Fan Powered R/C Airboat

[@Project-Air]

Let me know what sea-faring craft I should build next! 🚣‍♂️ 🚤 ⛵️

[@typxxilps]

That caspian seamonster or hydrofoil plane but I'm not sure if you hadn't tried something similiar 2 years ago

[@flyingdebris9363]

Idk if this would help or not but maybe a higher c rating battery will be able to withstand the big amp draw

[@flyingdebris9363]

But you should build a boat that can carry a rc car😜 but maybe put foam in the car so it floats and get a little blow up boat

[@Project-Air]

typxxilps I’m just going to leave this here 😉 kzbin.info/www/bejne/pZPTfISlfqd5jdU

[@DriftTrainis2awesome]

ft sea duck

[@MasterControl90original]

We want to see it going full throttle!

[@Project-Air]

Me too!

[@darysparta9676]

@@Project-Air probably the batteries getting a bit too hot and the internal resistance increasing. you should have put, in my opinion, a small air vent going from the back of the thrust tube down into the internals of the boat to redirect some of the airflow and cool down the parts, also maybe punch some holes in the hull in front of the turbine to make the air that get pushed out recycle

[@Lozzie74]

DarySparta batteries hold chemical energy. The hotter they get, the more current they can release due to chemical kinetics (Arrhenius equation). There is still a limiting overall max which he is experiencing. A vent wouldn’t have helped. Cooling is needed to stop thermal runaway and permanent damage, not increase current capability.

[@darysparta9676]

@@Lozzie74 the more you know! this sounds strange to me but looks.like you have more evidence supporting your thesis. I can tell you not all batteries behave like this as we did an experiment back in school and discovered that batteries terminal voltage decreases with increased temperature which is also to be expected due to dissipation of heat which should be useful energy. Also, it's known that resistance in metal conductors increases proportionally to heat, and since batteries are not only made of chemicals but also metal components this is also to be taken in consideration.

[@keithmiller3084]

Check your radio programming as it might be in your

[@FrankA-973]

Do not move on!!!! Perfect this build were all counting on you!!!! Better battery for starters!!!! Keep it alive!

[@Project-Air]

I'll be building a new hydroplane in the winter with all I've learned from this design in mind. It'll be bigger, have wider sponsons, be powered by a huge motor, etc. I think this current one is limited, not just by the battery; it leaks and will end up falling apart from the inside 😂 - I think it's time for an upgrade.

[@mickoberhaus7543]

Liked the video. I'm glad you took the time to explain the reasons for everything

[@yodecaf]

One of the cool things (even though inefficient) about using an EDF is that it doesn't disturb whats below that lake. Always a concern when im running a boat at a public lake!

[@spencerboaz2385]

You may try a higher C rated battery like a C75 you may also be able to go to a higher S rating like a S6 or S5 if your motor is rated for it . You could also try putting a slope backward on your rudder . I would try putting a bit of toe-in on your sponsons , so the faster it goes the less drag it has . Awesome job . I have been watching a lot of videos on air boats the high speed ones like you have built and they have given me many ideas . I have a number of different motors from drone builds from 2212 to 5802 and up to 18" props . But I have never built a RC boat so I would like to thank you and all the others for all the ideas .

[@keithallso9157]

Looking a lot like Bluebird K7. Very nice. Donald Campbell would love this

[@TK42138]

Great video, the design looks good. My first thoughts on watching the video was that water ingress into the EDF was causing rpm to drop thus no full power, however as you demonstrated towards end of the video, the battery pack just couldn't provide the amps needed. Great proof of concept, great channel. 👍

[@sacrificialrubber779]

HYDROFOIL!!!!👍🏻👍🏻👍🏻

[@CuervoRC]

It would be great if you made a hydrofoil. I made this one but it didn't work well at all, the torque of the propeller rotated it, but I think simply making it wider would work. www.thingiverse.com/thing:2966914

[@Project-Air]

The good news for you is that I’ve already started on one 😁😁

[@sacrificialrubber779]

Awesome! Can’t wait! 3D printed or foam board?👍🏻🤔🤔🤔

[@entrad157]

Fantastic!! A great build pal well done loved the video thanks for posting.

