Our Vulture 2 rocket spaceplane crammed with more power

Our magnificent Vulture 2 spaceplane is in bits for the last time as we make the final modifications before declaring the aircraft fully operational - at least in the hardware department. Our Vulture 2's dismantled avioncs During a recent test, we identified a couple of problems - a dodgy port canard servo and a a lack of …

[sibster]

Why not use a standard RC lippo ?

Why the choice for the AA lippo's and not a standard RC lippo pack, they come in all shapes and sizes and would be lighter then those AA's

[Stoneshop]

Re: Why not use a standard RC lipo ?

Three reasons: temperature, temperature and temperature.

[Gordon 10]

Weight and trim?

Aren't they now a serious problem?

[Missing Semicolon]

All those batteries!

It must weigh a ton.

At this point I'd recommend a stand-back-and-look-at-it-all moment, both for power and the total payload.

There really is a lot of kit in there. Much of it basically IT kit, not flying kit.

The power too looks cobbled together. Why not use a sufficiently large LiPo battery (enough cells to bring the peak current down), and add individual down-converters for the various subsystems. Instead of bunging in hobbyist "modules", investigate using proper fixed-output boards which produce the correct voltage anyway. Less complexity and an integrated approach should add lightness and reliability.

Frankly retail AA's in pp3-clip holders is asking for trouble - even if you do solder to the pips instead of using a snap.

Sorry to snipe, but there's a lot of dosh and time riding on this, and it would be a shame if it all went west because of a loose connection.

[Anonymous Coward]

Re: All those batteries!

Seconded. The idea of all those pressure connections in series is a bit worrying; just too many single points of failure.

[Lester Haines]

Re: Re: All those batteries!

Two things - LiPos will not work at the expected temperatures. Full stop. The Ultimate Lithiums are the only batteries for the job, and we know because we've got a rack of high-altitude balloon flights under our belts.

Regarding the connectors - there will be no connectors for the mission itself. All connections will be soldered.

[Missing Semicolon]

Re: All those batteries!

I bow to your superior (hard won) experience!

I'd still suggest a single pack with appropriate switching regulators for the various bits and peices, though.

[Lester Haines]

Re: Re: All those batteries!

I repeat: We are not using LiPos.

Fair point about the springs/studs. The batteries will be securely fixed, rest assured.

[Holtsmark]

Re: All those batteries!

Lithium chemistry works if kept warm. For this, some electricity from the battery can be sent through a heating jacket that surrounds the battery. (The red-orange stuff in this picture: http://www.lange-aviation.com/htm/english/products/antares_20e/img_battery_module_xl.html )

However, "coffee-pack" LiPos depend on outside air pressure to press anode, separator film and cathode together. This pressure is not available at altitude, which is why the cells in the link are potted Li-Ion cells which do not require ambient pressure (As a matter of fact, a relatively large number of these cells are currently in orbit).

[Peter Simpson 1]

Re: All those batteries!

What Missing Semicolon said. Take a step back and look at how many separate battery packs you're using.

A single large power pack and individual (switching) downconverters for the loads is the way to go, because I expect weight and balance will soon be a concern.

According to its web page, the 3DR power module for the Pixhawk will accept up to 18V input, so why not hook it and the CC-BEC servo battery eliminator to the 8-cell pack and do away with the four cell pack entirely?

[Hans Neeson-Bumpsadese]

Re: All those batteries!

Separate batteries sounds better to me than a single battery pack, as it provides some redundancy. One fails and you lose a component....battery pack fails, and every component fails

[Pen-y-gors]

Defence?

As weight's no object, how about adding a couple of air-to-air missiles to protect the heroic Playmonaut from gun-totin' redneck Merkins flying drones?

[Lester Haines]

Re: Defence?

Well yes, but a defensive capability comes under the "mission creep" banner. Next time, maybe...

[WalterAlter]

Re: Defence?

That would be overweight, BBQ eatin', pickup drivin', wife beatin', snake handlin', beer drinkin', bronco bustin', Bambi huntin', football watchin', wet T-shirt oogling, pit bull lovin', gun-totin' redneck Merkins for you 3-finger, 3-color low resolution lovin' loyal subjects

[Neil 38]

Assume the Castle Creations BEC is a switching BEC?

Nothing in the documentation for the Castle Creations BEC states it's a switching BEC, I assume you've checked that out?

If it's a linear BEC then it'll draw the same current from the power source regardless of voltage and dissipate the difference as heat. A switching BEC is more efficient but may introduce interference.

Edit - yes, the user guide does mention switching. As you were.

[Lester Haines]

Re: Assume the Castle Creations BEC is a switching BEC?

BEC was recommended by Andrew Tridgell - he's used 'em before, so we bow to his experience.

[8-{>]

Battery clip springs...

