RCM&E Dec 2018 - Ruckus Review Update

[PatMc]

3 minutes ago, Peter Jenkins said:

In what way PatMc?

The wing incidence & motor thrust line are tied in a fixed relationship in flight. If wing incidence is changed on the ground that relationship changes by the same degree to a new fixed angle. The tailplane is an in flight variable incidence trimming device for the wing AoA, it doesn't alter the wing incidence /motor thrustline separately.  

[Peter Jenkins]

10 minutes ago, PatMc said:

The wing incidence & motor thrust line are tied in a fixed relationship in flight. If wing incidence is changed on the ground that relationship changes by the same degree to a new fixed angle. The tailplane is an in flight variable incidence trimming device for the wing AoA, it doesn't alter the wing incidence /motor thrustline separately.  

Just read through my posts and it is actually GG's post that introduces the tail plane incidence to the motor/wing incidence issue.  So, I am not wrong in what I said as at no stage did I bring motor down thrust, wing and tail incidence together.  Ergo, I'm not wrong.  GG has introduced tail plane incidence where I didn't.  

 

Hope that clarifies matters.

[Nigel Heather]

Please don’t let my question cause people to fall out. 🙏

 

So where I am:

 

The first thing I did was to add some elevator - that reduced the effect and left it flying what I consider properly at low throttle.  I didn’t try adding lots of elevator to try and level out at throttle because the elevator is clearly deflected already so that didn’t seem the right answer - more like curing the symptom rather than the fault.

 

I then more than doubled the down thrust, it may have made a small amount of difference but not much.  Again adding more seems like curing the symptom.

 

Unfortunately, I don’t have access to an incidence meter - it would be great to see what it is but unfortunately I can’t.

 

So next flight I will loosen the wing and slip in some card near the leading edge, retighten and see what that does - I’ll let you know, won’t be until Wednesday at the earliest.

[Learner]

29 minutes ago, Nigel Heather said:

Please don’t let my question cause people to fall out. 🙏

 

So where I am:

 

The first thing I did was to add some elevator - that reduced the effect and left it flying what I consider properly at low throttle.  I didn’t try adding lots of elevator to try and level out at throttle because the elevator is clearly deflected already so that didn’t seem the right answer - more like curing the symptom rather than the fault.

 

I then more than doubled the down thrust, it may have made a small amount of difference but not much.  Again adding more seems like curing the symptom.

 

Unfortunately, I don’t have access to an incidence meter - it would be great to see what it is but unfortunately I can’t.

 

So next flight I will loosen the wing and slip in some card near the leading edge, retighten and see what that does - I’ll let you know, won’t be until Wednesday at the earliest.

Are you trimming it at too low throttle, I would trim it at cruising speed around 1/2 throttle. If thats to fast maybe 3s would be better.

Edited August 19 by Learner

[Nigel Heather]

20 minutes ago, Learner said:

Are you trimming it at too low throttle, I would trim it at cruising speed around 1/2 throttle. If thats to fast maybe 3s would be better.

It's not too fast, it's just that as soon as I throttle above 25% (or so, it is just a guess) the plane climbs rapidly and I have to throttle back to stop it disappearing into the clouds.

[Learner]

45 minutes ago, Nigel Heather said:

It's not too fast, it's just that as soon as I throttle above 25% (or so, it is just a guess) the plane climbs rapidly and I have to throttle back to stop it disappearing into the clouds.

No doubt you've tried but doesn't some down trim improve it at half throttle? I was taught to trim straight and level at half throttle, then fine trim from there.

Edited August 19 by Learner

[Nigel Heather]

1 hour ago, Learner said:

No doubt you've tried but doesn't some down trim improve it at half throttle? I was taught to trim straight and level at half throttle, then fine trim from there.

I’ll try that, but I’m concerned that the trim will be quite significant.  With the trim as it is at the moment it is very easy to see the deflection.  Having an elevator with significant deflection at neutral just seems wrong.

[PatMc]

2 hours ago, Nigel Heather said:

It's not too fast, it's just that as soon as I throttle above 25% (or so, it is just a guess) the plane climbs rapidly and I have to throttle back to stop it disappearing into the clouds.

Have you read Mike Freeman's post that I quoted, particularly the part I highlighted in red ?

