Pitch trim wanted for a gyro

[Rampant Rat]

I urgently need an electro-pneumatic pitch trim actuator for my recently modified Sycamore. I fitted a new rotor head with a hydraulic pre-rotator and now have a problem with the amount of effort to hold the stick back. Powers that be say I need to fit a trim to relax the pressure on the stick and that it will be needed for different flying conditions - 1 up or 2. I didn't have this problem with the old Sycamore before but it now needs 2 hands on the stick to hold it level when 1 up. can anyone shed some light on this and does anyone have a spare/new/used trim actuator for sale?

[PieterKotze]

RR,

The best man for your problem is Eric Torr. He has successfully fitted several trims on Xenon's, Magni's etc, so I believe he is your man. Contact him on 083 335 4622 or gyrosa@corpdial.co.za for help.

Pieter

[mak]

Rampant Rat

Just for interest, why did you decide to go the hydraulic pre-rotator route. What do you gain in pre-rotation and what is the additional weight on your gyro?

[AVR]

Greetings Rampant Rat.

Is your max pre-rotation speed the same when engine oil is cold and engine oil is hot?

Regards
Ashley

[mak]

Rampant Rat

I am not a technical guy, but if the installation of a pre-rotator change your flying characteristics, it hasn't been done right. Also if it change your flying characteristics and the "powers that be" tells you that it is normal and you now need a pitch trim in order to hold the stick, then hopefully the "powers that be" will then also know that under these conditions you now need a mod approval for this installation. Did the "powers that be" do a mod approval for this?

[Rampant Rat]

It's difficult to answer some of the questions without apportioning blame for the change in flight characteristics but I'll do my best...
The decision to add a few kilo's to my already heavy and old Sycamore was out of concern about reliability. The Gyro will be flown in future in one of the most remote and inhospitable regions on earth, in NW Botswana. Being on the ground with a failed friction pre-rotator wouldn't be fun, and I am told that the flexible pre-rotator cable has a habit of breaking when you need it most. I have to say, after some adjustments and new belts I had the old pre-rotator running up faster than most modern systems, before I decided to have the mod done. As the saying goes, if it ain't broken, dont f%#K with it. Good advice. I estimate the additional weight after removing the perfectly good redundant equipment to be about an extra 5 Kilograms. Add to that the new MGL Oddysey wiring and instruments, leather seats, and a post Xmas stomach gain of the PIC and you have an extra 15 Kilograms that wasn't there before. But it's a Sycamore, and looks aren't everything....
The mod is approved I am assured, and it has been done by a reputable AMO with extensive Sycamore experience. But I can't vouch for that, the paperwork after the mod is spilling out slower than the lengthy time it has taken to get it to test flight stage.
I haven't flown the Gyro myself yet, but am told by the pilot who did, that the stick is heavy towards the back and 2 hands are needed to pull back on landing. I don't have an official explanation yet but I've been told that the trim will take the pressure off the stick. It would be the normal thing to ask the same AMO to do the Trim installation but I am aware that they are unable to accept any more projects because of their already overflowing bucket of work. Hence my message asking for good advice from the Gyro community.
I haven't yet been able to test the hydraulic pre-rotator myself under hot and cold conditions to see whether there is a difference in pre-rotation speeds with cold or hot oil, but my understanding of hydraulics is that pressure is not dependent on viscosity or temperature, but flow will be easier with hot oil. If the hydraulic pump is governed by speed, then it looks like a hot start may be marginally slower at the same motor RPM. If the hydraulic pump is pressure regulated, then there should be zero difference in rotor speeds, hot or cold at the same motor RPM. I believe that the hydraulic pump is pressure regulated in this particular modification.
I won't be baited to reveal the AMO, some Gyronuts have probably already started pointing fingers without really knowing the facts. My intention is to get good advice from you all and find a solution to the stick problem. I had a dream last night that I broke the stick off on a short landing and had to climb over to the back seat before taking control again. It could happen couldn't it?

