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Russian Helicopter Mil Mi-6

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Re: Russian Helicopter Mil Mi-6 - downloadlink in the first post

Postby Blender3D » Wed May 19, 2010 5:36 pm

The reason why you can't fly on one engine is simple (or at least what I think the reason is): Usually the engines aren't running at full power. Maybe at 75% or 80%. But that would mean that one had to adjust the default thrust for the engines to 0.75 or 0.8. If you the adjust the code via factors that you have the same flight-behavior as now with both at 100%, then you should be able to fly on 1 engine that is running at 100%. I hope you understand what I mean.

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Re: Russian Helicopter Mil Mi-6 - downloadlink in the first post

Postby HHS » Wed May 19, 2010 5:46 pm

Blender3D wrote:The reason why you can't fly on one engine is simple (or at least what I think the reason is): Usually the engines aren't running at full power. Maybe at 75% or 80%. But that would mean that one had to adjust the default thrust for the engines to 0.75 or 0.8. If you the adjust the code via factors that you have the same flight-behavior as now with both at 100%, then you should be able to fly on 1 engine that is running at 100%. I hope you understand what I mean.

--Blender3D


Yep, I understand. Currently I'm not sure if we really can map the engine-rpm to reltarget...
But your reason sounds logical. Hmmm...I will maybe tomorrow try to figure out how to let rune the engines at lower power....
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Re: Russian Helicopter Mil Mi-6 - downloadlink in the first post

Postby Maik » Wed May 19, 2010 6:20 pm

Hello,

some remarks to the "engine" code for helicopters in flightgear. The actual "engine" isn't a real engine. All you can define is the target rpm and the engine power. The governor is a very simple pd-regulator as written in the readme.yasim file.

To get more realistic engines there are two different possibilities:
1) modifiy the source code to connect YASim engines with the rotor code
The problem is, that the actual YASim turbine-engines are very simple. The result would not differ much from the actual status.

2) simulate the complete engine with Nasal. Therefore you need to set the target of the governor to a very high value (e. g. 10; using the <control> subelement ROTORRELTARGET). Also engine-accel-limit need to be set to a high value, e.g. 100. With this trick the governor does not regulate the torque of the engine. With a <control> subelement ROTORENGINEMAXRELTORQUE you can directly set the torque of the engine. (If you simulate two engines just pass the sum of their torques).

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Re: Russian Helicopter Mil Mi-6

Postby HHS » Thu May 20, 2010 8:29 pm

Thanks Maik for the explanation!

I think I've found out why mapping of the engine rpm to the main rotor doesn't work correct with the code above.
It assumes that both n2rpms a summarized bevor applying to the main rotorshaft.

For a two-engine heli it would like that:
Both engines are connected per gears with main rotorshaft. The gears transmit the power of both engine to the main rotor shaft. The rpm isn't summarized.
When just one engine is running (due to failure; not yet started...), we indeed just have half power.
But the running engine has still full rpm, which are transmitted to the rotors. Means the rotor will run though with full rpm. But when we raise the collective the power will maybe not be enough to keep the needed rotor rpm alive. Depending on the single engine power the rotor rpm will drop quite fast.

For an Ec135 40-50% 2x are enough to hover. But in EMS-config, from a high platform it needs 2x 75% Power.
With failure on one engine the other can provide 128% for a short time, but 22% are still missing...

So we have still to find out now how we can simulate this.
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Re: Russian Helicopter Mil Mi-6

Postby Blender3D » Thu May 20, 2010 9:08 pm

If you choose small thrust values (like 1lbs) you could use the thrust value as a projection of the power. So if you have a maximum thrust of 1, you just have to multiply this with 100 and you have the percent of power. That is the value you need. Then you can add the values of the two engines and you have what you need.

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Re: Russian Helicopter Mil Mi-6

Postby Maik » Thu May 20, 2010 9:28 pm

Blender3D wrote:If you choose small thrust values (like 1lbs) you could use the thrust value as a projection of the power. So if you have a maximum thrust of 1, you just have to multiply this with 100 and you have the percent of power. That is the value you need. Then you can add the values of the two engines and you have what you need.

--Blender3D


Hi Blender3D,

I don't think that this will work. If I understand you right, you would like to use two YASim jets to simulate two shaft-turbine engines. But @ constant altitude and temperature the thrust of a jet engine is "only" a function of its rpm. But the shaft turbine engine in a helicopter will always run a the same rpm independent from the produced torque / power.

