surface effect craft questions

[dalcazar]

hey ppl

I have a pet project designing a surface effect craft, I hope to eventually make it a class III but for now it will be a class II only. And I have a few questions

I've been considering using rotary engines on it to get some extra reliability (its between that and diesels), this engine choice goes more in hand with ducted fans than with propellers so I was wondering if there is any difference in performance other than extra thrust at takeoff, such as better performance at sea level or at altitude. the lower noise level also makes it more attractive since it would be operating out of harbors.

Also, what are the best airfoils for a class III WIG craft? I am considering using a tilting wing to induce more ground effect so the shape of the airfoil in itself won't be providing all of the effect. I hope to do this in order to have a cleaner aerodynamic profile at higher speeds and in free flight. is there any already designed airfoil that is a compromise between normal and the special purpose surface effect foils?

I hope to have some more questions soon as well as a few sketches to share with you so I could get some input on concept viability.

best regards

Demian

 

[rb1957]

rotary sounds like a good choice (good power to weight)
diesel ? ... sounds more like a ship engine !
ducted fan ? ... despite all the hype some years back, maybe the complexities outweigh the advantages; also thought the duct was more to do with reducing noise than improving power (particularly power to weight)

i'm not an aerodynamist, but thought you'd want a thick airfoil for ground effect (maybe the argument is more like you can afford the thickness due to the benefits of ground effect).
tilting wing ? ... sounds like a lot of complexity for probably a very small return

good luck

 

[MikeHalloran]

A stowable, steerable ducted fan might make sense for navigating in a harbor, and a small, lightweight rotary makes sense for powering that. But it's really an auxiliary engine.

Making an ekranoplan lift itself out of the water takes a _lot_ of power. If it's going to lift anything other than itself, gas turbines are pretty much your only choice for a power source. They could power ducted fans, as in turbofans.





Mike Halloran
Pembroke Pines, FL, USA

 

[dalcazar]

Thanks for the replies, very helpful.

I was thinking about using PAR thrust, but I've come up with what might be a viable alternative by accelerating with wings at a normal pitch angle, then when lift-off speed is attained, the wings pitch back to form a cushion under the wings by effectively ramming air under them by virtue of speed. The speed loss would be translated into vertical motion. Very true, the tilting wing is a major design complication but it would allow for higher cruise speeds.

I've considered using laminar flow wings instead of thick airfoils in conjunction with the tilt wing in order to keep landing and take off speeds low but still be able to shoot for a 200 knot cruise speed. Due to the abundance of frontal drag inducing area, thinner wings are very desireable, can anyone voice their oppinion on this? The wing area should be big enough to provide adequate lift without running at very high speeds.

Due to the design of the craft, including engines in a place where they could produce PAR thrust would make the craft hideous and one of the main goals is to make it an attractive vehicle. and it looks nothing at all like an ekranoplane, nor does it use any of the operating principles. The final craft would be amphibious, although the prototype will be either a seaplane or land-based but not both, I have also envisioned a launching system using a linear induction engine or some form of catapault to overcome the initial power investments.

gas turbines are nice, but I'm not envisioning a large full scale craft so their fuel consumption would be a serious downside, I actually had originally envisioned a single gas micro-turbine powering a generator, power would then be transfered electrically to eletric motors in the nacelles to power the fans themselves, good torque and variable speed, but the combination of the turbine, the generator and the electric motors would probably weigh twice as much as regular 4-stroke engines. maybe ok for staying in ground effect but not for entering true flight. The diesel engine alternative would simply make it more fuel compatible with the fuels available at harbors.

One of my original reasons for using ducted fans before choosing rotary engines was to be able to vector the thrust laterally to help in harbor navigation as you mentioned.

 

[MikeHalloran]

I have the impression in the back of my mind that laminar flow wings don't like running at high angles of attack, and don't like getting wet. I could be wrong; it happens often enough.

The idea of tilting the wing to start rotation scares the crap out of me, because you have to un-tilt the wing, really fast, to stop the rotation. You can probably find footage of drag boats and unlimited hydroplanes doing the continued rotation thing just before self- destructing. Perhaps you were thinking of a fore/aft biplane like Langley's Aerodrome, with two tilting wings and a fuselage that magically stays level?

Large wing area implies either a large span, which becomes a liability when water- borne, or a large chord. Rotating a wing with a large chord puts the trailing edge in the water unless the craft is very tall, or the center of rotation is near the trailing edge, which introduces a lot of extra structural weight.

The linear induction engine is commonly called a railgun. Unless there's been a breakthrough, they require a pretty large pulse of power, and also require complete replacement after each use. Maybe you can acquire some JATO bottles.

Many interesting challenges await you.








Mike Halloran
Pembroke Pines, FL, USA

 

[dalcazar]

the craft is in fact a fore/aft tandem wing design, I wouldn't otherwise consider a tilting wing for that exact same reason you mention.

when I say linear induction I'm thinking more along the lines of an alternating induction system like the superman rides at six flags or a maglev train instead of continous induction such as a railgun, I don't think the craft (not to mention the passengers) would stand up very well when being accelerated from 0 to mach 8 in about 0.2 seconds.

but the main question and purpose of the post remains, what would be the airfoil of choice? I would specifically like some airfoil designations, your best recomendations will be taken into account!