Ground effect for blended wing body turboprop planes

[Czcibor]

I wondered about possibility of using ground effect by blended wing body, turboprop planes.

Purposes:
-to save fuel (for example for flying tankers);
-to return partially damaged plane;
-to hide under radar and become visible for ships in the last moment;
-to allow flight of overloaded plane, that would start behaving like plane after burning big part of its fuel (even if it required assisted take of).

Assumption:
-this plane is by not optimized for using ground effect but for normal flight;
-turboprop, so slow flight is OK for engines;
-plane operates mostly low quality AI, thus there is no problem of pilot tiredness;
-3at pressure on this exoplanet.

 

[stedwards]

Nice. Lifting bodies would be a cool thing and an expected variation over earthly Heavier Than Air vehicles in a denser atmosphere. As the atmosphere got denser HTA vehicles would morph from Cesna to Tuna.

What is the composition of the atmosphere? Lift is proportional to gas density rather than pressure.
Can you assume the atmosphere has oxygen to burn fuel?

 

[Czcibor]

Nice. Lifting bodies would be a cool thing and an expected variation over earthly Heavier Than Air vehicles in a denser atmosphere. As the atmosphere got denser HTA vehicles would morph from Cesna to Tuna.

Yes, easier to take off but awful drag reducing speed at low altitudes.

(I also like high pressure as it Earth like... almost)

What is the composition of the atmosphere? [...] Can you assume the atmosphere has oxygen to burn fuel?

91% N2
8% O2
~0,4% CO2 (varies, pending on amount of frozen on mountain tops on the dark side of planet; cold place in spite of green house effect)
The rest: noble gasses and water wapour

Lift is proportional to gas density rather than pressure.

Shouldn't, according to ideal gas constant pressure and density be quite well related?

 

[HuskyNamedNala]

Ground effect aerodynamics and flight aerodynamics produce very different designs. The stereotypical wing for a GEV (ground effect vehicle) has a very large chord with a low aspect ratio. On the other hand, flight aerodynamics generally favors high aspect ratio wings for efficiency. The ground effect vehicle wing has not been optimized yet. This is not the case for commercial and military aviation, which is why so many aircraft look similar - we have 100 years of data.

 

[snorkack]

I wondered about possibility of using ground effect by blended wing body,

How blended?
Fuselage is useful to carry tail and give it leverage.

-3at pressure on this exoplanet.

What is the gravitational acceleration?

Lifting bodies would be a cool thing and an expected variation over earthly Heavier Than Air vehicles in a denser atmosphere. As the atmosphere got denser HTA vehicles would morph from Cesna to Tuna.

...making the glide ratio correspondingly worse.
It is a flying wing that produces some gain in glide ratio. And ground effect again some.

cold place in spite of green house effect)
The rest: noble gasses and water wapour
Shouldn't, according to ideal gas constant pressure and density be quite well related?

Density depends significantly on temperature, as per ideal gas law. Also depends on composition.

-to allow flight of overloaded plane, that would start behaving like plane after burning big part of its fuel (even if it required assisted take of).

Assumption:
-this plane is by not optimized for using ground effect but for normal flight;

Where is the plane designed to take off from and alight to?

 

[stedwards]

Shouldn't, according to ideal gas constant pressure and density be quite well related?

For the same gas, yes. But compare hydrogen gas and O₂ at the same pressure. The density of hydrogen is about 1/16th that of O₂.

 

[Czcibor]

How blended?
Fuselage is useful to carry tail and give it leverage.

I thought about tailless. Assuming that I understand it correctly it has better aerodynamic properties. The drawback it is harder to steer, however in B-2 it was overcome by proper software, thus I think should be manageable.

What is the gravitational acceleration?

I thought about something around 8.5 m/s2.
(I'm not 100% sure how low gravity can I assume, before the atmospheric loss becomes significant)

Where is the plane designed to take off from and alight to?

For full load I thought about assisted take of in this style:
http://www.airbus.com/innovation/future-by-airbus/smarter-skies/aircraft-take-off-in-continuous-eco-climb/
(except that done by electric rail cart - not because electric rail car is so great, but in the setting there is inexpensive electricity and ready production line for train carts... ;) )

However, I also toyed with idea of possibility of using not fully loaded plane as hydroplane. The shape would be awfully improper at start. However, in such dense atmosphere the plane would be designed to fly with low speed, moreover stall speed would be really low. So I think in line plane -> sliding like hydrofoil -> hovering like GEV -> finally taking off.
Feasible or not speacialy?

