Announcement

Collapse
No announcement yet.

Classic Motor Glider from Scratch

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Classic Motor Glider from Scratch

    I cannot let this theme "Flyomtaler, tester & byggeblog Seilfly" remain unused any longer, thus I plan over the next few months to describe a new project to research, design and build a known amateur conversion of a classic two seater glider into a motor glider at one quarter scale.

    I have long wanted to attempt to set my 54 years experience of building model aeroplanes in the traditional way on paper and what better subject than the glider which I first trained and flew solo on at 14 years old with the Air Training Corps/Royal Air Force in Northern Ireland - Slingsby's T31B Tandem Tutor. Large numbers of the type became surplus to requirements during recent years and some of them have been acquired by amateur builders for conversion into an economic motor glider designated T31M.

    I hope in this process to highlight the history of the type, to describe the research process for documenting and designing a presentable true scale model, and further to report on the drafting and building process including all the tips and building methods that one learns over the years. I make no bones in expressing my personal dislike of the ARF direction that our hobby has taken in recent years although I use them myself for convenience - they have their place but cannot fill the pleasure of seeing your own creation in the air.

    Quarter scale is choosen since a number of members at Røyken and Hurum choose this scale to form an embroyo interest group for building and flying classic gliders (pre-glass) and Golden Age light aeroplanes (glider tugs) in a relaxed and gentlemanly manner for the shear pleasure of it.

    Quarter scale has been choosen as a size which still requires only limited investment in gagetry in comparison with the very large sailplanes of the IGG for example (although they are enormous fun also). Building in quarter scale also uses material dimensions that can still be easily handled by old farts like me (the fingers and eyesight are not as supple as they used to be). Thirdly, larger models always in general fly better and more sedately than the smaller models.

    My only reservation is that because of my medical history I am forced to write these words in the english language although most of you out there know that I have very little problem to read and speak norwegian. I hope you all will forgive me this necessity (it would be worse if I used the celtic) and feel free to converse in your native language.

    If I can in this way increase the interest, particularly among the younger enthusiast, to build model aeroplanes in the traditional way I will be a very happy chapie.

    Pictures

    1. T31M Conversion
    2. T31B in ATC Service
    Attached Files
    Last edited by Celtic-Griffin; 13-03-07, 23:02.
    Ken Bates
    Never Mind the Label

  • #2
    Thanks for your interest Pål.

    On the question of build time and cost my honest answer would be I have no idea - this being a hobby for relaxation and pleasure I have never timed any of my past projects and in my situation fortunately time is no object - I will however on this project keep a log and regularly report times and material useages for each stage. I am also fortunate in having built up quite a store of basic materials over the years, however by logging material useage it will be possible to build up a costing stage by stage considering current material prices.
    Ken Bates
    Never Mind the Label

    Comment


    • #3
      Har shortkitene av Slingsbyene fra TM kommet?

      Det er for tiden to andre i klubben min som bygger hver sin Hall Cherokee fra TM shortkit, og jeg selv har bestilt et short-kit av nettopp Tutoren. Ble noe ventetid, men sånn er det vel når man skal ha saker som akkurat er i ferd med å gå i produksjon...
      Absolutt ikke NLF-medlem lenger!

      Comment


      • #4
        Dette blir veldig morsomt å følge med på Ken.

        Håper på mange og detaljerte innlegg så vi ferskingene kan lære masse om scratchbygging.

        En dag, når ungene har flytta ut tenker jeg, skal jeg også vie en mye større del av livet mitt til byggeprosjekter. Slik det er nå har en knapt nok tid til å fly desverre
        Mvh
        Torbjørn Gustafson
        www.trmfk.no



        Will fly for food

        Comment


        • #5
          detta så spenende ut ken! gleder meg til og se og lese mer om dette
          Robert
          Hole El-Flyforening

          Comment


          • #6
            Researching the Project

            Well, one week has now elapsed and the time available has been usefully used to establish the necessary documentation for the project.

            For any scale project the first requirement is for a good three view and this will be required if the finished model is to be eventually entered in competition. Fortunately for this project an excellent three view is to be found together with a detailed history of Type 31 in Martin Simons book "Slingsby Sailplanes - A Comprehensive History of all designs" - a book which is a must for all who are interested in the development of gliding in Britain.

