effect of vortices on an aerofoil lift dynamics behind another one

[tylor2000]

I know this is probably a specific answer behind a specific question, but I'm in the planning stages of an aerospace add-on(ship/plane) which involves a construction similar to Horatio's multi-plane( http://en.wikipedia.org/wiki/Horatio_Frederick_Phillips )and want to make it as realistic as possible and need a general pointer.

My problem is the vortices behind one aerofoil and it's effects on the aerofoil behind it. How far back do I need to put a successive airplane behind another in terms of a length ratio, and even then does it effect the lift charateristics no matter how far back I put it? Is this the one reason his multi-plane had such a hard time getting off the ground? I'm in the process of figuring/calculating this out for myself but am consulting you guys for input. Partially because I know theory and engineering don't always go hand in hand, and I'm far off from being an aerospace/aerofoil engineer. (which is a huge understatement) )

thanks,

tylor2000

---------- Post added at 09:43 PM ---------- Previous post was at 09:39 PM ----------

oh, by the way I have the vertical component (tri-plane, bi-plane) down pat. No help needed there.

tylor2000

 

[agentgonzo]

I don't know for certain, but I remember hearing ages ago that the next plane coming in to land after a 747 has to be about 5 miles behind due to the turbulence from the 747. I think that's more to do with the engines than the aerofoils though.

 

[tylor2000]

Yeah, I had that in mind too when I was thinking of this. About small planes behind bigger ones having the possibilities of flipping over and such. But yeah maybe the engines have more to do with that. I'm just trying to cover all the bases (or at least any major ones) so people aren't like, "Hey! that is totally unrealistic! How is it supposed to do that!" when captain kirk, obe one kanobe, or jean luke picard isn't supposed to be jumping off, or beaming down from, this particular craft.

Having a graphene, bucky ball, carbon nanotube, some thing or another as of yet fictitional or undecided composite built structure with an aspect ratio over 152+ is pushing the envelope enough already.

I was reading about the voyager that circled the globe back in 1986, and how it was made of graphite, it's construction, as a object of inspiration for this. If you can make something that can go that far how about something that can go that high? But I'm getting off topic already. I should probably make a separate thread about this...

tylor2000

 

[Sunhillow]

Hi

the most enduring turbulence created by large airplanes are the wingtip vortices. See http://en.wikipedia.org/wiki/Wingtip_vortices

 

[Kozak]

How far back do I need to put a successive airplane behind another in terms of a length ratio, and even then does it effect the lift charateristics no matter how far back I put it? Is this the one reason his multi-plane had such a hard time getting off the ground? I'm in the process of figuring/calculating this out for myself but am consulting you guys for input. Partially because I know theory and engineering don't always go hand in hand, and I'm far off from being an aerospace/aerofoil engineer. (which is a huge understatement)

There's no way to calculate vortice effects explicitly for the moment, and likely there will not be one - as these problems are solved by CFD now. But I can give you some hints:
1.In normal non-stalled flight vortices are produced only on the wing ends and extend very slowly. That means, they will not have significant influence for the discussed design;
2.Due to their slow propagation, if one wants to fully avoid the interference, the only way to do it is to make the rear wing narrower than forward one.
3.Vortex creation depends on wing loading. For an aircraft that takes off at ~50kph (and has a "blurred" wingtip), that value is surely high - hence the vortexes created are negligible.

I think that's more to do with the engines than the aerofoils though.

No, it's solely due to wingtip induced vortices. Jet engine exhausts always go through a set of blades to eliminate rotation and direct all energy into propulsion.

 

[ex-orbinaut]

I don't know for certain, but I remember hearing ages ago that the next plane coming in to land after a 747 has to be about 5 miles behind due to the turbulence from the 747. I think that's more to do with the engines than the aerofoils though.

It is actually more dangerous to approach in a light aircraft on the same glide path behind a 757. They are notorious. Jet blast is one thing, but it is more of a factor if you are taking off behind another aircraft rather than landing. On approach it is, indeed, the vortices that cause the hazard.

