In-Air Recharging

[DamoRC]

Ignoring the battery safety aspects of the problem there is a simple mechanism that could be used simply, reliably, and without the need for absolute precision.

First thing would to have 2 trailing cables from the "Tanker" plane. they should be far enough apart that the empty plane's propeller would not catch them. Also each cable would be a different polarity. i.e. One positive and one negative. At the end of each trailing cable there would be a metal cup shaped contact with a high strength magnet on the "Tanker" side of the cup. The rim or lip of the cup would be soldered to the trailing cable.

On the "Empty" plane there would be 2 probes fixed to the planes wings, (one each wing). Each probe would be for a single polarity and have a similar cup and magnet arrangement as fitted to the trailing cables from the "Tanker" plane. The magnets should be oriented such that the opposite terminal is repelled if held close. Ie north pole to North pole or south pole to south pole.

The probes could be as simple as a couple of BBQ skewers with the contact and magnet attached.

When the "Empty" plane approaches the "tanker" the probes would be magnetically attracted to the trailing wires and the metal ends would be the electrical contacts for the passing of the charge current.

Just a basic and simple approach!

Have fun!

Ah, but it doesn't support re-charging while inverted!

Seriously though, wouldn't a single point of contact for the planes be better in term of being able to engage receiver plane to tanker - like the probe-drogue approach? The different polarities could be separated by geometry in the single attachment point/cup/plug/drogue thingy. (note - also doesn't support re-charging while inverted)

DamoRC

 

[CatholicFlyer]

Ah, but it doesn't support re-charging while inverted!

Seriously though, wouldn't a single point of contact for the planes be better in term of being able to engage receiver plane to tanker - like the probe-drogue approach? The different polarities could be separated by geometry in the single attachment point/cup/plug/drogue thingy. (note - also doesn't support re-charging while inverted)

DamoRC

@DamoRC I was thinking after seeing @Hai-Lee post the refueling tanker or recharging tanker, should have hook ups on top, bottom of the plane and then out the back for different batteries for different planes.

 

[Hai-Lee]

Ah, but it doesn't support re-charging while inverted!

Seriously though, wouldn't a single point of contact for the planes be better in term of being able to engage receiver plane to tanker - like the probe-drogue approach? The different polarities could be separated by geometry in the single attachment point/cup/plug/drogue thingy. (note - also doesn't support re-charging while inverted)

DamoRC

It may look better but positioning and contact capture could be a serious drawback.

The setup I proposed has the ability to hook up as the plane flies close to the contact cables. also being a magnetic contact the forces to break the contact in an emergency is totally unimpeded. With a single probe containing 2 contacts, (in a coaxial arrangement I assume) there is the possibility of snagging the cable if the planes alignment is suddenly varied and either the cables ripped out, the cables pulled so severely that an internal short develops, or the cables will not disconnect and then a double death spiral!

Sorry if I seem a little pessimistic but safety first and besides the cemetery is full of optimists!

As for the inverted charging that has never been a requirement for military in-flight refueling systems and with the 2 cable system it is possible if the cables are long enough and the hook up is completed prior to rolling inverted!

Have fun!

 

[DamoRC]

I was thinking more along the lines of the following pic. The drogue and probe would be shaped to allow entry in one orientation only (for example here I used an XT60 type of shape). The drogue would have aerodynamic tom foolery attached to keep it hanging upright and reasonably level. The probe (and drogue possibly) would have spring loaded contact points and there would be magnets at the ends of the probe and drogue to hold secure during charging.

@DroneRocket Guy - see what you've started? You better get that plane finished and another one built because we will have all sorts of things for you to try out soon!

DamoRC

 

[Hai-Lee]

I was thinking more along the lines of the following pic. The drogue and probe would be shaped to allow entry in one orientation only (for example here I used an XT60 type of shape). The drogue would have aerodynamic tom foolery attached to keep it hanging upright and reasonably level. The probe (and drogue possibly) would have spring loaded contact points and there would be magnets at the ends of the probe and drogue to hold secure during charging.

