I Need Expert Help

[KenSandyEggo]

I will call Jim Vanek on Monday for his advice but would like to know what I did wrong here. I may have an idea, but it doesn't all fit together for me. When I ordered my rotorhead and new cheek-plates, I told his tech that I would have the cheek-plates leaning back 1.5 degrees from vertical. The SC head is not adjustable with fore and aft tilt, so the rotor-head angle has to be set by how the mounting holes in the upper cheek-plates are drilled.

I got the rotor-head mounted to the cheek-plates and the cheek-plates to the lower, vertical mast with the 1.5 degrees lean-back. However, when I placed my leveler on the rotor-ring, I was only reading around 10 degrees lean-back. This is in the most upright position with the cam adjuster. So I finally went to the most rearward position of the four positions to get my 19 degrees lean-back and -1 forward tilt. This left my cheek-plates leaning back 11 degrees. If I recall, this is what Jim told me the SC gyros have.....the mast leaning back 11 degrees. So I'm initially surmising that the cheek-plates were not drilled to my specs, but the 11 degrees back SC specs.

I did a hang-test with me and 5 gallons of fuel and got 5 degrees nose-down. However, my control-sticks are now about 6 inches forward of where they were at the grips. Instead of the stick pulling back to my belly, it only pulls back to about a vertical position. It goes the full arc forward, but I have to lean forward to get it there. The new cheek-plates and the old ones are the same length, as are all my control-rods.

Seeing as I had full movement on the stick, just repositioned forward from where it used to be, I went and did some fast taxis and attempted to lift off the runway. It was pretty quiet at the airport yesterday evening, so they let me play on the cross-runway, which is about 5,000' long. I made 4 runs back and forth. I spun up to over 200 rrpm and started slowly building up speed. I noticed that the stick wanted to stay all the way back and I had to push hard forward to move it. She just kept running on the ground and didn't seem to want to lift off. I added full power and she just mushed off the ground at a slow speed. I pushed the stick as forward as I could, and she picked up some speed, but only to about 40 m.p.h. max and kept mushing and wallowing. The rotor-speed never really built up to max flying speed either. It stayed below 300 every time.

I'll throw out my theory and then would like to hear from others. Obviously I was way behind the power curve, even with the stick full forward. I'm guessing that I have too much back-tilt of the cheek-plates and maybe SC did drill the cheek-plates correctly and I should have tried my original position. I must have done something incorrectly when I thought I was only getting 10 degrees rotor-head tilt-back, but the ship was level.

I can get someone to help me lean back the rotor system and I can turn the cam to go to my original 1.5 degree lean-back of the cheek-plates. This will bring the mast forward a total of 9.5 degrees from where I have it now. With my control-rods at the front of the mast, won't tilting the cheek-plates forward move my stick even more forward, or do I have the geometry in my head backwards? I believe that I have to get the cheek-plates untilted to a more forward position and my sticks adjusted properly.

I can't recall from my original build, but will I likely have to loosen my sticks from the cross-bar and reposition them once I have the correct rotor-head angle? Will I just be able to have my sticks bent back as some others have done? If I'm showing 19 degrees lean-back, why won't she fly? Thanks in advance for any input.

[Harry_S.]

WOW Ken...you gave a lot of stuff there. I'm not thinking like an engineer now, but as an RAF driver.

I may be wrong here but...I think you went from hole position 3 to position 1?!
If this assumption is correct, if it were me, I would move from position 1 to 2, and go for a spin-up. If it improves...I would change to pos. 3 and try that. If that improves even more...I would go to 4.

Off the top of my head I would think you have way too much rotor tilt to even fly?!

That's just my opinion Ken.

Anyway, I hope someone comes on here and helps you out.


.

[Mayfield]

Hi Ken,

I'm not totally sure, but it sounds like you need to reclock your stick.

Remember when you first built the aircraft. You rigged the head and stick where you wanted it and then drilled the holes in the steel cross tube at the base of the stick and in the steel cross tube at your rear control fork.

Then you inserted the bolts and clamped every thing up.

If that is the problem you'll just need a foot or so of 1/2 inch (I think) .065 4130.

R/S

Jim

[KenSandyEggo]

Yes Harry, I originally was in 3 with the old rotor-head, but I wanted to be in 4 with the new rotor head. Presently I'm in 1.

[KenSandyEggo]

O.K. Jim, thanks for refreshing my memory. First I need to get her to fly correctly and then redo the sticks on a new cross-bar. I remember setting the stick a few inches forward from my chest (now my belly) in the full aft position. I think that I will take Harry's advice and move the cheek-plates forward in increments until I have the right configuration. Actually, I'll wait to speak to Jim to make sure my upper cheek-plate holes were configured for a 1.5 degree lean-back from the vertical, lower mast.

[C. Beaty]

Ken, all those angles are confusing.

With the rotorhead centered between stops, the machine with you on board and half a tank of gas should hang 0-3º nosedown measured at the rotorhead.

The easiest way of doing this is to cut a pair of wooden wedges from a 2 x 4 and lightly tap them between torque bar and stops, locking the rotorhead in neutral. The stick, if the pushrods are properly adjusted, will be at the midpoint of its travel.

It makes no difference whether the rotorblades are installed or not.

[rehler]

Ken,

As a starting point I suggest you:

1. Set the mast slope where you need it for balance

2. With the gyro (keel) level check the angle of the totor head when exactly centered fore-aft. It should be close to 9 degrees rear low. If not then your check plate holes are probably not correct and need to be redrilled

3. I would also ask someone with a Sparrowhawk using Sport Rotor blades to do the same check on their gyro and compare it. Is their rotorhead at 9 degrees, or something else.

I would do this checking before you do any stick changes.