Can't get my plane up in the air

[Cochise17]

I run v.1.05.1028 (unmodded) via Steam.

I'm on science level 45, I think (I've unlocked science worth 45 xp). For the next line of science I will need 90 xp (science points) (not opened yet).

I'm trying to build a plane, but can't for the life of me get it off the runway. Yes, I know, I don't have enough engine power. I only have the J-20 Juno Basic Jet Engine unlocked (plus Small Circular Intake and Mk-1 Liquid Fuel Tank).
I tried with three engines on my plane, to no avail.

Do I need to unlock more science to get off the ground? Or am I going at it the wrong way.
Love the game, but I'm still a newbie :rolleyes:

Cochise Edited November 22, 2015 by Cochise17

[Taki117]

A picture of your craft in the SPH with CoM and CoL indicators would do wonders here, but I suspect the issue has something to do with your CoM/CoL(Center of Mass/Center of Lift) relationship and/or your CoM/Landing gear placement. Your first option should be to move your rear landing gear closer to your CoM, Landing gear are like the pivot point of a fulcrum. The closer it is to the balance point (your CoM) the easier it is to turn your aircraft around them. That being said, you don't want them too close together, or you will nose up unexpectedly on the runway and destroy your engines.

Option two is that your CoL is too far from your CoM. The CoL needs to be close to, but slightly behind the CoM, this causes your plane to be ever so slightly unstable, allowing you to perform various maneuvers. Another problem might just be a lack of pitch authority. Without a picture of your aircraft though, that last one is hard to diagnose.

[Goomblah]

Screenshots would help immensely.

Three Junos should be plenty for small aircraft. What kinds of speeds are you getting up to without liftoff? Adding more wings or adjusting the angle of the wings to gain more lift will reduce your takeoff speed to manageable levels (50m/s is a good benchmark to shoot for, but anything <100m/s is generally survivable on landing).

It's also possible that you don't have enough control authority. More/larger control surfaces further from the CoM/CoL will help.

[GDJ]

A single Juno engine is good for a 4-5 tonne aircraft if it's well balanced and designed, two Juno's will push a 7.5 tonne aircraft to just shy of 285 m/s. They have plenty of grunt for light aircraft.

Post a pic of the build screen with the COL, COM, and COT markers highlighted. We'd be delighted to help.

[Venusgate]

Two things I can think of that have nothing to do with engine power:

One, your "landed" state has the front wheel(s) lower than the rear wheel(s) (you never know, some people make tail draggers!) which means in your take-off state, the wings' Angle of Attack are below 0, fighting their uplift with some downward lift.
Two, Not enough wings/control surfaces. Try building a plane with one juno, but like 80% wing and four control surfaces, not including a standard tailfin/elevators, just to play around with what TOO MUCH control/lift feel like :P

[Val]

If you need some inspiration, you're welcome to take a look at my early career craft, the [B][URL="http://kerbalx.com/crafts/7307"]A-1 Pioneer[/URL][/B].
[TABLE="width: 400"]
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[TD][URL="http://kerbalx.com/crafts/7307"][IMG]http://i.imgur.com/1LmRENE.png[/IMG][/URL][/TD]
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There's also a great plane building guide [thread=52080][B]here[/B][/thread], though the drag info is outdated, and it's missing advice regarding [spoiler=Angle of Incidence]Like most of us, you were probably taught that lift works like this.
[IMG]http://mail.colonial.net/~hkaiter/miscimages/wingairflow.gif[/IMG]
Pictures showing lift from cambered wing profiles without Angle of Attack. It's not wrong, but it's also not the full picture. Which means we all have a tendency to mount wings with zero Incidence. On top of that KSP defaults to wings mounted that way. When really we shouldn't.

At least 2 things are missing in relation to KSP.

[LIST=1]
[*]Camber in wing profiles only provide part of the lift, in most flight regimes.
[*]KSP does not model cambered wing profiles.
[/LIST]
Which means [B]wings in KSP always need Angle of Attack to provide lift[/B].