[weedy]

HI,

As an ex Sycamore owner / pilot let me say what i know.
The standard Sycamore has two trim springs which are ground adjustible, so you should be able to trim out the gyro for a certain weight and speed, e.g. one up at 80mph. From there stick forces should not be excessive.
Further more all the ones I looked at also had an electric trim for making inflight adjustment effective over 10-15mph range.

Hope this helps a bit.

[Rampant Rat]

Thanks Weedy,
I know about these adjustable trim springs. Mine are adjusted almost fully up which gives assistance for backward movement on the stick. Does a small amount of adjustment on these springs make much difference?

[mak]

Rampant Rat

I am sure you realize yourself that this installation has been done incorrectly and I advice you to take it back to the AMO to fix it and quickly before it kills someone. Surely you can't think that it is right to fix an obvious life threatening problem with another add on. What happens the day that your trim fails due to an electrical failure or whatever reason. Would you then be able to control the plane.
Firstly I think you need to insist on seeing the "Mod Approval" and if no luck at the AMO then contact CAA and see if they have anything on record. If the AMO can't produce the Mod Approval the chances are good that they don't have a Mod Approval, why else can't they produce it immediately. Just pull it out of the file and give you a copy.
Don't you think it would have been easier and lighter just to have carried a spare pre-rotator cable or install a second/backup cable.

[Learjet]

wise words mak

[Wagtail]

I have been made aware of this posting and I have been asked to help so please, here are a few more points to this. This Mod was not done by the AMO or myself. I specifically informed the owner way back that we will not have time to actually perform the job. He saw the advantages of the hydraulics and after discussion I agreed to sell him all the parts and verbally advise him on the installation. With the leather seats and new Instrument panel the gyro 's Weight and balance is now 3 kg's more.
The Mod application, blanket approval and letter from CAA is on file, that is the stuff I sorted for him after hours in my private time.
The story about the trim is rather alarming to me as well. I have not even flown the machine myself so I cannot comment, what I did see was that the two trim springs were the wrong way around, instead of pulling the head back, they actually pulled the head forward. Last weekend I was about to test fly the specific gyro with the intention of adjusting the rotor balance and setting the pitch trim. I got as far as changing the trim spring position and ground runs.
I totally agree with what MAK said about the danger in trusting springs or cables to control a rotor. Any rotor system must be such that in the event of trim failing either way, ( complete cable break, or complete runaway trim), the stick and rotor head must still be controllable with moderate force. This particular point was one of the iterations which held up the final rotor head layout for a few rounds in the early years of the 33 and 36 ft rotor development.
I trust that after I got my hands on this gyro this coming weekend Rampant will be satisfied. There is always an advantage with the electric trim, but it is not absolutely necessary.

Regards

[Rampant Rat]

And a few more points that should be noted by our wise Forum...
I didn't say the mods were done by the AMO - I clearly said quote "I fitted a new rotor head with hydraulic pre-rotator"
I also said that the "The mod is approved I am assured, and it has been done by a reputable AMO with extensive Sycamore experience"
If some of you read anything else between the lines, well that's how it seems to be on this forum.
I fitted the rotor head and hydraulic system at Wagtail, under advice and verbal instructions from Johan, who I have great respect for.Understandably he has limited resources and a high work load. The fact that 10 months after starting the mod the aircraft is still sitting in the hangar was what prompted me to ask the wise members of this forum for assistance to identify the reason for the stick pressure and if anyone could shed some light on the issue. Nothing more.
I have PM'd Johan, and thanked him for his characteristic helpful desire to "get his hands on this gyro this coming weekend" and sort it once and for all.

[Wagtail]

Thanks Rampant. It will look strange that we are communicating on a public forum but I am not able to log into email till the weekend. Just before I left for the survey I got a gap to perform the actual test flight. Good news, if you are here on Saturday we can go and fly. After two adjustments the trim is now hands off at around 80 - 90 mph. One of the guys will collect two new springs before Saturday and that will give us hands off around 65-70 two up.
Regards

[mak]

Thanks for helping out Johan

[Rampant Rat]

You see! Us Gyro mense are a strange bunch, most of the time we do things differently, but we always find a friendly solution to our problems. Thanks Johan, see you Saturday