Back door approach for VTOL design
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Back door approach for VTOL design
I am considering a new approach for the design and development of an ultralight fixed wing VTOL. The idea is to build an aircraft that is more or less a conventional fixed wing ultralight and then add vertical thrust devices a little bit at a time. Instead of trying to build a craft that must takeoff and land vertically (very risky), how about a craft that has limited direct powered lift for shorter landings but not vertical?
The wing would take over the job of support in case of power failure so autorotation ability can be abandoned. This would allow high disc loading for the powered lift system.
So, consider an ultralight that stalls at 30mph without any powered lift, then add about 200lbs of direct lift. It would then stall at maybe 20 or 25mph. The test pilot could get very practiced with short landings. Then the next aircraft designs could have more and more thrust until hover is finally achieved. This sort of incremental approach would yield usable aircraft and the interest in the aircraft should remain strong until the final goal is reached. This is the approach the Wright Bros. used when they moved from gliders to powered flight.
I'd be interested in any comments.
Slowrotor
The wing would take over the job of support in case of power failure so autorotation ability can be abandoned. This would allow high disc loading for the powered lift system.
So, consider an ultralight that stalls at 30mph without any powered lift, then add about 200lbs of direct lift. It would then stall at maybe 20 or 25mph. The test pilot could get very practiced with short landings. Then the next aircraft designs could have more and more thrust until hover is finally achieved. This sort of incremental approach would yield usable aircraft and the interest in the aircraft should remain strong until the final goal is reached. This is the approach the Wright Bros. used when they moved from gliders to powered flight.
I'd be interested in any comments.
Slowrotor
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You asked for it. 
Slowrotor,
Some rambling comments;
Your post implies that the final objective is vertical takeoffs and landings. Should this be the case, then 'VTOL' will be a 'must' on your list of design objectives, IMHO.
You mention 'safety' and 'ultralight' so these will be high on this list. Other objectives such as low cost, ease of piloting, simple maintenance, etc. may also be close to the top of the list.
It can be shown that a small STOL craft is equal to or superior to a comparable Gyrocopter in all categories, but, you want eventual VTOL.
___________________________________________
A bit of musing about temporarily stored energy;
The engine converts stored energy from gasoline to inertia. The wing and the rotor then convert stored energy from inertia to lift.
The wings of the airplane and the blades of the rotorcraft are functionally identical.
Before takeoff, the wings and the blades both require the engine to provide them with inertia. At takeoff, this 'developed inertia' is combined with the continuing engine power and an increase of the airfoils' pitch.
Power-on and power-off landing are also functionally similar, in that some of the previously developed inertia is consumed just before the touchdown.
Two major differences are;
~ The airfoils on the airplane are going in a straight line whereas the airfoils on the rotorcraft are going in circles. This results in the rotorcraft's L/D being less efficient.
~ The 'stored' inertia of the airplane is much higher because it is based on the total weight of the loaded craft not just the weight of the blades. Upon the loss of engine, it means a slower transition into stall.
A rambling about a concept;
It would be a significant advantage for STOL aircraft and for rotorcraft, if there was a simple, low cost and low weight means of storing more energy in this zone between the engine and the wing or rotor.
How about;
Use the engine to convert some stored energy from gasoline to compressed air BEFORE takeoff. Store the compressed air in a very strong but very lightweight carbon filament wound cylinder.
For the STOL aircraft;
Three or four strategically located air jets are located about the craft.
All air jets have vertical thrust only.
On takeoff and on landing (with or without engine), they contribute a short duration of lift and flight-control for VTOL.
For the rotorcraft;
A Roots type compressor/air-motor is located in the power train.
During warm-up the Roots loads air into the cylinder.
The rotors do not have a conventional collective. What they have is a torque-pitch coupling.
If the engine were to fail, the loss of torque will lower the blade pitch for autorotation.
Controlled releasing of the air from the tank into the Roots will apply torque and thereby immediately increase collective pitch.
In addition, this air is contributing to the rotation of the rotors.
The rotorcraft will require twin rigid rotors, of course.
Slowrotor,
Some rambling comments;
Your post implies that the final objective is vertical takeoffs and landings. Should this be the case, then 'VTOL' will be a 'must' on your list of design objectives, IMHO.
You mention 'safety' and 'ultralight' so these will be high on this list. Other objectives such as low cost, ease of piloting, simple maintenance, etc. may also be close to the top of the list.
It can be shown that a small STOL craft is equal to or superior to a comparable Gyrocopter in all categories, but, you want eventual VTOL.
___________________________________________
A bit of musing about temporarily stored energy;
The engine converts stored energy from gasoline to inertia. The wing and the rotor then convert stored energy from inertia to lift.
The wings of the airplane and the blades of the rotorcraft are functionally identical.
Before takeoff, the wings and the blades both require the engine to provide them with inertia. At takeoff, this 'developed inertia' is combined with the continuing engine power and an increase of the airfoils' pitch.
Power-on and power-off landing are also functionally similar, in that some of the previously developed inertia is consumed just before the touchdown.
