Hover Ceiling - 4,000m OGE/IGE?

[Zorrin]

The manual states that the Ka-50's hover ceiling is 4,000m which is fair enough. But it doesn't differentiate between In Ground Effect or Out of Ground Effect.

 

Nor does it give you more exact figures for OEI performance... Has anyone found this in the manual or can someone from ED shed some light on this?

 

Thanks!

[wickedpenguin]

Ground effect is dependent on wingspan and the distance of the aircraft from the surface. It's usually only felt when the aircraft is within 1 to 1.5 times its wingspan above the surface. For instance, in the Cessnas I flew, ground effect was only noticeable up to about 50 feet AGL.

 

With helicopters - according to Wikipedia - "the effect occurs when the helicopter is within one blade length of a hard surface."

 

So, you're talking either 4000m... or about 4007.25m if you're hovering directly above the summit of a 4000m meter mountain. :)

Edited June 14, 2009 by wickedpenguin

[Zorrin]

I see your point wickedpenguin, but - a helicopter still has separate IGE/OGE hover ceilings, I just wanted to know what the IGE or OGE is compared to the stated 4,000m. At a guess, given that the service ceiling as stated in the manual is 5,000m that the 4,000m is an IGE ceiling. If that's the case, what's the OGE ceiling?

 

For example the Bell 429 has:

HIGE (ISA) 12,000 ft 3,658 M HOGE (ISA) 11,000 ft 2,835 M (data from: http://www.bellhelicopter.com/en/aircraft/commercial/bell429_prodSpecs.cfm, where ISA represents International Standard Atmosphere - or +15 degrees C surface temperature and a surface pressure of 1013mb)

 

But with the 429 figures you have to accept that it is still in flight testing so those numbers may be subject to change. However, the fact that there are separate HIGE/HOGEs doesn't.

[AlphaOneSix]

I was just reading an Mi-17 fight manual, and it only lists a single hover altitude as well, and does not mention whether it's IGE or OGE. So my opinion would be that there is not a published hover altitude specifically for IGE and OGE.

 

If you have not yet noticed, the Russian method of flying helicopters is very different from the rest of the West. Russian flight manuals include only a very concise performance chart, not at all like the voluminous performance charts you see in Western flight manuals. In other words, there are no OEI performance charts, you just have to follow the limits on max N1, max EGT, and minimum NR.

[71st_Mastiff]

:music_whistling:Zorrin get back to building the bombs and stay off Black Shark...:thumbup:

[HellToupee]

I see your point wickedpenguin, but - a helicopter still has separate IGE/OGE hover ceilings, I just wanted to know what the IGE or OGE is compared to the stated 4,000m. At a guess, given that the service ceiling as stated in the manual is 5,000m that the 4,000m is an IGE ceiling. If that's the case, what's the OGE ceiling?

 

For example the Bell 429 has:

HIGE (ISA) 12,000 ft 3,658 M HOGE (ISA) 11,000 ft 2,835 M (data from: http://www.bellhelicopter.com/en/aircraft/commercial/bell429_prodSpecs.cfm, where ISA represents International Standard Atmosphere - or +15 degrees C surface temperature and a surface pressure of 1013mb)

 

But with the 429 figures you have to accept that it is still in flight testing so those numbers may be subject to change. However, the fact that there are separate HIGE/HOGEs doesn't.

 

Wouldn't the only difference be the above ground level and the above sea level?

[Zorrin]

Not at all HellToupee, because AGL/ASL has no bearing on a helicopter's ability to hover. It's usually limited by the air density and any references to hover ceilings would be measured ASL.

 

Thanks Alpha, at least that settles that then!

 

Mastiff: I like Black Sharking :D Makes big boom boom!

[miguez]

HellToupee (nice name!), Zorrin is right, when published, over ceiling IGE and OGE can be considerably different, due to air density.

 

For example, Eurocopter's Dauphin lists 2600 meters for OGE and 3350 meters for IGE, huge difference! For more, read here, and further reading here.

 

Best regards,

[Yo-Yo]

I was just reading an Mi-17 fight manual, and it only lists a single hover altitude as well, and does not mention whether it's IGE or OGE. So my opinion would be that there is not a published hover altitude specifically for IGE and OGE.

 

If you have not yet noticed, the Russian method of flying helicopters is very different from the rest of the West. Russian flight manuals include only a very concise performance chart, not at all like the voluminous performance charts you see in Western flight manuals. In other words, there are no OEI performance charts, you just have to follow the limits on max N1, max EGT, and minimum NR.

