it in a hover about 300' out. Sat there for a few secs. acted fine so I punched the collective and pushed her forward, dropped out again. Put her back into tail in hover and brought it back in slow (I stink at autos so I was going to make it as easy as possible). Got her back in landed hit THOLD and it just sat there revving and picking up a little speed. I hit the switch 3 or 4 times, nothing. Then I see something bouncing around in the canopy.

Anyone see anything wrong with this pic.?



You would not believe how long it takes to burn a 1/4 tank of fuel and a 2 oz. header tank at 1/4 throttle. No one around to take a stick or anything to pop a fuel line off. So I stood there for probably 10 mins. hovering around with a head speed of about 1700. So there you have it a Pantera with a TT70 can hold a hover at about 1/4 throttle. Also here is a good point to get a 2.4Gig radio. Metal to metal chatter at 15,000 RPMs and no way to shut it down.

It was kind of funny after I got it in and figured out what was wrong. Just stuck there watching the fuel run out. I am just glad that it stuck at 1/4 throttle and not at closed or worse yet WIDE OPEN.
06-19-2008 02:09 AM
 
 
Ray Fernandez
Elite Veteran
Location: Guam (U.S.A.)

That actually happened to me to. I using a TT36 and the throttle arm broke off.

I've seen it somewhere (sometime ago) on RR where some pilots actually incorporate a small spring to use should something like this occur. The spring acts as a automatic throttle cut if and when a throttle arm breaks off.

Ray Fernandez - GUAM
06-19-2008 02:14 AM
 
 
billm
Key Veteran
Location: Liberty Lake, WA

LOL. Done that man!
My linkage slipped and I kept the ship with a little bit of neg pitch for five min untill she quit. I remeber other chap had the same thing happen. He got so scared of the thing going into a chicken dance. He thru his shoe at it. It did the dance!

My name is Billm. Cough, and I'm a Heli Holic
06-19-2008 02:31 AM
 
 
heli_headcase
Key Veteran
Location: Hovering around Atlanta

Odd...

I believe the throttle barrel on that TT 70 has an internal preload spring on the high speed needle side of the carb body. The spring's purpose is to push the barrel sideways and eliminate play between the cam slot machined in the barrel and the guide pin that fits into that slot. Makes for much more consistent low-speed mixture because the barrel can't move sideways without rotating first and that way the relationship between the air flow and fuel flow metering stays consistent.

The unwanted byproduct of this spring and the cam slot in the barrel is the spring will force the engine to full throttle when left unrestrained and aided by some engine vibes. Why didn't your 70 go wide open after the arm fractured? Good thing it didn't but there are some other forces at work here that should be investigated. Give the barrel's nut a push and see if it springs back to you. It should freely push back with no drag. Will only move a few thousandths of an inch but always detectable.

Then try rotating the throttle barrel while lightly pulling on the shaft and nut. Is it smooth or do you feel rough spots and catching? If it's rough you may have contaminants in the cam slot and these could allow the carb to stick in flight or wear the cam pin.

Lastly: What caused the stock metal throttle arm to fracture? Vibration! The fan runout was too great and the vibes transfered to the carb linkage and broke the arm. It will happen again if the vibration isn't reduced or maybe you can find an OS .32 plastic arm to use in place of the metal one.

Some casual observations while my food is cooking.


HHC

So many heli's - too little time...
06-20-2008 02:03 AM
 
 
billm
Key Veteran
Location: Liberty Lake, WA

Heli,
Nice call on the problem.
NTSB could not any better. You have had the same thing happen to me several years ago.
Locktite the bolt on the carb arm next time.
You and I have learned the hard way.
Time for me to throw something on barby.

My name is Billm. Cough, and I'm a Heli Holic
06-20-2008 03:51 AM
 
 
mavrick#1
Senior Heliman
Location: ON, CAN

sorry for the bad pic

I use a spring, and it has saved a Trex600N already this year.
Great idea, I got here on RR.



A good day????......... is not crashing :)
06-20-2008 05:57 AM
HOMEPAGE  
 
 
Mr.HillBilly
Senior Heliman
Location: Salesville, OH - USA

Mavrick are your running 2.4Gig. It looked like that spring is right on your CF. But it is a good idea, I will prob. do something like that with the OS70 when it gets here. It would not have done any good to put a spring on the TT. It broke the whole arm off so there was nothing left that the spring could have hooked to.

That throttle arm was bent and twisted when I was using it, but I did not look at it since it was only a test motor and would not be staying that long anyways. I guess that is what I get for being lazy.

I think the Heli. gremlins are after me right now anyways. Last night I was playing with the Hawk and I had radio control when the motor was off, but as soon as I would start to spool it up I went dead stick. Here the plug from the switch was just about pulled out of the RX. All the rest were fine just the power plug.

Dang old gremlins anyways.
06-20-2008 01:09 PM
 
 
jbeech
rrAdvertiser
Location: Sanford, FL (Orlando area)

A retired command sergeant major, my Dad called it PM, or Preventive Mmaintenance. Folks, I've said it before but I don't get tired of saying it (nor did my Dad, who passed away last year, God rest his soul). Basically, at the end of the day, as I clean the machine before putting it away, I look over everything - to include wires. I mean touching and feeling everything as I go with an eye to finding "anything" suspect. Would you have found the bent, i.e. incipient and soon to break throttle arm? Maybe not, but you'd be surprised how you seemingly don't "ever" find anything . . . until you do. Then you'll think "wow" that could have been trouble if I'd not caught it! Anyway, I promise you it only takes one instance of you finding something to sharpen you right up. Good discussion.


John Beech - GM (and janitor)
Audacity Models
06-20-2008 02:56 PM
 
 
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Audacity Models Pantera 50 - Tiger 50 > This could have been scary.
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