Aerodynamics thread

[delft]

I have a request:

Does anyone have any information (research papers preferred) on aerodynamic properties (lift, drag calculations, etc.) for aircraft or UAV with either of these configurations:
1. Lifting body (something like the electric icarus)
2. boxed wing (something like that UAV from Chengdu)

If not, technical specifications from other existing aircraft that utilize these configurations would be helpful too.

I have not, I'm sorry.
But for a lifting body I would think of Facetmobile, rather than electric icarus. A great way to reduce weight and manufacturing effort.
Box wings have the advantage that you greatly reduce induced drag but the details of connecting the wing tips en the wing tip fence seems to have defeated early practicioners except those of about 1910. A major advantage should be reduced structure weight. I would think it would be ideal for a very high flying craft.

 

[T-U-P]

A major advantage should be reduced structure weight. I would think it would be ideal for a very high flying craft.

My intuition tries to tell me boxed wing would be heavier because of the extra structure involved, how does this design reduce weight?

@Air Force Brat:
After some searching, I really can't find any modern day boxed wing aircraft that have made the prototype stage except the Chengdu UAV that we've all seen here

 

[Air Force Brat]

My intuition tries to tell me boxed wing would be heavier because of the extra structure involved, how does this design reduce weight?

@Air Force Brat:
After some searching, I really can't find any modern day boxed wing aircraft that have made the prototype stage except the Chengdu UAV that we've all seen here

Designer Burt Rutan of scaled composites, created the model 58 and 59 boxed wing or joined wing agricultural aircraft, although it was never prototyped, there were models. One of the supposed advantages was for a more survivable craft in the event of a crash, the boxed structure giving added rigidity at a reduced weight. I believe Boeing also played with an unmanned vehicle, but your Chengdu Soaring Eagle or whatever is indeed a neat bird, now a lot of the beauty of such a design is no doubt the KOOL factor, never, ever, never ever ever, count out the KOOL factor, only pretty airplanes fly good, really! Yes I am smiling, but here goes, The boxed structure places the rear wing higher than the front, in clean undisturbed air, the boxed structure enables the two wings to have the benefits of a very narrow high aspect wing such as a glider, long and slender in a shorter more compact and more rigid wing, the main benefit here is weight, as one wing supports the other it eliminates the need for external struts or internal structure, reducing induced drag and weight all at the same time, while the narrow chord enables a more laminar flow. So rather than have a long droopy wing that needs internal structure [heavy], or external bracing struts or cables [draggy], the rear wing with its narrow chord laminar flow, actually functions as a lift strut for the slightly longer main wing, resulting in a high aspect ratio, low drag lifting structure, that is very strong for its weight, in addition to its vertical stab, the vertical support at the end of the top wing, boxes the wing structure and provides an end plate or winglet for the top wing, as well as directional stability about the yaw axis, and separates the main vortices of both wings, also notice the winglet on the main wing, again providing yaw stability and an end plate effect for efficiency.

So, even though at first blush I'm thinking geeky gimmick, its actually quite smart, in effect providing a long, narrow chord, high aspect ratio lift package, in a compact, efficient package, and as the wings converge near the center of the aircraft, they can all four be filled with fuel or sensors. Now this is not new per se, but it is a smart application given the requirement for a long narrow thin wing for a high aspect, laminar flow wing for efficiencies at high altitude.

Although this will seem like mindless drivel to some, feel free to use it without attribution, as my gift to a fellow aeronaut, and hopefully it will prime the pump so to speak, and get your own creative juices flowing. And finally, go learn to fly, your ahead of the game already, and you will soon be able to "see" airflow, in much the same way a glider pilot has to "see" lift. AFB

 

[usaf0314]

Designer Burt Rutan of scaled composites, created the model 58 and 59 boxed wing or joined wing agricultural aircraft, although it was never prototyped, there were models. One of the supposed advantages was for a more survivable craft in the event of a crash, the boxed structure giving added rigidity at a reduced weight. I believe Boeing also played with an unmanned vehicle, but your Chengdu Soaring Eagle or whatever is indeed a neat bird, now a lot of the beauty of such a design is no doubt the KOOL factor, never, ever, never ever ever, count out the KOOL factor, only pretty airplanes fly good, really! Yes I am smiling, but here goes, The boxed structure places the rear wing higher than the front, in clean undisturbed air, the boxed structure enables the two wings to have the benefits of a very narrow high aspect wing such as a glider, long and slender in a shorter more compact and more rigid wing, the main benefit here is weight, as one wing supports the other it eliminates the need for external struts or internal structure, reducing induced drag and weight all at the same time, while the narrow chord enables a more laminar flow. So rather than have a long droopy wing that needs internal structure [heavy], or external bracing struts or cables [draggy], the rear wing with its narrow chord laminar flow, actually functions as a lift strut for the slightly longer main wing, resulting in a high aspect ratio, low drag lifting structure, that is very strong for its weight, in addition to its vertical stab, the vertical support at the end of the top wing, boxes the wing structure and provides an end plate or winglet for the top wing, as well as directional stability about the yaw axis, and separates the main vortices of both wings, also notice the winglet on the main wing, again providing yaw stability and an end plate effect for efficiency.

