4 ms·

In a tandem wing configuration like this it is unwise to make the forward wing the low one. This is because at high angles of attack (think takeoff, landing, lo

In a tandem wing configuration like this it is unwise to make the forward wing the low one. This is because at high angles of attack (think takeoff, landing, low speed flight, climbing) the rear wing will end up in the “dirty” turbulent wake of the first wing. Wings are much more efficient in “clean” smooth air. The lower lifting efficiency in situations where you need high lift (see previous list of high angle of attack settings) makes a design dangerous. If you’re interested in this sort of stuff, this is the best book I’ve found on the subject, it is very practical and written with the engineering minded amateur designer in mind: https://www.amazon.com/Design-Aeroplane-2e-Darrol-Stinton-dp-0632054018/dp/0632054018/ref=dp_ob_title_bk https://www.amazon.com/Design-Aeroplane-2e-Darrol-Stinton-dp...

kashkhan 6y ago
check out Quickie and Q2 https://en.wikipedia.org/wiki/Rutan_Quickie https://en.wikipedia.org/wiki/Rutan_Quickie t tails on most business jets etc.
- jackyinger 6y ago
  There are certainly successful exceptions to this rule. In the see exceptions I’m sure that the engineering was done to mitigate the risk. For instance with T tails, the designer would hopefully either place the elevator high enough to be out of the dirty air, or do the analysis to make sure it functioned well in he dirty air.
  - baybal2 6y ago
    Rutan Quickie is subject to deep stall, and it has an AOA never exceed limit because of it.
    - kashkhan 6y ago
      all configurations have advantages and disadvantages. Most civilian jets have tails which are mounted higher than the main wing. The position matters when you are talking about not getting into stall and then recovering from a stall. A lower tail is definitely better for an inexperienced pilot or a pilot in a bad situations. And the safety records of high wing planes like Cessna 172 speak to that.
  - kashkhan 6y ago
    there are a lot of exceptions. In case of Business jets it's almost a rule to have a t tail.
- mannykannot 6y ago
  There was, in fact, a serious problem with T-tailed jets: Superstall, an irrecoverable stall where the turbulent wake of the stalled wing over the stabilizer and elevator prevents recovery. A crash of a BAC 111 prototype led to the development of stick shakers and pushers, as stalling presents an unacceptable risk in these cases. It is exacerbated with swept wings having a tendency to stall at the wingtips first, as this typically creates a pitching-up moment.
  - kashkhan 6y ago
    When first discovered it was new, but now almost all bizjets have t tails. So it definitely wasn't a fatal flaw but an engineering problem with the configuration.
    - mannykannot 6y ago
      Indeed - there is certainly nothing inherently risky about T-tails, as the many T-tailed sailplanes with relatively docile stall/spin characteristics attest.
nabilhat 6y ago
It's terrifying. From your comment I was thinking negative stagger like has been done for a few designs in the past, not a lower wing that sweeps the entire length of the aircraft, with the upper wing at the tail. The angle where the rear wing is exposed to interference from the lower wing ranges from 15 degrees through 90. Losing lift on that rear wing, which there is a massive range of opportunity to do, will yank the rug out from under the back of that aircraft. How often will this design suddenly decide to fly tail-first tens of feet away from touching down on the tires?
starpilot 6y ago
This is really how all box wing configuration aircraft are laid out. Here's one from Lockheed: https://www.cbsnews.com/pictures/nasas-big-ideas-for-the-future-of-flight/3/ https://www.cbsnews.com/pictures/nasas-big-ideas-for-the-fut... Here's a concept from Elytron: https://rotorcraft.arc.nasa.gov/Publications/files/Grima_Theodore_Revised_FINAL_1144_100416.pdf https://rotorcraft.arc.nasa.gov/Publications/files/Grima_The... The advantage is lower induced drag during cruise. You do analysis to validate controllability during high-AoA regimes. As with every design choice in aviation, it's a tradeoff.
baybal2 6y ago
Buy you also get help from the ground effect on takeoff, but year a possibility of rear wing stall puts an and to any talks about virtues of the design.
souprock 6y ago
Nearly all aircraft have that problem with the tail. A major exception is aircraft with an inverted V tail, like the Lazair ultralight and the MQ-1 Predator drone. Another exception is the flying wing, like the B-2 Spirit, but that certainly isn't an aerodynamically low-risk design. Another exception is weight-shift ultralights that look like tricycles hanging under flying wings.

