VTOL, deflected slipstream question

[slowrotor]

Of the known VTOL (vertical takeoff or landing) configurations, the deflected slipstream type has the most potential for further development in my opinion because the wing provides some support after power loss (hopefully).

My question is:
Does the wing provide lift in a zero airspeed hover?
Or is it just prop thrust deflected down?

VTOL types charted here:http://www.vstol.org/wheel/wheel.htm

Thanks
slowrotor

[NickLappos]

slowrotor,

The question you ask is interesting, but what is the difference between deflected propwash and lift? In my book, they are really the same thing.

Look at some ecranplanes for interesting games you can play with bent engine/prop exhaust! They start the engines and pick up to a low hover! And they are the size of big transports.

http://www.airforce.ru/english/aircraft/ekranoplanes/orlenok4.jpg

http://www.airforce.ru/english/aircraft/ekranoplanes/

[SASless]

Nick,

Is that eight and two or five and five....what would be the numbering logic on that....I would have to take off my shoes and socks to keep up with the engine start/shutdown drill?

[slowrotor]

Nick,
The Ekranoplane cannot climb vertically above the gas "pillow," if I read that description correctly.
Interesting, but I need to get above the trees vertically.
You may have guessed that I am looking at all vertical flight schemes for ideas to use in a new sport or personal craft.

Consider this: Current RC model airplanes can easily "hover" using prop thrust alone. Even electric models can now hover on half throttle.

I think a fixed wing that could hover would have several advantages over the helo, namely easier for a non pro to fly and safer in the 0-100agl range.
It could be sort of a cross between a helo and an airplane.

A full size craft must lift a payload, so direct prop lift is not sufficient with any low cost engine I would be able to use. But if the prop disc was larger for vertical lift and the wing added additional lift from the slipstream... that could be interesting.
To answer your question, "what is the difference between propwash and [wing] lift"?
Wings are a more efficient lift device normally, but they need forward air speed.
The deflected slipstream configuration may get added lift from the wing. If it does, the system would be worth further study.

[SASless]

Slowrotor...

That concept was tried once before....I forget the aircraft....delta winged thing with counterrotating props...turbine powered aircraft. Tookoff and landed to an articulated lorry wagon stood on end. It flew well but was a real bear to land. I will do some research and find the make and model. One aircraft that I had in mind was the Lockheed XFV-1, another is the Ryan X-13. Of course Lu will say he pulled the chocks on the XFV-1.

[Kyrilian]

slowrotor
I think what you'll find is that for the most part VTOL programs (as shown on the 'wheel' failed due to three related reasons:
Performance
Controllability
Complexity

oh, and of course Cost

The reason helicopters have large rotors is that for vertical flight, the larger the rotor disk the better the hover performance. Recall the equation for rotor-induced power (and I hope this is readable):

(thrust^(1.5))
--------------------------------------------- = (induced power)
sqrt(2 x (disk area) x (air density))

Also recall that (disk area) = pi x (rotor radius)^2

Therefore, as you halve the rotor radius, you double the power required. That's pretty huge! Keep in mind that this does not account for viscous effects, but it still gives us an idea of what changing the rotor/fan size will do to required power.

So if you take a vehicle that's 2500lbs, the induced power to lift it if its rotor is the size of that on an R-44 is just 105hp. Now if you want to take an airplane with a 8ft diameter prop (ala RC aircraft hanging off its prop), you'd need 432hp. Four 2ft diameter fans (Moller?) would require 864hp. Again, add viscous power losses to all these. In any case, you can see how reducing the size of the prop/rotor can have a compound effect, as going from 105hp to 432hp will obviously require a larger and thirstier engine. This engine then has to lift it's weight as well. And on, and on...

Controllability is another problem that plagued many of those programs that actually did get off the ground. The tail-sitter that has been mentioned I believe was horribly difficult to takeoff and land, requiring the pilot to fly a hook on the nose/belly of the aircraft onto a hook or loop (can't recall the exact design) attached to a small tower. The performance/load carrying ability was much less than comparable aircraft, and I guess the benefits were simply outweighed by the cost/complexity and lack of controllability.

Obviously, with enough complexity (and cost) an aircraft can be built to carry any load and perform to most standards. However, the complexity to control and the cost to obtain the desired performance is often not worth it. There's always a trade-off in aircraft design. Aircraft tend to have limited airspeed envelopes (helicopters are slow, lightly wing-loaded prop planes can't hover or go really fast, and jets can only go fast). Compound helicopters, tilt rotors and VTOL jets like the Harrier and JSF gain complexity and cost to expand their envelopes.

I realize that the above hasn't directly addressed your question about deflected slipstream VTOL aircraft. Consider the above as you look at these designs. To obtain the wide speed envelope that is the holy grail of VTOL design requires a complex flap mechanism (cost + weight) on a deflected slipstream aircraft. The small propellers are inherently inefficient and require loads of power to get you to a hover. As links from the wheel state, the Ryan 92 VZ-3 crashed, presumably due to control difficulties and could only fly with some forward speed due to a lack of power. The other two were tether tested but didn't go further.
I see your point about the engine-out glide capabilities of an aircraft with a wing. The relative wing size of these aircraft is small. Without engine thrust I'm sure the stall speed is quite high. What happens when you're hovering, or just flying slower than the stall speed and the engine quits?

