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Old 09-11-2019, 07:28 AM   #1
VampireNZ
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Default No Ground Effect

Complete lack of ground effect - heli will either drift all the way down and hit the ground without stopping IGE, or with the slighest collective will continue to rise well above ground effect. Not how helicopters work...you can hover along nicely on a cushion of air - I know, I have done it in a A109.
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Old 09-11-2019, 09:52 AM   #2
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There was ground effect last time I checked.

The Gazelle has a smaller rotor than the Huey/Hip and GE occurs at a lower height and is less pronounced.

The DCS Gazelle overshoots the GE equilibrium point, so tends to bounce around the equilibrium rather than settle into it (like the Huey) - to enter a GE hover (in DCS), the oscillation/overshoot needs to be corrected for using the collective.

I don't know how DCS's GE oscillation compares to the Gazelle's real behaviour, as the dev's. have stated flight test info. from other Gazelle model's can't be used.

AFAIK, the flight model is due a rework.
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Old 09-11-2019, 10:14 AM   #3
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GE here too, not very strong, but it is there.


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Old 09-11-2019, 04:10 PM   #4
xvii-Dietrich
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Quote:
Originally Posted by VampireNZ View Post
Complete lack of ground effect - heli will either drift all the way down and hit the ground without stopping IGE, or with the slighest collective will continue to rise well above ground effect. Not how helicopters work...you can hover along nicely on a cushion of air - I know, I have done it in a A109.
Attached is a track demonstrating the ground effect in the Gazelle.

I use the hover-servo to stop lateral drift and focus on the air cushion. There are then three lifts and descent tests. In the first, I come down at 0.75 hm/min and in the second at 1.2 hm/min. In these cases, I stop on the air cushion, but bob up a bit thereafter due to the establishment of equilibrium between the air volume and the initial downward momentum. In the last drop, I descend at 2hm/min. This is enough to "punch through" the air cushion and just touch the ground, although it then rises again a bit to sit on the air cushion. So, yes, ground effect is there.

I do not know if the exact distances, accelerations and times are correct, but there is a ground effect. Also, I do not know how the SA342 would compare to and A109 (due to the different mass, rotor pitch, rotor foil, number of blades, engine shaft-hp, etc.) in that regard.

However, it is certainly not correct for to claim that the DCS Gazelle shows a "Complete lack of ground effect".

That said, if you have found some alternatively circumstances that suggest otherwise, please post a track so we can take a look. Maybe there was something in the helicopter setup, or you were descending far too fast, or there was some other effect (such as 50 deg C at high altitude on the Persian Gulf map)?
Attached Files
File Type: trk groundeffect.trk (590.6 KB, 4 views)
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Old 09-11-2019, 07:54 PM   #5
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Just try flying the helicopter without any AP activated. As I said it should make no difference if you are moving slightly - you can move around at slow speeds bobbing up and down on your cushion of air with a steady collective.

I am climbing and descending at considerably lower rates than that. E.G. immediately after liftoff let it slowly just float up in the air, then lit will float back down again and gently bounce off the ground, no cushioning effect at all. It is literally like the rotor disc produces no downwash whatsoever.
To hold a steady hover altitude I need to constantly adjust the collective by fractions of a mm, when in reality these micro-climbs/descents should be cushioned by the downwash GE.
Also just FYI I am not an idiot - normal temps at sea level in the minigun variant, and I am not dropping the collective and auto-ing into the ground wondering where the GE is.....

But I will make a track, as it seems this is needed. I really didn't even consider it as it is so blatantly obvious.
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Old 09-11-2019, 08:15 PM   #6
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Quote:
Originally Posted by VampireNZ View Post
Also just FYI I am not an idiot - {...}
I didn't say you were.

I was merely suggesting a few things that you might have overlooked.
I also made a track for you to demonstrate it working, along with an explanation of what I did.

I was only trying to help.



Ditto for your other thread.
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Old 09-12-2019, 09:51 AM   #7
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I may get grumpy with new aircraft fairly fast, but am man enough to admit I was a little harsh.
I noticed the flight I was using to test out the Gazelle had quite a high surface wind - so set it to zero and the GE is much improved and performs closer to what I would expect. (I don't like my heli flying to be too easy in still conditions - but prob not the best way to test out a new aircraft!)

Definite reaction of the helicopter within the 1 rotor span of the ground, and it will float up and down into and out of GE as expected (as it floats up, eventually gets too high and lift reduces, so drifts back down into cushion and lift improves so descent stops). You can comfortable sit in GE in a steady hover. Also drops out of GE once above approx 5 knots also, so good to see.
Several other strange handling characteristics noticed, but that was definitely my main concern! So my apologies
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