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 |
#51
|
|||
|
|||
Guy Alcala wrote:
Mike Marron wrote: "Gord Beaman" ) wrote: how can a wing's design decide that?...I'd think that only the elevators could control the AOA?. Also see: F-8 Crusader Why? An example of an a/c that was able to vary its wing's angle of incidence in flight. Correct. This was presumably intended to be read as followup to his other message, where he postulates that Al Minyard was referring to AoI rather than AoA, but that assumes you're familiar with the F-8. Incorrect. As you said above Guy, it was just an example of an A/C that was able to vary its wing's angle of incidence in flight. I have a slightly different reading of Al's intent, but we can let Al tell us what he meant. Like I've said, I generally tend to give people of the doubt instead of automatically assuming they're wrong so I can come back with some gratuitous, knee-jerk, argumentative retort like Gord does. In other words, even my ab intitio, pre-solo student pilots know that angle of attack is created by the tailplane providing a force (positive or negative) in the direction of the lift of the wings. Depending on whether the wing lift is foward or aft of the CG, the elevator will have to produce positive or negative lift to rotate the A/C about its lateral axis. Basic stuff, hence my willingness to give Al the benefit of the doubt and assume he meant angle of incidence rather than angle of attack. I could be wrongly misinterpreting Al, but I'll sit back now and let Al tell us what he meant. -Mike Marron CFII, A&P, UFI (fixed-wing, weightshift land & sea) |
#52
|
|||
|
|||
On Wed, 10 Sep 2003 07:53:32 +0100, Dave Eadsforth
wrote: Agree with all of the above analysis - and thanks for the useful summary of aspect ratios; both the B-24 and the B-29 must have glided well... To enlarge on my 'thick wing section' description, and working from memory of a book read long ago (which can be fatal), I recall that Davis conceived of a wing section that was based on a mathematically deformed circle, which he believed would give a more laminar flow. The thicker, 'teardrop-shaped' aerofoil section that resulted was also very useful structurally, given that he wanted to combine it with a high aspect ratio wing. Of course, any wing section inboard of the engines was going to have its airflow messed up considerably by a few minor essentials; like engine nacelles and de-icing boots etc etc, but the wing outboard of the engines may have performed as Davis believed it should during cruise. True that the high aspect ratio conferred most of the advantages of L/D ratio, but perhaps Davis's ideas on the wing section itself should not be forgotten. Cheers, Dave Thanks. I knew that Davis had designed a laminar flow section, but was unaware that the section had increased thickness. Interesting stuff. Al Minyard |
#53
|
|||
|
|||
Mike Marron wrote:
Also see: F-8 Crusader Gord Beaman wrote: Why? Guy Alcala wrote: An example of an a/c that was able to vary its wing's angle of incidence in flight. This was presumably intended to be read as followup to his other message, where he postulates that Al Minyard was referring to AoI rather than AoA, but that assumes you're familiar with the F-8. I have a slightly different reading of Al's intent, but we can let Al tell us what he meant. Al Minyard wrote: Yep, I meant AoI, but my source called it AoA, so I slavishly copied it that way. Common error, but I knew you meant AoI not AoA. Al Minyard: I agree that the F-8 was somewhat unique in its ability to vary the AoI. Not true. Thousands (perhaps tens of thousands) of "variable incidence" A/C (e.g: flexwing, weightshift A/C known as "trikes") have been manufactured and are in widespread use throughout the world as cropdusters, towplanes, aerial observation and photography platforms, trainers, recreational and military special forces A/C. I happen to have logged almost 2,000 hrs. in these magical variable incidence machines myself. Of course, trikes aren't the only variable incidence A/C, Jack Northrop's revolutionary flying wing designs such as the XB-35 strategic bomber and XP-56 and XP-74 fighter planes were also variable incidence. Of course, then there's the B-2 Stealth bomber. Unlike a conventional 3-axis A/C, the angle of incidence and angle of attack in all of these A/C are the same during flight. The primary difference between my own personal "variable incidence" A/C and the B-2 with regards to stability is that the B-2 incorporates a computerized gust load alleviation system (GLAS) to counteract air turbulence forces whereas I use my chest and biceps to counteract turbulence! Either way, watching a tailless, flying wing land is pure poetry in motion and flying one is pure sex. Al Minyard: Of course, with the fuselage horizontal pitch at 0, AoI equals AoA :-) Exactly right. -Mike Marron |
#54
|
|||
|
|||
