StarDestroyer.Net BBS

New month, new competition entry and this time it's a helicopter. The bullpup SMG won so I got to pick, and like a bloody idiot I once again picked something I've never made before. Helicopters! I decided on the road less travelled and went for a transport design, so I need some input from you military types and know-it-alls as to what's way wrong with the basic design. It's a big bugger, designed to hold a fair squad of guys and maybe a hummer or two as well. it'll have 4 retractable double-wheeled landing gear in the side pods and maybe some guns and shit. Go to it...

http://www.axeman3d.com/posts/helo2.jpg
http://www.axeman3d.com/posts/helo3.jpg

I'm not much of a 3D artist, I don’t have that much experience, but I like the overall shape. What prog are you using?

Looks good to me. Kinda reminds me of a Chinook helo.

Looks a bit too conventional. You ever think about maybe doing something with side-by-side intermeshing rotors?

Looks like a cross between a Chinook and a Commanche.

I like it. Its funky.

Looks good. It obvoiusly needs work, but it's not bad.

The rotor hubs need a lot more detail. They're very complex affairs that allow the rotor blades to have variable pitch, and to allow the entire assembly to tilt in the desired direction.
I think if you split the central disks vertically, and ad small rods from the main shaft of the rotor to the point where blades connect to it, it'll be primo.
And the overall design itself is just fine.

Well Frank, it's just a placeholder affair until i get round to that area, although from my research they're a fair representation of the very latest bearingless enclosed rotor heads being used on the next generation of Helos. It is a fairly conventional design, nothing too drastic, but I'm kinda limited that way by the subject. If we go too far into the future with our projection then we're into anti-grav and jet powered helicopter replacements, not actual rotary winged craft as the contest specified.

This is just by way of a computer doodle, it only took me 20 minutes to knock up in Lightwave and it shows the general layout and look I want to go for. I wanted a larger, beefier looking transport than the Chinook, it looks too skinny for my liking, and this is the shape I came up with. I did consider Kaman-style intermeshing rotor blades but it doesn't really translate well to a transport helo, a bit too unstable and dangerous to those moving around on the ground next to your helo.

My favourite helicopter is the CH-53 family, they're big and tough and look very muscular and menacing, but every time I try to make a similar design it comes out as a rip-off. That's the main reason i went for the double rotor. The reason i posted here was in case any of the guys in the services could spot something very wrong with the design, they might have insights I dont and I rather find out now than later.

The turbines should be at the back, like in the Chinook, as it is, the CG is too far forward, and the back rotor is lightly loaded, there is a unbalance between the two rotors, causing a lot of problems.
The rotorblades look good, increase a little bit more the chord for a slight nudge of future.

There will also be another two engines in the rear, balancing it up somewhat. Not sure yet if I'll mount them externally on the sides of the rear rotor pillar or if I'll embed them partially or fully in the pillar itself, but they will be visibly there. As for rotor design, it's hard to tell what's the best to go for. Some have the endpieces like the ones I made, possibly to increase area or to cure some problem, others have a sudden change in sweep angle neer the end where the tips are approaching the speed of sound. Also, should I have them bearingless AND twisting, rather than more conventional ones which rotate to vary the pitch? Any ideas gratefully received people, my rotor research is proving fruitless...

No need to have 4 engines, since 2 turbines provide enough power (the Huey, originally, had only 1 and did Vietnam pretty well...), if you mantain the engines at the front, you'll still have balancing problems, since the engines at the back will have to be a lot heavier, just so the CG can move back, not adding the weight of the gearboxes, oil, hydraulics and whatnot.
Yeah, engines at the front look cool, but in this case, realistically, they are unworkable.

Rotors:
The end tips are good, but your argument to cure problems isn't the right answer. Propeller design (which the rotors are part of) is an area of heavy research, and most problems are usually solved at an early stage, not after it's being installed on the helicopter.
Do a search for the Lynx, and it's rotor (forgot the goddamn name of the project), the tips are very similar to yours, and allow for high-speeds. (Suitable for the Lynx, we don't see it being applied on other helicopters.)

A little lesson in propellers, if you want heavy loads to be carried, diminish the number of rotations. Also, by increasing rotations, you'll increase the sound produced by the helicopter, since the rotor tips will be approaching the speed of sound, and we don't want that, just compared the sound from a Puma (4 - heavy), with the sound of a Gazelle (4 - light), and a Bell (2 - light).