We'll see once again how all these factors (controllability, thrust capability, engine out performance, complexity, etc) play out when (if) Attila Melkuti flies his AMV 211. It's not quite a deflected slipstream, but I'm not sure where else it would go on the 'wheel'. See the current issue of Popular Science (The Daring Visionaries of Fringe Aviations (http://www.popsci.com/popsci/aviation/article/0,20967,1006774,00.html) ), which refreshingly has a rather objective view of several different designs, including Moller's ubiquitous Skycar and the AMV 211.

Keep thinking of stuff :ok:

[zeeoo]

Thanks Nick for this VERY interesting link.. more culture..
thanks

[Lu Zuckerman]

To: slowrotor

Back in the late 1950s the University of Mississippi worked under contract to the US Army to develop a low speed aircraft that could take off in a very short distance. The Army bailed an L-19 to the U of M Aeronautics department. They removed the wings and stripped the upper skin from the wings. They increased the structural integrity of the wing and then reskinned the wings. Over the metal skin they added several layers of fiberglass. On the lower part of the wing they added two hydraulically driven turbines. The inlets to the turbines were ducted into the underside of the two wings. After this was done they added a hydraulic pump and associated plumbing to the engine connecting the output of the pump to the two turbines. The two turbines were cross-connected for redundancy.

When this was completed they drilled thousands of small holes in the upper side of the wings. On the first demonstration they proved that the turbines could suck a great deal of air through the holes with the turbine effluent providing a slight amount of thrust.

On the first and subsequent flight tests the L-19 lifted off in about 100 feet of takeoff run and was flown at about 25 miles per hour. The air above the wings (boundry layer) was sucked into the wings and out the turbine exhaust creating an extremely low pressure on the wings surface.

In later years this was demonstrated on a specially constructed F-16 and several other aircraft.

:E :E

[slowrotor]

Kyrilian,
Thanks for your interest and the link to other crackpot inventors like me.
This electronic forum is just fabulous.
I am quite sure that others such as Moller are likely to have poor results with small ducted fans.
(I think Moller is more into investment scamming then actual vertical flight, he should know better)

Check out this NACA report number 1263 "Aero characteristics of wing-propeller combinations at angles of attack up to 90 degrees"
http://naca.larc.nasa.gov/reports/1956/naca-report-1263/index.cgi?page0001.gif

The report kind of gives the impression of the possibility of vertical takeoff but does not actually say that the wing lift is enhanced at zero forward speed.
I mentioned the hovering RC models because I feel they could recover and land from a power loss in a low hover better than an RC helicopter.
Back in the 70's I built a chanute type biplane hang glider and a friend towed me with his motorcycle.
I went up fast to about 50 feet and then my friend looked back and noticed that I was too high so he STOPPED... well I just came straight down and landed on my feet and was not hurt because the glider had a very low wing loading.
It came down like a parachute.
A helicopter that loses power at 50 feet will not make a soft landing,of course. And ducted fan lift systems are worse.
I am thinking about something like an ultralight with one or more large disc propellers with nearly the same low disc loading as a helicopter.But retain the aircraft controls for simplicity.
Kyrilian, you are correct about getting to complex.
Thats why I want to incorporate fixed wing simplicity with rotary wing lift.

Lu,
You have described an enhanced boundary layer control system.
Great for STOL, it can increase the Cl of the wing in forward flight but would be of no use in a zero airspeed situation. I am shooting for a full hover.

Still not sure if it is possible to produce lift on a motionless wing with a prop. Just because some experiments crashed in the 50's wont stop me if the basic physics suggest it could work.

[Dave_Jackson]

slowrotor;

The idea is to use the primary source of power to pre-create an additional source of energy, which can augment the primary source, during take off. For example the overspeeding of a rotor, before lifting off.

That is a crazy example, but the following one is much more realistic.

It's an airplane that consists of two parts. Part 1 is the wings, engine and propeller. Part 2 is the fuselage and payload. The total GW ratio between the two parts is probably 33% and 67%.

To takeoff, part 1 is flown VERTICALLY to an elevation of 200 feet, and then leveled out. The wing then acts as a parasail while most of the engine's power is applied to winching up the fuselage and payload. Parts 1 and 2 meet and couple together at 100 feet and 50 mph. They then fly off united.


:confused: Somehow, this idea sounds like deja vu. :confused:

[slowrotor]

Dave,
Your first example is less crazy I think.
I think somebody tried flying a helio courier in circles with a long line to the ground for retrieving small items.

By the way, I did read the human powered heli book at the Seattle Public Library.
Just for reference, I have no plans to use my own feeble power.

I just made an experiment with my electric RC heli and a cardboard wing, mounted on a digital scale for thrust testing.
Result: 190 grams lift with wing in place and 200 grams lift without wing.
Conclusion: wing does not add lift.
So.... I guess that answers my original question.

Thanks for your interest.