We often call a glider flight a "sled ride" if there's no lift found, because it's a downhill ride all the way from release to touchdown. But since this was the last Saturday before Christmas, let's call it a sleigh ride. And this day of soaring involved some frost and ice!
The forecast was for 450 or so fpm of lift up to 5000 or 6000 feet, but there were hints of an inversion which could defeat the lift. I was determined to fly regardless of lift, because I had not been in the air for about a month. It was very clear due to recent rain, and had been cold overnight. There was frost on the wings of the Grob and the PW5, which I have never seen at Hemet before. T commented on my blog post about the water collecting in the PW5's spoiler boxes and horizontal stabilizer, so we checked the boxes and were surprised to find ice. And not just a little skin of frost - a hard layer of ice a good quarter inch thick and about a foot long! It took quite a bit of work to break it up and pull it out so it would not interfere with the spoiler arms. Then we checked the drain holes in the boxes... one on each side was plugged with dirt, which explains why the water accumulated. Something else to inspect and maintain. There's something to learn every day on every flight!
I planned to take a high tow because I expected there to be no lift. The ground temperature was above the trigger temp, but if the air was too stable that wouldn't matter. On the way up, I decided to use the Outside Air Temperature (OAT) display as I have mentioned before. On the ground, it registered 25C, or 77F, which is way more than the 63F thermometer in the shade on the shed was indicating. So the dark runway must have been heating the air just at ground level. I didn't watch the OAT right after takeoff, but at about 400'-500' AGL it was already down to 16C. It kept going down fairly rapidly as we climbed, and then it stuck at 9C at about 1500'-2000' AGL and stayed there all the way up to 3800' AGL where I released. So there was a definite inversion layer - a big thick layer of 9C air that was not getting any cooler! I knew that I would not find any lift in that zone.
The flight was nice anyway, even if was a sleigh ride. The visibility was incredible! Usually we have some haze or smog, but this day was crystal clear. I could see quite a ways out into the ocean, and the sun was lighting up the water like gold. The mountains and all the lakes were gorgeous. This is why I fly.
I played around a bit with airspeed and sink rate, trying to get the minimum possible sink. Maybe sometime I'll take notes on them and see how they compare with the published polar.
I did find a few bumps at 1200'-1500' AGL, below that inversion layer. I circled a few times and found nothing better than zero sink. All too soon it was time to come in and land. My flight time from 3800' AGL was 26 minutes, or 146 feet per minute - right at the theoretical minimum sink rate for the PW5.
A reminder for the new year: the Air Safety Foundation recommends that your first flight of the year be with an instructor. Not a bad idea!
Thursday, December 27, 2007
Thursday, December 13, 2007
Blown out
It seemed like everything was conspiring to prevent me from getting in a flight last weekend. I had planned to give a friend a ride on Sunday. But the weather is always iffy this time of year, and a series of cold fronts have been moving through. Saturday was rainy (and I was busy anyway). Sometimes the day after a storm is good soaring weather, but this day still had substantial wind in the forecast, so I waved the friend off and decided to go out myself and see if it was flyable. Hemet is often a calm place when there's wind all around... and the thermal forecast looked usable. Really cold air aloft!
Due to other morning commitments, I arrived at the field about 12:30. A few people were flying, a pilot reported some wave lift earlier in the day... so I decided to go ahead. Delay #1 came in the form of rainwater in the PW5's spoiler boxes. I'd never paid much attention to it before, but we checked and found at least an inch. Tipping the glider onto each wing drains the water out of holes, but it takes a while. It collects in the horizontal stabilizer, too. So, to you other PW5 guys in the club: plan on about 15-20 minutes of extra prep time after a rain!
Delay #2 came in the form of an unfavorable wind direction. This is the first time I have ever seen the tow operation reverse directions at HMT. Should be no big deal, right? Except that now the starting end of the runway is a LONG way from the tiedowns. So I need the help of club members to push out (I can push the PW5 myself to the close end of the runway.)
Delay #3 came in the form of more complicated operations using the reversed runway. I won't go into details, but it involves more work to keep the runway clear for landings and for tow plane operations, and fewer good landing options.
There were other little things along the way, minor equipment issues. I finally was lined up on the runway, next in line for takeoff at about 3:30, a little late in the day especially in winter. But as I always tell people, I'd rather take a sled ride than stay on the ground - gotta stay current and proficient! And the view of the freshly snowed mountains promised to be spectacular.
And then the wind picked up! For several minutes it was at least 15-20 knots, and was shifting direction about 30 degrees. The PW5 really does not do well with much crosswind, and it seemed to me this could be the start of and end-of-day wind increase. If I took off, and then the wind got stronger while I was up... well, as I mentioned, the landing options are a bit more restricted when operating the other way on this airport. So I cancelled and pushed off.