View attachment 113691

@DroneRocket Guy - see what you've started? You better get that plane finished and another one built because we will have all sorts of things for you to try out soon!

DamoRC

That would work if you could aerodynamically stabilize the cup so that the airflow doesn't cause it to jerk around in flight. Also assuming that the cable NEVER gets slack enough to allow for the flight angles between the planes to exceed the easy release of the magnet grip. If the cup can bind at an angle then when the cup and nose get bound together it will cause the issues mentioned previously.

Reminds me of the difficulty we had in first and second generation Laser communications links. Aligning them was the equivalent of threading a needle from a distance of 3 metres using a broom stick handle to hold and position the thread.

Have fun!

 

[DroneRocket Guy]

I think magnetically-bound connectors might not be the best choice as they could be difficult to disconnect at will. A mechanical latching system might work better, possibly incorporated into guides that bring the connectors together.
Perhaps the best way to experiment with the 'contact system' would be to initially leave out the recharging part and just try to link-up in flight for a tow. Unless, that is, you choose a system (like probe-and-drogue) in which the line is not normally under tension; but I think such a system would be much harder to link up with (particularly if you're not using FPV on the receiver 'plane) than one where the tanker can overtake the receiver trailing a kind of grapple that 'snags' a hook or loop on the receiver.

Electromagnets might also work.

also @DroneRocket Guy @DamoRC what do our pilots use in the Airforce and Navy when hooking up, is it a switch?

I believe it is automatic. Air Force uses flying boom and navy uses a cable.

Ignoring the battery safety aspects of the problem there is a simple mechanism that could be used simply, reliably, and without the need for absolute precision.

First thing would to have 2 trailing cables from the "Tanker" plane. they should be far enough apart that the empty plane's propeller would not catch them. Also each cable would be a different polarity. i.e. One positive and one negative. At the end of each trailing cable there would be a metal cup shaped contact with a high strength magnet on the "Tanker" side of the cup. The rim or lip of the cup would be soldered to the trailing cable.

On the "Empty" plane there would be 2 probes fixed to the planes wings, (one each wing). Each probe would be for a single polarity and have a similar cup and magnet arrangement as fitted to the trailing cables from the "Tanker" plane. The magnets should be oriented such that the opposite terminal is repelled if held close. Ie north pole to North pole or south pole to south pole.

The probes could be as simple as a couple of BBQ skewers with the contact and magnet attached.

When the "Empty" plane approaches the "tanker" the probes would be magnetically attracted to the trailing wires and the metal ends would be the electrical contacts for the passing of the charge current.

Just a basic and simple approach!

Have fun!

This is a awesome idea. It would solve the problem of a really big connector and decide it in two.

Also a quick update on other uses for this. The connectors on the plane could be used for ground charging. Also Right now I am only able to do paper diagrams as I am on vacation without my computer so expect harrible diagrams LOL.

Thanks for the suggestion and support everyone! Safe flying

 

[DroneRocket Guy]

I was thinking more along the lines of the following pic. The drogue and probe would be shaped to allow entry in one orientation only (for example here I used an XT60 type of shape). The drogue would have aerodynamic tom foolery attached to keep it hanging upright and reasonably level. The probe (and drogue possibly) would have spring loaded contact points and there would be magnets at the ends of the probe and drogue to hold secure during charging.

View attachment 113691

@DroneRocket Guy - see what you've started? You better get that plane finished and another one built because we will have all sorts of things for you to try out soon!

DamoRC

Wow that was exactly what I was thinking! I even was referring to the shape of an xt60/30

 

[DroneRocket Guy]

Air to Air refueling works best where the energy density of the fuel is high, and the energy flow is massively in excess of the energy expenditure rate.

