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helicopter design features

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helicopter design features

Old 27th Oct 2017, 10:23
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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 !!!
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Old 27th Oct 2017, 11:50
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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.
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Old 27th Oct 2017, 17:01
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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???
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Old 28th Oct 2017, 13:10
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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!
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Old 28th Oct 2017, 20:05
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stilllearning,

The parts of the aircraft that the manufacturers got wrong are known as "helicopter design features"
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Old 29th Oct 2017, 10:20
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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 ...
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Old 29th Oct 2017, 10:38
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to perform better than others
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.
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Old 29th Oct 2017, 17:00
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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...
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Old 29th Oct 2017, 20:13
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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.
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Old 29th Oct 2017, 22:25
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I am looking for technical answers
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.
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Old 30th Oct 2017, 07:27
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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?
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Old 30th Oct 2017, 08:19
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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.
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Old 30th Oct 2017, 19:42
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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
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Old 30th Oct 2017, 19:55
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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.
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Old 31st Oct 2017, 10:52
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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.
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Old 31st Oct 2017, 11:49
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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...
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Old 31st Oct 2017, 18:35
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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
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Old 31st Oct 2017, 18:43
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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.
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Old 31st Oct 2017, 22:23
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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
 
Old 1st Nov 2017, 12:18
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Great comments! Thanks
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