How nimble will it be?

[Gunfreak]

So I know little about helicopters outside what I can read kn Wikipedia or what I pick up in various war memoirs about helicopters pilots.

So I'm wondering how nimble will it be?

If we compare the various "small" helicopters DCS has or will have we get.

 

Huey 2300kg and 1100 HP.

BO-105 1300kg and x2 420hp

Gazelle 900kg and 590hp

Kiowa 1700kg and 650hp

The Kiowa doesn't seem to have much power to weight ratio (about the same as Huey) 

Now of course there's more to nimbleness than just power to weight ratio.

Hence me asking you guys who know more, how will it handle? 

[Bozon]

Regarding the Gazelle, 590 hp is for the SA-341. SA-342 variants had more powerful engines (may differ between sub-variants, there are many and I am in no way an expert on helicopters), wikipedia mentions 870 hp, which is crazy power loading for a 1 ton helicopter, compared to the others in the list (numbers as above, I didn’t confirm their stats).

To get some intuition into the power loading, we can convert it to climb rate units:

75*hp/mass_kg = rate_m/s

This is if somehow miraculously 100% of the power was used to pull the helicopter up (not real of course). Ordered increasing:

For the OH-58 numbers: 29 m/s (5685 ft/m)

Huey by the above numbers: 36 m/s (7056 feet per min).

Mi-24 from wikipedia, empty 8500 kg, power 2x2200 hp: 39 m/s (7637 ft/m)

Mi-8MT from wikipedia, empty 7100 kg 2x1950 hp: 41 m/s (8104 ft/m)

BO-105, above numbers: 48 m/s (9533 ft/m)

For the SA-341, above numbers: 49 m/s (9672 ft/m).

SA-342 assuming ~1000 kg and 870 hp: 65 m/s (12,836 ft/m)

 

So the SA-342 really stands out in terms of its power loading and the OH-58 is at the opposite end. In helicopters the power loading is expressed differently than in fixed wing aircraft, so it is not a simple indication of speed, or lift capacity. I think that the most clear expression would be how abruptly you can rip the helicopter off the ground, which explains DCS Gazelle’s leaping so easily into the air.

Edited April 17, 2023 by Bozon

[Ramsay]

3 hours ago, Bozon said:

SA-342 variants had more powerful engines (may differ between sub-variants, there are many and I am in no way an expert on helicopters), wikipedia mentions 870 hp, which is crazy power loading for a 1 ton helicopter, compared to the others in the list (numbers as above, I didn’t confirm their stats).

AFAIK the more powerful Astazou XIV engine provides additional power when operating in hot climates, high altitudes, etc. but is of limited benefit near sea level or in temperate climates where the limiting factor will likely be Max torque.

This is a quote comparing  civilian 341 and 342 helicopters 

Quote

There is no difference between a 341 and 342 except some 'upgraded' components like a different style bearings on the fenestron, some changes here and there. Regarding the engine, IIIA vs XIV there is indeed a power difference but the engine produces the same amount of power until the bypass is closed (you can see a hole on the right side of the engine cover). This valve is open in normal circumstances. If it needs more power (high DA, very hot conditions etc...) the valve will close. So at sea level, there is no difference except more fuel burn. In my opinion, no use in our colder climates.

http://www.aviafora.com/forums/forum/helicopter-fora/gazelles/343-shrieking-gazelles?p=985#post985

Edited April 17, 2023 by Ramsay

[BaD CrC]

Dev told me once that if you are good with the Gaz, you should be able to handle the "nimbleness" of the Kiowa.

[Avimimus]

It'd be interesting to see how the Mil Mi-2 (URP?) would compare... definitely the lowest power-to-weight ratio of the small helicopters, but with a relatively larger rotor disc.

[zerO_crash]

Since this thread got revived recently, let's point out and correct a few things:

 

a) The original posted specifications are wrong, and impractical. Going off IRL and manuals, the weights are too low (they are lower than a completely defueled and disarmed aircraft in some instances). Also, it makes it very impractical to calculate the power-to-weight ratio just going off empty machines (no fuel). Rather consider MTOW, and you'll have a practical reference in each case. 

 

b) Obviously, pure power cannot be translated to climb rates. There are so many factors affecting whether a helicopter is good at climbing, speed, hovering, lifting, etc... that it's worth a book on each of these parts alone. The climb rates posted earlier, are complete fantasy. Not only do helicopters have restrictions on what is maximum allowed climb rates (durability and service life), but even the highest performing helicopters in the world will barely reach around 30 m/s in hover (Ka-50, and a couple others in civilian version). While one can pull more that momentarily, it's not really a measure one way or the other. Even from hover, it is only a select metric which doesn't by itself define a "good" (subjective and inadequate word) helicopter.

