Rocketmagnet

Hi all,

I would like to build my first RC airplane. However, I much prefer making things that are practically impossible, so, rather than getting a kit I would like to make up my own plane. To make this project as hard as possible, I would like the plane to have the following features:

1. Stereo gimballed cameras at the front, a bit like an owl's head, so I can fly it with a VR headset on. (not too hard)
2. The ability to make a zero speed landing. (hard)
3. Some feet and legs, so it can absorb the impact of the landing, or possibly land on a perch. (hardish)

It's number 2 that I would like some advice about. Does anyone have any experience making a plane which can do a very low speed or zero speed landing? Doing some research, I think the plane will need the following:
1. Wings which can reshape themselves considerably to be able to provide maximum lift at the low landing speed (slats and flaps)
2. Wing load, gyroscope, wind and ground speed, angle of attack and acceleration and ground distance sensors.
3. Computer control for the landing.

There are two ways I can imagine landing at zero speed. The way some birds do it is to fly below the landing point (a perch), then fly up towards it, reaching an almost zero speed apex just at the landing point, then grabbing it with their feet, and using them to come to a complete stop. This sounds physically possible, but requires some way to accurately sense the perch, which would need either an electronic perch, or a good realtime vision system onboard.
The other way is to land on the ground, but I can't imagine how it could be possible to come to a stop in the air, without needing to fly below the ground, and without flapping the wings.

I would prefer the land the second way. Can any aerodynamics experts suggest whether or not they think this is physically feasable? I am not interested to hear from people telling me that this will be a difficult/impossible project. I know, that's why I'm interested in it.

Many thanks in advance for any replies.

Hugo

OffroadBEAR

My Feedback: (2)

Do some research on the XFY-1 Pogo. Its not completely impossible because its been done, but.....

Anything is possible, the only two factors hindering you are your fabrication skill and wallet size.

Louis4sun

Hi

One french hobbyist made a VTOL plane with 4 rotors/props
VTOL 4 rotors/props are vertical
Transition : tilted props (2 carbon tubes rotating = per pairs)
Horizontal cruise : 4 props classical
THe plane aspect is traditional : wings + tail surfaces

Louis

Rocketmagnet

Hi guys,
thanks for your quick replies. I guess that making anything akin to a helicopter, with rotors in all directions feels a little bit like cheating. What I had in mind was more of an Airplane which can do a zero speed landing. Perhaps more like a bird.

We have plenty of high tech fabrication technology and manual skills in our workshop, so making it shouldn't be too hard. What is hard is working out the concept, modelling the aerodynamics, designing the mechanisms, working out what to sense and how to sense it, and writing the control software.

I'd love to hear any more ideas people have about slowing a plane to zero speed both horizontally and vertically at ground level. It is aerodynamically and energetically feasible? Maybe it would need to flap the wings once to kill the final bit of speed, while providing lift?

Hugo

OffroadBEAR

My Feedback: (2)

The XFY-1 is not a helicopter and its not really akin to a helicopter.

I think you want to build a robotic radio controlled bird.

An airplane has a wing, which generates the lifting force required for flight. This lift force is only generated when air is flowing past the wing. A wing cannot generate lift when the air velocity around it is zero.

Also, look for radio controlled ornithopters. You could start there for a base. Are you wanting to start an R&D project for an engineering company or a school design team challenge?

Rocketmagnet

Hi OffroadBEAR,

Thanks for your reply.

You're right. I'm sorry I called it one. But in that picture it is landing a bit like a helicopter though isn't it? Rotor on top, providing lift.

It's not so much the birdyness I'm interested in. It's more of the zero speed landing (and the VR headset). I'm not that keen on ornithopters. I always thought they were irritating flapping things. But, yes, robotic is the right word. Partly controlled by an onboard computer, and partly from the ground. In a similar way I believe a modern fighter jet is controlled. The pilot instructs the computer, and the computer takes care of the surfaces to control what would otherwise be an unstable plane. (correct me if I'm wrong).

What I really have in mind is an airplane which could make a zero speed landing. If it must have some features of a bird in order to achieve this, then so be it.

Are you saying that it's strictly impossible for an airplane to make a zero speed landing? It's surely possible in theory to land on a perch above ground.

Perhaps better questions are:

What's the theoretical lowest landing speed?
What could you do to push this towards zero?
What's the theoretical lowest perch for landing at zero speed?
What could you do to push this towards zero?


Neither. I work at a robotics company, but we don't do this kind of project commercially. Some of us were just interested in it as a hobby. We have access to all of the equipment in the lab in our spare time (machining centers, CAD/CAM, electronics etc) and we live for fun and difficult projects. We have very little experience with RC planes, but then we had very little experience making robots when we started.


Many thanks

Hugo

OffroadBEAR

My Feedback: (2)

Okay, I think I understand you a little better now. Its not that I am trying to hassle you or anything, but a little reading into fundamental aerodynamics goes a long way.

Basically, an airplane has to have forward "freestream" velocity to fly, that is, it must have air flowing over its wings. A wing just sitting there in space does not generate lift. I guess you could call it a landing, but if a plane's forward speed is reduced to zero, its wing stops generating lift and it gains velocity downward resulting in a crash (landing of sorts). If it pitches forward whilst moving downward, it can generate lift again, but pitching downward changes the flow velocity in relation to the wing.

A bird on the other hand is an entirely different animal (pun intended). A bird's wing has camber like an airplane's wing, but this camber can be affected by the bird's muscular movements. The angle of attack of the bird's wing is also highly variable depending on muscular movements. An ornithopter only replicates the up and down motion of a bird's wing, but does not include the forward-backward motion and rotational motion of a bird's wing, nor does it replicate the muscular movements of a bird.

I would think it is highly improbable that you could accomplish a robotic bird that is actually capable of flying due to the amount of equipment you want along with the equipment needed to flap wings. Wind tunnel models have been made replicating all three movements of an avian wing, but to my knowledge, a working, flying robot bird has not been made yet (I could be wrong), so here's your chance.

Get the book "Model aircraft Aerodynamics."

BMatthews

Birds tend to fly up to a full on extreme angle of attack stall and USUALLY climb up to stall just before their fall puts them on a perch or leaves them a few inches above the ground from where they fall to a "landing". This is going to take some very good reflexes and familiarity with the craft. In effect they don't fly to a landing so much as superstall their way to zero airspeed and do it all with grace and balance.

Sort of like for us how walking is a constant series of falls that we catch just in time to avoid a face plant. It seems like nothing until you examine the dynamics of walking. Being in robotics I suspect you realize how we take stuff like this for granted until you try to duplicate it mechanically and using algorithms in processors to operate mechanical muscles.

Altering the wing isn't hard but I think you'll find that programming in the responses will be extremely tough. All I can say is good luck and you're on your own.....

TFF

A lot of birds at that last second before touchdown sweep their wings from back to front creating the wing speed to keep the lift( plus the camber changes and flapping), but it is not sustainable as they have to reach back again which would make them stall; the instinct of perfect timing. The air has to flow over the wing to fly; If you had a plane that had a top speed of 30 mph flying in a 30 mph headwind will be flying at 30 but it wont be making any headway; it will stand still. The helicopter works because the wings are moving even if the speed is not forward, and helicopter aerodynamics are a whole other bag too. Actually the pogo is pretty common with the 3d stuff and a guy in my club has a 3d plane that is designed to do that with a cruciform tail.

Dorsal

My Feedback: (17)

NO, a zero-speed landing is only possible when the runway is a treadmill traveling at or above the stall speed of the airplane in the direction opposite to the airplane's flight.



Sorry, I just had to throw this into the mix.

Rocketmagnet

Hi everyone,

Wow, thanks for all the replies, this is great. I don't mean to grumble, but the replies are a little along the lines of "this is practically impossible" and less along the lines of "assuming this is almost possible, how can we get as close as possible to it?"


Yes, absolutely. Which is why I rephrased the questions as:

What's the theoretical lowest landing speed?
What could you do to push this towards zero?
What's the theoretical lowest perch for landing at zero speed?
What could you do to push this towards zero?

It's surely possible to do a pretty low speed landing, if you're a good pilot. You could do a slower one if the plane was designed with low speed landings in mind. I bet it's possible to do an even slower one if you could have superhuman reflexes, and lots of sensing. You could maybe push it really close zero if the wings could make one hard flap just as it came into land. Maybe it could take advantage of ground effect for a little extra lift? Maybe this could be slow enough that the feet could grip the ground / perch and bring it to a full stop.

In fact, I think it would be impossible for me personally to do it. Which is why it needs to be an automatic, computer controlled landing.

Yes, brilliant, This exactly what I'm imagining. The plane would need to dump all of its kinetic energy in a controlled manner, riding very close to having an accident, but using sensing and computer control to keep it stable.

Yes, it would be awesome to make wings which can alter their shape like a bird's wing. I think this is more feasible than flapping, because it requires a hell of a lot less power. I'd love to make a wing like that.

Yes. But what I was thinking is that it could learn. You get it to do landing after landing, all day, each time it tweaks its parameters to bring the landing speed closer and closer to zero. Trying to program it and get it right is practically impossible.

I will take a look at the book "Model aircraft Aerodynamics" over the weekend.

