Backseat with the Thunderbirds - CAFB 2011

Discussions about the U.S. Air Force Air Demonstration Squadron
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Lawndart
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Post by Lawndart » Fri Mar 18, 2011 11:01 am

Ells wrote:Most of the time we're at 80-82% in transitions and then power up to 90% for the loops and rolls, powering back to 80% on the way down with boards.
My power range is from about 84.7% to 85.3%. No boards, no power changes mid-maneuver. That was the point I was trying to make. ;)
Ells wrote:It will be interesting to see how much difference wind and turbulance will make. How much were you thinking of adding LD?
A realistic amount, but this would only be for the pure challenge in leading, having to account for drift and crab angles on every maneuver and setup with the wind pushing your velocity vector away from where your nose is pointing. The spectators wouldn't see the difference at all, so there's no added visual benefit. I'd also leave turbulence off, because there is absolutely no way that can be simulated accurately in the sim since we lack the "seat of the pants" feedback.
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Post by Ells » Fri Mar 18, 2011 12:52 pm

Yep I got that LD :wink:

Also I didn't think it would affect the other pilots that much as they are so close to boss to notice any difference, apart from synchro (solos) for their setups too.
And of course to the crowd, it will be the amazing show that it always is.

Like you say a great challange for Boss to take all that into account.
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Post by Teej » Fri Mar 18, 2011 3:22 pm

Rhino wrote:I can't wait to see that Diamond 360 of yours flown at real world params. Good luck!
It's...uh...fast. :D

The D360 in the aforementioned, as yet un-seen by most, VFAT '09 show was faster than '08s.

It's even faster now. :D
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Post by Sinister » Wed Mar 23, 2011 12:57 pm

Well... Getting back to the video... :wink:

It was very interesting to see how HIGH #6 got about #3's wing on the Delta Loop... I have to admit, it took me by surprise but then again I thought about the view from the crowd. They won't see that... just the awesomeness of the DELTA formation.

But yes... was cool to see the similarity in the sight picture.
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Post by Lawndart » Wed Mar 23, 2011 1:44 pm

Sinister wrote:It was very interesting to see how HIGH #6 got about #3's wing on the Delta Loop...
"INTO THE FLOAT" - Boss has to be very careful not to ease forward too much or he'll send No. 6 to the moon! ;)
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Post by Beaker » Wed Mar 23, 2011 2:17 pm

Man... not going to lie, that looked like a LOT of movement in that video to me! :shock: Not at all points of course, but there were some pretty radical over-the-wing movements... not a concept I'm used to coming from the Blue Angels camp. Of course, airspeed, aircraft size, etc, are factors. Nuke did look pretty smooth in that roll, from what I could see.

LD you said something to the effect of (convective) turbulence creating little or no extra relative movement. I'll agree with that, but add that in real life, that turbulence would be a distraction. (Visually and physically) Wind is (apparently) a much greater factor in the cockpit, because of the way nearby aircraft can disturb flow.
Frazer wrote:As a glider pilot, I experienced quite often that one wing is lifted and the other dropped. This can be quite violent as the air around a thermal drops with a similar speed.
Been there, but it IS a much different story with a heavier aircraft. Even in just a small single engine recip, turbulence has a much different feel. (Partially due to the longitudinal force of the powerplant "drawing" the aircraft through the air, but also due to the weight of the aircraft.) My experience stops at a mid-size recip twin (Seneca,) which chops through stuff pretty easily by comparison as well. I'd imagine what you perceive as radical in a glider will more or less feel like "texture" in a 25,000 lb heavy metal jet.



LD - Great to hear you guys are back to tackling problems/changes with the usual analytical style. :) Keep at it so we can see a show this year!
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Post by Teej » Wed Mar 23, 2011 2:55 pm

There is an epic difference between:

Glider:
Wing loading: ~ 5 pounds per square foot
Aspect ratio: ~ 20:1
Speed: 60-80 knots
Weight: 1000 pounds

Fighter:
Wing Loading: ~ 85 pounds per square foot
Aspect ratio: ~ 3:1
Speed: 350-450 knots
Weight: ~ 25,000 pounds

Winds can definitely affect lines and timing. A strong enough wind could also make it rough (especially on the low alt solo passes) due to turbulence over ground features (hills, buildings, trees, etc).

