How to lose time inflight
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all you have to do is divide your ground speed by 60 to calculate the nautical miles per minute. Using a ground speed that is a multiple of 60 makes the math simple. It’s NOT a precise calculation because a nautical mile is not 6000 feet, but it’s close enough. And at low level KCAS is essentially ground speed.
420 KGS = 7NM/min
480 KGS = 8NM/min
540 KGS = 9NM/min
600 KGS = 10NM/min[…]
If on the other hand you’re up around FL180, 350 KCAS should put you somewhere around 480 KTAS. But then you have a different navigation problem and you have to adjust for winds…the Jurassic multiple of 60 technique doesn’t work because your HUD indicated/calibrated airspeed is significantly different than your ground speed. Thankfully the jet is smart.
To expand on this, at higher altitudes, you can also use Mach (which is TAS relative to local speed of sound) to get a good enough approximation of ground speed…
Take your Mach number, e.g. 0.80, and multiply by 10. You get 8NM/min KGS. That times 60, and you get KTAS 480. Weather will influence the exact result, but it should be within an acceptable margin of error (a difference of perhaps 0.02 Mach, or 12 knots, usually).
Like this, it becomes relatively easy to figure out how long you need to get to a steer point and how fast you should be flying, even without the onboard computers telling you.
E.g. Cruising at Mach 0.80, with a steerpoint about 60NM ahead. 60NM / 8NM/min = 7.5 minutes to get there. Say your TOT is 10 minutes from now, you know straight away you’ll be 2.5 minutes early and should reduce to an average speed of Mach 0.60 (60NM / 10min = 6NM/min = Mach 0.60; either by pulling back throttle or orbits / dog legs).
Conversely, if your time to TOT would be 6 minutes, you know you should be flying Mach 1 to reach it, and can decide whether you can afford to burn the fuel required, or call in that you’ll be late. -
This stuff is great, keep it coming! So what I’ve gathered so far is:
Plan to be a little early, and build a route that allows for you to cut corners, or hold/dog-leg to adjust as necessary. Putting the hold prior to the push steer makes logistics of package coordination easier. Low ALT KCAS/KGS are essentially equivalent at the speeds we’re talking about, and Mach values can be roughly used at higher altitudes for the same nm/min calcs.
For climbs, use the -1 table (I’ll look that up when I get the chance) and most descents should be penetrations at 350KCAS, boards out.
So if we’re talking RL, do modern pilots calculate GS and ETA/TOT by hand via checkpoint dist/time in a combat sortie? Or do they just use the DED and only resort to by hand stuff if it fails?
Thanks again guys, this is great info.
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Low ALT KCAS/KGS are essentially equivalent at the speeds we’re talking about
Not entirely. You calculate ground speed from KTAS (= your actual speed through the air) instead of KCAS.
At low levels, however, KCAS is close to KTAS… For KCAS -> KTAS calculation, a good estimate is to add 5kts per 1000ft. E.g. 350 KCAS at sea level = 350 KTAS, but 350 KCAS at 10,000ft = 350 + (5 * 10) = 400 KTAS.
To get ground speed, all you need to do is add or substract head-/tailwind-component to KTAS. E.g. 450 KTAS with 50kts headwind = 400 kts ground speed, while 450 KTAS with 50kts tailwind = 500 knots ground speed. This is why an airliner flying Mach 0.85 from Europe to the US takes longer than one flying Mach 0.85 to Europe (EU -> US, you’re flying against, and US -> EU, you’re flying with the Atlantic jet stream).
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Curious, I’ve never heard of the 5kts/1000 to account for KCAS KTAS differences. I wonder how accurate that is (for off the cuff calculations).
I understand that GS is from KTAS not KCAS/KIAS, but to clarify, for planning purposes would it not be acceptable to assume they’re pretty close at NOE low level? KCAS and KTAS are within a few knots of eachother, and max winds would be around 30ish kts, which is <10% airspeed delta, unless there’s a crazy front moving through or hurricane haha. Or would it just be easier to account for them when plotting? I’m interested in the way this is actually done when planning for a mission.
