Hawker 800xp LRC Fuel Flows

[hawker-piloto]

Hey Guys.

Was wondering if anyone can share what fuel flows they use for flying LRC on the HS-125?

[localizer28]

not sure whom you mean by "they".

Fuel flow (at a constant Mach) depends on temperature. If it's warmer than ISA, you need less power to maintain the same speed, so therefore the fuel flow decreases, and vice versa.

Anyhow, if I need to do LRC on the XP, I usually set power to maintain M.70 and the FF will be somewhere in the range of 1300, if the temperature is on your side you might be lucky to get it down to about 1250. Try to cruise as high as possible (check the tables for maximum cruise weight in your QRH).

Good luck and safe flying ;-)

[shamrock48]

I agree with the above. Don't try and be tempted to get to FL410 (FL430 on my XP) too early. Let the wings get to no more than 5400 before attempting. Also try and keep the first hour burn to 2000lbs. ISA is a big deal on Hawker. 6hr 40m is the best I ever got with 1500 landing fuel. Great aeroplane 25 years of fun.

[imriozer]

I never knew the XP was certified to FL430??:ugh:
Flying for 6:40 is sure nice, what was the mean TAS on that flight? Was it a full payload flight?

Cheers,
Imri

[redsnail]

In the US it is certified for FL430, Europe however, is FL410.

[lk978]

The hawker is only certified to 41000 everywhere, It was originally planned to be certified to 43K (pressurisation system is set up for it) but i believe it was knocked down as part of the certification process.

pretty sure this is for everywhere as it is in the flight manual under the limitations section... Care to share the rego of the hawker going to 43K?

[localizer28]

hello guys,

check out the following link (EASA Type Certificate Data Sheet):

www.easa.europa.eu/certification/type-certificates/docs/aircraft/EASA-TCDS-A.085_(IM)_Hawker_Series-04-06042011.pdf

according to the EASA, the BAe.125 Series 800A and 800B (built in the UK) were originally certified to FL430, however the FAA only certified them for FL410 (check Note 69).

For those who can read German, the LBA documents (LBA TCDS) also show 43,000 for the 800B, but 41,000 only for the 800A:

www2.lba.de/data/bb/Flug_o2t/ta_2507_01.pdf (800A)
www2.lba.de/data/bb/Flug_o2t/ta_2507_02.pdf (800B)
(if the links don't work, just google the documents)

Checking the FAA's Type Certificates, all HS-125's are limited to FL410 period.

Being able to get to FL410 (with the exception of the 900XP, in most cases) depends on the combination of prevailing ISA conditions and actual takeoff weight. A very helpful guide is the "Maximum Takeoff Weight for Cruising Level" Table in the QRH. It might well be more beneficial to level-off at FL390 and do LRC there for a while and step-climb to FL410 after a good hour or so.

[deefer dog]

The reduced ceiling is to satisfy the emergency descent requirements. Other than that they could all go up to 430, but none, even the 900XP will get their in a hurry unless light, or it's lower than ISA.

[Kelly Hopper]

Fuel flow (at a constant Mach) depends on temperature. If it's warmer than ISA, you need less power to maintain the same speed, so therefore the fuel flow decreases, and vice versa.

You sure about that?

[localizer28]

yes, positive

[tommoutrie]

I think it might be a bit more complicated than that. On my plane (not a hawker) we burn 50lbs/h more for an increase in temp over ISA of 10 degrees (and 50lbs/h less when its ISA -10). So you would think that the most fuel efficient for us at the same mach is when its ISA minus a lot. But thats for the same MACH number and TAS obviously varies with temp so there's a bit of swings and roundabouts going on. I don't think ISA makes a busting lot of difference to our specific fuel burn (ie the amount of fuel we burn per nautical mile). You get more power when its cold because there's a bit more air (so you climb better) and you therefore get to a height where you have a lower fuel burn more quickly.

there are many variables. I think its a difficult equation.

[Silly Pilot]

If you take a look at the AFM or AOM wichever, you will see charts that give you settings for various altitudes, temps. It will give IAS and maybe N1 and fuel flow. After you have spent all that time familiarizing yourself with the AFM chart data and carefully making the adjustments, the end result is .70 mach.
For some reason on the Hawker they did not spend much time refineing this data.

In other manufacturers jets you may find in the books that the lighter the plane gets the slower you can go wich is designed to keep best lift over drag, as time passes you must make adjustments. These companies have spent more time on the lift over drag number crunching.

[Kelly Hopper]

If it is warmer than ISA you need MORE power to maintain said Mach No., not less.
Cold temps= better perf. Warm temps= worse.

You may be factoring many other influences but just on +/- ISA warm is bad, cold is good.

[tommoutrie]

well its true that the engines will provide more power at lower air temperatures because there's more more oxygen to burn. To achieve the same Mach number its true that you need more fuel going through the engine (so achieving the same mach number in cold air requires a slightly lower fuel burn). But thats not the whole story - TAS is the important number with respect to how fast you go over the ground, not mach number, and TAS increases with increasing temp. So a cruise of 0.8M at ISA plus 10 is faster over the ground that the cruise at ISA -10 at the same height (I think this is true and I'm quite happy to be told I'm wrong).

So working out the variation in the fuel burn for a given trip in a given time with varying ISA is a bit tough. And it gets more complicated than that because the aircraft will climb better in colder air (because the maximum power available is higher). So you get to height more quickly and therefore benefit from reduced fuel burn earlier.

I think you could work out a really complicated fuel burn schedule for maximum range which would constantly reduce as the weight of the aircraft reduced and also varied with local temp.

taint an easy question..

[stilton]

' think you could work out a really complicated fuel burn schedule for maximum range which would constantly reduce as the weight of the aircraft reduced and also varied with local temp.'


With the cost index set to 0 and in Econ mode that is exactly what the FMS on the B757 / 767 will do for you in VNAV, very handy on the 75 when we push the limits of the aircraft as we often do.

[deefer dog]

ISA + will always produce less range.

Hawker performance data included in the AFM is pretty comprehensive. Nautical Miles per pound of fuel is what you should be looking at, and it is included for above, below and at ISA, at different levels and weights.