Is this a good simple plane design?

[Cloakedwand72]

https://imgur.com/gallery/FgY4ZaG

Edited November 2, 2018 by Snark
Album link fixed for ya ;-)

[bewing]

Looks like your rear landing gear are a little too far back for comfort. Since you do not have canards, you will probably need to be able to "rotate" for takeoff.

You are using some kind of mod for your CoL, is that right? The CoL is in red, and is in front of the CoM? That won't work. Your CoL has to be about that same distance behind the CoM in order to provide stable flight.

 

[AeroGav]

@Cloakedwand72  Your pic didn't appear in my browser so i've edited the link in case other people can't see it as well.

6 hours ago, bewing said:

You are using some kind of mod for your CoL, is that right? The CoL is in red, and is in front of the CoM? That won't work. Your CoL has to be about that same distance behind the CoM in order to provide stable flight.

The Red ball means he is using RCS build aid.    The red dot shows where centre of mass will be when the fuel tanks are empty.   You can see it's marginally stable on full tanks (like a P51D Mustang ) but very stable when empty (borderline lawn dart ish).    He is using a mod for CoL -  that double graph symbol down on the toolbar is CorrectCoL.       Two thumbs up for having these mods installed, makes aircraft design much easier.   BTW,  that is an absolute metric  F-ton of fuel.   He's got a super efficient Wheesley engine,   that would circumnavigate many times over at a decent cruising altitude, maybe not if he just goes full throttle on the deck.

[AeroGav]

BTW, I'm noticing you've got Mechjeb installed.   It might not be an issue if you're using an autopilot,  but it doesn't look like the plane has very much yaw stability.   That fin has a fairly small lift rating and is fairly close to the centre of mass (when fully fuelled).     If you find  it keeps wandering off heading,  you can attach a wing strake to the upper surface of the wing, rotate it so it becomes a vertical fin,   then slide it backwards so it extends past the trailing edge.    This will have more lift rating and a longer lever arm to work with and will provide a lot of passive yaw damping.     You don't really need an active control surface on the fin,  but if you do want that ability you can clip the tiny mk4 elevons to the back of these.  

Here's an example of passive strake/fins (note, they are attached to outboard engines here, but can be mounted direct to the wing on a design like yours)

 

Edited November 2, 2018 by AeroGav

[Cloakedwand72]

On 11/1/2018 at 8:24 PM, bewing said:

Looks like your rear landing gear are a little too far back for comfort. Since you do not have canards, you will probably need to be able to "rotate" for takeoff.

You are using some kind of mod for your CoL, is that right? The CoL is in red, and is in front of the CoM? That won't work. Your CoL has to be about that same distance behind the CoM in order to provide stable flight.

 

How should My LG look like? Any whom that red RCS thingy is to give a empty fuel idea. So I can see where I'd like my COL. And I use current COL mod. And maybe other mods like wind tunnel in the future. 

On 11/2/2018 at 2:58 AM, AeroGav said:

@Cloakedwand72  Your pic didn't appear in my browser so i've edited the link in case other people can't see it as well.

The Red ball means he is using RCS build aid.    The red dot shows where centre of mass will be when the fuel tanks are empty.   You can see it's marginally stable on full tanks (like a P51D Mustang ) but very stable when empty (borderline lawn dart ish).    He is using a mod for CoL -  that double graph symbol down on the toolbar is CorrectCoL.       Two thumbs up for having these mods installed, makes aircraft design much easier.   BTW,  that is an absolute metric  F-ton of fuel.   He's got a super efficient Wheesley engine,   that would circumnavigate many times over at a decent cruising altitude, maybe not if he just goes full throttle on the deck.

Thank you! I'm a huge air-plane fan. I have those mods installed bye default. I'm thinking about wind tunnel mod but that's way in over my head. I use a structural fuselage then a MK1 jet fuel with a basic jet engine & the Default retro MIG looking engine. Any whom how do I show screencaps from imgur & link my KSP photos? Any whom how is my COM/COL correct & how should my tail set up look like & wheel base closer etc. ?

[farmerben]

 

 

What I do to post screenshots is open the image in a new tab and then copy that URL onto my post.  

I flew a near copy of your plane.  It looks like I set my landing gear further apart than yours...  Mine sat level on the runway.  

Good is partly a question of style.  I found it easy to do yank and bank maneuvers around the KSP buildings.  Easy to do Immelman maneuvers.  Easy to land.  

The biggest downside for me was high takeoff speed.  This would be easy to fix by ensuring the wings are not level on the runway, but angled up slightly (that could make it trickier to land however).  Once I was off the runway the pitch controls were fine, but due to massive wing area the G forces and drag braking caused by sharp pitching were the highest I've ever encountered (at least at low speed).  Yaw control and sideslip were a bit excessive compared to what I'm used to, but it worked and I didn't tailspin, besides that's easy to calibrate.  Roll was about perfect.  

This plane doesn't really need medium landing gear in the back, smalls are fine.  The wing surface was much larger than what I normally build, which is mostly a question of style.  

Overall I say this is a good plane and fun to fly.  

