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Hydrofoil Building Help (2nd Post Attempt)


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2nd Post which includes the craft download link. Craft on KerbalX.

 

Hey y'all. So I'm trying to build a hydrofoil for the Elkano Challenge. The problem is, the craft tips over to the front, or otherwise, 'dolphins', or short, rocks up-&-down then sent itself flying like hitting a wave. Can anyone help?

 

Frontinco Hydrafoil-1A

VXwZF9x.png

Craft on KerbalX.

Edited by FahmiRBLXian
I'm planning to do the challenge on Laythe.
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Hello and welcome to the forum!  Hydrofoils are great, and everything I learned I got from a lot of trial and error. So, I've been there :D

 

I downloaded you craft and had a play with it. I did a short video of the revised craft which is posted below.  Here are a few things I noticed.

 

1.  I could not get those aero foils to work at all. My hunch is they are the wrong shape and they are certainly not big enough.  Replace them with some proper wing sections.

2. Don't use the deploy function. Simply put a good angle on your foils to get the nose up.  

3. I always put the front foil slightly higher than the back. That cockpit generates lift, and if you are exactly parallel to the water, the slightest bounce can put you nose down, creating downforce on the front of your craft.

4. I ever-so-slightly changed the angle on the engines so the exhaust is pointing very slightly upwards. This generates a bit of downforce on the stern which helps with stability.

5. I moved the front foil farther forward.

6. I gave the foils a V-shape which helps keep things stable as well.

7. I added flaps to the front which you can turn down to pitch it up as you are gaining speed and then level off.

8. This craft is very over-powered. 

9. It still needs tweaking, and I recommend giving it a rudder.

 

Here are links to my two craft. Perhaps they will be useful

https://kerbalx.com/Klapaucius/Irving-88-Passenger-Hydrofoil

https://kerbalx.com/Klapaucius/Ilya-16-Passenger-Long-Range-Hydrofoil

Pictures and video below:

XbXpqDv.png

LFZutsj.png

 

 


 

Edited by Klapaucius
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Well, if you are intending to do an Elcano on Kerbin  then I've got a zillion quibbles with your design. I assume you are intending this craft to be amphibious? That is, it should rove over land, and hydroplane over the water?

To rove properly, you need the medium landing gear -- because it's steerable. Those goliath engines are extremely heavy -- I'd recommend a single panther instead. You can turn on the panther's afterburner to get up to speed, and then switch back to dry mode for efficiency. (But to do that you're going to need to reduce the weight a lot.) You're going to need to refuel several times, so have you thought about docking and fuel transfer? MK2 parts have very high drag, so they waste a lot of fuel. I would strongly recommend rebuilding with MK1 parts instead. Do you really need to carry 6 kerbals? Cockpits are very heavy things to drag around.

Using deployed ailerons as hydrofoils can work very well. They produce relatively low drag, and can be undeployed when you are not in the water to reduce roving drag even further.

But my fundamental question is: are you determined to stick with this basic design?

 

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1 hour ago, XLjedi said:

Is there a route on Kerbin that would allow you to circum-navigate the globe by sea?

No. You must make a land crossing at some point. As @bewing mentioned, wheels are essential and while there are wheels on this craft, there are none that are steerable.  @Klapaucius's design in the video looks pretty cool except that it's a sod of a long way around Kerbin so some speed comes in handy - it would have been good to see what happens when it was moving three times as fast. (And to see what happens when the CoM moves as fuel is depleted.) Although it's easy to make very fast boats, bad things tend to start happening when you push it over 100m/s so a maximum cruising speed of 95m/s has always seemed prudent to me.

I had a play with the boat - you can stabilize it by moving the foils toward the ends of the craft and adjusting the authority limiters. So I get it skimming across the water and full throttle it's doing 75m/s. Pretty sad with those two giant engines. I prefer Panthers, either one, two or four of them. You might also have a look at what parts you put in the water and do what you can to minimize the drag. I'd also suggest coming up with a design that sits just above the water - it's likely that you will have to make trim adjustments as you use fuel and craft sitting high above the water are easier, imho, to nosedive or flip when you start playing with the controls at speed.

At some point you'll need to refuel. Probably multiple times. You can either fly a tanker in to do it or carry mining/conversion equipment. Personally, I prefer the latter. You might also take note of the range of the boat in case you're tempted to go to Laythe.