So, even though at first blush I'm thinking geeky gimmick, its actually quite smart, in effect providing a long, narrow chord, high aspect ratio lift package, in a compact, efficient package, and as the wings converge near the center of the aircraft, they can all four be filled with fuel or sensors. Now this is not new per se, but it is a smart application given the requirement for a long narrow thin wing for a high aspect, laminar flow wing for efficiencies at high altitude.

Although this will seem like mindless drivel to some, feel free to use it without attribution, as my gift to a fellow aeronaut, and hopefully it will prime the pump so to speak, and get your own creative juices flowing. And finally, go learn to fly, your ahead of the game already, and you will soon be able to "see" airflow, in much the same way a glider pilot has to "see" lift. AFB

I'm sensing i have found a fellow AE

 

[paintgun]

I'm sensing i have found a fellow AE

you guys should post more and educate us mere mortals, although its fully on your discretion

i really appreciate posts like AFB's above

 

[Air Force Brat]

I'm sensing i have found a fellow AE

Thanks usaf0314, just an old airforce brat, my Dad would have made a wonderfull engineer and and was a great pilot and teacher, he created me in his own image, I'm sure I know what he was thinking about when I was conceived. I have loved airplanes since I was old enough to know my name was The Air Force Brat, my formative years were spent on Air Force bases, and around airplanes and flying, I was able to fly one of my Dad's 130e student's Cessna 195s at Nine, and crashed a real C-130e flight simulator at Sewart AFB that same year, "too much nose down trim", I can recall standing up and pulling the yoke with all my might only to auger in, way before sims had a view out the cockpit window, just black paint, but it was a full motion simulator, they turned off the motion and large siren that would have announced my death to the world mercifully. A sad lack of Algebraic talent left me without the one critical tool to be a real engineer! I would tell you what my Dad said about me, but it was rather condescending, if collegial, but I just love to fly although I have been scared to near death by events at times, my best compliment from my Dad was that I was a "natural pilot", his only poetic utterance was when I was learning to fly, he stated, "some days when I fly, I can feel myself all the way to the wingtips, other days, I can't feel a thing past my finger tips!". I confess, I have had a few of both days, and a lot of days in between! AFB thanks again for the kind words Bax.

 

[MiG-29]

Re: J-20 The New Generation Fighter Thread IV

Well, I am confident this is likely true, all modern fighter aircraft and even some larger aircraft are attempting to create a lifting body configuration, and it is very obvious on the J-20 and T-50, and likely to a lesser extent on the F-22. For the record I have stated that Dr. Song is very honest, I never said he wasn't a good salesman, and he had to sell the J-20 to the people who would be designing/building/buying and operating it, every good engineer has to be a salesman, right eng?AFB

.

As you said all modern aircraft create fuselage lift.

But the point of all modern aircraft is how to compromise and use tactics to beat the enemy.


I will exemplify.

Stealth aircraft are heavier than their regular non stealthy partners.

F-22 weighs more than a F-14 and F-35 more than a MiG-29 at empty weight.
F-35 has a larger cross section than F-16 with higher drag.
With the advent of UHF radars stealth has been reduced. so i ask you.

If Germany deploys its UHF pasive radar adds IRIS-T to a supercruising Eurofighter and meteors to AESA E-captors, how can you know stealth remains an option?

Tactics will be needed, because if the new German radars can do what Germany claims it can, Eurofighter still is an option.

All is compromises, T-50 has podded nacelles and engines, increasing the angular deflection sector but reducing drag on a less ideal configuration for supercruising, for such a reason T-50 has a very small nose cross section.
If you add radar blockers you reduce the volume and weight that S ducts increase but adds the need of a blocker.
Both S ducts and radar blocker reduce the efficiency of the air fed to the intake, you can see on 4th genration fighters they usually had straight inlets with no radar blockers in example F-15 and Su-27.

