Prandtl-d Aircraft

[Fulcrum]

This may not be the most appropriate location for this topic.

Some interesting claims concerning wing efficiency of what is essentially an 80 year old design.

http://www.engadget.com/2015/09/22/nasa ... rs-planes/
http://www.nasa.gov/feature/new-wing-sh ... ind-tunnel
https://www.youtube.com/watch?v=Hr0I6wBFGpY

Also, does anyone know how much money is spent on research within each field:

Commercial aerodynamics
Military aerodynamics
F1 aerodynamics
Automotive aerodynamics

[riff_raff]

There are very practical reasons that design is not used. While it has good efficiency in theory, once you consider all the various flight control surfaces required, the installation of engines and systems like landing gear, and where the crew and payload will be located, it does not look quite so good.

As for the amount of money spent each year on researching aerodynamic concepts, it is quite a large amount. But you should not perceive aircraft OEMs like Boeing or Airbus as being stupid. They have studied every aero concept that has ever been proposed. And there is a very good reason every commercial aircraft currently produced looks like it does. It's because that is the design that provides the best compromise of performance and cost.

[autogyro]

There are very practical reasons that design is not used. While it has good efficiency in theory, once you consider all the various flight control surfaces required, the installation of engines and systems like landing gear, and where the crew and payload will be located, it does not look quite so good.

As for the amount of money spent each year on researching aerodynamic concepts, it is quite a large amount. But you should not perceive aircraft OEMs like Boeing or Airbus as being stupid. They have studied every aero concept that has ever been proposed. And there is a very good reason every commercial aircraft currently produced looks like it does. It's because that is the design that provides the best compromise of performance and cost.

Unless someone else designs a short medium haul aircraft that eliminates the need for runways.
Then you just destroy the opposition.
Or when you copy a multi purpose combat aircraft and try to include VTOL which you also copied and find it will never work.
Then you simply carry on spending tax payers money and use the media to cover everything up.

[Cold Fussion]

The F-35 is normally gets a thrashing by the media.

[Tommy Cookers]

.....wing efficiency of what is essentially an 80 year old design.

in Prandtl's time planes had poor wing efficiency in flight because the wings were too big, sized for practical runway length
and a bigger wing is a disproportionately heavier wing

long since then this problem has been alleviated by lavish flap systems that greatly increase the lift coefficient when desired
such systems cause pitching moments that require a pitch trim authority that is impracticable without a length of fuselage ....
unless the aerodynamic stability is by design relaxed and replaced by artificial stability

the relaxation of aero stability is for public transport operations (ie airlines) severely limited by regulation
(beyond that limit a failure of the artificial stability system kills everyone)
such relaxation is bound up with potential for systems giving what we might call 'ride control' effects
eg the 777 and equivalents already have the permitted amount of these, to good effect

flap blowing (enabling smaller wings) is similarly banned for PT operations (though a key feature of the C-17 transport aircraft)

[NoDivergence]

Ha, I recognize my classmate in that groupshot from the Prandtl-D link.

The idea is that with twist, you can get yaw stability with a flying wing.

Add engines with nacelles, landing gear, payload/people, etc however, and all of a sudden you have a much larger flying wing with lower efficiency than the conceptual designs they are showing here.

[riff_raff]

Ever wonder why modern commercial jet aircraft with FBW controls still have such a huge vertical stabilizer? It's needed for yaw stability when you lose an engine.

Another known issue with these all wing concepts with significant sweep is positioning of the MLG. At takeoff, the rotation of the aircraft about the the MLG will result in the aft swept wing tips contacting the runway surface, unless a very tall landing gear is used.

[Tommy Cookers]

what is needed wrt yaw when losing an engine (at high thrust and low airspeed) is control authority, not stabilty as such
the flying wing/tailless design can have good yaw control from tip drag control (at large span)
707 on, airliners have in yaw some artificial stability from rudder 'yaw damper' and auto rudder control synthecising turn coordination
and now they (can) have automatic rudder control input (trim ie offset) wrt thrust loss as above (eg the ATR crash in Taipei)

the flying wing/tailless design is good on Mars as a very low wing loading is needed due to the very low density of the atmosphere
low wing loading means a large span, very large conventional designs tend to structurally inefficiency as the load is far from the lift
(they also tend to structural inefficiency to keep enough fuselage natural frequency eg in bending, due to the length)

so the airlines might go FW/T as the best way to get 1000-1500 seats (without windows of course)
an intermediate treatment is eg a double A380 (2 fuselages puts payload closer to the lift)
or Arado style (pod fuselage and 2 seperate tails each on a short boom far out on wing)

ideally for some purposes we might have artifical aerodynamic stability/ride control and FSW or even artificial structural stability


auto, Rotodyne was killed by Eland's inability to bleed enough for VTOL rotor-tip drive, so (impossibly noisy) ramjets were substituted

