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kitplane01
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Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 1:27 am

Suppose one wants to start the design of the C-17 replacement. The current C-17 needs 80,800 lbs per side. Now to engine choices...

1) Two large engines.
  • Lots of choices in this thrust range
  • all new and well developed and efficient
  • Fuel efficient so maximum range
  • Already in large scale production and therefore cheap
  • Less redundancy with a two engine aircraft (But the C-2 and the KC-390 exist)
  • Only two engines and they can be overhauled at commercial MMOs so maintenance is cheap
  • Most economical choice

2) Four old engines.
  • There are no new engines in the 40K thrust range
  • Old engines are less fuel efficient so less range
  • Good redundancy
  • already in developed but in large scale production so medium-cheap.

3) Four engines off the A320/B737
  • Only 35K thrust each, so the aircraft will have ~11% less thrust and therefore 11% less payload
    (But still almost twice the C-141 starlifter)
  • Lots of choices in this thrust range
  • all new and well developed and efficient
  • Fuel efficient so maximum range
  • Already in very large scale production and therefore cheap
  • They can be overhauled anywhere in the world at commercial MMOs so maintenance is cheap

1) Six engines off the A320/B737
  • No one has built a 6 engine plane in a long time
  • Only need 27K per engine, which is right in the heart of the A320/B737 range!
  • Easy to make your plane larger or smaller .. lots of thrust variant choices in this range
  • All new and well developed and efficient
  • Fuel efficient so maximum range
  • Already in large scale production and therefore cheap
  • They can be overhauled anywhere in the world at commercial MMOs so maintenance is cheap
  • But you need to overhaul 6 of them!
 
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LyleLanley
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 2:01 am

De-rated Gen-X
 
RJMAZ
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 4:30 am

The 97t A321NEO carries payload the same weight and distance as the 115t 757. A cleansheet C-17 replacement with the same payload/range would probably be 80% of the weight and total thrust.

So a 110t OEW and 220t MTOW would be about right. The design would want a thrust to weight ratio higher than a civilian aircraft. So four of the highest powered LEAP or Pratt GTF engines would be perfect around 65,000lb to 70,000lb of thrust per wing. Or being a twin it needs slightly higher thrust so two of the highest thrust GenX engines at 76,000lb engines would probably do the be job.
 
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Tugger
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 5:19 am

Always 4 engines. This is a military craft and I assume you are expecting it to be used in potentially dangerous areas. So 4 engines.

Tugg
 
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kitplane01
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 6:40 am

Tugger wrote:
Always 4 engines. This is a military craft and I assume you are expecting it to be used in potentially dangerous areas. So 4 engines.

Tugg


That’s an odd rule that no major nation has. There have been tons of two engine military transports. More than I can remember. But I think al of these are currently or very recently operational.

Japan - C2
Europe - C160, C235 C295, G222
US - C2, MV22, C-27
Russia - An 72
Brazil - c390
 
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kitplane01
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 6:42 am

LyleLanley wrote:
De-rated Gen-X


The lowest rated GenX has 70k thrust. You need 40k thrust. That’s not a derate it’s a new engine.
 
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kitplane01
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 6:45 am

RJMAZ wrote:
The 97t A321NEO carries payload the same weight and distance as the 115t 757. A cleansheet C-17 replacement with the same payload/range would probably be 80% of the weight and total thrust.

So a 110t OEW and 220t MTOW would be about right. The design would want a thrust to weight ratio higher than a civilian aircraft. So four of the highest powered LEAP or Pratt GTF engines would be perfect around 65,000lb to 70,000lb of thrust per wing. Or being a twin it needs slightly higher thrust so two of the highest thrust GenX engines at 76,000lb engines would probably do the be job.


I think your right that to carry the same payload we would now use smaller engines. But military requirements keep growing and armories fighting vehicles and cargo demand continues to grow. Compare the C-141 Starlifter at 40k thrust per wing with the C-17s 80k thrust per wing. Both were the main cargo planes of its day.

But if requirements stay constant that seems a good plan.
 
mxaxai
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 8:35 am

Question is, do you want stealth or not? Large high bypass engines are basically impossible to hide, so that requirement would lead to the use of multiple (4 or 6) smaller engines.
 
RJMAZ
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 9:14 am

kitplane01 wrote:
I think your right that to carry the same payload we would now use smaller engines. But military requirements keep growing and armories fighting vehicles and cargo demand continues to grow. Compare the C-141 Starlifter at 40k thrust per wing with the C-17s 80k thrust per wing. Both were the main cargo planes of its day.

But if requirements stay constant that seems a good plan.

It is very rare for any aircraft to be replaced with one of the same size or performance. But a C-17 replacement with the same payload and range requirement would most likely use two 787 engines if it was to operate more as a strategic airlift. If the aircraft was to also do tactical work then four LEAP or Pratt GTF engines would be more suitable.

If we look at the US it has 52 C-5M, 222 C-17 and around 650 Hercules. I definitely see all three airlift entirely replaced with just two aircraft models by 2050. One big aircraft will sit between the C-5 and C-17 and one smaller aircraft will sit between the C-17 and C-130J.

The smaller aircraft will come first around 2035 and I expect it to be a massive quad tilt rotor. It will be JMR-ultra. The C-17 fleet will then no longer see a rough runway or do tactical work so it should be able to get a life extension by reducing G limits. This should see the C-17 retirement line up with the C-5M.

The larger aircraft will then replace the C-5M and C-17 around 2045. It would be a very large but boring simple freighter. It could use a pair of say mature 777X engines giving an aircraft with around 100t payload. Or it could be a bigger quad using 787NEO engines which would make it as big as the A380.
 
GalaxyFlyer
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 1:43 pm

kitplane01 wrote:
Tugger wrote:
Always 4 engines. This is a military craft and I assume you are expecting it to be used in potentially dangerous areas. So 4 engines.

Tugg


That’s an odd rule that no major nation has. There have been tons of two engine military transports. More than I can remember. But I think al of these are currently or very recently operational.

Japan - C2
Europe - C160, C235 C295, G222
US - C2, MV22, C-27
Russia - An 72
Brazil - c390


First, a twin design would require more than 80,800 a side, probably 90,000-95,000 due to OEI considerations. New rudder, FBW changes, etc.

Second, four engines are really best, OEI options are much wider. On a military mission that cannot divert due to diplomatic or mission needs eliminates a twin. Even in the military, an engine loss equals divert; I’ve continued missions on three that would have been tricky on one.
 
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Tugger
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 3:06 pm

GalaxyFlyer wrote:
kitplane01 wrote:
Tugger wrote:
Always 4 engines. This is a military craft and I assume you are expecting it to be used in potentially dangerous areas. So 4 engines.

Tugg


That’s an odd rule that no major nation has. There have been tons of two engine military transports. More than I can remember. But I think al of these are currently or very recently operational.

