Slingsby T67 Firefly

[Erfolg]

I recently snapped up a model that was being cleared out by a fellow club memember. At the time what I actually saw was a airframe that looked most viable to both fly and build, that is really finish.

I was told that it was a Slingsby, most probably a T67, but all that passed over my head. i was far to interested in what needed doing. Everything else, I probably just nodded, whilst I was thinking how long to finish, what will I need to buy.

It was only on looking up Slingsby, that I realised what the model should look like. What was apparent was that the canopy is a massive part of the shape and character. I did not have one. Nor did I have any idea of where the kit originated, if I only had listened, unfortunately teaching an old dog new tricks is hard work.

I looked up various sites for plans, then posted a request for any info for whose kit or plan it might be. I even got the span wrong. Fortunately some one got it right, duff info no obstacle Billkits being the origin of the model.

Progress has been slow, partly down to my indecision and not having a plan, nor my own plan of how to progress the model.

I firstly had no idea about the wheel sizes although the torsion bar UC was there, plus no nose leg. Eventually I Emailed Bill, and received a helpful reply.

Then there was the issue of a canopy, which was initially solved by ordering a new canopy, which promptly arrived. By then I also had an older yellowing original canopy.

Then the issue of conversion from IC to electric became an issue.

I was also aware that the model is bigger (in span) than most of my electric sports type models. I have typically used 9g servos for everything. Usually a two servo wing, this is one central.

[Erfolg]

I have now made some progress.

I have created a hatch to load and arm the ESC.

I have installed a nose wheel assembly, which still needs some work

Both servos to the rudder and elevator have been accommodated. The rudder servo being a 9g at the back with a short push rod. The servo is an old Futaba 100.

I ordered two pilots at the same scale. Really, I thought. The smaller figure will used rather than the two intended.

I have installed a Futaba 128 for the torque rod ailerons, which is also completed.

I am waiting now for both the motor and collet spinner to arrive to allow the front end to be worked on.

The main issue is now the cockpit area, as the canopy is to small, although massive. I expect that the plan called for a dashboard type arrangement. So that is what I will now be attempting to do.

As for finishing I will be tissue and doping the fuz, then painting white. I will either film part of the wings white, or find something like Prymol to etch the part to be painted. It is to far to go to a LMS and mail-order is far to expensive in the UK to make this option viable for even a small sized order.

[Erfolg]

Although I had thought that not having a plan was not an issue due to the model being complete, I conclude that having access to one would be useful.

I have reduced the cockpit aperture to some extent, as I suspect that there was an intention to move away from the flat areas to something which suggested a shell type construction around the cockpit area.

I have been busy filling holes where cylinder heads went for a glow engine.

Now that I have constructed a stand of for the electric motor, I am starting to think about how to close the under side of the nose area, as this seems to have been left open for the exhaust silencer and probably access for fuel lines etc.

Unfortunately the marked centre lines onto which the IC motor mount was arranged, does not align with the horizontal centre line of the hole for the motor shaft. I assume that the plan called for a few degrees of up thrust. For the present i have repositioned my stand of with no up and certainly no down thrust, for the time being.

Before closing of the area, by an access hatch I have also created a hole for the 3 cables to the ESC, which will either go across the stand of, or under the Lipo.

Again a drawing of the nose area would have been helpful. It looks like my best course of action is to remove the triangulated balsa pieces at the bottom edge and then replace with sheet material, onto which rails can be fixed, to support the hatch. Looking on the Internet, there does seem to be both air intakes to the carburettor or fuel injection and also a flatish area where a pair of head lights are located.

Perhaps the biggest mystery to me is that it is pretty obvious that the full size uses a air cooled engine, which is of the flat type, as the intakes to the cylinder head are clearly visible. Having looked at literally hundreds of photographs, it is not obvious where the air outlets are, nor the exhaust outlets. It seems that photographers dislike any clear close uppish shots of the underside. This seems pretty typical with the midget air racers also.

[Erfolg]

I have now finished the model as far as being ready for test flying. The detail will wait until it is confirmed that it flies OK. If not well, I am not sure what to do with it.

I did have to change the elevator servo to a smaller one, as it was fouling the aileron servo.

[cymaz]

Very tidy! Not too dissimilar to a Trojan T. 28

[Bob Cotsford]

that looks right Erfolg, I'm sure it will fly well

[Redex]

Hi Erflog,

I know that this is an old thread but can you remember what powertrain was used in the Slingsby., particularly the LiPo. Also can you remember if the wing is flat or does it have an amount of diehedral added. Looks a really interesting model - hope it flew well.

[Erfolg]

Red

Some aspects of the model I did not build, which was the wing. There is dihedral, very little, although Difficult to say beyond minimal.

The motor is a Turnigy D3536/8 running on a 4s Lipo. I cannot get at it very easily it will be as a minimum a 2200, probably a 3200, from what I can see. On a 10*7 prop it draws 27 amps pulling approx 400 watts.

The model is still in flying condition, just not flown due to the weather and now the lock down. As a model it flies extremely well. There is only one issue and that is the very flat glide. With the model clearing the field boundary fence, with no head wind or very little it just lands in bounds, almost running out of strip. Needs flaps or spoilers or something similar.

The kit is from Bobs models, The design is a little different now. Having a FG nose cowl. It is a good model, looks easy to build, I am told it is most excellent value for money.

[Redex]

Just as an update to this thread , I am coming to the end of my Slingsby T67 Firefly electric conversion build and need a bit of information.

