Sea-Level Flameout on boat

[Lazarus MonkeyMan]

So, I've been playing around with pontoon-style amphibious craft for about a year, and I keep running into an issue with the Wheesley engines.  Just how many flippin intakes do they need?  I see that the intake requirement is high (29.6), and most intakes only provide 2 or less. I get "flameout, prop requirements not met."  Adding more intakes will eventually fix the problem- but by that point almost the entire surface of the craft is covered in intakes (and yes, they are pointed into the wind).  So is there some game mechanic that I'm overlooking?  Or do the Wheesley engines just not do well at sea-level?  Do I need fifty radial intakes to power one Wheesley?

HALP!

[FleshJeb]

Look at the intake speed of the ones you’re choosing. This gets added to the speed you’re moving to determine the amount of incoming air. (It’s slightly more complex than that at high speed). A backward-facing intake will only get the intake speed.

Some of the intakes have a speed of 30 or 40 m/s and those are the ones you want for this situation. Still, the Wheeslies are very hungry.

[bewing]

At a dead stop, it works better to use one of the intakes that has a hell of a lot of suction power, such as the nacelle -- rather than a passive intake like a radial.

[Lazarus MonkeyMan]

Thanks y'all!  I think I've figured it out, check me:

I think my problem is that the drag of the pontoons in the water is preventing speeds of over about 30-35m/s.  I think that's just too slow to keep them going 100%- because the engine is expecting a lot more air to be coming in because it expects to be going a lot faster than when pushing a boat through the water.

Do you think I'm in the ballpark?

[FleshJeb]

14 minutes ago, Lazarus MonkeyMan said:

I think my problem is that the drag of the pontoons in the water is preventing speeds of over about 30-35m/s.  I think that's just too slow to keep them going 100%- because the engine is expecting a lot more air to be coming in because it expects to be going a lot faster than when pushing a boat through the water.

Do you think I'm in the ballpark?

Yes. Drag is super-critical in water. Take everything you know about aerodynamic drag and apply it x1000. This is why all my water-craft are hydrofoils. Use just enough wing to lift everything but the wings out of the water. I use an angle of attack of ~3deg, and a dihedral between 5 and and 15 deg. This assumes the main body is flat to the horizon. Top speed in water is VERY sensitive and takes a lot of tuning.

[Lazarus MonkeyMan]

8 hours ago, FleshJeb said:

Top speed in water is VERY sensitive and takes a lot of tuning.

Nice!  So what kinda top speeds are you getting in water- and can you make your hydrofoil an amphibious craft that's stable/strong enough to go uphill? 

[bewing]

50 minutes ago, Lazarus MonkeyMan said:

Nice!  So what kinda top speeds are you getting in water- and can you make your hydrofoil an amphibious craft that's stable/strong enough to go uphill? 

400 m/s and yes.

It can also take off, fly, and land back on the water.

Edited June 19, 2019 by bewing

[FleshJeb]

7 minutes ago, Lazarus MonkeyMan said:

Nice!  So what kinda top speeds are you getting in water- and can you make your hydrofoil an amphibious craft that's stable/strong enough to go uphill? 

Note that that's hands-free, with no SAS, and a little pitch trim. Passive stability is key.

I think you'll learn more from seeing how it's built than me talking about it:

https://www.dropbox.com/s/tuj8tgno5lp42lz/Hotel Ferry.craft?dl=0

Instruction manual below:

Spoiler

I've updated it since this picture, but the controls are the same.

This is how you want it to look when loading rovers:

 

[Guest]

I wish I could like a post more than once @FleshJeb because that is an awesome piece of engineering. I'm so going to try my hand at hydrofoils one of these days...

[FleshJeb]

6 minutes ago, Brikoleur said:

I wish I could like a post more than once @FleshJeb because that is an awesome piece of engineering. I'm so going to try my hand at hydrofoils one of these days...

Thank you very much. I think, out of the couple thousand craft I’ve built, it’s probably my most thoroughly and elegantly engineered. (I learned so much about stability that it made me better at spaceplanes). I’ve got about 40 hours into it, and I could spend about 10 more before I’m satisfied.

[Lazarus MonkeyMan]

Yeah, I most definitely need to give hydrofoils a shot.  Thanks for the idea!

[Klapaucius]

3 hours ago, Brikoleur said:

I wish I could like a post more than once @FleshJeb because that is an awesome piece of engineering. I'm so going to try my hand at hydrofoils one of these days...

Hydrofoils are a hoot.  I built a few and consider them some of my best constructions.  Considering what you have built in the past, I am sure you will push the envelope.

[FleshJeb]

9 hours ago, Lazarus MonkeyMan said:

Yeah, I most definitely need to give hydrofoils a shot.  Thanks for the idea!

You're welcome. There are a lot of different options for foil layout: https://en.wikipedia.org/wiki/Hydrofoil

I think for stability, one in the front and two at 2/3 aft is probably the best--It puts more of the drag to the rear of the ship.

You can even make hydrofoils that don't lift all the way out of the water--They help reduce the hull drag by lowering the area in contact. I did one because I wanted the extra stability and tighter turning radius allowed by the side pontoons:

Spoiler

IIRC, she does about 80 m/s with half fuel (good enough to outrun active torpedoes and laser-guided missiles in the glide phase):

 

[Lazarus MonkeyMan]

Nice, thanks man!!!

[bewing]

This is powered by 6 whiplashes. It's not mine, but I made an improved version of it.

[Klapaucius]

One of mine.

 

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

 

[Lazarus MonkeyMan]

Nice!!!

[Lazarus MonkeyMan]

Finally got a semi-stable hydrofoil!