Just to add to the battery clip concerns. From previous rocketry experience the contact springs compress under thrust from the rocket motor and you will lose power as a result. Numerous spacked rockets whose altimeters lost power during the boost phase of flight testify to this.

[Lester Haines]

Re: Battery clip springs...

Noted, thanks.

[Anakin]

Re: Battery clip springs...

Why use standard AAA/AA.

I use 18650 nowdays. It's much better ratio energy/weight

Take a look at aliexpress.com/item/4-Pcs-3-7V-6000mAh-18650-Li-ion-Rechargeable-Battery-for-Flashlight-UltraFire-DropShipping/1782642510.html.

6Ah and 3.7v have all the juice you need

[Ugotta B. Kiddingme]

Re: Battery clip springs...

it would seem to me* that a simple solution would be to turn the pack round so that the spring is in the front. Then it would only compress on sudden DEcelleration. A few turns of electrician's tape to keep the batteries in the pack and that should do it, yes?

* I am not a boffin, nor do I have the requisite high altitude experience. Merely making an observation based upon available information presented herein.

[Lester Haines]

Re: Re: Battery clip springs...

That's fine for a single battery pack, but on the multiple jobs you have springs facing both ways.

[Anonymous Coward]

Re: Battery clip springs...

put 'em perpendicular to direction of motion?

[Stoneshop]

Re: Battery clip springs...

but on the multiple jobs you have springs facing both ways.

There are also holders that can take 4 AA (or AAA) cells in a single row, so you can have all springs at the right end

[Vic]

Re: Battery clip springs...

There are also holders that can take 4 AA (or AAA) cells in a single row, so you can have all springs at the right end

Tagged cells are more reliable, if a little more work to install...

Vic.

[Neil Barnes]

Just in case no-one's mentioned it, Lester

You might want to solder the batteries in!

[Lester Haines]

Re: Just in case no-one's mentioned it, Lester

Hello mate. That's about the size of it.

[Neil Barnes]

Actually, on a slightly more serious note

High G testing - you might want to tie a piece of string to the back end of this wee bolide and swing it around your head rather quickly, to simulate the launch forces.

Edit - the *front end* - the back will simulate the motor cutoff, but that will be a lower acceleration.

[Ugotta B. Kiddingme]

radio antenna

While I realize at launch altitude the low air density makes this a non-issue, as you descend through ever thicker air, a small fairing over the windward side of the radio antenna would make sense, would it not?

[John Brown (no body)]

Does it fly?

Yes, I know that's a bloody obvious thing to test and I'm sure it's been done but I don't recall seeing any hand launched glide test yet, especially since the weight factor seems to have changed significantly throughout the project.

[Elmer Phud]

Looks like . . .

. . . the Playmonaut has a handy cold box next to them - full of play tinnies, I hope.

[Alan Brown]

antenna

"The radio antenna, meanwhile, is well aft on the aircraft's underside, keeping it as far away from the GPS as possible:"

Surely a skeleton slot would be aerodynamically "cleaner" ?

You could stick one on the inside of the body (assuming fibreglass)

Example of a wideband one at http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=6094162 - and it has much higher gain than your wee stubby.

more math at http://psas.pdx.edu/SlotAntenna/

[Geoff Johnson]

Sort of seconded

I remember reading that the plane is made from nylon. Why do you need to mount the antenna outside?

[Lester Haines]

Re: Sort of seconded

Because there simply isn't another cubic centimetre inside that isn't right by the GPS. I have to been told to avoid that proximity.

[Pet Peeve]

What's the all-up weight of the vulture 2 now? This thing has to be getting heavy.

[Lester Haines]

14.3 tonnes, of which 14.27 is the batteries, apparently.

[VeganVegan]

you're ok then

but watch out if you ever get to 16 tonnes, at which point you will another day older and another day deeper in debt.

Joking aside, you can jam stuff into the springs in the battery holder, so that they cannot compress even when put under launch loads.

Also, can you manage to do a drop test, or a wind tunnel run? With all that weight, and the slender body and canard/wings, I would guess that it would fly very fast: vertically.

[Audiophiliac]

LiFe

Sorry you're probably sick of battery alternatives but, how about LiFe packs? Tried to find info on low temp scenario but couldn't find any...

[Andy The Hat]

Sod the battery alternatives - the decision looks as if it's been made for good reasons.

My concern now is trim - getting the weight distribution correct with those concentrated masses needs lots of careful work before you end up building the highest flying, remotely monitored catherine wheel ever ... Good luck!

[Probeshorts]

Centre of lift/centre of mass

Has the centre of mass now shifted significantly backwards then?

Unless you can also move the wings backwards we might have some real stability issues.

My experience is solely based on playing "Kerbal Space Program", but unless the centre of lift is just behind the centre of mass it won't be stable in flight...?

[Anonymous Coward]

so where is the COG now?

what does this do to the CoG of the aircraft now? what expected penalties to glide slope are expected?