HS 748 and the RR Dart

[yoohoo748]

Hello from Canada. I'm with a small regional carrier flying the 748 and have a few questions for any in the know for operating the Dart Series engines on the 748. Minor details, but perhaps important.
1) Normal Idle> 6675 - 7200?
2) Idle for 1 - 2 minutes prior to shutdown?
3) Boostpumps on for shut down untill engine spooled down?
4)anything else that didn't make it to the training manual or AFM or our SOPs

Thanks for the help. It seems like many people at our company have designed their own engine management regimes yet have nothing to back it up.

[scanscanscan]

One tip for you...
Know Max continuous power setting,and how to set and obtain it.
You will need it on one engine.
In the tropics it was necessary to fuel trim up to the recommended max cont EGT temperature.
This temp and rpm,if set would achieved the advertised max cont power.
A lower TGT at the correct rpm produced a lot less power, and a descent!
Ask your Captains to brief you about this,so you both are ready when it happens.

[4g_handicap]

Hi there,

We switch off 1 set of fuel pumps after landing and the other after spool down.

One colleague of mine claims that he could not start an engine once because the pumps had been switched off prematurely - don't know that facts of the matter, but decided not to risk it.

We also have a 2 minute idle time - as far as I know RR recomend at least 30 seconds, which our company made 1 minute and now only recently our engineers have asked us to extend this to 2 minutes. I generally try to follow the engineers recomendations, as there is often method to their madness(or is madness to their method). If it conflicts with a specific aspect of the AFM, ask them to explain the deviation.

Regards

[yoohoo748]

Thanks for the replies.

soddit : We operate RR Dart 534-2 and I think a 535-2 (on a 748-2B), with one of the 534's having the mod 1860.

[pigboat]

yahoo748, for what it's worth here's a few tips that worked for the Dart 529, either 7E or 8E. Probably apply to the 534.
Try to keep the starts as cool as possible. There are two schools of thought on how to do this. The first goes that you start at 100% fuel trim, or trim of the day, and while you get a higher start TGT because of the extra fuel, the engine will accelerate better and the TGT spike will be for a shorter period. The second school says to start at 0% fuel trim and the start TGT will be lower, but the engine will not accelerate as well and the the TGT spike will be for a longer period. We had a rule of thumb that if the OAT was below ISA, we used 100% fuel trim on start, if above ISA 50%. That worked well. Normal idle at 100% or trim of the day would be 6500 - 7500 RPM.
Some operators trim to zero fuel trim on descent. I always thought that was bulls**t - it just added an unecessary action to the descent checklist - but I suppose it does no harm. If you do trim to zero for descent, don't trim up past 50% until called for on the final check. You could concievably overtemp the engine if a large power increase was called for, for any reason.
On shutdown, the secret is to wait 'till the RPM and TGT's are stable before hitting the HP cocks. I've heard the figure of thirty seconds at stable idle/TGT bandied about. You should always leave one boost pump a side on 'till the prop stops. Keeps the expensive bits lubricated. The thing to remember is, the Dart is considered a stone age turbine. It will take a whole lot of abuse, but you can do real damage to it on startup or shutdown if you're not on your toes.

[ 16 December 2001: Message edited by: pigboat ]

[Air Conditioned]

Trimming to zero for descent - or at any time other max endurance - is pointless since the TGTs are well down once the levers come back. It will, however, do you an injury when you want power quickly. Even with the power levers full forward you may be seriously short until the trimmers are run up. I seem to recall this rated a mention in at least one accident report.

I don't know the current words in The Book, but it used to be that power was reduced from cruise (usually about 755 deg??) by trimming back to 730 then making further reduction by power lever at a fixed trim setting. This will give comfortable TGTs while manouvering, and useful thrust immediately by power lever movement alone.

[Shaggy Sheep Driver]

I once had a cockpit ride on a Viscount, and noted that the crew were quite concerned with these 'fuel trimmers'. What are they?

SSD

[4g_handicap]

SSD,

The Rolls Royce dart series of engines have a fairly unique method of setting power - it goes something like this :-

the throttle is connected to the propeller conrol unit(PCU), which conrols the RPM. It is also connected to the Fuel Control Unit(FCU).

This means that the power setting regime is fixed - ie you just open the power and go.

In order to allow more flexibility(I think probably to compensate for different atmospheric conditions), they had to invent a way of changing the amount of fuel flow(and hence the TGT), for a specific throttle position.