[trinidefender]

.....wing efficiency of what is essentially an 80 year old design.

in Prandtl's time planes had poor wing efficiency in flight because the wings were too big, sized for practical runway length
and a bigger wing is a disproportionately heavier wing

long since then this problem has been alleviated by lavish flap systems that greatly increase the lift coefficient when desired
such systems cause pitching moments that require a pitch trim authority that is impracticable without a length of fuselage ....
unless the aerodynamic stability is by design relaxed and replaced by artificial stability

the relaxation of aero stability is for public transport operations (ie airlines) severely limited by regulation
(beyond that limit a failure of the artificial stability system kills everyone)
such relaxation is bound up with potential for systems giving what we might call 'ride control' effects
eg the 777 and equivalents already have the permitted amount of these, to good effect

flap blowing (enabling smaller wings) is similarly banned for PT operations (though a key feature of the C-17 transport aircraft)

Many aircraft are still built in the shape they are simply because the surrounding airports and gates are built to accommodate that already. Include that almost all research is currently based on the typical pressurised tube with moderately swept wings distinct from the bodywork. That just means that it is a safe conservative design for airframe manufacturers as far as stress tolerances, production lines and aerodynamics are concerned, very few surprises and "new" R&D needs to be done.

Concerning control stability I am of the opinion that the regulations should be relaxed somewhat (no pun intended) all modern Airbus (and many not so modern designs) use complete fly by wire controls. Using the argument that if the computers (all about 5 redundancies if I remember correctly) fails then aircraft control is lost can also be applied to their FBW control systems. Not to the level of military aircraft but it is something that can be looked into in the quest of more efficiency.

Even the helicopter I fly has no direct action between the cyclic and collective and the hydraulic actuators, just 2 hydraulic systems. This helicopter is used for public transport. There is also a stability system that does much of the stability work, you don't realise how much it is working until you lose the system, granted the aircraft is still fly able without it, it is just very uncomfortable and very tiring.

P.s. Before somebody mentions the direct flight control logic used in Airbus' that can be used don't forget that this is still computers, it is just a control logic where the inputs on the flight controls are not filtered or altered by the computers and the bank, yaw and roll limits are removed.

Boeing was and probably still is looking at the use of a blended body and wing with a fairly long and swept wingspan. As far as I'm aware some of the main constrictions are:
1. Gates sizes
2. Runway/taxi widths
3. Public perception on what an aircraft should look like (yes companies do look at this)
4. Cost of R&D on such a new design especially as far as stress, fatigue life and aerodynamics
5. The regulations excluding relaxed control law in passenger transport aircraft
6. Lack of windows = unhappy passengers
From an aerodynamics point of view the design was looking promising.

[trinidefender]

what is needed wrt yaw when losing an engine (at high thrust and low airspeed) is control authority, not stabilty as such
the flying wing/tailless design can have good yaw control from tip drag control (at large span)
707 on, airliners have in yaw some artificial stability from rudder 'yaw damper' and auto rudder control synthecising turn coordination
and now they (can) have automatic rudder control input (trim ie offset) wrt thrust loss as above (eg the ATR crash in Taipei)

the flying wing/tailless design is good on Mars as a very low wing loading is needed due to the very low density of the atmosphere
low wing loading means a large span, very large conventional designs tend to structurally inefficiency as the load is far from the lift
(they also tend to structural inefficiency to keep enough fuselage natural frequency eg in bending, due to the length)

so the airlines might go FW/T as the best way to get 1000-1500 seats (without windows of course)
an intermediate treatment is eg a double A380 (2 fuselages puts payload closer to the lift)
or Arado style (pod fuselage and 2 seperate tails each on a short boom far out on wing)

ideally for some purposes we might have artifical aerodynamic stability/ride control and FSW or even artificial structural stability


auto, Rotodyne was killed by Eland's inability to bleed enough for VTOL rotor-tip drive, so (impossibly noisy) ramjets were substituted

TC do you have more information about the rotodyne? Would like to do more reading up on it. Wonder what the fuel burn was like on it. Did they manage to get around the icing problem with rotors I.e. A de-icing system that creates a huge mess and has to be cleaned off after every flight? Not to mention rotor hubs and blades aren't very maintenance friendly, blades having a typically short TBO (time between overhaul). Retreating blade stall is also a major limiting factor of autogyros.