            A little bit of background:

            Slingsby's Type 31 Tandem Tutor prototype, designated T31A, first flew in 1949 as a two place development of the single seat T8 Tutor and the design was also influenced by the primary Hols der Teufel. The glider used the same wings as the Tutor and basically was the same aeroplane with the extra seat and additional bracing introduced. I won't say too much about the T 8 Tutor since Joo is waiting for a part kit for this glider from Tom Martin (TMRC) - by the way JOO Tom has delayed delivery to carry out improvements on the kit worth waiting for - I am sure JOO will describe the building of the kit on this forum. The prototype had no aids for approach control, however spoilers were added on the production version designated T31B. The new glider was welcomed by the clubs as a major advance on the single seat ab-initio training which was in vogue at the time. Success was assured when the Royal Air Force accepted the type for the air cadets, 131 were taken on strength under the name Kirby Cadet T.X.Mk.III. The type was used by the RAF from 1950 until the mid 1980s and it is interesting to note that one particular example made over 120,000 flights totalling about 6,000 hours. Browsing my old log book I see that I flew seventeen winch launches of between 3 and 4 minutes before being sent solo (one left and two righthand circuits) to gain my A and B certificates (bet if I was a very proud 14 year old when I came home that evening and bored the pants of my school chums the following week) - my how things have changed - I then went on to become an instructor on the type.
            At the end of service with the RAF, a large number of T31B's were offered on "The Great Sale" at a very reasonable unit price to private clubs and owners and as we now know considerable numbers have been restored by vintage glider enthuiasts and for conversion to T31Ms with the installation of Volkswagen 1600 engines.

            But back to the project:

            The choice of which T31b my model should represent was difficult, but the choice has fallen on G-BZLK pictured below. An article describing this conversion appeared in Popular Flying Association magazine very recently and can be read here:

            http://www.pfa.org.uk/PF/2007/Mar%2007/Rich.pdf

            To design a scale model perhaps the most important aspect is to design the airframe structure such that it will tolerate the flight loads which are to be expected at the same time keeping the weight as low as possible - in this respect I am going to cheat just a little and have acquired a drawing of another T31M model issued by one of the model magazines too a smaller scale but drawn by a reputable designer. This is for another prototype G-BOOD also pictured below. Why don't you simply scale it up you might ask - the answer to that is that if you scale up dimensions the end result is an over-engineered and unnecessarily heavy model.

            The other aspect is to establish detail, wing to fuselage mounting, tail mounting, strut mounting, hinges, instrument panels and all the other small details which together make an acceptable scale project. Here I have been lucky in that I have found on the web a detail package of a T31B restoration done in Holland by Jan Forster and christened "Chris Wills" and prepared by a french modeller for a scale model of this particular aeroplane. Chris Wills is the founder and honorary chairman of the VGC - Vintage Gliding Club and the son of the well known ornithologist and gliding pioneer, Philip Wills. I have included some pictures of this T31b as the clear doped fabric shows the underlying structure particularly well and highlights its wooden structure suitable for modelling.

            Well that will do for this week, during the next week I hope to begin drafting and building the model and if all goes well will be back with you all next Sunday - meanwhile the perspective drawing below I think shows the beautiful if very angular charm of the Type 31, meanwhile.....
            Attached Files
            Last edited by Celtic-Griffin; 18-03-07, 17:07.
            Ken Bates
            Never Mind the Label

            Comment


            • #7
              Making a Start

              Any time available this last week has been used to get a build start. Since they will be required in order to rig the fuselage correctly under construction I always prefer to build the wings and tailplane first. In this instance a start has been made on the tailplane. The tailplane on the T31M is a very simple design consisting entirely of straight lines and angles without a curved section. Considering this and the fact that this model is to be a one off we can drop the need for a detailed drawing and draw the parts directly on the balsa using a sharp 4B pencil. This is possible because I prefer "balsa core" type of construction and so start by cutting the plan view of the tailplane and elevator halves from 1/16" balsa sheet - as I said the structure can be drawn directly on either side of this central core.

              Choice of Balsa

              Balsa is a natural material which comes in different densities and grains so it is important to choose the best balsa for the job in hand.

