• Administrator
  •  
    Before your membership becomes valid, you will receive an email that must be answered.
    Please check your spam folder or this email.
     

SF33 1/6 scale

Fans and Thermals.
User avatar
Peter Balcombe
Posts: 1399
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: SF33 1/6 scale

Post by Peter Balcombe »

Does that mean that it all looks good now Steve?
Peter
User avatar
Steve Naidamast
Posts: 22
Joined: 25 Jun 2021, 17:51
Location: New York, USA

Re: SF33 1/6 scale

Post by Steve Naidamast »

So far Peter, the gluing appears to be going well. I am going to do some more this afternoon.

Looking at the bottom front part of the wing ribs, it appears an additional bottom piece of stripping will have to be added to the Leading Edge in order that the skinning of the bottom part of the wing will meet the bottom part of the Leading Edge properly.

I have received an order of Balsa stripping that should take care of all of it.

As far as the skinning goes, I was thinking of using 1 inch wide/ 1/16 inch thick stripping. Though this will incur slightly more gluing, it will avoid any depressions or bubbling in the wood.

As I had mentioned in my last email, I did not understand what you meant by the following statement you made in a previous email to me...
>>>
You could pin a length of strip Balsa placed along the very front of the skin into the composite LE, but you will need to stop glue sticking to this piece, say by putting a strip of cellotape along it to act as a release layer.

<<<

Could you please clarify.

Thank you...

Steve
User avatar
Peter Balcombe
Posts: 1399
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: SF33 1/6 scale

Post by Peter Balcombe »

Steve,
What I meant by the comment was:

As I normally just fit the false LE to the ribs & then sand this down flush with the rib front profile before adding the skins, I can fit the skins down onto the ribs and the false LE, overlapping the false LE by a couple of mm. The skin front can also be held down using many strips of masking tape placed around the LE from top to underside.

However, if you have a composite LE (main LE strip already fitted to the false LE, each skin has to be fitted with its front edge butting up against the LE & hopefully also sitting down onto the top of false LE.

My suggestion was to (just after the skin has been put in place against the LE strip) pin a temporary strip of wood along the top front of the skin in order to ensure that the skin stays down against all ribs & flat in between them. The cellotape (or similar) acts as a release layer to make sure the temporary strip can be easily removed again once the glue has dried. (surplus glue may seep upwards through the front joint line & grab the temporary strip!)

Hopefully all is now clear.
Peter
User avatar
Steve Naidamast
Posts: 22
Joined: 25 Jun 2021, 17:51
Location: New York, USA

Re: SF33 1/6 scale

Post by Steve Naidamast »

Peter...

Thank you for your explanations. It is all clear now.

I am being quite careful with my gluing. For example, I have only placed glue on the front of the wing-rib face currently dry only about half way up the rib-face. This way, no glue seepage will occur at the top of rib where the skinning is supposed to lay.

To strengthen the fronts of the wing ribs I am planning on adding triangular strengtheners to each side of the rib front, whereby the strengtheners will be glued to the back of the Leading Edge and to the sides of the rib fronts.

The strengtheners are approximately 1/4 inch on its triangular sides.

Steve
User avatar
Peter Balcombe
Posts: 1399
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: SF33 1/6 scale

Post by Peter Balcombe »

Steve,
I had assumed that your false LE is butt jointed to the rear of your LE & that you would be fitting/glueing your skin hard up against the straight rear face of the LE in order to get a good bond to ribs, False LE & LE.
Thus glue needs to be in the area of the skin/LE joint & my experience is “ if it can happen, then sure as eggs it will at some point” ;)
Peter
User avatar
Steve Naidamast
Posts: 22
Joined: 25 Jun 2021, 17:51
Location: New York, USA

Re: SF33 1/6 scale

Post by Steve Naidamast »

Peter...

I have been writing my own documentation on my progress with the my build of the SF33.

I have just completed the third document in this series. They are all titled with document numbers. In this case, documents 1 through 3.

I thought you would be interested in reviewing them so I have attached them with this note.

Steve
The Schriebe SF33 Motor Glider - Build Document 2.pdf
(414.82 KiB) Downloaded 100 times
User avatar
Peter Balcombe
Posts: 1399
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: SF33 1/6 scale

Post by Peter Balcombe »

Hi Steve,
I’ve just read the 1st episode so far, but seem very thorough.

A couple of comments, some of which you are probably already aware, but I mention them just in case …

Although the SF33 was designed & hand drawn by Cliff Charlesworth many years ago, Cliff Charlesworth died at least 5 years ago. Laser Cut Sailplanes is run by Cliff Evans. The text indicates that Cliff Charlesworth/Cliff Evans & LCS are all the same person.

As you mention, the plan doesn’t quite tie up with the laser cut parts in some areas. This due to a number of factors: 1. The accuracy of the original hand drawn design;
2. Variations in the original paper plan copy scanned for digitising.
3. Part cutting accuracy
4.The variations in the printed plan due to paper moisture content (particularly when printed)

Part cutting accuracy will be within a ‘thou’ or so of the CAD drawing , although they do tend to have a cut edge roughness which can prevent sliding fits (particularly on the harder ply part). As you say, this can be solved by a quick rub with sandpaper.
Most errors are largely due to the original plan & printed paper moisture content between original printing & use.