[@air-headedaviator1805]

Great job James, after a long time this hydro seems to finally be getting near to perfection. Now all you need is a higher C battery

[@Project-Air]

Yep it’ll be great to take it to the next level 💪

[@crudboy12]

Get a higher C rating battery or connect 2 4s in parallel for double the amps

[@thecaptainnoodles]

Double the capacity not amps. Double the amp hours not the amps it gives out

[@simen9485]

@@thecaptainnoodles What are you on about?

[@theadventuresofshellyandfr5618]

Correct sir! boats need high C rated lipo batteries with thick wires & big plugs . There is much more drag on the water then say an rc car on 20c batteries. Get 50c or larger for boats.

[@afrog2666]

@@thecaptainnoodles No, parallel doubles both capacity and discharge..

[@afrog2666]

@@theadventuresofshellyandfr5618 You can`t just say "50C for boats" I have small models that are fine with 2200mAh 20C for instance, it all depends on size and output.. If that`s say, a 1000W EDF running on 4s, you need about 70A plus some headroom, that means a 4s 2200mAh 30C or higher will do, a 4s 4500mAh 20C will deliver 90A so that`s plenty. C rating alone means nothing, just saying..

[@sobattutorial69]

great fun playing RC boat racing bro... 👍

[@dronecamper4905]

That’s very cool! Makes me want to go get a RC boat! Thanks for sharing. Awesome video. 👍🏼😃

[@TomleyRC]

I love making EDF vehicles, this is really cool. Nice work. 😎

[@Alcreatepl]

Damm this airboat thicc I can't believe it moves using only fans!

[@hamishburnettbrowne9811]

you should make a 1 lb mini battle bot. i am working on one right now and its a really fun project. keep up the good work!

[@MCsCreations]

Pretty impressive build, dude! Fantastic boat!!! 😃

[@Brian-ff7tw]

Wow what a beautiful piece of water you have to use there!

[@thecraftking113]

very cool project again.👍👍👍 love my ender3 as well

[@TheRandomMechanic]

Nice work ! it looks a lot like bluebird k7 .

[@SpacefarerIndustries]

for a channel named project air, you sure do a lot of boat models. Not that I don't enjoy it, I like fast anything.

[@Project-Air]

Spacefarer yeah I guess it’s just anything that interests me and has some link aircraft. This one uses airplane parts so there’s your link 😉🙂

[@hawkkim1974]

it's nice design actually. I like the boat shape.

[@mikea683]

That lake looks very familiar! great video dude!

[@WizardofTruth]

Seems like the boat needs more powwaa baby :-)

[@rmdcade1717]

Shame the battery wasn't able to fully support the EDF. Looks like a ton of fun regardless.

[@greg0063]

Great project, it looks correct at speed, it's just a bit nose down. If you do continue with it maybe move the battery back a little.

[@savneetsinghrairai6823]

Wow it works well like the one used in hydroplane world speed record with a jet engine

[@koalatails6391]

An improvement on your previous boat. EDFs suck a heap of power, so it is probably battery sag. The solution is a better battery, higher C rating or more cells. Even an increase size (Mah) with the same C rating & cell number will boost the power, but add a small amount of weight. Good luck.

[@aljensen7779]

You asked for suggestions on what to build..... Try an Ekranoplan.

[@Project-Air]

kzbin.info/www/bejne/pZPTfISlfqd5jdU&t :)

[@aljensen7779]

@@Project-Air Thanks, I just watched that one again - but that project didn't really get so far, huh? I was hoping, since there's such a lack of Ekranoplans in youtube world, that maybe you or someone would revisit this idea. I also want to build one but need more info than [what I'm sure] you started with. Thanks for the reply. Watch for me later this year, dude, cause I'll be putting 'some thing' together. And if you're interested, here's my channel - which lacks considerably in flying machines but is still all RC. Check out 'Al Jensen - Blast! RC'

[@gryfandjane]

What a strange experience; seeing a boat of that shape and color streaking across Coniston is just eerie. It looks so much like Campbell’s K7.

[@Project-Air]

True! Thanks Gryf

[@kimscheie]

good on you young guy ...keep it going

[@rodgeyd6728]

Lake District 🤔 Coniston Water 🤔 And it's not raining !! . Excellent video, you know what to build now don't you ? Bluebird .

[@Project-Air]

Haha, yeah! And here you go. kzbin.info/www/bejne/bHTHkH6fo5qSbcU&t

[@denniscrabtree2170]

Keep working on it, and I’m sure you’ll get it! Nice concept!

