Sunday, May 18, 2008

A Weird Flight

This should have been a great day. I'm still trying to figure out whether I was just off, or just unlucky, or whether there was something wrong with the aircraft.

We're in a heat wave, but the temperatures aloft were good, so the thermal forecast looked great. I forecast a thermal index of -3 at 5000' MSL, and thermals to 10,000'. The NWS thermal forecast was even more optimistic: 1100 feet/minute to over 14,000'. As I was driving in, I could see CU popping over the San Bernadino mountains to the north at 10:30. They were popping all around the Hemet valley, and over San Jacinto by 11:30, though small. I planned my flight as if I were going to the top - took all my cross-country gear. This would be the first time I used the EDS oxygen system that we just installed. I swapped my O2 tank for the club's tank.

It was hot. Forecast was 101F. When I pushed out it was 108. "But it's a dry heat." That's really true... 108 at Hemet feels like 95 to 100 at home. I make sure to drink a lot of water before and during flights. I had to spend some extra time squatting and bending working on some issues in the PW5 cockpit, but even so, the heat was not unbearable.

The audio vario on the flight computer was acting up. The volume control failed, as it has done before, and when that happens it squawks at full volume. I taped some cardboard over the speaker to make it tolerable. You can't turn it off separately... the computer, vario, and radio are all on one master switch.

The Volkslogger was gone - I assume it was packed up with the Grob for next weekend's campout. So I used my stand-alone GPS unit, and made sure to keep it out of the sun. This was one of the few times I had no problems with it starting up or accidentally shutting off.

Takeoff was the first weird event. I had a couple of equipment problems getting set to take off... just annoying stuff with belts and hoses. I knew that the density altitude would be high, what with the 108F heat. AWOS's altimeter setting and DA were missing, so I just assumed it would be high, and was not surprised that the tow plane consumed most of the runway before lifting off. But I was very surprised to find that the PW5 was still on the ground when the towplane took off! I eventually lifted off, but was way below the towplane. I glanced at the spoiler handle - it was forward. (I didn't tug on it to see if it was locked.) I've had one or two tows where the plane took a very low path, but that was not the case - he seemed to be climbing OK but I wasn't. I felt like I was going slow, likely to stall (unlikely on tow, and the ASI showed 50 to 55 knots), so I was reluctant to nose up too much. I considered aborting, and kept my hand near the release just in case. I think we were up to 700 or 800 feet before I was in "high position" where I belonged. Weird!

I let off a little below 3000' AGL after passing through several spots of 10kt lift. After losing some altitude and then finding a thermal, I gained 1000' and was back up to about 4700' MSL. But I was having to work for it. My plan had been to thermal up high enough to try the southern hills to get me to San Jac, so I headed that way. I found nothing but sink as I headed south, so I stayed over the little canyon where I started. I found ragged little thermals. I used the thermal helper on SeeYou to analyze where the best parts were, but never felt really centered in them.

Weird item #2: I seemed to be flying faster in thermals than I wanted, often creeping up to 55 or 60 kts. Once when flying straight, I went to pull the trim back to help keep me slowed down, and found that I had already trimmed back to #3 (I know it was at 5 or 6 on takeoff).

Weird item #3: I was hearing some wind noise from behind me on the right side, as if the canopy were ajar - and this was over the extra-loud speaker. I made sure no hoses or anything were stuck in the opening.

Weird item #4: I seemed to not be flying as coordinated as usual. When circling to the right in lift, my yaw string was usually off to the right. I was always having to take off some right pressure. That's weird because I had noticed over the last few flights that I was coordinating really well, effortlessly.

I began to think that there was something sticking out or open causing drag and noise (#3), maybe on the right side (#4), or somehow causing me to nose down (#1 and 2).

The sink was outvoting the lift, so I had to get closer and closer to the airport. I could see some other gliders thermaling over the Three Sisters (which is not far from the airport), but even that was too far for me. I spent a bunch of time at about 1200' AGL trying to work some pitiful lift, and eventually had to give up.