Two major differences are;
~ The airfoils on the airplane are going in a straight line whereas the airfoils on the rotorcraft are going in circles. This results in the rotorcraft's L/D being less efficient.
~ The 'stored' inertia of the airplane is much higher because it is based on the total weight of the loaded craft not just the weight of the blades. Upon the loss of engine, it means a slower transition into stall.
A rambling about a concept;
It would be a significant advantage for STOL aircraft and for rotorcraft, if there was a simple, low cost and low weight means of storing more energy in this zone between the engine and the wing or rotor.
How about;
Use the engine to convert some stored energy from gasoline to compressed air BEFORE takeoff. Store the compressed air in a very strong but very lightweight carbon filament wound cylinder.
For the STOL aircraft;
Three or four strategically located air jets are located about the craft.
All air jets have vertical thrust only.
On takeoff and on landing (with or without engine), they contribute a short duration of lift and flight-control for VTOL.
For the rotorcraft;
A Roots type compressor/air-motor is located in the power train.
During warm-up the Roots loads air into the cylinder.
The rotors do not have a conventional collective. What they have is a torque-pitch coupling.
If the engine were to fail, the loss of torque will lower the blade pitch for autorotation.
Controlled releasing of the air from the tank into the Roots will apply torque and thereby immediately increase collective pitch.
In addition, this air is contributing to the rotation of the rotors.
The rotorcraft will require twin rigid rotors, of course.
Last edited by Dave_Jackson; 4th Dec 2005 at 06:12.
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Slowrotor, my take on this is that multiplanes deserve another chance. Monoplanes only have huge advantages in terms of parasitic drag reduction, particularly at high speed. At low speeds multiplanes come into their own, since for a given wingspan you can produce huge amounts of lift. It is no coincidence that all of the early flight attempts, with the limited engine powers available, were biplane or triplane. I have even seen footage of a conventional bicycle getting airbourne (only briefly, due to control loss)!
Why not design an ultralight that has an additional wing set or two? When established in flight the auxiliary wings could be folded back out of the airflow, but they would be pulled forwards for landing. Perhaps you could have a mechanical arrangement so that the lower aux wingset moved forwards, and the upper aux wingset moved backwards - This keeps flight symmetry, and avoids high control forces. Maybe even a drag servo on each set depending on whether you wish to deploy or stow...
Mart
Why not design an ultralight that has an additional wing set or two? When established in flight the auxiliary wings could be folded back out of the airflow, but they would be pulled forwards for landing. Perhaps you could have a mechanical arrangement so that the lower aux wingset moved forwards, and the upper aux wingset moved backwards - This keeps flight symmetry, and avoids high control forces. Maybe even a drag servo on each set depending on whether you wish to deploy or stow...
Mart
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Graviman,
Your point about additional wings is well taken. I think a very wide wing is better than two skinny wings for a number of reasons. But for very slow flight and hover wings become useless of course. I figure for an ultralight, about 3lb/sq/foot wing loading best for slow flight on the wing and a powered lift rotor-prop for slower flight .
Dave,
I see you are thinking about rotorcraft basic physics. Me too.
I agree that hover is needed for just a few seconds and therefor an efficient craft would be optimised for cruise (fixed wing) rather than optimised for hover as in the case of a helicopter. Look at birds, they only flap hard for a brief hover landing to save energy. Your observation that a fixed wing can use the mass of the whole airplane for a slower glide descent rate is interesting. That's why I think a powered lift fixed wing would be safer in the hands of a sport pilot.
Stored energy..... I will think about that. I was thinking about adding another engine for powered lift simply because I thought it might be simpler.
Your point about additional wings is well taken. I think a very wide wing is better than two skinny wings for a number of reasons. But for very slow flight and hover wings become useless of course. I figure for an ultralight, about 3lb/sq/foot wing loading best for slow flight on the wing and a powered lift rotor-prop for slower flight .
Dave,
I see you are thinking about rotorcraft basic physics. Me too.
I agree that hover is needed for just a few seconds and therefor an efficient craft would be optimised for cruise (fixed wing) rather than optimised for hover as in the case of a helicopter. Look at birds, they only flap hard for a brief hover landing to save energy. Your observation that a fixed wing can use the mass of the whole airplane for a slower glide descent rate is interesting. That's why I think a powered lift fixed wing would be safer in the hands of a sport pilot.
Stored energy..... I will think about that. I was thinking about adding another engine for powered lift simply because I thought it might be simpler.
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. Modifying Flight by Darwinian Evolution or Unintelligent Design? 
Slowrotor,
Some more un-thought-out thoughts about compressed air assist for an aircraft.
The engine will be bigger than normal so that it can provide good STOL, therefore during cruise some of the excess power could be used to 'top up' the tank.
The wall of the compressed air storage cylinder could also serve as the fuselage aft of the pilot's seat. This will maximize it's size and minimize the additional weight.
The pressure of the air flowing out the wings to the tips will not be exceptionally high, therefore the modifications to the wings should be minimal.
