St4rdust

KSP Loading... Preview: Breaking Ground - Propeller and Helicopter Blades

Recommended Posts

 

On 7/5/2019 at 1:01 AM, Tonka Crash said:

The helicopter blades look like your modeller used a toy quadcopter or wind turbine as his reference. These rotors don't look like any blades I've ever seen on a real helicopter. Helicopter rotors usually a constant chord and if there is taper it's only near the tips.

One exception doesn’t make the rule, but I’m going to assume that for modelling purposes short, stubby blades were preferred over long ones. And we do have a real world example of short stubby helicopter blades (and also the answer to “why?”)

300px-MV-22_mcas_Miramar_2014.JPG

Share this post


Link to post
Share on other sites
1 hour ago, Azimech said:

Check the turboshaft topic, sort of parallel discussion about this.

 

I see nothing in that thread that addresses the claim number you made, care to quote the specific part?

Share this post


Link to post
Share on other sites
On 7/5/2019 at 1:05 PM, Azimech said:

Guess I'll really only focus on piston engines, gearboxes and suspensions from now on <_<

We don't know that, yet.

Yes we do, one part propellers from mods don't get funky when they speed up.

Share this post


Link to post
Share on other sites
34 minutes ago, Quoniam Kerman said:

Yes we do, one part propellers from mods don't get funky when they speed up.

We know it's possible to make a one-part propeller assembly (that's not actually a a propeller it just converts ec into forward thrust) but we don't know if the stock parts will behave in any way like that.

Share this post


Link to post
Share on other sites
1 hour ago, Kerbart said:

 

One exception doesn’t make the rule, but I’m going to assume that for modelling purposes short, stubby blades were preferred over long ones. And we do have a real world example of short stubby helicopter blades (and also the answer to “why?”)

300px-MV-22_mcas_Miramar_2014.JPG

Strictly speaking that's not a helicopter. Tilt rotor blades have to deal with different design issues than helicopters rotors. The blades have more in common with normal airplane propeller blades than helicopter rotors.

Share this post


Link to post
Share on other sites

Strictly speaking, when the engine pods are rotated up, it is a helicopter.

Helicopter literally means rotary wing (well, spiral wing, from the greek Helix= spiral and pteron=wing). Prop and rotor blades are fundamentally the same as a wing. Anything designed to hover/fly with prop thrust providing the lift, is a form of helicopter.

Google:

"noun

 
a type of aircraft which derives both lift and propulsion from one or more sets of horizontally revolving overhead rotors. It is capable of moving vertically and horizontally, the direction of motion being controlled by the pitch of the rotor blades."
 
 
Merriam Webster:
"Definition of helicopter (Entry 1 of 2)

: an aircraft whose lift is derived from the aerodynamic forces acting on one or more powered rotors turning about substantially vertical axes"

 

Share this post


Link to post
Share on other sites
2 hours ago, Tonka Crash said:

Strictly speaking that's not a helicopter. Tilt rotor blades have to deal with different design issues than helicopters rotors. The blades have more in common with normal airplane propeller blades than helicopter rotors.

Design issues that apply to KSP too, perhaps? Low RPM --> High Torque (for the same amount of power). To transfer that torque you'll need more material at the root. Strictly speaking you don't need it, but there'll be plenty of folk here to point out you do.

As for "not being a helicopter" - that's a matter of definition. They're not propellers either, and they had to be put in some category.

Share this post


Link to post
Share on other sites
25 minutes ago, Kerbart said:

Design issues that apply to KSP too, perhaps? Low RPM --> High Torque (for the same amount of power). To transfer that torque you'll need more material at the root. Strictly speaking you don't need it, but there'll be plenty of folk here to point out you do.

Different design constraints apply to KSP since it's a game that doesn't simulate real world aerodynamic flow or material properties.

What you may be seeing as more material at the root, I see as an optical illusion created by the twist of the blades which is due to needed for an efficient propeller design for cruise performance. Also the root is fatter than aerodynamically necessary to incorporate a folding mechanism for shipboard storage.  

A closeup of a MV-22B's rotor and engine tilted slightly upward.

36 minutes ago, Kerbart said:

As for "not being a helicopter" - that's a matter of definition. They're not propellers either, and they had to be put in some category.

If you want to categorize them, they are referred to as proprotors on tiltrotor designs. They are their own beast compared to propellers or helicopter rotors. They are a compromise design needing to cover both vertical takeoff/landing and economical cruise performance, but not optimized for either case. They are bigger than needed for cruise and really smaller than desired for hover. In the case of the V-22 there are a lot of other constraints that come into play from shipboard compatibility that also affect the final design.

