Page 39 of 40 FirstFirst ... 29 33 34 35 36 37 38 39 40 LastLast
Results 571 to 585 of 587

Thread: Tailless Aircraft - Reflex and other design issues

  1. #571
    Registered User
    Join Date
    Jul 2014
    Location
    Rochester, NY, USA
    Posts
    2,195
    Likes (Given)
    33
    Likes (Received)
    857

    Re: Tailless Aircraft - Reflex and other design issues

    I recently discovered The Great War project/program on YouTube. German show, 100th anniversary of WW1. Interesting and often stuff I never knew. Including viewpoints from the "enemy".

    And there's a spin off show, an American collector/scholar of guns, was asked for photos, because the regulatory rules make it hard to get & show WW1 arms, and the "company was afraid of guns" in the political climate. C&Rsenal then started a video primer in parallel to the Great War guys, and I'm binging on the more than 100 videos of in depth history. You may not care about the subject, but I find the mechanical evolution fascinating, and the procurement process is frustrating, amusing, and the same with aircraft as artillery or small arms.

    Committees that sometimes have priorities that hindsight shows were wrong, equipment choices based on doctrine from previous experience that no longer applies, etc.

    How does this apply to home built planes?

    In WW1, The German high command had a series of fighter plane competitions to choose the next new fighter. It was a time of very rapid development, and fads embraced, sometimes without understanding.

    The famous Fokker triplane was in response to a British Navy plane, that used high aspect ratio, short chord wings, in triplane layout, to improve pilot visibility. It was a success, albeit in small numbers, so Germany must have airplanes to keep up!!! The Fokker product was a failure at the British goal, visibility was awful, but the Germans didn't know that was the goal! It did use cantilever wings, a major advance ( that the British Sopwith didn't have ) that led to the famed Fokker D.VII. And the highly maneuverable Fokker triplane was a success for it's own reasons. For a short time.

    A later competition would lead to the adoption of the parasol Fokker D.VIII, which was too late to influence the war, but did lead to a few parasol fighters between wars. If WW1 had lasted months longer, the parasol fighters might have been the standard model for years, instead of the low & mid wing machines we now think of as normal.

    Even more interesting, another offering from Fokker at the same competition, was a low wing, cantilever fighter, that would have become the shape of things to come, more than a decade ahead of the 1930s designs that were independently evolved without the influence of a successful model in 1918. That didn't happen because the High Command didn't like that the low wing monoplane had poor visibility, straight down.

    This leads me to ask, how important is looking straight down?

    Obviously it became less of a factor in fighter design, over the years.

    It's still important for helicopters and gyros, with hovering & very steep approaches. Presumably somewhat important for STOL ops.

    And any planes that lose forward visibility on landing are problematic to varying degrees.

    Is there a standard from a century of flight on visibility, or is it a thing of fads, designer preference, and shifting priorities?

  2. #572
    Registered User BBerson's Avatar
    Join Date
    Dec 2007
    Location
    Port Townsend WA
    Posts
    10,712
    Likes (Given)
    1621
    Likes (Received)
    1901

    Re: Tailless Aircraft - Reflex and other design issues

    On landing, virtually all pilots (even helicopter) are looking ahead and slightly down to the intended touch down zone.
    The helicopter pilot will scan straight down perhaps only in the hover. But usually can't see the other skid anyway, so carefully feels the way on the last two feet down to the surface.

  3. #573
    Registered User
    Join Date
    Apr 2014
    Location
    Flint, Mi, USA
    Posts
    1,483
    Likes (Given)
    390
    Likes (Received)
    391

    Re: Tailless Aircraft - Reflex and other design issues

    The point is that a many designs got passed over for reasons unrelated to their actual merit, so success isn't the defining criteria of a good design.

