Artifical Gravity & Inertia Dampers

[HG_B]

Ahem... Tacoma Narrows Bridge....

Ahem... Not exactly what happened http://en.wikipedia.org/wiki/Aeroelasticity#Flutter

A Scout ship isn't elastic. The forces from any "lift" where almost nothing. Different animal.

In addition, this isn't the same as a roof where wind is only blowing over one surface. You're thinking of how they design chimneys and such. In short, to have a bad effect on a huge slab of rigid, heavy metal lying a few feet above ground, you need winds of several hundred miles an hour.

 

[Vladika]

Bad example. The roof experiences that effect because of the lowered pressure as the wind isn't blowing beneath it, only over one side. A slab exposed on both sides to the same wind doesn't experience that effect.

Still is a good example. The thickness of the scout ship certainly does allow for two different and separate effects. Same as a building on piles or stilts. Wind on top, wind on bottom.

You are correct, to a degree about a "flat sheet". That would fail, in all probability, due to a harmonic wave situation. (Or simply a "flapping flag" effect.)

As for "Galloping Gertie", the bridge deck was not stiff enough so harmonic wave effect did it in. All modern suspension bridge designs learned from this and you will see a much deeper structure, often a truss system or a "box" cross section.

 

[HG_B]

Still is a good example. The thickness of the scout ship certainly does allow for two different and separate effects. Same as a building on piles or stilts. Wind on top, wind on bottom.

So, so at best. A roof uses ZERO airflow on the underside. A Scout ship, no where near that differential. But it could happen with a wind of many hundreds of MPH.

 

[Vladika]

So, so at best. A roof uses ZERO airflow on the underside. A Scout ship, no where near that differential. But it could happen with a wind of many hundreds of MPH.

That was my point in saying it shouldn't be a problem on Earth but might be on other planets. Wind forces on Earth just aren't going to effect a typical Traveller Starship, whatever it's configuration. They're just to heavy.

(For an oversize "flying wing" I'm not going to state that as a given.)

Assumption, on my part, is that we are talking about "on the ground".

 

[PFVA63]

Hi,

Here's a link to some info on the turbulence impacts and response of the M2-F3 lifting body describing some of the issues that this type of craft experienced.

http://books.google.com/books?id=iB...gQ6AEwCQ#v=onepage&q=HL-10 turbulence&f=false

Specifically the attached link notes that:

"The gust response of an unwinged is considerably different from that of winged aircraft. In conventional aircraft, turbulence primarily affects the vertical, felt in the seat of the pants. In a lifting body, turbulence primarily affects the horizontal, producing small amounts of sideslip disturbance, resulting in a high-frequency rolling sensation. This was particularly true at low elevations where turbulence could be most severe.

...

Mysterious upsets occurred at altitude as well, usually during the powered portion of a profile. The pilos found these upsets 'spooky'. The program engineers hypothesized that these upsets were caused by wind shears. ..."

As such, I'd still suspect that a body like a Scout/courier would still experience some form of dynamic disturbances while operating in an atmosphere.

 

[HG_B]

As such, I'd still suspect that a body like a Scout/courier would still experience some form of dynamic disturbances while operating in an atmosphere.

Except, the type S hull isn't a lifting body. It is symmetrical, flattened pyramid (arrowhead). So other than they most critical element, you're onto something.

 

[PFVA63]

Hi,

Actually I believe that a flattened pyramid is a lifting body, especially when operating at an angle of attack to its direction of travel.

 

[HG_B]

Hi,

Actually I believe that a flattened pyramid is a lifting body, especially when operating at an angle of attack to its direction of travel.

No. It is actually less of a lifting body than a flat board.

 

[Carlobrand]

The average person really has no real concept of wind forces power or effect.
...

That would be me. Well, not completely: I lived in Houston for a few years before I moved to this godforsaken desert, went through two hurricanes there, so I've got some vague idea of wind's power. However, there's a big difference between having respect for it and knowing how it actually works. I am learning a lot in the course of trying to follow this discussion, and you guys are a whole lot easier to understand than the Wiki articles:

"... turbulence or turbulent flow is a flow regime characterized by chaotic and suspectedly stochastic property changes ..." o:

 

[aramis]

No. It is actually less of a lifting body than a flat board.

USAF is using flattened pyramids as lifting bodies for some drone tests. The angle of attack is Critical to their lift, but they DO generate lift.

 

[PFVA63]

USAF is using flattened pyramids as lifting bodies for some drone tests. The angle of attack is Critical to their lift, but they DO generate lift.

Hi,

Thanks for the additional info. As I understand it, technically a flat board can also be considered a lifting body when operating at an angle of attack.

 

[aramis]

Hi,

Thanks for the additional info. As I understand it, technically a flat board can also be considered a lifting body when operating at an angle of attack.

Give me enough thrust and control over the direction, and I can make even a pig fly... but unless I can get asymmetric airflow, I can't get aerodynamic lift. A flattened pyramid can get aerodynamic lift. A flat sheet, if the air is not flowing along the plane of the sheet, develops aerodynamic lift.