The cylinder will extend to near the tail of the plane, therefore the tail thruster would consist of only a valve, an expansion chamber and a discharge, which might be located under the horizontal stabilizer and in front of the elevator (& flaps?).
________________________________
Put the fuel in the same tank and then ignite the vapor at the discharge locations.
________________________________
Carbon filament wound cylinders are very very strong and very very light. An example
If the cylinder can hold sufficient air to provide 20 - 30 seconds of assistance to the conventional thrust and control, I'll race you to the patent office.
Dave
Edited to add the following.
The Slepcev Storch ~ stall speed 22 mph
The e.Volution Car ~ 124 miles before being refueled with compressed air.
Last edited by Dave_Jackson; 5th Dec 2005 at 00:57.
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VTOL
Dave,
Check this guys VTOL proposal. http://www.aeromobile.com/aeromobile...ol1/vtol1.html
He does have some good ideas for hovercraft but I am not sure about his VTOL.
I cannot understand how his claim of zero pitching moment on the huge flap could be true. Any ideas?
slowrotor
Check this guys VTOL proposal. http://www.aeromobile.com/aeromobile...ol1/vtol1.html
He does have some good ideas for hovercraft but I am not sure about his VTOL.
I cannot understand how his claim of zero pitching moment on the huge flap could be true. Any ideas?
slowrotor
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Slowrotor
I agree with your two comments. There was a half-hour documentary on hovercraft a couple of nights ago and some of this gentleman's work was featured.
His work does conjure up another crazy idea to go on the pile. It was mentioned in the documentary that for hovercraft a radial fan is better than an axial fan. This is because it distributes the thrust out to the periphery of the 'disk area'.
In addition, rotorcraft books say that during an autorotative descent, the rotor provides the same lifting force that a parachute of the same diameter would. This implies that if one were to locate a motor and radial fan in a hole at the top of a parachute, one should be able to have a VTOL device, albeit with limited lateral speed.
Last, and far from least; the lb/sq-ft force on a parachute is very low and the strength of the parachute's skin is relatively weak. An airplane's wing is subjected to a greater lb/sq-ft force and therefore must be stronger. It would be interesting to try and conger up an idea where a 'so-called parachute' could be transitioned into a 'so-called wing', or wings, During this transition the lb/sq-ft lifting force will increase but the overlapping fabric of the parachute would proportionally support this higher disk loading.
Now back to watching your Seahawks.
I agree with your two comments. There was a half-hour documentary on hovercraft a couple of nights ago and some of this gentleman's work was featured.
His work does conjure up another crazy idea to go on the pile. It was mentioned in the documentary that for hovercraft a radial fan is better than an axial fan. This is because it distributes the thrust out to the periphery of the 'disk area'.
In addition, rotorcraft books say that during an autorotative descent, the rotor provides the same lifting force that a parachute of the same diameter would. This implies that if one were to locate a motor and radial fan in a hole at the top of a parachute, one should be able to have a VTOL device, albeit with limited lateral speed.
Last, and far from least; the lb/sq-ft force on a parachute is very low and the strength of the parachute's skin is relatively weak. An airplane's wing is subjected to a greater lb/sq-ft force and therefore must be stronger. It would be interesting to try and conger up an idea where a 'so-called parachute' could be transitioned into a 'so-called wing', or wings, During this transition the lb/sq-ft lifting force will increase but the overlapping fabric of the parachute would proportionally support this higher disk loading.
Now back to watching your Seahawks.
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parachute
Dave
"rotor provides same lifting force that a parachute of the same diameter would provide" That is correct. But the helicopter disc loading is much heavier than a normal parachute and the descent is very high in a helicopter.
Indeed, the parachute descent may be better for sport helicopters and VTOL because the rate is slower. Also no pilot reaction within "1.1seconds" would be needed, a huge difference. And a parachute doesn't need 200ft of altitude to spin up in rpm.
A wing can be a fixed parachute. The low aspect ratio disc shaped ARUP, built in the 1930's I think, had the capability for "parachute landings" at a 40 degree glide slope.
For slow sport aircraft, the lift/drag of a large wing may replace autorotation.
"rotor provides same lifting force that a parachute of the same diameter would provide" That is correct. But the helicopter disc loading is much heavier than a normal parachute and the descent is very high in a helicopter.
Indeed, the parachute descent may be better for sport helicopters and VTOL because the rate is slower. Also no pilot reaction within "1.1seconds" would be needed, a huge difference. And a parachute doesn't need 200ft of altitude to spin up in rpm.
A wing can be a fixed parachute. The low aspect ratio disc shaped ARUP, built in the 1930's I think, had the capability for "parachute landings" at a 40 degree glide slope.
For slow sport aircraft, the lift/drag of a large wing may replace autorotation.
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Somemore thoughtless thoughts.
But the helicopter disc loading is much heavier than a normal parachute and the descent is very high in a helicopter.
In addition, the ballistic parachutes for light airplanes must be reasonably strong.
For slow sport aircraft, the lift/drag of a large wing may replace autorotation.
