Performance charts (rejoins)

[JaBog32_Dirty]

Hi Thunderbirds and Practicegroup,

I made those performance charts for you all. Haven't verified them yet (it's late), but I'm pretty convinced that data integrity is sufficient.
I wanted to make rejoins quicker without overshooting Lead, so I needed data about how the flightmodel decelerates. This is what came out:


1st Graph:
www.alderwasguckstdu.de/Bilder/Speed%20Loss%20F-16.png
...gives you an Idea of how the F-16 in VTB configuration decelerates over time. Straight & level, Power idle, no Speedbrakes!


2nd Graph:
http://www.alderwasguckstdu.de/Bilder/O ... Rejoin.png
...tells you when to pull the power back to idle depending on Leads airspeed and your overspeed (closure rate). Straight & level, Power idle, no Speedbrakes!
Example: Lead flies 400Kts IAS, you approach him from behind with 550Kts IAS (150Kts overspeed). Pull power back to idle at a distance of 0.6NM to reach his speed when you're exactly abeam his wing. Cool, huh?

And there is one important thing that I really want to add! I don't want to be a smartass, and I certainly DONT want to tell you guys how to fly. You do that pretty well without me. I did this simply cause I enjoy it, and I feel like not sharing it would be stupid.

Dirty

...and btw, I won't show up to practice for a few days. My girlfriend grounded me!!!!!

[Lawndart]

Very interesting concept Dirty! I can see how this could be useful in learning a distance out where you need to be powering back. I'd also like to point out another technique we use very frequently which is adding pull to the airplane to slow down for the rejoin. Where you come in on lead from above, first in lead pursuit, then slowly going pure pursuit and with 100-150 knots of overtake. You throttle down (just like you said, although a little closer) and then "level off" with more G's on the jet to bleed off the excess speed. As you start bringing the nose up you should now be going from lag to pure pursuit without ever really dropping below lead's altitude. It's a little more dramatic and harder to do well, since there's less room for error and if done poorly you run a good chance of overshooting. If done correctly however, it looks faster and more precise! This is the type of rejoin used before the Thunderbird pitch (for landing) when the Diamond joins up again after the crossover.

I definitely like your enthusiasm and info, which will be useful for level join ups!

LawnDart

P.S. So, your "Boss" grounded you...

[JaBog32_Dirty]

Well, actually I grounded myself preemptively because I really like my "Boss" and don't want to end up beeing a solo pilot

Yeah, for those charts I took the most conservative approach. Every little bit of additional drag makes the rejoin more "crisp" (is that the word you're using?) but at the same time narrows down the margin for errors and calls for a more precise execution of the manoeuvre. The problem with the induced-drag-braking-method is that it's nearly impossible to describe mathmatically and put into a graph.
Time permitting, I will add dashed lines for speedbrake-extended performance.

Basicly, what those graphs are saying is:
No need to take the power back earlier than the distance taken from the graph.

Primarily, I wanted to give the practicegroup a rough guideline with which to start practicing thier own rejoining technique.

Dirty

[Lawndart]

Well, actually I grounded myself preemptively because I really like my "Boss" and don't want to end up beeing a solo pilot

LOL, good point!

Basicly, what those graphs are saying is:
No need to take the power back earlier than the distance taken from the graph.

Simple and clear, I like it! Then to stretch this further, if you're using induced drag and/or brakes to slow as well you can always feel your way even closer before idling the throttle.

Primarily, I wanted to give the practicegroup a rough guideline with which to start practicing thier own rejoining technique.

Rejoins are as necessary as formation itself. Can't have one without the other... It won't make a big difference, but we aim to have lead holding 350 knots for the rejoins. Just some FYI...

LawnDart

[JaBog32_Dirty]

Now I added the dashed lines for speedbrake-extended performance (you may have to hit the "reload" button). It is clearly visible that speedbrakes give you about twice the parasite drag, and so only about 1/4 of distance is required to decelerate to Leads speed.

Those speedbrakes seem to be a litte bit too effective for my taste,...

