[Norfolk'n'Good]

Whatever your doing to this old girl,   your doing it well,  it could not have gone to a better caretaker

Allo............ Alan's after summit 

Can I have a ride in her when she is done?

What size are those props Ian they look huge for a 22    My old one runs same as it did when new but I find a 18x6 wood is a struggle for it.  A 16x6 or 15x8 swings better but still no race engine.

[Cornish Pixie]

'Tis a definate mate, it'll be all sorted out by then.

Ian.

In that case I will have to be there to see it  

Simon

[idigbo]

What size are those props Ian they look huge for a 22    My old one runs same as it did when new but I find a 18x6 wood is a struggle for it.  A 16x6 or 15x8 swings better but still no race engine.

The props are Smart 18x6, cut down to 17. They rev quite well still but throttling isn't quick, but why would anyone want it so on this model

Slow is best especially on the HP42 since models, and the full size nose over if the top throttles are opened to quickly

[Pup Cam]

Looking great Ian.  Very nice work as ever.   

I know someone who will be very pleased to see progress being made again

Alan

[rcfanuk]

Looking forward to seeing this one in the air Ian, that additional tail area should make knife edge easier

Steve

[idigbo]

Looking forward to seeing this one in the air Ian, that additional tail area should make knife edge easier

Steve

Might have to stick a couple more motors on it though!! This evening I made the templates and some of the ribs to replace the leading edges of the top wings where the slats are. These are recessed in from the wing section so the slats when retracted, are flush with the rest of the wing section. Some images show them retracted fully flush, others slightly proud. Mine will be flush. The slat itself will be laminated from balsa with a glass skin for stiffness and a sharp trailing edge. The plan is to lay up the bottom skin of the slat directly onto the sheeting below it, for a nice fit. We'll see.

Ian.

[Neate HI BALL]

Grate Ian,it looks really good
John

[Neate HI BALL]

Hi Ian,
How are you getting on with Helena? Is she going to be ready of Barkston ?

John

[idigbo]

Not for Barkston but thats a warbird doo!!

Picking up the cnc cut linkages and brackets for the slats tomorrow evening. The wings have had the ribs renewed in the section where the slats go, since they retract back fully into the wing profile. Had chance today (whilst waiting for paint to dry) to have a look at the wiring. Since this is an over 20kg aeroplane it needs to have dual radio systems. I'm doing it the simple way and splitting it as follows. The throttles split into pairs, upper and lower. Each pair has a single servo with a linkage to the two motors. One Rx will have lower throttle, left aileron and lower elevator plus the rudders. The other Rx will have right aileron, upper elevator, upper throttle and both slats. I have set up the throttles on the Tx now. They have been mixed with a slowing of opening of the top throttles. Both throttles close at the same speed. This is an attempt to stop the nose over characteristics of the full size and also models (from model pilots I've spoken to) due to the high top motors. I'm going to run it on the standard exhausts initially, but may change them at some point if I get moaned at!! Sounds great but does have a bit of bark to it.

Ian.

[idigbo]

Here are a few pics of the brackets mounted on the new rib parts. They have been assembled on a simple jig to ensure they all line up properly. The ribs need hollowing out yet for the pushrod fixings which will be 3mm clevis onto bushed holes half way up the rear actuation rod. There are 16 parts to each mechanism, plus another 4 pushrods and a torque tube so accuracy is the key.
It is essential they are free acting since there will be nothing but wind to move them. A servo on each slat will be able to lock them shut. I could at a push fit a pushrod to the torque tube to make them fully servo operated, but I want to try wind first. Its also important that the linkages don't flop sideways since the actual slat won't retract as it will hit the wing leading edge either side. Now these brackets are sorted, I can fit the ribs in place and sheet the upper leading edges, ready to laminate the slat lower surface in situ for a snug fit. In the pic of the rib with brackets and actuation rods in place, the upper bolt (inline with the bottom wing section) is a stop for both the inner and outer movements. When out, the rear rod rests against it. When in, the front rod pulls against it for a nice positive fit with no binding.

Ian.

[idigbo]

I must have been naughty, restricted to two pics a post!!

Ian.