[@remkojerphanion4686]

For more stability you may set the sponsons further out (make the thing wider). Cool project!

[@Project-Air]

Remko Jerphanion yeah I think I’ll do this on the next one!

[@aspectcarl]

Looks and sounds great!!! 👍

[@mjproebstle]

its not a plane, but a cool mod and good result despite issues. cheers!

[@VindicatorJones]

You are also suffering from torque roll. The boat is coming unstable and wanting to turn on the rotation axis of the single engine. To counter it, you really need another engine that rotates in the opposite direction to counter torque roll, just like you did with the propeller version. But awesome effort.

[@VindicatorJones]

@Cerus98 I know what torque roll is, as a pilot you have to be extremely mindful of it when increasing power in a performance prop aircraft. If you look at 0:03 you can see the boat raising the left float while digging in the right float due to torque roll. Once you start having differing friction levels on those floats, the boat is going to become very unstable and want to turn to the right constantly, and possibly dig the float in and flip the boat.

[@marc_frank]

@Cerus98 i built an airboat with only one motor and large prop similar to a round nose hydro it also has a torque roll issue it doesn't matter where the motor is, for it to induce a movement on the whole body of whatever it it mounted to, trough it's torque the effect just becomes less, the further away it is from the axis that goes through the cg

[@marc_frank]

@Cerus98 what would this be called?

[@edekaRc95]

Really cool! But you should use an Intake-Lip on the EDF. This should increase thrust by about 20% and also the efficiency (Oliver from wemotec told this in forums). Also I would not use Zippy Compact batterys. I only made bad experience with them, normal Turnigys are much better and do not cost much more.

[@Project-Air]

Absolutely agree! Unfortunately the intake-lip for this edf blew off in flight when the edf was used to power my EDF Glider 😂😂😂 I should invest in some new electronics.

[@willasproth]

ProjectAir you should 3D print a new lip

[@koalatails6391]

RcUpKoelsch Totally agree about the Zippy Compact batteries. I unfortunately purchased one not long ago, it’s been a disappointing experience. I have to adjust my timer from 5 minutes to 4, whenever I use it.

[@Peter-qn7qx]

Fun boat

[@petermarshall7753]

More fun sailing

[@jorgenelsonfelix52]

Excellent spectacular. Saludos desde Buenos Aires Argentina 👋😎

[@Project-Air]

jorge Nelson felix thanks! Best wishes from here in the UK :)

[@jonneduke65]

Go big mate and combine your skills with a flying boat 😁

[@TastierBackInThe80s]

You're assumption was correct. A higher C rated battery would have made more thrust. EDF pulls a lot of current from the battery. I learnt this from my early days of flying foam EDF jets. That skimping on cheap low C rated meant less power of even audible surging can be heard at full throttle as the plane would fly past.

[@fourbypete]

You should 3d print hydro foils for it. And a foil rudder.

[@cool5tuff]

If you're printing a thrust tube, you ought to make an inlet ring as well. Its probably more important than the tube.

[@warnerjohnson1338]

I say, old chap, how about a bubble cockpit canopy, (as fitted to a Mark 9 Spitfire, and with a live mouse « pilot » to enjoy the high speed runs. This would provide us with some jolly good sport don’t you reckon?

[@cybershadow81]

You definitely need an inlet lip on your next EDF project. You'll get a lot better performance.

[@LuisLPRCs]

Nice! Sounds like a jet. 😎😎😎😎😎😎😎

[@shelbyseelbach9568]

Yes, the electric jet motor sound like a jet. Very good.

[@LuisLPRCs]

@@shelbyseelbach9568 Sounds like the real thing.

[@shelbyseelbach9568]

@@LuisLPRCs it is the real thing. It is a boat powered by a jet motor.

[@TheFSFLensman]

Look into a "canard" hydroplane with two points to the rear and one forward....

[@mjproebstle]

sailboat next pls 😁

[@keithallso9157]

I have a copy of Ken Norris designs of Bluebird K7. They changed a lot over the years building up to 6th of Jan 1967 when K7 did it's last run when sadly Donald lost his life .