In KSP it doesn't matter, you could probably use any of the new propeller or helo rotors for a tiltrotor design.

As far as calling the V-22 a helicopter because it hovers isn't really relevant. Any aircraft with sufficient thrust to weight ratio can hover. Even a biplane:

 

Share this post


Link to post
Share on other sites
Posted (edited)

Despite how KSP treats them, in real-life lift and thrust are simply forces that counteract other forces in flight, and is not dependent on the method of generating the force.  Lift is any force that counteracts the pull of gravity, and thrust is any force that counteracts drag.  Helicopter blades and propellers are not the same, from an aerodynamic design standpoint.  Yes, they both spin and direct air to produce a force, but that's about it.  Helicopter blades are indeed airfoils, which is why they are termed "rotary-wing"; propeller blades are more akin to a boat's propeller screw, which is why they are also called airscrews.  A helicopter blade and propeller blade are shaped quite differently because they operate in different aerodynamic regimes.

A helicopter rotor system spins to produce lift, gently lifting the aircraft off the ground, after which it is tilted in a direction to offset the lift vector to generate thrust in the direction it is tilted.  But for the most part, helicopter blades operate in an environment where the air is moving horizontally through the rotor disc, which leads to complex aerodynamic effects such as dissymmetry of lift and retreating blade stall.

Propellers on the other hand operate in an environment where the air is rapidly passing perpendicular through the disc's rotational plane, and they must be shaped accordingly. As @Tonka Crash said, the V-22's blades are not helicopter blades per se.  They are a hybrid called prop-rotors.  The V-22's prop-rotor blades are designed in such a way to be sufficient to produce lift/thrust force whether air is passing across the rotor disc in "helicopter mode", or passing through the disc at relatively high speeds in "airplane-mode".  But the blades are not as efficient as rotor blades in producing vertical lift, nor are they as efficient as propellers at producing horizontal thrust.  Their "small" diameter is in fact a function of mission, not aerodynamics.  In order to operate on board naval amphibious task force vessels like LHD's where space is limited, the rotor blades themselves are somewhat "clipped" (even then the width of a V-22 with engines running is over 84 feet!).  This clipped diameter and prop-rotor hybrid design has led to the V-22 having very poor auto-rotational capabilities compared to conventional helicopters, as well as a much larger "height-velocity avoid" region.
_______________________________________________

Now, regarding how KSP treats thrust as a named computer-coded force within the game appears to be different than how it handles aerodynamically produced force vectors (that can be displayed via the F12 key).  From what I've observed, and I could be wrong because I'm not a coder or modder, propeller engine assemblies and helicopter rotor system parts from some of the more popular mods are coded in a way to mimic engines, and produce KSP-calculated "thrust"; whether that thrust is directed downward to lift the craft, or directionally to thrust the craft in a direction.  "Lift" in KSP is aerodynamically-generated from the movement of parts with "lift" values through the KSP atmosphere, and the vectors of the computer-coded "lift" force is generated perpendicular to the part, regardless of the total aerodynamic properties of the craft itself.  This is the core difference of how FAR handles aerodynamics compared to the stock system.

Regarding the differences of the propeller parts vs helicopter blade parts, I imagine that the main difference is strictly the choices in length.  The longest propeller blade is the same length as the shortest helicopter blade.  I imagine they are treated the same way within the KSP physics engine, but have their coded aerodynamic values balanced in such a way to achieve the desired effect of what a player would expect from making a propeller engine and a helicopter rotor system using the said previewed R121 and R7000 engines.

EDIT:......Annnnnd, ninja'ed by @Tonka Crash

Edited by Raptor9

Share this post


Link to post
Share on other sites
On 7/6/2019 at 3:54 AM, Chryssalid 8492 said:

I give it about five minutes tops.:)

That sounds like a challenge...

Share this post


Link to post
Share on other sites

I especially like how the blades are separate from the engines, allowing any and all configurations to try out! I can't wait! :D

Share this post


Link to post
Share on other sites

so now we have all parts for a dragonfly mission in KSP, great.

Share this post


Link to post
Share on other sites
Posted (edited)
8 hours ago, JERONIMO said:

so now we have all parts for a dragonfly mission in KSP, great.

But.... we already did... These new models look nice, but I'm still waiting to hear how they are different from the normal aero surfaces that we have been using.

We've been told that they don't work the same, and don't have the same "issues", but ... how? They are still aerodynamic surfaces that produce lift. We have aerodynamic surfaces that produce lift... I really want to know what these do differently, and what the functional difference is between the 2m prop and 2m helo blades.

Edited by KerikBalm

Share this post


Link to post
Share on other sites
4 hours ago, KerikBalm said:

But.... we already did... These new models look nice, but I'm still waiting to hear how they are different from the normal aero surfaces that we have been using.

