Go Back  PPRuNe Forums > Aircrew Forums > Rotorheads
Reload this Page >

Sikorsky SB-1 flies for first time

Rotorheads A haven for helicopter professionals to discuss the things that affect them

Sikorsky SB-1 flies for first time

Old 29th Sep 2020, 02:02
  #201 (permalink)  
CTR
 
Join Date: Oct 2007
Location: Texas
Posts: 160
FLRAA speed requirements lowered to 230 knots?

I thought the Army wanted the FLRAA to have a top speed of 250 knots, and potentially up to 280 knots. However I was advised today that the Army was dropping the requirement down to 230 knots. Can any one confirm?
CTR is offline  
Old 30th Sep 2020, 16:55
  #202 (permalink)  
 
Join Date: Feb 2015
Location: USA
Posts: 118
Originally Posted by CTR View Post
I thought the Army wanted the FLRAA to have a top speed of 250 knots, and potentially up to 280 knots. However I was advised today that the Army was dropping the requirement down to 230 knots. Can any one confirm?
Honestly, other than that Sikorsky press/media day, I canít find an official looking requirement for 230 knots. Everything I can find says 250 knots as a threshold speed and 280 knots as objective. Has the Army given them a lower bar to clear?
SplineDrive is offline  
Old 15th Oct 2020, 01:46
  #203 (permalink)  
 
Join Date: Mar 2005
Location: Poplar Grove, IL, USA
Posts: 859
Defiant at 211 kts s&l, 232 in a descent, 2/3 prop torque.
https://news.yahoo.com/amphtml/sb-1-...131114297.html

IFMU is offline  
Old 15th Oct 2020, 14:43
  #204 (permalink)  
CTR
 
Join Date: Oct 2007
Location: Texas
Posts: 160
Thanks IFMU,

In the article text was my earlier question answer:

ĒWASHINGTON ó The Sikorsky-Boeing developed SB-1 Defiant coaxial demonstratoraircraft hit 232 knots in a descent, and 211 knots in straight and level flight, meeting the U.S. Armyís speed requirements for its future long-range assault aircraft it plans to field by 2030.Ē

However I believe any new lower speed requirement of 230 Kts would be in level flight, not in descent.

CTR is offline  
Old 15th Oct 2020, 14:51
  #205 (permalink)  
 
Join Date: Mar 2005
Location: Poplar Grove, IL, USA
Posts: 859
At 2/3 power and 211 kts S&l, I'd project 258 kts max s&l.
IFMU is offline  
Old 15th Oct 2020, 15:15
  #206 (permalink)  
 
Join Date: Nov 2010
Location: Earth
Posts: 646
Originally Posted by IFMU View Post
At 2/3 power and 211 kts S&l, I'd project 258 kts max s&l.
Interesting extrapolation using only one data point.

Lets establish a curve based upon Sikorsky's own statements:

https://www.janes.com/defence-news/n...5-kt-in-flight

The Sikorsky-Boeing SB>1 Defiant coaxial helicopter on 9 June reached a new top speed of 205 kt in flight while using less than 50% of the installed propeller power.


https://www.defensenews.com/digital-...hits-230-knots

211 knots in straight and level flight...the aircraft was using about two-thirds prop torque and engine power to achieve the speeds.

So that's 205 kt @ "less than" 50% power, followed by 211 kt @ 66% power, which would yield a best case blistering 224 kt at MCP (empty)
SansAnhedral is offline  
Old 15th Oct 2020, 15:42
  #207 (permalink)  
 
Join Date: Dec 2000
Location: Arlington, Tx. US
Posts: 613
So that's 205 kt @ "less than" 50% power, followed by 211 kt @ 66% power, which would yield a best case blistering 224 kt at MCP (empty)
And 4 months to go 6 knots faster. So basically at this blistering pace of development we can expect MCP in 8 months.
The Sultan is offline  
Old 15th Oct 2020, 16:47
  #208 (permalink)  
 
Join Date: Mar 2005
Location: Poplar Grove, IL, USA
Posts: 859
Originally Posted by SansAnhedral View Post
So that's 205 kt @ "less than" 50% power, followed by 211 kt @ 66% power, which would yield a best case blistering 224 kt at MCP (empty)
So - you are using a linear relationship between power and speed? Care to explain?

My quick estimate was by the square root of the increase of power. Also how do you know the weight? Any flight test program I've been involved with at Sikorsky has never been anywhere near empty weight.

IIRC you said you were a key player on the X2, which means you know the effect weight has on speed for an X2 rotor.

Edit: my bad, you said you did a bit on X2. So maybe you don't know.
IFMU is offline  
Old 15th Oct 2020, 17:32
  #209 (permalink)  
 
Join Date: Feb 2015
Location: USA
Posts: 118
I don’t really think the data from press releases is sufficient to build any sort of credible speed-power polar, even for trash-talking purposes. The time required to advance another 6 knots is a legitimate issue, though. Makes me wonder if the 205 knot speed claim earlier was actually in a descent as well.
SplineDrive is offline  
Old 15th Oct 2020, 18:03
  #210 (permalink)  
 
Join Date: Mar 2005
Location: Poplar Grove, IL, USA
Posts: 859
Originally Posted by SplineDrive View Post
I donít really think the data from press releases is sufficient to build any sort of credible speed-power polar, even for trash-talking purposes. The time required to advance another 6 knots is a legitimate issue, though. Makes me wonder if the 205 knot speed claim earlier was actually in a descent as well.
I agree on all points here.
IFMU is offline  
Old 15th Oct 2020, 18:21
  #211 (permalink)  
 
Join Date: Nov 2010
Location: Earth
Posts: 646
Originally Posted by IFMU View Post
So - you are using a linear relationship between power and speed? Care to explain?
You're right. Assuming linear was probably being generous on a fuselage+rotor like SB1.



