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Slider Glider! My take on a home design sloper


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CTR

Good idea EssexBOF, especially  the fuel tubing.

How did you ensure the tail halves didn't slide off?

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satinet
17 minutes ago, CTR said:

Sorry to say,  if you have 0.25mm clearance of a rod in a tube (assuming they are both parallel) and in this case the tube is 17mm long,  the resulting angle is +/- 0.8425243 deg of 'wiggle' irrespective of the diameters in question.

imagine the rod is loaded so at one end it is against the top of the tube, the other end is against the bottom of the tube. That's 0.25mm clearance down from the top of the tube.

Consider it as a simple triangle made up of 1/ the upper inside edge of the tube, 2/ the top outer edge of the rod and 3/ the clearance dimension forming the 3rd side of the triangle. Makes no odds how far away the other side of the tube & rod are.

 I agree that the percentage of diameter is different which influences the wear characteristics; the smaller diameter will suffer earlier in life than the larger diameter.

Yes you're right now i think about it. 

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EssexBOF
44 minutes ago, CTR said:

Good idea EssexBOF, especially  the fuel tubing.

How did you ensure the tail halves didn't slide off?

Used to bend them slightly, where they slide onto each tail plane half, don't over do it just a slight curvature works fine. Never had one come off. Used o set the wire up by placing fuselage on the board, so as the wing seat or joiner was parallel to the board.Pivot wire slid into position with epoxy in place. Two pieces of scrap balsa the same height under each side. Then check for squareness to fin, from above with tri square. Leave to set. Used to use 14swg wire.

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CTR

14swg on what size of model?

I am pondering using bearings with K&S tube through them, flush to the outer faces of the bearings. The horn bonded to the tube. Then use a wire or carbon rod through the tube such that it can be removed for transport. The tube keeps the horn in place.

1/16th ply facings will be more than strong enough for the bearings to fit in. Bearing size 4mm id 13mm od and 4mm wide. I’d use 4mm dia carbon rod for the stab to slide onto. Just need to come up with a neat method of securing them during flight.

All ideas welcome 😏

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EssexBOF
11 hours ago, CTR said:

14swg on what size of model?

 

Used on models up to 12 ft span.

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oipigface
12 hours ago, EssexBOF said:

On the later glider designs I built, that used an AMT, I reversed engineered it by having the tail plane halves pivoting on the wire, that was fixed into the fin. This meant there was no slop at all. True the wire had to remain in the model, so I used to loop a piece of fuel tubing over it for storage.

I think this is a feature of the Graham Woods design that I am mimicking. When I looked at it, I thought why not do the same thing only leave the rod free to pivot? Now you’ve given me more food for thought.

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oipigface
11 hours ago, CTR said:

14swg on what size of model?

I am pondering using bearings with K&S tube through them, flush to the outer faces of the bearings. The horn bonded to the tube. Then use a wire or carbon rod through the tube such that it can be removed for transport. The tube keeps the horn in place.

1/16th ply facings will be more than strong enough for the bearings to fit in. Bearing size 4mm id 13mm od and 4mm wide. I’d use 4mm dia carbon rod for the stab to slide onto. Just need to come up with a neat method of securing them during flight.

All ideas welcome 😏

Sounds identical to what I am half way through making. Except as I just indicated to EssexBOF, I’m wondering whether or not to make the joiner removable. A big advantage of buying a bit of tube is that you don’t have to drill a hole in it!

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CTR

I haven’t looked into it in detail yet; but I know the K&S brass tube sizes slide into each other, but don’t know the tolerance/ clearance.

Also, not sure if there is a good fit in a metric bearing as I think the tubes are imperial / swg related.

It would be great if there was a tube of diameter that fits well into a 5mm I’d bearing, and with a 0.5mm wall thickness. Then I could use a 4mm carbon rod. However, it’s not possible to ‘bend’ the carbon to form an interference fit with the tailplane halves. Do you think that only bedding the smaller rod would be adequate to secure the stabiliser halves?

 

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oipigface

I’m planning to use 2x 5mm CF rod as my tailplane joiners. The plane I have just started work on is not intended to be a high-performance machine, and I have had no trouble with similar setups on other planes. If I suddenly became really worried about the tailplane halves falling off, I’d probably think of fitting retaining screws, but I’d probably first just make the joiners longer.  

What lateral forces are these surfaces subject to in flight? My guess is not much.

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  • 2 weeks later...
CTR

Been spending my time working on an all moving tail version of the Slider Glider:

Reading up on the merits of AMT -v- traditional elevator it appears that AMT wins in small application, but elevator is more efficient for larger movements.

From this, my quirky brain thinks that we should be able to get the best of both by a variable camber, AMT. It’s probably been done before, but I couldn’t find any hints; so here we go with my approach.

The design had to be as simple as possible, reliable, single servo, stiff enough so the stab’ doesn’t wobble and as light as possible.

This is specific to the Slider Glider because it has a significant swept back LE on the stab’ so the pivot point is a little further back than normal. I wanted to find the best position to have a reasonably balanced  result to reduce the servo loading, but it’s beyond me to try to account for the forces due to the camber change added to the basic AMT. Also the angles of deflection are a bit ‘suck it and see’.

Working on the old adage ‘If it looks right, it probably is’🧐.  

