Retracts? - I have a cunning plan!

Some time ago I bought a set of lightweight (2kg max) electric retracts from Hobbyking. I did not have any specific use in mind but I was interested to see how they operated and how 'heavy' they actually felt.
Although they do exactly what they are supposed to so far they have just sat in the drawer.

Even whilst i was building the Petiterina I kept asking myself could it have been built in the same sort of way but to the original Ballerina size - 52" span instead of 40"?
Of course one of my considerations was that had to be small enough for easy transport as a 'one piece' plane and that small size meant the lightweight characteristics of Depron could be used to the full.
However my Depron Cessna Skymaster is 53" span and is also in one piece but then as a belly lander without undercarriage it is easier to transport and store.

So now the cunning plan.
1. So far I have not built a plane that could usefully use the retracts.
2. An original size all Depron Ballerina would be quite an interesting structural challenge.
So can I achieve both goals by fitting retracts to a 52" Depron Ballerina?
Further with the U/C retracted the Ballerina would be no bigger to transport and store than my Skymaster so it too can be a one piece plane.
Next couple up a pair of the retracts to see how much current they take - just 0.9 A peak!
This means I might be able to get away with running the retracts and everything else from a common BEC! :woohoo:
Now its likely weight.
It will be 1.3 times the size so if I keep its construction as structurally efficient as the smaller Petiterina is should be 1.3 cubed times the weight or 31 oz.
So far so good.
The final bit is just how easy, or not, would it be to fit retracts into the Ballerina wing.
As a tail dragger the main wheel is about in line with the wing leading edge. To retract sideways into the body of the wing would require some complex hinge angles.
The simplest solution is to adopt the P51 strategy with wing root leading edge extensions to give the wheels somewhere to go.

This solution also means the wheel well is well clear of the main spar and there is no CofG shift as the wheel retracts.
The problem is the two retracts are the only bits I have to hand! :ohmy:

That cunning plan is a masterpiece.

It is as cunning as a fox what used to be Professor of Cunning at Oxford University but has moved on and is now working for the U.N. at the High Commission of International Cunning Planning?

Re geometry - does this help?
Durafly Spitfire. (retracts powered from the bec that runs the rx, etc.

I actually looks like Durafly have cheated a bit on the geometry.
On the full size the U/C mounting is a bit further back - it had to be to be clear the leading edge torsion box - so the pivot angles are a bit more extreme.
On my proposed Ballarine retracts I am just being lazy and keeping everything simple.
It will look a bit like a Harvard although the wheels are proportionally somewhat bigger.
Before going any further I have got to build some softly sprung U/C legs.

Before I went any further I thought it would be useful to draw an underside 'view' to get an idea of what the undercarriage would actually look like rather than show construction detail.

The intention would be to join the two retract units together with a fabricated box girder so that much of the load would be contained.
The next problem is how to achieve a robust but springy undercarriage leg that is simple and light.

I still don't have the space for another 'big' plane but if the Ashbourne scale day does not go well I might! :woohoo:

"Not having enough space" is a poor excuse so it looks like I will build a lightweight 52" span Ballerina with retracts!
The first issue is how to mount the retracts in a lightweight Depron wing without using substantial amount of (heavy) wood.
On the Petiterina it 4" long legs are secured quite successfully onto the Depron by large acetate plates. Could the same sort of technique secure the retract unit directly onto the wing ribs?
The easiest way to work out how to do it is with a small test piece of wing just the wing spar and two ribs.
First a bit of wing spar.

A balsa/Depron/balsa box spar all in 3mm material.
Then the retract unit suspended between two ribs.

The face of each rib is clad in acetate and is a tight fit over the body of the retract.

The small lugs and retraining screws take none of the landing load but are simply to prevent the retract from moving sideways.
The completed wing test piece skinned in 2 mm Depron with a 6 mm Depron leading edge.

The undercarriage leg is also only a test being bent up from a piece of wire coat hanger!
Under test with a 2.5" super light weight Depron wheel.

It takes just 650mA peak!
So far so good but how well this all works in practise will very much depend on the final weight (and thus the landing speed) of the Depron Ballerina.

Dont know if this will help Q , but some time ago I bought a foamie with retracts. These were secured through the wing with 4 legs from the plastic retract mount which went right through the wing and on the top of the wing was a square plastic plate which was screwed to the legs making an open box construction which even though there were a few heavy landings they never moved

Garry

Looks good so far Q, but will the acetate be sufficient to spread the landing loads? Have/will you done/do any tests in that direction too?

I have a vested interest as I do like the idea of a depron structure in a FF scale model, but landing loads can be a bit heavy to say the least!

The only test so far is this.

Holding just the Depron it is possible to lift the 2lb weight which is quite a bit more than the likely all up weight of the plane. In fact it almost puts a permanent bend in the coat hanger wire!
I am confident the mounting is structurally strong enough which just leaves the effect of shock loads. What I really need is a softly sprung long stroke oleo leg that is simple, robust, compact and light.
Still thinking about that!

Don't want much do yer LoL. I was going to say doesn't it depend on how thick the acetate is ? :evil: [badass]

OT
Yes indeed the thickness of the acetate is critical.
The trick is to ideally arrange that in an 'arrival' type landing first the leg bends then the retract unit tears out of the acetate then the acetate tears from the Depron then the whole leading edge section breaks out of the wing.
Any more serious than that and its a likely bin bag job.

As the retract seemed to work and 'felt' strong enough, time to start actual building.
In order to fit the retracts the Depron ballerina will have a 'stand alone' balsa/Depron/balsa spar rather than having the flanges incorporated into the wing skin as on the Petiterina.

A "box" spar at the root tapering to an "I" beam towards the tip.
The actual wing tip will have no spar, just a Depron web.
To better support the thin acetate it is now 'sandwiched' between Depron ribs.


Unusually the wing is built up off the face of the spar.

One advantage of building like this is you have an 'operational' retract leg and wheel to ensure the wheel well is in exactly the right place and thus can made a close fit.

Some retract testing during construction of the wheel well.

Where possible I am cutting out two sets of everything so hopefully the other wing will be a bit quicker to make!

The retract cycle with the wing underside skin in place.
.

Looks good Q but a very tight fit will not allow any distortion from a less than perfect landing.