Japan - C2
Europe - C160, C235 C295, G222
US - C2, MV22, C-27
Russia - An 72
Brazil - c390


First, a twin design would require more than 80,800 a side, probably 90,000-95,000 due to OEI considerations. New rudder, FBW changes, etc.

Second, four engines are really best, OEI options are much wider. On a military mission that cannot divert due to diplomatic or mission needs eliminates a twin. Even in the military, an engine loss equals divert; I’ve continued missions on three that would have been tricky on one.

This was thinking in my simplistic response post.

For the mission a C-17 replacement is intended for, which is large, critical cargo into and out of middle-of-nowhere regions, you can't rely on requiring all your power from one engine on one side and continuing out on your mission. "Circle back and land" is not always an option for this type of aircraft/mission. So 4 engines.

I get that even 3 engines is no guarantee, but it is more so than 1.

Tugg
 
johns624
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 4:47 pm

kitplane01 wrote:
LyleLanley wrote:
De-rated Gen-X


The lowest rated GenX has 70k thrust. You need 40k thrust. That’s not a derate it’s a new engine.
He was talking about if it were a twin.
 
johns624
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 4:47 pm

kitplane01 wrote:
Tugger wrote:
Always 4 engines. This is a military craft and I assume you are expecting it to be used in potentially dangerous areas. So 4 engines.

Tugg


That’s an odd rule that no major nation has. There have been tons of two engine military transports. More than I can remember. But I think al of these are currently or very recently operational.

Japan - C2
Europe - C160, C235 C295, G222
US - C2, MV22, C-27
Russia - An 72
Brazil - c390
Those are all much smaller planes.
 
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kitplane01
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 5:08 pm

RJMAZ wrote:
kitplane01 wrote:
I think your right that to carry the same payload we would now use smaller engines. But military requirements keep growing and armories fighting vehicles and cargo demand continues to grow. Compare the C-141 Starlifter at 40k thrust per wing with the C-17s 80k thrust per wing. Both were the main cargo planes of its day.

But if requirements stay constant that seems a good plan.

It is very rare for any aircraft to be replaced with one of the same size or performance. But a C-17 replacement with the same payload and range requirement would most likely use two 787 engines if it was to operate more as a strategic airlift. If the aircraft was to also do tactical work then four LEAP or Pratt GTF engines would be more suitable.

If we look at the US it has 52 C-5M, 222 C-17 and around 650 Hercules. I definitely see all three airlift entirely replaced with just two aircraft models by 2050. One big aircraft will sit between the C-5 and C-17 and one smaller aircraft will sit between the C-17 and C-130J.

The smaller aircraft will come first around 2035 and I expect it to be a massive quad tilt rotor. It will be JMR-ultra. The C-17 fleet will then no longer see a rough runway or do tactical work so it should be able to get a life extension by reducing G limits. This should see the C-17 retirement line up with the C-5M.

The larger aircraft will then replace the C-5M and C-17 around 2045. It would be a very large but boring simple freighter. It could use a pair of say mature 777X engines giving an aircraft with around 100t payload. Or it could be a bigger quad using 787NEO engines which would make it as big as the A380.


This two aircraft replacement would be great ... if large quad tiltrotors had an operating budget less than a ton of gold per hour.
Seriously, sounds great but a C-130 costs $9000/hour and the much smaller MV-22 costs $17000/hour. That's (round numbers) twice as much for half the aircraft.

https://comptroller.defense.gov/Portals ... 19_b_c.pdf
Last edited by kitplane01 on Tue Oct 05, 2021 5:28 pm, edited 1 time in total.
 
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kitplane01
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 5:10 pm

johns624 wrote:
kitplane01 wrote:
Tugger wrote:
Always 4 engines. This is a military craft and I assume you are expecting it to be used in potentially dangerous areas. So 4 engines.

Tugg


That’s an odd rule that no major nation has. There have been tons of two engine military transports. More than I can remember. But I think al of these are currently or very recently operational.

Japan - C2
Europe - C160, C235 C295, G222
US - C2, MV22, C-27
Russia - An 72
Brazil - c390
Those are all much smaller planes.


The C-2 and the C390 are rather large, if not C17 sized. They carry armored fighting vehicles and are more likely to land in the bush than a C-17.

Only the US and Russia builds C-17 sized military transports, and Russia does not have engines large enough to use just two.
 
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kitplane01
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 5:27 pm

Tugger wrote:
GalaxyFlyer wrote:
kitplane01 wrote:

That’s an odd rule that no major nation has. There have been tons of two engine military transports. More than I can remember. But I think al of these are currently or very recently operational.

Japan - C2
Europe - C160, C235 C295, G222
US - C2, MV22, C-27
Russia - An 72
Brazil - c390


First, a twin design would require more than 80,800 a side, probably 90,000-95,000 due to OEI considerations. New rudder, FBW changes, etc.

Second, four engines are really best, OEI options are much wider. On a military mission that cannot divert due to diplomatic or mission needs eliminates a twin. Even in the military, an engine loss equals divert; I’ve continued missions on three that would have been tricky on one.

This was thinking in my simplistic response post.

For the mission a C-17 replacement is intended for, which is large, critical cargo into and out of middle-of-nowhere regions, you can't rely on requiring all your power from one engine on one side and continuing out on your mission. "Circle back and land" is not always an option for this type of aircraft/mission. So 4 engines.

I get that even 3 engines is no guarantee, but it is more so than 1.

Tugg


Two thoughts

1) Something like 99.99% of all C-17 missions are to a hard runway already controlled by the US.

2) Suppose you could have a 4 engine C-17 replacement, but could afford to operate 10% fewer, and each one had 10% less range. Would you take that deal?
 
johns624
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 5:33 pm

kitplane01 wrote:
johns624 wrote:
kitplane01 wrote:

That’s an odd rule that no major nation has. There have been tons of two engine military transports. More than I can remember. But I think al of these are currently or very recently operational.

Japan - C2
Europe - C160, C235 C295, G222
US - C2, MV22, C-27
Russia - An 72
Brazil - c390
Those are all much smaller planes.


The C-2 and the C390 are rather large, if not C17 sized. They carry armored fighting vehicles and are more likely to land in the bush than a C-17.

Only the US and Russia builds C-17 sized military transports, and Russia does not have engines large enough to use just two.
They have less than half the capacity of a C17. Also, USAF planes are more apt to be used operationally, so they know what it really takes.
 
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Tugger
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 5:40 pm

kitplane01 wrote:
Tugger wrote:
GalaxyFlyer wrote:

First, a twin design would require more than 80,800 a side, probably 90,000-95,000 due to OEI considerations. New rudder, FBW changes, etc.

Second, four engines are really best, OEI options are much wider. On a military mission that cannot divert due to diplomatic or mission needs eliminates a twin. Even in the military, an engine loss equals divert; I’ve continued missions on three that would have been tricky on one.