As LiPo batteries require a maximum charge rate much less than the max discharge rate, should not be fast charged when hot, should never be charged in a enclosed space, should always be monitored, and finally should not be charged in close proximity to inflammable materials this could be an interesting spectacle if anything goes wrong.

DON'T forget to video it!

Have fun!

I was planning on powering the airplane via the recharging plane as that will allow time to cool the battery down and charge the supercapasitor charging device which can then charge the cool battery duirng non power intesive flying.

 

[DroneRocket Guy]

I'm sorry that it is taking me quite some time to reply to everyone. I did not expect this thread to blow up so fast! Also everyone please don't give your hopes up I'm still in middle school and that gives me a almost non-existent budget but I hope I can make 2 airframes and simulate a charging on the ground as the electronics of the planes (not the in air recharge elements) is a bit too much. If anyone wants to help (please no money sorry it just get a bit to complicated at that point) feel free to contact me at aaronaerospace12@gmail.com. I would love to give my design out to everyone here as I can also not attend flight fest (to far from me) but I would love to see my design be put to use at flight fest or anywhere. I hope everyone understands!

Thanks!

 

[sprzout]

I could see so much going wrong with this, though...Get the polarity wrong, get too much juice going into the receiving plane, have it go over the charge of the battery since there's no charging circuit to limit voltage...Well, as Hai said, I'd have firefighters on hand that know how to deal with LiPo fires and explosions!

It's an interesting thought, but for electrics, I just don't see it happening. Gassers would be more likely to try this with, but I'm not sure how that would work out, since many of them have pressurized tanks to keep fuel being fed to the engines when they're inverted, etc...

 

[DroneRocket Guy]

I could see so much going wrong with this, though...Get the polarity wrong, get too much juice going into the receiving plane, have it go over the charge of the battery since there's no charging circuit to limit voltage...Well, as Hai said, I'd have firefighters on hand that know how to deal with LiPo fires and explosions!

It's an interesting thought, but for electrics, I just don't see it happening. Gassers would be more likely to try this with, but I'm not sure how that would work out, since many of them have pressurized tanks to keep fuel being fed to the engines when they're inverted, etc...

Don't worry about safety I plan on doing this the NASA way. Every subsystem and system would be tested a few times to insure that it will be safe and work with other parts.

 

[JTarmstr]

This is an great thread and I hope somebody tries this b/c it would be awesome, however one problem I see is that keeping the aircraft in sync would be hard, unless you had DJI level stabilization. Real pilots when refueling, have the perfect view to match speed with the tanker and its still one of the most challenging aspects of missions (behind landing on aircraft carriers) because they have to touch the throttle so lightly to match speed, in RC that kind of sync will be really challenging. @Hai-Lee mentioned using magnets but unless you have electro magnets which you could turn on and off, they have to be strong enough to hold on and weak enough that when you want to detach you could pull away. I what I would suggest and I know this is crazy, but what if you had a cargo plane and used a trapeze style recovery system and then recharged? then using a servo to detach. this would be challenging to do also but I just wanted to throw the idea out there.

 

[DroneRocket Guy]

This is an great thread and I hope somebody tries this b/c it would be awesome, however one problem I see is that keeping the aircraft in sync would be hard, unless you had DJI level stabilization. Real pilots when refueling, have the perfect view to match speed with the tanker and its still one of the most challenging aspects of missions (behind landing on aircraft carriers) because they have to touch the throttle so lightly to match speed, in RC that kind of sync will be really challenging. @Hai-Lee mentioned using magnets but unless you have electro magnets which you could turn on and off, they have to be strong enough to hold on and weak enough that when you want to detach you could pull away. I what I would suggest and I know this is crazy, but what if you had a cargo plane and used a trapeze style recovery system and then recharged? then using a servo to detach. this would be challenging to do also but I just wanted to throw the idea out there.

Ya attaching would be the main problem besides charging.

 

[DroneRocket Guy]

Ah, but it doesn't support re-charging while inverted!

