Tow-plane pilot for gliders is a dangerous profession. A simple mistake by the glider pilot can kill the tow plane pilot, with not enough time to react. I saw this happen in person once (https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/G...). Gliders and towing them is neither easy nor safe.
In gliding, tow upsets are pretty common and, in rare cases, can be fatal. An out-of-position glider out can _easily_ and very quickly overcome the tow planes elevator authority (ability to pitch up or down) which leads to accidents like this. This video does a good job explaining explaining the root causes and potential dangers (https://youtu.be/5cpqFzhM9dY?si=J7GxP1dI9Xopy3xu). Also read the comments from testimonials from other glider pilots.
This is my biggest concern with this concept as well. Towing things is challenging because the tow plane's center of gravity can change drastically depending on the forces on the glider it is towing -- if the glider deploys its spoilers / crabs in a crosswind / gets in your wake turbulence you're not going to be able to predict how it changes your CG (and your control authority) without training or experience. Also, with gliders, the tow plane is traveling at around 60MPH to 90MPH, with a decision window of 2-3 seconds. Commercial planes travel at ~500 MPH... The concept seems like a hard sell to the pilot unions. I bet they've thought about this though.
> An out-of-position glider out can _easily_ and very quickly overcome the tow planes elevator authority
Would this not be trivially solvable with a system that detects the situation (e.g. by measuring the forces acting on the towing plane's attachment point) and detaches the tow? If in the final concept the towed plane would be unmanned and wouldn't contain fuel, even a crash would not be particularly catastrophic.
You misread. It causes the crash of the leading plane, not of the following one, so the glider having no fuel is completely irrelevant
As for a system that measures forces, that’s not likely to work either. Transient forces are OK, but the same force over a little bit of time is enough to force a nose down attitude that is unrecoverable. Attempting to draw the line unequivocally between the two is difficult because it depends on conditions, weights, centers of gravity, and many other things.
They didn't misread, what they're saying is that the lead plane would detect conditions/forces that would result in a tow upset and then cut the tow tether. There's a video in this thread that shows that currently, in manned gliders, the glider pilot can and has a responsibility to release if a tow upset is happening.
The force at the attachment point is constantly changing and depends on several factors.
- the weight of either airplane.
- the performance of the engine on that particular day (varies by altitude / airspeed / temp / mixture / type of fuel / ...)
- the instantaneous weather conditions
- the performance characteristics of either plane.
- slack in the rope (no tension to two times the weight of the glider)
- the glider's towing position (below / above wake)
- crosswinds
- the glider's preferred towing position (depends on visibility from the cockpit, e.g. if someone has a phone or a tablet on the dash, the towing position will be different)
So it isn't really a trivial problem, especially when false positive or false negative will lead to a crash.
notice how he's always on the stick. Also notice how fast it goes from stable to unstable positions.
> even a crash
Recklessness is never the answer in aviation (or coding matter of fact). Practically, good luck convincing insurance to cover a 100 ton (any appreciable cargo load) plane that might fall out of the sky on any property in the general vicinity.
So now we are dropping shipping containers with wings out of the sky when things go south with the towing.
In order to make such a contingency safe, we'll need swathes of ground that are clear of any population so that these things can crash without collateral damage.
If you have a corridor of land that's void of population between your origin and destination, then you might as well, you know, lay down some tracks or tarmac and get rid of the whole flying business altogether.
Now, if you have a body of water between your points this might be a better suited plan I think.
This product is for towing behind another aircraft, but what about winch towing?
A winched glider implements flight with renewable electricity and it does so efficiently because the power and motor never leave the ground!
A glider can climb up to 5000 feet and travel 50x that before making a landing. Wouldn’t it be glorious to see cargo being autonomously slung from site to site across the world, powered entirely by green electricity?
The we simplify it by putting the winch on rails, and give the glider wheels, then we can chain them together and then we’ve reinvented the railroad, badly.
