bzfrank's blog archive for October, 2012 - RC Groups
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Archive for October, 2012
Posted by bzfrank | Oct 09, 2012 @ 10:32 PM | 6,277 Views
Towing a flag is fun and can be done quite easily. It works exactly like towing a banner but requires less power and can be done by smaller planes (depending on the flag size of course). The following works for me:

Above images my biplane (loosely based on an Udet Flamingo) with 1.80m wingspan towing a 90x60cm flag. Also a 120x90cm one works fine with this setup.

This scheme describes how to attach the flag. It also works for a banner.

For takeoff place the flag flat on the ground, straighten the line and slowly increase speed. It will move to an upright position once in the air automatically.

Attach the line to the tow release, which should be located about 10-20% of the fuselage length behind the GC. Now for the important part: Be sure the line runs below the elevator! In the air the flag is always below the airplane, so the line will otherwise press on your elevator and that can ruin a perfectly good day. Also don't fly too fast, the flag will add quite some drag and will flutter at higher speeds, beside it does not look good.

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Posted by bzfrank | Oct 08, 2012 @ 09:46 PM | 7,400 Views
A while ago I built a Windrider/HK Mig-3. A wonderful bird to look at but it turned out to be a beast in the air. When flying at lower speeds it did just fall out of the air - tip stall without any warning, its name was Mig-3.

After some crashes and rebuilds I gave the Mig-3 to a colleague and forgot about it.

Well, almost - when I stumbled over a HK Mig-3 on eBay I know I had to try again and this time make it fly, and fly well.

Isolate the issue

The Migs tip stall issue comes from several causes.

One is the wing geometry, a wide wing in the center and quite small tips. While scale in appearance (and true to it - the original Mig had quite unpleasant stall characteristics) its always cause for alarm. Its problem is that on such a wing the tip tend to stall before the root. Several things can be done to prevent this from happening:

- reshape the wing - gives good results as the VQ Mig-3 shows but impossible to change later for an ARF bird (and besides it does not look scale anymore!)

- geometric twist, decrease incidence of the outboard leading edge by some degree - usuall works fine but also impossible to change later as well. The Mig-3 has no such increased incidence at the tips.

What is possible later is to raise both of the ailerons a few degrees. This reduces lift but also the tendency for a stall however only slightly.

- different airfoils tip / root. Likewise impossible to change for a ready-made plane.

Well, that leaves one more thing: Tubulators

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