  4. #574
    Registered User Himat's Avatar
    Join Date
    May 2011
    Location
    Norway
    Posts
    2,737
    Likes (Given)
    1710
    Likes (Received)
    636

    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by Topaz View Post
    ...
    This entire discussion has become quite "silly," in the sense that there's no design requirement context in which all these notions are being discussed, lots of "black magic" design theories are being thrown around, and deep, meaningful discussions are being held about whether things like vortex lift is "better" on circular planforms or delta-like planforms. The latter is particularly frustrating when any rational design process involving "vortex lift" is either well outside the capabilities of those discussing it or, if they do have the capability, they're ignoring it completely in favor of a "design process" that seems to primarily consist of the statement, "I think...".

    If one wants to have a "dreamers" discussion about what looks neat and is desirable from an aesthetic point of view, or even a pure construction concept standpoint, then fine. But despite repeated calls for substantiation from several people, including myself, I'm still seeing unsupported statements - unsupported by actual aerodynamic theory, standard design methods that have proven viable for decades, or even historical precedent - that this or that low-AR design is clearly better overall at some vague and unspecified broad class of design missions. And, when myself or others have asked for some kind of substantiation for those claims, we're either pointed at a shaky amateur video of an existing design "flying great" - without any metrics or performance data - or told that we're dismissing low-AR designs as unworkable, or other accusations that we say they "can't climb" and so on. None of which any of us has ever actually said....
    The discussion also gets defocused as when comparing the merits of high and low aspect wing designs the metrics are not held constant. Tailed designs of one aspect ratio is compared to tail less designs of the other and large part of the difference in performance may come from tail or not. Not the aspect ratio of the wing.

    Then the merits of a moderate to high aspect ratio wing with flaps and brakes are compared to low aspect ratio wing without either. Turning this around, with no flaps and no brakes the airplane with the high aspect ratio wing may have to be designed with excessive drag impairing on the speed range to have decent handling characteristics when landing. The low aspect ratio wing may pitch up for braking.

    All in all, it is design to requirement. Just observe how different formulas are arrived at in aerodynamic text books. At constant span, induced drag does rise with increasing aspect ratio.

  5. #575
    Registered User
    Join Date
    Mar 2016
    Location
    Austria
    Posts
    259
    Likes (Given)
    21
    Likes (Received)
    72

    Re: Tailless Aircraft - Reflex and other design issues

    At constant span, induced drag does rise with increasing aspect ratio.
    You forgot to say: At any given airspeed (for both wings).
    At max L/D for each wing, the higher A/R wing will have lower induced drag in many configurations.

  6. #576
    Registered User Himat's Avatar
    Join Date
    May 2011
    Location
    Norway
    Posts
    2,737
    Likes (Given)
    1710
    Likes (Received)
    636

    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by ypsilon View Post
    You forgot to say: At any given airspeed (for both wings).
    At max L/D for each wing, the higher A/R wing will have lower induced drag in many configurations.
    You are correct that I should have stated at equal airspeed, equal airplane weight and atmospheric conditions for both planes. Nevertheless, the high aspect ratio wing will have higher induced drag, drag due to lift, even at best L/D if span is held constant. The reason is the Cl term in the Cdi equation. The lift coefficient that have to increase as the aspect ratio increase and wing area decrease to provide the same lift.

  7. #577
    Registered User
    Join Date
    Mar 2016
    Location
    Austria
    Posts
    259
    Likes (Given)
    21
    Likes (Received)
    72

    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by Himat View Post
    You are correct that I should have stated at equal airspeed, equal airplane weight and atmospheric conditions for both planes. Nevertheless, the high aspect ratio wing will have higher induced drag, drag due to lift, even at best L/D if span is held constant. The reason is the Cl term in the Cdi equation. The lift coefficient that have to increase as the aspect ratio increase and wing area decrease to provide the same lift.
    No, the Cl doesn't have to increase. The airspeed for best L/D increases. At best L/D the induced drag is pretty much 50% of the overall drag. The lower A/R wing will have more (shear and form) drag, and therefore also more induced drag. Otherwise one could increase the performance of sailplanes simply by increasing wing cord / lowering A/R and adding more ballast to the ship. That doesn't work though. High performance sailplanes are high A/R for good reason.