Some more questions:

What do you think the wing should look like during the "super stall"?
How could it tell if it was making the perfect stall? i.e. what sensors would it need? Is the wing load/torque/angle an important factor?

Many thanks for all your help

Hugo

HalH

My Feedback: (12)

What about the Harrier ! Also the new F-35.

MustangAce

My Feedback: (3)

I have done a zero airspeed landing with a 88" wingspan Yak 54. I'm sure many 3d pilots have done this as well. With a little wind, point the aircraft into the wind and do the elevator maneuver. Full up elevator all the way to the ground right before it hits add a burst of power and ease up on the elevator a little. The landing is a little tail first and mains can hit a little hard.

Rocketmagnet

No, that's still cheating. The Harrier is more like a magical hovering machine.

This is more like it.

So, what's the pitch of the plane when it touches down? It is pointing straight up? Was both the horizontal and vertical velocity close to zero?

Hugo

MustangAce

My Feedback: (3)

Probably around 15 to 25 degrees nose high.

Rocketmagnet

Oh, wow. That's not much at all. I was expecting you to say something like 45 degrees. Was the angle steeper just before touchdown?

Hugo

rmh

Its all a matter of wing loading and available thrust
Zero landing speed ( forward speed) is common amongst 3D small electric setups vectored flight - extremely high AOA and a blip of power and elevator at last instant - the the model noses up - hesitates then drops down.
It is how we land ours in a rough field. larger models make progressively harder contact - still possible tho

dbacque

My Feedback: (3)

You might consider slowly building up to this project rather than going big bang. Prototype the various pieces before integrating into one vehicle.

You say you want to build your first R/C airplane. Is this your first build, your first airplane, your first flight?

Rocketmagnet

In the past I have built a single wing for a school project. And I have flown a couple of total beginner RC planes. So I'm really a total beginner here.

However, it's not the first thing I have built. I have 16 years in the robotics business (I started when I was 14, and have been doing it full time since I was 21. I'm now 31). I have built several humanoid robot arms and hands, including about half of the one pictured. The thing about robots like that is that all the parts are so tiny, so I have a ton of experience building tiny fiddly things, including really very dense electronics. I am experienced in hand crafting, as well as CNC machining. And writing software, including firmware, control and physical modelling, and CAD packages for electronic design.

Hugo

Jim Thomerson

I was out trimming a freeflight model at a small local airfield. Two Aeronca cropdusters came in for a landing. They approached perpendicular to the runway, came over the electric lines, and stalled onto the runway, turned on the ground and taxied maybe 50 feet into the hanger. I was impressed. So a conventional airplane can make a darn slow landing!

Rocketmagnet

This is sounding better and better. I reckon that if there was competition held every year, to see who could make a plane do the shortest landing, in no time at all, people would regularly be doing zero speed landings.

Hugo

CrateCruncher

My Feedback: (1)

When I saw this thread the first thing I thought of was the routine step-off landings that paraglider pilots perform. They do it by pulling the trailing edge of the parasol wing down in a drastic arm gesture, effectively slowing airspeed to zero and stalling the wing just as their toes touch the ground.

Since this is a brainstorming thread I would throw out that perhaps you could design a wing that pivots about an axis just before touchdown. The extreme AoA would scrub forward speed without the craft zooming in an ideal world. Actual results may vary........

Scorpion Racing

By zero speed landing, I am assuming we are talking ground speed? All you need is a head wind equal to the stall speed of the aircraft, thus eliminating any foward motion needed. You could also increase thrust and the angle of attack to stop foward motion, and do an elevator landing. Not a hard feat at all, most 3D pilots do it all day long.

No matter how you look at it, you have to compensate for the forces of gravity on the aircraft to stop foward motion and land at zero ground speed. No matter if you use rotors (Helis), thrust vectoring (Harrier), thrust and high AOA (3D elevator landing) or a good headwind to do it.

Good Luck and enjoy the testing!

Rocketmagnet

Thanks guys for your replies,

Yes, a friend of mine said the same thing. They just walk out of the landing as if they were taking a stroll in the park.

Brilliant, I love suggestions. You mean the horizontal (pitch?) axis? So, would it be better to rotate the wing, rather than pitch the whole plane? I guess you could rotate the wing quite rapidly because of its lower mass, and the tail could stay off the ground if the body was horizontal.

But what if there isn't one ?

I'll look into that, thanks!

Hugo

CrateCruncher

My Feedback: (1)

Right Rocket, pitch the entire wing about a horizontal axis from 0 to x degrees somewhere near the wing's center of lift. You would have the extreme AoA while the fuse remains parallel to the ground allowing you to get much closer to the landing surface before stall. You might even build in an autonomous rotation thats mapped to ground height and airspeed. That way the pilot performs a smooth touch-down landing every time. Would it work? Who knows?