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Category: Archive 2013

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1. F1B LDA
2. USA 2015 team selection
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On Trimming an LDA F1B Model

LDA-B models tend to fly straight as on rails until they lose steam and wobble into their course. About a month ago at Wawayanda, in a strong wind, my LDA-B model actually did a large loop, fortunately missing the ground to clock a minute plus result.  Carrol Allen suggested taking out some wing wiggler to help the model rotate during the burst.

All my B models have a Vivchar double wing wiggler, but I only wiggle the left wing during the climb. Although I’ve tried to use the right wing wiggler (which reduces the wing twist and comes out at 7-10 seconds), it did not seem to make a difference. So, following Carrol’s remark, I hooked up the right wing wiggler.

The results were spectacular (after some trimming). The model climbs and rolls nicely into cruise, without a VIT bump or hesitation. The launch has to be steep, as the model tends to fly straight initially.  Of course one use a single wing (left) wiggler, but it will have to be a compromise between the burst and cruise. In a Vivchar model, the left tailing edge is typically raised by .060”, the right by .020”.

The conventional wisdom is that a LDA-B model should fly with a fix pitch propeller. Instead, I’m using a 13 degree variable pitch front end and the model is perfectly happy. The motor runs seem to be short and one has to increase the blade’s cruise pitch a bit.  A number of observers claim that the model whistles in burst but they probably have better hearing.

No, I have not attached an altimeter to check the altitude. LDA-B models don’t glide as well as models with conventional wings and have a nasty tendency to start stalling after a while in laminar conditions. Fliers have tried various fixes and I use single layer tape invigorators at 50% and 65% of the wing.

Aram

Editor's comment:

Aram - I also have found that a VP hub is better than a FP and used an altimeter to test this. Incidently Vivchar is about to release a VP hub that will help with LDA airplanes as it has a low high low pitch cam.  A umber of people have already modified Vivchar VP hubs to do this.   I have found that using Vivchar's "LDA-like" wing I can get at least 15 meters more altitude than with his similar conventional airplane.  This is a Eppler airfoil with a big Phillips entry but more flap than other LDAs so it probably has more drag than the Eggleston sections in common use. This airfoil seems to handle turbulence better than some of the other sections.  Maybe an indication the amount of "LD" in an LDA F1B is the length of the VIT .  With a conventional airfoil I have about 4 seconds while with this LDA I have about 5.  I have watched Michael Seifert testing one of Stepan's models with a Eggleston LDA and he had about 7 seconds of VIT

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