[@walrus4046]

Brings back not very nice memories from my childhood of the tragic Bluebird accident

[@davecooper5951]

Hi James - nice project. Might be worth investing in an ammeter / wattmeter combo to get the best out of the on-board electrics. Also, a comment below refers to an "intake lip" - this could lead on to some full 'ram-air' ducting experiments to maximize the thrust from the EDF ? Does the LiPo pack have some cooling ? Maybe a small gain here too...

[@ERPP8]

So cool! Did you mean to make it look just like the Bluebird K7? Because that just makes it cooler.

[@waynebeasley8700]

A 70mm edf needs at least a 50C battery…..otherwise the voltage tanks. Also, did you calibrate the ESC?

[@albertraich3492]

Cool, remove the rudder from the water and set a new one in the tail, behind the ducted fan like a plane, it will reduce drag and power consumption. 👌

[@marc_frank]

that wouldn't have as nuch autority could also cause it to not tack as well so that it enters a turn by itself

[@albertraich3492]

images.app.goo.gl/9W1ambLtrgXCwHqF7

[@albertraich3492]

Take a peek to do this Air boat

[@marc_frank]

@@albertraich3492 i made a round nose hydro

[@arvince99]

You’ll get more thrust if you put a front housing flange on the edf.

[@lloydprunier4415]

The video of the first runs looked like the grainy historical vids of the Loch Ness Monster sightings! Hope to see more runs with higher power battery. EDFs seem to really need mo power!

[@schlegs0043]

U should try spraying hydrophobic spay on the bottom so it slides better.

[@donwimberley4772]

The torque of the motor is pushing the sponson on the starboard since to sink somewhat ? Maybe moving it further from center would level it out ???

[@brokearcader6625]

How heavy would a 3d printed boat/water craft be? You could make it so the fan is like integrated into the boat itself (kind of like the fan in the front on batman's car) I have so badass many I may just do this myself.

[@tedsmith6137]

Looks good. It seems to roll to the right, (under power?). Could be torque reaction as it seems to level when the power is cut. Perhaps some straightening vanes in the exhaust will remove the swirl from the airflow. Keep experimenting, there are not enough who do it.

[@paulbrouyere1735]

Why don’t you try a pointed trailing edge for your floaters? Could reduce drag a lot!

[@stuartnorton111]

Thanks! Great work!

[@andreatanzi3191]

Once it lifts speed is not too bad considering the current geometry. I think you should fine-tune the angles (fan vs sponsons), since you are loosing a lot of energy by contrasting forces !

[@kwakukumi4729]

That design is causing drag. The end is lifted and the front is push downward. Repositioning the EDF to angle it to decrease the resistance may lead to be better performance. You can see it in the video.

[@daos219]

Very cool! I'm not totally sure, but there were a few instances where I thought I saw the effect of the impeller's torque on the boat at high rpm. I dunno if it's possible to add another counter-rotating piece, or somehow offset the torque, but if I'm totally off, that's fine too. Either way, really cool build!

[@daos219]

@Cerus98 yeah, I fly a paramotor, torque is something I have to deal with. Though in my case all it does is turn me a bit because my motor is offset to counter the roll it gives. Like I said, that's what it looked like to me, one side of the craft seemed to dip lower as power was added. Buuuut maybe I was just imagining it...

[@daos219]

@Cerus98 that makes more sense, I suppose. I'm not even sure which way the impeller spins, come to think of it. Thanks

[@daos219]

@Cerus98 ah. So I was totally wrong. My apologies. It looked to me like it was leaning the same direction the impeller was spinning!

[@bohan9957]

If you add a front intake lip for the EDF, you'll get slightly higher thrust. These EDFs do not like turbulent air in front of the fan.

[@antonblebann6823]

I Think, the rounded Frontfloats pulls a lot of weak Air behind them, try to shape it more like the Trailing Edge of Airfoil, that can make it a few mph faster, keep going, good Idea, wish You Succsess👍🏻👍🏻👍🏻

[@thewhiteeazye2728]

Its the blue bird RC K7

[@eagleflight7349]

Possible cause of "browning out" may be the ESC does not have current capacity for the edf at full throttle. ESC's will shut, slow down when over loaded.

[@FarmerFpv]

It's Mad Max on water. :)

[@chamowllie]

I hope you figured out the battery situation. EDFs really suck batteries down quick. Get a high C rating battery and shouldn’t have a problem. For EDFs I would stick with 40C or better. Anything smaller than that your battery will die quickly and puff. Good luck!