    As said for any given airspeed the lower A/R wing will produce less induced drag than the high A/R wing of the same span. For any given Cl the high A/R wing does better.

  8. #578
    Registered User Himat's Avatar
    Join Date
    May 2011
    Location
    Norway
    Posts
    2,737
    Likes (Given)
    1710
    Likes (Received)
    636

    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by ypsilon View Post
    No, the Cl doesn't have to increase. The airspeed for best L/D increases. At best L/D the induced drag is pretty much 50% of the overall drag. The lower A/R wing will have more (shear and form) drag, and therefore also more induced drag. Otherwise one could increase the performance of sailplanes simply by increasing wing cord / lowering A/R and adding more ballast to the ship. That doesn't work though. High performance sailplanes are high A/R for good reason.

    As said for any given airspeed the lower A/R wing will produce less induced drag than the high A/R wing of the same span. For any given Cl the high A/R wing does better.
    Note the detail, I said at constant wing span.

    Lift = *air density * speed^2 * wing area * Cl
    Aspect ratio = Wing span squared/ wing area
    Turn it around:
    Wing area = Wing span squared / Aspect ratio
    Substitute and you get:
    Lift =1/2 * air density * speed * (Wing span squared/Aspect ratio)* Cl
    Hold airplane weight, that is lift, air density, speed and wing span constant the Cl have to increase as aspect ratio increase.

    The crux is that at constant weight, lift, and span, the high aspect ratio wing always has to operate at a higher Cl.

  9. #579
    Registered User
    Join Date
    Oct 2005
    Location
    Evans Head Australia
    Posts
    621
    Likes (Given)
    5
    Likes (Received)
    203

    Re: Tailless Aircraft - Reflex and other design issues


  10. Likes BJC, ypsilon, delta liked this post
  11. #580
    Registered User
    Join Date
    Mar 2016
    Location
    Austria
    Posts
    259
    Likes (Given)
    21
    Likes (Received)
    72

    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by Himat View Post
    Note the detail, I said at constant wing span.

    Lift = *air density * speed^2 * wing area * Cl
    Aspect ratio = Wing span squared/ wing area
    Turn it around:
    Wing area = Wing span squared / Aspect ratio
    Substitute and you get:
    Lift =1/2 * air density * speed * (Wing span squared/Aspect ratio)* Cl
    Hold airplane weight, that is lift, air density, speed and wing span constant the Cl have to increase as aspect ratio increase.

    The crux is that at constant weight, lift, and span, the high aspect ratio wing always has to operate at a higher Cl.
    Everything above is correct, however you said constant span, but not constant speed.
    What I said (maybe not clearly enough) is that at the same span the high A/R wing will reach it's maximum L/D at a higher speed with (possibly) less induced drag than the low A/R wing. The exact speed of max L/D depends on the parasite drag, but if the fuselage is very clean (as in: sailplanes) you get not only lower overall drag, but also lower induced drag at max L/D for the high A/R wing. As i said before at any given speed the low A/R wing will have less induced drag. That is trivial, of course.

    In your initial post you didn't contrain airspeed. If your requirements are indeed span and (low) airspeed, then at some point you'll have to increase area which means lowering A/R. No surprise either.
    Last edited by ypsilon; February 25th, 2019 at 03:51 AM.

  12. #581
    Registered User
    Join Date
    Jul 2014
    Location
    Rochester, NY, USA
    Posts
    2,195
    Likes (Given)
    33
    Likes (Received)
    857

    Re: Tailless Aircraft - Reflex and other design issues

    If span is not constrained, but stall speed is, then increased AR allows lower area.

    Correct me on that, please.

    Or.... Increased L/D allows lower area?

    Either assertion fits the facts if you look at wing area on modern hang gliders. http://www.moyesusa.com/products.html

    These are all roughly the same planform, a flying wing. The Malibu has a thinner airfoil and much more exposed structure than the other 3, more twist, so if you prefer to keep it as oranges to oranges, just consider the 3 models with the buried cross spar.

