Reaching the same conclusion myself. The problem stems from the quest for still air. Having done loops in a glider and felt my own wake, I can understand the standard approach for helis.

I wonder about some of the thrust vectoring systems out there. Obviously FAST lateral rotation of the rotor system is an absolute must, requiring maybe accumulators or aero-trim control.

If it's gravity you're trying to overcome, it's gravity you have to understand...

Mart

The lead posting should have read XSTOL (eXtreme Short Take-Off & Landing) craft not XVTOL.

Graviman,

True, stability and control during slow speed may require fast redirecting of vectored thrusts.

Another complementary idea might be that of elevating the airfoil while its area is being significantly increased. This raised center of lift visa vie the center of gravity should assist with stability.

Dave,

Both very true. I found it quite interesting that the Cheyenne was able to use the prop to autorotate. A similar approach might drive the hydraulics in autorotation.

Actually I was thinking along the lines of using cyclic to position the rotor/duct assy. If the assy was rotated near (but above cg), and attached with a stiff damper instantaneous response woild be good. The system would gradually tilt to the optimum postion, but pilot wouldn't really notice any affect (other than some cross coupling)..

Mart

eXtreme Short Take-Off & Landing

Like an SSTO?

http://www.geocities.com/spacetransport/roton.html

The following is an idea for a commercial XSTOL craft that is capable of landing and taking off in three distinct modes from three different types of landing sites.

1) It lands and takes off in conventional flight mode from existing airports.

2) It lands and takes off in XSTOL mode from 'airparks', where the runways may only be a few hundred feet long.

3) It land and takes off vertically in XSTOL mode from special high utilization 'airpads' in congested areas. In this scenario, the vertical portion of the flight is assisted by ground based equipment.

OK, but what sort of flight mechanism are we talking here? Are you thinking along the lines of extreme high lift devices, with compressed air injection to overcome boundary/stall regions? This seems (to me at least) a little like the FanWing concept, except I don't know how fast FanWing can fly...

Mart

Graviman,

The fanwing concept might be part of the solution.

Some other ideas, from the Department of Demented Designs are;

For lift, the wings might be monoplane for forward flight and convert to staggered biplane for XSTOL. Another option might be to increase the wings surface area by unfurling an extremely strong fabric at slow flight.

For vertical thrust, the engine(s) might be stronger then that which is required for forward flight.  For slow speed flight a blower, (a little like the Lockheed Martin X-35) might connected and used to direct air to the wing tips ant tail.

For VTOL 'airpad' sites, which are located in congested areas and have high commuter traffic, the ground equipment might consisted of very high power vectored thrust equipment.  It would help support the craft just as a column of air supports a Ping-Pong ball. This equipment would be computer controlled and only operate for a couple of minuets at a time.
  

Dave

I don't suppose you've tried to figure out how big that fan would have to be?

Cheers

Greg Locock

Your probably right intermesher, just about anythings going to be cheaper than a tilt rotor.

Greg,

Might be possible to pickup a few good used fans from the AMES wind tunnel.

Just joking.

Dave

"For lift, the wings might be monoplane for forward flight and convert to staggered biplane for XSTOL. Another option might be to increase the wings surface area by unfurling an extremely strong fabric at slow flight."

Both very interesting ideas. Multiplanes were consigned to the history books after high speed development in the 30's. For slower aircraft they actually still make sense, a long as there is no interference between planes (ie have them angled on plane 7' rearwards). I had actually wondered about a human powered multiplane...

Equally a large prop could have it's thrust redirected by a multiwing. This in effect would behave like a fan wing, to really push down stall speed. It all sort of gets back to the idea of thrust vectoring. I still prefer cyclic control for the vector, since this is far more reliable than hydraulics. Being an ABT (active blade twist) fan, I'm suprised you don't jump at this soln!

"For slow speed flight a blower...might connected and used to direct air to the wing tips ant tail."

OK, but not for lift right? Again this is pointing towards thrust vectoring.

"...the ground equipment might consisted of very high power vectored thrust equipment..."

Hmmm, I think we discussed various filing categories the other day. The big problem here is the collumn won't reach very far up before it diffuses. Also, what if the collumn misses or fails!

Mart

GraviMan

All good points.

I still am very convinced that a craft with;
  ~~ Twin main rotors (no 10% power wasted on a tail rotor),
  ~~ Active Blade Twist (better L/D ratio over the area of the rotor disks), and
  ~~ Large chord/low tip speed, with pusher prop (faster forward speed),
is the best configuration for vertical flight, where high lift and reasonably fast forward speed are required.
__________________

This thread was not started as a means to improve on the above. It was started for the fun of it, and to contemplate configurations for scheduled commercial applications that are located between the above rotorcraft and larger long-range airplanes.

""For slow speed flight a blower...might connected and used to direct air to the wing tips and tail.""
"OK, but not for lift right? Again this is pointing towards thrust vectoring."

Agreed.

"Hmmm, I think we discussed various filing categories the other day."  
OK. Forget the ground based high-powered vectored thrust.
How about a ground based lower powered air thrust, which provides a 'ground cushion'  for the XSTOL craft to 'drop' onto?  A large mechanical catapult is used in conjunction with the air thrust to 'toss the craft up and forward during takeoff.