Nah. You've messing up something 4chan worked out years ago. You need a BLIMPTRAIN! Locomotive on rails towing a train of lighter than air vehicles that can detach under optimal conditions/location to deliver their cargo over the last mile.
Try loading 10 tons into some glider and shooting it up. First the winch would have to be absolutely massive, second its highly reliant on at least a bit good weather and nobody glides around during night. Pilotless doesn't remove danger of it falling onto some roof, so automation would have to be pretty much flawless.
Truck, you can load and send it much further than any glider can ever glide, any time, any day. Also throughput of highways is much bigger than airports, and you can deliver it literally to the target doors.
I've done a few gliding flights. They were all towed to height by a powered aircraft and then released. Winch launch is an alternative to towing, but sounded like a fairly terrifying alternative where you were yoinked into the air by a huge winch. The terror isn't an issue if the glider is pilotless. But IIRC they used something like a 7 litre engine to winch an incredibly light glider. Presumably it would require something really powerful to launch a cargo glider.
I did once fly as a guest with a winch start, and yes it is something. The ascend is pretty steep and the acceleration is powerful. The pilot did not find good lift and we had to land shortly after. My stomach did not like his curving around looking for lift, so I wasn't too unhappy about the short flight.
Is a glider basically joinked into the air by a large and fast winch, and then detached and the glider glides on it's own "power" back to the landing? Or is the winch at the destination, with a cable going _all_ the way across the landscape to where the launch point is, so that it can pull the glider over?
Winch launches are a lot like a kid with a kite. Run fast (wind in the winch) to get speed and up it goes. At its desired altitude, the glider disconnects and goes on its way. https://youtu.be/YePIJKs5me0 gives you an idea.
On a day with a decent breeze, it is possible to "kite" a glider up to very high altitude by letting the wire out again. But this is highly frowned upon because it means there is a very long (and nearly invisible) wire dangling right through the airspace used by other aircraft!
Thanks, I tried to look exactly this up, but couldn't find anything. Looking at that video, the only thing I could think of though was that cable, presumably detaching shortly after the video ended, and the cameraman is just standing there where the cable could presumably fall. It does not look very thick and heavy, but still!
Traditionally, winch cables are single strand steel (fencing) wire - I guess because that's cheap. But they break quite often.
Cable falls can be a problem. A cable falling over power lines causes all sorts of fuss!
Cable breaks can be terrible. The cable will spring back, whip around, and is incredibly destructive - hence the cage around the winch operator. I would not have been standing anywhere nearby and certainly not next-to or behind the drum.
The winch launches the glider and gives it speed from the ground that it can then convert into enough altitude (ie time) for the pilot to find a rising air current (ideally, I guess).
Edit: so yes, your first thought is correct. :) It's somewhat similar to an aircraft carrier launch except that the glider can get a lot more altitude out of it.
Hah, it wasn't a very meaningful response. It's OK for this community to have moderated my comment appropriately, especially given drpixie's much better answer! Yes, it's just like a kite!
I'm the wrong kind of engineer to work it out, but I'd be interested to know what the implications for the strength of the cable and specifications for the winch would be for a heavy cargo glider.
Thinking on, specifying the weak links and managing failed winch launches (which happen fairly regularly) is interesting to consider. Recreational gliders are light enough to be manoeuvred by hand, although old farm tractors are used to move them more than a few dozen feet. How would all that work?
Do you mean laying out 50 mile long cables from place to place with big engines on the ground that pull in a cable at a couple hundred miles per hour after a plane attaches to it? That wouldn't work. Not even if you skipped tow out a cable from your departure point so it could be reused.
And if you had a track for the cable to run in or a carriage holding the winch to drive travel along, then you would just make it rail freight.
No. Winch glider launches (which are not a new thing) use a ground-based winch to give the glider an initial impulse, and the glider uses that to gain altitude and then glide for a much longer distance.