 

c) Judging flight performance from two metrics alone, will again, yield very incomplete and biased results. For reference, while an Mi-2 has relatively low power-to-weight ratio out of the mentioned ones, it does have blades which are optimized for speed, making it the fastest of them all, as well as among the most capable in maneuvering. A Huey with its big two blades (main rotor) would never be able to pull of what an Mi-2 can, esp. security considered. Different rotor heads, different rotor speeds, different blade thickness and width, fuselage, aerodynamic properties, etc... are all factors that decide this. With the Huey, having relatively thick and wide blades, it slows down rotor speed very quickly at higher AOA (blade angle - collective level). Comparing that to three blades of the Mi-2 or Sa-342... it's basically outclassed in the dynamic aspect of flight. It is however a decent aircraft when it comes to lift though, considering it's wight-class.

 

Here are correct specifications to consider (don't extrapolate too much out of it though, it's a very basic metric to mention):

 

- UH-1H                - 4310kg/9500lbs MTOW       / Engine is Textron Lycoming T-53-L-13B with 1400SHP/1100kW power.

- SA-342M1         - 2085kg/4596lbs MTOW       / Engine is TURBOMECA Astazou XIV with 890SHP/663kW power.

- OH-58D             - 2358kg/5200lbs MTOW       / Engine is T703-AD-700A (250-C30R) or T703-AD-700B (250-C30R/1) or 250-C30R/3, all with 650SHP/478kW power.*

- Bo-105CBS-5    - 2500kg/5511lbs MTOW        / Engine is Allison 250-C20B with 345SHP/257kW power.**

 

*For those interested in the difference between these engines;

- 250-C30R featured a electronic supervisory fuel control system.

- 250-C30R/3 featured improved compressor airflow, air cooled turbine nozzle, low smoke combustor and a full authority digital engine control system (FADEC for short). Since we know that our OH-58D will have FADEC, we know that this is the engine that we'll get (latest and most capable).

 

**Since I cannot find any relevant information/documentation for the Bo-105PAH1A1, I referenced the Bo-105CBS-5 for which there is a flight manual available. Keep in mind that this is not a military version, as such, certain specifications will differ. The CBS-5, also known as "Superfive", is a variant of the Bo-105 which stresses increased lifting capability. As such, this variant will have blades optimized for lift, not speed (there are many other minor changes irrelevant for military application).

 

EDIT: Corrected MTOW of OH-58D after input from real OH-58D pilots. The NATOPS manual on OH-58D, does not contain updates relevant to operation, based on experiences from Afghanistan.

Edited March 30 by zerO_crash

[Bozon]

@zerO_crash, if you again read my post above you will notice that I explicitly state that the climb rates are not real and are simply different units for power/weight ratios. This is because 478kw/2495kg says nothing to most people. The question was “how nimble” so this was a very simplified way to give numbers that are remotely relevant to the question.

If you can give us better insight into the relative performance of these helicopters, by all means do! But all you did was to rehash in many words that the climb rates are not physical which we already knew, and update some numbers (which we appreciate) without providing any new insights into the “how nimble” question.

Edited February 10 by Bozon

[zerO_crash]

1 hour ago, Bozon said:

@zerO_crash, if you again read my post above you will notice that I explicitly state that the climb rates are not real and are simply different units for power/weight ratios. This is because 478kw/2495kg says nothing to most people. The question was “how nimble” so this was a very simplified way to give numbers that are remotely relevant to the question.

If you can give us better insight into the relative performance of these helicopters, by all means do! But all you did was to rehash in many words that the climb rates are not physical which we already knew, and update some numbers (which we appreciate) without providing any new insights into the “how nimble” question.

 

I am aware that you stated it, but I clarified why it's impossible to extrapolate that notion from these metrics alone. One could guesstimate that since the helicopter is relatively light (below 2500kg), that it'll be uneasy at handling. Uneasy, meaning nervous, which ultimately means nimble. That is, if you can control it. That goes without saying. The problem is, notice Sa-342. While it is nervous at low hover/low speed (below translational lift), howevee getting above translational lift, it becomes really stable due to SAS, fenestron and a relatively big tail fin. Such properties change the whole picture of how a helicopter handles.
 

Is the inital question of this thread poor? No. Actually, the answers, while presenting many mistakes in the metrics, don't really answer the question at all. The proper feedback here, would be a qualitative one from a pilot who has flown the helicopter. Keeping in mind that it would be highly subjective, and prone to wrong recollections (memory is overall not trustworthy), you could extract a sentiment with regards to the aircraft and its flying qualities. That's also why I mention Mi-2 vs. e.g. Huey (UH-1H). Based on metrics, it should be all in the favour of Huey, but it isn't, not even close.