[alanh]

Aye  up Sir Ian

I have a Z26 which has had a bash,I am willing to donate free . The secondary coil is bu@@red due to the earthing tag being bust and the insulator block and carb are damaged .I have turned it over in my lathe, the crank isn't perfect but not miles out . Von Sheephoven has had the silencer for his geared Z22 already .Its no prize but you could probably fix it with bits off one of the 22's( and a bash with Alan Cantwell's hammer if required)
Regards Alan
 

[idigbo]

Aye  up Sir Ian

I have a Z26 which has had a bash,I am willing to donate free . The secondary coil is bu@@red due to the earthing tag being bust and the insulator block and carb are damaged .I have turned it over in my lathe, the crank isn't perfect but not miles out . Von Sheephoven has had the silencer for his geared Z22 already .Its no prize but you could probably fix it with bits off one of the 22's( and a bash with Alan Cantwell's hammer if required)
Regards Alan

Top stuff Alan   The fall back plan is to fit 2, then 4 if still needed, Z26 if the Z22 are marginal. At the moment I am still confident that the 22 produce enough draft but its always nice to have a Plan B.... then a C etc.

Ian.

[idigbo]

Each aileron is just over 4ft long, about 6inch chord. They are hinged in the scale manner, below the bottom skin about 1.5 inch back from the leading edge. Power wise, there will be a single servo to each aileron. Problem I can see is that the aileron is fairly heavy and I can envisage the static load being fairly cruel to the servo especially taxiing etc. I was tempted simply to balance the aileron with an internal spring on the linkage, this would help the servo hold the aileron but not over bumpy ground etc. I now think that apart from lightening the aileron by replacing the hardwood trailing edge, I'll balance them by replacing a strip of leading edge with lead, cast to the section of the bits to be replaced. Am I right in thinking that the full size practice is to 'over' balance so the surface is deflected up? Or would neutral be more betterer in this instance?

Ian.

[CF-FZG]

I now think that apart from lightening the aileron by replacing the hardwood trailing edge, I'll balance them by replacing a strip of leading edge with lead, cast to the section of the bits to be replaced. Am I right in thinking that the full size practice is to 'over' balance so the surface is deflected up? Or would neutral be more betterer in this instance?

Ian,

You're correct that the full sized are balanced so that the nose of the surface is 'slightly' heavier that the bit behind the hinge


Mark

[idigbo]

More weight it is then    cheers Mark

Ian.

[Pup Cam]

More weight it is then    cheers Mark

Best leave those 26s alone then.  Dust of those 38s!

Alan

[idigbo]

It'll be reet Alan

The headbut smiley looked a bit like I'm moaning, not in the slightest
The servo's I'm fitting are Hitec 700 jobbies, more than enough for the job, even more so on a balanced surface.

Ian.

[CF-FZG]

More weight it is then 

Have you asked Pete about this, he could probably give you a more informed view, and possibly a ballpark figure, i.e. what percentage of the total weight = nose weight - (measured by a spring balance on the trailing edge).


Mark

[idigbo]

I'm hoping he'll be along at some point

Ian.

[PDR]

Well since you ask...

There are three reasons why control surfaces are mass-balanced in full-size practice:

1. It reduces the control forces (mainly elevator) and linkage stresses at low speeds. With the power of the servos we tend to use I'd suggest this one can be ignored.

2. It raises the critical flutter airspeeds  by increasing the resonant frequency of the wing/aileron system (and tail/elevator system, and fin/rudder system). This COULD be something we need to worry about, depending on the structural stuffness.

3. If the surfaces are "over-balanced" it can provide additional inertial damping and a smidge more stability - a disturbance that causes a wing to rise will initially result in the aieron on that side rising (because of the overbalance) which can correct it. This makes the aeroplane less tiring to fly, but the rigid control systems we use would get no benefit from it - in fact it would simply increase the servo current drains because the servos would be continually "fighting" these corrections.

So we're really only bothered about (2) - the flutter issue. Big control surfaces on floppy wings can benefit from mass balancing, and what you're aiming for here is neutral balance. If you use in-line counterweights then it's like a prop - you're looking for the surface having no prefered "rest" position. If you use offset (external) counterweights then you're looking for a definite "return-to-centre" resting position.

Whichever you choose the actual counterweight should be longdituenally aligned with the control horn so that the inertia of the counterweight doesn't twist the surface when control inputs are applied - the torsion spring that this represents can actually introduce a new flutter mode and cause the very problem you're trying to design out!

So if you have an external horn balance then mount it on the same aileron rib as the control horn, and if you use leading-edge balance (say with a stick of plumbing solder) then mount it across the front of the aileron horn position and make sure it is well braced with strong ribs to tie it to the horn.

