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
|
|||
|
|||
How high?
I'd like to get input on opinions on the "best" VFR altitude for a route.
It seems to me it's largely based on distance, winds aloft and comfort level. Do you have a "rule of thumb" trading off altitude (and therefore safety margin) to avoid headwinds? Or, if winds aloft are to your advantage, how high would someone go in a 172 class aircraft before returns diminish? |
#2
|
|||
|
|||
In a previous article, "John Harlow" said:
I'd like to get input on opinions on the "best" VFR altitude for a route. It seems to me it's largely based on distance, winds aloft and comfort level. Do you have a "rule of thumb" trading off altitude (and therefore safety margin) to avoid headwinds? Or, if winds aloft are to your advantage, how high would someone go in a 172 class aircraft before returns diminish? I want to be at least 4,000 feet, because it's quieter up there - there's very little VFR traffic, and the airliners are only passing through. If there is a few-to-scattered layer, I want to be above it because the air is smoother. Before I was instrument rated, I'd have to be careful it didn't turn into a broken layer when I wasn't paying attention. I don't like to fly above 10,000 because of the lack of oxygen, although I got up to 12,500 looking for a way though the storms coming back from Oshkosh. So generally I end up at 6,000 (or 6,500 if VFR) going west and 9,000 (or 9,500 if VFR) going east. -- Paul Tomblin http://xcski.com/blogs/pt/ I'm just waiting for the day that someone decides that "ignorant moron" is an ethnic group, and thus cannot be discriminated against. -- Christian Wagner |
#3
|
|||
|
|||
In article ,
"John Harlow" wrote: I'd like to get input on opinions on the "best" VFR altitude for a route. It seems to me it's largely based on distance, winds aloft and comfort level. Do you have a "rule of thumb" trading off altitude (and therefore safety margin) to avoid headwinds? Or, if winds aloft are to your advantage, how high would someone go in a 172 class aircraft before returns diminish? Some rules of thumb: A normally aspirated (i.e. no supercharger) engine such as found in a 172 will be running at about 65% power at 7000 density altitude with wide open throttle. Above that, you will have less power as you climb higher. Thus, there's usually not a lot of reason to fly much higher than 7500 MSL, unless terrain forces you higher. Below 3000 AGL, there tends to be lots of random traffic: people practicing maneuvers or instrument approaches, and flights entering or departing traffic patterns. Staying above 3000 AGL keeps you out of the worst of that. Below 3000, you also run into Class D airspaces, and there tends to be more turbulence (especially over rough terrain). Thus, there's usually not a lot of reason to cruise below 3000 AGL. It's usually not worth spending more than 1/3 of the trip time climbing. Consider radar and radio coverage. Below 3000 AGL, both tend to be spotty if you're not within about 10-20 miles of the charted boundary of a Class B or C airspace (or TRSA). |
#4
|
|||
|
|||
Our plane (Cherokee 235 -- normally aspirated 6-cylinder O-540) runs best
(highest speed, lowest, most even EGTs and CHTs, with lowest fuel burn) between 4500 and 6500 feet. These altitudes work fine here in the Midwest. We also like it there because it's usually smoother, and there is far less traffic. We're well above the guys working the pattern, and well below the "big boys" in the airliners. -- Jay Honeck Iowa City, IA Pathfinder N56993 www.AlexisParkInn.com "Your Aviation Destination" "John Harlow" wrote in message ... I'd like to get input on opinions on the "best" VFR altitude for a route. It seems to me it's largely based on distance, winds aloft and comfort level. Do you have a "rule of thumb" trading off altitude (and therefore safety margin) to avoid headwinds? Or, if winds aloft are to your advantage, how high would someone go in a 172 class aircraft before returns diminish? |
#5
|
|||
|
|||
John Harlow wrote: I'd like to get input on opinions on the "best" VFR altitude for a route. It seems to me it's largely based on distance, winds aloft and comfort level. Do you have a "rule of thumb" trading off altitude (and therefore safety margin) to avoid headwinds? Or, if winds aloft are to your advantage, how high would someone go in a 172 class aircraft before returns diminish? A lot depends on whether I'm alone or not. It's also the case that the various airspace restrictions around here do a lot more to determine my enroute altitude than anything else until I get south of the DC mess. If I'm alone and have strong headwinds, I'll stay down as low as 600' AGL to make time. If my wife is in the plane, I will go as high as is necessary to eliminate turbulence (if this is possible). I will go as high as 9,500' to make the best use of a tailwind, but I do not like to fly much higher than that, since flying higher makes me drowsy and leaves me with a headache. I have gone as high as 11,500 to get over a class-B. All my flying is done in the eastern half of the country without oxygen on board. If I had to deal with mountains higher than the Appalachians, it would be a different story. George Patterson Love, n.: A form of temporary insanity afflicting the young. It is curable either by marriage or by removal of the afflicted from the circumstances under which he incurred the condition. It is sometimes fatal, but more often to the physician than to the patient. |
