Aircraft speed is absurd or natural?

[AtomicIrishman]

Hi folks! I seem to be having a really unusual problem, no matter what I'm building, no matter how heavy it is, my heavy spaceplanes always seem to go supersonic(Hitting mach 1 in less than a minute!) And while thats neat, its not really fun and is frankly killing my enjoyment of the game. Now, I do have FAR installed and tons of other mods with spaceplane parts, but I dont recall any known jet airliner with standard turbine engines capable of hitting mach 1. Is there some setting or mod I missed that might be causing this?

[Human Person]

You're right. It's part of the reason I'm sticking to good ol rocketry.

[UmbralRaptor]

What sorts of engines are you using? (Relatedly, how long did it take a Concorde to go supersonic?)

[AtomicIrishman]

3 minutes ago, UmbralRaptor said:

What sorts of engines are you using? (Relatedly, how long did it take a Concorde to go supersonic?)

Im using some B9 engines I believe, theyre similar to standard jet liner's engines like you might see on 747's or 737's And as for the concord's acceleration, I cant seem to find an accurate source.

[Aegolius13]

I can't speak to modded engines, but the stock turbofans (Wheesley and Goliath) can go well past Mach 1.  Yeah, it's unrealistic compared to real-world equivalents, but I guess they figure KSP players want a little more speed (and I still find these engines too slow for my own use).  

Maybe it would work to either use fewer engines, or if you want to keep the same number around for aesthetic purposes, turn down the thrust limiters.

 

[Spricigo]

1 hour ago, AtomicIrishman said:

 but I dont recall any known jet airliner with standard turbine engines capable of hitting mach 1. 

Not for lack of capable engines,  but for several other factors.

e.g.  Noise is an important reason to not use supersonic airliners in real life but in KSP is totally irrelevant. 

[AtomicIrishman]

5 minutes ago, Spricigo said:

Not for lack of capable engines,  but for several other factors.

e.g.  Noise is an important reason to not use supersonic airliners in real life but in KSP is totally irrelevant. 

Right but when Im making a heavy bomber(similar in size and weight to a B-52,) Theres no way it should be doing mach 1

[Spricigo]

1 minute ago, AtomicIrishman said:

Right but when Im making a heavy bomber(similar in size and weight to a B-52,) Theres no way it should be doing mach 1

Fair point.  

But I keep mine: KSP vessel performance is not that far from what you expect from real life counterparts. However discrepancies will exist because of intrinsic divergences in the environment. Engines in game don't need to trade performance for reliability,  an unexpected change in cost of materials and fuel will not happens,  and the list goes on.  Those are factors that, while important in real life,  don't need to be made present in game and devs (and mod makers)  don't want to bring it (maybe not even had realised some of these ). 

I understand it can be frustrating if you are looking for that kind of depth.  But other than searching for,  or even develop it yourself,  a mod that implement it, I  don't see much that can be done. 

 

[UmbralRaptor]

I'm insufficiently familiar with the details of B9, but wanted to point out that depending on the engines selected and details of aircraft design, supersonic flight might be easy. Just because an engine "looks like" it belongs on a 747 doesn't mean it isn't perfectly suited to operate on a supersonic bomber.

1 hour ago, AtomicIrishman said:

Right but when Im making a heavy bomber(similar in size and weight to a B-52,) Theres no way it should be doing mach 1

Given the supersonic capabilities available to the B-70, B-1A, Tu-22M, T-4, and Tu-160, I'm uncertain about that.

[HebaruSan]

1 hour ago, AtomicIrishman said:

Right but when Im making a heavy bomber(similar in size and weight to a B-52,) Theres no way it should be doing mach 1

Just curious, why do you want to go slow? I'm not going to comment one way or another on whether it's realistic, but what gameplay activities are there involving flying planes below 300 m/s?

[Reactordrone]

A Wheesley has about the same thrust as a CFM-56. That's the same engine used on the 737 so build a 50-70 tonnes aircraft powered by two of them and see how fast you can get.

[AtomicIrishman]

21 minutes ago, HebaruSan said:

Just curious, why do you want to go slow? I'm not going to comment one way or another on whether it's realistic, but what gameplay activities are there involving flying planes below 300 m/s?

I just want to fly as fast as normal aircraft would fly, and if I want to build a supersonic craft, i can have that differentiation in the build. But if Im gonna build a plane similar to a B-52, Id rather it not go supersonic, thats all.. just how I want to play.

 

7 minutes ago, Reactordrone said:

A Wheesley has about the same thrust as a CFM-56. That's the same engine used on the 737 so build a 50-70 tonnes aircraft powered by two of them and see how fast you can get.

Ill give it a shot, thanks.

37 minutes ago, UmbralRaptor said:

I'm insufficiently familiar with the details of B9, but wanted to point out that depending on the engines selected and details of aircraft design, supersonic flight might be easy. Just because an engine "looks like" it belongs on a 747 doesn't mean it isn't perfectly suited to operate on a supersonic bomber.

Given the supersonic capabilities available to the B-70, B-1A, Tu-22M, T-4, and Tu-160, I'm uncertain about that.