[Tommy Cookers]

try this below ?
at a glance it seems an existing but unwanted plane/engine died off, and a non-existent larger plane/engine went non-funded
http://h2g2.com/approved_entry/A34788667

the belief that they were forced to use actual ramjets (such as existed for tip-drive helicopters) is not inconsistent with the above link

Bill Gunston's writings eg 'Plane Speaking' were my source iirc
I can't seem to get a page view of Plane Speaking via Google, somewhere I have a few pages copied for educational purposes
others who witnessed the noise (eg John Farley ?) have written about it

[riff_raff]

"Many aircraft are still built in the shape they are simply because the surrounding airports and gates are built to accommodate that already. Include that almost all research is currently based on the typical pressurised tube with moderately swept wings distinct from the bodywork. That just means that it is a safe conservative design for airframe manufacturers as far as stress tolerances, production lines and aerodynamics are concerned, very few surprises and "new" R&D needs to be done."

Then consider the latest designs of military transport aircraft like the C-17, A400 or KC-390. None of these aircraft designs were restricted by existing airport infrastructure considerations, yet they all use the same high-wing, tall vertical stabilizer, and large T-configuration horizontal stabilizer arrangement. The same as decades-old designs such as the C-141 or C-5.

[Just_a_fan]

Those are all cargo/military lift aircraft. High wings mean big cargo volume, high tails means easier off loading in the air and on the ground.

[trinidefender]

"Many aircraft are still built in the shape they are simply because the surrounding airports and gates are built to accommodate that already. Include that almost all research is currently based on the typical pressurised tube with moderately swept wings distinct from the bodywork. That just means that it is a safe conservative design for airframe manufacturers as far as stress tolerances, production lines and aerodynamics are concerned, very few surprises and "new" R&D needs to be done."

Then consider the latest designs of military transport aircraft like the C-17, A400 or KC-390. None of these aircraft designs were restricted by existing airport infrastructure considerations, yet they all use the same high-wing, tall vertical stabilizer, and large T-configuration horizontal stabilizer arrangement. The same as decades-old designs such as the C-141 or C-5.

This "almost all research is currently based on the typical pressurised tube with moderately swept wings distinct from the bodywork. That just means that it is a safe conservative design for airframe manufacturers as far as stress tolerances, production lines and aerodynamics are concerned, very few surprises and "new" R&D needs to be done" still applies.

You'll also be surprised how many of the same design concepts used by these aircraft are shared in commercial aviation. Therefore it simply makes sense for an airframe manufacturer to share design elements where possible to cut down on R&D costs.

As for the high wing, T-tail and long vertical stabiliser, just think of the environment where they will be operating. Short unprepared landing strips where STOL (short takeoff and land) performance is one of the main requirements. Pretty much every plane takes more distance to land than to take off.
1. Placing the wing higher moves it further out of ground effect, this means that a plane is less likely to float down the precious little landing distance as it flares to cushion the landing, low wings prolong this float. Float is great for a nice smooth landing, not so great for stopping quickly. The high wing also moves the wing and more importantly the engine intake away from the ground reducing FOD (foreign object damage) to the turbine blades.
2. The high T tail gives good control authority at low airspeeds, especially desirable when you have a low rotate and climb out speed and a low approach speed.
3. Large vertical stabiliser for the same reason as T tail. Have good yaw control at low airspeeds.

These characteristics are generally shared among most aircraft designed to do the roll of landing on short unprepared landing strips at FOB's (forward operating bases) because they simply work and solve many problems not faced in the commercial world.

[nic08]

I'm studying about f1 aerodynamics and this is the first time that I encounter. words are new to me, especially the drag. What is drag? it's all about hindering the downforce. I don't understand. guys, could lend some information about f1 aerodynamics? I'm not engineer so I don't have enough reference about the topic. I researched also the net, but it entails about the schools and refer to this site. I want to study the formula one, without studying in the university.