My Hobbyking Lancaster

[Cliff Bastow]

After a good few flights now I have to say that its not half as bad as I expected, I have quite a bit of aileron differential set. Also I have both ailerons set a couple of degrees down when at neutral to try to help with tip stalling.

As long as you do not slow it up too much and do not overbank it flies fine. It is a heavy bomber after all! If you do stall it the stall is nasty!

I think for the money its good and looks great in the sky so overall I am more than happy.

 

Edited January 23, 2023 by Cliff Bastow

[Phil Green]

Cracking photos Cliff.  I have the earlier version which I've never flown as the stories scared me!

I have wondered about removing the motors, escs & retracts and PSS sloping it, it would be much lighter in that format.

Puzzled by your aileron setup though?

Cheers

Phil

 

[leccyflyer]

Belting pictures Cliff and good to see that you're having success with this model. I picked one up yesterday from a clubmate - despite having had an unopened kit in the box for some years - and was busy researching the various issues when this popped up. All I've done so far is to change out the XT60 connector for my preferred 4mm gold bullets. I'm not planning on a maiden flight any time soon - there are some proper horror stories out there and the videos I've seen the Lancaster is flying like a Eurofighter at full chat.  😄

[Mike Blandford]

Also puzzled by the aileron setup, I would use UP aileron to try to reduce tip stalling (effectively providing washout).

 

Mike

[Cliff Bastow]

You are all correct, I should have posted up aileron, my mistake. 
Yes you do have to fly it fast, you can slow it down if straight and level into wind but power up before turning. It’s not as bad as it’s reputation, you just have to be careful.

[Phil Green]

I know its popular practise but I'm not convinced about "up aileron=washout".   

I'm not an aerodynamicist but my thinking is that its all about the angle of attack from the leading edge, at stall the upper flow breaks away well in front of the aileron hinge, by the time the flow gets to the aileron its all over, whether its up or down 🙂
Just my humbrol opinion....   but then I fly rudder-only models via a button...  😁

Edited January 24, 2023 by Phil Green

[Jon H]

28 minutes ago, Phil Green said:

I know its popular practise but I'm not convinced about "up aileron=washout".   

I'm not an aerodynamicist but my thinking is that its all about the angle of attack from the leading edge, at stall the upper flow breaks away well in front of the aileron hinge, by the time the flow gets to the aileron its all over, whether its up or down 🙂
Just my humbrol opinion....   but then I fly rudder-only models via a button...  😁

 

AoA is measured by taking the angle between the relative airflow and the chordline of the wing. Moving the aileron changes the chordline and as a result AoA changes as well. This is why an aileron moving down with the wing at its critical AoA will provoke a stall as it pushes the wing beyond its critical AoA. 

 

All that said, a deflected control surface will not be as efficient at preventing tipstall as the whole wing being twisted for the reason you mention. 

[PatMc]

38 minutes ago, Jon - Laser Engines said:

 

AoA is measured by taking the angle between the relative airflow and the chordline of the wing. Moving the aileron changes the chordline and as a result AoA changes as well. This is why an aileron moving down with the wing at its critical AoA will provoke a stall as it pushes the wing beyond its critical AoA. 

 

All that said, a deflected control surface will not be as efficient at preventing tipstall as the whole wing being twisted for the reason you mention. 

But as Phil has pointed out the relative airflow has also changed & dramatically so. 

[Jon H]

5 minutes ago, PatMc said:

But as Phil has pointed out the relative airflow has also changed & dramatically so. 

 

no it hasnt. With the wing at a fixed incidence of however many degrees the relative airflow will be the same no matter the change in the aileron deflection. AoA changes with deflection but relative airflow does not. if you pitch up then relative airflow will change but AoA changes with it across the whole wing. If you have cranked your ailerons up a bit you still end up with a lower AoA on that part of the wing. The idea being that the inner part of the wing stalls before the tips so you never end up in the situation Phil mentions with fully stalled airflow over the aileron. But, as i said, its not likely to be as effective as twisting the wing. 

[Phil Green]

A further (non-qualified) observation - raising the ailerons reduces overall lift, if compensated by some up elevator = the whole aircraft sits at an even greater angle of attack 🙂

 

Edited January 24, 2023 by Phil Green

[Jon H]

35 minutes ago, Phil Green said:

A further (non-qualified) observation - raising the ailerons reduces overall lift, if compensated by some up elevator = the whole aircraft sits at an even greater angle of attack 🙂

 

 

Yep that is indeed true for both aileron raising and washout generally. The key though is the centre of the wing reaching the critical angle first so its not really important. 

[PatMc]

2 hours ago, Jon - Laser Engines said:

 

no it hasnt. With the wing at a fixed incidence of however many degrees the relative airflow will be the same no matter the change in the aileron deflection. AoA changes with deflection but relative airflow does not. if you pitch up then relative airflow will change but AoA changes with it across the whole wing. If you have cranked your ailerons up a bit you still end up with a lower AoA on that part of the wing. The idea being that the inner part of the wing stalls before the tips so you never end up in the situation Phil mentions with fully stalled airflow over the aileron. But, as i said, its not likely to be as effective as twisting the wing. 