We've been told that they don't work the same, and don't have the same "issues", but ... how? They are still aerodynamic surfaces that produce lift. We have aerodynamic surfaces that produce lift... I really want to know what these do differently, and what the functional difference is between the 2m prop and 2m helo blades.

Some explanation from @JPLRepo that was posted during @Rocketology's stream. Maybe this will help a bit. 
bdnjywKFMVg.jpg

Share this post


Link to post
Share on other sites
Posted (edited)

Ok, so they separate from the rotor less (CoM offset like they have for jet engines)?

They "compensate" for the 500 rpm limit... how? this is what I want to know.

We also don't know about the difference between the prop and the helo 2.0m blades

Edited by KerikBalm

Share this post


Link to post
Share on other sites

Nice work, but how about some more "space" parts, like functional Habitat/science modules for stations/bases?  

Share this post


Link to post
Share on other sites

"blade pitch. via authority limiter.Which is there today, but doesn't work correctly using elevons as blades"

I am assuming this refers to how control surfaces often 'flip' deployed state (ie up vs down) when they cross the center of mass centerline.  If so this will be a big improvement.  Currently at high speed they spend a lot of cycle time slowly moving from state to state.  Try rapidly pausing rotating props and you often see it.

Share this post


Link to post
Share on other sites

Okay, I'm starting to feel spoiled with all the amazing additions to the game and its DLC...

That said, I've really seen this game mature, especially recently. Just need a visual overhaul and some nuclear reactor parts...

Share this post


Link to post
Share on other sites
Posted (edited)

So to address a couple of issues that have come up in this thread.

1.  The helicopter blades in those images were tilted back in a fashion to get them to fit within the image frame.  Like someone took a picture from near the root-end, which is making them look leaf-shaped.   The in-game ones are much closer to what you'd see in a real helicopter.

2.  The propellers, and to a lesser extent the helicopter blades, calculate their velocity/AOA from an artificially offset position.  This allows them to act like they're at a higher RPM than they actually are, to get around the PhysX RPM limit, with the consequent effect on AOA, drag, and lift.   They also use their own aerodynamic values with a lift peak closer to a realistic AOA value than standard KSP aerodynamics.   Pitching your blades is still 100% necessary, but the pitch amounts are more reasonable and realistic.

3.  The blades have been set up so you can deploy and use the authority limiter to adjust the pitch of the blade - which you can easily do with KAL.  So you don't have to set up a servo system to do variable pitch, and therefore  you can set up a propeller with just a rotor, two blades, and a nosecone and have a workable system.

These were on the drawing board for a while, but our time frame from BG meant we had lots of ideas that didn't get in.  We saw how many people were really interested in rotor craft though so the team pushed hard to get these into the 1.7.3 patch.  There are definitely a few things that we'd still like to do with them, but I think this will give a better & more aesthetic result than the elevon-based craft that the locale Kraken-mechanics have been rigging up up to this point.

Edited by Maxsimal

Share this post


Link to post
Share on other sites

@Maxsimal Thanks for clearing that up :D I'm waiting with anticipation to build some crazy helicopters when the patch comes out.

Share this post


Link to post
Share on other sites

@Maxsimal  Awesome! So I take it then that the electric rotors we have now when used with the Helicopter blades will work Aerodynamically the same as the Fuel based rotors. So lift properties won't be reliant on Fuel rotors versus electric rotors?

Share this post


Link to post
Share on other sites
5 minutes ago, mindstalker said:

@Maxsimal  Awesome! So I take it then that the electric rotors we have now when used with the Helicopter blades will work Aerodynamically the same as the Fuel based rotors. So lift properties won't be reliant on Fuel rotors versus electric rotors?

No.  The only core difference between the LF rotors and the electric ones are which resource is consumed.  There are of course other tuning differences.

In fact, the propeller blades should also work if you attach them to anything that spins fast enough - one reason we selected this approach is its a little more Kerbal (for better or worse!) than what you see in many mods.   You'll have to learn about propeller dynamics to build a craft that works well.  One of our testers suggests this video as a great resource, many of the dynamics of real world propellers apply to the these.
 


 

Share this post


Link to post
Share on other sites

Btw, this is what a helicopter blade looks like without the perspective issue.

 

Share this post


Link to post
Share on other sites
3 hours ago, Maxsimal said:

Btw, this is what a helicopter blade looks like without the perspective issue.

 

Is that picture from the internal Squad network? It doesn't show it on the forum and when I tried to open it in the new window, it just redirected me to kerbalspaceprogram.slack.com and requested a sign in. 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.