Seriously though, wouldn't a single point of contact for the planes be better in term of being able to engage receiver plane to tanker - like the probe-drogue approach? The different polarities could be separated by geometry in the single attachment point/cup/plug/drogue thingy. (note - also doesn't support re-charging while inverted)

DamoRC

Have no fear I think I have something where the charging plane and the recharging plane could both be inverted and it would still work. BTW here is a quick sketch I did. If I can I possibly might make a cad design today or tomorrow but I would not hold my breath.
https://drive.google.com/file/d/1D7H_blLH2jRK-6Bnvkax_P3Xam_9Uoeb/view?usp=drivesdk

 

[Fluburtur]

Charging in flight might take a while, just toss a charged battery out of the tanker with a parachute and have the other plane catch it! I think someone managed to catch some probe like that.

For real the technical difficulty of this is quite high so I would start training on the hook up procedure with a mockup probe right now, the piloting aspect of that seems pretty high as well.

 

[DroneRocket Guy]

I was planning on making a full working testing rig (exept for charging) with the back part of an airplane with the boom and the front part of a plane with a reseprical. It could be used for training and testing of the recharging equipment eventually.

 

[DroneRocket Guy]

Ok so here are some updates.
First i am starting making plans for the recharging boom. Hopefully I will have a non working model with all parts (a new one with parts that are not place holders will be done after this proof of concept) done this weekend.

Secondly I have a new method that should work better for charging. The plane that would be charging would have 2 batteries one that can power the plane for around 30 min and one that would be a main flight battery. The main flight battery would charge at the maximum charge rate decrese time charging and the second battery would power the plane during charging. And could be recharged by the main battery if needed for the flight profile. In order to save weight in the plane needing the charging the striped down charger that would provide the right voltages and charge rate would be housed in the charging plane. The battery being charged would be charged by only main plug.

Finally if anyone @DamoRC @Mid7night @localfiend (please don't feel obligated to help I was just wondering) wants to design a high cargo capacity plane for the project it would be a big help as I don't have much experience in foam bord aircraft design (I kinda know how to build them though and I am able to fly them.).

Thanks and safe flying!

 

[Hai-Lee]

Just a note on changing batteries. Most Rxs take a while to reinitialize after a power loss and during this period of time the plane is effectively out of control.
Better to have a UBEC powering the Rx, and servos permanently during the flight so where you are thinking of using a second or flight maintenance battery the UBEC would best be connected to such a battery. This could provide hours of control and isolate the plane from any issues related to a failed charge attempt including accidentally shorting out the Main battery.

Just thinking of safety again!

have fun!

 

[DroneRocket Guy]

Just a note on changing batteries. Most Rxs take a while to reinitialize after a power loss and during this period of time the plane is effectively out of control.
Better to have a UBEC powering the Rx, and servos permanently during the flight so where you are thinking of using a second or flight maintenance battery the UBEC would best be connected to such a battery. This could provide hours of control and isolate the plane from any issues related to a failed charge attempt including accidentally shorting out the Main battery.

Just thinking of safety again!

have fun!

Possibly a capasitor or two in the leads to the RX or from batteries could provide power during the time it takes to switch batteries.

Any plans for the boom are moving along well. I think we are going to need a dedicated boom rx and battery to power movement servos and a fpv cam. I came up with a good way to move the boom in 2 axis (roll and pitch)as you will see in the model. Only requires 2 servos and a 2 prong servo head for both axis.

 

[DroneRocket Guy]

Forget servos I figured out how to get rid of them!


Edit: more details I think I'll just use air restance to my advantage. It would be easy to impament but pitch would be near impossible with out a nother surface to catch air and provide stability. Any experanced pilots or builders have any recommendations on if pitch is nessesary and if so how to implement it? I plan on having roll stabilization on the receiving end too. That end would also have a funnel so that might correct slight pitch differences between the 2 planes. Also plans are almost done for the boom. After that it is time to make a model for the conector for 3d printing.