    None of these is as efficient as an ideal wing. Laminar flow is very limited, as the first seam in the upper surface trips the flow, if near imperceptible span wise ripples haven't already. The exposed pilot can be more than half the total parasitic drag. However, as a side by side comparison, those factors are about equal.

  13. #582
    Registered User
    Join Date
    Mar 2010
    Location
    krakow,poland
    Posts
    4,427
    Likes (Given)
    568
    Likes (Received)
    407

  14. #583
    Registered User Himat's Avatar
    Join Date
    May 2011
    Location
    Norway
    Posts
    2,737
    Likes (Given)
    1710
    Likes (Received)
    636

    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by Aesquire View Post
    If span is not constrained, but stall speed is, then increased AR allows lower area.

    Correct me on that, please.
    No, area and coefficient of lift do set the stall speed.

    Quote Originally Posted by Aesquire View Post
    Or.... Increased L/D allows lower area?
    In some cases, yes. An increased L/D, or rather Cl/Cd make it possible to operate at a higher Cl for the same Cd. If power constrained, the airplane can then have a smaller wing

  15. #584
    Registered User Himat's Avatar
    Join Date
    May 2011
    Location
    Norway
    Posts
    2,737
    Likes (Given)
    1710
    Likes (Received)
    636

    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by ypsilon View Post
    Everything above is correct, however you said constant span, but not constant speed.
    What I said (maybe not clearly enough) is that at the same span the high A/R wing will reach it's maximum L/D at a higher speed with (possibly) less induced drag than the low A/R wing. The exact speed of max L/D depends on the parasite drag, but if the fuselage is very clean (as in: sailplanes) you get not only lower overall drag, but also lower induced drag at max L/D for the high A/R wing. As i said before at any given speed the low A/R wing will have less induced drag. That is trivial, of course.

    In your initial post you didn't contrain airspeed. If your requirements are indeed span and (low) airspeed, then at some point you'll have to increase area which means lowering A/R. No surprise either.
    Evaluated at constant span and equal speed the formula for induced drag can be rearranged to:

    Cdi = k*Cl^2*AR

    If the airplanes are built to equal standards the only drag part that reduces with aspect ratio is the skin friction. This will change with the area that follow:

    Area = constant / AR

    If the high aspect ratio airplane does achieve a higher Cl/Cd than a low aspect ratio airplane then depend on if the skin friction at some point get larger than the induced drag. This at least at speeds below where wave drag gets significant.

    My conclusion is that increasing the aspect ratio work by reducing span loading. In some ways the dimensionless aspect ratio number mask this.

  16. #585
    Registered User BJC's Avatar
    Join Date
    Oct 2013
    Location
    97FL, Florida, USA
    Posts
    8,309
    Likes (Given)
    4629
    Likes (Received)
    5309

    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by Himat View Post
    Evaluated at constant span and equal speed the formula for induced drag can be rearranged to:

    Cdi = k*Cl^2*AR
    Not exactly. That is a formula for a non-dimensionalized induced drag coefficient, not the induced drag. If you work with actual induced drag, you will see that it depends on span, not aspect ratio.


    BJC

    edit. I’m a big proponent of always carrying / showing units with formulas and calculations. Doing so helps avoid confusing a coefficient with a physical quantity.

  17. Likes Himat liked this post

Similar Threads

  1. Discussion Thread: The design of a tailless flying wing
    By Aerowerx in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 479
    Last Post: August 2nd, 2017, 02:37 PM
  2. X-4 Tailless Design
    By rv6ejguy in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 9
    Last Post: January 25th, 2017, 12:25 PM
  3. Tailless Aircraft Configuration Poll
    By Aerowerx in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 40
    Last Post: November 17th, 2015, 03:35 PM
  4. Tailless Aircraft and Crosswind Landings
    By Aerowerx in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 11
    Last Post: July 23rd, 2015, 05:26 PM
  5. Tailless Design: Natureal Frequency and Stability
    By Aerowerx in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 18
    Last Post: January 3rd, 2013, 09:45 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •