Here is a dumb question from an ignorant ground-lubber:
NOTE My understanding of the physics of flight is limited to envisioning a little picture of a wing cross-section with arrows going above and below it…totally stops there.
That being cleared up: Is there anything that would prevent an airplane from taking off on a theoretical curved runway, turning as it takes off? Assume a curve as gentle or sharp as you need to to make your answer work.
Is it never done because it is impossible? Or is it never done because it is theoretically possible but would add so much to training, risk, etc. that it would be a foolish thing to try or build?
Thinking of this based on the observation that airport runways never deviate from straight, even with the often extremely high cost of land acquisition and expansion at airports…I figured if it were do-able, it would have been done somewhere, at some time.
Yes. Even though I don’t know what kind of curve you are talking about, it doesn’t really matter. A plane takes off when it’s wings provide enough lift to leave the ground. At that point the runway doesn’t matter. Even before there’s enough lift to take off the plane’s control surfaces control it’s attitude, so the runway hardly matters at all at the point of takeoff. It is similar to running down the beach into the water and starting to swim, the shape of the beach doesn’t affect how you swim once you are deep enough in the water.
The problem is not lift, it’s speed on the ground. As anyone with a driver’s license should know, you brake into a curve because the faster you go the harder it is to turn. Since the whole point of the runway is to give the vehicle space to accelerate, a curved runway would be counterproductive.
There’s also a practical problem. At the speeds an aircraft has to reach on a runway before it reaches take-off speed, and given the weight the aircraft, I doubt that it would be practicable to steer it round a curve simply by turning the nose-wheel. In any event this would be ineffective once the nose-wheel left the ground, so at that point the plane (if not otherwise steered) would veer off the runway. (Or, rather, the runway would veer off from under the plane.)
So the steering would have to be done aeronautically - even if there wasn’t enough lift to get the plane wholly into the air, there might be a sufficient effect to steer the plane to port or starboard.
But, of course, a plane steered aeronautically banks, with one wing rising and the other dipping. Which would be a bit of a problem for a plane moving at speed along the ground.
One thing I’ve wondered is if it’s feasible to build a bridge over the middle of a runway? Since planes always takeoff & land at the runway’s end, they’d always still be on the ground when they reach the middle and can just go under the bridge. Any reason why that wouldn’t work?
Don’t forget landing. I’m not a pilot but taking off from a curved runway doesn’t seem too bad, assuming it’s a gentle curve, but landing on one just seems flat out ridiculous.
A small plane on a long runway, or a plane that’s going around because it couldn’t land, wouldn’t necessarily be on the ground at the middle of the runway.
The point at which a plane lifts off varies depending on the size/weight of the plane, wind speed, humidity, etc. It would be hard to determine a point where you could depend on both a 747 and a Piper cub would still be taking off.
It would be much more sensible to build a tunnel under the runway.
My Dad mowed out a runway with about a 20° dog leg at about the 1/3 point. Needed added ground run when leaving heavy in the wet grass. No problem landing. ( Cessna - 180, 4 place tail drager with 240 HP )
Later years he used a oiled road along some property to land his Piper Comanche, 260, 4 place tricycle gear low wing ) Measured first, had 10 feet clearance on each wing tip at the choke point. Needed to stay in the middle. Fun one as I was a pilot by then and landed there often also.
Pvt strip N/E of Tulsa with a BIG power line across the middle. The strip was short. The hot lines hanging from insulators, 2 ground wires on top, as seen in may parts of the country. Short strip, even for a C- 180 and it was slightly downhill towards the middle where the power line ( E/W ) was coming for either the North or the South approach.
Had to be down before the wires on landing and stay on the ground until passing beneath them on takeoff. Due to the shortness of the strip, on a calm day, not even a Super Cub could land or takeoff of just one end with the wires their. Could get in but not out. In over the wires with out help from a breeze or out over them would be really tricky.