Even at the reduced speed over the top in a loop or roll...I find it tough to believe they'd even notice anything but the most severe gusty conditions...in which they'd probably not be flying a show anyway.

I'd love to hear what one of the actual demo pilots has to say about the subject, as I could certainly be wrong. I just don't see them even noticing 10-20 knot winds...or even 10-20 knot gusts...in terms of "turbulence" passing through the diamond/delta.
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Post by Lawndart » Wed Mar 23, 2011 10:29 pm

Beaker wrote:Man... not going to lie, that looked like a LOT of movement in that video to me! :shock: Not at all points of course, but there were some pretty radical over-the-wing movements... not a concept I'm used to coming from the Blue Angels camp.
The electric jet definitely isn't as dampened as the Hornet is, especially considering the Thunderbirds also fly at faster speeds than the Blue Angels.

That's why I said "interesting to see how much/little movement they have within the formation". It will undoubtedly be reduced as the season progresses, but even in videos from the 80's and 90's, there's quite a bit of minor movement within each formation when seen up close. This is all relative of course, and we can split hairs over the magnitude of these all day long.

As far as comparing the Blue Angels and the Thunderbirds is also a matter of the eye of the beholder...

There are definitely enough differences worth mentioning (some of which you already brought up), such as: Different jets (systems and controls), different sizes (wingspans), flying at different speeds and to some degree differences in training. However, they do have one thing in common - both teams execute their respective missions with high accuracy whatever the objectives might be!
Beaker wrote:LD you said something to the effect of (convective) turbulence creating little or no extra relative movement. I'll agree with that, but add that in real life, that turbulence would be a distraction. (Visually and physically) Wind is (apparently) a much greater factor in the cockpit, because of the way nearby aircraft can disturb flow.
This is why I'm not keen on turbulence in a flight sim, because it can't be simulated accruately unless you're in a level D, and even then it leaves something to be desired. The only feedback we get of turb in the sim is visual, which is hardly what you'd say in the real world... you feel it first and foremost!
Beaker wrote:LD - Great to hear you guys are back to tackling problems/changes with the usual analytical style. :) Keep at it so we can see a show this year!
Yessir! Some things can never be overanalyzed, hehe.
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Post by Teej » Wed Mar 23, 2011 11:03 pm

To expand on what LD said...

Remember the F-16 is inherently unstable vs. the F-18, requiring the computer to keep it flying.

To put it another way, as the BA diamond is cruising along with constant pull on the sticks the jets will pretty much respond in unison to any local changes/turbulence.

The F-16 FLCS on the other hand will be making adjustments to maintain whatever pull / roll it decides the pilot wants based on the pull.

A subtle difference, but I think that accounts for some portion of the movement.
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Post by Lawndart » Thu Mar 24, 2011 2:19 am

Valid point Teej.

I remember Grab (Ssgt. Grabham - not VBA's Grab) telling us back when the Thunderbirds first got the Block 52s on property and were making modifications to them, that the FLCS didn't like some of the things the team does with the jets... at all.
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Post by Beaker » Thu Mar 24, 2011 2:51 pm

Teej wrote:To expand on what LD said...

Remember the F-16 is inherently unstable vs. the F-18, requiring the computer to keep it flying.

To put it another way, as the BA diamond is cruising along with constant pull on the sticks the jets will pretty much respond in unison to any local changes/turbulence.

The F-16 FLCS on the other hand will be making adjustments to maintain whatever pull / roll it decides the pilot wants based on the pull.

A subtle difference, but I think that accounts for some portion of the movement.
Not quite accurate... the F/A-18 is unstable like the F-16 by default, aerodynamically. (lateral/longitudinal instability, etc.) That's the only reason it's coupled with an FBW FCS. (However, whether entirely through FCS or by design convention, it's a very stable ride.) It's just the same concepts, but a slightly "newer" FCS and design. (4 channel.... not really relevant to the discussion though.) The greatest difference I see between the F-16 and F/A-18 I see is the control design... any pilot will tell you it makes a world of difference. A short-throw pressure sidestick just isn't the best option for formation flying, in my mind. The Blues are able to maintain the spacing and stability they do at least partly due to the Hornet's control layout.