I suggest that you follow Mike's actions in moving the cg to as far back as you feel comfortable with. I'd advise doing this incrimentaly over several flights, adjusting elevator trim as necessary to keep the model flying level at cruise speed throttle setting. This should result in the model climbing at a reasonable, controlable rate when the throttle is gradually opened to full speed. 

It will almost certainly mean that at normal cruise the elevator is permanatly down several degrees. This looks untidy but the alternative is to either reduce the tailplane incidence or reduce the wing incidence, the latter will also effectivly reduce the downthrust by the same degree.   

 

PS I was just typing this post as you completed your's. The elevator deflection may look untidy & seem wrong but does no more than add an insignificant amount of extra drag, personaly I'd just live with it.  

Edited August 19 by PatMc

[Andy Gates]

Maybe a daft question coming up, but could the tailplane / elevator assembly have been fitted upside down - especially if it is a non symmetrical section?

 

The ones I have come across fly fine.

 

Try this.

 

Grab a length of string slightly longer than the fuselage.

Fix one end with tape at the centre line of the motor to the side of the nose.

Gently pull the string tight and tape the other end of the string at the rear of the fuselage just below the tailplane.

 

Now measure the centre points of leading and trailing edge positions of the tailplane and wing in relation to the string line.

 

That will provide a rough idea of your setup.

[PatMc]

22 hours ago, Peter Jenkins said:

Just read through my posts and it is actually GG's post that introduces the tail plane incidence to the motor/wing incidence issue.  So, I am not wrong in what I said as at no stage did I bring motor down thrust, wing and tail incidence together.  Ergo, I'm not wrong.  GG has introduced tail plane incidence where I didn't.  

 

Hope that clarifies matters.

Peter, I hadn't read your posts to any depth that I had any reason to doubt GG was quoting you accuratley. Perhjaps I should have prefaced my comment with "if Peter said that then ..."  My apologies for that. 

 

However having re-read my post that GG responded to quote " Ermm, isn't the effect of the motor thrust angle WRT the wing incidence ?

I.e. reducing the wing incidence is automaticaly reducing the motor's down thrust. " I now realise actually refers to advice you gave & IMO you did get that advice wrong. 😉

 

 

[Peter Jenkins]

Well PatMc

 

Motor down/up thrust is set against a fuselage datum.  So is incidence.  If you reduce incidence it has the same effect as reducing motor down thrust or increasing up thrust and vice versa.  If you disagree with that then draw the picture out and you will see the relationship between the two.

 

To be strict about this, I should say for the same airspeed you will need to generate the same lift force for balanced flight.  Reducing incidence means that for the same lift force at the same airspeed your wing needs to adopt the same angle of attack as before to generate the lift to balance the weight.  So, the fuselage datum line will have to be tipped nose up and we do that by using some elevator up trim. Now if you look at the motor thrust line which is tied to the fuselage datum that has been pitched up .i.e. the up thrust has effectively been increased slightly compared with where it had been.

[Learner]

10 hours ago, PatMc said:

Have you read Mike Freeman's post that I quoted, particularly the part I highlighted in red ?

I suggest that you follow Mike's actions in moving the cg to as far back as you feel comfortable with. 

Wouldn't moving the Cg further back make Nigels problem of excessive climbing with increased throttle worse?

[Stuart Z]

My Super 60 used to zoom towards heaven - until I moved the C of G forwards.

S

[Kim Taylor]

1 hour ago, Learner said:

Wouldn't moving the Cg further back make Nigels problem of excessive climbing with increased throttle worse?

Not in my experience - I put it down to having to trim additional up elevator to counteract the nose heaviness, then when you open the throttle / increase speed the up trim becomes excessive and up she goes. 

I've had similar on a foamy Riot, which I've got balanced either at or behind the recommended c of g, and a Wot4 woody ARTF, which if memory serves, was a good 15mm behind the recommended rear limit

KIm

eta I should add, that the method I use to set c of g is to trim for level flight at half throttle, then roll inverted to see what happens. When it flies inverted either hands off, or with a whisker of down stick, jobs a good'un

Edited August 20 by Kim Taylor
More info

[Nigel Heather]

6 hours ago, Kim Taylor said:

Not in my experience - I put it down to having to trim additional up elevator to counteract the nose heaviness, then when you open the throttle / increase speed the up trim becomes excessive and up she goes. 