kashkhan 6y ago

check out Quickie and Q2 https://en.wikipedia.org/wiki/Rutan_Quickie https://en.wikipedia.org/wiki/Rutan_Quickie t tails on most business jets etc.

jackyinger 6y ago
There are certainly successful exceptions to this rule. In the see exceptions I’m sure that the engineering was done to mitigate the risk. For instance with T tails, the designer would hopefully either place the elevator high enough to be out of the dirty air, or do the analysis to make sure it functioned well in he dirty air.
- baybal2 6y ago
  Rutan Quickie is subject to deep stall, and it has an AOA never exceed limit because of it.
  - kashkhan 6y ago
    all configurations have advantages and disadvantages. Most civilian jets have tails which are mounted higher than the main wing. The position matters when you are talking about not getting into stall and then recovering from a stall. A lower tail is definitely better for an inexperienced pilot or a pilot in a bad situations. And the safety records of high wing planes like Cessna 172 speak to that.
- kashkhan 6y ago
  there are a lot of exceptions. In case of Business jets it's almost a rule to have a t tail.
mannykannot 6y ago
There was, in fact, a serious problem with T-tailed jets: Superstall, an irrecoverable stall where the turbulent wake of the stalled wing over the stabilizer and elevator prevents recovery. A crash of a BAC 111 prototype led to the development of stick shakers and pushers, as stalling presents an unacceptable risk in these cases. It is exacerbated with swept wings having a tendency to stall at the wingtips first, as this typically creates a pitching-up moment.
- kashkhan 6y ago
  When first discovered it was new, but now almost all bizjets have t tails. So it definitely wasn't a fatal flaw but an engineering problem with the configuration.
  - mannykannot 6y ago
    Indeed - there is certainly nothing inherently risky about T-tails, as the many T-tailed sailplanes with relatively docile stall/spin characteristics attest.

nabilhat 6y ago

It's terrifying. From your comment I was thinking negative stagger like has been done for a few designs in the past, not a lower wing that sweeps the entire length of the aircraft, with the upper wing at the tail. The angle where the rear wing is exposed to interference from the lower wing ranges from 15 degrees through 90. Losing lift on that rear wing, which there is a massive range of opportunity to do, will yank the rug out from under the back of that aircraft. How often will this design suddenly decide to fly tail-first tens of feet away from touching down on the tires?

starpilot 6y ago

This is really how all box wing configuration aircraft are laid out. Here's one from Lockheed: https://www.cbsnews.com/pictures/nasas-big-ideas-for-the-future-of-flight/3/ https://www.cbsnews.com/pictures/nasas-big-ideas-for-the-fut... Here's a concept from Elytron: https://rotorcraft.arc.nasa.gov/Publications/files/Grima_Theodore_Revised_FINAL_1144_100416.pdf https://rotorcraft.arc.nasa.gov/Publications/files/Grima_The... The advantage is lower induced drag during cruise. You do analysis to validate controllability during high-AoA regimes. As with every design choice in aviation, it's a tradeoff.

baybal2 6y ago

Buy you also get help from the ground effect on takeoff, but year a possibility of rear wing stall puts an and to any talks about virtues of the design.

souprock 6y ago

Nearly all aircraft have that problem with the tail. A major exception is aircraft with an inverted V tail, like the Lazair ultralight and the MQ-1 Predator drone. Another exception is the flying wing, like the B-2 Spirit, but that certainly isn't an aerodynamically low-risk design. Another exception is weight-shift ultralights that look like tricycles hanging under flying wings.