While we’re on the subject of speeds, anyone know if the F-16 KCAS accounts for compressibility errors (EAS)? Just a random aside.
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To expand on this, at higher altitudes, you can also use Mach (which is TAS relative to local speed of sound) to get a good enough approximation of ground speed…
Take your Mach number, e.g. 0.80, and multiply by 10. You get 8NM/min KGS. That times 60, and you get KTAS 480. Weather will influence the exact result, but it should be within an acceptable margin of error (a difference of perhaps 0.02 Mach, or 12 knots, usually).
Yes that’s an excellent RoT, as long as you’re not up in the jet stream or don’t have a very long leg. Winter in North America, the jet stream winds are typically brutal. Typical cruise mach in the A320 is .78, our ground speed flying east to west you could estimate to be 420 KGS, and west to east 480 KGS. But in the winter…I’ve got pictures of my PFD showing a ground speed of 595 KGS at .78 mach. Fortunately for BMS that should not be a problem.
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Curious, I’ve never heard of the 5kts/1000 to account for KCAS KTAS differences. I wonder how accurate that is (for off the cuff calculations).
I understand that GS is from KTAS not KCAS/KIAS, but to clarify, for planning purposes would it not be acceptable to assume they’re pretty close at NOE low level? KCAS and KTAS are within a few knots of each other, and max winds would be around 30ish kts, which is <10% airspeed delta, unless there’s a crazy front moving through or hurricane haha. Or would it just be easier to account for them when plotting? I’m interested in the way this is actually done when planning for a mission.
While we’re on the subject of speeds, anyone know if the F-16 KCAS accounts for compressibility errors (EAS)? Just a random aside.
Yes…KCAS/KIAS is essentially KGS at low level. At least they were for 10 years of my life.
My apologies for showing my ignorance. I confess that current terminology eludes me, and if NOE is now a USAF term, then I’ll do the Homer Simpson head slap (D’oh). Nap of the Earth (NOE) is not an expression that applied to my tactical experience. We simply called what we flew “low level.”. We used terrain masking and ridge crossing techniques, but we didn’t fly nap of the earth. If we were really low…100’ AGL we called that VLA (vee-el-ay) for very low altitude. We had training requirements and qualifications to fly VLA. Again, referencing the Jurassic era, NOE is something helicopter pilots did due to their unique combat employment tactics. I know what BMS folks mean when they write or say NOE, and maybe it’s just semantics, or maybe other F-16 air forces say NOE. It just looks and sounds…odd.
In answer to the last question. The progression goes Indicated>>Calibrated>>Equivalent>>True the well known ICE-T acronym.
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Cool stuff thanks! Now for descent planning, is the 350KCAS with boards the main preferred method? Are there rough fpm or ft/nm estimates to help meet crossing restrictions by certain steerpoints? (I realize weight, GS, power setting will all have an effect, just looking for what you guys use to plan). Or is there some variant of the 3/6 - 6/3 rule used for descents in high performance aircraft?
I realize I may have hijacked this thread sorry, I’m just really enjoying this discussion.
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Fortunately for BMS that should not be a problem.
I do wish that was a problem we had, actually lol. They’re going to do winds aloft eventually or at the very least has been requested over the years lol. Come on Mav-JP you can do it!
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Cool stuff thanks! Now for descent planning, is the 350KCAS with boards the main preferred method? Are there rough fpm or ft/nm estimates to help meet crossing restrictions by certain steerpoints? (I realize weight, GS, power setting will all have an effect, just looking for what you guys use to plan). Or is there some variant of the 3/6 - 6/3 rule used for descents in high performance aircraft?
I realize I may have hijacked this thread sorry, I’m just really enjoying this discussion.
