Location of wings

[drgondog]

True, but the drag coefficent is depending from the object's shape.

First, due to the pressure gradient distribution, the mid-wing configuration makes a less draggy coef, from itself.

Two questions, particularly with respect to single engine propeller driven ships. 1.) how were pressure gradients measured in the 30's and 40's, and 2.) how were the effects of a wing immersed in a stream tube measured (or even more interestinly, calculated)?

Comment - calculating a pressure gradient distribution immersed in a propwash was then, and is now, impossible - to my knowledge - for a three dimensional subject.

The combination of a laminar flow model, for potential flow, using for eaxample a distribution of sources and sinks, then combining 'plugged in' positive pressure distribution to account for boundary layer separation is in itself an art for a simple wing, but applying a similar technique when adding a fuselage and the 3-D effects of a turbulent stream tube originating upstream is an order of magnitude more difficult.

Perhaps I misunderstood what you meant by a pressure gradient distribution method of calculation? and where it might be found in pre WWII literature.

Second, the total wing + fuselage assembled altogether drag is higher than arithmetic separate values for both components.
Total drag = wing drag + fuselage drag + interference drag. To reduce the last one, you use Karman fairings. Assuming even some (little) drag loss due surface increase, you win anyway more at the end, on drag coef reducing. The last one being significant.

The contribution to wing/body effect of vortex drag (due to wing twist, tip config, aspect ratio, wing/body interference, etc) is far more dependent on wing span to fuselage diameter ratio than any form of fillet, although a blended wing body approach like an SR-71 reduces wetted area drag components.

Your state would be true if the fairing (of any kind) re-intruduced laminar flow, or conversely reduced turbulent flow with respect to a low or high wing config - which leads us back to the question posed above regarding the immersion in a stream tube of turbulent (and rotational) prop wash.

Bringing us back to the question - how prove the thesis?

They are much more efficient ( they =Karmans) on rounded or oval section fuselage in mid wing position also, than on the others formulas.

Magnitude of 'much more' efficient even assuming that experimental values approximating real conditions (wind tunnel model with fully operating power plant/prop)

The P-38 demonstrated that wing fillet was added to the mid-wing configuration would reduce turbulent flow separation but again this was not immersed in a propwash stream tube.. furter there were no comparisons against a 'low wing configuration' to compare in a wind tunnel.

Third, all that jobs were maid in wind tunnels since early twenties, more that enough times. All results are published (by Eiffel, Göttingen, ONERA, TsAGuI centers ...) and available in much specialised scientific highschool libraries.

It's not a big secret/discovery. Maybe searching at the NACA site you can browse values on the WEB.

Regards.

I am unable to get to my own texts until I unpack.

My question regarding the mid wing vs low wing position is not so much the potential advantage of a mid wing vs low wing drag contribution , but of the relevance or magnitude of the wing/body contribution to the vortex, or total induced drag, when discussing prop driven aircraft.

 

[drgondog]

A pretty good article on total components of drag, and theri relative contributions, for this discussion.

Lift-Dependent Drag Items

 

[VG-33]

Hello drgong

I am unable to get to my own texts until I unpack.

My question regarding the mid wing vs low wing position is not so much the potential advantage of a mid wing vs low wing drag contribution , but of the relevance or magnitude of the wing/body contribution to the vortex, or total induced drag, when discussing prop driven aircraft.

Frankly, there's too much thinks i don't understand in you post. I'm afraid you went a question too far with me...

Two questions, particularly with respect to single engine propeller driven ships. 1.) how were pressure gradients measured in the 30's and 40's, and 2.) how were the effects of a wing immersed in a stream tube measured (or even more interestinly, calculated)?Comment - calculating a pressure gradient distribution immersed in a propwash was then, and is now, impossible - to my knowledge - for a three dimensional subject

1) You speak about 3D effects on turbulent stream... and you want me to explain the use of barometric instruments and and pitot tubes?

2) Don't you think the Navier-Stokes equation system includes 3D mouvements?Look at incompressible (simplified) conditions, for instance:
Navier?Stokes equations - Wikipedia, the free encyclopedia
Of course it takes a specialised programm to make it run, and rather a full work-station. You can run turbulent (rotationnal) NS system too, by including some other simplified conditions.

