T31M build log

[Peter Miller]

Most gliders do, some don't.  But then most gliders are mid wing, the T-31 has a parasol wing which is very high up.This gives a degree of pendulum stability.

 

I always recommend reading Kermode's "Flight Without Formulae"  A very simple book on flight written in the 30s and so good that it is still being published today.  This gives one an understanding of various aspects of how and aircraft flies.

[GrumpyGnome]

Just to complicate things, some gliders look to be without dihedral when on the ground, but exhibit a marked dihedral in the air due to the wings flexing - in this case, I'd aim to emulate the amount of dihedral when the aircraft is airborne.

[Basil]

21 hours ago, Peter Miller said:

Most gliders do, some don't.  But then most gliders are mid wing, the T-31 has a parasol wing which is very high up.This gives a degree of pendulum stability.

 

I always recommend reading Kermode's "Flight Without Formulae"  A very simple book on flight written in the 30s and so good that it is still being published today.  This gives one an understanding of various aspects of how and aircraft flies.

Peter , I have a copy, bought at your suggestion some long time ago. The subject of 'Dihedral' is not listed as a heading. Just a long shot you might know where it may have been covered?.( From memory only).

I have found some drawings of the T31 and there looks like there is a little, little being the operative word.

Thank you all for your input.

Bas

[Basil]

Peter , I have looked up the subject of 'Dihedral' and its effect, on the net quicker than the book. I understand a bit more now. Thanks

Bas

[Peter Miller]

Basically dihedral only works when and aircraft is side slipping. It creates a corrective force.  In fact sweep bac also has the same effect but you need more sweep back.

 

if you saw the article on my Insanity it was a classic example of how sweep back and dihedral only affect the stability when the aircraft is side slipping.  No one would believe that model would fly but it flew exactly like my normal aerobatic designs.

[Basil]

On 30/12/2021 at 13:27, Stephen Belshaw said:

Now moving on to the wings.

 

Peter suggests laying down the lower cap strips and sheeting, then bonding the spars to them, followed by the ribs and then the trailing edge and so on. I've never built a wing this way before, it seems the TE is notched to accept the ribs but the ribs are shaped to a fine point and would be the wrong angle as they flow in to the TE. Unless I'm misinterpreting something, perhaps Peter could shed some light on this for me?

Hi, I am quoting Stephen on this, but it is aimed at anybody that can help me here. I cant find any pics of the detail. I am rather confused, I understand from this that there is no upper & lower cap strips on the TE.The tails of the ribs are just let in to the TE. As a fairly new comer this does not seem to have much contact area in order to be of strength. I am also confused with the proccess of laying down everything then the ribs, as the area of the LE under the spar is curved.

Bas

 

[Peter Miller]

 Re the curved under surface of the front of the ribs.  You lay the leading edge sheet down flat. put the ribs on. Add the 1/8" leading edge sheet flush with the bottom of the ribs and then raised the lower LE sheet up and glue to the LE and ribs.

The cut away drawing shows that the wing has lower cap strips for the wing and also top cap strips.

 

 

 

 

[Basil]

Thank you, to the man himself.

Bas

[Peter Miller]

Always glad to help!

[kc]

Basil,

My understanding of what Peter said is that the lower LE sheeting is put down first and THE CAPSTRIPS ONLY START BEHIND the LE sheet. (probably  the capstrips do not go UNDER the LE sheet despite what the sketch seems to show?)

When Peter refers to " Add the 1/8" leading edge sheet flush with the bottom of the ribs "   he is referring to the vertical LE  ( sub LE behind the shaped LE  ) and I expect the ACTUAL leading edge sheeting is only about 1/16 to enable it to be bent up later.       

[kc]

Basil,

I have not built a T31 but I built a Peter Miller Swamp Rat which used a very similar wing building method which worked very well.  Thats why I explained the method.  Just follow the instructions Peter gives!      I used a spare length of tapered TE balsa as a wedge  to prop up the LE sheeting while the glue dried.

 

I slightly chamfered /curved the 1/8 vertical sub LE on it's lower edge so the lower sheeting would fit OVER it.    THe upper surface of the vertical sub LE was trimmed (sanded/planed)  later and the top LE sheeting also went OVER it.   Makes a strong joint.   Very easy method.

[Peter Miller]

KC has got it right. It is my standard wing building system and has been for a good few years now. It works so well.

 

The lower LE sheet is under the bottom spar. the cap strips butt up against the bottom spar.  