Does anyone on the forum know what the CofG should be for this model, the instructions do not state a figure and only refer to an OS .40 and radio gear position placement to achieve the CofG.

Many Thanks.

[Erfolg]

My CG is 80mm back, from where the two wing panels are joined. Hope that helps

The only difference I would make to the model is to install flaps inboard, to increase drag, when landing, as the model floats on like a glider. To much of a big deal to retrofit on my model as it uses torque rods, which would have to be stripped out, then the wing channeled for servo wires and the creation of servo boxes etc.

[Redex]

Thanks Erfolg I will try 80mm.

Alas I think I maybe already to late with flaps as I have already completed the wing. However I have installed a servo in each wing rather than the central servo method, so perhaps a retro fit after a few flights. I have also fitted a steerable nose wheel which seems ok but I used a 4mm nose leg as I think the supplied leg will not be up to the job on a 5lb model, and 3inch wheels for the grass strip.

Now just waiting for the pilot to arrive and complete a full power test - I'll post the figures for those who maybe interested, although it does not seem to be a very popular model kit judging from responses so far.

[kc]

Redex, it would be a good idea to calculate the average wing chord and allow for the sweepback of the LE on your model then calculate the theoretical CG position. Erfolgs model might not be the same kit as yours ( Erfolg mentions both BillKits and Bobs models) or it could have different sweepback of the LE from standard as he didn't build it.

BillKits have a Facebook page so you could ask them what the CG should be. But it should be marked on the plan- if any supplied- if not mentioned in the instructions.

By " retro fit" flaps I presume you would just do this electronically at the TX using different Rx channels for each aileron.

[Erfolg]

KC, I made a mistake in mentioning any other kit other than BillKits. I do know that it is a Billkits as a new canopy was obtained to replace the sad and yellow that the previous builder found.

I do understand that the kit has both improved and changed from my model. In that my models canopy did not fit the cut down (this could have been a build error). Also the front end of my model was built from sheet (as many older designs did) for a IC motor, I understand that that a FG cowl is now supplied.

KC, with respect to Flaps, There are non on my model. I have considered retro fitting as the wrong colour wing tips do annoy me. I seem to have picked the one Honk Kong trainer that used orange, the rest are red trims.

As to the need, seems that they would be very useful, in that in just clearing a hedge on the principle approach, the model does not touch down until past the middle of the field, even with a slight head wind. There is a modest slope downwards on the field that does not help in this approach.

The aim is not improve the stall speed, but to reduce the glide angle by making the centre section of the wing, more draggy, thus reducing the glide angle.

The take of run is surprisingly long, but this could be a function of small wheels on typically long grass and limited power when compared to many IC engined planes of similar size. Once airborne however, one of my nicer handling models, no obvious vices. Even though the wing is tapered substantially at the tips.

[Erfolg]

I had no nose leg, although the mains were installed. I have had issues with my nose leg as it was a little rigid, which led to issues to the nose area disintegrating, in that hatches popped and a few other minor issues.

As a kit there is little I can say, as I received a partially finished fuz, and a mostly finished wing, using Torque rods to the ailerons.. I think all the body snakes are fitted by me etc.

As a model, it seems that Billkits (judging by what I received) are very good value and the T67 flies well

[Redex]

Just to update on he kit - my recently purchased kit does not have a FG cowl and also the canopy does not fit the cut out, and has been a real pain to fit, again this could have been my build error too. I think all the wheels are to small for a grass strip which I have also changed out

[Redex]

I have also added two access hatches on the underside. One for access to the nose wheel steering arm and the second just behind the nose wheel for access to the ESC. I have also made the front nose block detachable so that the motor mounting screws can be accessed.

[Stuart Z]

I suppose you could try “flapperons”?

S

[kc]

Bill Kits are on Facebook now.

The Firefly seems a reasonable price now at £75

. It seems they also cut foam wings if you need that service.

[Erfolg]

The Piper seems a good bet. Although the span seems a little generous, yet if significantly generous will result in a model that will not be to taxing, with the option to reduce, at a later time.

[Redex]

So just as a further update to my previous post - the T67 is now finished with the pilot installed. The details of the power train and its results are as follows.

It has an EMAX BL2832/05 motor installed, 4S 3600 30C LiPo, 80A ESC, 13*6.5 APCe prop, with an AUW of 2334gms.

Using my wattmeter at full power it shows 14.23v, 52.3A, 753 Watts, hope this helps anyone who wants to build a BillKits Slingsby T67 Firefly electric conversion. Maiden flight to come.

[kc]

That is quite a lot of watts per pound Redex -about 147 watts per pound and a lot more than Erfolg used in his. Will lead to quite short flights -perhaps 4 minutes at full throttle . Do you think it need that much power? and how does that compare to your other models like the AcroWot?

[Erfolg]

My model makes do on 700 watts. Perhaps that should be seen as more than adequate for a commanding take off, the rest of the flight is quite comfortable on half throttle, other than loops etc.

[kc]

Erfolg - I thought you said 400 watts on 27th March?

[Redex]

I think by the time that the prop/motor efficiency is taken into account, its actually about 120W/lb which is OK and should give good flight time on half throttle. I have tried to 'standardise' on my LiPo's but can always prop down. I'd rather have to much power than to little.

[Erfolg]

I will have to check, my book has circa 700 watts max. I would be surprised I could fly on half throttle on 200 watts. I need the power to deal with the often longish grass on out field, on take of.

I do not remember going from 3s to 4s, although it could be a reason.

At present I am undertaking a repair plus making some progress on a new build, tomorrow I should be clear.