Benefits of no takeoff and landing to design

[joshspace]

If you would designing a drone like the scan eagle but optimising for large cargo and distance what would be the benefit of not having to take off and land apart from infrastructure and landing gear. How does that actually change the design of the aircraft, for example is the design case for aircraft determined by the engine's maximum thrust and the lift of the wings relative to the takeoff weight. Then from there there the design is optimised to ensure that operates efficiently as possible at the right altitude. Therefore if you didn't have to worry about takeoff then you could decide specifically for its operation at its optimum altitude?

 

[riggerrob]

If you did not need to worry about TO or landing speeds, you could get by with tiny wings, wings barely bigger than the "aileron mounts" installed on Lockheed CF-104 Starfighters.

Look at the first generation of Harrier jump jets. Since they depended upon engine thrust for take-off, they had tiny wings, barely big enough for cruise. They installed tiny wings to minimize hover weight.
Compare the size of Harrier Mark I wings with the larger wings installed on later variants (e.g. USMC Marrier AV-8B) which were optimized for rolling take-offs and could carry much heavier loads of bombs and fuel.

On most other airplanes, wing size is determined by the minimum size needed to land slow enough for a specific runway length.

Take-off length is largely determined by excess thrust. If you use a catapult to launch your drone, you can also get by with a small engine optimized for fuel efficiency in cruise flight. Then the engine only has to have enough excess power to climb to cruise altitude. Who cares about fuel efficiency during climb as that is only a short portion of the mission profile.

 

[Desertfox]

Just look at cruise missiles...

 

[Nicknick]

The way the can eagle lands wouldnt be very appropriate for cargo transport, that thing is swivelling around a vertical rope until it dissipated enough energy…

I only partially agree to the small wing argument, despite it is valid for most conventional planes. For the highest efficiency, you need a plane with a glide angle which is as close as possible to the glide ratio of the pure wing, there for a large wing with a wide span and a small fuselage is the way to go (like sailplanes). With that configuration and a given power (we will stay subsonic) you should fly with constantly with the best angle of attack which means, you need to fly extremely high to achieve an high speed.

I doubt, that the rope catching approach as well as the catapult start would really enable light weight freight drones, the forces at the landing would be enormous for a weight of let’s say one ton.

I think I’ve seen something in Popular mechanic or its German counterpart (“Hobby”) like a air matrass sled which should catch landing airplanes and accelerates them for the start. Doesn’t sound very practical, but still better than catching a rope an swivel around…

 

[Dynoman]

The landing gear represents about 2.5-5% of the aircraft gross take off weight.
The mission requirements will dictate whether it would make sense to do a way with the landing gear.

Using the Scan Eagle configuration and launch system as a model for the design, albeit a scaled up version being considered here, the Scan Eagle payload capacity is 7.5 lbs and a gross weight of 44 lbs. This is a payload fraction of 17% GTOW. Payload weight fractions range from 15-50% GTOW depending on size and configuration. If gear were added for a conventional takeoff the weight would have been approximately 1.8 lbs.

What size payload are you talking? Small UAV payload of 10 lbs transported 10 miles or 5000 lbs 1000 miles, etc.

The mission would also determine the best configuration. For example if you wanted to get a small payload (e.g. medical supplies to soldiers in the battlefield) to a location in the fastest way possible a rocket that deploys a GPS steerable parachute maybe the way to go. If it has to carry a lot of weight and return, then something similar to a large high wing aircraft with STOL high lift devices maybe best.

Form follows function.

 

[riggerrob]

The way the can eagle lands would be very appropriate for cargo transport, that thing is swivelling around a vertical rope until it dissipated enough energy…

I only partially agree to the small wing argument, despite it is valid for most conventional planes. For the highest efficiency, you need a plane with a glide angle which is as close as possible to the glide ratio of the pure wing, there for a large wing with a wide span and a small fuselage is the way to go (like sailplanes). With that configuration and a given power (we will stay subsonic) you should fly with constantly with the best angle of attack which means, you need to fly extremely high to achieve an high speed.

I doubt, that the rope catching approach as well as the catapult start would really enable light weight freight drones, the forces at the landing would be enormous for a weight of let’s say one ton.

I think I’ve seen something in Popular mechanic or its German counterpart (“Hobby”) like a air matrass sled which should catch landing airplanes and accelerates them for the start. Doesn’t sound very practical, but still better than catching a rope an swivel around…

Aspect ratio determines glide angle (aka. lift to drag ratio) while wing-loading determines stall speed and landing speed.

 

[Nicknick]

I totally agree, I just wanted to make clear, that, depending on the application, cutting down the wings to a minimum is not allway the best solution.