How to increase take-off speed....

[CaptainKipard]

......without increasing the thrust.

This is for the Skylon.

The thrust should ideally stay the same because it is already using the official numbers.

What other factors go into it?

I'm only reaching 150m/s. Skylon take-off speed is 160m/s and I think it's part of what's stopping me from taking off while still on the runway. The nose pitches up, but I have to drive past the end of the runway to get enough clearance for my tail so I can pitch up enough to gain altitude.

If there are other solutions to this, I'm interested as well.

[Wanderfound]

Reduce weight, reduce drag. Don't deploy flaps or deflect control surfaces until the last possible moment. And back up to make the runway as long as possible.

Your takeoff issue is more likely related to gear placement than speed, though.

[nli2work]

I don't think there's much else you can do to increase TWR besides either less mass; or higher Thrust; since you are restricted to the length of runway. Drag is less of an issue at the lower speeds. You can try reducing wheel collider friction in Unity, but that will probably have negative effects you don't want.

[Orange_Ignition]

Typically in real scenarios where aircraft applications needed shorter runways people came up with some creative ideas. With the advent of aircraft carriers, you had everything from take-off boosters to catapults like we use today, sometimes they tried(and failed with the launch boosters) to modify large aircraft to use shorter runways, but they got the most success when they lightened the big craft and/or used catapults. aside from velocity, your only other factors are weight and lift c.e.... catapults increase take-off velocity, so do launch boosters. but aside from a longer runway(not possible without other mod dependencies).

What harm will adding more thrust to the Skylon really do? aside from that the only out of the box thing i can think of is to give the landing gear more powerful motors that can push it that extra 10m/s? that or do a global weight decrease little by little, or cheat with adding more lift to the front canards?

Considering you want this to use the stock ksp runway, you don't have that many options, but im sure the community can get creative

edit: also what about trying to roll the skylon all the way back to the start of the runway( when you load there is some room(usually) behind you. would that give you the extra runway you need? also does the engine take a long time to build thrust?

Edited November 25, 2014 by Orange_Ignition

[sal_vager]

I made my own skylon style craft, and suffered from tail strikes if I tried to get the nose up far enough to take off.

My solution to this problem was to incorporate a tail wheel, so the craft could not only put its tail on the ground safely, but could also raise itself up on the tail wheel.

This allows it to get enough AoA without having to fall off the end of the runway

Plus it allows the craft to land tail first and lose speed safely before the main wheels touch down.

[CaptainKipard]

edit: also what about trying to roll the skylon all the way back to the start of the runway( when you load there is some room(usually) behind you. would that give you the extra runway you need?

No. I tried the extra long runway from Kerbin Side (Area 110011) and even there the plane would not go past 150m/s

also does the engine take a long time to build thrust?

Yes. I tried to build it up with the brakes on (like airliners do) but it makes no difference.

My solution to this problem was to incorporate a tail wheel, so the craft could not only put its tail on the ground safely, but could also raise itself up on the tail wheel.

I know Concorde had that, but I'd prefer to stay true to the official R.E.L design, and I haven't seen any evidence of a wheel like that.

mass/weight

I'm still in the process of reducing the available resources based on fully loaded test flights, so we'll see.

My wings and control surfaces are already at the maximum lift coefficient, based on even the most generous stock parts, so I'm not sure I can go higher.

[Wanderfound]

Keep in mind that if you're flying in stock aero, you're dealing with much higher drag than reality. And I suspect that the runways Skylon is designed to use may be quite a bit longer than KSC's.

[Hodo]

Set brakes before take off, start up engines. Let them spool to max power, then release brakes.

[NathanKell]

Real Skylon needs a many-kilometer runway to take off. You'll have to make some compromises to get it off the stock runway.

[Guest]

Try FAR. Using real numbers in stock aero is pointless. You will be getting way too much drag.

[CaptainKipard]

Try FAR. Using real numbers in stock aero is pointless. You will be getting way too much drag.

For sure. I just want the mod to be playable with stock aerodynamics too, so everyone can play.

[tetryds]

For sure. I just want the mod to be playable with stock aerodynamics too, so everyone can play.

Are you pitching up all the way until you exit the runway?

If you don't touch your controls and only fix the position to not kill yourself that will make you go a bit faster.

Also, keep the angle of attack as low as possible.

This works both in FAR and Stock.

[CaptainKipard]

Are you pitching up all the way until you exit the runway?

As far as I can without destroying the tail.

