Boeing-Sikorsky SB>1 Defiant (Model S-100)

flanker

ACCESS: Top Secret
Joined
Mar 20, 2008
Messages
928
Reaction score
203
"Twice as far, twice as fast" requires twice the horsepower
Actually since the UH-60’s engines are ~2,000shp it’s more like 3.5x the horsepower… hopefully the tactical advantages are worth it.
Yeah, velocity is squared so essentially you have to have 4x the power to go twice as fast, assuming everything else being equal. And considering Defiant is a goddamn whale...
 

TomcatViP

Hellcat
Joined
Feb 12, 2017
Messages
5,472
Reaction score
5,219
It's a banal error. I have explained that already so, sorry if it sounds a bit pedantic.

We assume generally in that kind of problem that engine power here compensate only for the drag. We also assume that drag is the dynamic drag, 0.5*rho*V^2*S (S being the surface of reference).

So in effect, it's correct to assume that when the speed is doubled, the dynamic drag is quadrupled (2V)^2=4V^2.

However, the power is the product of the Effort (here the drag) time the speed.
Hence 0.5*rho*4V^2*S*2*V=0.5*rho*8*S*V^3
Which is 8 time more than before!

That's a bit different ;)
 
Last edited:

sferrin

ACCESS: USAP
Senior Member
Joined
Jun 3, 2011
Messages
15,340
Reaction score
4,632
"Twice as far, twice as fast" requires twice the horsepower
Actually since the UH-60’s engines are ~2,000shp it’s more like 3.5x the horsepower… hopefully the tactical advantages are worth it.
Yeah, velocity is squared so essentially you have to have 4x the power to go twice as fast, assuming everything else being equal. And considering Defiant is a goddamn whale...
Kinda goes with being a cargo helicopter. ;) (And lets' not forget all that extra HP translates into lots more fuel required.)
 

VTOLicious

ACCESS: Top Secret
Senior Member
Joined
Nov 24, 2008
Messages
976
Reaction score
828
A turboshaft in the 7000shp class! And defiant has 2 of them...
Indeed lots of excess power that can be converted into lift and/or thrust as required. Btw, the turboshaft engines of the C-130 have a power output of ~4500 shp each.
 

sferrin

ACCESS: USAP
Senior Member
Joined
Jun 3, 2011
Messages
15,340
Reaction score
4,632
A turboshaft in the 7000shp class! And defiant has 2 of them...
Indeed lots of excess power that can be converted into lift and/or thrust as required. Btw, the turboshaft engines of the C-130 have a power output of ~4500 shp each.
A CH-53K has more HP than a C-130 and the same as the Mi-26 (22,500hp). (Though the Mi-28M bumped that up to a total of 27,600hp.)
 

VTOLicious

ACCESS: Top Secret
Senior Member
Joined
Nov 24, 2008
Messages
976
Reaction score
828
I was referring to the C-130 because of its turboprops. I would assume Defiant's prop consumes a similar amount of power in cruise flight above 200 kts.
 

Cordy

ACCESS: Confidential
Joined
Nov 5, 2019
Messages
194
Reaction score
170

TomcatViP

Hellcat
Joined
Feb 12, 2017
Messages
5,472
Reaction score
5,219
@Cordy : It's not the final engine! But we can see how the SB-1 config has a range much more related to its engine than Valor. Valor uses a winged configuration with all the inherent benefits on the cruise portion.

The US Army has certainly long realized that Defiant will never meet Valor on that segment of the mission. Hence, I don't think that, at this stage, where there is only two competitors left, this will bear any consequences. FATE or not fate.
 

yasotay

ACCESS: Top Secret
Top Contributor
Senior Member
Joined
Oct 19, 2006
Messages
3,106
Reaction score
2,024
With the down select looming this summer (if not delayed), a demonstration of long range flight is likely one of the last test cards. With the Army Aviation meeting at an appropriate distance, you can get the test done, and show off the product to the customer.
 

H_K

ACCESS: Secret
Joined
Feb 21, 2010
Messages
488
Reaction score
1,012
A 30 year old AW101 could have flown that mission faster, farther, with 2.5x the payload, and without stopping. Same size class.

… just to put the performance in context.

(I know, I know... Defiant may still have room to improve. Though honestly I'm perplexed why they only cruised at 175kts).
 
Last edited:

Avimimus

ACCESS: Top Secret
Joined
Dec 16, 2007
Messages
2,123
Reaction score
304
A turboshaft in the 7000shp class! And defiant has 2 of them...
Indeed lots of excess power that can be converted into lift and/or thrust as required. Btw, the turboshaft engines of the C-130 have a power output of ~4500 shp each.

One has to wonder if, at some point, that excess power would be better spent on a DEW rather than on speed? I wonder what the threshold is?
 

yasotay

ACCESS: Top Secret
Top Contributor
Senior Member
Joined
Oct 19, 2006
Messages
3,106
Reaction score
2,024
A 30 year old AW101 could have flown that mission faster, farther, with 2.5x the payload, and without stopping. Same size class.

… just to put the performance in context.

(I know, I know... Defiant may still have room to improve. Though honestly I'm perplexed why they only cruised at 175kts).
I must admit I am a bit perplexed myself at the rather mundane performance for this particular effort. It may be that there are insurances or FAA limitations that apply to an experimental aircraft of its size.
That is a wild guess on my part.
 

VTOLicious

ACCESS: Top Secret
Senior Member
Joined
Nov 24, 2008
Messages
976
Reaction score
828
We'll see how that turns out. It's up to the customer... However, both teams have delivered impressive technology demonstrators so far. I would love to see a picture of them next to each other ;)
 
Top