Fairey Delta 2

Congrats Simon

well done sir.
another nice model finished and flown.

With all the repairs made permanent and 'prettied up' here is a video of its second flight.

Not very exciting as I kept reasonably high.
Apart from the launch all the flight was at less than full power.
Glides quite nicely but it really needs much shorter grass for the landing as the tips of the elevons keep getting broken off!

Missed this first time round and for some reason, can't access the video...... but many congrats Q, a good job well done!

Andy
Thanks.
Sorry you can't access the video. It works ok for me.

Works fine this end Quorneng, congrats on the flight as well

Garry

Quorneng wrote: Andy
Thanks.
Sorry you can't access the video. It works ok for me.

Turns out it was a self-inflicted problem, I'd neglected to download the latest version of Flash Player which had blocked all further uses of the older version.

I've now had a look at the video and I'm bowled over. The flight characteristics look to be absolutely superb and the sit and speed of the model appear to be just right. It's a great shame Peter Twiss is not still around to witness it, I'm sure he would have appreciated it.

Again Q, thanks for sharing.

Andy

Andy
I was rather gratified on how it flew. The fact it flies so 'flat' is I believe down to the very thin section wing and its light weight.
The video was only its third ever flight so I was still getting to grips with its handling. Typical for a small span plane with a nervous roll response but fairly docile in pitch due to the inertia of the widely spaced battery and motor.
The characteristic that needs exploring is a tendency to 'roll over' in a climbing turn. It is particularly obvious twice in the video at 0.39 and 2.28.
Of course it may just me over controlling but it certainly felt like the wing dropped more than expected from the aileron input.
Possibly the 'pointy' wing tip is indeed stalling as the load increases and the air speed reduces. Certainly my Skyray with its 'ogee' delta does not do it to anything like the same extent.

Swept wing aerodynamics are subtly different to those of a straight wing. The lift characteristics of the latter fall off (stall) at about 15 degrees angle of attack (AoA) whereas the swept wing will continue to give lift up to much higher AoA and show a reluctance to stall. This is mainly due to the vortex that attaches to the leading edge at the root of a swept wing (I'm sure you've seen this in the smoke patterns off F16 displays). When the vortex detaches, the wing looses lift on that side which caused a 'departure from controlled flight' rather than a stall. Tie that up with a rolling moment due to sweep back which is very powerful when compared to that due to dihedral and you have an interesting combination. The rolling moment due to sweepback is also exacerbated by the increased wing sweep. Final point, although swept wings hold their lift up to much higher AoA than a straight wing, the maximum lift produced (the max lift coefficient) on a swept wing is always much less and the drag is significantly higher.

Looking at the roll-off on the video it looks like you are rolling and pulling at the same time. Therefore, I would say that it may be caused by:

1. Rolling moment due to yaw combined with the sweepback. The yaw could be caused by the aileron drag which is different for the upgoing and downgoing ailerons for a given deflection or it may be a slight distortion in the airframe as the 'G' comes on.

2. The vortex detaching or moving on one side and thus reducing the lift on that side. Causes could be airframe distortion as above or a slightly different wing or wing incidence on each side. Unlikely I know, but it may even be a small nick in the LE that attaches the vortex on one side but not the other - this is used as a trick by many full size designers to stabilise swept wings: fences, saw tooth LEs and slots in the LE are all common. Does the aircraft roll in the same direction in a left turn, or does it go with the turn?

3. Roll due to unqeual wing distortion under 'G'

It may be worth experimenting with:

1. Just roll in a climbing turn ans see if the roll rate changes as the speed falls off

2. Put on bank then with neutral roll increase the pitch - does the aircraft then roll

3. Do the above in either roll/turn direction.

4. Try rolling and pulling in a level turn in each direction.

5. Try rolling and pulling in a climbing turn in each direction.

With the info gained from the above, you should be able to narrow down the cause.........hopefully!

I hope that helps.

Andy Sephton wrote: Swept wing aerodynamics are subtly different to those of a straight wing. The lift characteristics of the latter fall off (stall) at about 15 degrees angle of attack (AoA) whereas the swept wing will continue to give lift up to much higher AoA and show a reluctance to stall. This is mainly due to the vortex that attaches to the leading edge at the root of a swept wing............

Or it just might have something to do with the massive amount of power they have.

Andy
Thanks. Yes I will try to explore the characteristic a bit further.
It not really a problem just as long as you remember it is there and avoid a tight climbing turn at low altitude! I suspect the full size needed to be treated pretty gently as well.
I did see it at Farnborough, I can't recall if Peter Twiss was actually flying it, but I do remember it did little more than some fast(ish) passes (rather boring for a 12 year old!) with no afterburner and was certainly not chucked about like the Hunter and Canberra displays.

The FD2 going through a fairly major update to remove the counter balance on the ailerons, a nose rebuild (it had got slightly bent) and a general tidy up of all the surfaces.

Hopefully landings will now be damage free!
As far as the flying goes I have added 30% expo to the aileron circuit which has certainly made executing a gentle turn rather easier.
Its only slightly odd feature is the roll. To the right it performs a very nice 'twinkle' whereas to the left it has more of a 'barrel' about it, presumably the effect of motor torque.

Quorneng wrote: Its only slightly odd feature is the roll. To the right it performs a very nice 'twinkle' whereas to the left it has more of a 'barrel' about it, presumably the effect of motor torque.

I'm not convinced about the engine torque, check that the aileron throws are equal, ie, both have the same down and up throw and be sure that the fudder is in the neutral position.

P.S. Also if you're flying mode 2 then it's possible that you could be accidentally feeding a little elevator in at the same time.

Old Fart
Certainly possible about the inadvertent elevator but I was very careful each time to only move the stick directly side ways.
Compared to the weight of the airframe the motor torque is quite significant and with the fan is right at the back there is virtually no exhaust tube so there is little flow straightening.

If I suspended it by at thread from its nose any steady state torque would be obvious and I might even be able to measure it!

'twas just a thought, you could try 2 degrees of side thrust and see what that does, never been convinced of the torque effect on front engine models though.