There are two methods detailed in the performance charts, the penetration descent and the max range descent. Both are flown far slower than you’d expect. You go idle for both, the penetration is done with boards open at 300 knots and allows you to get down from altitude very quickly. The max range is about saving fuel (and boy does it) and is done at idle capturing a speed between 215-230 knots depending on weight/drag factor and will save a boat load of fuel for you. In combat itself I usually just descend at my cruise speed as I’m not going to be slowing to 230 in the combat arena.
In combat on recovery you can combine the penetration descent with your tactical arrival procedure of your local airfield. Most penetration descents start 20-30 miles away from the field and for example in Kunsan as you come in on the TRP it’s a great way to get from say 30,000 to 11,000 to start the procedure…… and a lot of fun.
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Cool stuff thanks! Now for descent planning, is the 350KCAS with boards the main preferred method? Are there rough fpm or ft/nm estimates to help meet crossing restrictions by certain steerpoints? (I realize weight, GS, power setting will all have an effect, just looking for what you guys use to plan). Or is there some variant of the 3/6 - 6/3 rule used for descents in high performance aircraft?
I realize I may have hijacked this thread sorry, I’m just really enjoying this discussion.
Descent planning…do you mean flying a TACAN penetration or do you mean a combat descent to low level? In the Jurassic era RTB enroute descents and TACAN penetrations were flown at 300 KIAS/KCAS. That was also our cruise airspeed below 10K’ in the US when not in a MOA, Range or on published low level (IR-xxx or VR-xxx on Sectional Charts). In Korea is we used 300 for TACAN penetrations (and fly up Initial) or to simply save gas. As an aside, when the big mouth Block 30s showed up guys were coming up Initial at the speed of heat (big sh*t eatin grins on their faces due to their speed in Mil power). At some point the Wing DO (Deputy Commander for Operations) limited them to 450 KCAS. And to clarify, this was 450 KCAS in tactical formation, 4 ship box or 2 ship line abreast, when the Block 30 was brand new to Kunsan. In combat, base min risk arrival procedures might limit you to 300 or 350 for your safety.
[edit] Just checking my old AFM 51-37 (Instrument Flying) there is a note that says as a RoT plan to descend at 800-1000’ per NM or an 8-10 degree nose down pitch during the penetration. If you’re single ship you can use Idle and Boards (speedbrakes) as required including Full Boards, but if you have a wingman you MUST use some power setting above Idle or less than Full Boards for “wingman consideration.” You can imagine the difficulty for a wingman trying to stay on your wing when he has no margin for adjusting power or speedbrakes.
Combat descent…you can
- roll up (knife edge on a wing) and let the nose drop into a 30-45 degree dive
- roll inverted pull into 30-45 dive (don’t forget to unload to less than 1 G and roll right side up)
- perform a sliceback.
Throttle as required, start with throttle mid-range (halfway between Idle and Mil).
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Penetration, instrument, max glide descents are generally admin flying. If you’re coming into home plate and departing cruise for some recovery altitude then this sort of admin technique is indicated. Personally I like to hit < 30 (not less than 25) nm radius, 300 knots, 10kft altitude as the BMS ATC handles your flight much better. High and or fast and ATC struggles to make arrival a smooth one and inside 20 or 25nm your AI wingmen will decided for themselves to call their own approach and beat you to the bar. A pen. descent and then a low trundle for 30nm home isn’t super tacticool but it does make the ATC function smoother.
In a combat environment where neighborhood speed limits aren’t really a thing I wouldn’t slow down to 300 KT to descend. I was expecting Rho to be more detailed like how do you plan average ground speed or similar in a HI-LO-HI profile and you still want a solid TOT. The book does have performance charts but only for the range and pen. profiles which aren’t the first thing I’d pick in a gloves off fighting situation although it’s not the worst idea. I don’t understand the sliceback. I guess you could just take the GS at start and end, add them and divide by two, and then multiple by sine dive angle for a darn good approximation. That’s why you’d have a trim leg after that maneuver to iron out any inexact times or just rely on the whizbang electronics to sort it out.