The Tacoma Narrows bridge developed its harmonic vibration because the gusts developed lift, elevated, stalled, dropped, repeat. The lack of rigidity and the local topology resulted in this aerodynamic lift due to asymmetric airflow across the bridge deck. Plus, the airflow, due to the local topology, was already turbulent.

A flat sheet of material is a very poor lifting body if flexible and not under tension. And remember: flag flutter is literally caused by the same principles as aerodynamic lift.

 

[PFVA63]

Give me enough thrust and control over the direction, and I can make even a pig fly... but unless I can get asymmetric airflow, I can't get aerodynamic lift. A flattened pyramid can get aerodynamic lift. A flat sheet, if the air is not flowing along the plane of the sheet, develops aerodynamic lift.

The Tacoma Narrows bridge developed its harmonic vibration because the gusts developed lift, elevated, stalled, dropped, repeat. The lack of rigidity and the local topology resulted in this aerodynamic lift due to asymmetric airflow across the bridge deck. Plus, the airflow, due to the local topology, was already turbulent.

A flat sheet of material is a very poor lifting body if flexible and not under tension. And remember: flag flutter is literally caused by the same principles as aerodynamic lift.

Hi,

Thanks for the additional info. As I recall for a reasonably rigid wing, both shape and angle of attack impact the lift that it develops. Hence I can see where you are coming from with a non rigid flat plate being a poor lifting body. However, for a rigid flat shape, its my understanding that with an angle of attack it will develop lift.

Interestingly, with respect to uniform shapes (as opposed to flat plates), such as the conical shaped Apllo module with its curved bottom, it also acted as a lifting body upon re-entry (as I understand it). I also believe that the Mercury and Gemini Capsules also reacted similarly.

 

[SanDragon]

Ahem... Not exactly what happened http://en.wikipedia.org/wiki/Aeroelasticity#Flutter

A Scout ship isn't elastic. The forces from any "lift" where almost nothing. Different animal.

In addition, this isn't the same as a roof where wind is only blowing over one surface. You're thinking of how they design chimneys and such. In short, to have a bad effect on a huge slab of rigid, heavy metal lying a few feet above ground, you need winds of several hundred miles an hour.

Isn't that flirting with wing-in-ground effect?

 

[aramis]

Isn't that flirting with wing-in-ground effect?

Ground Effect is part of why aircraft can flip below stall speed.

During my flight instruction, i got a sortie on a Schweitzer S-32 Glider... I was 10 Kts BELOW full flaps stall speed, and stuck at 10' above ground level for over 500 feet of runway...when it finally did stall out, it dropped the last 10' in a single jolt. Mind you, stall was about 33kts... and it dropped out at about 20 Kts indicated airspeed....

And a 25kt gust while putting it away lifted the wheel, despite the flaps being retracted. And 4 CAP cadets. Without the four on the wing, it'd have flipped right over.

 

[Fritz_Brown]

An airliner isn't ANYWHERE in the weight range of a starship, for its volume. Maybe ~1/5 the weight at most.

Which is still a lot closer than a DeHavilland Twin Otter.

Here's a link to some info on the turbulence impacts and response of the M2-F3 lifting body describing some of the issues that this type of craft experienced.

Ah, yes, good to remember we do have experience with lifting bodies. Of course, they've only ever been involved in disaster. (1969 movie Marooned, and of course The Six Million Dollar Man.)

And remember: flag flutter is literally caused by the same principles as aerodynamic lift.

Yes. If you suddenly released the points holding it to the flag pole, it would begin flying. It would then collapse in on itself and fall to the ground, of course. But, that's why we don't build our starships out of thin flexible sheets of nylon fabric.

 

[PFVA63]

Hi,

Here is some info on the "dart shaped" DARPA "Falcon" Hypersonic Test Vehicle (Lifting Body).

http://en.wikipedia.org/wiki/DARPA_Falcon_Project

http://www.youtube.com/channel/HCoz99WxKWbDU

 

[Carlobrand]

It does, in fact, have a larger surface up top than on bottom.

 

[HG_B]

Hi,

Here is some info on the "dart shaped" DARPA "Falcon" Hypersonic Test Vehicle (Lifting Body).

It is NON symmetrical top & bottom. Do you understand what that means? The Type S IS symmetrical. Do you understand the effect of that?

I suggest a course on aeronautics at your nearest community college if you want to understand this topic in order to further discuss.

 

[Ishmael]

it doesn't matter if the profile is asymmetrical, its the airflow that matters.
Consider the many uses of symmetric airfoil, such as the NACA 00xx or NACA 00xxx series. One famous plane that used them was the Boeing B-17 where both the root and the tip were symmetric. Also many helicopter rotor blade profiles are symmetric. the Convair F-102 and F-106 are examples of interceptors with symmetric airfoils.

All the 'curved' asymmetric surfaces of an airfoil indicate is a non-zero camber. This affects the airfoils angle of zero lift, which works in conjunction with the wings angle of incidence to give the angle of attack in level flight.

The tradition curved asymmetric profiles are generally crap in supersonic flight, hence the interest in wedge and diamond ( double wedge ) profiles. These allow a more favorable location of shock waves and lowered wave drag at speed.

Controls, such as ailerons, and flaps allow control by altering the camber line of the airfoil changing its lift characteristics. Fowler flaps also increase effective wing area.