I know of a Cavilon in the states that the pneumatic system kept the pre rotator engaged and got so hot the shaft turned blue. The whole system had to be replaced.
This gyro is one that was built with issues. When I was asked to look at it the pre-rotator would engage at random times while on taxi. I told the owner not to fly it until it was fixed. It however had been flow that way by the building organization and dealer then delivered that way to him. They had the flights like that .
Kolibri;n1140902 said:
(The AR-1 does not have a flex-shaft, but an ELA/AutoGyro/etc. type drive-shaft.)
I have not tried to fly a Cavalon in the brake mode. I suspect it would not be a problem....Because the trim force is not very hard to overcome.
As I was trimming the stick force became very large indeed to the point that it was not manageable with one hand anymore and even with 2 hands with the more relaxed and unplanned way I had been sat it wasn’t easy.
I made a PAN call and turned downwind in the circuit with the intention to get back on the ground but at this point I have to say I was struggling with the stick forces, even two handed.
In summary, the aircraft will pre-rotate in this state, and will fly, except that when you trim you are now forcing the trim piston up into the rotor brake and stick forces are too high to maintain controlled flight for very long, worse there is a lot of confusion around what the problem actually is.
As it relates to comments on this thread you would not easily over come the stick forces involved and actually it is so un-natural that you would not feel comfortable doing so because unless you know what the issue is...but without knowing you would not want to remain airborne.
Good point to consider.The other element of discussion seems to centre on the Teleflex control cables which can be pinched but that is a focus for trained maintenance personal. I think one snag could be loose articles restricting at this point (I have a picture but cant upload its basically the point underneath the seat of the Cavalon where the control cable runs). That would seem a more likely snag than the control cable.
Results from a number of simulations with experienced pilots found that the combination of the overspeed warning horn
and underspeed stick shaker while in flight was an overly confusing contradictory set of messages for many pilots;
On the BRAKE/FLIGHT point. Rotor RPMs were not significantly affected but that would be an impression rather than an absolute recollection.
Ultimately the friction material and surface area are insignificant verse the aerodynamic forces at play.
63-51-00 Rotor Brake System
The rotor brake system consists of a brake pad mounted to a bracket which is hinged to the rotor head
bridge. With the pneumatic mode selector in BRAKE position the operation of the pneumatic trim
actuator is reversed so that increased pressure causes the actuator to push the rotor head up (or
level) and presses a brake pad against the rotor head disc. In order to increase brake pressure,
move the 4-way trim switch to aft. Note that this action will also push the control stick forward. At full brake
pressure the control stick will be maintained in its full forward position.
Fair enough, noted.The "Brake" position is really "Brake Armed". You have to take a second action to apply the brake. Rather than asking "Can you prerotate in brake mode?" the question should be "If a student engaged brake mode in flight, what would happen?". You do not fall out of the sky, nor does the stick go full forward with maximum force. Absolutely nothing happens. You would never know it was in brake mode if you never needed aft trim during your flight. Until you take the second step and build pressure use the trim switch, you wouldn't know the switch was in brake mode.
Results from a number of simulations with experienced pilots found that the combination of the overspeed warning horn
and underspeed stick shaker while in flight was an overly confusing contradictory set of messages for many pilots;
Thanks for your thoughts on this point, Phil. While you were descending in the pattern for a PAN landing, airspeed was sufficient to maintain flight RRPM.On the BRAKE/FLIGHT point. Rotor RPMs were not significantly affected but that would be an impression rather than an absolute recollection.
Ultimately the friction material and surface area are insignificant verse the aerodynamic forces at play.
63-51-00 Rotor Brake System
The rotor brake system consists of a brake pad mounted to a bracket which is hinged to the rotor head
bridge. With the pneumatic mode selector in BRAKE position the operation of the pneumatic trim
actuator is reversed so that increased pressure causes the actuator to push the rotor head up (or
level) and presses a brake pad against the rotor head disc. In order to increase brake pressure,
move the 4-way trim switch to aft. Note that this action will also push the control stick forward. At full brake
pressure the control stick will be maintained in its full forward position.
