Seaplane advice

[Klapaucius]

I was mucking about with stock seaplanes and got stuck due to a flameout while rescuing ANOTHER Kerbal (see thread if interested )

So, I decided to build my own rescue craft. Seeing as this is Kerbal, I thought I needed to do something appropriate, so I created this not-quite but-almost lifting body, using the the MK2 fuselage pieces as pontoons.  It's got heaps of room for passengers, and rewards a few lucky Kerbals with an inverted view. 

 

 

It flies fine, and I can land it on the ground without problems,most of the time I can land on the water without breaking anything, and I managed a top speed of around 1200 meters per second at an altitude 17,500 after switching out the Rapiers for Ramjets.

 

But I have two issues, one annoying, the other more problematic.

1. This thing will not go down the runway in a straight line. I've disabled the turning on the rear gear, reset the front gear several times, and unless Kerbal has micrometer to measure it, it looks dead centered to me. So why does it get to a certain speed and skate all over the runway? I've given up, and I just taxi off the runway and take off from the grass where there are less things to hit. (I have run into this issue with other aircraft in the past).

2. Secondly (and this is the bigger issue), once landed on the water, I cannot get off the surface again. Depending on how much fuel I have on board, takeoff speed is anywhere from just over 100 meters per second to 160.   However, once landed in the water, the fastest I can get is 70 metres per second. I get get it to briefly nose up a bit, but that is all. In the real world (assuming it did not come apart), this hull would be planing by now since that is around 150 mph.  It is acting like a displacement hull despite the shape and despite the high speed.  Extra engines do not seem to help. 

 

 

 

So any thoughts would be appreciated.

[bewing]

Search through the forums for "why is my plane veering left on takeoff" -- and you will find hundreds of threads, with a dozen different explanations and workarounds to try for alleviating the many sources of the problem.

I see that you've already looked into the "crooked landing gear" explanation.

"Passive Directional Stability comes from having low drag at the front of your vehicle and high drag at the back." Your problem still may be either aerodynamic, or automotive, though. So the first thing I always try is to set the friction of the front wheel to a very low number. If that works, it means your problem was fundamentally automotive in nature.

But if that doesn't fix it, then your problem is aerodynamic. Either wheelbarrowing, or some other low-speed instability.

 

[Klapaucius]

41 minutes ago, bewing said:

"Passive Directional Stability comes from having low drag at the front of your vehicle and high drag at the back." Your problem still may be either aerodynamic, or automotive, though. So the first thing I always try is to set the friction of the front wheel to a very low number. If that works, it means your problem was fundamentally automotive in nature.

 

Thank you, that pretty much fixed it. It still veers very slightly, but I was able to get all the way to the end of the runway with out any major issues. 

I confess I do not understand this bit of the gear. What is the point of the friction setting?  Unless you are braking, why would you want additional friction?

[bewing]

1 hour ago, Klapaucius said:

Unless you are braking, why would you want additional friction?

When you are parked on a slope, you want all the friction you can get. Fortunately, you can adjust the value during a mission.

And some designs need a friction boost at the back to keep them from spinning out on landing.

 

Edited May 12, 2018 by bewing