I've had similar on a foamy Riot, which I've got balanced either at or behind the recommended c of g, and a Wot4 woody ARTF, which if memory serves, was a good 15mm behind the recommended rear limit

KIm

eta I should add, that the method I use to set c of g is to trim for level flight at half throttle, then roll inverted to see what happens. When it flies inverted either hands off, or with a whisker of down stick, jobs a good'un

But my Ruckus isn't nose heavy.  The balance range is 80mm to 100mm from leading edge, mine is balancing at 90mm at the moment.

 

I can't see how moving it back will help things.

 

Going to try a few things tomorrow

 

1 - move CoG forward as I can do that very simply.  Everything I have read says this isn't the problem but worth a try.

 

2 - packing the leading edge.

[Kim Taylor]

2 hours ago, Nigel Heather said:

But my Ruckus isn't nose heavy.  The balance range is 80mm to 100mm from leading edge, mine is balancing at 90mm at the moment.

 

I can't see how moving it back will help things.

 

Going to try a few things tomorrow

 

1 - move CoG forward as I can do that very simply.  Everything I have read says this isn't the problem but worth a try.

 

2 - packing the leading edge.

With the greatest respect, you don't know whether it's nose heavy or not, until you get it trimmed correctly and check the c of g in flight, where it matters. The numbers are just that, numbers on a page and are a recommended starting point, not cast in stone.

But the plane is yours, you can do with it what you will, and I hope you get it sorted. 

Kim 

[Nigel Heather]

1 hour ago, Kim Taylor said:

With the greatest respect, you don't know whether it's nose heavy or not, until you get it trimmed correctly and check the c of g in flight, where it matters. The numbers are just that, numbers on a page and are a recommended starting point, not cast in stone.

But the plane is yours, you can do with it what you will, and I hope you get it sorted. 

Kim 

 

Well, if I had designed the aircraft myself then maybe.  But this is a mass-produced aircraft that has been around for at least 5 years.  Sure, it is not unknown for manufacturers to make typos in the instructions but this typically leads to lots of reports of problems form customers and inevitable an errata being published either the manufacturer or experienced fliers on forums like this.  This isn't the case for the Ruckus, it has 100s maybe 1000s of customers who haven't raised any concern.

 

Of course this does raise the question - why is my experience so different.

 

But on the balance of probability, if the manufacturer says that the balance should be between 80-100mm then I am pretty sure that is correct.

 

And as mine balances at 90mm I can't see how it's CoG can be massively out.

 

And finally, I don't understand how a nose heavy aircraft would want to strongly climb - I'm not saying I know better, just that I don't understand as it is the opposite to what I would expect - so I would appreciate an explanation.

 

Cheers,

 

Nigel

[PatMc]

22 hours ago, Peter Jenkins said:

 

On 18/08/2024 at 12:35, Peter Jenkins said:

 

Edited August 20 by PatMc

[Peter Jenkins]

20 minutes ago, PatMc said:

 

Hi PatMc

 

I did read the text before you deleted it and I hpld my hand up for getting my recommendation the wrong way round.

 

So, for a low wing aircraft,ike the Ruckus, an alternative to applying more down thrust is to increase the wing incidence.  This would require the TE to be packed.  For the same flying speed, you would need more down elevator trim to reach the same angle of attack as before i.e. the aircraft would be flying more nose down than before and hence more down thrust.

 

Sorry for missing your point first time.

 

Nigel Heather - please note the above.

[Nigel Heather]

5 minutes ago, Peter Jenkins said:

Hi PatMc

 

I did read the text before you deleted it and I hpld my hand up for getting my recommendation the wrong way round.

 

So, for a low wing aircraft,ike the Ruckus, an alternative to applying more down thrust is to increase the wing incidence.  This would require the TE to be packed.  For the same flying speed, you would need more down elevator trim to reach the same angle of attack as before i.e. the aircraft would be flying more nose down than before and hence more down thrust.

 

Sorry for missing your point first time.

 

Nigel Heather - please note the above.

Getting a little confused now.

 

Packing the the trailing edge would increase the incidence - is that what I need to stop the ballooning?

 

In my head that seems the opposite, wouldn’t it increase the lift and therefore, cause it to rise even more?