 

[stedwards]

Nice. Lifting bodies would be a cool thing and an expected variation over earthly Heavier Than Air vehicles in a denser atmosphere. As the atmosphere got denser HTA vehicles would morph from Cesna to Tuna.

...making the glide ratio correspondingly worse.
It is a flying wing that produces some gain in glide ratio. And ground effect again some.

You don't follow. As the density of the atmosphere approaches the density of the vehicle your wings become only valuable as control surfaces. This is why I asked about atmospheric composition. There isn't going be a sudden shift in optimal design from an airplane shape to fish shape. Depending on density there will be some optimal design shape between airplane and fish.

 

[snorkack]

I thought about tailless. Assuming that I understand it correctly it has better aerodynamic properties. The drawback it is harder to steer, however in B-2 it was overcome by proper software, thus I think should be manageable.

Tail also makes it easier to provide stability.

I thought about something around 8.5 m/s2.
(I'm not 100% sure how low gravity can I assume, before the atmospheric loss becomes significant)

A planet having 8,87 m/s2 has very much denser atmosphere than Earth despite being much hotter. About 3,2 bar nitrogen, too.

However, I also toyed with idea of possibility of using not fully loaded plane as hydroplane. The shape would be awfully improper at start. However, in such dense atmosphere the plane would be designed to fly with low speed, moreover stall speed would be really low. So I think in line plane -> sliding like hydrofoil -> hovering like GEV -> finally taking off.
Feasible or not speacialy?

How about seaplanes?
Hughes Hercules achieved height of 21 m above sea surface, and thanks to its wingspan of 97,6 m, still experienced ground effect at that height. Speed about 220 km/h.
A problem with ground effect is that staying in ground effect is inconvenient on rough ground. A plane with a large wingspan can climb higher above ground while still benefiting from ground effect.
In cold climate, frozen sea is also fairly level for a Hercules-sized plane (just pressure ridges). And also ice sheets are fairly flat, just snowdrifts and occasional crevasses too narrow to matter for Hercules-sized plane when not landing.

 

[Czcibor]

A planet having 8,87 m/s2 has very much denser atmosphere than Earth despite being much hotter. About 3,2 bar nitrogen, too.

Even in spite no magnetic field. I know. But here I toy with idea of an exoplanet that has its oceans not evaporated.

How about seaplanes?
Hughes Hercules achieved height of 21 m above sea surface, and thanks to its wingspan of 97,6 m, still experienced ground effect at that height. Speed about 220 km/h.
A problem with ground effect is that staying in ground effect is inconvenient on rough ground. A plane with a large wingspan can climb higher above ground while still benefiting from ground effect.
In cold climate, frozen sea is also fairly level for a Hercules-sized plane (just pressure ridges). And also ice sheets are fairly flat, just snowdrifts and occasional crevasses too narrow to matter for Hercules-sized plane when not landing.

In setting that I have such seaplane project would be killed immediately. A Zeppelin could do slow cargo lifting even better. (yes, 3 atm :D ) So the market niche is for something smaller and faster, but at best both vehicles should use the same engines.
Anyway I have the following problem (except that it is a SF so high tech /schizo tech is a must ;) )
-Such hydroplane was designed for thinner atmosphere;
-Such plane was designed with a bit old fashion materials - wood.

I simply wonder whether thicker atmosphere + carbon fiber + microchip would not change the calculation towards different design.

 

[Czcibor]

Anyway the desired plane would be:
-as fast as turboprop effectively allow;
-for passenger transport between continents; (interlarding is possible if necessary)
-can be easily modified for military purposes;
-have good aerodynamics.

Maybe BWB design is too complicated for that? And possibility to use as GEV just impractical? Maybe I should think about something much, much simpler? Like Tupolev Tu-95/Tu-114 with more composites and wingtips?

 

[snorkack]

Even in spite no magnetic field. I know. But here I toy with idea of an exoplanet that has its oceans not evaporated.

Line Venus on a more distant orbit, where oceans don´t evaporate?

In setting that I have such seaplane project would be killed immediately. A Zeppelin could do slow cargo lifting even better. (yes, 3 atm :D ) So the market niche is for something smaller and faster, but at best both vehicles should use the same engines.