Dave

"I still am very convinced that a craft with...is the best configuration for vertical flight, where high lift and reasonably fast forward speed are required."

Yup, agree with you on this. Non-newtonian is the only way to better this design, but that's not for this thread...

"How about a ground based lower powered air thrust, which provides a 'ground cushion'...A large mechanical catapult..."

Hmmm - I'll stick to non-newtonian methods! Seriously though, I think any aircraft capable of XSTOL should have it's own flight systems on board.

The catapult assisted launch makes some sense, assuming you are trying to reduce takeoff fuel mass. In reality you have to condider FMECA for various systems. If the winch fails, can you land safely or are you commited to a dangerous launch? It's bad enough with the V-22 "so long as all engines don't fail" approach, but including infrastructure into the safety equation is asking for trouble...

Mart

Hi Graviman,

I wasn't thinking of a winch and ramp but an actual medieval style catapult.   
In this scenario, the wings will always be parallel to the ground, therefor the 'air thrust' assists by removing the negative load on the wings, during the initial vertical portion of the launch.



Dave    

Hmmm, ground based infrastructure - generally called a "runway". Besides it looks bl**dy dangerous!

The appeal of VTOL or XSTOL is the ability to use off-beat airfields that would otherwise be overlooked. The concept you're suggesting limits the craft to specific airfields. If the objective is takeoff weight, then a dedicated launch vehicle is more appropriate, maybe a hover platform.

The real concern is that the aircraft has to be designed to handle this launch method, which means high g, high stresses. The final design is likely to be far more heavy and complicated that just fitting bigger tanks/engines.

I can see your reasoning though. Seperate rotary and fixed wing region of flight into a general flight profile. I just don't see it in practice. Besides would you want a sling-shot launch?

Mart

Graviman,

"The concept you're suggesting limits the craft to specific airfields."

A previous post elaborates slightly on "... is capable of landing and taking off in three distinct modes from three different types of landing sites..  The scheduled routing of a specific short haul XSTOL craft might cover 15 landing sites, but only one or two of  these site are in densely populated areas.  

In fact, the cost of establishing new 'airpads'  will probably be a fraction of the cost of establishing new airports.
_____________

I agree that there would be many things to be worked out with the craft.  Fortunately, the reliability of the ground equipment will not be a 'show stopper'.  This is because aircraft, and particularly VTOL craft, have to balance reliability against weight. The ground equipment can be as strong and system-redundant as is necessary.
______________

"a dedicated launch vehicle is more appropriate, maybe a hover platform."

Agreed. The objective of this thread is to consider situations where a large portion of the 'vertical thrust requirement' can be removed from the vehicle.

Dave   

You could catapault the passengers from departure to destination, hence removing the need for an aircraft!

Seriously though, I suspect that the FAA and CAA would both grimace at such concepts. Many solutions are possible, catapault making the most sense.

Mart

I like the idea of a catapult.  At one point I wanted to fly some sort of rocket glider to work.  I live in San Diego and I figured I could land on the roof of my work and have a couple safety nets up in case I over shot the landing.  I also thought an extra smaller rocket could be used for a go around.  In this situation, a catapult could be used to get some initial altitude before powering up the engine, to reduce noise for the people below.

Then instead of having some blower below you, you just have access to high pressure steam or something to power your rocket.  This could easily be made available and is pretty eco friendly as far as emissions go.  Although how one makes the steam then becomes important.  

One other idea, although impractical, was given to me when my father mentioned an airplane ride he took in france.  The pilot took him to a set of hills and landed on a runway going uphill at a very steep angle.  He said the landing roll couldn't have been more than 200ft (~60m).  And the take off roll was really exciting since they were headed down at such a steep angle.

So, is it concievable to have some sort of tilting of partially sloping landing pad/runway?  A rooftop seems a perfect place, but of course on the ground this won't work as well...

It works very well on land. At Lukla in Nepal you land on a 1 in 6 runway. Taking off is visually more impressive as you dive off the cliff, but inside  the plane it feels quite humdrum.

http://www.dangerous-airports.com/airports/l/lukla...

That is a 1000 ft cliff at the end of the runway.

Cheers

Greg Locock

Actually this is another area where hybrid electric technology can help the aircraft. Don't forget we are talking about ground runs here. If the high lift device could be quickly actuated, then you can put the full weight of the aircraft on the gear while below flying speed (or even downforce). The best solution would be variable AOA wings with serious leading edge devices, or even a trailing seperator to stop stall backwash.

The wheels would have very high power reluctance motors, designed to operate for a maximum of 10 seconds. On landing the wings would give up any lift, and motors go into full generator mode. On takeoff, motors accelerate aircraft up to unstalling speed. If wings could also produce downforce, and motors were traction controlled very high accelerations are achievable. Batteries (especially traction LiMH) offer exceptional power to weight (but are no good for energy to weight) so no problem here either regards mass - you only need a quick blast.

In combination with very effective high lift design, I suspect this would allow rediculously short runways to be used. With NASA considering MAGLEV, this looks promising...

Mart