Dave Eadsforth wrote:
snip To enlarge on my 'thick wing section' description, and working from memory of a book read long ago (which can be fatal), I recall that Davis conceived of a wing section that was based on a mathematically deformed circle, which he believed would give a more laminar flow. The thicker, 'teardrop-shaped' aerofoil section that resulted was also very useful structurally, given that he wanted to combine it with a high aspect ratio wing. Of course, any wing section inboard of the engines was going to have its airflow messed up considerably by a few minor essentials; like engine nacelles and de-icing boots etc etc, but the wing outboard of the engines may have performed as Davis believed it should during cruise. snip He was quite irritated that Consolidated didn't provide full covers for the main gear wheel wells, as he felt that defeated much of the drag reduction. Guy |
#55
|
|||
|
|||
Mike Marron wrote:
Al Minyard: Of course, with the fuselage horizontal pitch at 0, AoI equals AoA :-) Exactly right. -Mike Marron Ok, I see now why you said "see the F-8 Crusader". John emailed me this URL which partially explains it's wing shenanigans. http://pacificcoastairmuseum.org/200...Crusader/j.asp Quote from URL: "No, the wing isn't about to fall off. It was designed to do this so that the fast moving Crusader could slow down enough to land on the carriers. This also kept the nose of the airplane down during landing so the pilot could see." Unquote I still don't see the purpose here unless it's _only_ advantage is the second sentence in the quote there. Why would an increase in AOA 'help the a/c slow down for a carrier landing'?...of course it would 'slow down' BUT it'd now be way high on the glidepath TOO. Just as it would be if you hauled back on the stick...the _only_ advantage that I can see for this capability of the F-8 is to lower the nose for better visibility from the cockpit. Mind you, that must have been a large advantage imo. 'cause it seems to me that that'd be a big engineering project. Please guys, tell me where I'm wrong here... A/c is flying smoothly down a three degree glide-path, the wing's AoA is 5 degrees. AoI is zero. (guesses of course) Pilot pops the 'AoI switch', AoI becomes 5 degrees, AoA becomes 10 degrees, a/c tries to climb, pilot prevents that by pushing stick forward, AoA now returns to 5 degrees and a/c ~returns to glidepath. (Fuselage is now at a steeper angle than it was). I'll tell you what will help, explain where I'm wrong in calm terms or ignore this post. Insults about my lineage, my skin colour, my mental capacity etc will only make you look bad to the lurkers and won't affect me one whit. (I'm old and tough skinned). -- -Gord. |
#56
|
|||
|
|||
In article , Gord Beaman
?@?.? writes I still don't see the purpose here unless it's _only_ advantage is the second sentence in the quote there. Why would an increase in AOA 'help the a/c slow down for a carrier landing'?...of course it would 'slow down' BUT it'd now be way high on the glidepath TOO. Just as it would be if you hauled back on the stick...the _only_ advantage that I can see for this capability of the F-8 is to lower the nose for better visibility from the cockpit. Mind you, that must have been a large advantage imo. 'cause it seems to me that that'd be a big engineering project. Concorde went with physically lowering the nose (out of the pilot's view) and cranking the AoA right up. -- John |
#57
|
|||
|
|||
" wrote:
Mike Marron wrote: Al Minyard: Of course, with the fuselage horizontal pitch at 0, AoI equals AoA :-) Exactly right. -Mike Marron Ok, I see now why you said "see the F-8 Crusader". John emailed me this URL which partially explains it's wing shenanigans. http://pacificcoastairmuseum.org/200...Crusader/j.asp Quote from URL: "No, the wing isn't about to fall off. It was designed to do this so that the fast moving Crusader could slow down enough to land on the carriers. This also kept the nose of the airplane down during landing so the pilot could see." Unquote I still don't see the purpose here unless it's _only_ advantage is the second sentence in the quote there. Why would an increase in AOA 'help the a/c slow down for a carrier landing'?...of course it would 'slow down' BUT it'd now be way high on the glidepath TOO. Just as it would be if you hauled back on the stick...the _only_ advantage that I can see for this capability of the F-8 is to lower the nose for better visibility from the cockpit. Mind you, that must have been a large advantage imo. 'cause it seems to me that that'd be a big engineering project. Please guys, tell me where I'm wrong here... The other advantage of keeping the fuselage more level is that it provides more ground clearance at the tail, so you can increase the AoA (and fly slower) while still maintaining pilot view and sufficient tail clearance. Guy |
#58
|
|||
|
|||
