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Aug 24, 2019, 07:43 AM
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mustangwally's Avatar
Thread OP
Thanks gents for all this relevant advice. While I'm waiting on construction materials I could post the two pictures below showing the duct / fan layout, the ducting / fan comprising of 1metre (41") of the 1.8metres (70") overall length. The outlet being an ellipse of 100mm x 64mm. I will be using a 6S5000 battery to propel her and has been pointed out I may be down on power , hopefully 2000watts or so will give me enough grunt to get off the ground. Landa very kindly 3D printed the inlet ducting for me for which I am VERY grateful, I could never have made a duct like this conventionally.

The other picture shows how I'm tackling the all-moving fin and elevons. I'm not claiming any originality for this though I haven't seen it adopted elsewhere, It uses two nylon ball bearings in a tube with the elevon pivot rod held in the bearings. Very slop free and easy to rotate, no binding whatsoever, light (4gms each), cheap and above all , no penetration of the outlet duct. I thought the bearings were unusual but they're available on Ebay at about 10 for a fiver. Just imagine the weight-loss substituting nylon for steel races.

Whaddayafink??
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Aug 24, 2019, 08:04 AM
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Larry Dudeck's Avatar

trolley launching


I once built a trolley for launching my scratch built Piaggio P 166. This was prior to my bungee launching days.
The trolley I built included a separate receiver, battery and a servo for the nose wheel. Propulsion for the trolley came from the P-166's twin pushers.
At the local community college is a service road which traveled north to south. From the north end, the road had a 2 or 3 percent down grade.
My idea was to use the downgrade to help with the cart's speed. The speed generated by gravity when added to that generated from the twin props should have been enough to reach air speed.
Once the plane reached flying speed, it would lift off the trolley. At that point I would simply steer the trolley to the side of the road.

What could possibly go wrong?

What I didn't anticipate is the bumpiness of the road caused the plane to lift off the trolley before flying speed was reached. It rolled to the side, did a few cartwheels. That was the end of my trolley experiment.
Last edited by Larry Dudeck; Aug 25, 2019 at 10:49 AM. Reason: Poor grammar, spelling
Aug 24, 2019, 08:36 AM
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mustangwally's Avatar
Thread OP
Quote:
Originally Posted by Larry Dudeck
At that point I would simply steer the trolley to the side of the road.
It was about here when I started to have serious doubts.

Which stick would control the trolley ???
Aug 24, 2019, 02:15 PM
Registered User
Larry Dudeck's Avatar
Used the rudder channel. The plane only had elevator and ailerons. Obviously, the receiver channel was the same as that in the plane.
Aug 25, 2019, 04:38 AM
jofro
Guys, check how jets take off from the carriers, "full power" well before release! That's the safest way to bungee EDF.
Aug 25, 2019, 06:15 AM
Registered User
Larry Dudeck's Avatar
Depending on where the air inlet(s) are, full power launches could result in FOD.

An A10, ok. An F89, not ok
Aug 25, 2019, 05:58 PM
James L
TANGOSIERRAROM's Avatar
Good luck with your version of TSR2 mine flies well but is just a twin 55 mm set up so yours should be awesome.
Aug 26, 2019, 02:42 PM
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mustangwally's Avatar
Thread OP
Tangosierrarom :- Thanks for that, I hope your optimism isn't misplaced, long way to go yet.
Aug 27, 2019, 04:59 AM
jofro
Quote:
Originally Posted by Larry Dudeck
Depending on where the air inlet(s) are, full power launches could result in FOD.