As for scythe shaped rotorblades, the speeds involved must not be that big, and there's the centre of pressure of the blade to be considered, since they are extremely long, an offset center of pressure will cause unwanted torque and vibrations, something with nasty effects.
A larger chord will permit heavier loads to be carried, the only problem nowadays are the load problems on the rotor bearings, since having large blades cause unwanted torsion in the rotor.

Don't worry though, we're here to help you.

Judging by the rotorblade tips both rotors rotate in the same direction (counter clockwise when looking at it from above). Shouldn't they rotate in opposite directions like in the Chinook?

Sir Sirius wrote:Judging by the rotorblade tips both rotors rotate in the same direction (counter clockwise when looking at it from above). Shouldn't they rotate in opposite directions like in the Chinook?

Yeah, I spotted that when I did a test animation of the thing flying, it'll be fixed when I actually decide what type of rotors and blades to go for. I picked slow turning 5 bladed ones as they seemed to suit the size and application, but what the hell do I know? I also made the tips similar to the Lynx because I know the Lynx used to hold speed records, but again I don't know the details, I'll have to do some research.

I wanted 3 or 4 engines on the thing because it's a helluva size, at least half as big again as a Chinook, maybe more. I wanted lots of spare lifting power as I'm asking it to lift vehicles and troops in quantity, and I also wanted to have some redundancy in there as well. The chinook has an occasional fatal problem with it's gearing that interlinks the rotors, so in the near future I have cured that with electronics and multiple engines. Extra horsepower from more modern, lighter turbines cant be a bad thing either.

So, what's the recommendation for final blade config then? Size, tips, chord, number, whatever? I'm off to do a little digging on the subject, be back in a little bit

As long as you have 2 rotors, there will always be reliability problems, due to the mechanical connections from the engines's gearboxes to the rotors (specially the one farthest away). Puting more engines isn't going to cure the problem, probably it will compound it, but I understand what are you trying to achieve.

Now, that I think of it, the Merlin has 3 engines, one of it's points of sale being its reliabilty, but the engine is much smaller, and set in the middle of the other 2. Oh, well.


Brainstorm ideia: the turbines provide power to electrical motors, which in turn, power the rotors! This way, you can have smaller engines, the generators will be (fucking) heavy (you can cure that with technobabble), and there won't be long shafts and troublesome gearboxes, except at the turbines.


As for the rotors blades, 5 is good, length ok, tips nice, increase the chord a little bit to give a more future-look, and you're set!

Hmm looks like a good and sensible design (apart from the turbines like someone pointed out)

Kenny_10_Bellys wrote:New month, new competition entry and this time it's a helicopter. The bullpup SMG won so I got to pick, and like a bloody idiot I once again picked something I've never made before. Helicopters! I decided on the road less travelled and went for a transport design, so I need some input from you military types and know-it-alls as to what's way wrong with the basic design. It's a big bugger, designed to hold a fair squad of guys and maybe a hummer or two as well. it'll have 4 retractable double-wheeled landing gear in the side pods and maybe some guns and shit. Go to it...

http://www.axeman3d.com/posts/helo2.jpg
http://www.axeman3d.com/posts/helo3.jpg

Congrats on winning the competition last month.

Why are the side pods so big? Seriously, their volume is huge compared to the rest of the vehicle. I know this might be taking the piss slightly, but have you considered making the profile more triangular; blending the sidepods more into the main body so that tracked vehicles (traditionally wider at the bottom than the top) can fit more easily.

As to blade count, the worlds most prolific and powerful heavy lift Helicopter (Mil Mi-26) has 8 and they work fine, and allow the rotor speed to be dropped further without loss of liftpower (less strain on the engines, less fuel used, longer gaps between servicing).

You might want to look into somewhere up front to fit side doors as tey are pretty useful (if only for a gun to stick out of).

Lastly, is this bigger than a chinny? What's the maximum load you're looking at it carrying (Troop numbers/vehicle types)?

nice shape.

why do lightwave images always look so "grainy"?

It's due to the radiosity lighting effects. At least I seem to recall all of my friends images being grainy when he turns on radiosity.

As to what radiosity is, it's a method by which they try to simulate the ambient light more realistically than just assigning an ambient value. This helps make it look better usually.

They're grainy because I haven't turned on anything fancy like radiosity and anti-aliasing, they're just quick test shots. When I do a finished shot I use lots of AA and then run it through a mild (0.2 pixel) gaussian blur in photoshop to take any harshness away. All CGI pictures suffer a little from it, but these are because of the above and the fact the skin of the helo is like sandpaper, I haven't fixed the surface yet either.

