Can you help me build a long range 1000m/s plane?

[dboi88]

Thanks for all your help guys. I've managed to build the craft i was looking for. Thanks for explaining the fundamentals so well. I've been building fast crafts of all shapes and sizes now.

 

Hi, I'm having trouble building the plane i want. I've not much experience with planes at all, only ever built a couple of ssto's and even then i cheated the .cfg's .

So i've started with the stock Mk4 Revenspear. None of my design  attempts could reach more than 300m/s and this stock craft can reach 820m/s so i went with it. I need it to do as close to 1000m/s and have a range of 800km. This is the distance to my second base where i plan to eventually launch all my Kerbin rockets from and for shuttling crew and small payloads i need the speed, my big cargo plane takes 1hr10min to get there and that's far too long to do often. I also need a small cargo bay for the payloads. I've unlocked all plane science nodes. Here's the craft.

The problem i'm running into is the range, every time i add more fuel and gain range, i need more thrust, i add more thrust and I've lost the gained range. I find i need a certain amount of thrust to get to around 360m/s before it seems to just run away with itself up to 800ish if i can't get to 360m/s it's a long slow journey. If i get the 360 i always then quickly get to 800 but fall short on the range every time. I've tried all sorts of different altitudes but not been able to squeeze out more than a few minutes extra flight time. This has a range of about 550km and can just about get the to the 360 tip over point.

The ultimate goal would be to have a range of 1600km so i could air drop supply payloads instead of needing to land and refuel for the return journey.

I also tried drop tanks but any side tank made reaching any sort of speed immpossible.

If you can help me i'd really appreciate it.

Edited January 19, 2017 by dboi88

[Reactordrone]

You should probably switch to Whiplash engines, they excel at high speed flight. The Mk 1 cockpit is also going to get pretty toasty flying for extended periods at Mach 3.

[AeroGav]

1 hour ago, dboi88 said:

Hi, I'm having trouble building the plane i want. I've not much experience with planes at all, only ever built a couple of ssto's and even then i cheated the .cfg's .

So i've started with the stock Mk4 Revenspear. None of my design  attempts could reach more than 300m/s and this stock craft can reach 820m/s so i went with it. I need it to do as close to 1000m/s and have a range of 800km. This is the distance to my second base where i plan to eventually launch all my Kerbin rockets from and for shuttling crew and small payloads i need the speed, my big cargo plane takes 1hr10min to get there and that's far too long to do often. I also need a small cargo bay for the payloads. I've unlocked all plane science nodes. Here's the craft.

The problem i'm running into is the range, every time i add more fuel and gain range, i need more thrust, i add more thrust and I've lost the gained range. I find i need a certain amount of thrust to get to around 360m/s before it seems to just run away with itself up to 800ish if i can't get to 360m/s it's a long slow journey. If i get the 360 i always then quickly get to 800 but fall short on the range every time. I've tried all sorts of different altitudes but not been able to squeeze out more than a few minutes extra flight time. This has a range of about 550km and can just about get the to the 360 tip over point.

The ultimate goal would be to have a range of 1600km so i could air drop supply payloads instead of needing to land and refuel for the return journey.

I also tried drop tanks but any side tank made reaching any sort of speed immpossible.

If you can help me i'd really appreciate it.

It looks like you're using some modded engines there?

In terms of the stock engines,  Panther is no good if you want to go past 750 m/s,  it peaks there and thrust more or less falls to zero by 800.    It's going to be between the Whiplash and Rapier, which peak at 900 and 1150 respectively.    Looking at the atmosphere curves of these engines, thrust drops more slowly than air pressure up to 17km on the whiplash, then up to 22km on the Rapier.

Fuselage.   The mk2 fuselage has 3 times the drag of the mk1 but holds no more fuel.    It is more heat tolerant, but you 're using a mk1 cockpit.  Also parts at the front get the worst heat, if you were bothered about heat you could have just used a mk1 inline cockpit.   You can work around this problem, by adding an angle of incidence to your wings, but it's an "intermediate/advanced" technique.   Just stick to a mk1.

Wings - The big S wings and strakes should be used , they store additional liquid fuel.  You can build tail fins out of big S strakes too. 

For high speed with long range, you need to be flying at high altitude.  The higher the better, the lower your drag and fuel consumption.   But , you need sufficient wing area to cruise at your chosen cruising altitude with the nose 5 degrees or less above prograde.   If you are having to raise the nose more than this, you'll get excess drag.  

For getting through the sound barrier on an underpowered ship, what i do is climb subsonic (below 240) until the air gets too thin to support the plane without raising the nose more than 7 degrees above prograde.  Then i reduce the nose angle so it's only a degree or two above prograde, let the plane fall into a shallow dive, and start gently easing back up again above 440.

