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Old Sep 11, 2011, 03:56 PM
MrE
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United States, WA, Gig Harbor
Joined Aug 2007
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Here are some pics of the pull-spring setup.

well for some reason I cant seem to get pics to up-load.

I'll try again later - off to fly some more now.
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Old Sep 11, 2011, 04:42 PM
Herk
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Virginia USA
Joined Jun 2007
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MrE The push rods in this plane were originally balsa. When I did the current setup, I replaced them with 3/16 dia hollow pultruded Carbon fiber shafts. I did that because I damaged the balsa rods when I was removing them. They had worked fine for many years. I used the CF rods as replacements mainly just because I had them on hand.

I have used single string and pull pull setups over the years. Based on my experiences I don't care for either. Both work fine and my preference is more of a prejudice than for any good reason. probably mostly because they drift and are hard to maintain and adjust. If you used non stretching spectra or kevlar strings the single string system should work well for you on this model.

If you are having trouble uploading pictures, either they are not an acceptable format or, the file sizes are larger than what RCGroups allows.
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Old Sep 11, 2011, 06:49 PM
MrE
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Yeah, each option has its plus and minus features and i can certainly understand your prejudices - I have plenty of my own

In this case, the weight savings were a major design goal, so Im willing to put up with some trade offs to get there.

The way I have it setup, its easy to adjust the strings. As soon as I can get some pics loaded you can see how I did it. This setup also will lend its self to an easy removable tail structure - which I want to do on the Mirage.

Im going to guess your carbon tube linkages are probably in the 40 gram range for both of them including clevises, etc. Going with a pull-spring setup would let you remove perhaps as much as 150-200 grams or as much as 5 to 7 ounces from the nose area. Thats 5 to 7 ounces off the total weight of the model.

After flying the 2x6 and adjusting the CG, I now have the packs on the CG, so if I need balast I can just use larger packs. The down side trade-off to that is I have to remove the wing to get to them for charging.

I need to re-weigh it with the smaller packs and smaller esc to see how much lighter it is now and then crunch the new numbers with the smaller packs.

Based on how it feels in the air its looking very good to me so far.
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Old Sep 12, 2011, 12:55 AM
MrE
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United States, WA, Gig Harbor
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The numbers are very encouraging!

With about 24 watts/pound I am getting about 468 feet/minute climb rate. The very nice part about this is the amp draw in the air is only about 5 amps!

What that means is that with a 4 ounce, 40 watt peak power system, I can climb to around 500 feet 5 or six times (or do 2 or 3 1000 ft climbs!) and still have plenty of reserve soaring time on these small packs.

The pitch speed also looks good for windy day up-wind penetration. Keeping the nose down gets the model moving along at a pretty good clip.

The Mirage is going to weigh a few ounces more than the 2x6 and will likely have more drag from the larger size. On the other hand, it will be more efficient at climbing, so Im thinking I can use the same power system and prop for maybe 50 watts peak and I'll be good to go
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Old Sep 12, 2011, 06:56 AM
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I just think of it as pre ballasted on a plane like a mirage that's what it is, that plane will only fly better with a little weight.I,m going to build one after the Crimson is done.
And yes getting old sucks, at least we can fly, my Electra has in the last year been a excellent teacher, an E mirage would be so cool.The Electra has to be flown up to a certain altitude to get the best results, a Mirage will fly on a mouse fart.I cant weight to order my kit.
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Old Sep 12, 2011, 02:03 PM
MrE
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United States, WA, Gig Harbor
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I just picked up an Isthmus Models Mirage short kit from another RCGroups member. The laser cutting is beautiful. I'll be starting it later today or tomorrow.

Im a little surprised at the responses/lack of interest Im getting from most people on this idea of minimizing the power system weight.

Having a heavy power system is like ballast you cant remove. Im thinking of those dead calm or cloudy days when all you have are mouse farts. Wouldnt it be nice to at least have the option to soar at absolute minimum weights?

The Mirage is actually just a stepping stone towards my ultimate goal - a Bubble Dancer. The Bubble Dancer is one which does like to be light. This approach will really shine there.

As far as I can see its mostly positives going light.

Sure, it will take me an extra 45 seconds to get to ALES altitude, but when I get there I'll be a lot lighter.

If I did want to compete in an ALES contest, this power system can easily put out twice the power Im getting now with out being stressed and all I have to do is change the prop. Same weight twice the power. I could easily get at least close to ALES altitudes in 30 seconds and still be several ounces lighter than the competition when I get there.

