If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
|
Thread Tools | Display Modes |
|
#1
|
|||
|
|||
Bronze Badge question
80) What is the approximate proper airspeed to use when flying between
thermals on a cross-country flight against a headwind? a) The best lift/drag speed increased by one-half the estimated wind velocity. b) The minimum sink speed increased by one-half the estimated wind velocity. c) The best lift/drag speed with no regard to wind velocity. The SAA safety site gives the correct answer as "A". I have alway heard that when flying between clouds you did not consider the wind in your calculations. Maybe the tricky part of this question is the word "Thermals". |
#2
|
|||
|
|||
Bronze Badge question
As you'll see in questions 199 & 200, inter-thermal speed is
independent of wind direction when on a XC flight. Headwind only impacts speed to fly when flying to a goal on the ground outside the moving reference frame of the airmass. You are correct and there is a mistake in the quiz answer. wrote: 80) What is the approximate proper airspeed to use when flying between thermals on a cross-country flight against a headwind? a) The best lift/drag speed increased by one-half the estimated wind velocity. b) The minimum sink speed increased by one-half the estimated wind velocity. c) The best lift/drag speed with no regard to wind velocity. The SAA safety site gives the correct answer as "A". I have alway heard that when flying between clouds you did not consider the wind in your calculations. Maybe the tricky part of this question is the word "Thermals". |
#3
|
|||
|
|||
Bronze Badge question
1/2 Wind velocity should be included.
A better answer though may be "speed to fly' plus 1/2 the wind velocity. |
#4
|
|||
|
|||
Bronze Badge question
There's not an answer with "McCready" in it anywhere?
The answer from an XC perspective is to fly the appropriate McCready speed in order optimize the total distance you can cover in your soaring day. Answer "A" means you arrive at the next thermal with the maximum possible altitude retained--not likely a goal of anything but the most conservative, short XC flight. wrote in message ups.com... 80) What is the approximate proper airspeed to use when flying between thermals on a cross-country flight against a headwind? a) The best lift/drag speed increased by one-half the estimated wind velocity. b) The minimum sink speed increased by one-half the estimated wind velocity. c) The best lift/drag speed with no regard to wind velocity. The SAA safety site gives the correct answer as "A". I have alway heard that when flying between clouds you did not consider the wind in your calculations. Maybe the tricky part of this question is the word "Thermals". |
#5
|
|||
|
|||
Bronze Badge question
The key is the phrase "cross-country", because it means that you're
trying to get somewhere. If you want to stay up the longest time, then answer c) would be the best one of the 3 given. But if you want to cover a course in the shortest time, then a) is the best answer. -John wrote: 80) What is the approximate proper airspeed to use when flying between thermals on a cross-country flight against a headwind? a) The best lift/drag speed increased by one-half the estimated wind velocity. b) The minimum sink speed increased by one-half the estimated wind velocity. c) The best lift/drag speed with no regard to wind velocity. The SAA safety site gives the correct answer as "A". I have alway heard that when flying between clouds you did not consider the wind in your calculations. Maybe the tricky part of this question is the word "Thermals". |
#6
|
|||
|
|||
Bronze Badge question
Looking forward to racing against you guys who fly faster into a
headwind while out on course :-) Any additional distance achieved by doing that will be given up drifting backwards in the next (longer) climb. For this reason MacCready speed to fly doesn't account for headwind only estimated strength of next thermal. Best avg XC speed will be achieved through answer c. John |
#7
|
|||
|
|||
Bronze Badge question
You're on, John. In identical aircraft, you fly best L/D, and I'll fly
best L/D plus half the headwind. According to a spreadsheet called Polar.zip that implements Reichmann's Best Speed equations, in an ASW-19 with a best L/D of 50 knots, the interthermal flying times and climbing times are as follows: 50 55 60 65 70 knots 5.92 5.38 4.93 4.55 4.23 minutes, interthermal glide 1.53 1.54 1.61 1.72 1.87 minutes, climbing As you can see, I'll beat you with any headwind at all. Incidentally, Speed to Fly for this case is 80 knots. -John John Cotter wrote: Looking forward to racing against you guys who fly faster into a headwind while out on course :-) Any additional distance achieved by doing that will be given up drifting backwards in the next (longer) climb. For this reason MacCready speed to fly doesn't account for headwind only estimated strength of next thermal. Best avg XC speed will be achieved through answer c. John |
#8
|
|||
|
|||
Bronze Badge question
.... Best avg XC speed
will be achieved through answer c. Ok, answer C says "The best lift/drag speed with no regard to wind velocity.". So, my best lift/drag speed is 50 knots and I'm flying into a 50 knot headwind at 50 indicated. And, I'm going ... where? "A" is the correct answer, IMHO. Answer "A", in the above example, would get you a ground speed of 25 knots (75 - 50)- you're not going to do much better than that. The question, though, is poorly worded. Tony V. |
#9
|
|||
|
|||
Bronze Badge question
Tony Verhulst wrote:
.... Best avg XC speed will be achieved through answer c. Ok, answer C says "The best lift/drag speed with no regard to wind velocity.". So, my best lift/drag speed is 50 knots and I'm flying into a 50 knot headwind at 50 indicated. And, I'm going ... where? "A" is the correct answer, IMHO. Answer "A", in the above example, would get you a ground speed of 25 knots (75 - 50)- you're not going to do much better than that. The question, though, is poorly worded. Tony V. Ignore the ground, and just focus on the airmass. To get the maximum distance in that airmass in a given time, you want to fly MacCready. To the extent the wind is blowing in the wrong direction, your destination on the ground will be further away in relation to the airmass. But to get to the destination, you still will want to make the maximum distance through the airmass. Flying faster than MacC will just reduce your distance through the airmass, and that will also reduce your distance toward your destination. However, this assumes that thermals are fixed with respect to the airmass. In fact, to stay in a thermal you have to keep moving upwind in relation to the airmass. This means that thermalling will give you some extra distance toward your goal. So you want to spend more time thermalling and less time cruising, which you get by increasing your speed somewhat. It seems counterintuitive that you want to spend more time thermalling when you have a headwind, but I believe that is the correct answer. When you are thermalling, a headwind tends to move you upwind in relation to the airmass. A headwind does not have the same effect when you are cruising. |
#10
|
|||
|
|||
Bronze Badge question
Greg Arnold wrote:
However, this assumes that thermals are fixed with respect to the airmass. In fact, to stay in a thermal you have to keep moving upwind in relation to the airmass. This means that thermalling will give you some extra distance toward your goal. So you want to spend more time thermalling and less time cruising, which you get by increasing your speed somewhat. How much slower than the airmass do you think the thermals are moving? I don't notice the wind determined by circling to be significantly different than the wind determined by cruising, according to my Cambridge 302. And also, why would you get blown out of a thermal? Since you are circling in it, shouldn't you drift at it's speed, instead of the wind speed? -- Change "netto" to "net" to email me directly Eric Greenwell Washington State USA |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
The United States Bronze Star Registry | Otis Willie | Military Aviation | 0 | September 20th 04 01:52 AM |
USA Bronze Badge test. | Thomas Knauff | Soaring | 9 | July 17th 04 03:13 PM |
PFC Lynch gets a Bronze Star? | Brian | Military Aviation | 77 | August 2nd 03 11:15 AM |