They actually simulate that "constant back pressure" of a nose-down-trimmed non-FBW aircraft by hooking door springs from the cockpit pedestal to the stick shaft to provide enough force to keep the stick in a constant forward pull. (~ 40 lbs... ouch!) The Hornet has a constant 1 g trim algorithm, just like the Viper. It's running any time when auto flaps UP mode is in use... pretty much the entirety of the Blues demo. It also dampens un-commanded pitch rate (read: turbulence,) as I'm sure the Viper does as well.


About your last, LD... I'd assume the problem is age. I think "FLCS" is more than a bit outdated now. It was the first real implementation of FBW in a fighter aircraft...
Last edited by Beaker on Fri Mar 25, 2011 1:18 am, edited 1 time in total.
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Post by Teej » Thu Mar 24, 2011 4:33 pm

Beaker wrote:Not quite accurate... the F/A-18 is unstable like the F-16 by default, aerodynamically. (lateral/longitudinal instability, etc.) That's the only reason it's coupled with an FBW FCS.
Not that I'm incapable of being wrong by any stretch, but everything I've _ever_ seen disagrees with this. (The two jets being equal in instability).

I wouldn't ever say the -18 has the stability of a Cessna by any stretch. My impression has always been that the -18 has a very near "neutral" stability - kinda "edgy" in handling...as opposed to the outright negative static stability of the -16 in which the airframe (at least subsonic) is constantly trying to leave its stable flight attitude.

The difference being the -16 and the -117 would be flat out unflyable without computer correction, whereas the -18 would be difficult and potentially scary...but not impossible.

In the words of a test pilot on the -18:
Al Aitken, USMC...presumably retired since this is > 20 years old wrote:First, a very brief review of stability and control: The stability of any airplane is its tendency to return to equilibrium when displaced. Controllability is a measure of the ease with which the pilot can displace it from equilibrium. An extremely stable airplane might be very hard to control depending on the level of controllability. An unstable airplane may be impossible to control regardless of controllability. The F/A-18 I used to fly was designed with very relaxed static longitudinal stability-almost neutral. The relaxed stability and very strong controllability make it a highly maneuverable fighter-the airplane would be extremely difficult to control without the digital flight control computers.

vs. what Joe Bill Dryden (F-16 test pilot), quote not available due to Code One's website changes...about the F-16 not just being "relaxed stability" but actually negatively stable in pitch - if the control surfaces were neutralized and the FLCC disabled, the jet would swap ends at the very least and more likely tumble wildly.

ETA: I'm not posting this to be argumentative or anything, and we're definitely drifting off the topic of the post again. Just explaining my thinking is all.
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Post by Beaker » Fri Mar 25, 2011 1:17 am

Teej wrote:I'm not posting this to be argumentative or anything, and we're definitely drifting off the topic of the post again. Just explaining my thinking is all.
No no, on the contrary, I think it's good discussion! I think I was in error by interpreting your post to mean you thought the F/A-18 was positively statically stable. I was under the impression it was negatively statically stable, but I would certainly agree that it must be to a lesser degree than the Viper. I wouldn't have spoken up if you had originally phrased it as you did later.
Teej wrote:if the control surfaces were neutralized and the FLCC disabled, the jet would swap ends at the very least and more likely tumble wildly.
I will say that sounds a little extreme... but nearly uncontrollable, I'd buy. Input from the pilot might in most cases just have the effect of worsening deviations, and "extreme" maneuvering would be near-impossible.

As a further discussion point... the aerodynamic qualities of the Hornet are quite multifaceted and complex, beyond its stability. There's a lot of variables whose net effects I certainly can't reconcile with guesswork. Heavy reliance on vortex lift and that strong LERX lifting moment forward of CP, a large number of surfaces all on complex schedules, aeroelastic outer wing panels, slight anhedral, canted twin tails... the list goes on. It's a fascinating aircraft... very unique.
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