I had never talk about any pressure gradient distribution method of calculation and where it might be found in... Just about pressure hudge increase on wing roots, leading to pressure losses, you can reduce using some Karmans fairing leading to smooth speed/pressure vriation, and also by reducing the overall fuselage section on that (wing) place to follow the "streamlined body" law (Not the whitcomb one) for low speeds. The one that gives "rain drops" or Mustang canopy shapes.

For instance, the homebuilt Colomban MC 100
Modèles / Colomban MC 100 BanBi | Les FoxPapa en images

has it's max fuselage section behind the wing. Another way to reduce recompression drag.

A pressure gradient is just the vector of pressure variation applied in 3D space, nothing more...You can also find speed gradients, temperature gradients etc.... in life.


Just my five pence to contribute, since NACA's reports are available on web, not the TsAGuI ones:
The same thing (fortunately...), but in russian:

It would be surprising if TsAGI wind-tunnel was not correlating NACA's one...

Bringing us back to the question - how prove the thesis?

Like for the Lenz law, just by observing and using it effects ? More seriously, i took it from a booklet edited in 1989 by SibNIIA (siberian institute for aerodynamics) for sporting and homebuild planes. No demonstration, just advices for amateur plane builders.

Regards

 

[drgondog]

Hello drgong

Frankly, there's too much thinks i don't understand in you post. I'm afraid you went a question too far with me...

LOL - I doubt it VG - you are well suited for this debate.

Let me clarify the debate.

1. I do not dispute the results for the Wind tunnel tests which concluded that the mid wing configuration was superior to high and low wing. The reason for most gliders having mid or mid high wing mount is clear.

2. My debate is whether the real world results of a mid wing configuration (all else equal - wing plan form, fillet type, fuselage geometry, etc) is significant for a forward mounted propeller driven aircraft in which the mid wing is entirely immersed in a turbulent stream tube.

3. Further, my debate/question is what methods were in place to confirm/disprove such thesis of immersion in turbulent stream tube for mid, low and high wing combinations?

1) You speak about 3D effects on turbulent stream... and you want me to explain the use of barometric instruments and and pitot tubes?

Yes to the effects, no to the 'possible use' of barometric instruments explanation. I was asking if you were aware of any wind tunnel tests made in which the geometry variation of wing position was further tested with and without the effects of an operating engine to assess the importance when the wing/body junction was immersed in high speed turbulent flow behind an operating engine-propeller combination.

2) Don't you think the Navier-Stokes equation system includes 3D mouvements?Look at incompressible (simplified) conditions, for instance:
Navier?Stokes equations - Wikipedia, the free encyclopedia
Of course it takes a specialised programm to make it run, and rather a full work-station. You can run turbulent (rotationnal) NS system too, by including some other simplified conditions.

Yes - I am very aware and conversant on Navier Stokes and its application although my personal experience is nearly 35 years past. Having said this, the application of Navier Stokes to solutions for combined laminar and turbulent flow is a.) still in the theoretical stage today and simply far beyond the engineers of the 30's and 40's ability to apply to the design of aircraft - mostly because neither the computers or the numerical methods to use in the solution of NS existed then.

It was extreme leading edge when I was in Graduate school in late 60's.

I had never talk about any pressure gradient distribution method of calculation and where it might be found in... Just about pressure hudge increase on wing roots, leading to pressure losses, you can reduce using some Karmans fairing leading to smooth speed/pressure vriation, and also by reducing the overall fuselage section on that (wing) place to follow the "streamlined body" low (Not the whitcomb one) for low speeds. The one that gives "rain drops" or Mustang canopy shapes.

For instance, the homebuilt Colomban MC 100
Modèles / Colomban MC 100 BanBi | Les FoxPapa en images

has it's max fuselage section behind the wing. Another way to reduce recompression drag.

A pressure gradient is just the vector of pressure variation applied in 3D space, nothing more...You can also find speed gradients, temperature gradients etc.... in life.

We have no argument on thses points


Just my five pence to contribute, since NACA's reports are available on web, not the TsAGuI ones:
The same think (fortunately...), but in russian:

The plots are the same as the 1936 NACA Report Shortround produced earlier. I have read it, understand it, and it led to my questions regarding applicability/relevance/magnitude of 'delta' interference/vortex drag when immersed in a turbulent stream tube.

Like for the Lenz low, just by observing and using it effects ?

This is what I was asking - how does one compare the test results of a conventional wing tunnel model on test stands designed to record lift and moments and drag for models without engines - to the real world.

