BS6 EZB Questions

[bjt4888]

Hi All,

Since I'll be attending the indoor Nats for 2021 this year, I thought it would be good to build a few fun things to fly.

I'm in the middle of building Yuan Kang Lee's BS6 and have a few questions. I am building with some wood size modifications to target the weight to about 450 milligrams (mostly to get practice flying at this weight before attempting an under 400 mg version).

I've read the Hobby Shopper article dozens of times, so pretty much have that committed to memory. Also read pretty much all of Hip Pocket and INAV, but haven't built a light EZB before. So, probably these questions are pretty basic; sorry.

1. I see that the propeller on the plan, if full size, would be 12" dia and 1.375" chord and 5.25" blade length. The plan indicates 13.25" dia though. So, If I scale up 110% with the copier to create 13.25" diameter, this makes the blade length 5.75" and chord 1.5". Is this correct?
2. I see that there is no tailboom offset indicated on the plan. I think that I've read that only stab tilt and thrust offset are needed for left turn for EZB. Does this sound right?
3. Should I setup the wing with zero left wing washin?
4. For covering, would the recommended technique be to spray 3M77 (I know the "spray in the air and wave the part through the spray fog method) and then set the part onto the covering that is on the frame? Or, would the method I've seen in Josh's F1D video be better (flying surface set on a piece of foam core after 3M77 spray and covering on frame lowered onto it)?
5. I have formed curved parts by wetting, forming and baking many times, but found with these wingtips and stabilizer halves that after removing from the form they "sprung back" toward original shape a little more than I'm used to. Is this typical? Or, should I wet them and form and bake again?

Thanks so much. Here's a few pictures of the fun I'm having.

I'm going for the record for longest time between construction of EZB's. First one I built was in 1970 from the IMS kit as a 14 year old (still have it). This is the second one. Most of my model airplane time is spent coaching Science Olympiad students. I don't build for myself much.

Brian T.

[cglynn]

Hi Brian,

I built a BS6 to 450mg and can confirm it flies very well at that weight. 

I used the same prop as Kang noted on his plan, with zero modification.  I think the prop is a copy of one of Jim Richmond's, and Kang has made it work very well.  Both of those guys know their stuff, so I would be hesitant to modify the prop.  The difference in length between the blade and the final prop dia. is from setting the blade .75" out from hub center on each side.

My BS6 flies fine with stab tilt only, and a flat wing.  The torque forces from the prop, combined with tail tilt are enough to make the model turn, and it has been found that the flat wing will prevent the model from spiraling to the right when launched at high torque.  When wound to reach the top of a high ceiling, you may notice the circle opens up quite a bit until the torque burns off.  If you were to use the typical "wash in the inboard panel" you would find an uncontrollable right bank spiral death dive would likely result.  Though at 450mg, there may be enough strength in the MS to prevent that from happening.  I would still build the wing flat.

Use as little adhesive for covering as possible.  The spray fog method is in my opinion the easiest way to use the minimum amount of glue.  The trick to light EZB is to keep the surfaces as straight as possible.  Some will put the glued frame onto the film, and others put the film onto the frame.  Whichever method works for you to keep the frames dead straight is the one you should use.  If you look back through past issues of INAV, you will see all sorts of tricks those from decades past have used to get delicate frames onto film while keeping it all straight and true.

Spring back happens.  Overbend your pieces to account for it.  Make your forms with a little more curvature than is needed.  They will then spring back to the proper shape.  I used to just deal with the spring back and glue the parts in their appropriate places, under tension.  I don't recommend it as the induced tension encourages warps.

Hope that helps.  And have fun with your build.  The BS6 is a great design and flies well throughout a variety of weights.  In fact, my son (5yrs old at the time) built one as an all sheet model for flying outdoors.  Using the black MPC prop with the attached hanger/bearing and a 30" loop of 1/8" rubber, braided, he was able to get flights of over 2 minutes.  Not bad at all considering that model was far heavier than the designed weight.

CG

[bjt4888]

CG,

Thanks so much for the detailed feedback. This will help me quite a bit. I’ll be using all your recommendations.

Brian T

[piecost]

Brian, please let us know how you get on.