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Elf on a diet...


Reggie Perrin
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Reggie Perrin

Just a very quick little build thread...

I've wanted an Elf for a while and figured the winter period would be an ideal time to fettle one together whilst I couldn't fly. I've just finished the first of my Stream NXT's and needed a little light relief before tackling the second one. Best part of all, was it being an unstarted bargain from eBay...

Following advice from a few internet threads and Boffin from here, I'd decided to modify the Elf right from the start, there are enough stories on the net about wobbly tails, pitch instability and broken fuselages to suggest that whilst the Elf is a very good model, it can be improved... I also wanted it to be as light as possible with a capability to add ballast if needed.

Pictures at the bottom.

First thing to do was remove the epoxy plug in the front of the fuz, this serves as a mounting for the RC gear as you will all know but it doesn't travel far enough along the boom to reinforce where the taper starts and the wall of the tube is compromised. With perseverance, removal can be accomplished and leaves the tube nice and clean for the replacement.

A light but firm balsa dowel was tapered and sanded to fit, extending past the front wing mount. This was reinforced with carbon internally to provide some reinforcement local to where the taper starts. Bonded in with Zap, then cut and sanded back to follow the taper of the fuz. The balsa was lighter than the epoxy plug...

To cure the wobbly tail and pitch instability, the tail was pylon mounted and the control surfaces actuated with kevlar pull threads and torsion springs. The vertical fin was stitched on around the carbon supports to reinforce the join to the fuz. I routed out some 1/32nd control horns to suit for the elevator.

I thought about using tiny gear, 2gram digital servos and a tiny battery but didn't want to carry any nose weight and was concerned about the power of the tiny servos so followed advice and went for a fairly standard set up of 2 x SD100's and a 300mah single cell lipo. RX will be the Futaba 6004ff with an option for a 2 gram heavier RX if range is an issue and I need telemetry...

Total weight, with CG bang on is 95 grams ready to fly

Lots of thanks to Boffin for his enthusiasm and advice. Can't weight to give it a throw about now...

 

Reg

 

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  • 2 weeks later...

Neat one Reg.

My own Elf's nose improvements were post-breakage, but the rest of it is standard, tail and all.  I attribute any lack of performance to my own mediocre flying skills!

How have you solved the ballast challenge?

Jon

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Reggie Perrin

Hi Jon. 

I have room under the wing to place weights right on the c.g.  I will most likely have a small peg on the boom for 5g plates to fit over as that seems to be the lightest and easiest solution...

for now, any ballast is just sitting in the bay, far from ideal..

I'd like to be able to fly it first without ballast but since it's completion the wind speed has been constantly above 10mph... oh well...

if the wind speed is too high for the elf, I have plenty of other things to fly....

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Reggie Perrin

Very foggy this morning which meant only one thing... No wind..!

This gave me a great chance to maiden the Elf. Luckily I have a lot of open park space near me that I can fly in so with a quick check of voltage, I headed off.

The air was calm but sinky as hell and the wet grass meant that any flight that didn't end in a catch had the model picking up considerable water on all surfaces. It's frustrating how the smallest amount of water on the wings effects the performance so much.

With a good hours attendance at the field and approx 25 - 30 launches, I was happy that it was performing well. At 95 grams, it does lack penetration and the cg may be a couple of mm rearward but that's easily tuneable with ballast when required and moving the lipo further forward by a mm or two.

Looking at the trims afterwards, I have one click of right rudder and that's it. 

All in all, I'm very pleased..

 

Reg

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  • 1 month later...

Hi Reg

Meant to reply ages ago.  My own ballast solution uses either one or two rectangles of lead sheet, each 12.5g, which fit in the cavity in the underside of the wing centre-section, but which always slightly upset the optimum zero-ballast balance and elevator trim settings.  (Having done dive-tests, my Elf needed a streamlined blob of Blu-Tak under the fuse-fin join, to counteract the weight of both the nose-repair/improvement plus a tiny altimeter, now 108g.)

Ballast certainly makes some difference in the ability to penetrate back upwind in slightly stronger conditions, but 12.5/25g jumps are too large, so I'm going to make three new lead strips of 8g each.  To overcome the problem of trim being upset each time I insert, I plan to keep them the same size as the originals to fit the cavity dimensions but add lightening holes to one end and experiment to see which way needs the heavier end.

Jon

 

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