Kolibri;n1141765 said:Thanks for your thoughts on this point, Phil. While you were descending in the pattern for a PAN landing, airspeed was sufficient to maintain flight RRPM.
What I'm wondering here in relation to N198LT was if they had descended from 900 feet to about 150 feet and then found themselves over the trailer park.
Chris may have been naturally reluctant to then add power with such strong nose-down pitch. As you explained, "any small lapse or relaxation on the stick will see the aircraft bunt."
This trepidation could have allowed his airspeed to decrease, thus decaying RRPM and resulting in that plummet.
Regards,
Kolibri
Kolibri;n1141765 said:Thanks for your thoughts on this point, Phil. While you were descending in the pattern for a PAN landing, airspeed was sufficient to maintain flight RRPM.
What I'm wondering here in relation to N198LT was if they had descended from 900 feet to about 150 feet and then found themselves over the trailer park.
Chris may have been naturally reluctant to then add power with such strong nose-down pitch. As you explained, "any small lapse or relaxation on the stick will see the aircraft bunt."
This trepidation could have allowed his airspeed to decrease, thus decaying RRPM and resulting in that plummet.
Regards,
Kolibri
You're assuming normal cyclic control of the rotorhead, and the full availability of normal angle of attack range.The Cavalons I have flown would not plummet because of a lack of rotor rpm even in a prolonged vertical descent at zero indicated airspeed.
In an interview and a written statement, a witness stated he was driving southbound on the highway that paralleled the shoreline of the lake at the time of the accident. He said the gyrocopter was travelling northwest bound, about 300 feet above ground level "with very little airspeed" and appeared to be turning to the east. The gyrocopter then "entered an autorotation" then, when it reached "… about 150 feet the nose of the aircraft dropped immediately turning toward [the] east then back toward the north." The gyrocopter descended from view before a large fireball was seen.
Kolibri;n1141769 said:You're assuming normal cyclic control of the rotorhead, and the full availability of normal angle of attack range.
In this case of N198LT, I am not assuming that.
Rather, I'm postulating a full (or nearly so) forward rotor because of (air pressure reversed) aft trim applied in BRAKE mode.
Phil just described how extremely difficult it was to not bunt over, even while using both hands to pull back.
Fortunately for him and his student, they'd never climbed above pattern altitude, and they were able to descend at the rate forced upon them by the malfunction.
Had the student not switched to FLIGHT at 2-3 feet AGL over the runway, Phil may have difficulty flaring and could have wheelbarrowed in. (Phil, comments on that?)
Chris, however, seemed experience his trouble at 900-1000 feet, and not next to a runway.
He was probably trying to finesse airspeed, rrpm, and altitude into a manageable totality, while quickly identifying possible landing spots.
Not having full aft stick (while the rotor brake was simultaneously decaying rrpm) would have been a very tricky problem.
The "with very little airspeed" I read as Chris flying with reduced power at 300 AGL to avoid bunting over from the flattened rotor disk.
In my opinion, with what we so far know, he ran out of normal flight rrpm ("about 150 feet the nose of the aircraft dropped")
and no vertical descent was possible for him because of the very rigid forward rotor attitude.
_____
Phil, in your Calidus incident, after you'd input (reversed) aft trim and your disk was flattened, could you have hauled back on the stick
sufficiently for a vertical descent? I don't infer that possibility from your account.
Regards,
Kolibri
Kolibri;n1141765 said:Thanks for your thoughts on this point, Phil. While you were descending in the pattern for a PAN landing, airspeed was sufficient to maintain flight RRPM.
What I'm wondering here in relation to N198LT was if they had descended from 900 feet to about 150 feet and then found themselves over the trailer park.
Chris may have been naturally reluctant to then add power with such strong nose-down pitch. As you explained, "any small lapse or relaxation on the stick will see the aircraft bunt."
This trepidation could have allowed his airspeed to decrease, thus decaying RRPM and resulting in that plummet.
Regards,
Kolibri