It would work fine for sending small payloads short distances but unless you're in a hurry, it would be much easier to just send more mass by truck or train. One big benefit is having a truck or train being able to return to its origin without requiring another launch facility and also being able to travel in nearly all weather. There may be some use cases where drone gliders could airdrop payloads and return to their origin. But again, this requires very specific circumstances like good weather, a lack of roads, unavailability of av gas or jet fuel, and enough cleared space to launch a glider. I do see winches as a good way to launch lightweight fixed wing drones to reduce the amount of fuel and engine size required to deliver payloads. You'd only need to account for the fuel and power required to sustain cruise if you could winch a drone into the sky. You'd get even more distance if the drone was never intended to return like a kamikaze weapon. A small clearing in a field in Ukraine could launch cheap fixed wing kamikaze drones all day long.
It wouldn't work very fine at all. Gliding at low speed a minuscule payload 50-100 miles that you have to transfer to the airport at the departure point then from the airport at the destination will almost certainly take longer and be much more expensive in terms of infrastructure and worker cost than just driving it point to point in a delivery vehicle. It's also highly weather dependent, much more so than powered aircraft.
If you're really in a hurry you need a helicopter. Then pay your indulgences to some politician's shady "carbon credit" corporation if you feel guilty about your climate sin, or use a carbon-neutral manufactured kerosene for it, and then you're even greener and still cheaper than the unpowered spruce goose idea.
I don't think it's completely true. Higher weight increases the speed at which the glide ratio is optimal, and drag (parasitic drag in particular, unrelated to generating lift) increases with the square of speed. Basically, flying faster wastes more energy. That effect is going to dominate at some point, probably about 120 km/h or so with a typical glider. At 200 km/h, the glide ratio is garbage (but it's fun). I have flown gliders.
I'm not sure if simple descriptions of the phenomenon that glide ratio is independent of weight are missing an asterisk or if I'm just wrong...
A decent glider has a ratio of 1:40, an A320 1:17. Is the A320 a "bad plane" or is it optimized for higher speed with the corresponding worse glide ratio? (It also has engines that produce a lot of drag when gliding)
On another hand, there are CFIs, the FAA, books, etc.
I've only found one search result that agrees with you, so far, and at least a dozen that disagree, but the one that agrees with you has no math in it, and the ones that disagree mostly seem to depend on the same source info, so that doesn't feel conclusive in either direction.
The Wikipedia page on lift-to-drag ratio also believes weight does not matter to the ratio.
As a side note, your 200km/h example also sounds like it's just not the correct angle of attack or airspeed for the aircraft, so I'm not sure if that example applies?
As a separate reply, I'll add that I think finding where/if this breaks is pretty academic.
Eg: you wouldn't build a glider out of heavy material that gives you huge speeds but also huge sink rates.
So I think the entire glide ratio conversation mostly fits in the "your plane is fully loaded" vs "your plane is empty" scenario, and the point is that your best glide ratio will be constant, but you'll be gliding at higher speeds if you have more weight.
Gliders utilize Laminar profiles, while airliners use turbulent profiles.
The Laminar profiles perform better, but only when uncontaminated (no bugs or rain). Contaminated turbulent profiles perform better than contaminated Laminar profiles.
Since regulations state that you should carry fuel for the worst case scenario, it does not yet make sense to design airliners with Laminar profiles.
Naturally, manufacturers are looking for ways around this.
There is an asterisk that you have to be at the right glide velocity, but yes: they'll have the same glide angle. The leaden one will just go significantly faster. And yes, it does sound unlikely. That's why I made my previous comment.
Thanks for the links. Weight may cancel out of the equations, but (being a bit pedantic) I suspect 'glide angle in independent of weight' only holds up to a point. Taking things to extremes, if the glider is heavy enough that you are going to have to go supersonic then I suspect a lot of the assumptions become invalid.
NB/ spherical cows are unable to glide in a vacuum.