If you *can't* align the mass with the control horn (say because the only place to put it is inside an aerodynamic horn balance at the tip) then you must make the aileron (or elevator, or WHY) structure very stiff in torsion to avoid both f;lutter and structural fatigue problems.

Whadaya mean "fatigue"? Balsa doesn't fatigue?!

Wel actually it does, but more to the point these cyclic loads will cause age-related failures in glue joints done with rigid adhesives like cycano and epoxy. Tougher adhesives like PVA, aliphatic etc are less prone to this sort of failure.

£0.24 supplied,

PDR

[idigbo]

Cheers folks.

The aileron has two horns, fairly well spaced out up the surface. my plan was to replace a bit of leading edge with a cast lead strip, Are you saying that this needs to be inline with the horns, or can it be between the horns. I'm thinking there may be too much weight in one place, structure wise. Electrically, the servo will ore than cope wih the flight loads, I am trying to get rid of the chance of servo / component damage due to the physical weight of aileron behind the hinge during taxiing and bumpy ground, crap landings etc.

Ian.

[alanh]

PDR makes lots of good points; especially about the counterweight aligning with the control horn.
I think your best bet is to replace the big bit of tree forming the trailing edge to reduce overall weight,and the moment on the control horn . Flutter appart I can't see a flying problem, just the landing/taxing  loads. Why not drive both horns with two less powerful servos and spread the loads

 Alan

[PDR]

Erm...I hate to mention it, but mass balancing makes no difference to the surface "bump"  stresses, it just makes a difference to the way the surface *moves* in response to them.

If your surface has a heavy lump at the TE then when it is "bounced" in a heavy landing this lump tries to carry on, applying a stress through the ribs and into the linkages & hinges. If you balance this surface then it won't *move* when bumped, but exactly the same stresses will be appied to the aileron ribs, but as an equal and opposite stress comes from the counterweight the surface doesn't actually move, and the linkages don't see a load. So you won't stress the servo, but you still stress the ribs in the surface, and the hinges see *double* the stress because they get the combined load from the surface and the counterbalance.

Which bit is the concern? Servos, hinges or structure?

PDR

[idigbo]

Agree with what you say there 

But, what I'm trying to minimise is servo and linkage damage due to the inertia of the heavier trailing edge as the model taxiies over bumpy ground and the likes. The hinges, spars and ribs etc are amply strong enough to cope with the extra weight of the balanced aileron.

How should the surface be balanced then, to hang level, or with up deflection We had the power off this morning so had to do this unrelated to electrickery, so I removed the trailing edge, replaced with hardish balsa that weighed a quarter of the original hardwood, re hung and lashed some weight o the leading edge, just to gauge what would amount be required. Its going to take around 6oz to hang with up deflection, though when I make the weights they'll be split into 4 bits, two either side of the horns. The horns also have a hinge at the same point, but there are 4 hinges in total. These 4 bits will be at the very front edge along the aileron so it might mean less weight is required, but i still have to cover them yet.

Ian.

[Richard Crapp]

 It would upset me to add 6 oz to etch wing tip.

I think you are worrying about the ailerons 'rattling' as you taxi,
 it ain't going to happen!
You will probably taxi a short distance over grass, but the time the big soft wheals transmit a shock all the way out to the wing tip it will disappear.

If it was an Extra or the like,  a mass balance might be a good idea but as it still has an Aerodynamic balance and given that this thing is probably going to be the slowest model you have ever seen fly,  all you need is a good servo mounting and some stiff no slop linkage.

I would attack the wood behind the hinges with a Dremel sander before adding painful weight if you still consider it necessary.
Just me; i hate weight.

[idigbo]

It would upset me to add 6 oz to etch wing tip.

I think you are worrying about the ailerons 'rattling' as you taxi,
 it ain't going to happen!
You will probably taxi a short distance over grass, but the time the big soft wheals transmit a shock all the way out to the wing tip it will disappear.

If it was an Extra or the like,  a mass balance might be a good idea but as it still has an Aerodynamic balance and given that this thing is probably going to be the slowest model you have ever seen fly,  all you need is a good servo mounting and some stiff no slop linkage.

I would attack the wood behind the hinges with a Dremel sander before adding painful weight if you still consider it necessary.
Just me; i hate weight.

I've seen it happen a couple of times on folks aeroplanes with big surfaces. A bump on landing strips the 'sacrificial' gear in the servos. A few ounces on a model that weighs in excess of 75lb isn't going to make the slightest bit of difference to its performance. The ailerons are quite light apart from the old trailing edge, the ribs are 1/8" ish soft balsa. I'd much sooner add the weight if it makes the system more reliable. I haven't weighed the removed and new parts but I'd imagine that there won't be that much difference in the total weight of the old ailerons and the new balanced ones, its just in a different place. The 'bodge balanced' aileron I have now feels very light and smooth in operation.