Pilot in the pipeline patrol company went down on a curved road with 3 foot too long of wings on each side. About 10 Texas brush crowding the road. We took hi another airplane and brought a spare engine & tools and fixed the down C-150, beat out the wings a bit and used a pipe line right of way as a runway to get it out. It was straight with a berm dozed up 85 paces away. Good thing it was a C-150-150 (150 HP Lyc. for the engine & had manual flaps and we had left only about 5 gallons of fuel in it. ) Hit the berm with the nose wheel slightly lifted, snapped full 40° flaps instantly and popped about 15 feet in the air and just held level and waited. Glanced once at the airspeed indicator and
decided I did not want to look again. Got to the airport fine after I milked the flaps up.
C- 180, C 310Q turbo and other planes I have landed / taken off in a curve ground track due to wind mostly, length or amount of room to use and due to bad brakes.
Now all of this happened over a 10,000 hr and 30 year flying career so it was not the usual thing.
One last thing that I did do just because it was fun was when getting fuel at the end of a flight and ‘Gundermans’ little airport North of Tulsa
in an 1956 C-180, the fuel pumps were East of the runway a rather short distance. ( With the camera man & large mapping camera ) It was just far enough that doing a max effort takeoff, I could get the tail up a bit before the runway and then as we bounced off the asphalt on the West edge of the runway I would snap those wonderful manual 40° barn door flaps and about 50 feet later we would clear the bob wire fence and turn South for our home field.
Took a year before the camera guy would stop sucking air every time we did this. He got to where he would just keep doing his paper work, Bawahahhaa That old 56 would go & do many things that would crash the later models with the L engines and Improvements. ::: sheesh :::: Before the 310, we got one of the later C-180’s. It was a sick plane in comparison… Then came the C-310… Zoooooom !!!
This could be a problem if the plane just reached take-off speed, or just lifted the nose-wheel off the ground, just as it’s going around the curve.
(1) If you’re going to steer the plane aeronautically, that means banking the plane. If you’re that close to the ground, the lower wing might hit the ground.
(2) If you’re turning, the outside wing is flying faster than the inside wing, and has more lift. If you’re just at flying speed, you might find that the outside wing has just enough lift to be airborne while the inside wing doesn’t, in which case, see (1). If this happens while you’re at altitude, it’s called a spin (one wing stalled while the other wing still flying). If this happens while you’re really close to the ground, it’s called an incident.
That was my thought too. The sharper the turn, the heavier the bank and the more likely wing strike or stall. The reverse problem taking off. The outer wing would start flying before the inside wing, risk flipping the plane or at least ground-looping it with all the resistance on the inside wheel.
Plus, not just one wing taking off or stalling before the other. Consider taking off - as mentioned earlier, the front wheel for steering will be ineffective abve a fairly low speed. (I once took off with a strong crosswind, as soon as the front lifted, the plane headed into the wind - I had a short bounce where the front wheel at an angle just - fortunately - skidded instead of rolling or directing me) So you are using the control surfaces to guide the plane. However, you are accelerating too, so you need to constantly (carefully) adjust the angle of the rudder as the plane accelerates and the faster wind pressure on the rudder more effectively guides the plane.
Basically, unless you have no choice, fancy maneuvering during takeoff and landing is not a good idea. It just adds to the risk of becoming a statistic.
People fly model planes on control lines, wires that connect to one wing so that the plane flies in a circle with the pilot at the center. I read somewhere (although it may have been a rumor/hoax) about a guy who took off that way in his Piper Cub. He had a circular field on his property that was large enough to land but not take off, so he mounted a pole at the center and connected a cable to the wing of the plane. He’d travel in circles until he gained speed and some altitude, pull a release lever, and fly away.
The rudder is effective at takeoff speeds. A single-engine (propeller) plane will have a tendency to turn left, so you apply right rudder to keep it straight. If you built a runway with a gentle curve to the left you wouldn’t need the rudder. It’d be hard to get that just right, though.
I’ve got a book by that title, but not by that author.
Most single-engine propeller planes require right rudder to be used during takeoff and climb to prevent the plane from turning left… which it wants to do because of the spinning propeller. So if you had a runway that was basically north-south but curved to the north-west, then taking off north you’d have a left turn, but south you’d have a right turn. A left turn would be much easier to deal with (but straight is still better), but any curve would be terrible to land on.
There’s nothing really stopping you from taking off or landing from a curved runway, but there is no benefit so no reason to do it unless you’ve got a little mountain strip with terrain issues.
