The Diamond Roll

"How To" by our Pilot Staff
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Lawndart
Virtual Thunderbird
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The Diamond Roll

Post by Lawndart » Sat Jul 23, 2005 11:47 am

Part II of the more in depth technique posts here, this time describing the Diamond Roll. Once again, this is mostly from Lead's perspective, but having flown these in every position in the Diamond I'll give some brief input for the other positions as well.

Configuration
90%, 425 knots CAS, 400ft AGL

Callout sequence
Standby Smoke, Smoke On Ready Now
Nose Coming Up
Rolling Left and Rolling
Into the Float
Standby Brakes, Speed Brakes Down Ready Now
Slowing
Back in With the Pull
Easing Forward
Standby Smoke, Smoke Off Ready Now
Standby Brakes, Speed Brakes Up Ready Now

Technique
Starting at a distance of about 2nm from show center with an entry angle 30-45 degrees inbound towards the snow line and from in front of the crowd the Diamond starts its pitchup. The slower the maneuver is flown the easier it will be for each wingman to maintain his position, however the slower you fly as Lead, you'll hit a certain point where the nose will drop too rapidly on the back side of the roll and the "scooping up" required to save the maneuver will be too excessive for each wingman to stay with you. Flying faster solves this, although it's tougher for each pilot to make the small inputs and easier to make too large erroneous corrections while rolling. I always like to err on the slow side, but starting out flying Lead you should probably start a little faster and work your way to a slower entry speed as you get more comfortable with the gradual stick inputs versus how quickly you'll need to apply them.

So, here goes... Outside the marker at 400 knots, I'll call for "Smoke On Ready Now" and almost right away (as we're accelerating) "Nose Coming Up". Again exactly where you start pitching up depends on the speed, you want to be inverted as you cross show center and as we all know, there's no such thing as a perfect show, but you can come darn close. I use the 2.5nm marker as a reference and ballpark my distance either outside if I'm fast and inside if I'm slow. Just a matter of a second though, not by much. Ideally we're pitching up at no more than 425 knots just a hair inside the marker. As mentioned previously, our angle should be 30-45 degrees offset from the show line, so you might want to cross abeam the marker with the marker off to your left side (since the rolls are done show left to right for the crowd).

The pitchup is very similar to the pitchup I use in turnarounds. I always try to see "single digits" on the G. In other words, being so smooth that I can read almost every hundredth of the G as I'm applying it. I'll continue to increase the pull to about 1.7G's and as I reach this I should be near 15 degrees nose high and be making the "Rolling Left and Rolling" callout. On the second R in "...Rolling" is where the turn is begun, however considering comm's lag I'll delay my input slightly longer. Once the roll is started you want to gradually increase the roll rate and aim to have it set by 90 degrees (knife edge). As I roll past 45 degrees roughly, I'll call "Into the Float" and ever so slowly ease forward on the stick. Do this to fast and you'll send your wingmen off to a different planet. At knife edge I'll start the call for "Standby Brakes...", this is where your cadence and how fast you say it really comes into play and it depends on how fast you were initially, how rapidly the nose is starting down now and (God forbid) you actually forgot to start saying it! The goal is to have the boards fully extended by the time you're rolling through inverted. To make this maneuver easier on yourself as Lead, you want this call done and the brakes down by that time, so you can focus more on the hardest part of the maneuver as well as maintaining roll rate. Also, in a perfect roll, the boards are down in the same instant the nose pitches through the "0" line on the pitch ladder with your wings level and inverted. The On Top altitude varies, but if done on the slower side of the maneuver envelope as you start pitching up (400 knots), you would top out around 3K while a faster initial pull into the maneuver would yield around 4K+.

The roll rate should be consistent from 90 degrees of roll (knife edge) until 270 degrees of roll (opposite knife edge), however, this does not mean you'll be holding your stick absolutely still. It might appear that way, but as speed bleeds off you'll need to increase your roll input until about the time you're inverted (just to maintain rate) and once past inverted and the nose is once again pointing towards terra firma, you'll need to ease the stick input. This is most clearly seen if you extend the brakes too early and start slowing faster while still increasing stick deflection as the roll rate would speed up much faster once you've begun heading downward again (now holding too much roll input).