This was thinking in my simplistic response post.

For the mission a C-17 replacement is intended for, which is large, critical cargo into and out of middle-of-nowhere regions, you can't rely on requiring all your power from one engine on one side and continuing out on your mission. "Circle back and land" is not always an option for this type of aircraft/mission. So 4 engines.

I get that even 3 engines is no guarantee, but it is more so than 1.

Tugg


Two thoughts

1) Something like 99.99% of all C-17 missions are to a hard runway already controlled by the US.

2) Suppose you could have a 4 engine C-17 replacement, but could afford to operate 10% fewer, and each one had 10% less range. Would you take that deal?

1.) What are the combat/wartime situtations the aircraft will be able to operate in?
2.) Everything else must follow that decsion.

If you are suggesting a two airrcraft solution then you are talking a different scenario than yuor original thread topic. (Which would be more like "Options for C-17 replacement).

Tugg
 
RJMAZ
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 6:22 pm

kitplane01 wrote:
This two aircraft replacement would be great ... if large quad tiltrotors had an operating budget less than a ton of gold per hour.
Seriously, sounds great but a C-130 costs $9000/hour and the much smaller MV-22 costs $17000/hour. That's (round numbers) twice as much for half the aircraft.

The CMV-22 Vs C-2 greyhound debate is fairly simple.

The Osprey has equal payload range as the C-2.
When delivering cargo to a carrier battle group the Osprey can unload on dozens of large ships. There will be a ship closer to shore saving on inflight refueling. With the C-2 the aircraft carrier had to reduce fighter operations while it splits cargo onto smaller helicopters. The CV-22 can also go directly smaller ships or split the cargo on a LHD.

Each CMV-22 not only replaces one C-2 but also one helicopter. The cost is now in favour of the Osprey. Now if you put a cost on reducing carrier operations and extra inflight refueling with the C-2 when the carrier is further away then the CMV-22 is an absolute bargain.

Now in terms of the USAF with the large tilt rotor the cost savings are even greater. Currently cargo has to arrive by C-130J to a forward operating base in theatre. This base must be highly protected and an austere runway built at the cost of tens of millions of dollars per day. This base must be located within 200nm of the enemy as the cargo has to be put onto helicopters that are very short range to take it to the front line. Lots of fuel is needed for the cargo helicopters so the logistics cause the overall size of the forward operating base to become massive. A huge portion of casualties are from fuel trucks. A forward operating base like in Iraq or Afghanistan would get destroyed if we were fighting against a stronger opponent.

With the quad tilt rotor it will not only replace the C-130J, a pair of helicopters but also to the entire cost of the forward operating base. It could cost a ton a gold per hour and still be a bargain. Cargo will instead be delivered to a safe area 500+nm away from the enemy. They will deliver by C-5M, C-17, KC-46 and civilian freighters to a civilian runway or by ship to a sea port with easy access to fuel. This will be far away from the enemy and could even potentially be in a neighbouring country. The quad tilt rotor will then take cargo and vehicles straight to the front line with the Bell V-280 Valor.

This is the future. I expect the quad tilt rotor JMR-Ultra prototype to be unveiled in 5 years time and enter service by 2030. It will then replace nearly all C-130 aircraft by 2040.

This is why the C-17 and C-5M replacement will never do tactical work so it could be a big twin. If there is another large sustained conflict in a few years I could see an emergency bridging freighter needing to be purchased. The Kawasaki C-2 built by Boeing or LM would be the obvious pick.
 
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kitplane01
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 7:09 pm

mxaxai wrote:
Question is, do you want stealth or not? Large high bypass engines are basically impossible to hide, so that requirement would lead to the use of multiple (4 or 6) smaller engines.


Smart people disagree, but I want the lowest cost that transports the stuff to where it has to go. I don't want to send my transports to areas with operating enemy fighters, which has been the standard answer since air transport began.
 
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kitplane01
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 7:15 pm

RJMAZ wrote:
kitplane01 wrote:
This two aircraft replacement would be great ... if large quad tiltrotors had an operating budget less than a ton of gold per hour.
Seriously, sounds great but a C-130 costs $9000/hour and the much smaller MV-22 costs $17000/hour. That's (round numbers) twice as much for half the aircraft.

The CMV-22 Vs C-2 greyhound debate is fairly simple.

The Osprey has equal payload range as the C-2.
When delivering cargo to a carrier battle group the Osprey can unload on dozens of large ships. There will be a ship closer to shore saving on inflight refueling. With the C-2 the aircraft carrier had to reduce fighter operations while it splits cargo onto smaller helicopters. The CV-22 can also go directly smaller ships or split the cargo on a LHD.

Each CMV-22 not only replaces one C-2 but also one helicopter. The cost is now in favour of the Osprey. Now if you put a cost on reducing carrier operations and extra inflight refueling with the C-2 when the carrier is further away then the CMV-22 is an absolute bargain.

Now in terms of the USAF with the large tilt rotor the cost savings are even greater. Currently cargo has to arrive by C-130J to a forward operating base in theatre. This base must be highly protected and an austere runway built at the cost of tens of millions of dollars per day. This base must be located within 200nm of the enemy as the cargo has to be put onto helicopters that are very short range to take it to the front line. Lots of fuel is needed for the cargo helicopters so the logistics cause the overall size of the forward operating base to become massive. A huge portion of casualties are from fuel trucks. A forward operating base like in Iraq or Afghanistan would get destroyed if we were fighting against a stronger opponent.

With the quad tilt rotor it will not only replace the C-130J, a pair of helicopters but also to the entire cost of the forward operating base. It could cost a ton a gold per hour and still be a bargain. Cargo will instead be delivered to a safe area 500+nm away from the enemy. They will deliver by C-5M, C-17, KC-46 and civilian freighters to a civilian runway or by ship to a sea port with easy access to fuel. This will be far away from the enemy and could even potentially be in a neighbouring country. The quad tilt rotor will then take cargo and vehicles straight to the front line with the Bell V-280 Valor.

This is the future. I expect the quad tilt rotor JMR-Ultra prototype to be unveiled in 5 years time and enter service by 2030. It will then replace nearly all C-130 aircraft by 2040.

This is why the C-17 and C-5M replacement will never do tactical work so it could be a big twin. If there is another large sustained conflict in a few years I could see an emergency bridging freighter needing to be purchased. The Kawasaki C-2 built by Boeing or LM would be the obvious pick.


I really liked this post. I think that's a great argument for the future tiltrotor. But I have doubts.

How much of the future tiltrotor will be the mission you outlined, and how much will be just moving palleted cargo from one safe runway to another? Because year after year, that's the C-130s mission (I'm pretty sure). Because for *that* mission, the future tiltrotor is wildly expensive.