Ian.

Ps. Richard, I was watching an old video last night (on DVD) of a waterplane event in Cumbria, you were there flying a yellow amphibian, looked like an Anderson Kingfisher or similar, I'm guessing i was 1986 or so a cracking watch

[goldenballs]

Standing by to be shot down in flames for a 'dumb-ass' idea but....  Would there be any benefit in spring loading the aileron to dampen the effect of bumps; would the benefit outweigh the additional servo power required to deflect the control surfaces?

Garry

[idigbo]

Standing by to be shot down in flames for a 'dumb-ass' idea but....  Would there be any benefit in spring loading the aileron to dampen the effect of bumps; would the benefit outweigh the additional servo power required to deflect the control surfaces?

Garry

I was originally going to try that Garry, but figured the spring required to hold it up might put too much load on the servo on the down ailon bit, and still might not stop what I think might happen happen   I'm happy with the solution now. Like Richard says, it MIGHT not happen anyway, but I'm all for reducing the chances by whatever solutions are available

Ian.

[Richard Crapp]

That would have been the Teal Amphibian at Ullswater, 
 It is still hanging in my workshop, a bit dusty.
That was a big heavy thing it had a Zenoha 38 then a 62.   Really good fun times.

[alanh]

I'm trying to remember my rotation of rigid bodies .Is any additional weight away from the centre of rotation (hinge line) going to increase the moment of inertia of the aileron? I think is does .If I am correct then adding a balance weight will increase torque loads  on the control links/servos not reduce them when travelling over bumpy ground. (I'm a chemist not a physicist / engineer )

Alan

[idigbo]

I'm trying to remember my rotation of rigid bodies .Is any additional weight away from the centre of rotation (hinge line) going to increase the moment of inertia of the aileron? I think is does .If I am correct then adding a balance weight will increase torque loads  on the control links/servos not reduce them when travelling over bumpy ground. (I'm a chemist not a physicist / engineer )

Alan

Surely if the aileron is balanced when hanging on the hinges, then no matter what ground the model travels over, there will be negligable extra load on the servo or linkage, this load is on the hinges and supporting structure

Ian.

BTW Alan, I got a package from the postie this morning Many thanks mate. 

[alanh]

I hope the engine is some use I couldn't decide wether to fix it or not ;so problem solved!!

The hinge thing is just an idea. I'm a chemist who teaches A level physics sometimes , it needs an engineers opinion on wether is the aileron a hinged flap or a rigid rotating body .

Alan 

[PDR]

I'm an engineer, Jim - not a magician...



OK, so let's see where we've got to. In summary there is a concern about bump loads breaking the servos, but not the ailerons. This is a reason to balance the ailerons at neutral balance. There is (always, on a large model like this) a concern about flutter, and this is ALSO a reason to balance the ailerons at neutral balance. So it looks like neutral balance would be worth doing. Mount the counterweights where you like, but remember that the counterweight inertia is reacted against the aileron mass/moment  and the linkage, so bracing it directly to the aileron horn is favourite.

Gary - springs. Definitely a "bad thing"^(tm). Springs introduce phase lags that are effectively "undamping", so you don't want to do that.

Alan - rotation of rigid bodies (wasn't aware you'd seen the meme sahib in bed!). Well yes and no, but mainly no. Adding mass anywhere away from the pivot will increase both the moment of inertia and the radius of gyration. This will increase the torque required to *accelerate* the aileron from a fixed position (the transient case) but not the torque required to move it or hold it in position (the first and second steady-state cases). Insofar as servo/linkage loads are concerned the transient case loads are tiny compared to the second steady-state case, so this increase can effectively be ignored.

The point about balancing for flutter is that in an unbalanced surface there is a tendency for the surface to "lag" when the wing is moved. So if a gust pushes the wing upwards the surface will initially stay down and then start to follow. When the wing reaches its limit of flex it stops, and the surface carries on. This now applies "up" aileron which pushes the wing down, and so we have a positive feedback system⁽¹⁾ which (over a range of conditions) will oscillate. Balancing the surface gives it a neutral response to wing movement, so there is no feedback and no oscillation. This is of course a very simplistic description because it only considers one displacement flutter mode, but similar conditions hold for most of the flutter modes, and minimising  the distance between the pivot axis and the surface CG is ALWAYS a good thing^(tm) from a flutter perspective.