At 270 degrees of roll call for "Slowing" which means that you're now decreasing the roll rate and plan on stopping your roll input by wings level or there about. This is easily done by feel. The hardest part is right after you've called for "Slowing" and reapply back pressure with "Back in With the Pull". You'll need to compromise between the smoothest pull left in ya and the quickest application you can muster in order not to buy the farm. The goal is to be extremely smooth as you initiate this pull and then gradually pull just almost as much as you think you need, but not quite. As speed is building up your pull becomes more effective and it's easy to "scoop" too much right away and then realize you could have applied less pull initially, but as the ground is fast approaching and you're aiming to be back at 400ft AGL, things tend to happen fast. Optimally you'd want to gradually apply to correct amount sooner rather than later and hold a steady pull for a brief moment and then ease forward to make the altitude. The "Easing Forward" call is straight forward and the "Smoke Off Ready Now" as the nose is approaching level. Then all that is left is to clean up the boards and power back for the next maneuver. Just remember to hesitate a split second between each of these calls, since reaching for the smoke key, brakes and immediately powering back is a recipe to have one or more wingmen get a little loose.

Once you've cleaned up, you should be on the opposite side marker, roughly about 2-2.5nm from show center on the same heading as you came in on. If flown during a real show schedule, the next turn would be left for either the Arrowhead Loop or Hi-Lo Hit (following the Trail-Diamond Roll).

Control Inputs (Brief descriptions of each pilot's inputs during a roll).

Lead rolls left along his own axis and pulls initially (until "Into the Float" where he eases forward on the stick ever so slightly). Keeping consistent roll rate, staying on top of all the calls and their execution and parameters to achieve the same roll each time it's performed is the key. The back side pull ("Back in With the Pull") is the part most likely for Lead to pull ahead of the formation and loose them if done too abruptly and this requires the most focus on your inputs. Other than that, think of Lead as making a high-Slow Roll along his own axis over the airport in a very graceful way.

Right Wing needs left roll input (a little less than Lead), a handful of pull to "arc around" Lead, some left rudder rudder variations to maintain distance (depends on how much aileron input) and also a slightly higher power setting as his flightpath is slightly longer flying on the outside wing.

Left Wing needs left roll input (slightly more than Lead), a steady push forward on the stick, some right rudder to maintain distance (countering gravity and varies based on amount of aileron input) as well as a hardly noticeable lower power setting to roll around Lead on the inside wing. In other words, cross controlled and uncomfortable! Occasionally, even the Left Wing needs to pull to stay on Lead's wing, which is best described as "you're pulling and pushing at the same time" however weird that may sound.

Slot follows Lead's movements, with the exception of some additional float at the top (which requires added power as well). A deliberate delay on roll inputs is sometimes necessary to stay in the correct planform as to not let Lead "slip or slide" in front of you during the roll. In other words Lead's bank angle should be just a hair more than yours to the left during the roll.

Common Mistakes
Putting in too much rudder into Lead in the wing positions is referred to as "Toeing", while holding too much aileron or banking into Lead (while holding opposite rudder) is called "Cupping". Two terms actually used by #7, the Operations Officer during Thunderbird practices and shows. If you look at the form from above or below and see the nose of one of the wingmen pointing inward towards Lead, then he's toeing. If a wingman would have his wings banked inward towards Lead, then that would be cupping. These are things they look for and have radio calls for since it makes the formation look awkward as they're not maintaining the same "plane" so to speak. The whole idea is for the formation to look as if the wings of the jets have the same angle with the horizon and roll as one, while not deviating from paralleling each longitudinal axis with that of Lead's fuselage or axis. Accomplishing this while every pilot uses very different control inputs is as I'm sure you know easier said than done, but also what makes us appreciate and love what formation flying is all about!

That's all I have for now... Hope this helps!
LawnDart
Fireball
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Post by Fireball » Wed Oct 24, 2007 3:49 pm

During the Diamond Roll, should the lead try to eliminate any corkscrew movement through the air? In other words, viewed from above, should lead's flight path be a straight line along the ground, with no side-to-side deviation? Thanks for your help!
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Lawndart
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Post by Lawndart » Wed Oct 24, 2007 4:06 pm

No, it will appear like a barrel roll, since the "float" means the Boss eases forward on the stick ever so slightly while still carrying some G (i.e. Boss is still carrying some back pressure during the roll). Top-down it will look like a shallow S-turn starting to the left and then right over the apex; however, since the Tbrids roll rate is quite fast, the formation's heading really doesn't change much more than ~+/-10 degrees or so.

Note: The porcedure posted above was jotted down in 2005 (see post date). We fly it somewhat differently nowadays in LockOn and it cannot be accounted for being accurate in real life either.
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