Also, do the troops on the ground want C-130 sized cargo drops, or would they rather have cargo delivered in Chinook sized chunks? Because a large base will have a protected runway and a very small base doesn't need 50,000 lbs delivered at once.

What you've outlined is an important mission, but I wonder if it's the most common mission.
Last edited by kitplane01 on Tue Oct 05, 2021 7:20 pm, edited 1 time in total.
 
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kitplane01
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 7:17 pm

RJMAZ wrote:
This is why the C-17 and C-5M replacement will never do tactical work so it could be a big twin. If there is another large sustained conflict in a few years I could see an emergency bridging freighter needing to be purchased. The Kawasaki C-2 built by Boeing or LM would be the obvious pick.


There is an emergency, like a new war in Iraq/Afghanistan. We need something like the Kawasaki C-2. How long would it take Boeing or LM to build 50 of them, including the whatever procurement process and protests happen? Think it could be done in less than 8 years?
 
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kitplane01
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 7:19 pm

Tugger wrote:
kitplane01 wrote:
Tugger wrote:
This was thinking in my simplistic response post.

For the mission a C-17 replacement is intended for, which is large, critical cargo into and out of middle-of-nowhere regions, you can't rely on requiring all your power from one engine on one side and continuing out on your mission. "Circle back and land" is not always an option for this type of aircraft/mission. So 4 engines.

I get that even 3 engines is no guarantee, but it is more so than 1.

Tugg


Two thoughts

1) Something like 99.99% of all C-17 missions are to a hard runway already controlled by the US.

2) Suppose you could have a 4 engine C-17 replacement, but could afford to operate 10% fewer, and each one had 10% less range. Would you take that deal?

1.) What are the combat/wartime situtations the aircraft will be able to operate in?
2.) Everything else must follow that decsion.

If you are suggesting a two airrcraft solution then you are talking a different scenario than yuor original thread topic. (Which would be more like "Options for C-17 replacement).

Tugg


I meant a single aircraft to replace the C-17. It's mission will be whatever you think C-17s will be doing in 2040. My guess is that mission set would be similar to the current mission set.
 
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Tugger
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 7:37 pm

kitplane01 wrote:
I meant a single aircraft to replace the C-17. It's mission will be whatever you think C-17s will be doing in 2040. My guess is that mission set would be similar to the current mission set.

Then I honestly believe it will need to be 4 engine. The 10% options you are noting do not change much for the military as the primary requirements of range and theater performance will out do cost every time. For better or worse. And an engine taking a bullet or something else and failing will make it even more necessary for the flight to continue on.

Tugg
 
texl1649
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 9:58 pm

kitplane01 wrote:
LyleLanley wrote:
De-rated Gen-X


The lowest rated GenX has 70k thrust. You need 40k thrust. That’s not a derate it’s a new engine.


I believe below 50K GE is still partnered via Safran/CFM joint venture long term. Rumor is, they are scaling up the LEAP for the notional Boeing NMA or whatever it is to be called, to around 55K. If that happens, I’d assume it would be mature by the time any C-17 is drawn up on some computers in the 2030’s. I’d also expect Pratt won’t leave this space vacated, as it would make sense for them to finally expand out of the narrow body range again with a new GTF in this realm, particularly as there aren’t going to be any ‘big’ widebody projects anew anytime soon.
 
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kitplane01
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Re: Engine choices for the future C-17 replacement?

Tue Oct 05, 2021 11:22 pm

texl1649 wrote:
kitplane01 wrote:
LyleLanley wrote:
De-rated Gen-X


The lowest rated GenX has 70k thrust. You need 40k thrust. That’s not a derate it’s a new engine.


I believe below 50K GE is still partnered via Safran/CFM joint venture long term. Rumor is, they are scaling up the LEAP for the notional Boeing NMA or whatever it is to be called, to around 55K. If that happens, I’d assume it would be mature by the time any C-17 is drawn up on some computers in the 2030’s. I’d also expect Pratt won’t leave this space vacated, as it would make sense for them to finally expand out of the narrow body range again with a new GTF in this realm, particularly as there aren’t going to be any ‘big’ widebody projects anew anytime soon.


It all depends on Boeing/Airbus. If either make an airframe that needs a 40K engine ... problem solved. But Boeing has been sitting on the MMA idea for years, and Airbus has always said the solution that market space is an A321neo. For the purpose of this discussion lets assume there is no MMA, and that for Pratt/GE to make a new engine they will want to be paid quite a lot of money by the DoD, with the development costs not shared by Boeing/Airbus.
 
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SeamanBeaumont
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Re: Engine choices for the future C-17 replacement?

Wed Oct 06, 2021 12:26 am

kitplane01 wrote:
texl1649 wrote:
kitplane01 wrote:

The lowest rated GenX has 70k thrust. You need 40k thrust. That’s not a derate it’s a new engine.


I believe below 50K GE is still partnered via Safran/CFM joint venture long term. Rumor is, they are scaling up the LEAP for the notional Boeing NMA or whatever it is to be called, to around 55K. If that happens, I’d assume it would be mature by the time any C-17 is drawn up on some computers in the 2030’s. I’d also expect Pratt won’t leave this space vacated, as it would make sense for them to finally expand out of the narrow body range again with a new GTF in this realm, particularly as there aren’t going to be any ‘big’ widebody projects anew anytime soon.


It all depends on Boeing/Airbus. If either make an airframe that needs a 40K engine ... problem solved. But Boeing has been sitting on the MMA idea for years, and Airbus has always said the solution that market space is an A321neo. For the purpose of this discussion lets assume there is no MMA, and that for Pratt/GE to make a new engine they will want to be paid quite a lot of money by the DoD, with the development costs not shared by Boeing/Airbus.

Military Transport programs are not the source of funding for new engine programs within DoD. The result would be an off the shelf engine by whatever vendor the DoD mandated Boeing/LM/Boogaloo use. If you want a lesson learned on this just look at the A400.
 
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Re: Engine choices for the future C-17 replacement?

Wed Oct 06, 2021 3:32 am

kitplane01 wrote:
I really liked this post. I think that's a great argument for the future tiltrotor. But I have doubts.

How much of the future tiltrotor will be the mission you outlined, and how much will be just moving palleted cargo from one safe runway to another? Because year after year, that's the C-130s mission (I'm pretty sure). Because for *that* mission, the future tiltrotor is wildly expensive.

Also, do the troops on the ground want C-130 sized cargo drops, or would they rather have cargo delivered in Chinook sized chunks? Because a large base will have a protected runway and a very small base doesn't need 50,000 lbs delivered at once.

What you've outlined is an important mission, but I wonder if it's the most common mission.

Having the right equipment during a war is more important than having the right equipment during peace time.

