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Aug 22, 2019, 10:58 AM
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mustangwally's Avatar
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Tsr-2


I've been hankering to build an EDF for a while now and the TSR-2 has always been my 'go-to' image of a jet since I was an A.T.C. cadet in my early teens towards the end of the fifties. I realise that it might not be the best 'first jet' build but I probably haven't got the time or resources to build a starter / intermediate model. I have a plan well under way in Autocad of an 800mm wingspan, 1800mm long model which I am hoping to bring in at 8lbs. (or less if I can manage).

I have bought a Changesun 12 Blade 90mm EDF and a Turnigy SK3 90mm EDF 1500Kv Motor which will be run on 6S5000 Li-Pos. Casting around on the net I'd say about 75 % of retract equipped TSR-2s never complete two flights so my intention is to have no undercarriage but to use a bunjee powered trolley to help get 'first-motion' underway, (we have a grass runway at our club). Hence this first request for advice... Never having actually used a bunjee launch trolley before, I am intending to base mine on the drawing attached. Anyone with any relevant experience to proffer advice??
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Aug 22, 2019, 02:43 PM
EDF Jet Jam 2019, June 13-16
eatond's Avatar
Is there a reason you can't forgo the trolley and just launch off a ramp? Simpler is better in many cases. If it were me, having done many bungee launches before, I'd just launch off a ramp.

Dan Eaton
Aug 22, 2019, 02:58 PM
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union1's Avatar
This is my arrangement.
The bungee line is divided and one leg is attached to the axle and the other to the hook on the model so that the pull is spread equally.
Works well.
Latest blog entry: SR-71 for 2 x 70mm EDF
Aug 22, 2019, 03:37 PM
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mustangwally's Avatar
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Many thanks to eatond and union1 for their prompt responses.

eatond :- I hadn't really considered a ramp system as someone else at the club had abandoned theirs and I think went on to a trolley system though I never actually saw the model. I was also a bit wary of placing too much strain on the forward fuselage as the plane is pulled off the ramp.

union1 :- It took me a little while to spot the second line in front of the trolley. Two further questions spring to mind,

1/. Do you spin up the fan to say half power before triggering the trolley release and advancing up to full power on the take-off run with the plane taking flight, casting off it's wire and leaving the trolley behind, there-bye avoiding any hang-up? If not could you explain your take-off procedure please?

2/. Do you have any angle of attack built into the trolley?

Thanks again guys.
Aug 22, 2019, 03:51 PM
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union1's Avatar
I usually use a very low throttle setting just to get the air moving through the duct so avoiding drag from there, hit the release pedal then apply full throttle once the model has left the trolley.
It's a lot easier to do than explain and the process isn't nearly as violent as you might expect!
Latest blog entry: SR-71 for 2 x 70mm EDF
Aug 22, 2019, 04:22 PM
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mustangwally's Avatar
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union1, thanks again.

So really the plane is launched into the air by the bungee force alone, the fan really only taking over 'in-flight' so to speak. Oh, and does your trolley have any built-in angle of attack?
Aug 22, 2019, 04:42 PM
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union1's Avatar
Yup... Just a big old twang into the sky, taken over by the fan once it's up there! Lol
I use a rough approximation of rotation angle... say 10 degrees or so. I don't think it's critical, just enough to get away and not so much that there's any chance of stalling.
Latest blog entry: SR-71 for 2 x 70mm EDF
Aug 22, 2019, 04:57 PM
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mustangwally's Avatar
Thread OP
Brill, many thanks again.
Aug 22, 2019, 07:43 PM
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4stripes's Avatar
Is your SK3 motor an 8mm shaft? If so that is an ideal 8S setup which I use in some of my jets (also CS9012 fans).
Not sure the power will be much on 6S.
Aug 23, 2019, 04:39 AM
jofro
Quote:
Originally Posted by mustangwally
I've been hankering to build an EDF for a while now and the TSR-2 has always been my 'go-to' image of a jet since I was an A.T.C. cadet in my early teens towards the end of the fifties. I realise that it might not be the best 'first jet' build but I probably haven't got the time or resources to build a starter / intermediate model. I have a plan well under way in Autocad of an 800mm wingspan, 1800mm long model which I am hoping to bring in at 8lbs. (or less if I can manage).