[@bobwalden5853]

Hi James, see my reply about your Hydrofoils with "Ducks Feet" fitted to a Catamaran, then an aircraft wing was fitted that was hilarious. My stepped monohull boat using 6 NiMh cells and a brushed 540 motor was recorded at over 31MPH, still a UK record I believe. Try either of these?

[@mt-xx1tt]

I'm hear as I'm trying to digest every video on riggers as I need to make one . Higher c discharge will sort your probs I think . Good work young sir

[@aljensen7779]

Hi James - did you ever get this hydroplane running at full speed/full throttle? I was really hoping to see an end to the story. I'm working on my own hydroplane design, employing 2 EDFs w/ 6s batteries. If I may ask, what is your personal best speed ? And do you happen to know the world record for EDF-powered hydroplanes? Thanks for taking time to read a comment on such an old video. Tea ya later! 🙂

[@MatthewNovoselskiy]

I believe the world record for edf hydroplane is set by radical rocket on KZbin (kzbin.info/www/bejne/nGjUk6OchJJ0pZI) of about 48mph at 50% throttle on a 120mm edf, he never did a update for 100% throttle, so my guess is it’s still 48mph, which seems very easy to beat (if you have the right equipment), I’m thinking to put a second edf on mine after I’m done testing with one edf, so you might have some competition 😏

[@aljensen7779]

@@MatthewNovoselskiy Very cool - I'll look forward to the competition. If the speed record is indeed up for grabs, I want it. I spent this past summer using one EDF on a prototype outrigger - I never tracked it but it seems likely it hit 40mph a couple of times. Next summer the second edf is going onto a new body with (quite likely) a tail wing & independent power systems. Hope to see you next year, mate.

[@MatthewNovoselskiy]

@@aljensen7779 interesting, by the way, if you have a GoPro hero 5 or above, you can measure the speed through that, that’s how I will do it, also what edf do you have? I have a 70mm edf that makes about 5lbs of thrust on 6s, but I’m planning to put another after I’m done testing this one, so a lot 10lbs of thrust on a 5~lbs boat

[@aljensen7779]

@@MatthewNovoselskiy I have a gps speedmeter - it just didn't seem worth the trouble at the time. Regarding my EDF, something I learned is that a short or wide hull will be very vulnerable to the gyro twist and I've picked enough fights with physics to know a 2nd edf will make it worse so when choosing, I bought 2, 70mm EDFs, where one of them turns clockwise instead. That will cancel out the gyro. The company claims 7.25lbs of thrust, each, but I only measured 60amps of pull on 6s. The company says 89amps, so definitely not as much power. I have two 150amp marine ESCs and 2, 6s CNHL batteries. Still working out safety measures, like an emergency stop. What size of outrunner is in your EDF?

[@MatthewNovoselskiy]

@@aljensen7779 by size of outrunner I assume you mean the motor size? Anyways it’s a d2842 2300kv 6s

[@jimmynoname4089]

Just another fan boi

[@joshadams8108]

I wonder if altering the centerline of the fuselage would help reduce torque roll. Just having the sponsons shifted to side that rolls into the water more. It wouldn't add any weight, but might give a better balance under power.

[@robertsanders4651]

Funny that, I live about 2 miles from coniston lake (as its locally called) and have only just found this video

[@keaaul808]

May I recommend hinging the fan unit for rc of the vertical thrust for ultimate fine tuning? Maybe even gyro assist?

[@ДмитрийАлексеев-э8д]

Super!

[@thesunexpress]

Can't reach full throttle? Simple: drag. I had this exact issue years ago, nearly 3 decades ago---I am old---with a nitro / glow-engine boat. A simple mismatch between engine power & prop size, along with the natural drag of the boat design. A different type of epoxy-paint went a long way, as it will for you---but expensive for the purpose---but ultimately a slightly different engine/prop combo did the trick. I suspect the 3-D printed duct might figure greatly. You could screw around with different sizes, but you'll be surprised how much difference a smooth inner surface to the duct will make. Once moving through turbulent air at speed, along with the turbulence inside the EDF duct, you are basically running into a situation that would "normally" cause an un-start in an actual fuel-burning turbine. This is also the reason you can get full-boogie speed from the EDF from the stationary boat on land. #1 Try adding a bellmouth to the EDF, the 3-D printer is your friend. #2 Smooth the inside of the 3-D printed duct, a light 600-grit to 800-grit sandpaper will surely do the trick. #3 And most important of all: DO NOT GIVE UP!! Everybody knows the Brits are a tough and crafty bunch of indomitable shrews, don't let them down 😉 edit: @6:56 the large amount of near-vertical spray is an indicator, energy being wasted producing some nice spray but no forward thrust.