While Appendix 9 in the supplement is a must read for anyone interested in the nitty gritty pencil pushing perfection and concepts such as min fuel trajectory (e.g. CRUS HOME), MIL schedule, MAXAB schedule, max range, max endurance, etc. should be well known… tactical and coordination requirements usually dominate. Having the highest specific range at optimum altitude is a poor consolation prize when an unexpected missile blows you up at a sluggish 245 KCAS. Your fuel savings made a bigger fireball. The F-16 will deliver two MK84s an absolutely staggering distance when the full effort is made with regards to trajectory planning and it’s worth the exercise and demo.
Getting back to BMS most flights I fly caret off MIL schedule (rejoin 350 with AI first!) until cruise altitude and then turn it on. It generally shows ~250 to the next point due to the automated way the flight plans are generated which is almost exactly best range speed. A lot of BMS fliers climb and cruise from 1 to 2 at caret which is a goof especially if caret is less than minimum fuel trajectory speed (~330?). MIL climb schedule isn’t as super efficient as the minimum fuel trajectory (aka CRUS HOME), it’s really really really close like within 1%. It feels weird to fly so fast and flat but the math checks out. Formation flying at 290 knots in a climb sucks so much. If I’m feeling untouchable I just let it ride and go a more tactical pace thereafter. If I care to keep the speed up and solve time with geometry. If my ETA is within 2min earlier than DTOS that calls for a timing triangle. Longer than that I would enter a hold at the next point and manage leg lengths to push on time and speed. It’s sort of how racing sailboat ensure they cross the start line as exactly as possible in a regatta. If 2 or more loops are needed I try to get on a 4 minute hold schedule by making the weird one the first loop or two and standard thereafter. For package flights speed push and split I can only be assured of my proper position in the package if I am: 1. on course, 2. on caret, 3. current G/S = planned G/S. A lot of times people are happy when on caret but being on caret is only half the story. If you’re on caret of 461 RG/S but planned was 480 then you’re too far forward for example.
Post target it’s another MIL climb and due to the way the plan is generated I usually won’t be on timing any more especially if AI are multi-pass. Max range descent is almost exactly equal to the LDmax AOA of ~6.5° so penetration has got to be steeper. A nominal book value is 30kft in 20nm which is almost 15°. It’s worth it to fly a HOME profile once to appreciate how god awful slow and boring it is but by golly you can’t beat it for fuel sipping. Some day you’ll find yourself under bingo far from home and it’ll save your butt.
The helo terminology as I know it regarding flight altitude(s) with respect to terrain:
High, terrain no factor
Low, constant (singular) altitude terrain is a consideration
Contour, several level segments with planned changes which roughly conform to the terrain
NOE, flight which is constantly changing height due to the terrainThe “nap” of the Earth refers to all the fuzzy bits and features trees and houses and riverbeds and stuff. It would take a SH pilot to be down in the nap.
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Off topic. Great thread. The devil is in the detail: great example of why BMS is a such a good sim, and why this forum is great too.
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In a combat environment where neighborhood speed limits aren’t really a thing I wouldn’t slow down to 300 KT to descend. I was expecting Rho to be more detailed like how do you plan average ground speed or similar in a HI-LO-HI profile and you still want a solid TOT. The book does have performance charts but only for the range and pen. profiles which aren’t the first thing I’d pick in a gloves off fighting situation although it’s not the worst idea. I don’t understand the sliceback. I guess you could just take the GS at start and end, add them and divide by two, and then multiple by sine dive angle for a darn good approximation. That’s why you’d have a trim leg after that maneuver to iron out any inexact times or just rely on the whizbang electronics to sort it out.
Again I’m an example of the Jurassic era. [edit] In Korea back then we didn’t use LLTRs but we had Brickwall procedures. CENTAF Brickwall procedures and LLTR speed limits and ASLAR speed limits can be sticking points, disregard at your peril. Not suggesting you would be 300 KIAS crossing the fence, but you would be at a distinctly non-threatening airspeed. Brickwall procedures included changing your IFF, checking in with GCI/AWACS, being aligned with an inbound LLTR.