Make a paper airplane and drop it. It likely won't go much further than your feet. Throw it gently and it will go some distance. Throw it harder and it will go further. Glide ratio is the horizontal distance over vertical distance. The vertical distance is the product of (lift - mass)*t^2 where lift is a function of the shape of the wings and the airspeed. So given a higher mass and the same lift, the time to hit the ground will be less when the glider is dropped at 1000ft. Increase the airspeed and you'll have more lift to negate the higher mass. The increased airspeed also means your horizontal distance will be covered faster. The lead glider will travel the same path as the normal one but will be going a lot faster. The reason why gliders are built as light as possible is reduce the work required to lift them, the speed at which to release them, and the interia required to turn them. You also have the benefit of being able to land them at a lower airspeed without injury.
I assume it is a relevant enough concept to flying an aircraft (which also happens to be the context of TFA) that you learn about it while flying.
I guess another thing worth noting is that "glide ratio" isn't the same as "gliding" in the "flying a glider" context.
The space shuttle is probably the most famous glider, and was described as "a flying brick" and getting it to the ground at the right spot was very much a matter of glide ratio. Worth noting the space shuttle's speeds started off as hypersonic.
By comparison, a typical glider's built to be able to take advantage of air currents to regain altitude, and I'm not sure how weight affects that.
Weight affects speed with minimum sink. That affects the diameter of the circle you fly. Since thermals have more lift towards the center (assuming perfectly circular thermals), you are not able to circle in the strongest lift. So you climb more slowly.
You can glide faster with the same L/D, so that might be worth it if you try to optimize for speed.
Also, how much does it decrease the fuel economy of the towing plane?
I sure wouldn't want to be on a Boeing 7XX flight with one of these things in tow. Just imagine the possibility for human and machine error, the plane in tow could cause all manner of issues for the leader.
Ever tried riding a bike and towing someone on another bike or a skateboard? It's perilous. Now do it in the air. Gutsy.
I did a masters on design a autopilot to optimize fuel consumption in formation flight. What is interesting about the aerodynamics is that if placed in the upwash wake of the leader, you are essentially increasing the wing aspect ratio of the system, resulting in gains for both the leader and the follower aircraft. Feels very unintuitive but basically the donut spool is larger and the combined wing is bigger in the spool.
It looks like the prototypes land separately because they are converted aircraft. The production glider uses autopilot and is meant to land behind the main aircraft.
Their current implementation (or prototype?) actually uses a powered airplane instead of a glider, which has its engines on for takeoff and then switches them off during the gliding phase (https://www.aerolane.com/aerocart, "How planes fly with AC0 today"). This way it works of course, but I'm not convinced it would be possible to take off with a glider in tow when the lead plane is already near its MTOW (if you'd have to reduce the loading of the lead plane to be able to accomodate the glider, that would defeat the whole purpose of what you're trying to do)?
To be pedantic, an aircraft's MTOW is a function of the structural strength of the airframe and landing gear and doesn't depend on conditions. The Regulated Takeoff Weight is what depends on temperature, air density, headwinds, runway length, etc, and is driven by whether the plane can get airborne before running out of runway (with a lot of margin for contingencies.)
For many planes under good conditions (high density, high headwind) acceleration to takeoff speed isn't the limit, but only airframe strength. Under those conditions, you could tow significant extra weight. The existing fleet of older planes includes many that have had engine upgrades, so they can pull a lot more weight than their MTOW.
Runway length has to include room for a rejected takeoff, for when the engine loses power just before you get to rotation speed. I don't think it'd be fun to try to reject a takeoff with a heavily loaded cargo trailer behind you. The trailer must have its own brakes, but it sounds scary.
Perhaps the glider isn't strictly a glider but has some electric assist that's only used for takeoff and initial climbout? Electric achieves unprecedented power per weight when you only need battery for a minute or two.
If you can leave all the endurance for cruise and main climb to the lead plane, electric becomes almost trivial.
This seems to be the make-or-break aspect of the entire idea and the claim does seem incredibly suspect to me too. OTOH lying about something basic like this doesn't seem like a viable "business" idea. Is there any more documentation/evidence/explanation available for this?
