Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Torsional-Agility, High-Alpha, And EM Formula  
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Posted (5 years 11 months 1 week 3 days ago) and read 2751 times:

I'm wondering how having torsional-agility/super-maneuverability allows an aircraft with a light wing-loading, for a given thrust/weight-ratio, to sustain a given number of G's at a higher airspeed than would normally be allowed had the airplane not possessed torsional-agility/super-maneuverability?

Doesn't flying at high-alphas actually increase drag a lot especially as the alphas you're achieving exceed 45-60 degrees and approach 90-degrees? Also, wouldn't the lift vector be, at least partially at such high alphas in opposition to the direction of flight (ie. the force of lift is pulling up somewhat but also backwards as the plane's moving forward, which would provide a pulling force partially against the direction of flight, producing drag)


Blackbird

9 replies: All unread, jump to last
 
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 1, posted (5 years 11 months 1 week 2 days 21 hours ago) and read 2740 times:



Quoting Blackbird (Thread starter):
I'm wondering how having torsional-agility/super-maneuverability allows an aircraft with a light wing-loading, for a given thrust/weight-ratio, to sustain a given number of G's at a higher airspeed than would normally be allowed had the airplane not possessed torsional-agility/super-maneuverability?

As I understand torsional-agility/super-maneuverability, you tailor the aeroelastic response of the wing so that it unload as the G's increase. Basically, the wing protects itself by aerodyanmically unloading, so you don't need to carry as much strength. Sort of a souped up version of gust-load alleviation on commercial airliners.

Quoting Blackbird (Thread starter):
Doesn't flying at high-alphas actually increase drag a lot especially as the alphas you're achieving exceed 45-60 degrees and approach 90-degrees? Also, wouldn't the lift vector be, at least partially at such high alphas in opposition to the direction of flight (ie. the force of lift is pulling up somewhat but also backwards as the plane's moving forward, which would provide a pulling force partially against the direction of flight, producing drag)

Lift is, by definition, the force perpendicular to the freestream. Drag is, by defintion, in the direction of the free stream. So lift can never cause drag; they're orthogonal. That said, the wing actually experiences only one composite force, we just resolve it into lift and drag for convenience. As your alpha goes up the force on the wing goes up...both drag and lift increase, until you stall, at which point lift drops off but drag keeps going up.

Tom.


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 2, posted (5 years 11 months 1 week 2 days 9 hours ago) and read 2713 times:

Tom,

Wouldn't that mean that supermaneuverability and torsional agility are not exactly the same? I've seen old planes that were totally unstable doing crazy high-alpha maneuvers...

What allows the wings to unload?


Blackbird


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 3, posted (5 years 11 months 1 week 2 days 3 hours ago) and read 2685 times:



Quoting Blackbird (Reply 2):
Wouldn't that mean that supermaneuverability and torsional agility are not exactly the same?

I suspect they're not...what definitions are you using for each term?

Quoting Blackbird (Reply 2):
I've seen old planes that were totally unstable doing crazy high-alpha maneuvers...

That sounds right to me.

Quoting Blackbird (Reply 2):
What allows the wings to unload?

In a nutshell, having the right aeroelastic derivatives be negative. Specifically, you don't want to get into a positive feedback situation where loading of the wing distorts the wing in a way that increases the loading. If deflection tends to decrease wing loading (or lower the rate of load increase) the wing has some innate protection.

Tom.


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 4, posted (5 years 11 months 1 week 2 days 1 hour ago) and read 2683 times:

Tom,

What does negative aeroelastic characteristics look like?

What kind of distortions increase loading and what kind of distortion forms decrease loading?


Blackbird


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 5, posted (5 years 11 months 1 week 1 day 22 hours ago) and read 2666 times:



Quoting Blackbird (Reply 4):

What does negative aeroelastic characteristics look like?

I'm not really sure what you mean "look like"...they're numbers, basically. You can't tell by looking at the structural form what it's going to do, you'd have to analyze it.

Quoting Blackbird (Reply 4):
What kind of distortions increase loading and what kind of distortion forms decrease loading?

The classic example is a swept wing...the center of pressure and the shear center aren't usually in line, so as the wing bends under load it also twists. In a conventionally swept wing, unless you do weird things to the internal structure, the wing tends to "twist down", towards lower angle of attack, so as the wing load increases (for example, tightening a turn) the angle of attack decreases and everything stays nice and stable.

If you are in the opposite situation, like a forward swept wing or some of the early straight-wing fighters when they got going too fast, the wing "twists up" as it loads up. The angle of attack increases, which increases the lift, which increases the load, which increases the twist, which increases the angle of attack. You end up in a positive feedback loop that can, literally, rip the wing off.

Tom.


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 6, posted (5 years 11 months 1 week 1 day 11 hours ago) and read 2626 times:

I thought all wings twisted leading edge down as lift increased...

Blackbird


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 7, posted (5 years 11 months 1 week 1 day 1 hour ago) and read 2601 times:



Quoting Blackbird (Reply 6):
I thought all wings twisted leading edge down as lift increased...

It depends on the internal structure (shear center) and the airfoil. For obvious reasons, you want to design this way, but you can design them so that they don't.

Tom.


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 8, posted (5 years 11 months 1 week 1 day 1 hour ago) and read 2601 times:

Tdscanuck,

And the fact that the airfoils twist-down in response to load would provide good torsional agility?


Backbird


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 9, posted (5 years 10 months 3 weeks 1 day 2 hours ago) and read 2437 times:

Tom,

Please tell me if I'm wrong here -- pertaining to maneuverability, it would seem that torsional agility's purpose primarily to reduce lift at higher airspeeds during maneuvers to avoid excessive lift (which on a lightly-loaded wing equates to more drag at high-speed) effectively reducing the drag that goes with the extra lift (L/D ratio -- basically, when you add more L, more D ends up going with it) allowing a lower loss of airspeed than would typically occur (for a typical wing of that area, at these higher speeds for a given number of G's pulled.

Whether torsional agility would reduce structural weight, I'm not sure, but it's primary function seems to be to allow airplanes with larger wings to be able to sustain more G's at higher airspeeds, while still functioning well at lower airspeeds.


Blackbird


Top Of Page
Forum Index

Reply To This Topic Torsional-Agility, High-Alpha, And EM Formula
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
Hot And High Performance B773ER Vs. A346 posted Sat May 31 2008 00:16:46 by PolymerPlane
High And Hot Performance Of EMB 170/190 posted Sun Jan 2 2005 15:47:52 by Airline7322
Take-off Distance - "hot And High"? posted Tue Nov 20 2001 22:58:50 by Blackened
Complex And High Performance Ratings? posted Thu Oct 25 2001 20:03:36 by USAFHummer
And Old 767 Vs A New 330 (fuel Consumption) posted Sun Aug 3 2008 15:54:00 by RICARIZA
Max Fuel Weight, Cruise Power And Power Loading? posted Sat Aug 2 2008 00:57:16 by Singapore 777
SEA And The Blue Angels posted Fri Aug 1 2008 18:28:31 by Therock401
A340 Cargo Weight And Fuel Consumption Question posted Thu Jul 31 2008 15:12:29 by TheMirror
Pilots;Your Average Flt Hours Monthly And Yearly posted Wed Jul 30 2008 09:10:53 by Wing
Turning Engines And Cabin Evacuation posted Wed Jul 30 2008 02:48:13 by Jonjonnl

Sponsor Message:
Printer friendly format