In general, where laser cut parts do not form a fully interlocked structure, I go by the printed plan as you have done (no matter if it is slightly out or not). I find that even with fully CAD designed & large fully interlocking structures (where the assembly is totally driven by the cut parts) there are still significant difference against some printed plans ((say 10mm in 2 metres!). However, note that we are still talking about <1% variation.

With regards to construction, it is much easier to make up your wing structure using just the LE backing as you call it, rather than making a composite structure with the main LE. The LE is generally only fitted once the wing has been skinned top & bottom.
I would recommend the use of Aliphatic glue for general wood bonding as this dries hard, but is very sandable, whereas epoxy is too hard & you will probably end up taking off more surrounding balsa than you intend whilst trying to get any surplus cured epoxy sanded back. I only use 30 minute epoxy for high stress areas such as wing joiner attachment to man spars.

Finally, I tend to buy balsa sheet (4” wide generally) & cut strips as required - thus for the LE backing & LE it is a simple matter to cut a tapered width strip. You will need sheet material for the fuselage sheeting anyway.

At the end of the day, each builder has his own preferences, so the above is certainly not the only way to do it.
It’s what works for you that is the important thing.

Hope these comments are useful.
Peter
User avatar
Steve Naidamast
Posts: 22
Joined: 25 Jun 2021, 17:51
Location: New York, USA

Re: SF33 1/6 scale

Post by Steve Naidamast »

Hi Peter...

Thank you very much for your review. Your notes are very much appreciated.

Since you encapsulated your thoughts so well, I will incorporate them as a Preface by Britain's Senior Builder in the first document. This way, your thoughts will be included as is and a builder who reads my documents will be able to make a choice as to how he or she will proceed.

However, these documents, as you are aware, are my own experiences to date with this project. As a result, I try to detail my own mistakes as well, while providing corrections. This is specifically oriented towards the construction of the Leading-Edge, whereby my mistake was calculating the height incorrectly. I believe I state that in the second document. If not, I will review it again and include this information.

I have also discussed how to correct sanding gaps to the wing-ribs rear-ends if too much sanding is done, leaving a gap between a rib's rear-end and the Trailing Edge.

As to the bottom of the Leading-Edge, there appears to be little room for adding skinning, even though the wing ribs do arc up slightly against the back of the it. These rib upward arcs do not appear to be enough in order to comfortably add skinning Balsa. As a result, an additional strip of Balsa would have to be added and then sanded down to allow for this. I believe this would happen no matter what measurements would have been used with the height of the Leading-Edge.

Again, thank you for taking the time to read my writing...

Steve
User avatar
Steve Naidamast
Posts: 22
Joined: 25 Jun 2021, 17:51
Location: New York, USA

Re: SF33 1/6 scale

Post by Steve Naidamast »

Hi Peter...

I am down to the last 4 wing-ribs that need gluing. These are rib #s 1-4.

My question is that given the requirement to angle the the wing root-rib (rib #1) at an inward angle of approximately 16 degrees to acommodate for the aircraft's wing dihedral, is this inward angling done for both wing root-ribs or just one.

The plans do not make this very clear, in that the requirement is only shown against the left wing.

Thank you...

Steve
User avatar
Peter Balcombe
Posts: 1399
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: SF33 1/6 scale

Post by Peter Balcombe »

Steve,
Plans often show one wing only (usually Right wing) & you have to reverse print or trace onto the rear of the plan for the other side.
However, as the wings fit onto the fuselage sides on the SF33 (and as is usually the case), you have to make the 2nd wing a mirror image of the first, so yes repeat everything for the other wing, remembering that things are ‘handed’.
Thus for instance, you will find that aileron servos are usually mounted with horns both either on root or tip side, joiners on the root side etc.

I think the ‘dihedral’ you are referring to (if 16 degrees) is actually an angle in plan view at the root due to the fuselage width taper. This is just to make sure the wing roots are flush along the chord with the single piece main wing joiner. The wing dihedral (span-wise angle of the wing relative to the horizontal plane when seen from the front) should only be 2-3 degrees or so, to provide some lateral stability, but still allow the ailerons to provide adequate roll control.
The root rib is slightly angled in the vertical plane to ensure it sits flush with the fuselage given the small wing dihedral. (So the root rib may be angled in both plan view and vertical plane to sit flush with the fuselage)

Note that a trick to remember if you end up with a gap between wing root rib & fuselage, is to make a slightly oversize root rib for each side. Assemble each wing with this extra rib between wing & fuselage & glue it to the wing whilst the fuselage side is flush with the fuselage - leaving a small angled gap between wing & extra rib (ensuring no glue gets to the joiners or fuselage side of the extra rib). When the glue is dry, remove the wing & fill the gap between the original root rib & the extra rib before sanding back flush with the wing surface. The wing should now fit perfectly with no gaps.
Peter
Post Reply