An A10, ok. An F89, not ok
Full power launches doesn't seem to affect any of my models like "Hawk", "Phantom", " Stinger" or hundreds of launches with Hornet in the past, all with low air intakes, even with all the "roo-poo" on the grass strip. All I do is pull and let go, to KIS.
Dolly launches are fine off the smooth hard packed beach sand or bitumen strips, but pain in the neck off the grass unless you have putting green surface.
Aug 27, 2019, 10:31 PM
Registered User
Larry Dudeck's Avatar
Jofro,
You say you don't use a peddle release. In one of your photos it appears you are holding the plane by the vertical stab.
What kind of tension are you getting with the bungee?
With my launches I stretch the cord to somewhere around 16 pounds. I can not imagine the vertical stab on any plane of mine sustaining that load without ripping the vert. Stab off.
Aug 28, 2019, 02:58 AM
jofro
I have never used peddle release, too complex and troublesome, I prefer to keep thing simple and more efficient. LOL.
No, I don't hold it by the fin, it only appears, I install in most of models I design for bungee release, a 5-6mm carbon fiber tube that runs through the fuse for extra strength with some 10cm. pretruding at the rear as a handle hold.
At 16 pounds pull tension I would release any EDF at 16-18 pound AUW.
I stretch my very short 3m long, 10mm bungee cords to only same tension as the AUW of each model I release. Air cusion and the power unit does the rest after I let go with full power on. 1000% success rate, in my log books and all the documented YT videos over the last 9 years on RCG.
Aug 28, 2019, 06:40 AM
Registered User
Larry Dudeck's Avatar
So your plane is on the ground when you release the cord?

Just ruminating here for a moment.

Assuming a 10 lb plane, you would stretch the cord to 10 lbs of tension. Guessing the coefficient of friction on sand might be 0.1, the bungee is working against a load of only (10x0.1) one lb.
So the tension:load is 10.

So off grass, as in my case, the CoF of grass might be 0.05. With a 5 lb plane, the load on the cord would be 0.25 lbs. With 16 lbs of tension, the tension:load ratio is 64.

Never considered this angle before. Doesn't change anything in any way.

I have launched with full power before and the difference wasn't all that noticeable. In my case, on my field, the chance of FOD outweighs any launch impact. Usually the static thrust to weight ratio of my planes is 0.4 to 0.5.

What are the thrust:weight ratios your dealing with?
Last edited by Larry Dudeck; Aug 28, 2019 at 06:51 AM.
Aug 28, 2019, 06:47 AM
Foam addict
4stripes's Avatar
Yes, but are you 1000% percent successful?
Somehow it is hard for me to believe anything said when such exaggerations are made.
Aug 28, 2019, 11:52 AM
Registered User
Ianda217's Avatar
Derek,

It's not "Landa" - it's "Ianda" (upper case i).

I hadn't realised that you had started this thread - just saw it tonight (subscribed).

My edf test stand is available any time you want it. I can lend you the bifurcated exhaust outlet from my E.E. Lightning as well to do a comparison with your oval outlet.

The Lightning will also have no retracts but I was thinking of a simple dolly (no bungee) along the lines of the one that Gerry uses. My experience with the bungee for the Gloster Javelin was that it got in everybody's way on the runway.

You're also welcome to borrow the bungee - with or without the ramp.
Aug 28, 2019, 04:02 PM
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mustangwally's Avatar
Thread OP
Ianda :- Now it makes sense as a capital 'i'. I'm hoping to take you up on your test stand offer very shortly, I have our grandchildren here with us until the weekend so I should be in touch soon after they have gone home.

My bungee'd trolley idea was to build the trolley in 'off time' from the plane build, this would allow me to try bungee only, bungee + trolley and trolley only. Watching various ramp + bungee launches I got the distinct impression of a pretty violent change of direction as the plane left the ramp so I'm not intending using a ramp, (also as you say a ramp is a bit intrusive at the flight-line, at least the bungee clears the immediate area).

From my received comments there does seem to be a variety of strongly held opinions as to the 'best' method but luckily all seem to have a high success rate. I suppose the best thing is to give each a try and plump for the one which best suits the plane and pilot.

My glass-cloth rear duct has recently been superceded by a new version made from a layer found in an old LED television screen, (a long story). It's slightly lighter and smoother and takes on a very smoothly graduated transition from round to ellipsoid , I'm very pleased with it. I have piece left which might just be long enough to fit your Lightning. Worth a look anyway.


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