Edited August 20 by Nigel Heather

[PatMc]

Post deleted

 

Edited August 20 by PatMc

[PatMc]

11 minutes ago, Nigel Heather said:

Getting a little confused now.

 

Packing the the trailing edge would increase the incidence - is that what I need to stop the ballooning?

 

In my head that seems the opposite, wouldn’t it increase the lift and therefore, cause it to rise even more?

Incidence is merely a rigging reference, it's not the angle of attack (AoA) of the wing. AofA is the angle that the wing actually enters the air at. 

Increasing the incidence by packing the TE won't alter the AofA but will increase the downthrust.

However IMO my previous advice in moving the CG rearwards makes more sense & has already been tried & tested by Mike Freeman as described in the first page of this thread. After trimming a more rearward CG results in a lower AoA which in turn results in a wider airspeed range without "ballooning" but also make the elevators more sensitive which is why I say move the CG rearwards in increments over several trial flights adjusting the elevator trim each time. 

 

[Peter Jenkins]

45 minutes ago, Nigel Heather said:

Getting a little confused now.

 

Packing the the trailing edge would increase the incidence - is that what I need to stop the ballooning?

 

In my head that seems the opposite, wouldn’t it increase the lift and therefore, cause it to rise even more?

Hi Nigel

 

I would agree that it sounds odd.  Incidence is a fixed setting but what matters when an aircraft is flying is the angle of attack i.e. the angle between the wing and the air and that is controlled by the elevator.

 

Regardless of the angle of incidence, for a given airspeed and aircraft weight the angle of attack will always be the same as the lift force must support the aircraft weight and AoA is controlled by the elevator position.  With a greater angle of incidence, you will then need to raise the aircraft's tail to regain the AoA that establishes level flight.

 

That is why increasing the angle of incidence is analogous to increasing down thrust as for the same AoA the nose is now pointing down a bit more hence the increased down thrust.

[Nigel Heather]

8 hours ago, PatMc said:

Incidence is merely a rigging reference, it's not the angle of attack (AoA) of the wing. AofA is the angle that the wing actually enters the air at. 

Increasing the incidence by packing the TE won't alter the AofA but will increase the downthrust.

However IMO my previous advice in moving the CG rearwards makes more sense & has already been tried & tested by Mike Freeman as described in the first page of this thread. After trimming a more rearward CG results in a lower AoA which in turn results in a wider airspeed range without "ballooning" but also make the elevators more sensitive which is why I say move the CG rearwards in increments over several trial flights adjusting the elevator trim each time. 

 

 

I’m really struggling with this concept.  I’ve always been told that having a plane too nose heavy is better than having it too tail heavy.  That a nose heavy plane is more table and a tail heavy plane is more sensitive to the controls.

 

For example, often told that a plane advertised as with the COG forward makes a stable intermediate plane that is easy to fly but move the CoG back and it becomes aerobatic.

 

So if I have a plane that is balloon up and climbing fast as soon as I apply power why would moving the CoG backwards help that?  Why isn’t moving the CoG forward a more likely answer.  I’m not saying it is wrong, just that I don’t understand it because it is contrary to what I have been told in the past.

[Learner]

1 hour ago, Nigel Heather said:

 

I’m really struggling with this concept.  I’ve always been told that having a plane too nose heavy is better than having it too tail heavy.  That a nose heavy plane is more table and a tail heavy plane is more sensitive to the controls.

 

For example, often told that a plane advertised as with the COG forward makes a stable intermediate plane that is easy to fly but move the CoG back and it becomes aerobatic.

 

So if I have a plane that is balloon up and climbing fast as soon as I apply power why would moving the CoG backwards help that?  Why isn’t moving the CoG forward a more likely answer.  I’m not saying it is wrong, just that I don’t understand it because it is contrary to what I have been told in the past.

 

Me being a flyer with very little clue about aerodynamics, after trimming for straight and level at half throttle. would start with cg as it's the easiest to change and I would try both ways depending on elevator trim, move in small steps 5mm each time and then if no improvement try opposite way. Then at least you've proved to yourself how cg change feels. Thrustline would be next, Then incidence.

I have flown a ruckus which flew well but wasn't mine so unsure of the set up.

 

It may be worth trying to contact Mike Freeman if possible,  he may be able to give some advice as he's obviously flown the model type in question. 

Edited August 21 by Learner