Low G and Rrpm decay rate

Jean Claude

Junior Member
Jan 2, 2009
I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
with 925 lbs, I obtains 22.3 liter.
Realistic enough to validate my conclusion #48 between well fairinged tractor and usuel pusher, i.e consumption in the ratio 0.15/0.25
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Greg Vos

Active Member
May 26, 2019
Cape Town
R44/22 H269/300 MD 500 Magni (all); Xenon RST; DTA; ELA; MTO Trojan
Total Flight Time
Stoped counting at 2000
Has anyone seen rotor decay in a power hover. Seems logical to me that it could happen, always keep my eye on RRPM when doing them, but never seen much of a decay.
In the nose up condition with zero AIS and the use of throttle to hold position ( simulated hover for a few seconds in a no wind condition) will see the Rrpm decay slightly, the aircraft will start to fall gentry towards the ground fully controllable, once that happens the Rrpm will then recover we normally invite the nose down after that ( no abrupt movement on the stick) it’s really a non event, I teach this to students and converting pilots and it’s a great exercise to let them gain confidence with what I call stirring the porridge, and a great experience for the pilot to see and identify with how different the controls feel ( heavy slow response on the stick yet full rudder authority)

Take your gyro to a local ridge on a windy day you can sit in the lift region ( of the ridge ) and modulate power thereby simulation a hover 😁 if anyone were to see if from the ground it would appear they gyro is hovering

who says a gyro can’t hover 😉

Doug Riley

Platinum Member
Jan 11, 2004
As long as air is passing through the rotor disk at an angle other than edgewise, the rotor will turn. Loss of RRPM in a gyro happens when the airflow past the rotor disk is edgewise.

In steady flight, this "edgewise" condition won't exist for more than a split second. As the RRPM begins to drop, the gyro will begin to descend. This descent changes the angle of the airflow to the disk from edgewise to "from below." This stabilizes the RRPM and prevents further loss of RRPM.

The loss of RRPM from "edgewise" flow can become catastrophic if, instead of steady flight, the gyro follows a ballistic path -- that is, a downward arc that duplicates the path of a pitched baseball or an artillery shell. This arc-ed path can allow the "edgewise" flow to persist long enough for RRPM to decay to the point where the rotor may experience retreating-blade stall (destructive flapping).

But this can't happen in a simple vertical descent (or fake hover). The gyro then lacks the momentum to assume a ballistic path. Instead, the gyro simply sinks, with air passing into and through the disk at a large angle.