How to make my parafoil actually fly?

[Zeiss Ikon]

Just about 20 minutes after EVA parachutes appeared in 1.4, someone came up with a method of getting a Kerbal into a Command Seat with a deployed parachute (you couldn't deploy the 'chute while in the seat until 1.4.3) and used that method to build a parafoil trike.  They built a biggish monstrosity with folding wheels that must have come in at 4-5 T mass.

I'm trying to build the smallest, simplest parafoil the game will support.  I've got a setup with a single Juno, Mk. 0 Liquid Fuel Fuselage, Small Round Intake, and a Command Seat -- and then a pod on a launch clamp with a second Mk. 0 Fuel Fuselage to take a radial decoupler; the craft I'll fly sits on the decoupler before launch.  I get Jeb into the Command Seat, set the parachute to deploy "immediate" and deploy it, spool up the Juno, and decouple; the craft slide forward off the decoupler, descends as speed builds up -- and then, if I have more than about 20% power, the engine unit and Command Seat begin flipping, pitching up through 360 degrees every second or so.  This nullifies the thrust, so the whole contraption hits the runway about as far forward of the launcher as it was high.  So far, Jeb has survived every attempt, but the power unit does not.  SAS doesn't help, even if I add 1, 2, or 3 Small Reaction Wheel units (the Juno's alternator produces plenty of power to run these reaction wheels).

If I set power below 20% or so, the power unit doesn't flip, the whole shebang just plummets to the tarmac (with pretty much the same end result).

The originator of the stock parafoil craft didn't seem to have this problem, but then his craft was probably several times the weight of my 585 kg (without reaction wheels) contraption.

My question is this: What kept the power from flipping the original parafoil trike, yet allowed it to fly at 200+ m/s?

[Gargamel]

IIRC, he was kinda heavy on the control surfaces.  Lemme see If I can dig up the video.  I believe it was one of @hazard-ish's videos. 

Airfoils need air speed.  So you gotta get enough lift, and that means speed, especially initially.    Try making the launch clamps taller so you have some time to gain speed.

Offset your thrust so it's not flipping over.

Perhaps the extra mass is necessary to bring the CoM more inline with the CoT and keep the whole shebang nicely under the foil.  Ignore that bit. That makes no sense. 

MOAR BOOSTERS.

 

 

Here ya go, study away:

 

Edited May 27, 2018 by Gargamel

[Zeiss Ikon]

Ugh.  That's nowhere even close to a minimum-parts build.  As noted, there are lots of control surfaces buried inside that compact unit.

Meanwhile, I've come up with a way to take off from the runway, in theory.  In practice, it noses down and twirls around the nose wheel, even with full up pitch input (I'm not sure the reaction wheel is getting enough power by the time the landing gear starts causing trouble).  And it's bedtime for tonight; I'll fool with this more tomorrow.

[bewing]

First, you have to understand that your CoP and CoL are in the middle of the Kerbal. So your CoL is way above your CoM and even higher above your CoT, and you can't see any of this with a force readout in the editor.

What all of that comes down to is that reaction wheels aligned with your CoT aren't anywhere near enough to overcome all those torques.

I did a fair amount of experimenting before release -- and to the best I could tell, you absolutely had to have control surfaces to make a parafoil ultralight work at all.

 

[Gargamel]

3 minutes ago, bewing said:

CoP

Drawing a blank on this one, CoP?

[bewing]

Center of Pressure/Drag.

[blakemw]

This works for me:

I didn't put a lot of effort into getting the thrust offset angle perfect but it's close enough the single reaction wheel can counteract the effect. Also, it's air-launched. Though I've launched similar things on a monowheel in the past.

[Zeiss Ikon]

Okay, I got it flying.  In fact, at present, it's 25+ km from the west end of the KSC runway, climbing very slowly (1 m/s or less) through 1770 m altitude on appr. 14% power (just under 1 1/2 small divisions on the throttle) with SAS hold at appr. 14 degrees above horizon, with rate of climb/descent controlled with tiny throttle movements.  I expect to get 150+ km before fuel runs out.

@bewing, I don't doubt you're correct about the CoT vs. CoP, but I found that the small reaction wheel handles it just fine at this kind of speed (just under 20 m/s).  More power will result in a climb you can't trim out, but what I found was causing part of my problem originally was that the alternator in the Juno wasn't outputting enough power to give the reaction wheel full authority.  I added a battery, and got off the ground safely on the first try  By the time I hit 1000 m altitude, the alternator had caught up and keeps the battery in a fully charged steady state.  By then, I'd also adjusted the main gear to be wider and lower and moved it closer to the CoM, as well as lowered the nose gear and cut its friction to 40% (which greatly improved the takeoff roll).

It's a little touchy -- too much power, it'll nose up uncontrollably, too little and it'll stall and fall (I've recovered from one such incident in this flight).  Doesn't have the control authority (or I don't have the educated fingers) for aerobatics, but it's about as simple as a paramotor is going to get in KSP -- give or take landing gear...

Edit: now it's 65 km out, still flying on 1.8 kn thrust at 2416+ m altitude.  Fuel just now dropping to 60%.

Edited May 27, 2018 by Zeiss Ikon

[bewing]

Cool. Then you're better at it than me.

 

[Zeiss Ikon]

5 minutes ago, bewing said:

Cool. Then you're better at it than me.

Or after something different. 

[Jesusthebird]

Problem is...the chute doesnt work the same in the command seat vs freefall. So really the chute can only be used for lift wheres in freefall the kerbal has control of the lift, kinda like a moving control surface vs non moving wing surface. once deployed from a command seat its at a fixed point(way above the craft) so reaction wheels are needed for stability but will almost always tend  want to flip eventually. Id like to find a way to make the command seat act like its a kerbal on eva(minus walking and jetpacks lol) so the chute can be controlled and reactions wheels wouldnt be needed.

[Zeiss Ikon]

You're correct -- if you're in a command seat with parachute out, you've effectively got a very high parasol wing (with a lot of drag).  Further, if the power unit has too much thrust, it pivots around the attachment point of the parachute to the Kerbal -- I've seen my paramotor above spin like a whirligig in nose-up pitch while the parafoil just glides along.  Not sure now much of that is due to the unbalanced drag of the Kerbal in the seat, sitting on top of the engine/fuselage, but it's the same kind of behavior you'd get if you tried to fly with just the engine.