An interesting training experience in a Cavalon.

[perbgyro]

...pull the power to zero to enter a power off vertical descent (one of the required training maneuvers). She began to spin to the right and we both heard that strange noise a Rotax PSRU makes when the engine comes to a stop. The aircraft began to spin faster...

Some curiosity here... Taking the engine out of the equation by entering vertical decent after power off, does the gyro start to spin? If so, at what point (if any) would you possibly loose control of the gyro as pushing the stick forward wouldn't necessarily give enough rudder authority to counter the spin?

 

[Vance]

Good questions Paul.

Good questions Paul.

Some curiosity here... Taking the engine out of the equation by entering vertical decent after power off, does the gyro start to spin? If so, at what point (if any) would you possibly loose control of the gyro as pushing the stick forward wouldn't necessarily give enough rudder authority to counter the spin?

I don't have a good answer.

This is the first time I have done it with the engine stopped and she spun faster as soon as the propeller stopped.

I have found she reaches a spin rpm and stays there. I don’t know what it would do with the propeller stopped because we were not in a position to test it safely.

My experience is as soon as I lower the nose or add power the spin stops and the rudder authority returns.

I advise not adding power in the Cavalon at very low air speeds and bringing the nose up before adding power at very low airspeeds.

The Cavalons I have flown were all very docile performing this maneuver.

I always have plenty of altitude when performing a power off vertical descent because the most likely time for an engine to stop is during a power change.

With a carburetor on a Lycoming or Continental I feel it is important to pull carburetor heat when reducing power.

It does not appear to be necessary with a Rotax and in fact none of the gyroplanes I have flown with a 912 or a 914 had carburetor heat although it is available.

I may do a very steep slow airspeed descent when setting up to a short landing and I have found it takes around 150 feet to arrest the descent. In a 20kt wind I may fly backward over the ground. None of the gyroplanes I have flown will spin doing this maneuver. It may be the slight forward speed or the thrust from the propeller that stops it from spinning.

I have not experimented with minimum engine speed or airspeed settings so I don’t know where they are.

 

[C. Beaty]

In a vertical descent, the downgoing side of the propeller disc is exposed to greater airspeed than the upgoing side, producing asymmetrical thrust and causing rotation. If the propeller blades had flap hinges, the top of the propeller disc would tilt forward.
With dead engine, there should be no rotation unless the fuselage is whopperjawed or there is a high level of friction in the main rotorhead bearing. Ball bearings don’t normally have enough friction to make a difference.

 

[Vance]

I don’t have you knowledge Chuck.

I don’t have you knowledge Chuck.

In a vertical descent, the downgoing side of the propeller disc is exposed to greater airspeed than the upgoing side, producing asymmetrical thrust and causing rotation. If the propeller blades had flap hinges, the top of the propeller disc would tilt forward.
With dead engine, there should be no rotation unless the fuselage is whopperjawed or there is a high level of friction in the main rotorhead bearing. Ball bearings don’t normally have enough friction to make a difference.

The Predator will not spin in a vertical descent with the engine at idle although I have very little to no rudder authority.

The GPS will spin when I reach zero ground speed.

If I encounter a wind gust and I am descending over a spot on the ground she will turn into the wind.

The Cavalons I have flown in a vertical descent with the engine at idle will spin to the right unless I intentionally start the spin to the left by applying full left rudder before reducing power.

During this event when the engine stopped the speed of the spin to the right increased and the rudder was completely ineffective.

Releasing back pressure allowed the Cavalon to come out of the vertical descent spin before I was able to restart the engine.

I don’t know how to test the fuselage for being whopperjawed as I don’t understand the term.

It is my observation and the pilot under instruction that she spun faster when the propeller stopped.

 

[C. Beaty]

An airfoil that is symmetrical front to back, such as a venetian blind slat or even a completely flat airfoil, will autorotate in either direction once started.

Perhaps your Cavalon’s fuselage acts like an airfoil while descending vertically after RH rotation has been initiated by an idling engine.

You can prove this for yourself with a strip of aluminum, a nail and a stick. Give it a flip and hold it out of a car window.

A sticky rotorhead bearing would rotate the machine to the left.