 

Russian docs are usually divided to something like fight manual (pilot's instruction - what to do and what not to do) and so called "Practical aerodynamics" where not only performance tables are gathered but the basic aircraft parameters such as thrust curves, L/D polars, weight and balance, stability and controls, etc.

 

The ceiling for Russian helo is OGE only because, I think, the takeoff methodic for most of pilots requires check hovering close to OGE.

[Panzertard]

To quote wiki:

The phenomenon of wing in ground effect is caused by the ground interrupting the wingtip vortices and downwash behind the wing.[3] When a wing is flown very close to the ground, wingtip vortices are unable to form effectively due to the obstruction of the ground. The result is lower induced drag, which increases the speed and lift of the aircraft while it is experiencing the ground effect.

 

I wouldnt expect the ground effect to be effective above 30 meters - certainly not 100 meters. Ir do I misinterprete the article? :)

 

Is it be relevant to take this into account - if it's 4000 or 4030 meters?

Besides - are you really trying to hover at 4000? Crazy man ,... :D

[Zorrin]

Thanks Yo-Yo.

 

Panzertard: I think you're getting confused.

 

An Out of Ground Effect hover at 4,000m would represent a hover at an altitude (i.e. above mean sea level) of 4,000m. So this ceiling represents the highest altitude that the Ka-50 can hover while being outside of the effects of ground effect.

 

In Ground Effect hover ceilings are generally higher. The reason being that you may well be at an altitude (i.e. above mean sea level) of 4,500m but your height (i.e. above ground level) could be 2m - or close enough to the ground for the helicopter to be in ground effect where it can still maintain a hover relative to the reduced density of the air because of your overall altitude.

 

Whereas without the aided benefit of ground effect helping to increase the lift/decrease the power required to maintain a hover the craft runs out of available power at 4,000m.

 

And yes potentially if you are operating in mountainous regions and mountain FARPS, like those modelled in Black Shark, then an AGL height of 0m can be some 3,000m ASL.

 

So for example if you are at an altitude of 4,500m you could expect to be able to hover while maintaing a height low enough for ground effect, but you would not expect to be able to do hover outside of ground effect.

 

So, basically Panzer the way to think of it is that ground effect is affected only by height above ground level and is irrelevant to your altitude above mean sea level (within reason!).

[Panzertard]

Thanks Yo-Yo.

 

Panzertard: I think you're getting confused.

 

An Out of Ground Effect hover at 4,000m would represent a hover at an altitude (i.e. above mean sea level) of 4,000m. So this ceiling represents the highest altitude that the Ka-50 can hover while being outside of the effects of ground effect.

 

 

Ah, of course! - I get it - cheers :)

[Yo-Yo]

And, by the way, one can feel OGE/IGE trying to land heavy Ka-50 on the FARP at 3000 m. Or even at 2000 m.

[wickedpenguin]

I see your point wickedpenguin, but - a helicopter still has separate IGE/OGE hover ceilings, I just wanted to know what the IGE or OGE is compared to the stated 4,000m.

 

Interesting. Well, I stand corrected - and informed! I confess I've never looked at a helicopter's operating manual before and didn't know there were two separate values for IGE/OGE hovering.

[ericinexile]

Ground effect is dependent on wingspan and the distance of the aircraft from the surface. It's usually only felt when the aircraft is within 1 to 1.5 times its wingspan above the surface. For instance, in the Cessnas I flew, ground effect was only noticeable up to about 50 feet AGL.

 

With helicopters - according to Wikipedia - "the effect occurs when the helicopter is within one blade length of a hard surface."

 

So, you're talking either 4000m... or about 4007.25m if you're hovering directly above the summit of a 4000m meter mountain. :)

 

I've read the above a few times but maybe I'm missing something. Hover IGE makes a dramatic difference (15% +) in hover ceiling. The actual IGE ceiling has absolutely nothing to do with the math you stated (although your smiley suggests you do so in jest). The closer an airfoil is to a uniform solid surface the more efficient that airfoil becomes (lest induced drag).

[wickedpenguin]

I've read the above a few times but maybe I'm missing something.

 

No, you're not. I was.

Edited June 15, 2009 by wickedpenguin

[enigmatics]

And, by the way, one can feel OGE/IGE trying to land heavy Ka-50 on the FARP at 3000 m. Or even at 2000 m.

Or when flying in valleys and getting close to a steep rise to either side of Ka-50 causing the helicopter to bank away from the slope. That confused me the first time I witnessed it, having only half the rotor disc affected by IGE.

Edited June 15, 2009 by enigmatics