[@lukehattingh8735]

The rudder must make a lot of drag, have you tried to put the rudder up in the air stream.

[@michaelmcmenzie6928]

Is the esc getting enough cooling because if its not that will cause it to throttle down most boats have a water cooled esc

[@farmers2630]

Mike Brown beat me to it, but yeah add a HYDROFOIL!

[@geuzeg]

since your rudder is still dragging in the water, this causes the boat to slow down. This does not match your EDF. They tend to take a littlebit of air and accelerate it enormous, giving you lots of speed in the end, but lack of torque. Taking a bigger mass of air like you would with a prop provides this torque, needed to overcome the rudder drag issues.

[@deanwhite9386]

I dare you to build... a 3 state craft. Submarine, boat, airplane. in one device.

[@sonjagebauer2322]

Why are you not using an air ruder? It would be much more manuverable at high speed.

[@crypkrazee1903]

If you put a small turn fin on the inside of one sponson it will turn very quickly at higher speeds

[@Alex-kh8lp]

is there a way i could get the plans for this? Nice work.

[@petermarshall7753]

More fun with a sailboat

[@Chris-zu8ve]

You have too much friction from the large amount of hull in the water, You NEED lift like a hydrofoil boat is setup to pop out of the water. With the hydrofoil will allow you to lower the motor to just above the water to get your stability back. Im sure you can get it up over 100mph with hull out the water,

[@Project-Air]

Although there was too much friction on this particular EDF version of this hydroplane, I don't believe a hydrofoil is the answer to fixing the problem. If you check out my other video with the conventional motor/prop combo kzbin.info/www/bejne/sGOQeZaHabVnqck, the boat clearly lifts well out of the water and is allowed to skim along with the tiniest of contact points with way less drag than a conventional hydrofoil. I'm going to build a new larger hydroplane sometime this winter that will be designed with all of these lessons from this current design in mind - then we can aim at 100mph! Thanks for commenting! I appreciate your suggestions. :)

[@ZedNinetySix_]

Reminds me of Bluebird, R.I.P Donald Campbell

[@___echo___]

pretty sure this project was inspired by that

[@jeffevans3193]

Take that design and put lift hydro's under each pod.

[@henkormel5610]

Nice project man! As you probably know by now Chinese high C batteries suck. They are not able to sustain the current you need. I would advise to pick Hacker batteries as this is a German quality brand. These are not ridiculous expensive but just do what is written on them. Choose the biggest size you can fit, there is no substitute for Ah's. For example ; a 3500mAh 20C battery has a maximum discharge current of 70A. A 5000 mAh 20C battery instead has a maximum discharge current of 100A. I have owned several 'high C number' Chinese Batteries, they just don't last. You have to be lucky to buy them off the right batch. I never was lucky. The only thing the Hackers can't cope with is under voltage. So keep at least between 3.7-3.8V/cell static inside the battery. This is about 20% charge. This is also the storige voltage. This is under full load about 3.2-3.4V/cell depending on your load. EDFs are known for their high load on the batteries. A 70 mm fan draws easily 150A at full load. You were lucky the batteries couldn't deliver the current becourse your ESC would have burned out. For that kind of loads you need at least an ESC capable off 200A.

[@Dr_Jet]

The trailing (and side) edges of all water contact surfaces should have a sharp break. Otherwise, water wants to creep up around the rounded trailing edges from surface tension and consume energy to break away from the hull. Similarly, all ride surfaces must be dead flat, otherwise you are again wasting energy.

[@BTHenningsen]

Nice build. But it seams you have more weight on the right hand side on the boat. if you even it out you should get more stable at high speeds(when you reach hig speeds xD )

[@markpalmquist]

The speed would increase if you decreased the angle of attack of your 3 hydroplaning surfaces. They look a bit too steep.

[@matt6630]

You should build one with a mini jet engine.