UH-1H question
 

Maybe this should be in the mechanics forum but that mostly looks like fixed wing so Ill ask here. Have a UH-1H operated by a local sheriffs dept. When aircraft is powered(no engine or rotors turning) hear a weeep weeep weeep electrical tone coming thru the headsets. Which I assume is either engine out or low rotor rpm warning. This can be silenced with the rpm mute switch on the pedestal. Now when the aircraft is started and brought to idle or even 100 percent on the ground I get a different faster tone more like a woo woo woo woo woo coming thru the headset albiet faintly which can also be muted with the rpm mute switch. We thought the RPM Limit box was the problem and sent it out for troubleshooting. No problem found. came back and has same complaint after install. Does the UH-1H have a engine out tone that is different from the low rotor rpm horn? SHould I be hearing both tones when the aircraft is powered up but not running? The ARMY manuals we have arent of much help. We have now swapped N1 and N2 tach generators (same P/n) and are awaiting the pilots to return and run the aircraft (Monday) When aircraft is run all the gauges for N1, Rotor and turbine RPM are in the green operating range. Any help is appreciated. Ive been in the aircraft trying avionics off, pulling circuit breakers one at a time while aircraft was running to see if something might be bleeding over into the circuit causing a false signal triggering of this warning and no dice.

I seem to remember a lot of Radio Control Box breakthrough - but I couldn't type the tones on here!

There isn't an engine-out sound in a Huey, just the rising tone from the squegging oscillator for low RPM, silenced by the solenoid on the mute switch.

Sometimes the generator can put a noise through the headsets, as can the strobe lights and the transponder - try turning each of these off in turn when all is running.

When your second noise comes through, and you used the mute switch, did it stay in the mute position? Because when the rotor RPM are in the normal range, you cannot make the mute switch stay in the mute position, being a solenoid.

Rotors are a steady tone, Engine is Worble tone. Check the audio amplifier filters, or the voltages are low in the tach system. (wire rot?)
need the wire daigham for year & serial number. Any guess for now,

Anti-Coll?

Had this before several times…

Cause was a broken insulation on one of the wires, causing interference with the ICS when the Anti-collision light was switched on……
The engine noise covered this quiet "weep…..weep…..weep"...

Aren't you getting confused with a B206?

Any Huey I flew (air force, civil world) had only the rising tone for RRPM, no noise for engine out.

B206 has the bipbipbip engine out noise, and the constant beeeeep for RRPM, which is cancelled by putting the lever on the floor.

This sounds to me like the anti collision lights.

or a pulse light got the same problem on a 212 which needs rewire next year, pilots will have to suffer this summer bucketing.

But check your grounds best place to start.

Sorry for the delay, I work 4 and 3 and was off.

Weve tried the anti collision lights off and no change, one of the first things we tried before my original post.

The mute switch stays muted till you remove battery power, then it reverts back to normal mode.

The weep weep weep heard when battery is on and rotors not in motion is low rotor rpm which id guess is normal when the rotors arent in motion before start.

Ive tried pulling circuit breakers one at a time and avionics off while the aircraft is running and still get the different woowoowooowooo sound which again is muted when the rpm mute switch is activated.

Aircraft is UH-1H 71-20068

Thanks for all the replies.

Ok we've got it isolated to a bad cannon plug at the box cluster that contains the rpm mute switch, engine de ice, emergency governor switch, fuel valve, and the left and right transfer pump switches if you have the bladders installed in the cabin. Something is sending about 7 volts via two wires to the rpm limit warning box with the tone generator. If we pull the caution lights circuit breaker, the ignition system solenoid c.b., and the fuel xfr pump c.b. the voltage progressively drops as each of the above circuit breakers is pulled one by one.
So I guess we've got about a 46 pin cannon plug to replace. Also found bad was cannon plug going into the double tach on the N2 side. Only 3 wires on that one. Intermittent continuity between the three pins so im guessing carbon tracking due to deteriorated rubber on the back shell.

just a thought....if your LOW RPM AUDIO switch will latch in the OFF position with the N2 above 6300 RPM you have an additional problem. It should only latch OFF with N2 below 6200 plus or minus 100.