Formula for SGR

[Steve76]

Can anyone recall a simple formula for calculating SGR.
Its been a while.......:)

[heedm]

What is SGR?

[Steve76]

That was the tester...
Specific Ground Range.
Great to use when you are planning/flying IFR and you are planning on 600lb/hr but are actually burning more or sometimes less.

[Arm out the window]

Fuel flow divided by groundspeed -

lb (or whatever) per hr / nm per hr = lb per nm.

Is that what you were after?

[the coyote]

Fuel flow = lb (for eg) per hour
Groundspeed = nm per hour

Divide one by the other and you will get lbs per nm or nm per lb of fuel burnt.

600 lb per hour @ gs of 120 Kts = 5 lb per nm travelled or 0.2 nm travelled per 1 lb fuel burnt.

[Steve76]

Thanks for the replies AOW and Coyote.

Its been a while since I did those Aussie ATPL's.... negative experiences tend to be forgotten over time .......

I think I may have confused the issue. What I more accurately needed was a calculation of the actual fuel burnt considering DA etc.

eg: indicating a burn of 600lb but due to being at 20000' (dodging 737's in the 76) the actual burn is maybe 500lb's

Thanks for your time in reply... :)

[212man]

Why would you expect the actual fuel burn to differ from that indicated, unless you know that a particular a/c has unreliable fuel flow gauges?

That's one of the advantages of having a fuel flow indication: you can, in a/c such as the 76, juggle fuel burn vs groundspeed on long legs where you may be on the limits of range. Of course, with a 76 you have the Vne factor to contend with, along with headwind and FF. With the EC-155, you only have headwind and FF; TAS will only get better with altitude, up to about 10,000. Sorry, was that a plug?

[Droopy]

212man; I could do with a quick chat about matters Nigerian; will you email me if you're happy to discuss a couple of points. Thanks.

[the coyote]

Spot on 212 man, can't beat what is actually happening airborne.

If your really tight on planning it can be an advantage having some figures up front, but if your that tight you probably want the worlds most accurate wind forecasts too...

Obviously the actual figures depend on the model, the engine installation (and their condition) and the cruise power settings. Its a snack to take some notes in the one/s you fly at different levels, work out the DA's and the corresponding burn at the time and you'll get pretty good data to work with.

[ShyTorque]

Just go to the relevant FMS page and look it up...:)

[212man]

Well, yes naturally, but you can sound a little pretentious stating the obvious. Mind you, we have to manually enter the fuel flow into our FMS (UNS-1D), and on top of that, it isn't even a real fuel flow; it's a FADEC computed FF from the metering valve position.:D

[IHL]

Steve76 , I think what you are referring to is lbs per nautical mile.
In the very back right before noise abatement procedures of the 76 AFM there are a bunch of graphs for various altitudes, temperatures, and TASs. I think it is located under additional information or something similar, but for some reason it is not in the performance section. That should provide answers to the fuel flow secrets of the 76 universe.

Do any interesting tours lately ?

[212man]

That would be Specific Air Range then, would it not? If you had accurate wind aloft forecasts for various levels, you could then come up with expected SGR for each level, and plan accordingly.

[ShyTorque]

Sorry to sound pretentious then! No I'm not, it WAS only a joke...

Information in any flight manual is only a guide. However comrehensive the charts and graphs in the flight manual; experience has shown me that Sikorsky predicted fuel useage figures can be a little over-optimistic.

Specific fuel consumption is expressed as nm/lb. Some FMSs do automatically take the actual fuel flow and give an accurate fuel consumption / air range figure on the fuel page. When flying long offshore SARs (200 nm plus), we used the fuel pages while we compared different altitudes to see if we could improve our specific fuel consumption figure because often every drop counted and we had no diversion. The FMS calculated everything and took into account the wind effect, often the biggest factor for a helicopter.

One simple way of keeping tabs on your fuel is to make up a row & column table showing actual fuel contents, for example in hundreds, on the vertical axis on the left, and fuel flow, again in hundreds, across the horizontal axis across the top. Do the maths for flying times remaining and fill in the boxes.

When calculating my flight times remaining I added in my aircraft minimum landing fuel figure to make sure I didn't forget it (200 lbs in my case). For time to dry tanks, I look two rows up in the same column, i.e. for the actual gauge total indicated at the time of the check plus 200lbs. I added a note to this effect at the bottom of the table so I didn't forget what I was doing.

You can use this in the air either by looking at the fuel flow gauges if fitted, or a timed fuel drop on the aircraft contents gauges.

We are all well-versed in estimating time of arrival so all you need to do in the air is know your required flight time remaining, and check it against your endurance using the table.

Of course all you are doing is the arithmetic in advance but use of my accurate table has allowed me to confidently confirm I was able to continue to a SAR scene without the hassle of landing on an oil rig for a refuel; when you are getting low on fuel you do need to get those figures correct!

---------------

If anyone can tell me how to post an image file I will try to put an example of such a table here.

[Steve76]

Thanks for asking IHL :)
Moose was chilly and I doubt if I will try a 20min run in -35 degrees again. Did you know that your eyelashes will freeze together with just the littlest of sweat.......
Kenora was a blast. 7.4 in two days. What a beaut part of Canada.
How's things near the equator? Taught those aussies a thing or two yet?
Thanks for the replies guys. It is my understanding that SAR is more or less irrelevant and that SGR is the more accurate calc.
However, I cannot confirm this presently and I will re-read the replies and find some more info in the FMS and books.
Again, thanks.

[212man]

I don't think there is too much mystery to it: if you are flying at 100 kts into a 100 kt headwind, you could have the most amazing SAR but it would be meaningless as the SGR would be 0.

So SAR is only half the story. However, if you can predict SAR from the FM in advance and couple it with forecast winds the story changes.

You can't beat the actual SGR figure on the day though, and there is no simple formula for calculating it (as originaly asked).

[Nick Lappos]

212man, don't give up your flying job to be a math teacher! If you are burning fuel and going nowhere with zero groundspeed, you divide the fuel flow by zero and get infinite SGR, which means infinite fuel to go one mile. The "formula"makes sense.

BTW, this is not rocket science, guys. Take the fuel flow and divide by the ground speed. The pounds/hour divided by the miles/hour gives you pounds/mile, so you always know how far your gas will take you, a much better piece of knowledge that how many hours you have left.

The S-92 goes one better, it has the fuel gauge and the fuel flow gauge on the same scale, so the arrow of lbs/hr fuel burn points at the same bar that fills in the fuel amount. If the burn rate is half way up the fuel gauge, you have 2 hours gas remaining. If the burn rate arrow lines up with the fuel amount, you have 1 hour fuel remaining. (for example, burn 1000 pounds per hour, with 1000 pound of fuel remaining).

[212man]

Thanks Nick, I'll bear that in Mind.

In a practical, real world, mental aritmetic, single pilot type sort of environment, it is probably more relevant to know the nm per lb. That way, you can more readily assess the range available for a given fuel quantity remaining. So 0 nm/lb rather gives the game away that you aren't going to get too far. No doubt I'm wrong.

I am intrigued by the fuel symbology in the S-92 and will be interested to see exactly how it looks, some day. On the EC-155 there is a real time fuel flow figure for each engine on the fuel page, along with the quantities and an endurance remaining. It's fairly simple stuff, but you can see in a real sense how the endurance changes with altitude, directly, rather than having to calculate it fom the the figures yourself.