The US military plan is called Mounted Vertical Maneuver (MVM). The quad tiltrotor will take one medium weight or two lightweight vehicles directly into combat. A huge force can then be inserted anywhere in the battlefield allowing them to attack the enemy from the most vulnerable areas. Before the enemy can counter attack the quad rotors can pick up the forces and place them somewhere else.

Traditional combat usually involves the enemy placing ground forces on the side facing where the attack will come from. Iraq placed all its tanks facing the Saudi Arabian border during Gulf War 1. MVM causes the enemy to spread out its defenses evenly throughout the country making them much more vulnerable. The per hour cost of a huge tiltrotor could be 10 times that of a C-130J and it is still a bargain.

If the USAF had 500 of these large tilt rotors today they could probably effectively capture the most well defended cities in the world. Any adversary has their forces located on the border or coastline. The tilt rotors could drop 500 armoured vehicles and 5,000 soldiers right near the city inside a 30 minute window under the protection of stealth fighters and electronic attack jammers. They could storm the city centre and then by the time the enemy realises what has happened and started to send in their armour the US armoured forces could withdraw to a different extraction point where the tilt rotors would do the pickup. They could never hold the city but they could capture it for 24 hours with minimal casualties. None of this would even be possible without MVM that comes from tilt rotor technology.

kitplane01 wrote:
There is an emergency, like a new war in Iraq/Afghanistan. We need something like the Kawasaki C-2. How long would it take Boeing or LM to build 50 of them, including the whatever procurement process and protests happen? Think it could be done in less than 8 years?

There is no emergency now. The C-17 and C-5M fleet still has 20 years of usable life yet at the current rate of usage. A war burns up the flight hours really quick. Gulf War 1 was over in less than 6 months. I would estimate 5 years of service life of the cargo fleet was used up in that 6 months. The entire C-17's fleet could hit their service life limit at once if a new conflict happens. The C-17 fleet would need a large refurb at this point and the reduced availability might trigger a C-2 purchase.
 
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Re: Engine choices for the future C-17 replacement?

Wed Oct 06, 2021 5:18 am

RJMAZ wrote:
kitplane01 wrote:
I really liked this post. I think that's a great argument for the future tiltrotor. But I have doubts.

How much of the future tiltrotor will be the mission you outlined, and how much will be just moving palleted cargo from one safe runway to another? Because year after year, that's the C-130s mission (I'm pretty sure). Because for *that* mission, the future tiltrotor is wildly expensive.

Also, do the troops on the ground want C-130 sized cargo drops, or would they rather have cargo delivered in Chinook sized chunks? Because a large base will have a protected runway and a very small base doesn't need 50,000 lbs delivered at once.

What you've outlined is an important mission, but I wonder if it's the most common mission.

Having the right equipment during a war is more important than having the right equipment during peace time.

OK. But my question was about wartime. I think (and I'm willing to be educated) that even in wartime it's not obvious that the most common mission will be running supplies to unimproved fields. What was the most common mission for Marine MV22s during Afghanistan?

RJMAZ wrote:
The US military plan is called Mounted Vertical Maneuver (MVM). The quad tiltrotor will take one medium weight or two lightweight vehicles directly into combat. A huge force can then be inserted anywhere in the battlefield allowing them to attack the enemy from the most vulnerable areas. Before the enemy can counter attack the quad rotors can pick up the forces and place them somewhere else.
...
If the USAF had 500 of these large tilt rotors today they could probably effectively capture the most well defended cities in the world.


If the USAF put 500 large tiltrotors beyond enemy lines into the enemies capital city ... it would be the largest airborne invasion in about three generations. Maybe that's gonna happen.

You could not do this against a near peer ... China would shoot them down, and would survive the loss of any single city anyway. Also, no land wars with China. So I assume this is against Iraq/Afghanistani type enemies. No one is worried about our ability to initially take the capital city of such enemies.

I agree this is our militaries future vision, and that they are smarter than me .. I just have doubts.

RJMAZ wrote:
kitplane01 wrote:
There is an emergency, like a new war in Iraq/Afghanistan. We need something like the Kawasaki C-2. How long would it take Boeing or LM to build 50 of them, including the whatever procurement process and protests happen? Think it could be done in less than 8 years?

There is no emergency now. The C-17 and C-5M fleet still has 20 years of usable life yet at the current rate of usage. A war burns up the flight hours really quick. Gulf War 1 was over in less than 6 months. I would estimate 5 years of service life of the cargo fleet was used up in that 6 months. The entire C-17's fleet could hit their service life limit at once if a new conflict happens. The C-17 fleet would need a large refurb at this point and the reduced availability might trigger a C-2 purchase.


That describes the need. I asked how long it would take. When was the last time the US went from nothing to a fleet of 50 aircraft in less than 8 years? We've been at war for the last 20!
 
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Re: Engine choices for the future C-17 replacement?

Wed Oct 06, 2021 7:53 am

kitplane01 wrote:
What was the most common mission for Marine MV22s during Afghanistan?

The MV-22 couldn't do MVM as it could only transport two squads or a jeep sized vehicle and one squad. It was just working like a long range blackhawk.


kitplane01 wrote:
If the USAF put 500 large tiltrotors beyond enemy lines into the enemies capital city ... it would be the largest airborne invasion in about three generations. Maybe that's gonna happen.

Yes there will be no slow and massive build up over months on the border like in the first Gulf War.

With 500 tilt rotors in the first Gulf War the US could have won the war in couple days with no buildup. The Armoured division could have landed right outside Baghdad with 500 medium armoured vehicles and 5,000 soldiers. The city would be captured 100%. All it would have needed was a few F-15C to provide air dominance, a few F-117 to take out the power and a few Apache to take out the radars on the border. All of this strike package could have arrived with inflight refueling from a NATO country.

kitplane01 wrote:
You could not do this against a near peer ... China would shoot them down, and would survive the loss of any single city anyway. Also, no land wars with China.

Mounted Vertical Maneuver is an extreme capability and is far better than stealth in my opinion.

Let's create the scenario. Both sides today. Lets remove nuclear weapons from both sides but add only 500 quad tilt rotors to the USAF. The US could take Beijing with minimal casualties. F-35 and F-22 would first penetrate and provide counter air / SEAD and submarines would launch tomahawks. Growlers would provide jamming with the tankers and aircraft carriers sitting safely near Japan. The Tilt rotors would enter flying nap of the earth below radar.

By the time the Chinese identified the US armour is on the ground it would take more than 24 hours to get Chinese armour to drive to the area. Without armour in the way the US forces will travel swiftly. In 12 hours the US armoured forces could steam roll the capital while the 200+ stealth aircraft provide local area air dominance and SEAD. There is no way the US forces could hold the city for more than 2 days before a million Chinese soldier just surround the US armoured forces. But the tilt would return 24 hours later to pick everyone up. They might only lose 5% of the tilt rotors and vehicles in the surprise attack.