 

My answer is very simply cleaning up the mess with metrics posted here, and making you all realize, that based on your attempted reasoning, you don't, and connot, answer this question. This is one for a former pilot, really.

 

@Raptor9 You flew the OH-58D, besides AH-64, didn't you? If you did, would you mind chiming in with an actual pilot's perspective?

[Raptor9]

7 hours ago, zerO_crash said:

@Raptor9 You flew the OH-58D, besides AH-64, didn't you? If you did, would you mind chiming in with an actual pilot's perspective?

I never flew the OH-58D.

In any case, anyone will have plenty of opportunity to see for themselves when the module is released.

[zerO_crash]

I see, no problem then. I guess one will have to wait and see

[barundus]

MGTOW for the OH-58D is limited to 5200lbs.

[zerO_crash]

I was going off the OH-58D manual found here:

 

https://www.docdroid.com/ubI02yP/army-bell-oh-58d-operators-manual-pdf#page=383

 

Section 5-11. pnt. a: Here it states that maximum gross weight is 5500 pounds.

 

Are you referring to a limitation with regards to OH-58D (R) - limited effectivity of the material?

Edited February 25 by zerO_crash

[Coota0]

On 3/26/2023 at 2:15 PM, Gunfreak said:

So I know little about helicopters outside what I can read kn Wikipedia or what I pick up in various war memoirs about helicopters pilots.

So I'm wondering how nimble will it be?

If we compare the various "small" helicopters DCS has or will have we get.

 

Huey 2300kg and 1100 HP.

BO-105 1300kg and x2 420hp

Gazelle 900kg and 590hp

Kiowa 1700kg and 650hp

The Kiowa doesn't seem to have much power to weight ratio (about the same as Huey) 

Now of course there's more to nimbleness than just power to weight ratio.

Hence me asking you guys who know more, how will it handle? 

The fully articulated 4 blade rotor makes the KW extremely nimble. The KW is power limited. We often operated at max gross. Pilots learned that airspeed kept the aircraft from falling out of the sky in those environments. Operating at a 10-15% power margin.

In more forgiving environments the power margin would be 20-25%.

 

19 hours ago, zerO_crash said:

I was going off the OH-58D manual found here:

 

https://www.docdroid.com/ubI02yP/army-bell-oh-58d-operators-manual-pdf#page=383

 

Section 5-11. pnt. a: Here it states that maximum gross weight is 5500 pounds.

 

Are you referring to a limitation with regards to OH-58D (R) - limited effectivity of the material?

 

It was 5500 lbs at one point, but was reduced to 5200. This had to do with the aircrafts autorotational capabilities.

[zerO_crash]

2 hours ago, Coota0 said:

It was 5500 lbs at one point, but was reduced to 5200. This had to do with the aircrafts autorotational capabilities.

I infer you are a current/former army pilot, Coota0?

 

Was the readjustment in MTOW affirmed by a document (SOP/squadron policy/updated manual), or purely a norm based on experience gathered in the field?

[Coota0]

22 hours ago, zerO_crash said:

I infer you are a current/former army pilot, Coota0?

 

Was the readjustment in MTOW affirmed by a document (SOP/squadron policy/updated manual), or purely a norm based on experience gathered in the field?

Yes, I flew the KW. The -10 was changed to reflect the new gross weight.

[zerO_crash]

Gotcha! 

[barundus]

I infer you are a current/former army pilot, Coota0?
 
Was the readjustment in MTOW affirmed by a document (SOP/squadron policy/updated manual), or purely a norm based on experience gathered in the field?

The 5200 lb limitation was instituted via an ISAQ (Interim Statement of Airworthiness Qualification) in the 90s. Eventually it made its way into the operator's manual.
I don't have the ISAQs any more. You'll just have to take my word for it.


Sent from my SM-X710 using Tapatalk

[zerO_crash]

19 hours ago, barundus said:

The 5200 lb limitation was instituted via an ISAQ (Interim Statement of Airworthiness Qualification) in the 90s. Eventually it made its way into the operator's manual.
I don't have the ISAQs any more. You'll just have to take my word for it.


Sent from my SM-X710 using Tapatalk
 

 

I see. I'm asking specifically about a reference, because it's interesting to me through which channels such orders are passed on in the US Army. I haven't heard of the ISAQ, but that makes it even more interesting. I would imagine that one would want an interim document to gather batches of updates and test the proposed solutions, before passing it to the operator's manual. Good stuff!