This is where the fuel trimmers come in. It is calibrated from 0% to 100% - the full range being capable of regulating about 25% f the total fuel flow.

This means that at 0% fuel trim and full throttle it is possible that you will only be achieving 75% power.

Generally the colder ambient temperature, the more fuel trim you need, being anywhere from 85% - 100% when below ISA(depending on engine model)

Generally you have a table or mechanical computer where you enter with airfield elevation & temperature, that gives you the correct fuel trim setting for take off and landing(Go around). Theoretically you then just take the throttles and push them forward to the stops to get full power.

The main reason why the guys on the Viscount seemed so concerned with the trim is that once you have set a fixed RPM on the throttles, you adjust the TGT with the trimmers. The TGT's are very sensitive, and any time the OAT changes, it will require a trim change(in order to get the TGT back to the correct figure). This means that the pilots are constantly monitoring the TGT and adjusting, especially during the climbout.

Anyway, hope its answers your question.
:cool: :cool:

[Shaggy Sheep Driver]

Thanks, 4G. Very informative – I now understand what fuel trimmers are - a sort of ‘fine tuning’ for power given that the power levers select a set fuel delivery for the selected RPM.

However, I’m sure the Viscount had more than 1 lever per engine. I’m used to throttle and RPM levers on piston engines – what does a Dart have?

SSD

[pigboat]

SSD, the other lever you remember was the HP fuel cock, which opens the fuel supply to the high pressure fuel pump. You could say that the HP fuel cock is actually a dual purpose fuel/propeller control. On some Dart installations, it is a four, and on others a three position control. In the fully forward, or cruise lockout detent, you have caused the cruise pitch locks in the propeller hub to be hydraulically removed. In this position, the HP cock serves as a propeller control. The position behind that is fuel on, and the one behind that is fuel off, where the lever reverts to a fuel control. Behind fuel off is the fourth or feather position, where the lever again becomes a propeller control. In this position, it will cause the affected propeller to feather. On aircraft not equipped with two stop propellers - early Viscounts for example - there is no cruise lock out position.

[Shaggy Sheep Driver]

Thanks, Pigboat. No 'reverse' pitch position, then?

SSD

[pigboat]

SSD nope, no reverse. After touchdown, as soon as the weight was on the wheels, you were able to select ground fine pitch. This removed the flight fine pitch locks and allowed the prop to go to a zero blade angle. All ground operations are carried out in ground fine.

[Hudson]

Back in 1967 the RAAF obtained Avro 748's for its VIP squadron and School of Air Navigation.
Due to a series of cockpit mis-understandings while in the cruise (the captain down the back on the Elsen - which is the bog) a double generator failure occured and one engine was mistakenly feathered. It was a Keystone Cops type comedy with serious overtones.
The aircraft diverted to a country aerodrome where because of a now total electrical power failure (battery by now was flat) a flapless asymmetric landing was made.

At the time of the electrical failures the fuel trimmers were almost at the zero position, and of course with no electrics they were stuck in this position for good. This was potentially serious, because if an asymmetric go-around had been attempted, the remaining engine would have not been able to deliver full power due zero fuel trim. If nothing else it would seem wise not to move the fuel trimmers to zero for any descent unless the manufacturer requires it.

[Budgie69]

I operated 748s in Europe off and on from 1975 to 1990, so some of what follows may be a little out of date.

We used to operate to remote airfields with no engineering so learnt a few get you home tricks, the most useful of which are:
A stuck fuel trimmer can be "percussed" back into life fairly simply with a broomstick handle poked up from the u/c bay;
If the starter motor cuts out at around 2000rpm rather than 2500 it means that the starter clutch is about to fail.

We used to trim back for descent and leave the rpm at 14200 (or 13800). It became second nature to say to yourself on finals -"3 greens, trims set", and associate the two items.

The windscreen wipers perform primarily a decorative function, but the bottom couple of inches of the windscreen are kept clear by airflow from rain, salt spray etc, so by crouching down in your seat you can see for landing.

You probably have cockpit heaters, but even so I would reccomend warm boots, thick socks, long johns etc, for winter flying - you have probably already discovered this!

Get a good noise cancelling headset - buy your own if necessary. Noise damage is cumulative.

When landing on icy/slippery runways you will find that flying controls become less effective below 80 kts, and the nosewheel steering cannot really be used above 60. It is desirable to get throught this "period of terror" speed range as quickly as possible.

Using wing down you can land in very strong crosswinds.

Notwithstanding the above, it's a great aircraft, very solid and forgiving - enjoy it.