#6
|
|||
|
|||
"John Harlow" wrote in message
... I'd like to get input on opinions on the "best" VFR altitude for a route. It depends on a variety of factors. As has been pointed out, you get the most power with the least drag at around 7000' MSL or so. So for a normally aspirated engine, that's a nice target. But for short flights, it may be a waste of time to climb that high. For flights starting at high altitude, you may find 7000' is too low to keep you out of local traffic and away from terrain. If there are strong winds going in your direction, you may want to fly higher. If there are strong winds going opposite your direction, you may want to fly lower. If it's a hot, sunny day you may find it's bumpy down low and will want a higher cruise altitude. If it's a windy, turbulent day, you may find the air smoother at the middle altitudes. You get the idea. Each flight is different. Rules of thumb are nice, but you need to be considering all the factors anew each flight. I have a turbocharged aircraft, so generally speaking, higher is better. However, I still have to deal with headwinds and turbulence. But the winds aloft forecast isn't reliable enough to use it to pick a cruising altitude. So typically what I do is choose a cruising altitude independent of the winds aloft forecast. Then I just see how things are in flight. I gain about a knot in true airpspeed for every 1000' I climb, so that gives me a guideline for how much the winds need to change for it to be worth picking a new cruising altitude. Of course, if the ride is bumpy, I generally opt for a slower but smoother flight. For this sort of "wait and see" approach, it certainly helps to have good climb rates at pretty much any altitude (I'm still getting 500-600 fpm at 16,000' or so, and much better lower...when I'm flying at 10,000' +/- a few thousand, it only takes a few minutes to change altitude to a new, significantly different altitude). It would be less practical with a normally aspirated engine. Pete |
#7
|
|||
|
|||
Except in high winds aloft or bad turbulence, I have found that flying
low (safety permitting) generally results in the most optimum solution. Climbing higher for better tailwind doesn't buy more than a few minutes. Of course, the ratio of climb time to cruise time has a big effect too. There are too many variable to make a rule of thumb. What I do is try a few altitudes on DUATs flight planner and pick the lowest altitude that seems reasonable. "John Harlow" wrote in message ... I'd like to get input on opinions on the "best" VFR altitude for a route. It seems to me it's largely based on distance, winds aloft and comfort level. Do you have a "rule of thumb" trading off altitude (and therefore safety margin) to avoid headwinds? Or, if winds aloft are to your advantage, how high would someone go in a 172 class aircraft before returns diminish? |
#8
|
|||
|
|||
If I am flying a long trip (several hours), I will go up 2000' and see
if I get an improvement in groundspeed. If I do, I stay up there and my try another 2000'. Don't forget you burn less gas per mile up high, so even if you just go the same speed, you are ahead. Sometimes I call Fligh****ch and ask them for the winds aloft forecasts so I can plan my altitude. In the summer, if I go up high enough, sometimes I can get above the turbulence. But then you may slow down so you have the age old turbulence vs airspeed tradeoff question. If I am going west, leave in the morning, come back in the evening will get me less headwind west and more tailwind east as winds increase as the day goes on, statistically. Going east, leave late in the day and come back the next day, if possible. I do believe I have "outflown" the wind, that is, I have had more tailwinds than headwinds due to being able to pick times and altitudes flown. Although there is software that calculates best solutions, I don't have it. Might be interesting if the GPS mfgs put that function in their GPS's. Could be done, I suppose. ON long flights I don't have anything else to do, so might as well mess around with trying to make time and saving fuel. (Andrew Sarangan) wrote in message . com... Except in high winds aloft or bad turbulence, I have found that flying low (safety permitting) generally results in the most optimum solution. Climbing higher for better tailwind doesn't buy more than a few minutes. Of course, the ratio of climb time to cruise time has a big effect too. There are too many variable to make a rule of thumb. What I do is try a few altitudes on DUATs flight planner and pick the lowest altitude that seems reasonable. "John Harlow" wrote in message ... I'd like to get input on opinions on the "best" VFR altitude for a route. It seems to me it's largely based on distance, winds aloft and comfort level. Do you have a "rule of thumb" trading off altitude (and therefore safety margin) to avoid headwinds? Or, if winds aloft are to your advantage, how high would someone go in a 172 class aircraft before returns diminish? |
#9
|
|||
|
|||
In article ,
"G.R. Patterson III" wrote: John Harlow wrote: I'd like to get input on opinions on the "best" VFR altitude for a route. It seems to me it's largely based on distance, winds aloft and comfort level. Do you have a "rule of thumb" trading off altitude (and therefore safety margin) to avoid headwinds? Or, if winds aloft are to your advantage, how high would someone go in a 172 class aircraft before returns diminish? A lot depends on whether I'm alone or not. It's also the case that the various airspace restrictions around here do a lot more to determine my enroute altitude than anything else until I get south of the DC mess. If I'm alone and have strong headwinds, I'll stay down as low as 600' AGL to make time. If my wife is in the plane, I will go as high as is necessary to 600 feet AGL for cruise? Not a lot of think/plan time if your engine fails! |
#10
|
|||
|
|||
"John Harlow" wrote in message ...
I'd like to get input on opinions on the "best" VFR altitude for a route. It seems to me it's largely based on distance, winds aloft and comfort level. Do you have a "rule of thumb" trading off altitude (and therefore safety margin) to avoid headwinds? Or, if winds aloft are to your advantage, how high would someone go in a 172 class aircraft before returns diminish? First, I think previous posters have said it well when they pointed out all the variables involved and concluded that "the best altitude" is different for each flight. Second, a minor correction: An earlier poster said he gained about 1 kt TAS per 1000'. The rule of thumb is 2% per 1000' so I'd expect more like 2-4 kt TAS gain per 1000', assuming your cruise speed is between 100 and 200 kts. That can offset a slight increase in head wind. Third, no one so far has pointed out the added safety that higher altitude buys in the event of an engine failure. From 7500' and assuming a 10:1 glide ratio (about right in practice for most small GA planes, with a small safety margin added on), you can glide 75,000' or over 12 nm. From 3000' you can glide only 5 nm. In civilized areas, airports are often close enough that the 7500' cruise would allow an engine out landing at an airport, while the 3000' cruise would probably not. Of course, you'd also have to practice side slips and S-turns in order to dump any excess altitude as you approach the runway. (Altitude becomes your fuel, but unlike a power plane, you have to land with "zero fuel.") I fly a motor glider and, in glider mode, must constantly think in terms of altitude to make an airport. Even though the engine is there and it's always started for me when I've needed it so far, the prudent assumption is that it won't start. That thinking carries over to engine on time too, but I'll admit that with a 50:1 glide ratio and a turbo charged engine, I have it a bit easier than you power guys. Even considering their reduced glide ratios, I think many power pilots don't adquately consider their planes as potential gliders when they lose an engine. From the few stories I've heard, it sounds like, no matter how much the pilot has been taught that the engine doesn't make the plane fly, a gut reaction often takes over when the engine quits and tells the pilot the plane is going to fall like a rock. That's probably why all pilots I know who are rated for both power and gliders say that all pilots should do at least a few landings in a glider. It helps get over that gut reaction. Martin |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Revisiting lapse rates (From: How high is that cloud?) | Icebound | Instrument Flight Rules | 5 | November 26th 04 09:41 PM |
FS: 1988 "Aces High" (Military Airplanes) Hardcover Edition Book | J.R. Sinclair | Aviation Marketplace | 0 | August 23rd 04 05:18 AM |
Fwd: [BD4] Source of HIGH CHTs on O-320 and O-360 FOUND! | Bruce A. Frank | Home Built | 1 | July 4th 04 07:28 PM |
MT. DIABLO HIGH SCHOOL CONCORD, CA PHOTOS | MT. DIABLO HIGH SCHOOL PHOTOS | Home Built | 1 | October 13th 03 03:35 AM |
High Flight NOTAM | Kirk Stant | Military Aviation | 1 | September 10th 03 03:31 AM |