Instead, can we implement autonomous formation flying? Each aircraft can still have its own engines and control, but can make a V shape allowing the following planes to run more efficiently.
This has been attempted (for a military aircraft IIRC), and proved too difficult to be practical. It may now be possible, but it is more challenging that it appears from just watching our feathered friends.
The physical linkage aspect of this just seems so dangerous. As other commenters have pointed out glider tow accidents are a real thing. Luckily gliders are light and typically operating at low speed. Adding a 10,000 lb aircraft to this situation seems wild.
Airbus concepts like fello'fly[1] and GEESE seem significantly safer. I could see using something like a lead aircraft with several drones following in formation and breaking off for takeoff and landing operations. Reliable Robotics is already working on autonomous small cargo aircraft for these types of regional cargo operations.
The military gliders made sense because they were landing in hostile territory, usually nowhere near a runway for a return trip. Those gliders were pretty much a one-way, one-time-use vehicle. I guess the Waco glider could be used to argue that towing is technically feasible, but it was intended for a totally different use case. I don't see how it can be argued that it's more economical to run, especially considering the safety issues others have pointed out.
I'm no aerospace engineer but it seems like it would be more efficient to fly one single bigger plane than to tow a second one behind it. I suppose this might appeal to certain groups where they already own a plane, and want to increase capacity without buying a whole new plane. But the idea that it's 65% more efficient just seems pretty sketch. I could totally imagine some drug cartels using these though...
If you've got a bigger plane, you also need a bigger runway. This thing should increase the number of usable airfields. That could be interesting for avoiding more expensive routes.
It is, but that only happens at one end of the trip. It can still drop cargo on a smaller airfield at the other because the braking can be done independently by both.
Plus there's an interesting wrinkle here: a lot of the media on the site show the tow plane as one with engines, and not a glider. I'm sure that's because those are the aircraft they could get their hands on, so that's what they made it work with, but the option is there to have the towed plane powered on takeoff. Doing that safely, with the two aircraft tethered... that sounds like a mess. But it's an option!
"When towing Aerocarts, planes instantly double or triple their payload capacity. This is because their capacity is limited by the takeoff / landing weight – not what they can safely pull through the air."
But later, on "How it works" section it is apparent that the main plane still has to tow the cart behind it when taking off. What's the trick that makes this work? Extra set of wings?
Yes, the wings of the glider provide lift that otherwise would not be present. The engines still need to produce more thrust to pull the glider but that's expected, the extra cargo doesn't come free.
That... kind of makes sense. But (the way I* see it) modern large aircraft aren't very overpowered (otherwise they would be less efficient), so their engine power is just a little bit above what's needed to get them into the air with a "usual" runway size in ~ the worst possible conditions ("hot & high"). Which means that they would need ~ double the runway length to take off with a glider in tow? So this works with the small aircraft they're currently testing with (they just have to use a longer runway), but if they want to extend it to larger cargo jets, they would risk exceeding the limitations of existing airport runways?
________
* - someone who has an interest in aviation, but no professional background or training therein
There's no way to make these safe - it's almost comical and this could be an April 1st joke.
Case 1) how are you handling potential rapid TCAS climbs/decent? You're making the targets a lot larger and less responsive. If TCAS commands a decent and slow down, you will be overtaken by the tow.
Case 2) landings thay require rapid braking, such as short runways for emergencies or engine fires (rapid brakes used so emergency vehicles don't have to chase 2km to get to you)
Case 3) aborted take offs. Brakes will need to be more performant and reactive than the ones we have on the main aircraft
Case 4) taxiing across active runways now has reduced margins.
Case 5) go-around performance is diminished. Already sometimes tight margins on that, what happens if you need to do a go around but the landing gear on the glider collapsed and is now a ground anchor?
Really? Those who have had anything to do with gliders know there is plenty that can and will go wrong. Landing on-tow !?!? And what's the benefit - they might save a little in cruise, but they've got to get there (safely) first?