If you mount wings with no Angle of Incidence, then the whole craft needs to be pointed up for the wings to lift it.

When wings are mounted with Incidence, the nose can be lowered closer to the direction of movement (prograde), reducing drag from the fuselage. Drag from the wings will of course remain unchanged, but that is much less than drag from fuselage.

In real life [U]even cambered wings are mounted with incidence[/U], for the same reason.
[quote name='Wikipedia']"Wings are typically mounted at a small positive angle of incidence, [U]to allow the fuselage to have a low angle with the airflow[/U] in cruising flight. Angles of incidence of about 6° are common on most general aviation designs."

[URL="https://en.wikipedia.org/wiki/Angle_of_incidence#Angle_of_incidence_of_fixed-wing_aircraft"]Source[/URL][/QUOTE]

The amount of incidence you need depends on mass and wing area. I usually go for 5° Incidence (because that's easy to do in stock) and a wing area 1/8[SUP]th[/SUP] to 1/6[SUP]th[/SUP] of the mass in t. (not counting wing area from Mk2 fuselage)

This will result in the craft being able to fly completely level with the horizon at sea level (below 500 m), without losing or gaining altitude, at or just above Mach 1 (350 m/s) which minimizes drag at transonic speeds, where drag is very high and thrust is still low. This is more relevant for RAPIER powered planes that have less thrust than Whiplashes, until speed is above 400-something m/s.

[B]TLDR;[/B] But it also means that if you fly level at 10 km, then the prograde marker will start to pull above the nose around Mach 3 (900 m/s), and you can start following it up, to get a good angle for the transition to ballistic flight, with very little pointing away from prograde.[/spoiler] Edited November 20, 2015 by Val
Clarification

[pincushionman]

I'm going to have to agree with everyone else and guess that your rear gear is too far aft. The closer your gear are to the CoM, the less the aircraft's own weight counters the desired rotation.

You also need to make sure your pitch controls (elevators) are far enough from both your CoM and your gear to be effective - canards need to be far forward, and/or tailplanes must be far aft. As long as your gear are close to your CoM, far enough from one is far enough from the other.

Now, if you're doing a tail-dragger, it's not that important since you're already rotated back, and in fact the plane may naturally rotate forward during roll-up.

So the typical answer is to make sure your gear are near the middle. But there are other alternatives if you're constrained:

- Shorten your aft gear so you're already rotated when you start.
- Rotate the main wing upward in your design ("geometric" angle of attack). This achieves the same thing.
- Use oversize canard elevators and brute-force the rotation. This is very dangerous.
- The end of the runway is raised above the surrounding land. If you're careful, you can roll off the end of the runway at speed and rotate in the air. This is pretty much what is done on aircraft carriers. The key here is to not go so fast you lose control on the runway.

Again, seeing pictures would help as we're just guessing here. But you probably do NOT want more engine. Real aircraft get by with T/W on the order of 0.3. And since I assume you want to land and collect science, you're heading for rough terrain. You want low-speed takeoffs and landings, and more engine does not help you there.

[satnet]

I'm going to plug Keptin's aircraft design thread [thread]52080[/thread] or as I like to call it "how I learned to make planes that actually fly". It is pre-1.0 aerodynamics, but it is still pretty relevant (just ignore about half the complaints about the aerodynamics).

It covers gear placement (probably your problem) and how to balance a craft (probably your next problem).

[Cochise17]

Thank you for some excellent answers! I followed the advices given, and got it up in the air in no time. The CoM/CoL relationship was way off. I appreciate the help!

[Pecan]

[quote name='Cochise17']Thank you for some excellent answers! I followed the advices given, and got it up in the air in no time. The CoM/CoL relationship was way off. I appreciate the help![/QUOTE]

Excellent!
You will have noticed the first thing that people asked for was pictures ...
You are now in the perfect position to post 'before' and 'after' images, with an explanation of the problem and fix, in order to help everyone else who has a similar issue.
Please?