Small and medium wars could be won with a very small number of forces with MVM.
 
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Re: Engine choices for the future C-17 replacement?

Wed Oct 06, 2021 1:36 pm

RJMAZ wrote:
Let's create the scenario. Both sides today. Lets remove nuclear weapons from both sides but add only 500 quad tilt rotors to the USAF. The US could take Beijing with minimal casualties. F-35 and F-22 would first penetrate and provide counter air / SEAD and submarines would launch tomahawks. Growlers would provide jamming with the tankers and aircraft carriers sitting safely near Japan. The Tilt rotors would enter flying nap of the earth below radar.

By the time the Chinese identified the US armour is on the ground it would take more than 24 hours to get Chinese armour to drive to the area. Without armour in the way the US forces will travel swiftly. In 12 hours the US armoured forces could steam roll the capital while the 200+ stealth aircraft provide local area air dominance and SEAD. There is no way the US forces could hold the city for more than 2 days before a million Chinese soldier just surround the US armoured forces. But the tilt would return 24 hours later to pick everyone up. They might only lose 5% of the tilt rotors and vehicles in the surprise attack.

Small and medium wars could be won with a very small number of forces with MVM.

So to take the scenario further, what would be the point of taking the city to abandon it in 24 hours when the local forces arrive?
Is that not the scenario the USA did in Vietnam where the military claim they never lost a battle, but somehow they lost the war?
In war planning such scenario's, if the thought process is that you cut off the head of the snake to win the war, then there would be no need to abandon the city as the locals would surrender or elect new leaders rather than continue the fight. I think we all agree that such would not happen, nor would we want it to be another bridge too far.

I can see MVM being used to create a tactical advantage to win a battle in the same way that paratroops and helicopters are used today, more than that I think it becomes the REMF fantasies in playing computer games.
 
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Re: Engine choices for the future C-17 replacement?

Wed Oct 06, 2021 5:00 pm

RJMAZ wrote:
kitplane01 wrote:
What was the most common mission for Marine MV22s during Afghanistan?

The MV-22 couldn't do MVM as it could only transport two squads or a jeep sized vehicle and one squad. It was just working like a long range blackhawk.


kitplane01 wrote:
If the USAF put 500 large tiltrotors beyond enemy lines into the enemies capital city ... it would be the largest airborne invasion in about three generations. Maybe that's gonna happen.

Yes there will be no slow and massive build up over months on the border like in the first Gulf War.

With 500 tilt rotors in the first Gulf War the US could have won the war in couple days with no buildup. The Armoured division could have landed right outside Baghdad with 500 medium armoured vehicles and 5,000 soldiers. The city would be captured 100%. All it would have needed was a few F-15C to provide air dominance, a few F-117 to take out the power and a few Apache to take out the radars on the border. All of this strike package could have arrived with inflight refueling from a NATO country.


Surely the Iraqi army had more than 5000 soldiers stationed in Bagdad. Even more when they see the 500 large tiltrotors. And yes, that does take stoops from the Saudi border. But I really don't think 5000 troops take Bagdad on day 1.
 
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Re: Engine choices for the future C-17 replacement?

Wed Oct 06, 2021 5:01 pm

I don't think it is realistic in any of these scenarios.
A more plausible kind of scenario would be for destroying specific installations that are to big/complex for an aerial attack. For example if you want to dismantle Iranian nuclear weapon facilities...
Come in, destroy everything while part of the troops guard the perimeter, and come out.
But I doubt there would be a enough of these kind of missions to justify such a large investment.
 
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Re: Engine choices for the future C-17 replacement?

Wed Oct 06, 2021 5:14 pm

RJMAZ wrote:
kitplane01 wrote:
What was the most common mission for Marine MV22s during Afghanistan?

The MV-22 couldn't do MVM as it could only transport two squads or a jeep sized vehicle and one squad. It was just working like a long range blackhawk.


kitplane01 wrote:
If the USAF put 500 large tiltrotors beyond enemy lines into the enemies capital city ... it would be the largest airborne invasion in about three generations. Maybe that's gonna happen.

Yes there will be no slow and massive build up over months on the border like in the first Gulf War.

With 500 tilt rotors in the first Gulf War the US could have won the war in couple days with no buildup. The Armoured division could have landed right outside Baghdad with 500 medium armoured vehicles and 5,000 soldiers. The city would be captured 100%. All it would have needed was a few F-15C to provide air dominance, a few F-117 to take out the power and a few Apache to take out the radars on the border. All of this strike package could have arrived with inflight refueling from a NATO country.

kitplane01 wrote:
You could not do this against a near peer ... China would shoot them down, and would survive the loss of any single city anyway. Also, no land wars with China.

Mounted Vertical Maneuver is an extreme capability and is far better than stealth in my opinion.

Let's create the scenario. Both sides today. Lets remove nuclear weapons from both sides but add only 500 quad tilt rotors to the USAF. The US could take Beijing with minimal casualties. F-35 and F-22 would first penetrate and provide counter air / SEAD and submarines would launch tomahawks. Growlers would provide jamming with the tankers and aircraft carriers sitting safely near Japan. The Tilt rotors would enter flying nap of the earth below radar.

By the time the Chinese identified the US armour is on the ground it would take more than 24 hours to get Chinese armour to drive to the area. Without armour in the way the US forces will travel swiftly. In 12 hours the US armoured forces could steam roll the capital while the 200+ stealth aircraft provide local area air dominance and SEAD. There is no way the US forces could hold the city for more than 2 days before a million Chinese soldier just surround the US armoured forces. But the tilt would return 24 hours later to pick everyone up. They might only lose 5% of the tilt rotors and vehicles in the surprise attack.

Small and medium wars could be won with a very small number of forces with MVM.


How does the US get sustained air superiority over Beijing? China has 2000 air force aircraft, and a large number of land based missiles. The nearest plausible US air bases are 600 mile away, and I have a hard time imagining US tankers surviving over China. If the US floods S Korea with all these large tiltrotors and stealth aircraft, the Chinese will react by send aircraft, troops, and missiles north. China has 150 J-20 stealth fighters, and will have many more by the time your large tiltrotors are produced.

How do 5000 troops take Beijing? Surely the Chinese army can find more than 5000 to guard it. Especially since they have notice of the location of the US buildup.

How do these troops survive the coming storm when the Chinese army reacts? Even for 2 days. Heck, how do they survive the local population of 20M for 2 days?

Why does China fall when Beijing is (temporarily) taken? Wouldn't it be easier to just bomb Beijing, especially if you really have air superiority?

How do these troops leave? They're in the middle of a city, surrounded by an enemy converging on them , 600 miles from the nearest air base, deep in the heart of the Chinese air defense system.
 
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Re: Engine choices for the future C-17 replacement?