Maybe next weekend. Between the iffy weather and the extra stuff that occupies weekends during the holiday season, it may be another couple of weeks.
Due to other morning commitments, I arrived at the field about 12:30. A few people were flying, a pilot reported some wave lift earlier in the day... so I decided to go ahead. Delay #1 came in the form of rainwater in the PW5's spoiler boxes. I'd never paid much attention to it before, but we checked and found at least an inch. Tipping the glider onto each wing drains the water out of holes, but it takes a while. It collects in the horizontal stabilizer, too. So, to you other PW5 guys in the club: plan on about 15-20 minutes of extra prep time after a rain!
Delay #2 came in the form of an unfavorable wind direction. This is the first time I have ever seen the tow operation reverse directions at HMT. Should be no big deal, right? Except that now the starting end of the runway is a LONG way from the tiedowns. So I need the help of club members to push out (I can push the PW5 myself to the close end of the runway.)
Delay #3 came in the form of more complicated operations using the reversed runway. I won't go into details, but it involves more work to keep the runway clear for landings and for tow plane operations, and fewer good landing options.
There were other little things along the way, minor equipment issues. I finally was lined up on the runway, next in line for takeoff at about 3:30, a little late in the day especially in winter. But as I always tell people, I'd rather take a sled ride than stay on the ground - gotta stay current and proficient! And the view of the freshly snowed mountains promised to be spectacular.
And then the wind picked up! For several minutes it was at least 15-20 knots, and was shifting direction about 30 degrees. The PW5 really does not do well with much crosswind, and it seemed to me this could be the start of and end-of-day wind increase. If I took off, and then the wind got stronger while I was up... well, as I mentioned, the landing options are a bit more restricted when operating the other way on this airport. So I cancelled and pushed off.
Maybe next weekend. Between the iffy weather and the extra stuff that occupies weekends during the holiday season, it may be another couple of weeks.
Saturday, November 17, 2007
Final approaches
Some of us were talking about landings today, and one pilot mentioned something that I had just thought about a few days ago. I had been working with the polar (L/D curve) for the Grob 103, calculating appropriate speeds for flying it through sink, when this occurred to me. Each glider has a "normal" approach speed (assuming no wind). For the Blanik L13, it's 50 knots, for the Grob 103, it's 55. Each glider also has a "best L/D" speed (best glide speed). For the Blanik, it's 46 kts, for the Grob it's 60. So what?
- For the Blanik, the approach speed is faster than best L/D. If you pick up speed on final, your drag INcreases and you will sink faster, but then after the flare you will float farther in ground effect. If you slow down on final (down as far as best L/D), your drag DEcreases and you will glide farther until the flare.
- For the Grob, the approach speed is slower than best L/D. If you pick up speed on final (up as far as best L/D), your drag DEcreases and you will glide farther, and then after the flare you will float farther in ground effect. If you slow down on final, your drag INncreases and you will sink faster until the flare.
If this is not clear to you, get out the polar for your glider(s) and see where the "normal" approach speed lies in relation to the best L/D speed. If you are not clear on how the Angle of Attack affects the sink rate in a glide, read the excellent discussions in the book Stick and Rudder. It may seem counterintuitive, but in some aircraft (such as the Grob), pointing your nose down (up to best L/D speed) will make you land farther down the field. If you want to get down faster (ignoring the spoilers), pointing your nose up will cause the glider to "mush" and sink faster.
I'm not yet sure what to do with this information. The airbrakes surely have more effect on the sink rate than the speed does, and we try to keep the airspeed dead-on the recommended value (plus a wind adjustment). It does tell me that it's doubly important to not let a glider such as the Grob gain more speed on final, because both the glide and the float will be longer.
- I'm not an instructor. Please make sure to discuss this topic with your CFI-G! I'm interested in readers' (especially instructors') comments on this.
- I can't say enough about Stick and Rudder. Although it was written for power planes a long time ago, it is still a tremendous resource for learning about how an aircraft really works in the air. It is non-technical - no formulas, charts, or math, but you can tell that the author knows the technical background and he does an excellent job of explaining things in plain English. It really explains why so many things are counterintuitive in flying - and why it is so important to learn those "backward" concepts thoroughly, to overcome our instincts and ground-sense. Get yourself a copy and read it carefully. Then read it again!
Copilot
Today I shared a flight in the Grob 103 with L. Now that the days and therefore the lift periods are shorter, it makes more sense to do a couple of 2-person flights in the middle of the afternoon than to try for several individual flights and have some people miss the soaring times. Though it does mean that we can only log part of the time as PIC, the part when we are actually at the controls. This time L did the takeoff and all the soaring, because he was not happy with his previous takeoff and because he doesn't fly as often as I do. I did the landing and flew from the rear seat because that's what I want to work on in preparing for my Commercial rating. (I'll start writing about the Commercial soon.)