Of course, I found zero sink on the downwind leg, keeping me fairly high. My speed kept creeping up to 60-62 knots (no-wind pattern speed is 51), kind of reinforcing my feeling that the glider wanted to fly nose-down. I had a light crosswind on landing, and landed very well... but after just 32 minutes. Aargh! Very frustrating having such a short flight with the mountains beckoning! One other club pilot found very good lift (in the Blanik), and just came back when he ran out of water early. Another in the Blanik got beat down by sink and had an even shorter flight than I did.

I have to admit that I felt kind of "off" for the whole flight. Not enough to cancel takeoff, not enough to head back to the airport voluntarily. Partly the heat, partly the minor equipment problems, partly the annoyingly loud vario (couldn't hear the radio), partly feeling crowded by my stuff in the cockpit...

Back on the ground, I checked the stabilizer and it was latched properly and not at a funny angle. I looked under and around the wing roots, and found no tape gaps or foreign objects that would cause drag or noise. The PW5 had recently been assembled, but another pilot did a complete inspection, and I did a partial and had not noticed any problems.

When I was putting everything away, I noticed that my oxygen hose had pulled out of the socket on the EDS machine. And where it is placed, I can't see it due to the junk pocket. I probably would have noticed had I needed it, because I tested the system on the ground and the fresh, "cool" sensation of each EDS pulse was very noticeable.

So...
  • Is the PW5 just much more affected by high density altitude than I've ever noticed before, and I needed to help it take off?
  • Is there something open or out of alignment, causing drag or nose-down attitude?
  • Was I just "off" due to the heat, and eating lunch right before flying?

Maybe something with the rudder... maybe it's misaligned slightly to the right, accounting for #4, and adding drag? I noticed during Positive Control Check that my partner was applying more pressure than I liked, so maybe I missed that it's staying right... I seemed to have more right rudder than I needed, but then I go by the yaw string action, and I never paid attention to whether my feet were not balanced. I did not notice any undue yaw during takeoff or straight flight or landing.

Weird.

4 comments:

smiss said...

Hey Roger - as I was reading your latest post about the weird flight, I wondered if there were ballast issues (ie if someone light had loaded ballast in the ship that was missed). I can't recall if/where the PW5 has ballast, but it sounds like something wasn't right.

Roger Worden said...

I considered that, but I have never known anyone to use ballast in that ship. I would have noticed any behind/under the seat back, as I put the battery and my landout kit in. There's no room under the seat pad. And I think the ship was assembled and not flown the day before.

Two other ideas:

1. I've always placed the seat back in the most forward position because that's most comfortable. The manual requires that very light pilots (much lighter than me) place the seat there, so obviously its placement is enough to affect CG. So I should probably move it back a notch or two, though that may make it a stretch to reach the panel. I'll have to try it on the ground.

2. The manual says to place the trim at #1 or 2 (rearward) for very light pilots, and 5 or 6 for heavy. I've always had it at 5 or 6 just because I guess that's what I was told early on. So I should probably start with it at 3 or 4.

Maybe slightly forward GC, forward trim, and high density altitude all combined to make it feel nose-heavy.

One lesson learned is to go back and read the manual for each model of glider from time to time - there are things in there that we miss, or don't fully understand until our experience makes us receptive to them.

Roger Worden said...

> manual says to place the trim at #1 or 2

(for takeoff)

Roger Worden said...

Talked with another pilot who flew that hot day. I think the key to the low takeoff was the high density altitude combined with the trim setting. By having the trim back at the midpoint or further, the higher Angle of Attack was causing it to "mush". Trimming more forward (I got it backward in my previous comment) as I did last week causes the AoA to be much lower, reducing drag and allowing my speed to pick up faster, gaining lift without mushing. We'll see how this works next time I have high density altitude.