Wed Oct 06, 2021 8:32 pm

kitplane01 wrote:
Surely the Iraqi army had more than 5000 soldiers stationed in Bagdad. Even more when they see the 500 large tiltrotors.

They would land at night. Armoured vehicles have a force multiplier effect. 5,000 soldiers with 500 medium armoured vehicles could easily dominate 50,000 soldiers without armour. No country could have 100,000 soldiers and 1,000 medium/heavy armoured vehicles continuously sitting on high alert in every city. Even the US would be lucky to manage 1% of that.

To surround the US forces it would require a much larger force. If they were evenly surrounded in a ring the US forces would simply punch through the weakest point using satellite information to get to one of many extraction point options. Eventually every tank and soldier would leave their border positions and surround the US forces. At that point they might realise that the 500 US armoured vehicles were fully autonomous and there were no soldiers at all. Now the actual war starts.

par13del wrote:
So to take the scenario further, what would be the point of taking the city to abandon it in 24 hours when the local forces arrive?

This was in response to the statement that MVM could never capture a large city of a near peer country. MVM could capture any city due to the sudden large concentrated force. The only difference is it could not hold the city of a near peer. So it could not hold the city in Russia or China. But MVM with 500 quad tilt rotors could capture and hold every other city in the world.

Against a medium power the attack wouldn't need to be a single in and out. The tilt rotor fleet could inserting another 500 medium armoured vehicles and 5,000 soldiers every 5-10 hours.
 
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Re: Engine choices for the future C-17 replacement?

Wed Oct 06, 2021 9:07 pm

kitplane01 wrote:
How does the US get sustained air superiority over Beijing? China has 2000 air force aircraft, and a large number of land based missiles. The nearest plausible US air bases are 600 mile away, and I have a hard time imagining US tankers surviving over China. If the US floods S Korea with all these large tiltrotors and stealth aircraft

It doesn't matter how many 3rd and 4th gen jets attack the F-22, they will all get shot down. The F-22/F35 aircraft would not be loitoring over the city for hours. They would do multiple race circuits with aircraft one behind the other. Each aircraft might be over enemy soil for 20 minutes at the edge of their combat radius. If an F-22 launched all six AMRAAMs the aircraft turns around. The next F-22 aircraft behind then has another six ready. Any SAM site that lights up gets taken out. To put distance into perspective South Korea soil is only 500nm from Beijing. The tankers would have to be very far away and they would need a picket line of fighters to protect them.

This scenario has only been mentioned to demonstrate why the US desires MVM and that the future airlift requirements will need to be designed around this. So the C-17 replacement in the original post is not what will be purchased.
 
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Re: Engine choices for the future C-17 replacement?

Thu Oct 07, 2021 12:48 am

RJMAZ wrote:
kitplane01 wrote:
How does the US get sustained air superiority over Beijing? China has 2000 air force aircraft, and a large number of land based missiles. The nearest plausible US air bases are 600 mile away, and I have a hard time imagining US tankers surviving over China. If the US floods S Korea with all these large tiltrotors and stealth aircraft

It doesn't matter how many 3rd and 4th gen jets attack the F-22, they will all get shot down. The F-22/F35 aircraft would not be loitoring over the city for hours. They would do multiple race circuits with aircraft one behind the other. Each aircraft might be over enemy soil for 20 minutes at the edge of their combat radius. If an F-22 launched all six AMRAAMs the aircraft turns around. The next F-22 aircraft behind then has another six ready. Any SAM site that lights up gets taken out. To put distance into perspective South Korea soil is only 500nm from Beijing. The tankers would have to be very far away and they would need a picket line of fighters to protect them.

This scenario has only been mentioned to demonstrate why the US desires MVM and that the future airlift requirements will need to be designed around this. So the C-17 replacement in the original post is not what will be purchased.


I take this to mean you don't have total respect for the J-20s. They are almost as numerous as the F-22s, and are still being built. so by the time the tiltrotors arrive they will maybe outnumber the F-22s.
 
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Re: Engine choices for the future C-17 replacement?

Thu Oct 07, 2021 12:55 am

Actually, I don’t respect an AF without any combat experience, doesn’t matter what aircraft they’re flying. Pretty simple, there is no AF with the combat experience, tools, tactics of the USAF. It’s become a bit like the RN—centuries, or decades in this case, mean something. A friend said he went on missions in Iraq and the four-ship had over 2,000 of combat time total. That matters more than the plane.
 
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Re: Engine choices for the future C-17 replacement?

Thu Oct 07, 2021 2:03 am

Spot on GalaxyFlyer. I also think the US severely underestimates it's capabilities and overestimates it's adversaries to continue to get massive funding.

The supporting assets like tankers and transports these have all been purchased decades ago. Any country starting from scratch has to buy all these supporting assets along with the shiny new fighters.

Regarding the J-20 it is an excellent aircraft for China. The large size and layout allows for great speed and range to provide decent long range interception. It succeeds at pushing the AWAC and Tanker aircraft further out which greatly diminishes the reach of the fighters. I highly doubt the J-20 has a radar cross section as low as the F-22 or F-35. In terms of radar performance I highly doubt the detection range would be comparible.

A slight advantage in both categories results in a massive kill to death ratio. For instance If the F-22 can detect the J-20 at 30 miles and the J-20 can detect the F-22 at 20 miles then it will be a 10:1 kill ratio. If the F-22 can detect the J-20 at 40 miles and the J-20 can detect the F-22 at 20 miles then it will be a 100:1 kill ratio. The AMRAAM will be already within the no escape zone. Also as soon as a J-20 is detected there might be additional AMRAAM missiles coming from different direction. There will be fighter tracks running in multiple directions all over the theatre. So once the J-20 is detected the information would be sent to all F-22/F-35 fighters and there could be a dozen fighters within 100nm of the J-20. The closest F-22 that made the initial detection might not even launch a missile to avoid being detected. So the first reaction could be to disengage and pass on the target information to fighters at a safer distance. The fighters further away can then launch their AMRAAMs and even with their weapon bay doors opening they are too far away to be detected.
 
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Re: Engine choices for the future C-17 replacement?

Thu Oct 07, 2021 12:07 pm

Getting back on topic....
What is the real question to be answered? What should replace the C-17, or what engine choice should be used to upgrade the existing C-17s to extend the life? If the topic truly is a clean-sheet design, you don't start with engines, you start with the mission needs. So in 2050, what will the mission needs be? Will the mission still consider the island-hopping MVM tactics? If so, will it need to factor in electric propulsion? Will range be a factor? How does aerial refueling come into scope if electric propulsion is considered?
 
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Re: Engine choices for the future C-17 replacement?

Thu Oct 07, 2021 1:16 pm

Tugger wrote:
Always 4 engines. This is a military craft and I assume you are expecting it to be used in potentially dangerous areas. So 4 engines.