A generic NORDO recovery would include overflying the airfield at say 10K’ AGL and flying a penetration at 300 KIAS (30-45 degree angle off upon crossing the airfield, IIRC arc at 20 DME) roll out on TACAN or ARA final, inside X DME no faster than 250 KIAS with gear and landing light on, look for the light gun from Tower or RSU. Using the 30 degree cut and 20 DME arc would give you 50 NM to descend and slow to approach speed. How did I come up with 50? 20 NM outbound plus 10 NMs of arc (60:1 rule says at 60 NMs 1 degree equals 1 NM, so at 20 NM 3 degrees equals 1 NM. I have 30 degrees of arc to fly divided by 3 degrees/NM equals 10 NM) and a 20 NM final. Assuming your 300 KIAS equals your GS, then it will take about 6 minutes from overhead to roll out on final (the first 30 NMs divided by 5 NM/min = 6 minutes) add 6 minutes on final…12 minutes total. Oh an important point…in CENTAF you would fly this procedure so the final is to a runway that is the most easterly aligned. The conventional wisdom being your jet looks the LEAST threatening if you are on final from west to east. What if the winds favor a landing to the west? Circle to land or use pilot discretion and land with a tailwind.
Regarding HI-LO-HI planning. Dash 1 numbers in “tab data” that were simplified for three aircraft weights, 24K, 28K, 32K pounds with Max Range, 480 KTAS, and 540 KTAS. Our “Ladies’ Aid” (Inflight Guide) had a page with this info along with the distance and fuel burn to get to altitude. And prior to the arrival of the C model and its desk top PC to crunch numbers and load in the data transfer cartridge, we used the Whiz Wheel (E6B circular slide rule) to calculate ground speed. I know, really old school stuff.
But…we rarely flew HI-LO-HI profiles. Flying low level was infinitely more fun, and at the time the current state of ECM along with CENTAF’s less than ideal weather drove that tactic. It was only 1990 when the TAF started emphasizing HI-HI-HI. Our pre-planned Day 1 of the war missions at Kunsan were HI-HI-HI. My Certification against Toksan was a HI-LO-HI profile, but IIRC my TOT was a 10 minute window. My Certification against a target in East Germany was a LO-LO-LO (HI) with a window. My RF-4 experience with TOTs a bit different. They were typically not specified or given as No Earlier Than or No Later Than during Reforger or ORIs. The logic behind the NET or NLT being not to conflict with the strikers and get ourselves shot down by a friendly that didn’t VID us. At Red Flag that meant flying as an outrigger enroute for mutual support, split off to get your target (different than the strikers) and rejoin when the strikers come off target.
Regarding the use of a sliceback…it’s a TLAR maneuver. I briefed it in my Toksan Cert, fly past the target a planned distance (tactical misdirection) and sliceback to low altitude. I used it when entering a VR route north of Atlanta’s Class Bravo airspace. ATC had vectored me away from where I wanted to go. I got clearance below 18K’, canceled my IFR clearance, told my wingman on Victor (VHF) to “follow me, slice left.” My squadron used it in a 20 ship exercise down to Avon Park. Lead got clearance for our non-standard formation to get below 18K’, he canceled, while headed southeast away from Avon Park he got clearance from the Ranger into R-2901 and everybody sliced in sequence down to 500’ AGL. TLAR.
The helo terminology as I know it regarding flight altitude(s) with respect to terrain:
High, terrain no factor
Low, constant (singular) altitude terrain is a consideration
Contour, several level segments with planned changes which roughly conform to the terrain
NOE, flight which is constantly changing height due to the terrainThe “nap” of the Earth refers to all the fuzzy bits and features trees and houses and riverbeds and stuff. It would take a SH pilot to be down in the nap.
Yep, sorry if I confused. I know what the terms mean, just observing that NOE was not in my contemporary vernacular.