PDR

⁽¹⁾ Actually it's negative feedback with a phase shift, which if you remember your transforms becomes positive feedback. But that's just being pedantic.

[Spider Pig]

I;m intrigued by your suggestion to add the balance at the control horn. If we consider that the control system is 'rigid' (ie pushrods, servos, WHY) and that the aileron is not rigid (probably), surely a distributed mass (ie the aileron) balanced by a point mass (the mass balance) which is in fact mounted rigidly anyway since it's on the control horn, will, in terms of balancing for flutter and or bumps, induce bending (twist) along the length of the aileron, which, depending on the stiffness of the aileron, be a bad thing. This being no better than not balancing (since the control system is 'rigid').
Obv. for a "real" system where the stick is held by a hooman been and therefore the control system is not rigid things are different.

[PDR]

This would take a couple of minutes with a whiteboard, but I'll have to try to do it in words - so here goes.

I'm going to talk about ailerons, but the same applies to any control surface.

Ideally the control horn would be mounted at the spanwise centre of mass and spanwise centre of pressure of the aileron (which would also ideally be in the same place). Indeed this is how we decide where to mount the aileron horns in the full-size case. This means that the distributed bump loads would produce equal stresses either side of the horn.

Now let's look at what is happening the flutter case. The aileron is trying to move, but it is constrained by the hinges and the horn - it's constrained at a single point. If we rigidly mount a counterbalance at this point then the constraint and the balance have little or no spring coupling between them, so they will always be in phase and the primary flutter mode disappears.

But if we use a distributed counterbalance the tornsional stiffness of the aileron becomes a spring between the mas and the constraining point. This introduces phase lags and leads to a high risk of a torsional flutter mode.

For the bump case it makes little difference.

PDR

[Spider Pig]

.

Now let's look at what is happening the flutter case. The aileron is trying to move, but it is constrained by the hinges and the horn - it's constrained at a single point. If we rigidly mount a counterbalance at this point then the constraint and the balance have little or no spring coupling between them, so they will always be in phase and the primary flutter mode disappears.

Myeaybut the spring coupling between the aileron's mass and the constraint is still there isn't it?

But if we use a distributed counterbalance the tornsional stiffness of the aileron becomes a spring between the mas and the constraining point. This introduces phase lags and leads to a high risk of a torsional flutter mode.

The way I was thinking of it was as follows (this is on a blackboard you understand, none of this fancy modern nonsense)

Imagine your aileron is made up of many small sections, each one hinged and tied to the next one my a torsion spring. If we have a mass balance in the middle section, but none on the others, the end ones can flap up and down somewhat (ie if the wing is moved upwards by a gust, they lag)
If we mass ballanced each section individually, they would not.

Do that integration thing along the length and, etc etc

Granted if you then put a control input into the centre, there'll be a lag, but so long as those torsion springs aren't really stiff this will be the case anyway no?

[Richard Crapp]

I will just play devils advocate here a moment.

It is a scale model; right? you have to put the horn where it belongs. End of story.
 
If you feel you have to have the ailerons mass balanced for and aft that's OK and a good thing but unnecessary on a slow flying model that is sure to be over engineered. (for the non scale vibration)
However, adding weight to etch wing tip will add a momentum lag in all directions that may be noticed on the aileron control reaction and the rudder. That might spoil your day at a critical moment.   Over fussy? yes. but so is the scientific missive above. Not wrong, actually very interesting and truthful, just not for a model HP42

[alanh]

Hi PDR

My thinking about moment of inertia increase wasn't about accelerating the aileron more about decelerating it after a bump, which is Ian's main concern .Won't the increased rotational KE be potentially damaging to servos /links etc. if balance weight is added?

Alan

[idigbo]

I will just play devils advocate here a moment.

It is a scale model; right? you have to put the horn where it belongs. End of story.
 
If you feel you have to have the ailerons mass balanced for and aft that's OK and a good thing but unnecessary on a slow flying model that is sure to be over engineered. (for the non scale vibration)
However, adding weight to etch wing tip will add a momentum lag in all directions that may be noticed on the aileron control reaction and the rudder. That might spoil your day at a critical moment.   Over fussy? yes. but so is the scientific missive above. Not wrong, actually very interesting and truthful, just not for a model HP42

That'll be why the real ones ailerons are balanced then