It's about this big... http://www.axeman3d.com/posts/helo4.jpg

It can take a couple of Hummers or even Bradleys and some troops, and should certainly be capable of lifting something like an M1 underslung (thanks to it's 4 engines). Anyway that's what I'd like, a chinook on steroids. The sidepods hold the fuel and undercarriage, this thing will use a fair bit of fuel and retractable gear saves fuel and adds speed. A triangular cross-section isn't too lovely, and it makes side doors a bitch. I can fit doors just behind the cockpit, but I screwed it up so this is the version without.

Kenny_10_Bellys wrote:They're grainy because I haven't turned on anything fancy like radiosity and anti-aliasing, they're just quick test shots. When I do a finished shot I use lots of AA and then run it through a mild (0.2 pixel) gaussian blur in photoshop to take any harshness away. All CGI pictures suffer a little from it, but these are because of the above and the fact the skin of the helo is like sandpaper, I haven't fixed the surface yet either.

It's about this big... http://www.axeman3d.com/posts/helo4.jpg

It can take a couple of Hummers or even Bradleys and some troops, and should certainly be capable of lifting something like an M1 underslung (thanks to it's 4 engines). Anyway that's what I'd like, a chinook on steroids. The sidepods hold the fuel and undercarriage, this thing will use a fair bit of fuel and retractable gear saves fuel and adds speed. A triangular cross-section isn't too lovely, and it makes side doors a bitch. I can fit doors just behind the cockpit, but I screwed it up so this is the version without.

W00tX0rZ!

EDIT: Like my new Camaro paintjob (see "Fun With MSPaint!!!!" thread)? I even did the courtesy of doing a 3view of its Thumper cannons...

Kenny_10_Bellys wrote:
It's about this big... http://www.axeman3d.com/posts/helo4.jpg

It can take a couple of Hummers or even Bradleys and some troops, and should certainly be capable of lifting something like an M1 underslung (thanks to it's 4 engines). Anyway that's what I'd like, a chinook on steroids. The sidepods hold the fuel and undercarriage, this thing will use a fair bit of fuel and retractable gear saves fuel and adds speed. A triangular cross-section isn't too lovely, and it makes side doors a bitch. I can fit doors just behind the cockpit, but I screwed it up so this is the version without.

Fair enough, looking inside, you have a shitload of wasted headspace there, you could shrink the whole thing by 10% and still have a helicopter big enough to fit an M1 in, without the wasted internal headroom. As to the side doors, just shave a little off the front of the side pods and you're sorted. Don't forget an M1, or Chally 2 are only 3m tall (including the commanders MG), and the inside there looks to be closer to 4-4.5m based on a Humvee height of 1.8m.

Are you going to have the rear engines set into the cowling or seperate like on a Chinny (personally I think it would look good with them blended into the rear cowling). Also are you going to have any windows (troops like them as they can see where they are going, plus they, and the panels they are set in, are emergency exits on most heli's)?

On seating, you can have seats along the sides facing in and even with the smaller dimensions i mentioned above you could fit a central removable aisle of seats back-to-back facing out (when you have to lift in vehicles, you simply remove the centre aisle, and with anything below M1 size you can keep the side seating for troops, no worries).

For underslung loads, are you going with the Chinny solution of removing the floor panels to expose the loading bars (which is fucking brilliant as the troops inside can sit with their feet dangling out the bottom of the helicopter , though you have to be careful getting on and off as there is only a tiny lip to walk on next to the wall mounted seats ), or will you have the loading bars mounted externally, but recessed into semi-deep scallops in the bottom panels to prevent excess drag?

Scale is still flexible, but I wanted it to take a Humvee with ease and smaller tracked vehicles if it needed to, so I can play with size until I get it exact. I'm thinking recessed bars underneath for slinging points, I don't like the ideas of holes in the floor unless it's a hatch for fast roping or something, and that'll be opened inside. There will be a few windows, as you say they're also escape routes as well, and I'll work on the rear hatches and loading bay until I get a shape and size I like. I want workable doors and a decent ramp, that's the hard bit in anything like this, but I don't know if I'll go as far as a detailed interior yet. The engines will probably be recessed in the rear rotor pillar, it's certainly large enough to house them without difficulty. There'll just be intakes and vents visible on the outside to show that's where they are.

Kenny_10_Bellys wrote:Scale is still flexible, but I wanted it to take a Humvee with ease and smaller tracked vehicles if it needed to, so I can play with size until I get it exact.

Well maximum inside size will be 3m as that's the maximum height for the tanks and IFV's. After that go nuts.

I seriously doubt it could haul an M1, larger helicopters barely even lift a fraction of its weight. Even if you had the power, I don't think you could put it through the rotors.