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 |
#21
|
|||
|
|||
Help calculating Speed To Fly for headwind and tailwind
On Jun 1, 2:01*pm, Andy wrote:
On Jun 1, 9:52*am, John Cochrane wrote: That's a poor solution. A sticky knob that won't let you go below max range would be better. If it shows Mc 0 but it's really set at (say) Mc 2 because you're in a howling headwind, you need to know to cruise at Mc 2 and not to take any 1.9 kt thermals. If the indicator shows Mc 0 you don't know that Agree, but he seemed very sure that he had been told by his instrument designer that MC zero would alway yield max range glide since the computer knew the wind and would take account of it. Maybe I should ask Dave directly since the SN10 was the instrument in question. Andy Say what ??? No. No. No. No. (Did you hear me ?) NO. When flying into a headwind: Set MC 0 a note altitude surplus or deficit. As you increase MC, the deficit will decrease, reach a minimum, then increase again. The SN10 takes into account the effect of wind on each leg in future. That affects the average speed per leg, the altitude required per leg, and the surplus or deficit. All this is calculated at whatever MC setting you input. OK ? See ya, Dave "YO electric" |
#22
|
|||
|
|||
Help calculating Speed To Fly for headwind and tailwind
On Jun 1, 2:01*pm, John Cochrane
wrote: Agree, but he seemed very sure that he had been told by his instrument designer that MC zero would alway yield max range glide since the computer knew the wind and would take account of it. Maybe I should ask Dave directly since the SN10 was the instrument in question. Andy I pity our poor instrument designers. If they do nothing, mad pilots will write in "something's wrong with your instrument, as I lower Mc setting it shows me a worse glide angle!" If they make Mc=0 always the glide extending setting, mad pilots write in with "something's wrong, I select Mc 0 and it's telling me to fly 70 knots." If they set a sticky knob that won't go below the glide-maximizing Mc value, mad pilots will write with "something's wrong, I can't lower the Mc setting." John Cochrane While I am not arguing against the theory behind MC settings I would like to add couple of points which I am sure most of you are aware anyway: 1 - Using lower than calculated MC setting will hurt your speed much less than taking a wrong turn or wrong line, so don't get too anal about it. 2 - The theory does not take into account the terrain ahead, ground clearance, the probability to find another good thermal, the risk of getting out of glide of landable strips, the significant increased risk of landout, and your comfort level when getting low which will often translate (for most of us) in more time spending circling in weak lift and even unecessary deviations. For what it worth, my MC setting is usually between 0-3, regardless of wind. Ramy |
#23
|
|||
|
|||
Help calculating Speed To Fly for headwind and tailwind
On Jun 1, 3:23*pm, Dave Nadler wrote:
On Jun 1, 2:01*pm, Andy wrote: On Jun 1, 9:52*am, John Cochrane wrote: That's a poor solution. A sticky knob that won't let you go below max range would be better. If it shows Mc 0 but it's really set at (say) Mc 2 because you're in a howling headwind, you need to know to cruise at Mc 2 and not to take any 1.9 kt thermals. If the indicator shows Mc 0 you don't know that Agree, but he seemed very sure that he had been told by his instrument designer that MC zero would alway yield max range glide since the computer knew the wind and would take account of it. Maybe I should ask Dave directly since the SN10 was the instrument in question. Andy Say what ??? No. No. No. No. (Did you hear me ?) NO. When flying into a headwind: Set MC 0 a note altitude surplus or deficit. As you increase MC, the deficit will decrease, reach a minimum, then increase again. The SN10 takes into account the effect of wind on each leg in future. That affects the average speed per leg, the altitude required per leg, and the surplus or deficit. All this is calculated at whatever MC setting you input. OK ? See ya, Dave "YO electric" Dave - you made me curious. Does that mean if you are abeam of the home airport with a decent distance to run to a downwind turnpoint and back to the finish that the SN-10 will calculate altitude margin based on a single McCready setting for the entire way home or separate McCready solutions for each leg - and if so how does the pilot input separate values for each leg? I think the finish height maximizing solution to get you home could easily be, say, Mc = -2 for the downwind leg and Mc = +2 for the upwind leg. If the computer looks for a single McCready value as the solution from wherever you are it might not find a solution that gets you home. If the SN-10 does calculate separate solutions for each leg, does the pilot need to remember to reset the McCready at the turn, because if he doesn't as soon as he makes the turn the computer could suddenly go from indicating that he can make it to indicating that he can't. Also, does the SN-10 have the ability to set a negative McCready value for the downwind leg? I'm not sure any computer does this today as it is a complex problem to manage in such a way that the pilot can understand what's really going on. But on those long, dicey, late-in-the-day final glides around a turnpoint when the wind is howling and the thermals are all torn up it sure could help get you home. It may not happen all that often, but when you need it you really need it. 9B |
#24
|
|||
|
|||
Help calculating Speed To Fly for headwind and tailwind
On Jun 2, 5:45*am, Nine Bravo Ground wrote:
Dave - you made me curious. Does that mean if you are abeam of the home airport with a decent distance to run to a downwind turnpoint and back to the finish that the SN-10 will calculate altitude margin based on a single McCready setting for the entire way home or separate McCready solutions for each leg - and if so how does the pilot input separate values for each leg? Last Monday's club contest task put us all in exactly that position. The last turn of the area task was downwind of the finish and the winds were quite strong. It was blue in the last turn area so most of us made final glide altitude before entering the last area and went in just deep enough to make the best use of the altitude. For me the most difficult part of the puzzle is knowing what the winds will be on the downwind leg and whether it will be the same on the up wind leg to the finish. I have never flown with a glide computer that does a good job of knowing the winds at all altitudes and uses that wind profile, rather than a fixed value, for the final glide solution. As I was already over min time and not wishing to landout because the head wind on the last leg was stronger than expected I elected to turn early and fly home fast. I have no doubt I could have earned a few more points by going a bit further and flying slower on the last leg. Andy |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Stewart Headwind | Copperhead144 | Home Built | 2 | August 19th 08 12:58 AM |
Headwind? What's that...? | David Lesher | Owning | 6 | January 4th 08 08:17 PM |
How to tell my instructor to increase glidespeed with headwind? | Nik | Piloting | 66 | November 4th 06 03:35 AM |
boy it's changed; tailwind | [email protected] | Piloting | 8 | February 8th 04 04:03 AM |
Wittman tailwind | Harry O | Home Built | 7 | July 29th 03 11:13 PM |