Bass1

Hi, Today my Sukhoi throttled back to idle shortly after takeoff,I was lucky to land safely. I restarted the aircraft on the ground and after10 seconds it throttled back again. Thats when I realized it was the failsafe and not a linkage/servo problem. When I cycled the throttle stick full to idle and back I regained throttle control. Receiver battery checked at 5.1 volts under load and Trans. battery 10 volts. I understand that the battery failsafe will let you regain throttle control for a short time when you move the stick from idle to full.Would it be reasonable to suspect the receiver battery. I was the only one at my flying field today. I 've flown this aircraft about 10 times with no problems. The receiver is an R138dp Futaba and the Trans. is a 6XAs. Thanks for any help. Bass1

FLYBOY

My Feedback: (11)

Doesn't sound like fail safe to me. Should have locked out all the controls. I had something similar in a larger plane once and it turned out that I was getting interference in the radio from the noise produced by the ignition. I moved everything away and it was taken care of. Could you have some metal to metal rubbing somewhere making noise making your receiver? What engine are you running? What kind of throt pushrod are you using?

Bass1

I'm using a Saito 150. Upon further inspection I realized that I have a metal clevis at the carburetor. That in itself is not good! but why did it decide to do it now? And twice. I can't believe I did that!!

Geistware

My Feedback: (16)

No, battery fail safe will do just what was described on the throttle. Signal fail safe will do what you are describing.

I had something simular happen and what I found is that my pack was too small for the servos I was using and when I flew, it would load down the pack and the plane would go into battery failsafe. What servos and pack capacity are you using?

Bass1

Thats interesting! I'm using a Horizon Hobby 1400mah pack. Servos are:2 Hitec 505M.G. ailerons ,2 505B.B. elevators 1 505MG rudder.! standard airtronics for throttle. Did I mention the air temp. was 91 and the heat index was 100. The battery pack is located right behind the firewall and it probably gets pretty hot in there. Anyway I'm going to pull the battery pack and check thoroughly and change the metal clevis. Also after range checking, on the way back to the airplane, the little l.e.d. that says P.C.M. on the trans. blinked once. That was the first time I noticed this,but I never really looked at this before so I thought it was a normal thing.

Bass1

Also I'm using a standard Futaba switch(2 years old). A little more info: The reason I switched over to P.C.M. is because of past interference. I had some problems with the throttle surging and occasional unexpected and fraction of a second loss of control especially on low final. Some club members thought that I was too slow and the airplane was nearing stall, until one day it decided to throttle up all by itself at the end of the runway. There were alot of logging trucks in the area with huge C.B. radios and several people had interference problems. So I decided that the P.C.M might be a better choice. The trucks left the area and the P.C.M. seemed to fix the problem until yesterday. So I'm leaning toward the metal throttle clevis(A dumb thing in the first place). Maybe over time,the metal pin in the clevis enlarged the hole in the carburetor arm causing more vibration. Bass1

mglavin

My Feedback: (31)

I'd suggest the BATTERY FAILSAFE was activated. Your description of what transpired is a mirror of what should happen with battery failsafe.

What was the voltage of the battery? Under load? New battery? NiCD? Cell count? Did you charge it? Have you cycled the battery and or measured the capacity? Did it happen while you were using several control surfaces or under level flight conditions?

Definitely loose the metal to metal clevis! However this would not cause the problem you describe, if anything it would implement a control surface lock-out/failsafe (last known setting or pre-programmed failsafe settings).

Bass1

Battery was 1400m.a.h. 2 years old showed 5.1 under load. I believe 4 a nicads. It happened on first downwind turn after takeoff, and after landing during the restart on the ground. The battery was cycled about a month ago. Fully charged before going to the field. I had problems with the original F.M. receiver. Do you think the battery pack was faulty from the beggining? When the throttle stick was moved up and down I regained throttle control.Maybe a cold solder joint in the battery pack? Bass1

mglavin

My Feedback: (31)

Sounds like a battery problem to me.

Four or five cell?

NiCad or NiMH?

I'd cycle the battery and confirm the capacity with a unit that is able to record the mA capacity discharged.

It could be a bad connector, switch wire crimp a bad cell or other...
Do all the servo appear to work correctly? Any binding?

If nothing else, replace the battery with a known good one and see if the problem persists.

Geistware

My Feedback: (16)

Bass1, I have never heard of the servos that you say you have. I would recommend that you use the HD switch.

Bass1

I'm sorry about the servo models. I said 505 mg and 505bb, It should have read 605 mg and 605 bb.

Geistware

My Feedback: (16)

You should get 4-5 flights on that size pack with those servos and plane. I used 2 1300maH packs on my Giles and could fly 10 flights easy. Check for any binding that is draining/loading your system. Also can you check your charge amount after you have experienced failsafe? You may just have one servo that loads down the pack and put it into failsafe.

Bass1

All servos operate smoothly with no binding or noise. The pack was fully charged,reading 5.28 under load.The aircraft was flown oncewith no problems. The next flight is when the failsafe engaged. After landing, the Battery pack showed 5.1 under load.I think with the info I've received I'll get a new battery pack and heavy duty switch and double the amount of foam to make sure vibration is not a factor even though it range checked fine under half throttle. Seems it likes to do this under full throttle.

Geistware

My Feedback: (16)

Do you have your pack connected to the receiver through a "Y" connector? It could also be that your "Y" connector is not that good.

Bass1

While going through battery change and new H.D. switch harness I found a 3 inch extension I was using between battery pack and switch that looked pretty cheap(smaller gauge than the battery leads) also the connectors didn't fit tightly. I hope this contributed to my problem. Anyway everything is heavy duty now and new. Wish me well! Thanks for the help Bass1

amcross

My Feedback: (2)

"When the throttle stick was moved up and down I regained throttle control."

This is the definition of battery failsafe. Your battery is dropping below needed voltage, for whatever reason.

I would look VERY carefully for a failing servo, one that is probably only showing problems under heavy loads. I would also replace the switch with an HD switch or, ideally, an ideal switch which fails to ON instead of OFF.