I'm sure airports will really appreciate half-mile tethers, or whatever length you need for full-sized cargo planes, flopping about the runways (I assume they're aiming for full size because their little graphics doesn't show a little GA thing)
Even assuming a full size one doesn't fatigue off the tail of the lead plane, presumably any time a plane towing one gets into difficulty, the first thing they'll do is cut the towed thing free.
Also the website sounds like it was written by an over-caffeinated estate agent.
Farther down they talk about it being made for the regional cargo market, largely turboprop planes (e.g., Cessna Caravan). That's certainly what the brief video clips show.
I agree, I don’t see this working on existing commercial cargo planes without significant engineering challenges. I also don’t see this working for existing air control systems. I do see it working for private airfields designed for it and tow planes designed for it but that is out of scope. I wonder if they get their own adsb signal?
Yes, this was one of the first things that came to my mind: landing a towed glider right behind a motorized machine is just a bit too adventurous... Especially when winds a not 100 percent in optimum for a safe landing approach. Gliders should always eject mid air an land on their own.. Minimizing risks for any machine or even individuals
Landing with a towed plane behind you sounds terrifying. So much could go wrong. Also the glider is going to have very different flight characteristics from the tow plane.
Not to mention, what happens in the event of damage to the towed aircraft rendering flight operations impaired such that it affects the towing aircraft?
Unless "affecting the towing aircraft" means "ripping its tail off", in which case you're screwed no matter what height you're at. GA aircraft are probably a bit sturdier, but large cargo aircraft (based on large passenger aircraft) were simply not designed to pull anything, so I imagine you would need to add some kind of (pretty sturdy) reinforcement to the attachment point, which would mean extra costs and reduce the MTOW of the towing aircraft.
This concept raises more questions than the site answers:
* what's the point of landing in tow? The safety aspects and the failure modes are enormous
* it's unclear where the 65% fuel saving comes from. Riding the wingtip vortex on the inside produces downward momentum. In order to generate positive lift from the wingtip vortex, the follower has to be outside of it (e.g., gaggles of geese in wedge formation)
* taking advantage of wake flows, while possible (although 65% is highly improbable), would always be less efficient than optimizing a single airframe so that it minimizes the wake generation in the first place
* the site is missing footage of real flights. The 3 clips 10-seconds long are not showing what they claim to be showing. Also, does the "see flight tests" link work for anybody?
Taking an "optimist's advocate" position here (I share your scepticism):
65% are almost easy to achieve, with a bit of clever accounting: you'd look at fuel per ton-mile (that much is clear and perfectly fine) and then you just pick a tow plane that's maybe a bit overpowered but doesn't have much cargo capacity. If you look at fuel saving through that lense, the sky is the limit.
The contingency page in the pitch deck for when the "bigger plane is always more efficient" argument comes up would be looking at big end of the hypothetical size spectrum: when you want efficiency, a bigger plane means bigger wingspan. Air travel is in something not too dissimilar to the "panamax" situation on the oceans, everything on the ground stops at 747-sized (the A380 was carefully squeezed to mostly fit that profile). A formation can get a similar effect as a larger wingspan without exceeding runway dimensions.
(and as for landing in tow: perhaps some stupid legal angle, "it's all fully automated, but technically this is not autonomous because the lead aircraft pilot is in charge"?)
The reverse - tow plane lands separately - has some interesting challenges. If the tow plane lands first and messes up the landing, blocking the runway, the lead plane now can't land. Fine if you've planned the fuel for a round trip, and fine if there's a currently-usable second runway, but I can see a huge draw for this in being able to get interesting cargo loads into and out of smaller airfields where that won't be available.
If the tow plane lands second then it needs to loiter, gliding autonomously, for as long as it takes for the lead plane to land and get out of the way. And that sounds like a much harder problem to do safely, particularly with the lead plane's pilot having to pay attention to landing and unable to control the tow plane if it gets into a dangerous state.
I assumed this was about replacing "Airport 1 > Airport 2 > Industrial Park (trucks)" operations with airplanes which can drop cargo to multiple destinations.