I know this is probably a specific answer behind a specific question, but I'm in the planning stages of an aerospace add-on(ship/plane) which involves a construction similar to Horatio's multi-plane( http://en.wikipedia.org/wiki/Horatio_Frederick_Phillips )and want to make it as realistic as possible and need a general pointer.

My problem is the vortices behind one aerofoil and it's effects on the aerofoil behind it. How far back do I need to put a successive airplane behind another in terms of a length ratio, and even then does it effect the lift charateristics no matter how far back I put it? Is this the one reason his multi-plane had such a hard time getting off the ground? I'm in the process of figuring/calculating this out for myself but am consulting you guys for input. Partially because I know theory and engineering don't always go hand in hand, and I'm far off from being an aerospace/aerofoil engineer. (which is a huge understatement) )

thanks,

tylor2000

---------- Post added at 09:43 PM ---------- Previous post was at 09:39 PM ----------

oh, by the way I have the vertical component (tri-plane, bi-plane) down pat. No help needed there.

tylor2000

What exactly are you trying to calculate? From what you state you seem to be after interference drag, not wake turbulence. That WOULD certainly have been one problem with the aircraft portrayed in the pic. But the main problem in the design, as far I as can see, would be the boundary layer issue a series of wings set in such close proximity to each other in the vertical sense would produce (more so than the wings behind the leading set). The dynamic pressure produced under each adjacent upper wing would be "force feeding" pressure into the partial vacuum on the upper surface of the lower wing and negating it the chance of producing lift. Quite what the downwash effect of this would be is difficult to tell, but basically, it is only the top wing of each set in tandem that would be producing any "effective" lift, and the area of these combined falls far short of being enough. That would be my guess....

Edit: But on second thoughts, it is still an upward force on the foils, isn't it? Third law and that...

Another issue I see is the back stagger the wings would assume relative to the airflow at high AoA (slow flight), with each CP under the leading edge of the wing above it. What ever the root cause (and there are a few evident at a glance), there is certain to be airflow interference one way or another, somehow, which cannot be good, hmm?... Fascinating if somewhat flawed ideas in the "paddling pool days" by that ole Phillips fellow.

 

[tylor2000]

Thank you guys for your input. I'm mostly trying to make sure I'm not missing anything that I shouldn't be missing. I was a little worried about things like the bound layer transition turbulence/vorticies but now not really. You don't really see airplanes constructed like the multiplane of 1907 and so I was wondering about unknown complications due to the design. I'm thinking that with new materials the thing would be lighter and stronger then what was constructed back then and already know the stack(of planes) efficiency issues built in. You are not going to get 100% more lift out of each consecutive aerofoil added on top.

 

[ijuin]

The diminishing returns for having more airfoils is exactly why there were almost no non-experimental aircraft that had more than four wings stacked vertically--a quad-plane does NOT get twice the lift of a biplane.

 

[Notebook]

Jet blast is dangerous, even on the ground:
http://www.aviationexplorer.com/747_engine_blast.htm

N.

 

[tylor2000]

Jet blast is dangerous, even on the ground:
http://www.aviationexplorer.com/747_engine_blast.htm

N.

I wonder who they got to drive the car! Being in taped in san francisco it probably wasn't to hard to find the test pilot for that one!:speakcool:

 

[Notebook]

Must be Chuck Norris.

N.

 

[tylor2000]

Doesn't he live in Los Angeles? I was talking about just some random person on the street.

 

[pattersoncr]

Must be Chuck Norris.

N.

When Chuck Norris walks across the runway, the 747 ready for takeoff has to wait for his wake turbulance to clear.

 

[Notebook]

Doesn't he live in Los Angeles? I was talking about just some random person on the street.

He does, but he also makes house-calls

Seriously, I think its being towed by the fire-engine in front, some kind of quick release linkage.

N.