Suggestions for optimizing, expanding and/or flying this (entry level) jet?

[UmbralRaptor]

Ideally not involving unlocking additional parts, though I suppose I could go back and get the ones that I skipped or grab another node or two.

The craft layout: https://photos.app.goo.gl/sF77qEWnnG3iyMBF7

Believe it or not, the biggest stability problems are in roll. Yaw stability just doesn't show up as an issue, and it can survive having no yaw control at all. (reaction wheels are off by default). Pitch feels weird, so advice on improving that would be nice (though if it means reducing authority, I'd probably have trouble taking off?). Would swapping the pod with the aft strut or something be an effective way to reduce overall drag or increase stability? Landings also feel off, since it seems to bounce pretty easily. Advice on approaches / estimating glide ratios / when and how to best flare would be appreciated.

As configured, the only instruments are a thermometer and a barometer. The aft girder could be swapped out for a materials bay, and I could just hang goo canisters off the sides if needed. Also, I suppose I could swap either or both girders out for Mk0 tanks (empty to reduce weight or full for more fuel) to increase range. Adding crew space for tourists looks easy, though I'm worried about weight when my thrust comes from a single J-20 Juno.

Edited October 26, 2020 by UmbralRaptor

[Spricigo]

My 0,02 funds:

Some dihedral angle to help with roll stability and some wing incidence to help with..well, everything. Maybe a dedicated set of control surfaces for roll.

Swapping the girders for Mk0 fuselages seems like a no-brainer for me. And a 2nd pod behind the one you already have can at least eliminate the mismatched node transition (with only barometer and thermometer there is no need for pilot+scientist on board)

[jimmymcgoochie]

Try tilting both sets of wings up by 5 degrees (hold shift with angle snap on and rotate them once) which gives you more lift on the runway; alternatively move the front wheels to be slightly lower than the back ones so the plane sits with a slight nose up attitude on the ground. Do you have any aero control surfaces at all, or are you steering just with the pod’s reaction wheels?

I would be inclined to start again from scratch with something like the following:

Small nose cone or air intake > Mk1 pod > FL-200 fuel tank x2 with oxidiser and most/all of the fuel removed (or a Hammer SRB with fuel removed) > 1.25m nose cone. Put science bits on the sides of the pod.

Front wings two panels wide, rear wings one panel wide, angle both at 5 degrees up. Ideally you should put elevons on the trailing edges of both- the rear elevons will provide pitch control while the front ones should be used for roll control. One larger fin or preferably wing panel plus elevon as a tail, with elevon set to provide yaw control. Stick a Mk0 fuselage on each side, just under the main wings, with an air intake on the front and a jet on the back- two engines are definitely better than one as you’ll accelerate faster and to a higher top speed.

Put one wheel under the nose so it can steer on the ground- reduce the friction settings using advanced tweakables to greatly improve stability on the ground- and two fixed wheels just behind the centre of mass, shifted slightly up to give it a nose-up attitude on the runway. Alternatively, use four wheels for improved stability but losing the ability to steer.

11 or 12 parts for wings, 6 for propulsion, 4 or 5 in the fuselage, 3 or 4 for landing gear = between 24 and 27 parts, leaving another 3-6 for science gubbins, an antenna and/or battery. You could also add a science jr to the fuselage, or a parachute to the front of the pod and a decoupler behind it to eject if things go wrong- set both to activate on the same stage.

[swjr-swis]

I can't clearly see from your screenshots what parts or tech nodes you have available, but with what I think you have, I would do something like this:

https://kerbalx.com/swjr-swis/UmbralRaptor1

This is all tech level 4 or less. Single Juno as engine, two Mk1 pods (mono drained), a single LFO tank (Ox drained), and a service bay containing the science instruments you mention. 22 parts in all. It can cruise at around Mach 0.9 at 8-8.5km. Control surfaces have been tuned down to respond gently. Part count allows to add a parachute in the service bay if you want some safety margin in landings, but it doesn't really need it.

I also have a variant with 6 parts more, which uses two extra mk0 nacelles on the wings for a 3x Juno configuration that can cruise at Mach 1.73 and 14.5km and can get anywhere on Kerbin with fuel to spare. 28 parts total. It's basically this same plane with just the two nacelles added in mirror symmetry, vertically centered and horizontally one fine notch behind CoM center.

 

Edited October 27, 2020 by swjr-swis
updated with screenshots