The forecast was for just about 250 fpm of lift, and the day just reached the calculated trigger temperature. There was a lot of haze in the air, clearly showing an inversion. The previous flight reported no lift, so we didn't have high hopes. We let off at 3100' AGL, above the inversion, and we never got that high again. I worked hard at spotting sources of lift and keeping a general lookout. Twice I did find crows nearby, higher than us, and we were able to find some lift under them. I also spotted swallows very close - we nearly hit one - and they can be helpful because they are often hunting bugs that have been brought up by a thermal.
We found some weak lift and worked it extensively. All we got out of it was about 300 feet, and combined with some zero sink, we accomplished a 42 minute flight. I think for a while we were at the junction of two air masses, because to the west the ground was far less visible due to brown haze, and to the east it was much clearer. But there was no obvious shear line lift.
The Grob's wheel brake is kind of weak (we'll be working on it next week) so we wanted to have plenty of space to land in. So another pilot recommended I use the little dirt strip that the tow plane lands in, which I've never done before. It worked out fine... I could perhaps have floated a little further (eased the stick back to a higher angle of attack and landed with less speed) but it landed smoothly and straight. Actually, landing in that spot helped avoid sun glare which can be a problem in the late afternoon. I get to log a whopping 5 minutes of PIC time.
Flying like this with another pilot is fun. We can share ideas and learn from each other, but it's more relaxed than flying with an instructor. And we split the tow fee.
The forecast was for just about 250 fpm of lift, and the day just reached the calculated trigger temperature. There was a lot of haze in the air, clearly showing an inversion. The previous flight reported no lift, so we didn't have high hopes. We let off at 3100' AGL, above the inversion, and we never got that high again. I worked hard at spotting sources of lift and keeping a general lookout. Twice I did find crows nearby, higher than us, and we were able to find some lift under them. I also spotted swallows very close - we nearly hit one - and they can be helpful because they are often hunting bugs that have been brought up by a thermal.
We found some weak lift and worked it extensively. All we got out of it was about 300 feet, and combined with some zero sink, we accomplished a 42 minute flight. I think for a while we were at the junction of two air masses, because to the west the ground was far less visible due to brown haze, and to the east it was much clearer. But there was no obvious shear line lift.
The Grob's wheel brake is kind of weak (we'll be working on it next week) so we wanted to have plenty of space to land in. So another pilot recommended I use the little dirt strip that the tow plane lands in, which I've never done before. It worked out fine... I could perhaps have floated a little further (eased the stick back to a higher angle of attack and landed with less speed) but it landed smoothly and straight. Actually, landing in that spot helped avoid sun glare which can be a problem in the late afternoon. I get to log a whopping 5 minutes of PIC time.
Flying like this with another pilot is fun. We can share ideas and learn from each other, but it's more relaxed than flying with an instructor. And we split the tow fee.
Saturday, November 03, 2007
Test flight
The last couple of weekends we were unable to fly due to the high winds and some restrictions at the airport due to heavy firefighting activity. So I was eager to fly any of the aircraft, for any length of time. My preference was to fly the Grob 103 because I plan to take some passengers up in it in a couple of weeks.
So today I took a short flight in the Grob to check it out after a repair. Although an A&P mechanic actually approves the return to service, our club practice is to have a private pilot take the glider on a test flight before it is flown solo by a student pilot or by an instructor and student. So I planned to take a 2000' tow in the morning (before lift started working) and then land. I actually let off at 1800' AGL because there seemed to be some lift. I never found anything useful, and landed with an 11-minute flight.
I had to leave fairly early in the afternoon because of family plans in the evening. The way the tows and the glider scheduling worked out, I didn't get a chance to fly later. Others seemed to be staying up, reporting 2 to 5 knots of lift.
I now have 77.5 total hours logged.
So today I took a short flight in the Grob to check it out after a repair. Although an A&P mechanic actually approves the return to service, our club practice is to have a private pilot take the glider on a test flight before it is flown solo by a student pilot or by an instructor and student. So I planned to take a 2000' tow in the morning (before lift started working) and then land. I actually let off at 1800' AGL because there seemed to be some lift. I never found anything useful, and landed with an 11-minute flight.
I had to leave fairly early in the afternoon because of family plans in the evening. The way the tows and the glider scheduling worked out, I didn't get a chance to fly later. Others seemed to be staying up, reporting 2 to 5 knots of lift.
I now have 77.5 total hours logged.
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