Dirty

[Burner]

A little more on rejoin technique. You want to go lead pursuit of course to catch up to lead, no more than 650knts on the jet for multiple reasons but mostly so things don't get too out of hand too fast. You want to come in above lead to have a nice picture of the situation, have gravity working for you, and to be out of lead's flight path so you can do a nice pull to kill speed. Once you can visually pick out the formation its time to bring the throttle back and pop the brakes down to about 200knts closure. Once you can visually identify each individual plane you have to play it by ear, no more than 100knts is a good assumption.

Now for the transition to pure pursuit, put your velocity vector just behind lead's tail (not really lag pursuit b/c lag pursuit is to put you on lead's flight path well b/f you get to him). What you're looking to accomplish is an abrupt pull, as many G's as possible, that transitions you from coming down on lead to being on lead's flight path and slightly below and behind him. The closer you are after you finish this maneuver the better you have done. If you finish this maneuver and you see you're still going to overtake you can initiate another hard pull by continuing your pull up until you're above lead, then rolling inverted and pulling again. This is unorthodox and would probably get you grounded in the real world, but it does work.

If you're going to overtake go underneath, fall back then try it again, don't try to join up from the front falling back. Overall remember the more extreme and abrupt the stick pull the more speed you will kill. When you're first practicing this maneuver aim well behind lead and work your way forward as you get better, the ideal is you pull, get the brakes up and throttle up a bit to pull into position within seconds.

[Lawndart]

I'll second one thing that Burner pointed out. I always try to have 100 knots of overtake by the time I go completely visual contact for the rejoin.

I won't argue with the master of formation flying himself (Burner) regarding technique, but my approach is a little more conservative and gradual on the pull (application of induced drag) than what Burner described.

And I do agree with Dirty that the speed brakes feel too effective, although this definitely works in your favor for the time being (until they revise the flight model in the sim).

1's Out!

[Trapper-FreeBirds VFW]

Curious Jabog, what data did you use to generate those charts? Also what fuel load. Thanks

[JaBog32_Dirty]

I used the F-16 (F-15) with no external loads, 50% Fuel with Flaps 1. Exactly like the Thunderbirds fly. All testflights were done at 500ft MSL.

on this one:
http://www.alderwasguckstdu.de/Bilder/S ... 20F-16.png
All I did was pull the throttle back at high speed, and then note speed vs. time.

this one:
http://www.alderwasguckstdu.de/Bilder/O ... Rejoin.png
was derived from the graph above using some magic-math I superimposed a constant motion (Lead) with a decelerated motion (Wingman rejoining) and verified it with a couple of testflights.

3 hours work while waiting for my girlfriend in the library.

Dirty

[Lawndart]

Speaking of techniques regarding rejoins. "Blipping" the boards work well for minor adjustments while in formation that are just big enough that throttle and slowdown won't arrest the momentum. When we talk about drastic rejoin attempts you have to be agressive, yet I try not to look out of control at any time (in other words not maneuvering as if I was dogfighting). One technique I use for rejoins is to open the boards and coast. This seems normal (as it should) and the common mistake would be to overshoot, since you'd be coming in too hot. As long as you timed the initial rejoin speed fairly well, the second most common mistake is not closing the boards soon enough, right after a hectic slowdown and starting to fall back again (as long as you never actually overshot). My remedy for this is (here's the technique) using idle, boards and as much induced drag as I can in my level-off from lead pursuit and then anticipate the bleed off in speed and power up well before I feel I would need to, with the speedbrakes still down! The boards open is the key to this working. This in effect "slows" the overtake, rather than killing the momentum completely and once you go brakes up you're already powered up close to the formation or lead's power setting. "Blipping" the boards or feathering the throttle is usually enough at that point to maintain distance and close up those last few feet without falling behind or drifting away. Coming in from above helps too as this gives you "pull" (induced drag) to play with and means you won't need to jockey the jet around like a mad man when you misjudged your inbound overtake in a level rejoin altitude. If you look at the diamond rejoin after the 4 plane cross this is exactly what everyone does and the reason for each wingman starting their rejoin from a few thousand feet above lead after #1 says: "...and Pull!" (during his half-cuban). Just some additional food for thought...

LD