Rotation speeds

[forthbridge]

Just playing around at X68 (Shuttle runway - for reasons which will become apparent....)

I overloaded the 1-11, Trident and the '10 to the tune of 4500 lbs, and trimmed for takeoff.

Interesting comparisons...

V2 for the 1-11 was 153 kts - it rotated at 151 kts
V2 for the Trident was 168kts - it rotated at 151 kts
V2 for the '10 was 158 kts - it rotated at 192 kts....!!!!!

As I'd set the trim, I just opened them up and let the A/C have it's head, so the speeds are not when I pulled back but when the planes natuarally rotated.

Any reason why the '10 was so 'sluggish?

Needless to say I have not attempted landings yet...

[Garry Russell]

No idea Jim

But I think the important thing is that the models perform as they should at the correct weights and settings....which they do

Any extremes out of the envelope would be a waste of the developers time and impossible to verify if the real one would behave as such even if they wanted to...so a pointless excercise

We're more about realism here :think:

Garry

[forthbridge]

Hi Gary/all - true enough - what I should have posted was that although I was mucking around with the heavier weights, and quoted the figures for that,

the main point of my question was that at max TOW, the 1-11 and Trident nose up at V2+10, and are airborne by V2+20 - the '10 does not begin to rotate until V2+30(ish) and it's V2+40 by the time it lifts - what is the reason for such a gap in the difference from V2 to rotation?

(Incidentally, the reason I was mucking around with the extra weight was to see if it made a difference - and it did - and the 'gap' remains the same from 100% TOW to overloaded) - I didn't go lighter....

It actually is making me 'think' that the Trident isn't as tardy as I always thought - it actually seems to be getting more nimble!
*EDIT:

[Garry Russell]

Hi Jim

The Trident is not the ground hugger popular ledgend has it, although I guess the crews would have liked more get up and go.

If it was.....well ask yourself this...how many Tridents over ran runways because they couldn't take off???

Also of note is a friend of mine flew VC 10's for BOAC until just before BA and he always applied the term gripper to any early jet that took off nose high with lots of smoke and noise but not climbing as well as the visual seemed to indicate.

He always called early 125's and One-Elevens grippers.

Like the term Jumbo becoming stuck to one type when it was initially applied to a class, the Trident made the name it's own.

Being a Ten pilot most types would have looked grippers..in those days.. although the Comet and Caravelle could put on quite a show at times :o

I knew the term gripper for years before I heard it applied to Tridents as such although the 1C was sometimes referred to as a bit of a gripper

They did seek to inprove performance and shorten the run as they would with any type but for it's day it was not that unusual and even though the run was long it was used at airports with adequate runway. Trident 1E used to go to Jersey CI when the runways was shorter than it is now (BKS & Channel), and BA used 2E for a time just before their final retirement. G-ARPB also made flight to Jersey when still being used by HSA for developement.

The VC 10 was something else and built for relitively short runways so my mate must have looked at most things as inferior.

Certainly not dangerous as the often used phase notoriously difficult to leave the ground idicates, it just had to be set up properly and there were a number of incidents involving other jet types because crews were not observing correct speeds and settings in the early days.

In short if you flew by the numbers it did just what it's was suppose to.

Garry

[cstorey]

I think the problem is that you are trying to compare apples and oranges. V2 has nothing whatsoever to do with the rotation speed, or lift off speed at any given weight. It is the speed which must be achieved, a.s.a.p after takeoff, to give full control of the aeroplane in its T/O configuration if an assymetric engine failure occurs. As you are probably aware, the authority of both ailerons and rudder is fairly directly related to Indicated Airspeed , and until the V2 is reached , there is not sufficient authority to counteract fully the swing and secondary roll couples which occur where assymetric thrust occurs

Furthermore, in the real aeroplane, a gross overload will have different effects according to where in relation to the Centre of Gravity the overload is positioned. It will certainly affect radically the theoretical T/O trim settings, so that a forward of CG overload will require considerable nose up trim to give any effective elevator control at all

Thus I'm afraid that your "test" has no validity at all - and Tonks will correct me here, but I think the common result of an outside the envelope CG position (usually aft) on a VC10 is that because of the layout of the aeroplane and in particular its fuel distribution, it sits on its tail on the ground!

One further point - all 3 of the aircraft you chose in fact have V2 rather lower than equivalent weight a/c with underwing engines, because the lever arm of the assymetric thrust is so much greater , and it is not usually possible to counter this merely by increasing the rudder area

[petermcleland]

Any tiny change of elevator trim would make nonsense of those numbers. VR is not supposed to be a figure at which aerodynamic natural rotation will occur. It is the speed for a given weight that the pilot rotates the aircraft.

[forthbridge]

Thanks for that - before I continue - can Peter - or anyone - answer this: Is it 'feasible' to allow any A/C to 'lift off' with trim alone and NOT use the stick?

I am basically thinking flight testing.....???

Second - I made two mistakes - first I was using the C1K - not a standard '10 - and second I for some reason looke at V2 not rotation speeds - although the lift off speeds are correct...

Third - I was 'clowning' around with this specifically as I was practising with the Trident, and X68 specifically so I would not run out of runway. I had my eyes on Vr, and was surprised that as I went to pull back, the A/C lifted itself at Vr - unlike the VC10 (C1K) I normally play with - this basically set me looking at the 1-11 and VC10 also - out of interest.

Now, I set up a flight, and started the recorder, and after the engines were spooled up I released the brakes at 20 seconds.

I did this three times, one for each aircraft, which was loaded up with it's default fuel and payload, and set up for takeoff as per the manual for each type.

The 1-11 and Trident were close, but the C1K was a gripper.

Using a standard '10, I find the all three Aircraft lift within 2-3 seconds of each other, which is very interesting (to me).

It was purely an exercise in 'lets' see what lifts first done by allowing the A/C to do it as I'm not that accurate in timing the pull-back at Vr....

But... the 'normal' '10 is not so reluctant to lift itself as the C1k.....

[petermcleland]

It would not be realistic for any airliner to rotate itself at VR...The set trim for take-off would be such that a backwards movement would be required on the yoke to make the aircraft rotate. Fighters would be different and it would be normal to feel the stick sometimes needing to be held a little foreward to prevent a premature lift off. Small GA aircraft will normally lift themselves off the ground without any stick movement, depending on how many people and bags are on board.

[forthbridge]

Thanks Peter

I need to get more precise and pull-back at Vr! :flying:

[forthbridge]

Cheers Tonks (and all). It's not something I've actually considered much before - I basically set the A/C up as per the instructions, wait for Vr and pull back - had it not been for the fact was at X68, I would probably not have even realised that this is a phenomenon in FS!

To be honest I usually fly out of places where the '10 will (just) get airborne at MTOW...

About the only thing I've discovered (on the models that is) is that the Standard 10 'rotates' on it's own at Vr or thereabouts, whereas the C1K does not.
(Which is not really of much use when properly flying the thing!!)

Thanks for the info however - I genuinely thought a properly trimmed A/c *would* lift itself almost naturally!

CHEERS