Can thrust vectoring enable use of flaps on pure delta wing?

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Thomas Marks

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I'm considering tractor propeller driven flying wing with vertical stabilizer only.
This is an open question seeking feasible approach.

Possible options:
  • hidable EDF at the front
  • tilted prop rotor
  • collective pitch thrust vectoring (swashplate driven)
  • retractable canard fins to divert the thrust down
  • your suggestion, please
Problems to overcome:

Stability. Change of angle of attack either intentional or by air conditions changes wing lengthwise distribution of lift. Is it manageable for human to safely maintain stability in such conditions and if not - for a computer?

Thrust availability. Approaching landing the forward thrust is minimized, so there should be close to 90° downward thrust line deflection.

Thrust agility. All options are fine except probably EDF. They are pretty responsive but it may be not enough. What about a nozzle limiting the output?

So, is it viable to add enough nose-up moment and stability by vectoring thrust to counter the nose-down moment produced by flap extension, thus allowing the use of flaps to decrease speed and angle of attack at landing?

Thanks in advance.
 

Aesquire

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The basic problem is that the effect of a flap, or elevator, varies with airspeed, while a balancing thrust does not, or worse, may be less at higher speed. That could make your craft unstable in pitch. Which is Bad.

The mechanical complications of tilting the engine, or worse, a hinged shaft drive to a propeller, is a lot more work and weight than movable control surfaces on the trailing edge of the wing.

So...theoretically it can work in a narrow speed range, but not outside that range. I don't recall a successful plane that uses the system you propose.

My no math mental image could be wrong. But it seems impractical to me.
 

berridos

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With the Delta this propellerwind creates lift so that the induced drag will be less. So where traction propellers have less efficiency with other aircraft it gives benefit with the Delta.
Dont want to hijack your thread, but dont you think the approach should focus on large leading edge slats that dont change the pitch as flaps do? On a delta the chord is large and the wingthickness allows for plenty of room to fit the drooped nose mechanism.
 

Dana

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What happens when the engine quits? Will it still be controllable?
 

Thomas Marks

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The basic problem is that the effect of a flap, or elevator, varies with airspeed, while a balancing thrust does not, or worse, may be less at higher speed. That could make your craft unstable in pitch. Which is Bad.
The balancing thrust will do the same thing as conventional tail, take the role of elevator from flaperons at the landing.

My no math mental image could be wrong. But it seems impractical to me.
This is obviously a complication, but an airplane with a stall speed over 80km/h is impractical to me as well despite all the attractiveness of a delta configuration.

theoretically it can work in a narrow speed range, but not outside that range. I don't recall a successful plane that uses the system you propose.
Do you mean just a low speed range? This is what I'm aiming for: landing.
 

Thomas Marks

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What happens when the engine quits? Will it still be controllable?
If the engine quits at landing where this scheme is designed to help, immediate nose-down stall will occur most likely leading to a crash. This is why it is important to have redundancy here:
  • EDF - 2 of them placed longitudinally
  • retractable fins - will work fine, as the engine is at idle anyway
  • Tilted prop - two engines on one shaft / parachute deployment, other ideas?
Increased reliability of electric engine should lower the risk as well.
 

berridos

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This is a must as well. Do you think it would be enough to reach ~ 40km/h landing speed.
leading edge devices add about 0,5 lift. That never would make for 40kmh. On top i fgot a feeling that the devices have to be nonconventional for deltas as the landing attitude is over 30º.
 

TFF

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Authorities generally consider stall as a natural flying of the aircraft. In their eyes, they will considered your craft already stalled and flying only because of the augmented power. They will not consider that as a 40 km stall but a 80 km stall that can do something else. Measuring stall is usually power off, 1g deceleration until it drops.
 

Toobuilder

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What is the mission of the aircraft? More specifically, is there an existing aircraft that meets the performance requirements, or is there some outlying segment of the flight envelope that drives you to the unique and complex configuration in your OP?
 

Aerowerx

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Get a copy of "Tailless Aircraft in Theory and Practice", if you don't have one yet.

It talks about putting no-pitch-change flaps on a flying wing. If located properly they will be pitch neutral, but requires a swept wing.
 

Topaz

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What is the mission of the aircraft? More specifically, is there an existing aircraft that meets the performance requirements, or is there some outlying segment of the flight envelope that drives you to the unique and complex configuration in your OP?
This. "It would be cool!" can be a perfectly valid reason, if it's worth it to the person spending the time and money. For the rest of us, what requirement does a thrust-vectoring propeller, delta-wing aircraft satisfy that, say, a conventional STOL bush-plane does not?
 

Thomas Marks

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To cut a long story short: I want a bush plane with double the cruise speed.
They are awesome and fun to fly but car speed can't take you where, say Pipistrel Virus will.
 
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Topaz

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To cut a long story short: I want a bush plane with double the cruise speed.
They are awesome and fun to fly but car speed can't take you where, say Pitistrel
Virus will.
Okay, fair enough. IMHO, it's easier to make an airplane like the Virus land in a short distance than try to get a delta-wing to do so. Plus a delta isn't much help to cruising speeds at low-subsonic speeds.

Just a suggestion, but looking at a clean airplane like the Virus, with good flaps and a larger motor, is likely to get you closer to your design requirement a lot easier and with less complication. Plus be much easier to use in day-to-day flying. Obviously your mileage may vary, but that's the way I'd approach this design mission.
 

Toobuilder

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If you have not done so, then list your minimum requirements in valid, definable units. Things like:
160 knot cruise
25 knot stall
500 pound useful load
4 hours endurance...

Then work on the easiest to implement configuration that meets the above requirements.

Not sure if you fall into this category, but many new designers pick the configuration FIRST, then try make it fit in the requirements, or worse, modify their requirements to fit the design.
 

Thomas Marks

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If you have not done so, then list your minimum requirements in valid, definable units.
I have put some interesting (and reference) configurations into this spreadsheet https://docs.google.com/spreadsheets/d/1SGK_is-R1lgW5lgIff3CNpK6R52SmUzpb6J944VdoS4 where I mark best / good / bad spec. As you can see there is not a single model without yellow field while quite a few are good enough.

If I missed something worth mentioning, please tell, I would add it to comparison.
 

Aerowerx

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Properly designed flaps on a swept wing (as in "Tailless Aircraft") would be a lot easier to build, and more dependable, than designing a thrust vectoring system.
 

Riggerrob

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As for installing flaps on a tail-less delta or flying wing …. we have seen tilting centre trailing edge on Swift UL glider. We have also seen a few split flaps on late 1940s vintage experimental flying wings. They all seem to be close to the centre of gravity to minimize pitching.
Am I reading this concept correctly?
 
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