 

 

Edited January 18, 2017 by AeroGav

[Reactordrone]

As an example, I just circumnavigated Kerbin in this aircraft in about an hour. Had 800 fuel left in the tanks on landing. Top speed was over 1200m/s but I had to drop to about 1000m/s sometimes to cool down the cockpit. 

 

Edited January 18, 2017 by Reactordrone

[dboi88]

Thanks so much for your help.

1 hour ago, AeroGav said:

It looks like you're using some modded engines there?

The two larger engines were tweakscaled panthers, i could fit any more on there.

1 hour ago, AeroGav said:

In terms of the stock engines,  Panther is no good if you want to go past 750 m/s,  it peaks there and thrust more or less falls to zero by 800.    It's going to be between the Whiplash and Rapier, which peak at 900 and 1150 respectively.    Looking at the atmosphere curves of these engines, thrust drops more slowly than air pressure up to 17km on the whiplash, then up to 22km on the Rapier.

Yep they were my problem, i was completely topping out at 820 every time. I've switched to the whiplashes and they are doing the job perfectly.

1 hour ago, AeroGav said:

Fuselage.   The mk2 fuselage has 3 times the drag of the mk1 but holds no more fuel.    It is more heat tolerant, but you 're using a mk1 cockpit.  Also parts at the front get the worst heat, if you were bothered about heat you could have just used a mk1 inline cockpit.   You can work around this problem, by adding an angle of incidence to your wings, but it's an "intermediate/advanced" technique.   Just stick to a mk1.

I needed the mk2 for the cargo bay. I had a working craft but it kept blowing up at 1200m/s so i switched to mk2 cabin and crew cabin for 4 seats seeing as the new craft was plenty powerful.

1 hour ago, AeroGav said:

Wings - The big S wings and strakes should be used , they store additional liquid fuel.  You can build tail fins out of big S strakes too. 

I've not changed the wings yet i just made them bigger. But i'm going to give that a go and see if i can get even more range out of it.

1 hour ago, AeroGav said:

For high speed with long range, you need to be flying at high altitude.  The higher the better, the lower your drag and fuel consumption.   But , you need sufficient wing area to cruise at your chosen cruising altitude with the nose 5 degrees or less above prograde.   If you are having to raise the nose more than this, you'll get excess drag.

I hadn't appreciated this at all. At 19,000 i get 12 mins of fuel, at 22,000 i get 1hr35mins! The bigger wings are what allowed me to reach this altitude where i had no chance of getting past 12km previously.

1 hour ago, AeroGav said:

For getting through the sound barrier on an underpowered ship, what i do is climb subsonic (below 240) until the air gets too thin to support the plane without raising the nose more than 7 degrees above prograde.  Then i reduce the nose angle so it's only a degree or two above prograde, let the plane fall into a shallow dive, and start gently easing back up again above 440.

I'll remember this but this thing will climb straight to 22,000m of the runway and be at 1350m/s when it get's there.

1 hour ago, Reactordrone said:

You should probably switch to Whiplash engines, they excel at high speed flight. The Mk 1 cockpit is also going to get pretty toasty flying for extended periods at Mach 3.

Yep they did the job. and yep that mk1 went boom!

34 minutes ago, Reactordrone said:

As an example, I just circumnavigated Kerbin in this aircraft in about an hour. Had 800 fuel left in the tanks on landing. Top speed was over 1200m/s but I had to drop to about 1000m/s sometimes to cool down the cockpit. 

I just completed my mission, dropping a KIS container with some emergency supplies at Baikerbanur, got there and back with fuel to spare! I'm going to refuel and go back out and see how far this baby can go!

Again thanks for all your advice, i couldn't have done it without you.

Safely back at KSC 

[bewing]

The first thing to understand is that MK2 parts have about 3 times (or more) of the drag of MK1 parts. So you absolutely want to minimize the number of MK2 parts -- and you certainly don't want to use MK2 for your entire fuselage.
Second, engines. Wheesleys max out a little over 600 m/s but are very efficient. The panther engines have 2 modes, dry and wet. In dry mode, they max out at 700 m/s but are pretty efficient. In wet mode they have a max speed of a little over 800 m/s and are slightly less efficient. Whiplashes max out at about 1400 m/s and are a little better than wet panthers. It is fairly easy to get 1600km range.

I understand you want cargo bays to drop your supply payloads. MK1 parts do not have cargo bays, so you need to use an MK2 cargo bay.

So what you want is a design that has MK1 parts for all the front fuselage, a MK1 to MK2 adapter, and then the MK2 cargo bay. This puts the draggy part in back where it will do some good for your stability. Then another adapter and a whiplash. BigS wing parts for free fuel storage.