Even the hotrod low drag/FE X2TD fuselage power required slopes up with airspeed on the upper end of the envelope

Originally Posted by IFMU View Post
IIRC you said you were a key player on the X2, which means you know the effect weight has on speed for an X2 rotor.

Edit: my bad, you said you did a bit on X2. So maybe you don't know.
Most definitely not a key player on X2. However I do have a copy of AGARDograph 197 on my desk at the moment.

Last edited by SansAnhedral; 15th Oct 2020 at 18:44.
SansAnhedral is offline  
Old 17th Oct 2020, 01:06
  #212 (permalink)  
 
Join Date: Dec 2010
Location: USA
Posts: 80
Originally Posted by SansAnhedral View Post
Interesting extrapolation using only one data point.

Lets establish a curve based upon Sikorsky's own statements:




https://www.defensenews.com/digital-...hits-230-knots




So that's 205 kt @ "less than" 50% power, followed by 211 kt @ 66% power, which would yield a best case blistering 224 kt at MCP (empty)
Fascinating discussion so far; there's something in the Defense News article that puzzles me: "...232 knots in a descent, and 211 knots in straight and level flight, meeting the U.S. Armyís speed requirements for its future long-range assault aircraft..."

How does "...232 knots in a descent and 211 knots in straight and level flight..." meet FLRAA requirements? Am I missing something"?
Commando Cody is offline  
Old 17th Oct 2020, 16:33
  #213 (permalink)  
 
Join Date: Feb 2015
Location: USA
Posts: 118
Originally Posted by Commando Cody View Post
How does "...232 knots in a descent and 211 knots in straight and level flight..." meet FLRAA requirements? Am I missing something"?
It doesn't and to Lockheed's credit, I don't think they have officially claimed it does, but some journalists have gotten "excited" about the 232 knot value.
SplineDrive is offline  
Old 17th Oct 2020, 19:24
  #214 (permalink)  
CTR
 
Join Date: Oct 2007
Location: Texas
Posts: 160
Defiant Total Flight Hours?

Has Lockheed or Boeing recently advertised how many total flight hours the Defiant has accumulated to date?
CTR is offline  
Old 18th Oct 2020, 04:14
  #215 (permalink)  
 
Join Date: Feb 2015
Location: USA
Posts: 118
Originally Posted by CTR View Post
Has Lockheed or Boeing recently advertised how many total flight hours the Defiant has accumulated to date?
i read 23 hours in one of this weekís articles.
SplineDrive is offline  
Old 18th Oct 2020, 17:52
  #216 (permalink)  
CTR
 
Join Date: Oct 2007
Location: Texas
Posts: 160
23 Flight Hours in17 Months?

Originally Posted by SplineDrive View Post
i read 23 hours in one of this weekís articles.
Thank you SplineDrive for the information. But is that information from a recent press release? Itís been 17 months since first flight.
CTR is offline  
Old 18th Oct 2020, 19:50
  #217 (permalink)  
 
Join Date: Dec 2010
Location: USA
Posts: 80
Originally Posted by CTR View Post
Thank you SplineDrive for the information. But is that information from a recent press release? It’s been 17 months since first flight.
Actually, in three days it'll have been 19 months. On August 28 SansAnhedral posted a quote from Graham Warwick (a reliable source) indicating that SB>1 had flown 20 hours. So given the nearly two months that have elapsed since then, three more hours would be in line with its average flight rate (actually it's somewhat better than their average rate) since first flight.
Commando Cody is offline  
Old 18th Oct 2020, 19:53
  #218 (permalink)  
 
Join Date: Dec 2000
Location: Arlington, Tx. US
Posts: 613
From above article:

Defiant was close to hitting the 230-knot goal in June when it reached a speed of 205 knots. The demonstrator hit 100 knots in January.
Again the PR department falls down, in what world is 205 kts close to 230? Time to rename the Defiant BS-1. Also, in one of the articles itís claimed they fly on average once a week, so 16 flights since the June 205 knot flight if they are to be believed.

With the four months between press releases I have pondered what serious problems are crippling the program. When one of the pilots commented that the June-ish test card called for a 30 degree bank, but they did 45 degrees instead I suspected flight control issues (no competent flight test pilot would intentionally miss the targeted bank angle that much). Four months is about right for a flight control software mod so that accounts for one of the claimed sixteen flights. We know the S-97 top speed has been reduced to the 180 to 200 kt range by excessive drag and brutal vibration. It is a safe bet one or both of these are issues they are having to address as they are minimizing the FLRAA requirements to avoid outright cancellation.

Any one want to give odds on another press release this year?
The Sultan is offline  
Old 18th Oct 2020, 20:52
  #219 (permalink)  
 
Join Date: Dec 2010
Location: USA
Posts: 80
Actually Sultan, maybe we should be giving props to the PR department rather than denigrating them. Their job is to promote the company's interests and put the best spin on what's going on. Their job is to keep accomplishments in front of the audiences' and customers' eyes. They really haven't been given a lot to work with here and so they're doing the best they can with what they have.
Commando Cody is offline  
Old 18th Oct 2020, 23:13
  #220 (permalink)  
 
Join Date: Feb 2015
Location: USA
Posts: 118
Originally Posted by The Sultan View Post
Any one want to give odds on another press release this year?
Put me down for another press release in mid-December highlighting the hundreds of ground turn hours accumulated on the test beds and "thousands" of hours of simulations in various integration labs as totally validating the design. Probably a mention of a 220 knot level flight achievement, too. Unless of course, the Army lowers the FLRAA requirements further, in which case we'll hear breathless claims of meeting all requirements and being the next step in Army aviation.
SplineDrive is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.