Help - Helos at High Altitude

[FlyBaby 659]

I recently purchased the Eiger Park Scenery that has some high altitude (11,000 ft+) Helipads for launch.

I can't get the B412 or the Cabri G2 to take off at these high altitudes, the engine don't seem to have enough power.

I get an over torque warning in the B412 and lose all tail rotor authority when taking off...it barely get off the ground, but then spins.

I am sure that there is a setting or something that I am missing...any ideas?

 

[Paraffin 2,197]

I haven't flown my Bell 412 that high, but as a first stab at it, I suggest checking your payload and fuel weight. Try a very light loadout for pax/payload and half fuel. 

Also try one of the more basic liveries, because extras like SAR winch, nose radome, external fuel tanks  and sling cargo extras are configured in the livery selection, and will add extra weight. You want a stripped-down helicopter at those altitudes.

I don't have the Cabri G2 model, but the service ceiling for that one is only 13,000 ft. It's a piston engine, which if I have this right, doesn't do as well in the thinner air as turbines like the 412. Also the maximum ceiling doesn't usually refer to takeoff ability, just what you might reach in cruise. So that might be a realistic limitation for the G2. You want power to spare, and not too much weight to operate at those altitudes.

Edited May 26, 2019 by Paraffin

[Humpty 751]

at that altitude you probably have less density hence not enough engine power and the rotor blades don't bite the air. Hence difficulty taking off.

 

Edited May 26, 2019 by HumptyDumpty

[FlyBaby 659]

Thanks for the responses!

[jcomm 5,939]

Further to what Zulfi posted above, 

you have 

here: https://www.maunaloahelicopters.edu/library/Rotorcraft_Flight_Manuals/Bell_Helicopter/412.pdf

an excellent source for info on the Bell 412 operational limits.

On pages 1-10 and 1-11 you can find a chart that lists 14k feet as the limiting density altitude for IGE in the 412. Beware that depending in the temperature ( above / bellow ISA ) in your "flight" you can actually be at a higher / lower density altitude than the one your altimeter reads.

You can find here a simple Online Density Altitude Calculator.

Yet, you don't have to bother about:

- Relative humidity

- Geopotential Height

because X-Plane (*) models none of these in terms of their effects on altimeter readings / aerodynamics / engine performance...

 

(*) The same applying to FSX / P3D / AEFS, pretty much all mass user base desktop flightsims. Flight Gear has an "advanced weather engine mode" that models these effects, but in it's default mode it's the same as the others... DCS World and IL-2 Great Battles include a simplistic but effective model of Geopotential Height variation with temperature, but do not model the impact of moist in density altitude. ELITE XTS models it all, Aerowinx PSX models Geopotential Height variation - actually a MUST for any serious airliner operations simulator... Weather effects are "word not allowed" 😚 in pretty much all flight simulators, but people tend to worry mostly about the looks ... the shaders.... the cars and flows at the gates...

Edited May 26, 2019 by jcomm

[Paraffin 2,197]

I just ran a couple of quick tests with the X-Trident Bell 412. I don't have the OP's Eiger Park Scenery so I can't try those helipads. Instead I found a couple of high altitude airports in the XP database where I could load the helicopter:

Lhasa Gonggar Airport, Tibet -- 11,712 ft (3,570 m)

Daocheng Yading Airport, China -- 14,472 ft. (4,411 m)

Daocheng is the highest altitude civilian airport in the world. The helicopter was set up like this:

Default (white) livery, no extra gear
1000 lb. payload
590 lbs. fuel (1 hour endurance)
11,492 lbs. takeoff weight (400 lbs. shy of maximum)
Weather was clear skies set to 60 deg. F ambient temperature

With both airports, the Bell 412 felt a little sluggish compared to lower altitudes, but it was able to lift and climb just fine, with torque below the redline.

The test at Daocheng was funny, because I noticed the cockpit slowly getting darker compared to the outside view, until it was completely black. Took me a minute to remember that helicopters aren't pressurized. 😄 I didn't get the hypoxia blackout at Lhasa Gonggar. 

Anyway, the 412 does fine at these altitudes, as long as you're not overloaded, or both high and hot (high ambient air temps). I don't own the Cabri G2 so couldn't try that one. 

[HighBypass 2,339]

As a related aside - I searched for Daocheng airport on google maps - seems the Chinese have done a great job of hiding 4 km of runway... try and zoom in to the coordinates for a nice plan view and ... nothing there apart from the normal bleak terrain.

[Paraffin 2,197]

Yes, Daocheng is interesting! I just checked Google Earth and couldn't find it either. Maybe a civil-military dual use thing?

Anyway, it's listed as a 3D airport in the X-Plane database, so someone must have added it to the Gateway. But it doesn't have the "flying saucer" terminal building, just some fuel tanks at the end of the runway. An interesting airport to practice high altitude landings and takeoffs.

I remember being surprised a few years ago, trying to take off in XP with a DC-3 in one of the airports in the South American Andes range. Reciprocal engines really don't like high altitudes! Especially in Summer, with warmer temps.

[FlyBaby 659]

9 hours ago, Paraffin said:

I just ran a couple of quick tests with the X-Trident Bell 412. I don't have the OP's Eiger Park Scenery so I can't try those helipads. Instead I found a couple of high altitude airports in the XP database where I could load the helicopter:

Lhasa Gonggar Airport, Tibet -- 11,712 ft (3,570 m)

Daocheng Yading Airport, China -- 14,472 ft. (4,411 m)

Daocheng is the highest altitude civilian airport in the world. The helicopter was set up like this:

Default (white) livery, no extra gear
1000 lb. payload
590 lbs. fuel (1 hour endurance)
11,492 lbs. takeoff weight (400 lbs. shy of maximum)
Weather was clear skies set to 60 deg. F ambient temperature

With both airports, the Bell 412 felt a little sluggish compared to lower altitudes, but it was able to lift and climb just fine, with torque below the redline.

The test at Daocheng was funny, because I noticed the cockpit slowly getting darker compared to the outside view, until it was completely black. Took me a minute to remember that helicopters aren't pressurized. 😄 I didn't get the hypoxia blackout at Lhasa Gonggar. 

Anyway, the 412 does fine at these altitudes, as long as you're not overloaded, or both high and hot (high ambient air temps). I don't own the Cabri G2 so couldn't try that one. 

Yep, reducing the overall weight does the trick. I was at about 8,000 lbs takeoff weight with 1 hour of fuel.

I don't know who I am going to rescue all slimmed down, but at least I got it off the helipad without a problem. I will increase the gear load and see what happens, but thanks for looking into to this further.

[Humpty 751]

Yes lowering the weight at that height will help , density altitude will also depend on the temps. 

Someone at a group who is a real world coast guard pilot told me sometimes they need to throw the heli in high and heavy situations. 

Use that density calculator Jcomm posted its very helpful to know what your altitude and density factor will be.