Plus all the components are cheaper and smaller, which makes it an easier fit into small fuses.

Another plus is lower weight at the nose and tail which will make for better yaw response and better thermal turning.

I really dont see any down side unless you're so impatient that an extra few seconds of climbing is just toooo slow

Well, there is one other downside - if you set it up to have the packs on the CG it makes for more trouble to change/charge packs.

Im going to see if I can work something out on the Mirage. Maybe move a former a bit to allow the packs to slide in from the front or back. They are small enough to make that work I think.
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Old Sep 12, 2011, 02:24 PM
Herk
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Virginia USA
Joined Jun 2007
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MrE

This ancient Mirage of mine has had several lifetimes.

In one of it's earlier setups I had a rather heavy high power German motor with a big battery pack. The model weighed about 5 pounds and it flew great. It had a very impressive climb and the glide was very flat. It would even work a thermal well.

Because of the size of the battery pack, I had it installed in a gondola that was attached to the bottom of the fuselage under the CG.

If you want to be able to change and charge multiple packs on your model, you might want to consider something similar - though obviously very much smaller and lighter
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Old Sep 12, 2011, 03:40 PM
MrE
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Thats a real testament to the quality of the Mirage. Makes me even happier Im building one
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Old Sep 13, 2011, 07:58 PM
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Granada Hills Ca.
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Hi E

This is my scratch E bird built in 85' that has a 100" mirage wing and open sticks on the rear fuse to make it light, all we had were Astro motors that were on the heavy side & heavy batterys too.
The AUW is 43 oz and with todays power set ups i could take a ton of weight out , being the motor was so heavy i had to build a short nose too so if i put a new motor in it i could make a new longer nose and that would look a lot better.
Thought you would like to see the 4 panel poly wing set up as i have always liked this look over a 3 panel.

G Don
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Old Sep 13, 2011, 11:26 PM
MrE
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Thanks for posting those shots! I agree, I like that wing poly set up better.

Im also liking your stick built fuse. I may have to try that myself!
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Old Sep 13, 2011, 11:56 PM
life long racing nut & modeler
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Granada Hills Ca.
Joined Nov 2009
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Hi E

When i joined the glider club in 80' Ed Slobod was a member and so was Blane Rawdon so needless to say it was talent city for glider design and also Dick Odle the R08 guy, the first day at the field there was 5 or 6 Paragons so i got a kit and started in the build.

To me Ed just hit the poly angles right on the money so each of my scratch planes have had the same poly wing angles of 4 and 11 on the tips for each side as it gives the planes a very gracefull look over a flat center wing.

G Don
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Old Sep 16, 2011, 07:08 PM
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Beautiful plane, great to see another old one,that one should probably fly again to.
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Old Sep 16, 2011, 08:53 PM
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Granada Hills Ca.
Joined Nov 2009
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Hi Doc

Thanks for the kind words on my E bird, i have a few hicups in my get along and if i can over come them it will sure be flying again most likely with a new power package and a longer nose to balance the CG and have a nice light floater E ship.

With the 60" Woody roadster and this one at 100" and a motorized Paragon at 120" and the big 144" roadster i will have a neat bunch to pick from for any kind of day and weather, that is the game plan so i won't have to worry about pulling back a line with these wobbly old legs and enjoy some flying again after 22 yrs away from all the fun !!

G Don
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Old Sep 16, 2011, 09:42 PM
MrE
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United States, WA, Gig Harbor
Joined Aug 2007
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Don, Thats a large part of my motivation as well

I have several more flights on the 2x6 with various props including several with some APC folders.

So far it looks like as little as 24 watts/pound will work just fine on light wind days. Up to maybe 5 mph or so.

Once the wind comes up above say 7 mph and/or it gets turbulent then a little more power is necessary.

Yesterday and today it was a little blowy and rough so I propped up to about 32 watts/pound. Thats a much better level when its rough. Even with really bouncy air I was getting in the 500-600 ft/minute climb rate.

At that level, I can still get an easy 4 or 5 climbs on these 640 mahr packs although 3 or 4 would be better to allow for more reserve if you catch a long ride.

I think Im going to try this exact setup on the Mirage for starters. Its the type of model that you really dont want to fly in really rough air anyway.

Im now convinced that light weight power systems with Very Low Power loading is a viable option for e-soaring.
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