If you look at some of my other builds you should find sets of pictures that show this well.

[Basil]

Thank you both. For some one like me it is difficult to picture the whole in your mind before attempting the real thing. So many things have to be correct for it to work.

Bas

[Peter Miller]

As I say. Look at other pictures in my various builds. A picture is worth a thousands words is so very true.

[kc]

Basil,

Stephen Belshaw's photos of 3rd Jan and 6th Jan 2022  shows this aspect of the wing build clearly.

 

Also he shows how to notch the TE using 3 ( midget? ) hacksaw blades taped together.  Note that midget blades can have the pins pressed out easily if you want to have them for this sort of use.  ( tap them with a hammer over the vice open jaws )  2 normal hacksaw blades fine or rather used ones gave the correct width for my model.    Personally I would have put the TE ( already notched ) on at first stage and use the notches to space the ribs.

[Basil]

On 26/01/2022 at 17:47, Stephen Belshaw said:

Wing retaining "click" fixings installed, female part bonded in and the male half threaded in to suit with the amount protruding varying the tension:

 

 

 

They come with a wedge for prising them apart which will preclude the need for tugging on the more delicate parts of the wing:

 

Stephen, can you tell me if the correct fitting depth of male in female means the male is pushed through until in ratchets on the rear of the female or just pushed in to catch on the annullar ring on the inside of the female. If the latter I suspect that the rings will soon wear down to an  almost smooth surface.   I look forward to hearing your views.

Bas

[Stephen Belshaw]

Basil, these images from Topmodel probably explain it better than I can:

 

 

[Basil]

1 hour ago, Stephen Belshaw said:

Basil, these images from Topmodel probably explain it better than I can:

 

 

Thanks Stephen, that does explain it well. The instructions in the pack are not so good. Thank you for your help of late.

Bas

[Stephen Belshaw]

Agreed Basil, the included instructions are somewhat vague. I have just fitted a pair to another model (Topmodel Element) which has a lightweight open structure so not much to get a purchase on when trying to push the wing panels together. I made it easier by lubricating them with some vaseline, they still hold well when locked in place.

[Basil]

Stephen , like the idea of the lubrication.

Bas

[Basil]

On 24/01/2022 at 12:57, Stephen Belshaw said:

A little bit of work on the cowl, I had already printed the dummy engine halves (VW air cooled boxer) and was wracking my brain as to how I could complete the exhaust system using only bits I could find knocking about the workshop. In the end a combination of brass tubing, piano wire, electrical cable, balsa and a yoghurt pot did the trick and gives a reasonable (I think) representation of the prototype.

 

First job was to cut out the area around the engine and fix some balsa on the inner face to give me something to glue to:

 

 

 

I fabricated the exhaust by soldering the brass tube parts in a simple jig:

 

 

 

The basic components:

 

 

 

A bit of painting .......................

 

 

 

.............. gives me something that looks like this:

 

 

Stephen, I am trying to fit spoilers/air brakes to this T31m. Worked out a system using wire /axle type hinges. Fixed once attached, before covering. Scrolled down and saw yours finished but loose. How do you manage to do this please. Do you re-fix the hinge after covering?. If so how please.

Cant get my head around it. the linkage was difficult enough.( first picture of this group). Mnay thanks.

Bas

[Stephen Belshaw]

Basil, I fabricated the brake "blades" by laminating balsa/ply/balsa with a cut-out in the ply to accept the nylon hinge, you can see on my photos the knuckle of the hinge visible. It needed a lot of dry fitting and fettling to get the clearances required for smooth operation. The underside of the cut-out in the wing was reinforced with 1/8" balsa strip which also allowed me to cut a slot to accept the hinge. I then covered the brakes before glueing them in position, I have to say that it was a lot of faff but I wanted them as extra security due to the tight landing area of what was then my usual flying field.

[Basil]

17 hours ago, Stephen Belshaw said:

Basil, I fabricated the brake "blades" by laminating balsa/ply/balsa with a cut-out in the ply to accept the nylon hinge, you can see on my photos the knuckle of the hinge visible. It needed a lot of dry fitting and fettling to get the clearances required for smooth operation. The underside of the cut-out in the wing was reinforced with 1/8" balsa strip which also allowed me to cut a slot to accept the hinge. I then covered the brakes before glueing them in position, I have to say that it was a lot of faff but I wanted them as extra security due to the tight landing area of what was then my usual flying field.

Many thanks.

Bas