I designed  the  geometry to move the main stab’ +/- 4 deg. and the elevator to add about another 15mm of camber at the TE. These are both incremental but with the elevator continuing to deflect more after the AMT portion has reached 4 deg.

Tried to upload a short video of the trial linkage but it’s too large! I’ll have to work out how to reduce the size. Suffice it to say, it consists of just 3 pieces. The main small block with a tube through it for the main pivot, a short ‘drop link’ and a special design of control horn. All works well in theory. Only drawback is that to use it on a different model requires a modification to the geometry. This is quite simple (done 3 already to get it looking right). Can’t underestimate the benefit of a 3d printer!

Proof of the concept hopefully not too far away but have to make another fuselage to support the new tail design. If anyone is interested I’ll upload a CAD image.

 

 

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CTR

Progress to date on the AMT:

Changed the fus’ tail end to raise the tailplane above the fus’ . Thought this was a good idea as it would make it less vulnerable on landing.

Designed the linkage to fit in a 3/8” / 9.5mm thick fin. 

Wanted to have the main joiner removable. This posed a problem trying to get a good fit through the tube to eliminate wobble. After a bit of experimentation, managed to swage down the K&S 5mm x 0.45 wall brass tube by 0.1mm to make it a good slide fit for the 4mm carbon pivot rod. Really pleased with the result. Now there will be only 10.5mm of brass tube protruding each side of the fin when the tail is removed, and no elevator horn floating about When the joiner is removed for transport.

In the process of making the new fuselage, just waiting for the balsa delivery.

Will post pictures when it’s done.

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  • 1 month later...
CTR

Latest Update: Made the modified fuselage ready for the tail. Was able to make the tail end slimmer as the feathers are not glued to the top of it.

Built up the fin with a 6.3mm core and 1.6mm each side. This allowed me to have a cavity for a lever. This meant I could keep a straight 2mm carbon pushrod from the servo to below the fin, then the lever shifts the motion up vertically by 32mm inside the fin. Top end has a ballpoint to another short, horizontal pushrod going to the rudder.

The 2mm carbon rod for the all-moving tail & elevator also runs virtually  straight down the fuselage under the rudder one and emerges at the tail end.

Net result is an AMT which is limited to +/- 4 deg. with and elevator capable of +60 / -45 deg. On top of that. Way more than needed, all from a single servo and pushrod. Total weight penalty compared to a standard AMT is about 7.3g due to the aluminium tube continuous hinge and 2mm carbon hinge pin for the elevator.

Photos should give a good idea of the result before covering it all up! As per normal for me (left handed) the images are inverted 🥴 Blame it on this right hand world!

You can just see the rudder ball link on the side of the fin too.

Just to preempt questions: Why did I do it? Because I could!

Going back to a previous posting; AMT=better at small deflections, elevator better at larger deflections. Trying to have the best of both.

 

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mikef

I admire a man who can build standing on his head some of the time....

 

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CTR

All that blood to the brain helps me think!

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mikef

Can you sketch your pitch control linkage please? - I've been wondering about it since you mentioned that the explanatory video was too big....

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CTR

Here you go Mike. Didn't need to think too much for this one 😁

The 3 linkage parts ( body, horn and drop link ) were 3d printed and the drawing only shows the port half from the vertical CL (had to show port for obvious reasons!)

Hope it makes sense.

AMT drawing.jpg

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oipigface

Ah well, there’s nothing new under the sun!

On p82 of Sailplanes 1920-45 Martin Simons writes of the Darmstadt D-28 Windspiel: ‘The rudder was of an ingenious double action type. The front portion of the vertical tail was not a fixed fin but moved as a rudder. To it was hinged the rear portion, geared in such a way that it moved twice as much as the front segment.’ That was in 1933, when students at Darmstadt Technical University tried to build as efficient a sailplane as they knew how. The plane held the world distance record for a short time, but was wrecked when a powered plane landed on it at Griesheim aerodrome. It was replaced by the slightly heavier D-28b, which was also a good performer. Both planes were very pretty.

It is not clear from Simons’ description whether the two parts moved in concert or in opposition, although I think that the description of the gearing suggests the latter.  It looks to me as if your elevator does the former. My grasp of formal aerodynamics is insufficient to analyse the issues here properly, but my intuition (always a bad guide!) tells me that an oppositional setup would induce less drag all other things being equal.

Does anyone know?

By the way: Congratulations on a most ingenious piece of work!

 

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CTR

You’re right that my design works ‘in concert’. The idea being an increased camber in unison with the change in tail AOA, increasing the ‘lift’ in the same direction.  I’m hoping that the onset of stall of the tail with significant deflection will be delayed, reducing drag too. Beyond me to actually work it out, but it seemed a good idea at the time.

In my mind, It really depends on the radius from the centre of rotation of the glider with elevator deflection, and where the perpendicular line from that centre intersects the extended chord line of the wing etc.etc.

My initial thought about the rudder portion moving in the opposite direction equates to leading and trailing edge landing flaps on airliners. Significant increase in lift in the direction opposite the camber and loads more drag. 🤔 Could be aerodynamically more efficient in full size modest manoeuvres; but we’re involved with more radical antics! Definitely food for thought.

Swapping the top link pivot and the elevator hinge pivot in the sequence would reverse the action. Anyone up for trying it?

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