So, something like this looks like it beats all your requirements (if you want a craft file, just say so):

 

[dboi88]

1 hour ago, Reactordrone said:

As an example, I just circumnavigated Kerbin in this aircraft in about an hour. Had 800 fuel left in the tanks on landing. Top speed was over 1200m/s but I had to drop to about 1000m/s sometimes to cool down the cockpit. 

I know i'm doing something right then, i just removed a fuel tank and managed to circumnavigate kerbin for the first time at around 1300m/s, 55 mins on touch down and then i screwed it up and crashed  . I came back on fumes though! had to turn off the two biggest engines about 20km when mechjeb said i had 19 seconds of fuel left.

30 minutes ago, bewing said:

The first thing to understand is that MK2 parts have about 3 times (or more) of the drag of MK1 parts. So you absolutely want to minimize the number of MK2 parts -- and you certainly don't want to use MK2 for your entire fuselage.
Second, engines. Wheesleys max out a little over 600 m/s but are very efficient. The panther engines have 2 modes, dry and wet. In dry mode, they max out at 700 m/s but are pretty efficient. In wet mode they have a max speed of a little over 800 m/s and are slightly less efficient. Whiplashes max out at about 1400 m/s and are a little better than wet panthers. It is fairly easy to get 1600km range.

I understand you want cargo bays to drop your supply payloads. MK1 parts do not have cargo bays, so you need to use an MK2 cargo bay.

So what you want is a design that has MK1 parts for all the front fuselage, a MK1 to MK2 adapter, and then the MK2 cargo bay. This puts the draggy part in back where it will do some good for your stability. Then another adapter and a whiplash. BigS wing parts for free fuel storage.

So, something like this looks like it beats all your requirements (if you want a craft file, just say so):

 

I'm going to see if i can make a plane with all mk1 parts for shuttling crew. I'll see if i can get something to go that fast with only one engine. My current design ended up with around 3700km range so i can make something much smaller for crew transports.

[AeroGav]

17 minutes ago, dboi88 said:

 

I'm going to see if i can make a plane with all mk1 parts for shuttling crew. I'll see if i can get something to go that fast with only one engine. My current design ended up with around 3700km range so i can make something much smaller for crew transports.

My tip - start with an inline cockpit and some crew cabins, then put engine nacelles either side of the crew area.    Now add fuel tanks ahead of and behind the crewed bits.     That way you got fuel tanks ahead of the cockpit, to absorb heat (and any landing crashes).

One engine at the back forces you to put the crew areas up front to balance the empty mass of the ship (with fuel going in the middle), and the cockpit gets heated.  If you put crew in the middle and engine at the back, with fuel up front, then the plane becomes tail heavy and unstable as fuel burns off.  

[Wanderfound]

You shouldn't need anything big and complicated for this.

Try something similar to this, but with the LF/O tanks swapped for pure LF and the RAPIER swapped for a Whiplash.

 

 

Note the slight wing incidence; to minimise fuselage drag, you want to set it so that your nose is pointed prograde when you're flying at speed. A few degrees is usually enough.

Edited January 19, 2017 by Wanderfound

[AeroGav]

One more thing - the OP has met his aims, but it's worth talking about the Breguet Range Equation for aircraft - depends on % of takeoff weight as fuel, lift:drag ratio and engine efficiency (ISP).

Lift:Drag ratio is highest subsonic, i've seen over 10 to 1 at 120 m/s, falling to 6:1 at 240.   Then it really takes a dive.  Between 0.9 and 1.2 mach, you'll have a hard time getting even 2:1.    Then it recovers somewhat, basically from mach 1.3 up to orbital speed,  l/d ratios are about the same , and i've managed 4.3:1 with some aircraft.

So, if time is no object, go subsonic.   Avoid transonic like the plague,  but most likely we're talking about a mach 1.3+ design.

If you're happy with less than mach 2,  you can make something that runs on panthers in non-afterburner mode,  with 9000 ISP these supercruising designs can be very economic.

However, Panther (dry) thrust falls off a clifff above mach 1.9.    And if you want to go faster than that, there's not much difference in the engines (afterburning panther - 4500isp,  whiplash 4000,  rapier 3200).    Bearing in mind that l/d ratios are about the same at mach 1.5 vs mach 6, there is no reason to go slow.  In fact,  a new factor starts to take over above mach 4, which makes things more economical the faster you go.

>>Orbital freefall.   Above mach 4,  orbital freefall effect supports an increasing proportion of your plane's weight, so you need less lift.   Given the same lift:drag ratio, that means lower drag is possible.     To realisise this theoretical advantage, you of course have to be holding nose at 5 degrees above prograde, and be at very high altitude.  Somewhere between 22km and flameout height (the higher the better).

TLDR - build a mach 1.6, 15km supercruiser using dry panthers - if that's not fast enough, then build a rapier bird to fly at mach 5.5 at 25km.