              Firstly density is particularly important for use at the tail of any scale model to avoid the eventual need for balast in the nose . A simple rule is to remember that the maximum weight of balsa for tailplane construction should be 10.5 grams for a standard 30" x 3" x 1/16" balsa sheet, so with a gram scale it is possible to grade your material stock.

              The second criterion for tailplane build is that the balsa should be straight grained and not cross grained. Straight grained balsa has longitudinal even grains and is of a pale colour whilst cross grained balsa has a mottled appearance of short irregular grains and generally of a deeper colour. Cross grained stock can be set aside for ribs and bulkheads etc.

              So having made a start on the tailplane I will proceed to draw the tailplane components unto the 1/16" central core and construct the strip balsa structure on either side of this central core. I will photograph each stage and introduce the pictures next time.

              See you next Sunday.....
              Ken Bates
              Never Mind the Label

              Comment


              • #8
                Hello everybody,

                First off, I'm sorry but I am an English only speaker and not even an aero-modeller! However, I am the builder and owner of Slingsby T31m G-BZLK, so I registered in order to post this. I happened upon this thread when searching google. I typed in "Cadet 3 motor glider" and this page came up ... (well you have to do something when the airstrip is waterlogged and you haven't flown for a while!)

                Ken,

                I must say I'm flattered that you have chosen my aeroplane to replicate and if I can help in any way let me know. I can provide any pictures or dimensions you'd like and possibly even a photocopy of the drawings? You mentioned the cockpit so here's a picture for your information.

                http://www.ivan.pfanet.co.uk/cadet3.jpg

                http://www.ivan.pfanet.co.uk/instr1.jpg


                Feel free to email me ivan@pfanet.co.uk for any help.

                Good luck with the model, I'll be very interested to see how it turns out

                Ivan
                Last edited by ivanmanley; 25-03-07, 14:56.

                Comment


                • #9
                  Here is another perfect example of cooperation and cameraderie among amateur aviation buffs.

                  For a scale modeller, direct contact with the owner of his prototype is of some considerable importance as the search for perfection continues. I wish (as I am sure others of you do) to welcome Ivan to our forum and hope he will continue as time permits to contribute to my project and perhaps some anecdotes from G-BZLK flying during this coming season.

                  I know that his further participation will significantly enhance this thread.....WELCOME IVAN & WELCOME G-BZLK.....
                  Ken Bates
                  Never Mind the Label

                  Comment


                  • #10
                    Thanks for the warm welcome,

                    I recieved your email Ken and will respond shortly (my email server is playing up "I can recieve but not send")

                    My strip has finally dried enough to fly from, and as today was glorious, I dragged "LK" from the hangar and gave her a very thorough check over as she hasn't flown for some time. I started the engine and let it warm through whilst generally going over the airframe for winter damage rust ect. I then had to go back to work for a few hours but rushed back once finished. Engine restarted, I clambered in and carefully taxied over the bumpy ground to the end of the strip. Temperature and pressure ok, a last full and free check and away! The T31m is a great STOL aeroplane and is off and climbing within 100 metres. This flight was just to get back into the swing of things, so after a bit of gentle handleing I climb a little bit to do some stalls ... stalls? She just mushes and flutters around with the airspeed so slow it won't even register! To get any sort of a break I had to leave about 2200 rpm on and sharply pull back on the stick. The air was so still I was happy to fly around at 35 knots over the coastline at 200 metres high. Sitting in the well protected but open cockpit at that speed and height is like sitting in an armchair watching the world slowly drifting past below and isn't the slightest bit cold or uncomfortable. If you open the throttle she will fly at 65knots, but that's very blustery and whilst it helps get you about, it isn't nice. A good comprimise is 50-55 knots and that is the speed I tend to fly most of the time if going anywhere. Although not fast, it's a pleasure, so why worry about getting there quickly?

