Data for standard Trinitus 108 grams glass:

How to trim a Trinitus (Danish / English) - description of settings, movements with a bit of theory and pictures.

Henrik Nielsen has taken pictures of his way of assembling his Trinitus - 1 - 2 - 3. Be aware that part of the work he has done is due to that fact that his version was a special one, where he had to trim the trailing edge, cut the rudders free, hinge them and make the vipers.

Trinitus design - the history of the model

In the autumn of 1997 we seven pilots in Denmark decided to build what we thought would be the best all round glider so far. We intended to use it for ordinary thermal flying and for competition in F3B- and F3J-contests. We had many ideas and opinions about span, aspect ratio, area, wing forms and airfoils but after serious thoughts, sketches and calculations together with a few grips in the aerodynamic darkness we agreed on the shown model.  

But how did we get to this??

This piece is of course about our model, but I have tried to generalize, so our method of approach can be used on your new designs as well.

 What does an all round glider need?

  1.    It needs a low sinking speed, to give you a long flight if you happen to not find a thermal./ termik. Low sinking speed also gives you longer time to find that thermal.

  2.    It needs to be able to fly fast, so flying isn’t restricted to 3 Wednesdays a year (this is also the case in other countries than UK!) . Since we are also aiming at F3B we want it to fly very fast

  3.    It needs a flat glide, to give you a greater searching area

  4.    It needs a high maximum lift ability, to give you a good launch. Good launch height gives you  more time to find a thermal.

  How do we obtain these 4 qualities?

  ad. 1.    Low sinking speed is obtained by using an airfoil with what is called high Cl-max (equals high lifting ability), generally speaking this means an airfoil with a great camber combined with a light plane. You also need a wing with a high aspect ratio so the induced drag is minimized (i.e. a narrow wing). Unfortunately you also need a broad wing to prevent the Reynolds numbers from getting too small when flying slowly.
Cl means lift coefficient.

ad. 2.    Great speed is obtained  by using an airfoil with as little drag as possible when it is almost not lifting. Thin symmetrical airfoils has little drag when not lifting at all. Low drag is also obtained with a broad wing because the Reynolds number increases. Because we wanted to fly F3B we do unfortunately have to turn 3 times, so our wing does also need to be able to lift the plane around those three times. The lifting ability is made the same way as above - high aspect ratio. And a heavy plane adds to the speed.

ad. 3.    A flat glide is obtained by using an airfoil with least drag when lifting a little (Cl about 0,1-0,3). Drag can also be minimized with a great aspect ratio which minimizes the induced drag, but since the Cl when gliding is not very great, the induced drag is also small. This makes the whole thing very fluffy!

ad. 4.    To get a good launch you need an airfoil with a high lifting ability - look at #1  

The airfoil in the wing is the first thing to decide upon and the airfoil we are looking for needs to have:

ad. 1.    Great camber

ad. 2.    Very little camber  

ad. 3.    Small camber  

ad. 4.    Great camber

  At the same time we need:

A.  A light plane

B.   A heavy plane

  As you can see the 4 (6) demands a not very easy to get at the same time - this yields for a compromise. The only way we can get close to the first 4 is by using flaps and flapperons. This way we can modify the airfoils camber during flight - hey, this is a great idea - has anyone thought of this before?? J!!

The worse you are at finding lift, the more you need #1. The better you are at detecting thermals the higher priority you can give #2 and #3. Flaps can give you #4 with any airfoil.

If you build light and then make room for ballast you have both A and B.

The airfoil

After all these thoughts we began our search for the perfect airfoil. The only one we found suited to our demands was the HQW 2/8, which Helmut Quabeck made for his F3B-plane “Master Piece”. This airfoil is a bit on the fast side but we think highly of our thermal searching skills - and we use flapperons!

Helmut has previously designed airfoils. Back in ´81 came his first airfoils - the HQ-series. In ´83 he came 2’nd at the F3B WC in York with one of the now older airfoils  HQ 1,5/9 (this is still a good airfoil). The new sections are presented in his book from ´94:“Design, leistung und dynamik von Segelflugmodellen” - it’s a great book (and in German).

The size and plan form

F3B planes normally had a span of about 2,7-3,0 but the trend in ´97 said that a span of  3,1-3,2 meters was maybe better. In F3J the best planes used to be about 3,3-3,6 meters,  but to get better all round (= rough wetter) performance the span was generally decreasing to about 3.2-3,4 meters.  With this in mind we settled for 3,2 meters equals 126”.

To get a flat gliding angle even at low speeds we needed a high aspect ratio, but without the tip chord being so narrow that tip stall would be the order of the day. Too high aspect ratio gives a thin wing that needs lots of carbon to be strong enough . We decided on an AR of 16:1, which gave us an area of 64 sqdm.

To make the airfoil as precisely as possible and to make it easier to make identically planes we wanted to make a mould. Making it by hand takes a lot of work and is not as precisely as when milling it  - what did we do? We wanted the best all round glider so far so did we have any choice? We got the positives milled. This way we could also make a plan form with curves in every direction we wanted.

Now it was time to hit the drawing board.

In ´94 Martin Hepperle (the airfoil designer who made MH 32 etc.) was thinking about the air moving around the tip of a wing. When he was through thinking, he told about his thoughts in Ösnabrück, and Stefan Siemens wrote about Martins thoughts together with Horst Torunski in the German magazine ”Flug- und Modelltechnik” 1+3/97. They found that at the outermost 10% of the wing you shouldn’t worry about the critical Reynolds number. Among other things, this is the reason for all the tip lets you see on gliders today. They do also increase the stability when circling in lift. This knowledge, my fiddling with an ordinary elliptical wing form and thoughts about swept back tips, gave us the resulting Trinitus wing plan form.

This is the raw positive wing, milled in southern Germany

This is the top of the positive wing mould - it shines!

The rest

The fuselage is made with one eye and two hands on the plug and the second eye on a V-Ultra plus fuselage. It’s not a copy - we made it from wood and by hand, but they are very close, though ours is a little longer and not slimmed behind the wing. For ballast we did use one single tube with a diameter of 27mm and a length of 330mm. There was is room for an obscene amount of lead. Today I use a smaller tube with room for about 550-600 grams. The V-tail is modified from an Europhia-V-tail mould John had in his workshop. Today I'm in the process of making a new cross tail to add to the existing fuselage.