helicopter design features
 

I know that among the users in the forum there are some wise men that might want to share knowledge...
I would like to learn what makes a helicopter more capable than others to perform hot&high.
Is it only a matter of engine??? If so... what makes an engine to stand better than others hot&high conditions???
If aerodinamic design of the heli itself makes any difference???
Any knowledge welcome ...I'm stilllearning !!!

To get more lift and to catch thin air means you need:

Big blades (longer chord) = more drag = more power = more weight (TMP & Trans) = more fuel ....

As a "system" you are chasing your tail to improve the performance on the dificult end.

Agile, all that is true, but when looking at performance charts, some have steeper lines than others, meaning that some helis loose performances faster than others when it comes to altitud and temp...WAT charts might get quite different from ones to others...what is that makes it work that way???

It might not be just engines - for example, I wouldn't like to try to operate a NOTAR at high altitude, despite how much power it has. Rotor blades on some machines can slow things down somewhat. Ans of course, pilot skill!

stilllearning,

The parts of the aircraft that the manufacturers got wrong are known as "helicopter design features" :rolleyes:

RVDT when I started this thread "design features" meant just the opposite: what makes the differences to perform better that others...
Probably the main point to begin with is to mount engines that don't reach their max performances at low levels and need quite high alt&temp to get near their max compressor RPM's ... but probably there is more to it that is what I was looking for ...

Better in what way? Whenever something is made "better" a price has to be paid elsewhere ie made worse. Big horsepower may give you great payload lift or high altitude capability, but at the expense of increased fuel consumption and reduced range. Mine would have been "better" had it been fitted with adequate ventilation, nothing more, it ran out of puff at high altitude or high temperatures, but since we were a sea level operation in mild temperatures it mattered not. On the plus side, because the engines were operating at high power in the cruise fuel economy was great.

megan, if I want a good performet hot&high I wouldn't buy a good performer at sea level. As simple as that... again: I am looking for technical answers not arguments on fuel consumption or airconditioned equipment...

there is no bulls eye answer to your question.
people will continue to take random shots at your target until you have your winner.

This is not an easy question to answer. Helicopters have been arguing with gravity since DaVinci first put ink on paper and everyone is "stilllearning". No manufacturer has perfected the perfect hot/high helicopter combination as of yet.

No disrespect but this is actually a professional pilot's rumour network?

If you want the right answers go to the right place?

There are a ton of books out there - start with Ray Prouty's books as they are pretty easy going yet tackle the questions you are asking.

One factor.
Turbine engines are most efficient when run at design (max continuous?) power.
So an engine that is powerful enough at altitude, will be inefficient at lower altitudes and power settings.

Probably similar with blades (big ones on top, and the tail feathers.)
IE the design that works well in thin air, might be high drag for the lift they generate in dense air.

As usual, “compromise” is the name of the game.

Does that help?

If you look at something like the Lama horsepower is the main factor to get performance at altitude.
A very powerful engine derated at lower altitudes to be able to perform at high altitudes.
The lama had a three bladed rotor system but a two bladed rotor system is the most efficient at altitude due to less parasite drag than a multi bladed system.

T&S and Fadecdegraded all that makes perfect sense and is the type of knowledge I was looking for ... important aspects of design. Thanks
RVDT...if you don't know just pass on and go to next thread ... don't understand your attitude ...NAMASTE

fadecdegraded - yes but you have less aerodynamic damping at altitude and the higher blade inertia with only two blades can make handling less desirable, especially coupled with a teetering head (as most two blade rotors are) it's all about Lock number apparently.

For someone who claims to have an ATPL and flies a 330 and be a TRI/TRE you do seem a little short on basic knowledge, just my observation. I think RVDT rumbled you.

Compromise..... And technical choices....That's all. Depending the result wanted : Speed, high and hot, maniability, Mountain flight, noise, payload etc.... The II Intelligent Ingeener make different choice to reach what the customer/market want...No more no less... And sometime you fly a very quiet helicopter without any defense on the pedal in high mountain... or very speedy helicopter but with a poor payload...
The perfect helicopter is only perfect for his customer and his use...

Megan is very good for you to see so many things about my knowledge through a few words and comments ...
After 40 years flying all I can say is that I am stilllearning and everyday I ignore a few more things about these wonderful machines and how they fly...
Again NAMASTE

Airbus (Eurocopter) designs have always been better high altitude machines. Bell and Sikorsky seem to be designed for operations near sea level. Having flown a Bell 205A into helipads at 13,000 MSL, I can tell you that the tail rotor was very limited, and autorotation ability was almost zero.