                    I'd promised to just be an hour as dinner was in the oven, so I thought five minutes last play were in order A couple of chandelles and then the T31's party piece in my book ... the Stuka like dive! With the throttle shut and the prop disk providing drag, plus airbrakes (actually spoilers) the nose can be pointed VERY downhill until the speed reaches a dizzy 75 knots! It feels really impressive and certainly gets the ears popping! I flutter around the kind of circuit to land, again very slowly due to the stillness of the evening with just 2000 rpm on (remember, a VW is higher revving than most four stroke aero engines, so 2000rpm is virtually ticking over). Chop the throttle and glide in using the airbrake to adjust descent for a perfectly smooth touch down which is another of the T31's attributes. It's a very flattering aeroplane to land with it's low wing loading, so I just pretend to be good.

                    If anyone (and there are plenty!) has ever flown a T31 glider, I can tell you that as a motor glider ... the old brick has found it's ideal retirement. Instead of endless two minute circuits, she has suddenly broken free to live out retirement disgracefully ... so now she sits in the hangar at the end of each flight with a smug grin knowing she has made her pilots day!

                    Ivan
                    Last edited by ivanmanley; 28-03-07, 01:46.

                    Comment


                    • #11
                      I seem to be good at killing the conversation?

                      Ivan

                      Comment


                      • #12
                        Not in the least Ivan - Norway closes down for one week up to Easter and this one has been a 'B' with extreme weather - we all wake up again on Tuesday next.....

                        Meanwhile I have been doing a little on the project and will be back very soon with some pics.
                        Ken Bates
                        Never Mind the Label

                        Comment


                        • #13
                          Now that Easter is over its again time to build some more on the T31M project - work on the tailplane is progressing and I have now taken some pictures for my next build report - HOWEVER I HAVE HIT A SNAG.
                          My pictures range from about 570 KB bytes to 620 KB bytes in JPEG format whilst the forum limit for downloads is 146.5 KB bytes - being relatively computer illiterate I'm stuck SO THIS IS A CRY FOR HELP FROM ALL YOU PC BUFFS OUT THERE, WHAT DO I DO?
                          Ken Bates
                          Never Mind the Label

                          Comment


                          • #14
                            Originally posted by Celtic-Griffin
                            Now that Easter is over its again time to build some more on the T31M project - work on the tailplane is progressing and I have now taken some pictures for my next build report - HOWEVER I HAVE HIT A SNAG.
                            My pictures range from about 570 KB bytes to 620 KB bytes in JPEG format whilst the forum limit for downloads is 146.5 KB bytes - being relatively computer illiterate I'm stuck SO THIS IS A CRY FOR HELP FROM ALL YOU PC BUFFS OUT THERE, WHAT DO I DO?
                            Hi Ken

                            You click on this link
                            http://download.microsoft.com/downlo...ertoySetup.exe

                            and choose "run" in the box that pops up, and the program will download.
                            You then click "run" again to start the install. You then go through the wizard.

                            When installed the program lets you right-click any image in windows explorer (file browser) and then choose "resize pictures". You can then choose between small, medium and large. In most cases small will do just fine for pictures to post on the forum.

                            Good luck, and be shure to let med know ( PM, mail, anything) if you can't get it to work for You
                            Mvh
                            Torbjørn Gustafson
                            www.trmfk.no



                            Will fly for food

                            Comment


                            • #15
                              Thanks for the replies. As for the language problems ... I'm ashamed to say that I'm typically English and very poor at speaking or indeed reading ANY other language.

                              I took G-BZLK to the first fly-ins of the year on Easter Sunday. The first was at the Dorset airfield of Henstridge and the second at the ever popular Popham airfield in Hampshire. The route to Henstridge was over the Solent (entrance to Portsmouth harbour) to Cowes on the Isle of Wight then back across to Stoney Cross in the New Forest and on to Henstridge. It took one hour and fifteen minutes and was very bumpy over the New Forest. The fly-in itself was very interesting with such aircraft as two SE5a replicas, a Focke Wulf 190 replica and various Austers, Cubs, Pitts ect



                              www.ivan.pfanet.co.uk/fw190.jpeg

                              www.ivan.pfanet.co.uk/henstridge.jpeg

                              The second leg to Popham took one hour and the home trip 45 minutes. It was a great day out even if the viz was very hazy! It was the first decent test of fuel consumption, which worked out at around 12.5 litres an hour at 55 knots.

                              Ivan
                              Last edited by ivanmanley; 13-04-07, 06:43.

                              Comment

                              Working...
                              X