Wing dropping

[bert baker]

Why do some plane constantly roll left, when they have been set up with incident gauges and all thrust lines correctly set up,,,,

Three planes I have been asked to test fly last weekend all suffered the same problem

One was with a small glow and the others were 30cc petrols one two stroke and one four stroke

[Martin Harris - Moderator]

Assuming the lateral balance is OK, then it's most likely due to torque reaction - the propeller turns clockwise from the cockpit's point of view, so torque is opposite to this, causing the port wing to drop.

 

Edited By Martin Harris on 17/04/2018 19:04:25

[Former Member]

[This posting has been removed]

[Stuart Z]

Torque reaction to motor /engine running

Also possible, but could be either way, wings out of balance?

 

S

Edit

I see that others have gotten on the page before me.

Edited By Stuart Z on 17/04/2018 19:07:12

[Denis Watkins]

Like you Bert, I maiden a few and invariably trim right, some rudder, and some aileron

On getting back down we check lateral balance more precisely, and two out of three will need a small screw in the right wingtip.

Most certainly torque reaction too, but correctly propped, and trimmed for cruise unless a 3D, usually sorts it

Daft as it may sound, recheck the C of G with a fellow lifting each wing tip,

Often I find they slightly lean back at the field when they assumed spot on at home

Edited By Denis Watkins on 17/04/2018 19:19:22

[bert baker]

We checked lateral balance on two of the and come to the Duno conclusion

[bert baker]

Posted by David Mellor on 17/04/2018 19:04:56:

Engine (motor) torque causes a left-banking tendency unless countered by right thrust setting on the mounting plate.

I shall get one of them to put more right thrust applied

[Former Member]

[This posting has been removed]

[bert baker]

Going to be hard as all three are one piece Wings,,but surely that would show up when we tested for lateral balance,,,

One one of them I put a pair of incedence gauges one on each wing section and along each length the were identical,,

My mate has confirmed he had already tried extra right thrust to one of them

[Denis Watkins]

Fin

Check out the fin assembly geometry, and for integrity

That nothing is able to move or be slack in elevator or rudder

[bert baker]

This one is a Mick Reeves 1/6 spit,,, glass fuz pre moulded so can't be wrong,,

Rudder and elevator secure ,,

Have redone lateral inverted,,, did show a slight tendency to be left wing heavy so have added a small weight to right wing, next is to recheck right thrust

[trevor wood 2]

Looking at your spitfire photograph, that square lump sticking into the airflow below the starboard wing will cause asymmetric drag. The yaw/roll coupling produced by the wing dihedral would then result in a turn to the right.

[Martin Harris - Moderator]

It might be worth considering gyroscopic precession effects caused by the nose dropping during the stall - possibly more likely than side thrust issues which I don't believe would cause wing dropping. Did you try an inverted stall - the results could add some light to the discussion...

I have to say that the picture above suggests that the right wing is heavy - was this taken after adding weight?i

Trevor, wouldn't a yaw to the right tend to induce the right wing to drop?

Edited By Martin Harris on 18/04/2018 00:39:46

[Former Member]

[This posting has been removed]

[Piers Bowlan]

Even with laterally balanced models, not only torque but also slip-stream effect will cause the aircraft to roll in opposition to the rotation of the propeller. The prop slip-stream rotates around the fuselage and impinges onto the rudder asymmetrically, causing a sideways force and a yaw to the left. Since roll is the further effect of yaw, this in turn causes a roll to the left. How large the rudder, the tail moment length, the power of the engine and importantly, how much dihedral the wings have, will all influence how large the slipstream effect is. The greater the dihedral the greater the yaw/roll couple.

Like torque, engine offset will counteract torque and slip stream to some degree or at least improve things. Also rudder trim will counteract the yaw but both torque and slipstream will be at a maximum at full power (during take off/ go-around). Mixing a bit of rudder with throttle might improve handling during these phases of flight if thought necessary.

Edited By Piers Bowlan on 18/04/2018 08:47:00

[bert baker]

Was taken after adding weight,

Will see how it goes later today

[bert baker]

The engine is a NGH 30 four stroke,,, it has the smallest recomeded prop 15/10,

Now wondering if the pitch is two harsh for plane

[DaveyP]

@ Piers

Spot on explanation

[Martin Harris - Moderator]

Posted by Piers Bowlan on 18/04/2018 08:29:23:

Even with laterally balanced models, not only torque but also slip-stream effect will cause the aircraft to roll in opposition to the rotation of the propeller. The prop slip-stream rotates around the fuselage and impinges onto the rudder asymmetrically, causing a sideways force and a yaw to the left. Since roll is the further effect of yaw, this in turn causes a roll to the left. How large the rudder, the tail moment length, the power of the engine and importantly, how much dihedral the wings have, will all influence how large the slipstream effect is. The greater the dihedral the greater the yaw/roll couple.

Like torque, engine offset will counteract torque and slip stream to some degree or at least improve things. Also rudder trim will counteract the yaw but both torque and slipstream will be at a maximum at full power (during take off/ go-around). Mixing a bit of rudder with throttle might improve handling during these phases of flight if thought necessary.

Edited By Piers Bowlan on 18/04/2018 08:47:00

I wonder how much slipstream effect there would be at idle during a stall test, though. My (very empirical) guess would be that it wouldn't contribute enough yaw to cause a significant wing drop as the airflow over the fin at the stall should still be providing significant weathercock stability. Unlike the very significant effect at high power, low airspeed, during take off...

[bert baker]

Cross wind today and farmer is spreading nitrogen

Did a couple of taxis and wimped out,,, not point making life hard,,, as there is a another day

[DaveyP]

Martin, At stall speed there are many other factors to take in to account.

I've flown many aircraft that have a totally benign stall and others you really don't want to be in...............

When the wing stops flying, i.e. Stalls, the control inputs ideally should be neutral for a quick and safe recovery.

Standard practice is nose down to unstall the wing and power to regain altitude.

Too low when this happens never ends well, whether full size or model.

Happy flying

[Piers Bowlan]

A wing stalls when it's critical angle of attack is exceeded. This can occur at any speed and any power setting, as it is just the angle of attack that is relevant as far as at what point the wing will stall. I said point not speed. We tend to think of a deliberate stall occurring with wings level, throttle closed and at a slow speed. However, apply power and keep pulling back on the stick and now the aircraft will stall at a much lower speed. Now try dropping some flap, applying full power and pull back on the stick enough to maintain height whilst watching the speed decay. The aircraft will now stall at a slower speed altogether but it is not just the speed that changes, the behaviour of the aircraft at the stall will change too. ( I am not discussing 3D planes here)

A model may be deemed to be a 'pusycat' following a low power wings-level stall entry, where it simply nods and mushes earthwards in a fully stalled state, - recovering instantly once the stick back-pressure is released. Now to make things 'interesting' move the batteries further aft and add some ballast for good measure! Put the same model into a steep right hand turn. Steepen the turn, maintaining height with elevator, and speed with more power until full power is applied. Now the aircraft will stall at a much higher speed and without warning, swiftly droping a wing ( usually in opposition to the direction of the turn) and autorotate into a spin. Your 'pusycat' has turned into a tiger! Some aircraft display more of this 'tiger' behaviour, particularly if they have high wing loadings and highly tapered/thin wings. Build light and chose models with thick/blunt wing sections if you prefer pussycats to tigers - but tigers can be fun too! (just remember to wear your bicycle clips and always carry a bin bag)