The wing incidence is irrelevant - it's only a rigging angle.

The airflow is turbulent from the point that it breaks away from the top surface as the stall angle is approached, the ailerons are by then playing no part in determining the  AoA. 

[Jon H]

1 hour ago, PatMc said:

The wing incidence is irrelevant - it's only a rigging angle.

The airflow is turbulent from the point that it breaks away from the top surface as the stall angle is approached, the ailerons are by then playing no part in determining the  AoA. 

 

Pat, you are wrong and im not. I cant be bothered to argue about it, just go look it up

 

Edited January 24, 2023 by Jon - Laser Engines

[PatMc]

14 minutes ago, Jon - Laser Engines said:

 

Pat, you are wrong and im not. I cant be bothered to argue about it, just go look it up

 

Jon you seem to be arguing about the wrong scenario.

Most people deflect both ailerons upwards when they attempt to use them as a substitute for washout.  

[Phil Green]

My possibly misguided point was that whats happening at the trailing edge is irrelevant, its all over by then.

John sorry I dont follow the assertion that the direction of airflow into the leading edge and over the aerofoil would change because something changed at the trailing edge!

I dont think the aileron-affected "chord-line" is a real concept, a deflected aileron doesnt twist the wing, it doesnt change the angle at which the airflow hits and splits over/under at the leading edge, and to my way of thinking, at a stall AoA the airflow will break away from the top surface just the same regardless if the aileron was up, down or absent!

Imagine a Clark Y mounted rigidly in a wind tunnel.  For a given airflow you slowly increase its incidence to the airflow.  At some point the upper flow will delaminate mid-chord and it stalls.  Now imagine repeating the very same process but this time with the aileron tilted up say 5° . 

My guess is that it wont make a jot of difference, the breakaway will happen at exactly the same angle to the airflow because everything of interest here is happening  on the upper surface between the leading edge and around mid-chord, well before the aileron comes into play.

I'm not an aerodynamicist and I'm not insisting that this is right and that is wrong, I just dont see any evidence that up aileron = washout and whilst it seems to me to be a bit of a whacky suggestion that it does, I'd be more than happy to be proven wrong 😉

Cheers 

Phil

 

 

 

Edited January 25, 2023 by Phil Green

[Jon H]

10 hours ago, PatMc said:

Jon you seem to be arguing about the wrong scenario.

Most people deflect both ailerons upwards when they attempt to use them as a substitute for washout.  

 i know, just invert the drawing

[Jon H]

8 hours ago, Phil Green said:

 

I dont think the aileron-affected "chord-line" is a real concept,

 

 

 

 

Chordline moves with control surface deflection as shown in the diagram i posted, its just a fact im afraid. You also get a change in camber, drag, and a bunch of other stuff not relevant to this conversation. If i still had my aerodynamics notes from uni i would share them, but i ditched them years ago. When doing spin training in gliders i could induce a stall/spin using ailerons as the downgoing aileron would stall the wing. We practiced this as a stall/spin accident is most likely in the base/final turn and its pretty fatal normally so knowing the warning signs is helpful. 

 

Raising the aileron will reduce the AoA of the tip. How useful/effective it is is another story. Washout is definitely going to be more effective but without that option, i would give it a go.  

 

However, i suspect the root cause of this Lancaster's stalling problem is not the wings but the engines. It has 4 of them, covering probably 60-70% of the wing area in nice high speed prop wash. Only the outer wings are dealing with relative airflow at the airspeed of the model. As a result they will stall first when loaded as the high speed airflow from the props reduces relative AoA on that part of the wing. Yes there are complicated factors regarding the corkscrew shaped nature of the slipstream, but in simple terms it will prevent stall by reducing AoA. With increased load factor in a turn, plus yaw the outer wing will have reduced AoA and the inner wing increased AoA as a function of the differences in airspeed on the two wings as you yaw round the turn. This is a result of the outer wing drawing a larger circle than the inner one in the same amount of time. The change in airspeed changes the relative airflow and consequently the AoA changes. 

 

Anyway this manifests as a roll into the turn so you add aileron. The down going aileron increases AoA, it also adds drag, yaw(if not corrected) and this can be enough to stall the inside wing causing a spin due to the asymmetric nature of the stall. 

 

Also if this model has things like panel lines moulded into the wing surface fill them up and get rid of them. All they will do is disturb the airflow over the wing as they are probably going to be the equivalent of a 5 inch chasm in the wing if you work out the scale factors and applied it to the full size. 

 

 

[Martin McIntosh]

Just looked at this thread and have not read all of it, but may I add my experience with one of these?

Bought one many years ago because the Lanc is my favourite aeroplane, in fact I built the TN 11 ft one.

As it came, the battery pack had been moved to the rear for some obscure reason but by cutting out some material at the wing centre it could be moved to the front to get the cg correct.

I replaced the tail end linkages, got rid of the steerable tail wheel and put a micro servo in the rear, linked by carbon rods to now functional rudders.

With a considerable amount of coupled aileron and rudder it flies just fine.

A mate had one also and added flaps fixed down at 20-30 deg. but I have not tried that.