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1/4 Scale Salto

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Peter Balcombe
Posts: 1178
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

1/4 Scale Salto

Post by Peter Balcombe »

Although the H101 Salto was originally available in the Pat Teakle Sailplanes range, the fuselage mould had been damaged beyond repair at some time before Cliff took over the reins, so sadly this aerobatic model has not been available.
However, Cliff has recently managed to obtain an unused original fuselage & John Hall has worked his magic on it to produce a new mould, plus while he was at it, modify the wing section from the original Ritz1 variety.

After lots of discussion & comments/advice from other modellers, plus the desire to make a model that is relatively easy to build, the new fuselage has an HQW2.5/12 wing section, giving a thin section with no need for washout.
Although the use of substantial carbon joiners was considered, it was decided in the end to go for a pair of 15mm steel joiner strips mounted in wing tubes & which just fit between the main spars. Dihedral is provided via a ‘scissors’ type joiner fuselage box which takes the wing joiners in an interleaved arrangement.

The main spar assembly is made up as full box section at the root, changing to a 'C' beam at the aileron taper break. Scale rotating TE airbrakes are used & the built-up structure is sheeted in 0.8mm ply (or perhaps GRP sheet) prior to glassing the finished wing. Time will tell how this aspect pans out

Anyway, with a set of laser cut parts supplied by Cliff, the build of the first wing has just started.
The pics show the initial build of the RH wing root end, with all normal ribs attached to the lower main spar & rear spar web + root end rear web doubler. The Liteply false LE is notched into each rib & the notched rear spar web also helps locate everything - which is just as well as for some reason, the plan has printed undersize :(
4 ply angled ribs will be added at the root end to form the edges of the 2 TE brake cutouts. Again, these notch into the structure to take up the correct positions.

The front spar web (again doubled at the root end) will be slotted in shortly prior to the section of root ribs between the spar webs being removed to insert the joiner tub assembly (2 brass tubes + 2 spacers, reversed between wings to get interleaved joiners in fuselage ;) )
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Peter Balcombe
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Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale Salto

Post by Peter Balcombe »

With the outstanding lower rear spar inserted to complete the basic framework, attention turns to the joiner assembly.
This is made up using interleaved brass tubes and 3mm spacers, epoxied together to form a solid block as shown. The root rib sections between the spar webs were then removed using a razor saw & tidied up with a sturdy file to leave a clean slot.
Note that the joiner assembly needs to be cleaned up to reduce its overall thickness to that of the joiner tubes (16mm) as it will be a very neat fit between the spars at the outer end, so any thicker & the upper spar will not sit down correctly.

Once happy with everything the joiner can be epoxied in place.
Note that the joiner tube arrangement will need to be reversed for the 2nd wing In order to allow the 4 joiner strips from both wings to interleaved in the fuselage without having one wing in front of the other.
(I arranged the forward brass tube at the front on my RH wing, so the spacer will need to be at the front on the LH wing.)
Attachments
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Peter Balcombe
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Re: 1/4 Scale Salto

Post by Peter Balcombe »

Top main spar glued in place using epoxy (mostly to get a really good bond in the joiner area).
Have also added a strip of 0.8mm ply at lower TE to tie the vulnerable rib ends together (temporarily supported using a spruce strip as a straight edge whilst the glue dries.
I will probably add a similar ply strip on the top to finish forming the TE before I start to address the TE airbrakes. (The wings are likely to be sheeted with 0.8mm ply anyway).
Attachments
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John Vella
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Re: 1/4 Scale Salto

Post by John Vella »

Peter, neat work. Why are you covering the wings with 0.8mm ply? I have covered 2 models with 0.4mm ply which does a good but expensive job. Regards John.

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Peter Balcombe
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Re: 1/4 Scale Salto

Post by Peter Balcombe »

Hi John,
I designed the built-up wing structure on the basis of 0.8mm skins because:
(a) I didn’t have enough spare thickness to get any sensible joiner/spar in with my normal 1/16” balsa sheet skins
(b) With a faster aerobatic type of model, I wanted a firm wing surface
(c) I wanted to use a firm sheet surface for the scale type TE airbrakes
(c) There was the possibility of 0.5mm ‘ish’ grp sheet being made available.