The B-52 has a max velocity of 622mph, its not built like the ones you mention, those are lots of swept wing, high velocity craft.. the B-70 alone looks like a concord.

Edit: Im not looking to make supersonic bombers as much because every time I build anything resembling a common airliner it still goes supersonic unless I give it crazy weight.

EDIT EDIT: The thing is, my aircraft are hitting the soundbarrier super easily and I cant figure out why, even using some stock engines.

Edited July 20, 2017 by AtomicIrishman

[Weywot8]

@AtomicIrishman, not entirely sure how you've built the plane. Anyhow, I suspect that for your case use, there are few points contributing to your disappointment

• Play-ability considerations means that the engines produce similar thrust to their real life counter-parts (e.g 757 engines) but weigh 50-80% less than their real life counterparts. Not entirely sure about their thrust curve profiles either but it would be safe to bet that those are skewed to produce higher performance either. Like what @HebaruSan was implying.
• Build specific issues - are you carrying 140t of fuel like the B-52 bomber? Is it truly a 230t B.U.F.F.?
• Stress tolerance of the real B-52's wing - isn't that also a reason for speed limitations? FAR let's you reduce the structural strength of wing joints in exchange for lighter weight. But watch those wings disintegrate at higher speeds! The B-52's operational endurance and range partially reflects this tradeoff. With high drag at the trans-sonic range killing fuel efficiency most aircraft designs consciously choose to be sub-sonic and optimize around that, including wing tolerances. Having said that, the rated V_max is kinda like a "best before date" - the actual V_NE (Never Exceed, unless you are OK with potential permanent structural damage) can be higher by 10-15%
• And lastly - the B-52's has old, heavy engines that produce something like 35% the thrust of a 757 engine.

Flipping this line of thought around, if the B-52 (which can do a respectable Mach 0.9, easy) had the same build & performance characteristics as your KSP plane, it too can hit Mach 1.  Especially if the pilot is anything like Jeb and completely ignores fuel efficiency considerations and just floors it from the runway. Also, no birdstrikes at low altitude on Kerbin and other safety considerations...

Edit: @AtomicIrishman, I think you mean delta wing - the B-52 has swept wings

Edited July 20, 2017 by Weywot8

[EpicSpaceTroll139]

Do you have the AJE (advanced jet engines) mod? It modifies jet engine performance to be more similar to real life. Without it jet engines can seem overpowered in FAR. 

It might also be helpful to have a picture of your plane. You may have just stumbled on a design with really low wave drag or something.

Edited July 20, 2017 by EpicSpaceTroll139

[AtomicIrishman]

9 hours ago, EpicSpaceTroll139 said:

Do you have the AJE (advanced jet engines) mod? It modifies jet engine performance to be more similar to real life. Without it jet engines can seem overpowered in FAR. 

It might also be helpful to have a picture of your plane. You may have just stumbled on a design with really low wave drag or something.

It doesn't look like theres an up to date version of AJE but Ill try it out, has somebody else picked up the project or is there a new version I havent seen?

 

19 hours ago, Weywot8 said:

@AtomicIrishman, not entirely sure how you've built the plane. Anyhow, I suspect that for your case use, there are few points contributing to your disappointment

• Play-ability considerations means that the engines produce similar thrust to their real life counter-parts (e.g 757 engines) but weigh 50-80% less than their real life counterparts. Not entirely sure about their thrust curve profiles either but it would be safe to bet that those are skewed to produce higher performance either. Like what @HebaruSan was implying.
• Build specific issues - are you carrying 140t of fuel like the B-52 bomber? Is it truly a 230t B.U.F.F.?
• Stress tolerance of the real B-52's wing - isn't that also a reason for speed limitations? FAR let's you reduce the structural strength of wing joints in exchange for lighter weight. But watch those wings disintegrate at higher speeds! The B-52's operational endurance and range partially reflects this tradeoff. With high drag at the trans-sonic range killing fuel efficiency most aircraft designs consciously choose to be sub-sonic and optimize around that, including wing tolerances. Having said that, the rated V_max is kinda like a "best before date" - the actual V_NE (Never Exceed, unless you are OK with potential permanent structural damage) can be higher by 10-15%
• And lastly - the B-52's has old, heavy engines that produce something like 35% the thrust of a 757 engine.

Flipping this line of thought around, if the B-52 (which can do a respectable Mach 0.9, easy) had the same build & performance characteristics as your KSP plane, it too can hit Mach 1.  Especially if the pilot is anything like Jeb and completely ignores fuel efficiency considerations and just floors it from the runway. Also, no birdstrikes at low altitude on Kerbin and other safety considerations...

Edit: @AtomicIrishman, I think you mean delta wing - the B-52 has swept wings

Thank you for all the helpful tips and comments, ill look into all of it <3

[tseitsei89]

On ‎20‎.‎7‎.‎2017 at 8:49 AM, AtomicIrishman said:

 

The B-52 has a max velocity of 622mph, its not built like the ones you mention, those are lots of swept wing, high velocity craft.. the B-70 alone looks like a concord.

Just one more thing I didn't see mentioned. I think that KSP's drag model unfortunately doesn't really care if your wings are swept back or not