If you don't touch your controls and only fix the position to not kill yourself that will make you go a bit faster.

Yep, I'm only pitching up at the last moment.

Also, keep the angle of attack as low as possible.

Why? This goes against everything I've ever been told.

[Wanderfound]

Why? This goes against everything I've ever been told.

More AoA = more drag. You want enough AoA to lift off, but no more.

[tetryds]

Why? This goes against everything I've ever been told.

What Wanderfound said, ideally you want zero AoA until you have enough speed to pitch up and takeoff.

If you keep any AoA until this point you are losing energy as it's adding drag without really lifting you off.

[White Owl]

In a perfect world and perfect scenario, the ideal takeoff technique is to lift the nose just barely enough so the whole airframe is aligned directly with the relative wind, to minimize drag as much as possible. Accelerate to take off speed, then pitch back slightly, until the wings' angle of attack is just enough to lift the plane. Balance airspeed and vertical speed from there while you accelerate some more, then it's business as usual.

Making this work in stock aerodynamics... it's a replica vehicle so we don't want to change the mass or the thrust. Drag is going to be horrible, no matter what you do. I think you're left with tweaking lift values. Maybe make the wings lift just a tiny bit more?

[Sochin]

What about JATO's, I know not very realistic but its an option.

[Orange_Ignition]

i'm going to agree with some of the posters here and say stock aero may be the problem with a true to life representation here(although the runway could still be too short), people playing on stock may not mind that their engines push a bit more air than their FAR/NEAR counterparts... maybe create a mm config for stock vs far?

[HoY]

What's your thrust curve look like in the engine cfg?

[CaptainKipard]

What about JATO's, I know not very realistic but its an option.

I want to keep it authentic.

What's your thrust curve look like in the engine cfg?

I copied them from B9 and modified slightly. If you want to know what it looks like, use FloatCurve editor

atmosphereCurve
{
	key = 0.0006 3132 0 0
	key = 0.11 3600 0 0
	key = 1 3022 0 0
}
velocityCurve
{
	key = 0 0.850 -0.0007
	key = 300 0.75 0 0
	key = 1500 1 0 0
	key = 1650 0.88 -0.001758357 -0.001758357
	key = 1800 0 0  
}

[HoY]

Try adding this to the curve, if its not too put of the realm of possibilities. Currently you are starting at 85% at 0m/s, and by the time you hit 150m/s you lose throttle down to 80%, and will continue to lose it all the way to 300m/s. just added another key to give you 90% at 180m/s before it starts losing thrust. I apologize if you've already looked at this, but just from your explanation it sounds like you need the thrust to stay constant or increase at that point, rather than decrease.

atmosphereCurve
{
	key = 0.0006 3132 0 0
	key = 0.11 3600 0 0
	key = 1 3022 0 0
}
velocityCurve
{
	key = 0 0.850 -0.0007
	key = 180 0.9 0 0
        key = 300 0.75 0 0
	key = 1500 1 0 0
	key = 1650 0.88 -0.001758357 -0.001758357
	key = 1800 0 0  
}

[CaptainKipard]

No that's unrealistic. A real curve has only one hump. This has two.

Google "jet airspeed thrust curve" and have a look at the images.

[Wanderfound]

No that's unrealistic. A real curve has only one hump. This has two.

Google "jet airspeed thrust curve" and have a look at the images.

As has been mentioned upthread, however, realistic aircraft TWR statistics and realistic aircraft speed simply cannot coexist with incredibly unrealistic stock aero.

You're going to have to either boost the performance or just accept that in stock aero it's going to perform about as well as the real thing would if you dropped it into a giant bowl of soup. For much the same reason.

I suspect that anyone who is both interested in spaceplanes and cares about realism is already using NEAR/FAR, though. There are still substantial numbers of stock aero spaceplaners, but realism is not their primary concern.

[CaptainKipard]

I suspect that anyone who is both interested in spaceplanes and cares about realism is already using NEAR/FAR, though. There are still substantial numbers of stock aero spaceplaners, but realism is not their primary concern.

That's a good point.

Also @Hoy after I copied that curve in my response and double checked it and it's not actually humped realistically, which would further lower the performance at low altitudes. Thanks.

Edited November 26, 2014 by Cpt. Kipard

[nli2work]

you can set up a more realistic curve for FAR|NEAR; and a flyable curve for Stock Aero. just embed the FAR|NEAR configs as an MM patch in the part config, outside of the PART{}.