So at the end tactics are the difference, to put you an example the Zero was more agile than the Hellcat, but with the right tactics the hellcat beat the Zero most of the time.

MiG-29 was also a disappointment in during the 1990s not because it was a bad dogfighter, but because the F-15 used tactics that forced the MiG-29 into fights it never could use its advantages.

J-20 has in its canards the problem to solve more drag at cruise flight and radar deflectivity of its all moving canards and lack of TVC nozzles, add its ventral fins, you can see it has weak points in the design as T-50 or F-22 do.


To beat an enemy you need to avoid to fight in the way it will use its strengths, all these design teams are thinking how smart and out fly the opposition using the strengths of their designs.

It seems Europe and Germany consider UCAVs and their new radar will be enough to defeat stealth fighters even still flying Eurofighters.

As a note Rafale has canards better positioned than J-20 and a smaller cross section, however it lacks full blown stealth.( see Rafale supercruises at Mach 1.4 with engines no more powerful than those of MiG-29s or F-18Es)


To put it in context Rafale has lerxes, better optimised canards than J-20 and wing fuselage blending but lacks stealth in the way J-20 has.

If Europe can detect stealth aircraft, believe me Rafale is not a push over, it is a supercruising jet with very high agility.

 

[Engineer]

Re: J-20 The New Generation Fighter Thread IV

There's one thing about canards and horizontal stabilizer that's been bugging me and I hope you guys can help answer me.

By using the horizontal stabilizer to control pitch and angle of attack, is the g-force on the pilot far less than it would have been the case with canards because the pivot is at the rear of the plane and not near the cockpit? If it is true, is it one the chief reasons the Americans don't use canards?

The pivot is at the center of gravity, and has nothing to do with the pitch control surfaces.

The g-force felt by the pilot is a result of continuous change in direction of flight, and has little to do with pitching motion.

The Americans did consider use of canard on occasions, as have happened with the

Please, Log in or Register to view URLs content!

. However, American engineers have other priorities so those designs never made it to production aircraft.

 

[MiG-29]

Re: J-20 The New Generation Fighter Thread IV

[The canards do not kill lift, they provide pitch control, and they add to the total lift produced by the aircraft throughout the speed range, one of their many advantages and one of the reasons Dr. Song has used them to add lift and increase the speed of pitch transitions throughout the speed range. ALL fighter aircraft of modern design incorporate "lifting body technology so that the fuselage configuration adds to the total lift produced and increase efficiencies.

no sorry you are wrong.

Canards add lift at high alpha, when the aircraft is a 30 degrees yes there they add lift, at 0 degrees they do not, at cruise flight flying straight like a liner, the canard wake kills lift because turbulance is added to the main wing.
Supersonic cruisers like T-4 or XB-70 for a reason set their canards forward away from the wing.

F-22 for such a reason uses tailplanes, it is a compromise, yes F-22 does not have the added lift at high AoA of J-20, but at supercruise the F-22`s wing loses less lift, add the TVC nozzles and F-22 saves fuel and tailplane deflection.


F-22 for that reason does not use a canard and the TVC nozzles add the extra few degrees of turn a canard might add.

T-50 uses Levcons for the same reasons since levcons do not downwash the wings killing lift.

However J-20 can use its canards as control surfaces and sweep the wing higher thanks to canards.

All these jets lose something and win something.

 

[Engineer]

Re: J-20 The New Generation Fighter Thread IV

no sorry you are wrong.

Canards add lift at high alpha, when the aircraft is a 30 degrees yes there they add lift, at 0 degrees they do not, at cruise flight flying straight like a liner, the canard wake kills lift because turbulance is added to the main wing.
Supersonic cruisers like T-4 or XB-70 for a reason set their canards forward away from the wing.

F-22 for such a reason uses tailplanes, it is a compromise, yes F-22 does not have the added lift at high AoA of J-20, but at supercruise the wing loses less lift, add the TVC nozzles and F-22 saves fuel and tailplane deflection.


F-22 for that reason does not use a canard and the TVC nozzles add the extra few degrees of turn a canard might add.

T-50 uses Levcons for the same reasons since levcons do not downwash the wings killing lift.

However J-20 can use its canards as control surfaces and sweep the wing higher thanks to canards.

All these jets lose something and win something.

Actually, you are wrong. The wake that you spoke of is the vortex which creates lift through energizing air flow above the wing. What's more, the canard not generating additional lift at zero angle of attack does not mean they produce negative lift. Get your facts straight.