TOPIC: 3D printed model for Jetex/Rapier/Tender

Thank you sir.

On the picture it looks as though the motor alignment is also a bit nose down compared to the wing lower surface, (is the wing undersurface flat?).

Is this an illusion or is the motor tilted a bit?

No illusion, you are right, the motor is also tilted down to give down thrust, I should have mentioned that too but this aged brain forgets things!!! That is only an L1 model so you can see how much these quick little flyers need their down thrust, it was also a trend to have forward CG's on Rapier models to counter any loopyness but I like my models to glide well and balanced mine to achieve that.

Thank you Howard. I suspect I'm going to be 'crowdsourcing' (as the young folks say) more trimming advice in the near future!

I'd certainly prefer to get an underslung motor configuration working. The trough mount makes for a heavier model. The rear fuselage is hollow and the extra plastic to make the trough plus the balsa and aluminium brought the weight back up.

So now I'm working on a new motor mount and a downthrust tab.

But do you really need all that strength there, could you not leave out the plastic trough and the balsa and replace it with a trough made from paper and ali foil only? Alternately, I have used a piece of thin food tray alu. as a trough with no support at all except at the front and rear, as here on my Swift.




Roger Adds:
this is good stuff from Howard, who knows his onions. Foil over paper is one option; I've used is the foil from a large disposable baking tray, like the ones they sell for roasting turkeys. The foil is thick enough to be bent and moulded to shape (it's aluminium) but still very light.
I also use 1/32" Balsa with 'Carplan' sticky back exhaust repair foil. The advantage here is that the wood gives a measure of insulation.

You could always add a 'motor pod (the Typhoons I've seen seem to be festooned with pods of various types) and a downthrust tab.

Thanks guys these are great suggestions. My next attempt will go back to a centre line external store type motor mount. Aft of that alli tape over 1/32 balsa and a downthrust tab.

I will try and source a turkey baking tray for further trials. Thank goodness the grocery stores are open.

I'm also adding a little cavity in the nose for lead shot.

For this weeks not so thrilling instalment I can report a bit of success on the flying field. In order to make it easier to launch I’ve got an underslung motor on the 3D printed Typhoon. After some unsuccessful attempts under power I followed the example of Howard’s Hawk, I put a down thrust tab under the rear fuselage.

With this I managed to get a powered flight. This was using one of Dr Z’s red L2s from this years crop. Admittedly it was on the second launch attempt but then it climbed away with a trail of smoke worth of a J79. It gained a bit of height but the glide was unimpressive. This version weighs 41gm with a loaded motor.

Following a further debrief with Roger and Howard I moved to a larger tab just 2 inches aft of the nozzle & set at 45 degrees. I found some thin aluminium in the form of the cans of those strange looking energy drinks. This was thin enough to cut with a craft knife and then trim with scissors. I stuck masking tape on the metal and drew my dimensions on the tape before cutting it to size with the scissors. A word to the wise for our younger readers. Please don’t use mother’s best dressmaking scissors for cutting the can. Or if you do make sure she doesn’t see you!

This time it got away first throw and ascended with a bit of stally kind of climb, the descent too was a bit stally but at least it was still airborne when the motor quit!

However, I’ve not yet achieved consistency. Two further attempts this morning were not successful, symptomatic once more of insufficient down thrust I think. The drink can aluminium while easy to cut it is just too easy to bend. And one tends to set the model down on it! And maybe I can form a stiffener ridge into the material so as not to add any further weight as the tab was clearly flapping about in the stream of the Rapier exhaust..