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Re: Russian Helicopter Mil Mi-6

Postby Blender3D » Fri May 21, 2010 12:05 pm


I don't think that this will work. If I understand you right, you would like to use two YASim jets to simulate two shaft-turbine engines. But @ constant altitude and temperature the thrust of a jet engine is "only" a function of its rpm. But the shaft turbine engine in a helicopter will always run a the same rpm independent from the produced torque / power.


That would mean then that you just have to write a control-program that controls the throttle so that rpm will always stay constant. In addition one could program a user-controlled governor that will be used to give the pilot the control over the engine power.

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Re: Russian Helicopter Mil Mi-6

Postby HHS » Fri May 21, 2010 1:56 pm

You have to know how a turboshaft-engine works.

http://en.wikipedia.org/wiki/Turboshaft
as I understood usually N1 is the first shaft used by the compressor and combustion chambers.
N2 is the power shaft and attached by gears with the rotorshaft. Both shafts in the engine aren't connected each other.

So N2 should be always have the same rpm, while N1 can change.

Edit: also see: http://inventors.about.com/od/jstartinventions/ss/jet_engine_4.htm
The turboshaft engine is designed so that the speed of the helicopter rotor is independent of the rotating speed of the gas generator. This permits the rotor speed to be kept constant even when the speed of the generator is varied to modulate the amount of power produced.
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Re: Russian Helicopter Mil Mi-6

Postby Maik » Fri May 21, 2010 8:23 pm

Hi,
Blender3D wrote:That would mean then that you just have to write a control-program that controls the throttle so that rpm will always stay constant.
--Blender3D

Yes, exactly. This control program is a governor.

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Re: Russian Helicopter Mil Mi-6

Postby Maik » Fri May 21, 2010 8:26 pm

Hi,
HHS wrote:You have to know how a turboshaft-engine works.

So N2 should be always have the same rpm, while N1 can change.

Yes. But if you use an YASim jet there is no link from n2 to the rotor. The rotor does not give any torque to the jet. Therefore n2 will change with changing the power of the jet.

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Re: Russian Helicopter Mil Mi-6

Postby HHS » Fri May 21, 2010 8:42 pm

Maik wrote:Yes. But if you use an YASim jet there is no link from n2 to the rotor. The rotor does not give any torque to the jet. Therefore n2 will change with changing the power of the jet.

Maik


Yep, that's why I gave up using YASim engines, unless sometimes there is yasim engine support for helicopters.
So I guess currently there is no better way than using nasal.
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Re: Russian Helicopter Mil Mi-6

Postby Blender3D » Fri May 21, 2010 9:56 pm

As I understand turbo-shaft-engines, the power and rpm of the shaft that turns the rotor depends on the thrust produced. Then one could use the thrust of a yasim-jet-engine to simulate this.

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Re: Russian Helicopter Mil Mi-6

Postby HHS » Fri May 21, 2010 10:07 pm

Blender3D wrote:As I understand turbo-shaft-engines, the power and rpm of the shaft that turns the rotor depends on the thrust produced. Then one could use the thrust of a yasim-jet-engine to simulate this.

--Blender3D


well: http://www.nva-flieger.de/_tl/index.php/theorie/aerodynamik/hs/triebwerksleistung.html

Aturbo shaft engine is like a wind wheel:
If you blow a wind wheel you need indeed a certain power to to keep the rpm. But when somethings slows down the wind wheel (On the helicopter the increasing AoA of the blades; speed of the heli etc...) you need more power.
Problem is, that that there is no connection between the rotor and the YASim-engine.
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Re: Russian Helicopter Mil Mi-6

Postby Maik » Fri May 21, 2010 10:24 pm

Hi,

Blender3D wrote:As I understand turbo-shaft-engines, the power and rpm of the shaft that turns the rotor depends on the thrust produced. Then one could use the thrust of a yasim-jet-engine to simulate this.

--Blender3D

in principle: Yes. But I am not sure that this approach has an advantage vs. using the "engine" of the rotorgear or using a few lines of nasal simulating a simple turboshaft engine? The fuel flow is not realistic. The engine does not see any load, it is always idle. On a real turboshaft engine N1 (and not only N2) decreases if you increase the requested torque. YASim jet engines do not have an startup sequence.

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Re: Russian Helicopter Mil Mi-6

Postby Blender3D » Fri May 28, 2010 5:42 pm

New cockpit-details:

Image

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