You want to go high altitude? You want less engines. Just look at the Lama and B3 Squirrel (altitude record for helis I think).

This should give best power to weight you can get (with sufficiently powerful engine obviously - efficient because you only have single gas generator to drive). Clearly you need to strip out any excess weight too (no redundancy like twin hyds for example).

I would also design the rotor for efficiency at high altitude (it'll fly like a pig at low level though). You would have to design control phasing for the altitude (Lock number effects) - you see this going wrong when flying a "sea level" helicopter at 20000ft - forwards back left and right all get skewed around. I would also increase control gearing/control power as everything gets a little sloppy on the controls.

I think a lower rotor speed would also be a good idea. The speed of sound is lower at altitude (ie lower temperature) so tip effects would kick in earlier. Longer blades might cause problems with tip effects so I think broader chord is the way to go.

Just some thoughts

Great comments! Thanks

Where is "Vertical Freedom" when we need him? supporting the merit of the B3 fantastic altitude performances...

Well, one of the Testpilots at Airbus said, that the 145T2 would be able to perform nicely at high altitude but they werenˋt allowed to extend the graphs to what is possible by Airbus France....
And thatˋs a twin and I ˋm willing to belive the guy beeing TQ limited all the time with both engines working with bleed valves open at MCP.....

FB-

That's a great point about twins being gearbox torque limited under most operating conditions (AEO). While engine performance will typically be adversely affected by lower pressure and/or higher temperature atmospheric conditions, the performance of the gearbox remains largely unaffected.

Consider the example of the EC145 twin. Each of its Arriel 1E2 engines has a T-O rating of 738shp and an MCP rating of 692shp at SL/ISA. The MRGB has a (AEO) T-O rating of 1040shp and an MCP rating of 848shp. You can see that the engines have plenty of power margin above the MRGB limit at SL/ISA, 42% at T-O and 63% at MCP. I don't have specific performance data for the engine, but it would require a reduction in power of 218shp per engine at T-O and 268shp per engine at MCP before matching the MRGB power limits (AEO).

In order to assist the threadstarter with his back yard construction project.

Make it a single. Unless you have someone to reliably and consistently pay the bills and want to scale the whole thing up to account for the lost payload.

As the target design altitude increases so will the tr thrust/mr thrust ratio, unless you really enjoy directional challenge.

Make the engine big. The higher the intended alt. The larger the "size"of the gas producer to the lonely power turbine(s). Make it torque out first, sooo much more intuitive and linear for judging your power situation. Even if it means pushing more fuel drums around.

As much as it is a safety feature it is a psychological salesmanship feature. That is...make the cabin small in relationship to the installed power and the size of the rotor disk. Everyone will be consistently amazed when it is loaded to the headliner with junk and full of fuel and "always flies away" Brings in more money with a second trip at lower elevations. Otherwise it gets really tiring explaining why only 30% of the seats can be filled. Hard on a girls reputation too especially if she is made by Bell.

Lock number / control cross coupling concerns, I am willing to bet aren't a problem this planet. We could ask VF about this. Fly by wire parts are found in the electrical section of the hardware store however.

On a side note, protecting the dignity of the Bell ladies. The 206L4 ha t/r, 417(eagle 407 hp) and 214b I am confident would happily keep up with the beloved ecureil b3. Though on a design note it is interesting to watch a spec. L4 walk away from a spec. 407 above 8000' pa ISA +20.

Hope this helps. Send pictures.

With a twin you will always have oversized engines to be able to fly away on one engine. No point making the Transmission larger (and heavier) as that is not the design goal for a category A helicopter. The twin is there for redundancy and not heavy weight lifting.

I reaaly appreatiate all your imputs
I am in no way trying to build anything, it just got my attention looking at a SuperPuma FM (AS332L2) that is limited for land/take off to 7000 ft DA ... for such a "powerfull" heli does not seem much altitud for a landing or take off...
That is way I wanted to know what differences are there is design that gives extra values when it gets hot&high.
Of course if you what to land above 20.000 ft you don`t take twins ... but that is not my curiosity. What I would like to learn is if such type of rotor performs better that others, type of compressors, blade design...and such.
I understand that is quite technical but I am sure there are some of us around that know somethings about all this.
Thanks to all of you in advance

Now that would be worth hearing. The cross coupling definitely does happen - I've seen it. It wasn't that bad though.

Great points about the size of the cabin though.