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Old 10-16-2017, 03:07 PM   #1
Smokin Hole
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Default Bug (maybe) and General Impressions after 10/17 Patch

I love this little helicopter. But not in its current form. I have lots of what I perceive to be errors, particularly it's continued lack of stability and predictability (reply, "Helicopters are supposed to be unstable!" if you wish).

But an error that I am pretty confident with is the Gazelle's amazing performance in a sustained steep turn. Do this:

Start up in the desert at a moderately high altitude spot. Arm with enough HOTs and fuel to be at max takeoff weight. Lift into a hover and note power required. Now gently accelerate forward to whatever speed that roughly 90% collective (bottom of yellow torque) will hold; probably something around 200 kph. Now roll into a turn either direction with at least 45 degrees of bank. Apply a little bottom rudder to keep the nose down (yes, I am aware that this is not proper technique). Try to concentrate on a constant altitude but don't change the collective. Note after a sustained turn of several rotations that you are maintaining 200 kph with the same power setting. In fact I GAIN about 5 - 10 kph. I won't do the math here but basic trigonometry says that the lift vector (the hypotenuse) will need to be much longer in order to maintain altitude (VCL). And this goes without even getting into sources of added drag like my bottom rudder.
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Old 10-17-2017, 01:55 AM   #2
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Thanks,

I will test this with our internal testbed and the DCS 2.1 version to see what is going on.

The following should be similar to any helicopter out there

Bank Angle -------- Increase in Tr (%)

0 ---

15 --- 3.6

30 --- 15.4

45 --- 41.4

60 --- 100

[resource US Army aviation]

The percentages shown are not a direct torque percentage, but the percentage of torque increase required based on aircraft torque to maintain straight and level flight. That is, if indicated cruise torque is 48% and a turn to 60 degrees is initiated, a torque increase of 48% (96% torque indicated) is required to maintain airspeed and altitude.

As mentioned I will check that tomorrow
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Old 10-17-2017, 05:12 PM   #3
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Thanks Borchi!
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Old 10-17-2017, 06:19 PM   #4
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Quote:
Originally Posted by borchi_2b View Post
Thanks,

I will test this with our internal testbed and the DCS 2.1 version to see what is going on.

The following should be similar to any helicopter out there

Bank Angle -------- Increase in Tr (%)

0 ---

15 --- 3.6

30 --- 15.4

45 --- 41.4

60 --- 100

[resource US Army aviation]

The percentages shown are not a direct torque percentage, but the percentage of torque increase required based on aircraft torque to maintain straight and level flight. That is, if indicated cruise torque is 48% and a turn to 60 degrees is initiated, a torque increase of 48% (96% torque indicated) is required to maintain airspeed and altitude.

As mentioned I will check that tomorrow
Borchi,

first of all, thanks for the info. But could you state where exactly you got the numbers from?
Tbh, i can't believe they are true and the same for every helicopter.
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Old 10-17-2017, 06:46 PM   #5
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These numbers are from a Flightmanual of the US Army that is called manuvering flight handbook.
I talked to one of my us army contacts and these numbers do fit well for the majority of all helicopters cause it takes all into concideration and it deals with coeficient calculations of rotors. There is way more described in these manuals and I do know that the us army does not come up with made up numbers cause lifes depend on it a lot, so exil, you can believe the numbers
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Old 10-17-2017, 07:49 PM   #6
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Quote:
Originally Posted by borchi_2b View Post
These numbers are from a Flightmanual of the US Army that is called manuvering flight handbook.
I talked to one of my us army contacts and these numbers do fit well for the majority of all helicopters cause it takes all into concideration and it deals with coeficient calculations of rotors. There is way more described in these manuals and I do know that the us army does not come up with made up numbers cause lifes depend on it a lot, so exil, you can believe the numbers
Hey sorry, my question wasn't supposed to be offensive.

I was just confused because i didn't read your post carefully enough. I thought, you would state that you always have to add 41% TQ to maintain a level flight at 45° bank. No matter what your current used TQ is at that moment.

But you are totally right! It depends on the load factor which is increasing during a turn. As stated, it is in fact always like that in every helo. It's just physics.
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Old 10-18-2017, 12:11 AM   #7
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@exil:
I dd not take anything as offense. Just tried to explain where the numbers come from. But unfortunately I have no such numbers specific tot he gazelle at the moment. Trying to get the correct numbers for her cause they differ a bit in little do to some specific factors, but it would fill a complete page to explain why and where it comes from and how the manuver is flown and so on and so on. Simulating a rotor is not comparable to a fixed wing at all from which we could generate windtunnel simulations as soon we have the airfoil. A rotor is a bit more complicated.

I like the phrase " a bit "

So as you guys can see, I am striving to find good and reliable intel on certain things. Funny is that real pilots never think of such intel cause they just fly and do the things they have to do.
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Old 10-18-2017, 01:16 AM   #8
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Even without the hard data. (I am a pilot, not a coder and obviously not an engineer), much of the difficult math you have already done to get the helicopter into a hover with a plausible power setting. More math and tables were needed to accelerate to speed with a given amount of weight and drag. There isn’t much hard stuff left to do in a steady-state turn. You’ve lost an easily calculated amount if vertical lift component and must compensate with enough power to cover the diference. The Army’s numbers seem right. In my example we were using 90% power to hold 200 kph leaving us 10% in reserve to climb. The Army percentages are the amount of that ten percent that is eaten by the bank angle (or load factor).

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Old 10-18-2017, 04:41 PM   #9
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@smokin hole:
I had some talks yesterday to an us army pilot and a royal army pilot about these numbers.
It was a very interesting talk to bth and how they approached these numbers from different perspectives. We even talked about stuff lick musing and such, but at some point we have to understand that DCS is a game/simulations even with its own limits and there is now way that real life will be simulated to 100%. For that you would have to start a simulator engine from sratch and make a concept what you want to simulate in which detail.

Still we add details in the fm as soon we have solved values and aspects of how to include the intel
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Old 10-18-2017, 04:43 PM   #10
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Quote:
Originally Posted by borchi_2b View Post
@exil:
I dd not take anything as offense. Just tried to explain where the numbers come from. But unfortunately I have no such numbers specific tot he gazelle at the moment. Trying to get the correct numbers for her cause they differ a bit in little do to some specific factors, but it would fill a complete page to explain why and where it comes from and how the manuver is flown and so on and so on. Simulating a rotor is not comparable to a fixed wing at all from which we could generate windtunnel simulations as soon we have the airfoil. A rotor is a bit more complicated.

I like the phrase " a bit "

So as you guys can see, I am striving to find good and reliable intel on certain things. Funny is that real pilots never think of such intel cause they just fly and do the things they have to do.
Good to know and thanks for the reply.

I know, there are lots of more components to it than just the load factor. But it not only aplies to airplanes. Load factor is used for helicopters too. So, the numbers you've stated are more or less simply that: the correlation between bank angle and load factor (and therefore the percentage of extra TQ needed to maintain altitude and speed).

It works pretty well now with the Gazelle! I don't know what exactly you did with the last FM update, but it seems to work fine for me. I even tried different bank angles yesturday with the calculated extra TQ needed and it worked well (in fact, it still is very tricky to hold a 60° bank angle while maintaining altitude and speed - but this is mainly a Joystick vs real life cyclic issue)!

But, sorry, i'm hijacking a thead...so i will stop here
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