Hindenburg has top speed 135 km/h, cruise speed 125 km/h. And is 245 m long.
Hercules is smaller and faster. Its designed cruise speed is 408 km/h.
And concerning turboprops, how about Saunders-Roe Princess? Wingspan 66,9 m with floats retracted. Designed cruise speed 579 km/h.

 

[Czcibor]

Hindenburg has top speed 135 km/h, cruise speed 125 km/h. And is 245 m long.
Hercules is smaller and faster. Its designed cruise speed is 408 km/h.

Using more modern tech one would get it a bit faster. And thanks to 3atm insane load. For cargo transport (I thought especially construction in remote areas), that should be good enough.

And concerning turboprops, how about Saunders-Roe Princess? Wingspan 66,9 m with floats retracted. Designed cruise speed 579 km/h.

I still wonder about how her optimised for swimming hull and penalties related to that in air. I still think how to avoid it...
-micro-bubble drag reduction?

-flattened plane (double bubble) + foldable hovercraft?

So something like this:
http://gizmodo.com/5900927/are-mits-double-bubble-planes-the-future-of-air-travel
but with hovercraft; wings much higher not to touch water; turboprops
?

 

[snorkack]

Using more modern tech one would get it a bit faster.

Not much. In which way?

And thanks to 3atm insane load.

No.
The total weight of Hindenburg in 1 atm was 216 t
Of which empty weight was 118 t
Remaining 98 t useful load included
59 t fuel
4 t oil
8 t ballast
leaving 27 t payload, including "Misc", provisions, crew,
In 3 atm, lift would triple, but empty weight, drag and fuel load would do the same. That 80 t still would not compete well against a much smaller jet plane like MD-11F.

 

[Czcibor]

Not much. In which way?

Better materials that cause less friction, more efficient engines, possibility to optimize shape on computer, etc.

No.
The total weight of Hindenburg in 1 atm was 216 t
Of which empty weight was 118 t
Remaining 98 t useful load included
59 t fuel
4 t oil
8 t ballast
leaving 27 t payload, including "Misc", provisions, crew,
In 3 atm, lift would triple, but empty weight, drag and fuel load would do the same. That 80 t still would not compete well against a much smaller jet plane like MD-11F.

Why are you trying to multiple only the effective payload? Shouldn't you rather add roughly 2 times its total weight?

Anyway, keeping all parameters the same: 200,000 m3 of lifting gas. Now the envelope is the same, but you get 3 times the lift? 1m of N2 under 1 atm - 1,16 kg. 1m of H2 0,184. So now we displace 3 times as much air. 200 tones for each additional atmosphere.

27+200*2=427 tones.

So it could transport over 3 empty MD-11 planes (each 129 tones).
They would not fit into any realistic cargo bay, so such three cargo planes would have to dangle below a zeppelin and ruin its aerodynamic. ;)

 

[snorkack]

Why are you trying to multiple only the effective payload? Shouldn't you rather add roughly 2 times its total weight?

No, because:

In 3 atm, lift would triple, but empty weight, drag and fuel load would do the same.

These added 2 times total weight mostly go to 2 times added empty weight and fuel.

 

[Czcibor]

No, because:

These added 2 times total weight mostly go to 2 times added empty weight and fuel.

So in 3 times denser atmosphere I should use 3 times thicker envelope? Use 12 tones of lubricant?
3 times more fuel and ballast because even with modern tech would still vent hydrogen instead of using it as fuel? Be unable to reclaim ballast water from burnt hydrogen?

(I think that the problem here is comparing it with designs many decades more modern, and showing that such designs are better. While Hindenburg was earlier design than B-29)

With fuel - you have partially a point - concerning speed. Hindenburg was optimized for passengers. For cargo it could slow down a bit thus reducing the fuel consumption (well maybe divide the speed by 3^(1/2)). Then keeping extra cargo would not be a deal.

 

[snorkack]

So in 3 times denser atmosphere I should use 3 times thicker envelope?

You are tripling the weight of your payload. So yes, unless your envelope is to be torn up by the weight of the payload you are hanging off it. (On the other hand, lower gravity does help with payload fraction). Also if you are keeping the same speed in 3 times denser atmosphere, you are tripling the drag force so again you must triple the envelope strength and weight unless it is to crumple under the engine power.