The boat I used to go around Kerbin used just two canards to lift most of itself just clear of the water. The four Panthers used wet mode on full tanks before switching to dry mode in pairs and were progressively throttled back to stay under 100m/s. Best of all was finding a fuel flow priority sequence that made any pitch/trim adjustment unnecessary. This was the first boat I ever made and embarrassingly enough, it's still probably the best (and it's not that good either).

Traveling around Kerbin - three quarter throttle in dry mode  - 100m/s.

4r74V9O.png

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Like a 4hr trip just to get from KSC to southern ice shelf doing 120-ish m/s...    I'm sure I could create something that would do it, but can't say that I'd want to spend a lot of my time like that.  Problem is, hydroplaning does not lend itself too well to time acceleration, and you'd have to make this trip in mostly 1x time.   For an amphibious hyrodfoil, I'd probably look for a north-south route and try to utilize the smoothness of the ice caps. 

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7 minutes ago, XLjedi said:

For an amphibious hyrodfoil, I'd probably look for a north-south route and try to utilize the smoothness of the ice caps. 

Once you've been around Kerbin in a boat that's also a rover, you can look forward to doing it again in a rover that's also a boat and a polar route is for sure the best for this trip. Helps if the rover can climb up onto the ice shelf. (This puppy went through the water upside down)

LPNVxr2.png

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4 hours ago, mystifeid said:

 Although it's easy to make very fast boats, bad things tend to start happening when you push it over 100m/s so a maximum cruising speed of 95m/s has always seemed prudent to me.

 

There are a couple of designs out there that can do well over that and remain stable.  The problem becomes fuel.

This one here

https://kerbalx.com/flipnascar/Pride-of-Veere---Hydrofoil

will do 120 easily and as the fuel runs down, will slowly inch its way up. I got it to 160mps just as the fuel ran out. I just let it run and it went gangbusters without touching a thing. 

 

This one is a bit touchier to get on plane (and to keep it from just taking off into the air and flying), but will do over 200 before coming apart

https://kerbalx.com/kerbalwerks/Hydra-4

 

I don't worry heaps about realism, but it is good to note that going 100 mps is over 200mph.  At 160 I am doing 357 mph or 576 kph. That is well beyond anything in the real world as far as hydrofoils go and 40mph faster than the world speed record for any watercraft.

 

4 hours ago, mystifeid said:

  @Klapaucius's design in the video looks pretty cool except that it's a sod of a long way around Kerbin so some speed comes in handy - it would have been good to see what happens when it was moving three times as fast.

It will do up to 60 pretty well. Anything above that and it gets unstable. Also, with those big fans, you have to be back off and allow it to accelerate slowly. The temptation is to gun it at start, and by the time you are approaching 60, you cannot cut the power fast enough since they need time to spool down, unlike Panthers or Ramjets.

 

4 hours ago, mystifeid said:

Once you've been around Kerbin in a boat that's also a rover, you can look forward to doing it again in a rover that's also a boat and a polar route is for sure the best for this trip. Helps if the rover can climb up onto the ice shelf. (This puppy went through the water upside down)

LPNVxr2.png

Awesome!  This would be a perfect entry for my new challenge:

 

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2 hours ago, Klapaucius said:

There are a couple of designs out there that can do well over that and remain stable.  The problem becomes fuel.

I'm sure there are a shedload of great boat designs out there but you're right - the range of the craft is nearly as important to me as speed. I think it took me about twenty hours all up to go around Kerbin and I stopped to mine ore seven times although my tanks were usually far from empty. Without an ISRU, if you had to fly a seaplane in each time, well, that might add to that total time.

And for an equatorial circumnavigation of Laythe - using an ISRU to refuel - you need a range of about 1200 - 1300km.

The first time around Laythe, I ran out of fuel in the middle of the Degrasse Sea. That left a bad taste so I went back again with the boat below - with two Panthers, it had a range of well over 2000km at speed so after splashing down with full tanks, it needed to be refueled just once to complete the circumnavigation. But it was a pita to drive.

0fK3N7A.png

Edited by mystifeid
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A nicely overpowered and engineered hydrofoil can cruise at 400m/s without doing anything destructive -- just so long as all you do is go straight. :D But boy does it suck down the fuel.

 

Edited by bewing
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1 hour ago, bewing said:

A nicely overpowered and engineered hydrofoil can cruise at 400m/s without doing anything destructive -- just so long as all you do is go straight. :D But boy does it suck down the fuel.

 

Wow, that's fast. What sort of range I wonder? And yeah, my boats suck but I never try to build the Mona Lisa. Twenty hours around Kerbin includes design/test/mission time. I think it would be easy to spend that long just learning to build something that went 400m/s.

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