 

 

 

 

Edited November 9, 2018 by farmerben

[Rayder]

On 11/7/2018 at 7:42 AM, Cloakedwand72 said:

How should My LG look like?

Your rear landing gear are a pivot point. If the wheels are too far back you'll find you need a high speed before the craft will pitch up.

If you bring the gear further forward closer to the CoM, the craft will pitch easier and you'll lift off easier. Ideally you want it as close to the CoM as possible, but not in front. Being a touch behind is best, so that the craft doesn't tip backwards.

You also need to consider ground clearance. Having your landing gear further forward means the rearmost portion of your craft has the potential to contact the ground. You can either limit how much you pitch up, or you could add a small wheel there to prevent impacting the engine on the runway.

On 11/2/2018 at 2:24 PM, bewing said:

You are using some kind of mod for your CoL, is that right? The CoL is in red, and is in front of the CoM?

I'm not sure on OP's mods, but I know in RCS build aid the red CoM indicator is an average CoM (between full and empty tanks). It's handy for placing RCS thrusters so that 'on average' you won't have an excessive torque when translating.

Edited November 13, 2018 by Rayder

[Guest]

It'll fly. If you want to improve it, here are some things you could look at:

• Too much wing, unless you're going for some really esoteric mission. You should be able to do a decently easy landing with about half the wing surface you have now. This is gonna be really floaty!
• Too much fuel.
• Landing gear too far back. Also medium LG is overkill, small is more than enough for something this size.
• Wing is horizontal, should be pitched just a tiny bit: this way your body will be aligned with your vector and you'll produce less drag.
• It's gonna be squirrelly to fly. Consider adding either a tailplane or canards and putting the rudder as far back as it can go. Also set the control surfaces so only the wingtip ailerons control roll, and the rudder only controls yaw.
• The engine is way overpowered for something this size, but then again more power = more fun so I don't know if that's a problem really. Something this size would fly just fine with a single Juno.
• If you want more control on landing, consider adding an airbrake.

[Chumpes]

the center of mass shall remain in front of the center of drag, which is not the case here.

 

[Guest]

19 minutes ago, Chumpes said:

the center of mass shall remain in front of the center of drag, which is not the case here.

 

How can you tell where the centre of drag is, just by looking at the picture?

[Rayder]

2 hours ago, Brikoleur said:

How can you tell where the centre of drag is, just by looking at the picture?

Centre of lift, different name for the same thing.

You want to keep your CoL behind the CoM at all times. If you don't, without enough control authority your nose will flip around.

[Boris-Barboris]

What is center of drag?

[Guest]

2 hours ago, Rayder said:

Centre of lift, different name for the same thing.

 You want to keep your CoL behind the CoM at all times. If you don't, without enough control authority your nose will flip around.

I thought you meant centre of pressure. And it doesn't have to be behind the CoM, it just mustn't ever be in front. Which means that that craft is marginally stable with full fuel load, and will get stabler as fuel drains. The centre of pressure could throw a spanner into the works though (or, conversely, could help, I can't tell just by looking at the picture).

[Chumpes]

in my point of view

center of drag = center of lift = blue spot = "hypothetical point at which the application of the sum of aero-forces will induce the same momentum as what is observed on the actual plane"

in fact this is not perfectely true because aero-forces = drag + lift

On ‎11‎/‎14‎/‎2018 at 10:46 PM, Brikoleur said:

And it doesn't have to be behind the CoM, it just mustn't ever be in front.

hum... something that mustn't ever be in front of should better be placed behind =))

 

i.e. : the blue spot behind the brown spot

 

you can try mooving the principal wings a little bit forth and back and see the effect on manouvrability

Edited November 22, 2018 by Chumpes

[Guest]

Just now, Chumpes said:

center of drag = center of lift = blue spot = "hypothetical point at which the application of the sum of aero-forces will induce the same momentum as what is observed on the actual plane"

It doesn't quite work like this. 

Try building a biggish spaceplane with a flat nose: for example, a rocket-powered one that you launch ballistically and recover aerodynamically. Place the CoL well behind the CoM.

As likely as not you will find that it turns cartwheels on the way down. This is because of the flat nose. It doesn't produce lift, but it does produce drag, and the centre of pressure won't be where you expect it to be... if you're going fast enough.

Conversely, if you have a pointy nose and a draggy tail, at high speeds the plane will be stabler than you expect if you're just going by how the blobs line up.

Another experiment you can do is put the CoL well below the CoM, but still behind. Again at high speeds -- and sometimes not so high speeds! -- the craft will flip cartwheels.

IOW what you're saying is an approximation of how it works, but it is not exactly like that, and the differences are very real and very significant, if you're building anything that doesn't have completely lawn-dart geometry.

N.b., I don't know enough about real aerodynamics to be able to say if this is Kerbal physics or real physics, but in any case this is what happens in KSP.

[Chumpes]

yes you are right brikoleur

the problem of the game ksp is that the blue Arrow/point should be representative of overall aero-forces (that depend on the speed and plane angle), not only so called "ksp lift" that is not strictly the lift (vertical) because some portion of this "ksp lift" can be transformed to drag (horizontal), by tilting the main wings for example (blue Arrow no more strictly vertical).

Edited November 22, 2018 by Chumpes