Tugg


I love the 4 engines F-35 !
 
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Re: Engine choices for the future C-17 replacement?

Thu Oct 07, 2021 2:30 pm

Aesma wrote:
Tugger wrote:
Always 4 engines. This is a military craft and I assume you are expecting it to be used in potentially dangerous areas. So 4 engines.

Tugg


I love the 4 engines F-35 !

A.) This is a thread on a potential C-17 replacement.
2.) The F-35 has a completely different task and mission.
III.) That WOULD be a pretty awesome thing and a sight to see!! :rotfl:

Tugg :wave:
 
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Re: Engine choices for the future C-17 replacement?

Thu Oct 07, 2021 4:39 pm

The only airframe that will make sense as a C-17 replacent (other than a C-17 clone) would be a BWB high wing transport with a ramp.

The advantage is obvious. Higher efficiency means longer range. Engines can be configured as 2, or 3 for redundancy. 4 would be overkill with the higher by-pass turbofan.

Both Boeing and Airbus have flight tested models and probably have gobs of wind tunnel data. All that is left is to wait for an RFP and scale up to full size.

bt
 
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Re: Engine choices for the future C-17 replacement?

Thu Oct 07, 2021 5:35 pm

aumaverick wrote:
Getting back on topic....
What is the real question to be answered? What should replace the C-17, or what engine choice should be used to upgrade the existing C-17s to extend the life? If the topic truly is a clean-sheet design, you don't start with engines, you start with the mission needs. So in 2050, what will the mission needs be? Will the mission still consider the island-hopping MVM tactics? If so, will it need to factor in electric propulsion? Will range be a factor? How does aerial refueling come into scope if electric propulsion is considered?


But requirements need to be written with an understanding of what those requirements will cost. If carrying 300 troops can be done with existing engines, and carrying 320 troops requires an entirely new engines .. that should matter when setting the capacity requirement.

My guess is that a military transport will be the last thing electrified. They fly fewer hours/year than a civilian transport and therefore should favor a capital cost reduction over an operating cost reduction compared to a civilian transport.

My guess is that the C-17 replacement will need to be optimized for a longer range than the C-17. The C-17 was designed while "rush troops to Europe" was the thinking, and now "rush troops to Asia" is more relevant. (Of course the C-17 has a long range .. but it's optimum range carrying a full payload is less.)
 
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Re: Engine choices for the future C-17 replacement?

Thu Oct 07, 2021 5:37 pm

bikerthai wrote:
The only airframe that will make sense as a C-17 replacent (other than a C-17 clone) would be a BWB high wing transport with a ramp.

The advantage is obvious. Higher efficiency means longer range. Engines can be configured as 2, or 3 for redundancy. 4 would be overkill with the higher by-pass turbofan.

Both Boeing and Airbus have flight tested models and probably have gobs of wind tunnel data. All that is left is to wait for an RFP and scale up to full size.

bt


I agree that a BWB might work better for a military transport than a civilian transport.
1) The lack of windows is not as bad
2) The increased sensation during roll do to more seats off the center axis is less of a problem for the military
3) minor stealth benefits for free

But back to engines. How many would you like and which ones. Let's assume making a whole new design is prohibitively expensive (arguable, but assume for now)
 
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Re: Engine choices for the future C-17 replacement?

Thu Oct 07, 2021 7:02 pm

It makes no sense to define a new transport with the same characteristics as the C-17. The C-17 fleet size will be over 100 planes 25 years from now. Better to position the new transport in a different space than either the C-17 or the C-130, probably somewhere in between.

A big issue in mobilization is getting the vehicles forward, standard cargo can be handled by commercial cargo planes. The C-130 and C-17's can operate from a prepared airfield close to the front, an efficient transport can handle getting the equipment to that prepared airfield. Still short field but use of a much better runway remove some of the biggest load cases.

BT's BWB using a high wing, rear ramp makes excellent sense. I would go further and indicate the cargo bay could be heated but not pressurized, more forward would be a pressurized passenger compartment for say 40 pax. Not being pressurized allows for a rectangle shaped hold which fits much better into a BWB as well as getting the cargo floor closer to the ground.
 
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bikerthai
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Re: Engine choices for the future C-17 replacement?

Thu Oct 07, 2021 11:02 pm

What is the scenario where you would need to deploy quickly with a fleet of C-17? Any war with China would need to slow build up of troops. There would not be an invasion of the mainland.

You have bases in Japan and Austrailia to stage. The only potential in invasion scenario would be to the relief of Taiwan. And you do not do it with a fleet of C-17. For clandestine drop you need some stealth characteristics and most probably fly from Okinawa or Darwin.

bt
 
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kitplane01
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Re: Engine choices for the future C-17 replacement?

Fri Oct 08, 2021 3:22 am

bikerthai wrote:
What is the scenario where you would need to deploy quickly with a fleet of C-17? Any war with China would need to slow build up of troops. There would not be an invasion of the mainland.

You have bases in Japan and Austrailia to stage. The only potential in invasion scenario would be to the relief of Taiwan. And you do not do it with a fleet of C-17. For clandestine drop you need some stealth characteristics and most probably fly from Okinawa or Darwin.

bt


When you need to get heavy AFVs to Iraq or Afganistan quickly. Even just enough to make an initial fighting force.
 
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bikerthai
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Re: Engine choices for the future C-17 replacement?

Fri Oct 08, 2021 4:22 am

kitplane01 wrote:
When you need to get heavy AFVs to Iraq or Afganistan quickly.


That was 20 years ago. And we will have the same capability for another 15-20 years.

We are talking about airlift in the Pacific Theater what parameter is most important there.

bt
 
RJMAZ
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Re: Engine choices for the future C-17 replacement?

Fri Oct 08, 2021 4:26 am

If that is the requirement there are multiple ways to solve it.

A C-17 sized can land vehicles straight to a dirt strip. The C-5M can land twice as many vehicles to a civilian runway. Both aircraft brand new today might cost a very similar price per aircraft due to the STOL and austere performance adding cost and complexity. So the C-5M carries twice as many vehicles per dollar.

I would say it is easier to have a C-5M type aircraft delivering the vehicles to the theatre and then a smaller tactical airlift carrying the vehicles one at a time to the battle area. The tactical airlift might be able to do eight trips in the time it takes the C-5M style aircraft to make one long trip from US.

Overall the cost of the tactical airlift and the C-5M style strategic airlifter would be cheaper than just lots of C-17 style airlift. In terms of vehicles moved per dollar.

So the C-17 type aircraft is actually a bad way to do it. A jack of all trades, master of none. But when the C-5 is no longer being built and the C-130 is too skinny to fit a decent vehicles then the jack of all trades was the only option for the USAF.

But doing it from scratch today you would want a C-5M and a A400M sized aircraft paired together. The quad tiltrotor paired with the C-5M style is

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