I have bought a Changesun 12 Blade 90mm EDF and a Turnigy SK3 90mm EDF 1500Kv Motor which will be run on 6S5000 Li-Pos. Casting around on the net I'd say about 75 % of retract equipped TSR-2s never complete two flights so my intention is to have no undercarriage but to use a bunjee powered trolley to help get 'first-motion' underway, (we have a grass runway at our club). Hence this first request for advice... Never having actually used a bunjee launch trolley before, I am intending to base mine on the drawing attached. Anyone with any relevant experience to proffer advice??
I found the easiest way to bungee launch, is off the model's belly. No need for dolly, etc. to complicate things. Just add few ply skid fins to protect servos, and use it as a bungee hook, all you have to do is pull and let go and off you go!
2019 0106 152405 091 (3 min 32 sec)
(Stinger launch)
Aug 23, 2019, 05:08 AM
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mustangwally's Avatar
Thread OP
4stripes :- Thank you for your response, especially from someone with experience of the same fan.
Yes it has an 8mm shaft, I had to get the fan boss bored out from 5mm. The way I read the original Hobby King advert it came with an 8mm boss and an adapter but I was mistaken. I read quite a few comments on the page which were quite positive about using it on a 6S system but you may well be right to think that the power may be well down. I'm hoping in the next fortnight to get the motor / fan combo tested with the inlet and outlet ducts fitted . This should give me a better idea if the project is viable or not.

jofro :- I built a 2/3rds size Depron quickie to try out with a bungee but I did find it a bit awkward to hold the model under tension without straining the model and at the same time holding the transmitter ready for use. I think I'd feel more comfortable with a triggered trolley but thank you for sharing your experience and for the great pictures.
Aug 23, 2019, 06:41 AM
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Larry Dudeck's Avatar
The big problem with a trolley is how do you secure the plane to the trolley? A bumpy field might cause the plane to leave the trolley before minimum air speed is reached, resulting in a stall and crash.
Since you're using a bungee to pull the trolley just eliminate the trolley all together. From my experience, a ramp is not needed. I have bungee launched numerous plane over a thousand times, most right off the grass.
I stretch the cord so the tension is about 3 times the weight of the plane. The initial launch might be as high as 5 times the weight but you will quickly figure out the optimum tension.
I launch power off and apply power as soon as I see daylight between the bottom of the plane and the grass.
I use a peddle type release which leaves both hands on the tranny.
Aug 23, 2019, 10:16 AM
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mustangwally's Avatar
Thread OP
Larry Dudeck :- Mmmm, food for thought there, our field is not 'bowling green' smooth so there could be a problem with the plane bouncing off the trolley. The plane hook will have return bend on it which should stop it parting company with the trolley but as you point out the trolley may not be necessary. I have a Canadair seaplane which weighs seven pounds that I fly mainly off the grass. Like the TSR-2 it has a flat hull and I find it reluctant to 'get away' sometimes. This was one of the reasons I favoured wheels, to help get a quick 'first movement' and then get the fan involved to assist the bungee as the stretch started to fade.
The airframe wood should be delivered within the next two weeks which gives me time to build a trolley for a trial of the rival methods. However, and I see merit in both methods, whichever system I adopt will have a trigger release. Thanks also for your tip about bungee tension / plane weight, I hadn't read that before.
Aug 24, 2019, 03:08 AM
jofro
Quote:
Originally Posted by jofro
I found the easiest way to bungee launch, is off the model's belly. No need for dolly, etc. to complicate things. Just add few ply skid fins to protect servos, and use it as a bungee hook, all you have to do is pull and let go and off you go!
https://youtu.be/che-rztnyhw (Stinger launch)
Very little tension is needed to bungee EDF jet off the belly, the power unit does the 1/2 of the job. I use only one to one tension to all up model's weight. The larger the model is, the more stable and easier it takes off.
Aug 24, 2019, 06:42 AM
Registered User
4stripes's Avatar
Regarding weight and power. Typically models that weigh close to 3kg will fly really well with a properly matched 6S setup. Since yours will likely be closer to 4kg I think you will need to run your setup on 8S. All you need is an ESC that can handle the cell count. I use the YEP 120 HV type with the SK3 and CS9012. It will pull under 110 amps with timing set to zero with a completely full 8s pack (peak).

The only thing is that this setup can explode if not built properly or if the fan is defective. Unfortunately I have had very bad luck with the Changesun fans from Hobbyking. Several exploded before I figured out they had a bad batch made from inferior plastic. The blades are lighter and noticeably much more flexible than the stronger ones made with the proper material. It is all in the Changesun thread from years ago. I never had any issues with the fans bought from X-Flight.


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