Regards

VG - Below, from your Wiki link - is exactly the point I was making about Navier Stokes and the limits I experienced 35 years ago in its application to turbulent flow.

Turbulence
Turbulence is the time dependent chaotic behavior seen in many fluid flows. It is generally believed that it is due to the inertia of the fluid as a whole: the culmination of time dependent and convective acceleration; hence flows where inertial effects are small tend to be laminar (the Reynolds number quantifies how much the flow is affected by inertia). It is believed, though not known with certainty, that the Navier–Stokes equations describe turbulence properly.

The numerical solution of the Navier–Stokes equations for turbulent flow is extremely difficult, and due to the significantly different mixing-length scales that are involved in turbulent flow, the stable solution of this requires such a fine mesh resolution that the computational time becomes significantly infeasible for calculation (see Direct numerical simulation). Attempts to solve turbulent flow using a laminar solver typically result in a time-unsteady solution, which fails to converge appropriately. To counter this, time-averaged equations such as the Reynolds-averaged Navier-Stokes equations (RANS), supplemented with turbulence models (such as the k-ε model), are used in practical computational fluid dynamics (CFD) applications when modeling turbulent flows. Another technique for solving numerically the Navier–Stokes equation is the Large-eddy simulation (LES). This approach is computationally more expensive than the RANS method (in time and computer memory), but produces better results since the larger turbulent scales are explicitly resolved.

It has been enjoyable to debate this.

Regards,

Bill

 

[Timppa]

No position of a wing is really much of a factor in true stability.

Even from purely empirical standpoint this is not correct. Mostly:
Low winged aircraft have dihedral
High wing aircraft have anhedral.
Mid winged aicraft have straight wings or slight dihedral.

So it must be a factor.

 

[drgondog]

Even from purely empirical standpoint this is not correct. Mostly:
Low winged aircraft have dihedral
High wing aircraft have anhedral.
Mid winged aicraft have straight wings or slight dihedral.

So it must be a factor.

Timmpa - It is in Roll and I stated that earlier but you are correct in correcting the statement above. The dihedral/anhedral is particularly important at low speed roll control

from earlier post - the Entire statement "No position of a wing is really much of a factor in true stability. adding dihedral to a low mounted wing does however improve rolling moments, particularly at low speed, and all things being equal the high wing may be slightly better relative to roliing stability"

 

[VG-33]

This is what I was asking - how does one compare the test results of a conventional wing tunnel model on test stands designed to record lift and moments and drag for models without engines - to the real world.

Bill

AFAIK, not for 1932-33 wind tunnels, they were to small or to weak to contain a full -scale plane running at max power.

There were indirect joukovski methods to calculate propeller- fuselage mutual influence (again the charming equation systems with partial derivates as for Navier-St), or simplified approximated ones from wind-tunnel tests. From TsAGI:

No global integrated method of course, rather corrective ones, since benefits from blowed propeller tube on Cl, for instance were well known. I saw on web a Liliental polar with blow effect, and without, for a I-15; but can't remember where and when now. Probably at Sukhoi ru forum, too long ago...

Regards

VG-33

 

[drgondog]

AFAIK, not for 1932-33 wind tunnels, they were to small or to weak to contain a full -scale plane running at max power.

There were indirect joukovski methods to calculate propeller- fuselage mutual influence (again the charming equation systems with partial derivates as for Navier-St), or simplified approximated ones from wind-tunnel tests. From TsAGI:

No global integrated method of course, rather corrective ones, since benefits from blowed propeller tube on Cl, for instance were well known. I saw on web a Liliental polar with blow effect, and without, for a I-15; but can't remember where and when now. Probably at Sukhoi ru forum, too long ago...

Regards

VG-33

VG - I would love to have an english translation of that paper if you ever find one. It has been enjoyable to exchange thoughts on this subject.

Regards,

Bill

 

[VG-33]

VG - I would love to have an english translation of that paper if you ever find one. It has been enjoyable to exchange thoughts on this subject.

Regards,

Bill

I will translate, but later. Let me look after plane behavior within the prop current tube and without it, before.

Fig 227 drawings for instance, are representing speed braking (loss) curve for a motor gondola on wing, 1)without cylinders, 2)with them, 3)and with a ring cooling. All relative for different relative sizes and prop. distance.
There should be an equivalent from NACA or Farnborough WT trials.