"Gord Beaman" ) wrote:
Ok, I see now why you said "see the F-8 Crusader". John emailed me this URL which partially explains it's wing shenanigans. http://pacificcoastairmuseum.org/200...Crusader/j.asp Quote from URL: "No, the wing isn't about to fall off. It was designed to do this so that the fast moving Crusader could slow down enough to land on the carriers. This also kept the nose of the airplane down during landing so the pilot could see." Unquote I still don't see the purpose here unless it's _only_ advantage is the second sentence in the quote there. Why would an increase in AOA 'help the a/c slow down for a carrier landing'?...of course it would 'slow down' BUT it'd now be way high on the glidepath TOO. Just as it would be if you hauled back on the stick... Haven't you heard the old axiom, "pitch for airspeed, power for altitude?" (See below). the _only_ advantage that I can see for this capability of the F-8 is to lower the nose for better visibility from the cockpit. Mind you, that must have been a large advantage imo. 'cause it seems to me that that'd be a big engineering project. The F-8 won the Collier Trophy for the year's (mid 1950's) greatest achievement in aviation. Besides just increasing the visibility, the variable incidence wing also enabled the sleek and very fast fighter to maintain the slower speeds required for carrier ops. Please guys, tell me where I'm wrong here... A/c is flying smoothly down a three degree glide-path, the wing's AoA is 5 degrees. AoI is zero. (guesses of course) Pilot pops the 'AoI switch', AoI becomes 5 degrees, AoA becomes 10 degrees, a/c tries to climb, pilot prevents that by pushing stick forward, AoA now returns to 5 degrees and a/c ~returns to glidepath. (Fuselage is now at a steeper angle than it was). You're not just along for the ride so before you start flipping switches and reconfiguring the A/C for the approach and landing you anticipate changes in airspeed, drag, power and stick pressure etc. so as to stay on the glideslope w/o exceeding your critical angle of attack. In other words, in your scenario above when the pilot increases the wing angle of incidence (7-deg's), he simultaneously adjusts his pitch and throttle settings as needed so as to remain stabilized on the glideslope. He just doesn't gaily "pop the AoI switch" and then react to what the airplane does...he thinks ahead and anticipates what the airplane will do and plans accordingly (e.g: "fly the plane" and pitch for airspeed power for altitude" etc.). Maybe an F-8 driver can jump in here and explain better than I can. I can only tell you that when landing my variable incidence A/C, I can adjust the wing's angle of incidence (instantly if I wish) simply by pushing the control bar full forward (unlike a conventional airplane, the stick is situated horizontally so it's called a "bar"), or pulling the bar full aft into my gut. And I can coordinate the wing angle of incidence/attack and throttle depending on the type of landing (e.g: short field, soft-field, crosswind, solo or 2-up, wet or dry wing, etc.) fully stabilized on the glideslope w/o porpoising up and down and/or making any radical changes in airspeed... -Mike ( could land 3 times [crowhop] on an aircraft carrier Marron |
#59
|
|||
|
|||
Mike Marron wrote:
In other words, in your scenario above when the pilot increases the wing angle of incidence (7-deg's), he simultaneously adjusts his pitch and throttle settings as needed so as to remain stabilized on the glideslope. He just doesn't gaily "pop the AoI switch" and then react to what the airplane does...he thinks ahead and anticipates what the airplane will do and plans accordingly (e.g: "fly the plane" and pitch for airspeed power for altitude" etc.). Of course Mike, I understand that but I just broke it down so that it's easier for me to describe. I still don't see what this AoI control will do _other_ than give the pilot better downward visibility for landing and less drag for high speed operation. Is there some other aspect that I'm not seeing?...or is that it in a nutshell?... It doesn't help to compare conventional a/c with ultra-lights because I don't understand them very well. -- -Gord. |
#60
|
|||
|
|||
Guy Alcala wrote:
The other advantage of keeping the fuselage more level is that it provides more ground clearance at the tail, so you can increase the AoA (and fly slower) while still maintaining pilot view and sufficient tail clearance. Guy Yes...that makes sense, perhaps they designed the a/c for very high speed flight by having the AoI very low to reduce drag but needed to increase the Aoi for landing to, as you say, allow 'eventless' landings... -- -Gord. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Long-range Spitfires and daylight Bomber Command raids (was: #1 Jet of World War II) | The Revolution Will Not Be Televised | Military Aviation | 20 | August 27th 03 09:14 AM |