BE 76 duchess

[malc4d]

Does anyone know what the pilot side squat switch controls, also the passenger side squat switch...?

How do l know if it has unfeathering accumulators...?

[dirkdj]

Both side swat switches are safety devices to prevent retracting the landing gear on the ground. However, don't rely on them since even a moderate taxi speed or a bump in the runway can close/open? the switches and let you retract the landing gear while still on the ground. Just pretend they are not there and retract/lower the landing gear at a sensible altitude.

I don't know about BE76 and unfeathering accumulators, but on my airplane they were used to help unfeather the prop after an intentional engine shutdown by moving the prop out of feathering range so it could start to windmill by itself. They look like air pressure containers in the engine compartiment and should be refilled with air pressure during inspections. Your maintenance people should know if they are installed or not.

[LFS]

The duchess actually uses pitot pressure to prevent you retracting the gear on the ground as apposed to weight like most light twins.

[rug-rats]

The duchess actually uses pitot pressure to prevent you retracting the gear on the ground as apposed to weight like most light twins.

So in theory in very strong winds when tied down the gear could be fooled into retracting?

[S-Works]

No the Duchess has squat switches as well.

[malc4d]

Thanks so far guys

The pilot side has 6 wires, guessing now that it controls the down / up lock and heater ...........

Passenger side has 4 wires, down / up lock...............

I know what an accumulater is, p.o.h says " if " yours has them fitted........

Its a weekend, what maintenance people.....;)

[malc4d]

Ok. seems 'our ' Duchess has unfeathering accumulators........... Pitot pressure stops gear retraction on the ground.......... :ok:
Now what do the squat switches do............:confused:

[S-Works]

My understanding of the squat switches is they work in conjunction with the static system to prevent ground retraction and that they also operate the Red/Green lights to show gear state.

I have never seen a Duchess fitted with un-feathering accumulators! I know it is possible, just personally not flown one with them.

I can email you a copy of the POH and the Multi Engine training notes on the one I use most frequently if it helps you.

[LowNSlow]

The one I flew in Southampton many moons ago had the unfeathering accumulators. Overall I remember it as a nice little aeroplane, much better built than the lovely Twin Com I did the rating in.

[flightlevel1985]

I did my rating with a school at Bournemouth and their BE76 were fitted with the unfeathering accumulators. Made it nice and easy for the engine restart.

[maxdrypower]

I trained at bournemouth too our duchesses also had unfeathering acs . Cant quite remember but it certainly has some sort of squat / weight on wheels switch in its undercarriage to prevent retraction on the ground . It should technically not be possible to retract the gear on the ground , but cabair did conclusively prove it is possible in the not so distant past

[malc4d]

Thanks guys......
Bose. Thanks, but have the poh. dosen't say in there what the switches do either. .........

[S-Works]

No neither does mine, having sat and read it earlier. I am pretty sure that I was told they worked as part of the gear warning and ground retract prevention system.

I will be interested to see what you find out.

[421C]

other things they might do on a light piston twin
- reduce current in pitot and stall heat circuits, making them warm enough to check on the ground and prevent icing, but not too hot to avoid burning them up without normal flight airflow
- Mode S transponder switching between GND and ALT mode (can also be done by coupling to GPS groundspeed)
...but I'm with Bose, on a BE76, most likely gear retraction preventition

[philknight29]

Hey,

The switches on the Duchess are Micro switches that complete the circuit for the Green Safe lights.

The Gear retraction system is energized through pressure switch's in the Pitot's. Energizing the system at between 49 and 51 knots.

[dirkdj]

The squat switches are there to prevent a dumb pilot from retracting the gear on the ground, if they would trigger the three green lights for gear down, you wouldn't get three greens until safely on the ground when the squat switch closes because of weight on the wheels. Not much use for three greens then, you would have found out the hard way if they are down and locked.

[philknight29]

DirkDJ,

If you read the manuals it's all in there, there are no Squat switches there is only Pitot Pressure. Get it up on Jacks and you'll see that the switches make contact even if there is no weight on the wheels required.

The many I have flown don't have WOW switches, only the pressure system. If your one is different then ask a Mechanic to explain what it's for. Because they left the factory without them.

I still maintain that the switches are for the lights, next chance I get I will get one up on the jacks and check them out.

Ta.

[philknight29]

Just found the POH and I will quote from page 7-12 of August 1980.

SAFETY RETRACTION SWITCH

To prevent inadvertent retraction of the landing gear on the ground, a safety pressure switch is installed in the pitot system to deactivate the hydraulic pressure pump circuit when the impact air pressure is below 59 to 63 knots.

Discuss....

[dirkdj]

The original poster was asking what the squat switches do on a BE76. On my BE36 they prevent retracting the gear with weight on the wheels, in addition there is a 'Magic Hand' system with a sensor in the pitot system to lower the gear automatically when below a certain airspeed and below a certain manifold pressure. Two other Beech types I have flown had the same arrangement (but not the Magic Hand). I know the BE76 is not part of the Bonanza/Baron family and may well have another gear system but I think Beech always uses a squat switch for the same reason. On my aircraft the three greens are activated by microswitches sensing the position of the gear retract rods, not the squat switches. The squat switches are on the main landing gear legs, the microswitches for the greens indication are inside the cabin below the pilots seats, next to the landing gearbox.

[malc4d]

From the maintenance manual..

... ' down and locked switches - one on each main gear side brace and one on the nose gear drag brace;..'

...' the in-transit.....light (red) is illuminated anytime the the grear is in transit..........hydraulic pressure up to 1550 psi will cause the pressure switch to break the circuit ....causing the intrans light to go out. '

'..when the gear reaches the down and locked position... the locked switch is actuated and the respective down (green) indicator will light.....'

'..The air pressure switch is a safety device that prevents the gear from being retracted until an air speed of 59 to 63 kts per hour is obtained. '

Still they must do more, if the pilot side has 6 wires, passenger side 4 wires. will look at the nose one tomorrow....do they control the heater ?


Now if only l could copy and past the page here......(tried but it wont paste.....)

[Dan D]

The duchess actually uses pitot pressure to prevent you retracting the gear on the ground as apposed to weight like most light twins.

So in theory in very strong winds when tied down the gear could be fooled into retracting?

No, unless the wind is about 55 Kts and you decided to pull the gear handle up. An example of how it works. You come to the airport, do your preflight inspection, but forget to pull a pitot tube cover off. You taxi for take off and everything seems OK. When you accelerate for take off, you notice the airspeed indicator doesn’t work. If the runway is short and you can’t stop any more, you have to continue. The plane lifts off, you pull the gear lever up, and you hear a buzzer! The gear doesn’t retract, you have 3 green indicator lights on. To stop the buzzer sound, you have to move the gear lever down again. Now you have to fly a pattern and and land. After that, pull that pitot cover off making sure nobody seas you. 😊 That’s the reason why you have to verify “Airspeed alive” on take off roll. This plane can be easily flown without an airspeed indicator, simply by numbers, sound and feel. That means that you really have to know the plane well. I owned a BE-76 for 14 years and know a guy to whom that happened. When a fire truck full of guys he knew pulled by him, his face was red. How do I know that? I looked in a mirror. 😂