Proper Plane Design and Flight for Career Kerbin Surveys?

[ekstrj]

Hi all,

I've gained so much information from this board and from the huge wealth of video tutorials (especially Scott Manley's). What I can't find though despite trying to search using a wide variety of keywords and phrases is how to most efficiently design planes to fly around Kerbin. I'm playing through Career mode and have a huge amount of various scientific survey contracts around Kerbin, so I've started to shift from rockets to planes.

I'm at the point where I've unlocked the Turbo jet engine, and I've made a decent plane accounting for intake, center of lift being slightly behind the center of mass, and the shifting of the center of mass due to fuel consumption. The problem is that I can't find how to calculate the most efficient altitude, speed, incline, etc. to make sure I can make it to all of the spots halfway across the globe and still have enough fuel to get back. Here's my problem:

I can fly it at low altitudes (2-5 km) and turn off the various Intake components to reduce drag. The speed however isn't nearly as fast as higher altitudes.

I can fly at higher altitudes (8-12km) and maintain at least .20 air intake, but if I don't keep adjusting the pitch with S, the plane wants to constantly tip the nose slightly downward killing my altitude and wasting fuel. If I increase the physical time warp, the plane severely pitches down and strangely the air intake drops to almost 0 within a second or two.

If I try to go any higher (14km+), I notice the plane start to have the reentry flames (I assume due to the overall velocity of the craft), and within a short time the velocity vector points down toward Kerbin and I'm unable to adjust the pitch upward at all. The pitch essentially gets locked until I reach a significantly lower altitude (~6km) despite me being able to fly at 8-12km without issue normally. What exactly is causing this effect, and how can I prevent it through design or flight?

I guess the main question is if I'm using Turbo Jet Engines, what kind of altitude should I target, what kind of speed should I target at that altitude, and how do I prevent this pitch-lock phenomenon and maintain a high altitude? Also, can I design my plane such that without intervention it maintains a level resting pitch (or in other words keeps the nose level and not pointed toward the ground)? Do I not have enough lift with my wings?

Thank you in advance for your assistance, and I apologize if somehow I missed the answers to these questions while searching. I can take a picture of my craft if it'll help.