Hello all, will after much consideration & against my better judgement I started this kit last week. Its just about ready for Coverite Microlite silver covering. So far she weighs 4.1oz w/ all RC gear. With only 103 sq inches this is going to be very interesting! :-()

Motor:18-11 2000kv from Hobbycity Online
Servos:2ea Blue Arrow 3.6
ESC:Turnegy 6A
RX:Corona 4ch
Battery:2S 250mah Lipo
Prop:GWS 6030

Best regards,
Dale

A few more detail shots-enjoy!

Dale

Very nice work!

looks great , will you have a water rudder?

Thanks Geoff & LF. I'm not sure if this will ROW or not having never tried it before, so I'm thinking of hand launch & land on grass..........if the snow ever goes away. It only has aileron/elev right now to save weight.

Dale

I think your going to be just fine weightwise. I have the Dumas Wedell Williams at nearly the same wing area (perhaps a shade less) and it really turned out to be a great flyer at about 6.5 ounces.

If anything makes it interesting, it'll be the aerodynamics induced by the floats. Will be watching.

One of my all time favorites. I look forward to a flight report.

Pete

Great project, watching with interest.
Rich

Very cool! Subject and work. You did great keeping it that light with all the gear in it. I agree that if anything 'bites' you it will be the floats.

But, the larger GB E that I did flew much better after I added the wheel pants (and it was 8oz and 144sqin ). The weight and drag down low actually helped the stability. With the power you have I predict it will fly good!

Good luck.

charlie

I'm impressed with your nerve in giving this a go! It's a lovely looking model - I've only seen it built once before, in free-flight form, and it looked fantastic - as does yours so far. Hand launch and land on grass looks like the way forward. to me.

Sky-thanks for the info, I remember your WW & it was very nice!

Thanks all for the support-hope to cover this next week & hope the snow melts & some grass shows up.

It has a great deal of mass below the center of fuse so the ailerons may not be effective. This is the one of the smallest RC jobs I've tried so we'll see.

Dale

Dale,
This looks great!
I've spent a lot of time reengineering one of these (haven't built it). I think your weight is great and should work fine at under 6 oz. I don't like the stock float mounts. Have you changed these? Also the weight of the under slung floats and the side area in front of the center of gravity make the SB 6 very unstable. Every SB6 I have seen spirals in as a result of this instability (mass coupling and being divergent in yaw). I would add a clear sub fin about half the size of the stock rudder and fin.

To Charlie's observation if the spats helped it was probably a result of moving the CoG a little forward. Under slung weight and under slung drag usually add to instability. IIRC spats are added to lower the landing gear drag. Not just look good.

There is a fallacy that under slung weight adds stability as a result of the "pendulum effect". In fact it causes instability. Think of an airplane flying straight and level now try to turn it. The lower weight will try to keep going in the original direction causing what looks like an over rolling input causing the start of a spiral dive.

I would place my batteries as high up in the fuselage as possible on the SB 6 after obtaining the proper fore and aft CoG.

Love what you did with the engine cover and aft engine fairing.
I see that you sheeted the bottom of the floats. How was this done, and are you happy with the results?

Very nice start,
Konrad

Konrad,

The spats did not change the CG at all. Drag change was probably insignificant. Now, side area did increase significantly, but, in my case was balanced ahead and behind CG. I would share your concern about the side area of the floats and tail surface area. The GB had significantly larger tail surfaces than scale since it was designed for rubber FF. Since the S6B model was not really intended for flying, enlarging the tail surfaces might be a really good idea.

I would be concerned about the change in drag with angle of attack and will it be helpful or not. Be aware that the S6B was designed for high speed flight and hard turns, not for much of anything else.

Lowering a CG has always been good for me with regards to stability. Most instability problems I have seen were because of high CG (both in full size, wind tunnel and model). It does hamper aerobatics though.

charlie

Originally Posted by portablevcb

Konrad,

I would be concerned about the change in drag with angle of attack and will it be helpful or not. Be aware that the S6B was designed for high speed flight and hard turns, not for much of anything else.

charlie

The S6 and S6B both were notorious in their lack of stability in yaw.

Don't have any insight as to the movement of lift (drag) as a result of the changes in the angle of attack. As there is so much lifting area on the pontoon ahead of the center of gravity I think it must be taken into consideration when determining the center of gravity. I think that Dumas has done this with this kit.

I have found that in my wind tunnel testing, the wind tunnel does a very poor job at predicting mass coupling. On this point I think we will have to agree to disagree.

I wonder if the TV show Myth Busters would want to tackle this esoteric debate . Really just kidding!

Charlie

Did I miss something? I thought the Dumas 24" racing jobbies were designed to compete in the FAC racer events- hence they should fly. Yes, I've got one of these too- I'm still kicking around the Astro Firefly, but I'd also do full house. I'm NOT doing it rubber.

Konrad- spiral instability can actually go the other way- the rudder may be too large. Often with rubber ships, the trick is to allow the rudder to flop freely, and control the turn with the fin. Especially true for airplanes without much dihedral and a relatively short fuse. I'm wondering if the effects of the floats are to give the airplane a shorter effective fuse moment. Also- draggy airplanes are generally easier to trim. Biplanes often get away with much smaller tail surfaces than monoplanes relative to either fuse area or wing area.

Sam