However, as the model is almost certain to be glassed anyway, then a glassed 0.4mm skin is probably another practical option & possibly easier to apply on a smallish model ;)

John Vella
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Location: UK

Re: 1/4 Scale Salto

Post by John Vella »

Peter, the scale t.e airbrakes are a great idea and are a big feature on the full size. The 0.4mm ply skins glassed will do the job well with plenty of torsional stiffness for the aerobatics. Regards John.

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Peter Balcombe
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Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale Salto

Post by Peter Balcombe »

Back to the Salto at last, so a quick update.
Having completed the tailplane design, Cliff has cut the parts & the initial build has started.
The pic below shows the main structure, to which will be added a solid ruddervator. Each tailplane half carries its own servo, with a short external pushrod to the ruddervator horn. The tailplane attachment is via rear joiner & short front incidence dowel. The main joiners are staggered in each tailplane to allow the fuselage tubes to be crossed.
Cliff has come up with a neat single servo connector housing which can be fitted flush in each fuselage tailplane root, complete with standard servo connector. The tailplane servo connector can be easily plugged into this during rigging.

On the wing front, the only recent progress to report is the addition of the brake hinge line spar doubler strips between each rib (bevelled in the brake sections), plus fitting of 1/16" balsa sheet lower surface covers between each rib in the brake areas - the brake lower surfaces will hopefuly close to lie flush with these covers in due course.
I've decided to fit additional angled riblets to define the brake end faces before adding any sheeting in order to have a tidy facing to each brake and wing surround and also to hopefully be able to remove the brake by cutting between the riblets.

I think that I will go with Ian's suggestion of using 0.4mm ply sheeting & hope that the lower brake blade forward surface will be stiff enough once glassed, particularly as this area is likely to be exposed to ground contact if the brakes are not closed before touchdown.

I'm still trying to sort out the best assembly sequence to try to ensure a best fit & operation, whilst not having to go back into the structure :?
Attachments
Tailplane half1_small.jpeg
Tailplane build2_small.jpeg
Tail servo connector.jpeg
Wing lower brake closures.jpeg

john greenfield
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Re: 1/4 Scale Salto

Post by john greenfield »

Peter Balcombe wrote:
13 Jul 2020, 19:15
Hi John,
I designed the built-up wing structure on the basis of 0.8mm skins because:
(a) I didn’t have enough spare thickness to get any sensible joiner/spar in with my normal 1/16” balsa sheet skins
(b) With a faster aerobatic type of model, I wanted a firm wing surface
(c) I wanted to use a firm sheet surface for the scale type TE airbrakes
(c) There was the possibility of 0.5mm ‘ish’ grp sheet being made available.

However, as the model is almost certain to be glassed anyway, then a glassed 0.4mm skin is probably another practical option & possibly easier to apply on a smallish model ;)
Hi Peter

Just a few comments on ply wing skinning.
Please be aware that most 0.8mm ply sold in the UK is actually 0.95mm thick (event though marked as 0.8mm). This adds a considerable amount of extra weight to the model as 0.95mm ply is almost 20% heavier than 0.8mm.
).4mm ply, even if glassed is still quite prone to splitting with rough handling. Splits start in the middle of rib bays if the sheeting is flexed by say picking the model up. Once the split has started it will grow as the wing flexes.
My preferred choice is 0.6mm ply. Most people do not know that this thickness even exists but it is readily available from companies such as SLEC. It is much stronger than 0.4mm with no tendency to split and much lighter than 0.8 (0.95mm). It is also much easier to apply to curved surfaces as it is more flexible than thicker ply.

AEB
AEB = Aeronautical Energiser Bunny (with thanks to CW)

roo Hawkins
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Joined: 18 Mar 2015, 20:12
Location: Northamptonshire

Re: 1/4 Scale Salto

Post by roo Hawkins »

Hi Peter all looking good. I have just taken delivery of the salto plug fuz so will be starting a build as well. But I am cutting blue foam wings with carbon spars. But will not be doing a build thread this time.
Attachments
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Peter Balcombe
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Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale Salto

Post by Peter Balcombe »

Ah, you got the modified original :)
I will be very interested to see how yours turns out, particularly with regard to weight & ease of build.
What type of brake are you intending to use?

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