BillHarris

I finally got my Clancy Lazy Bee finished and I did her maiden flight last weekend. This is a fun plane to fly!

It flew very well, but I note that the elevator requires considerable downtrim when the engine is run at high throttle settings. On 1/2 or 1/3 throttle, the elevator needs _zilch_ trim for level flight. This is a 40" Bee with an OS 15 FP engine. The plane balances at the rear of spar.

I've not checked the engine downthrust (yet), but I figure that it needs 2-3 degrees total. I disremember whether to reference it against the chord line or the wing bottom, but I'll check it tonight.

Other than that I need to wrap the tank in a bit more foam, I had problems with fuel foaming.

CafeenMan

Sounds like you know what the problem is. If the plane pitches up with application of power and pitches down when the power is pulled back you need positive incidence in the stab or down thrust. Did you have a question?

BillHarris

>Did you have a question?

Nope, just double-checking.

I've been lucky on the several other planes I've built and haven't had to change the downthrust other than what existed from simply following the plans. I'll check and measure it tonight.

Nearly lost the Bee on the first takeoff: she nosed way up and nearly got into a stall. With the OS .15 it is somewhat overpowered and by holding the nose somewhat level I quicky got enough airspeed to fly and get up to a comfortable altitude

Thanks!!

BillHarris

Yep, that is what it was.

Measuring incidences with a Robart meter and setting the incidence of the stab to zero, here is what is there:

wing saddle +2.5 deg
chord line +3
stab -0-
engine thrust +0.5

Placing 0.041" shims between the upper engine mount bolts and the firewall should give about -2 deg downthrust.

n553302

Yep, your right, I have several friends with Bee's and a noticeable amount of down thrust has made all of them fly better.

n553302

Yep, your right, I have several friends with Bee's and a noticeable amount of down thrust has made all of them fly better.

CafeenMan

I've never seen this plane fly, but I have seen it. Looks real draggy.

I would put that power to good use by going to a high diameter, low pitch prop. Something like a 9 x 3 (if you can find one).

BillHarris

It is draggy, with a real thick flat-bottomed airfoil. The all-up weight is 2 pounds and I have _heard_ that a .15 is more engine than it needs. But whatever, it flys around all day at 1/4 throttle and gets real lively at full throttle. I may put floats on it some day, so the extra engine will be useful.

Even with 3 degrees of downthrust it does have a tendency to climb strongly at full throttle (although it is much better behaved now). With a little more weight in the nose it cruises nice and level with no elevator trim.

I plan to try a 9x3 (or other dia/pitch combos) some day. Right now it turns 14,400 max with a Master Airscrew 8x4.

Question: since it's going to be flying a LOT of part throttle, is there an optimum RPM for an .15 glow engine to cruise at? For example, my BMW motorscooter is not happy below 3000 rpm and likes to run at 5000-5500 rpm.

CafeenMan

I couldn't tell you what the RPM is, but my plane Great Gonzo would not come down with an 8 x 4 prop running as slow as it could without quitting. Most of the time I had to kill the engine to land the plane. It had an O.S. .15 CV-A. Great Engine, but I needed a 9 x3 and nobody carried one. I think APC makes one though. If you can't find a 9 x 3, try an 8 x 3.

It won't hurt the engine to idle all day long.

BillHarris

I'll fiddle with different prop dia/pitch and see what works best.

The last item is the fuel tank. I'm using the specified Sullivan 2-oz Slant tank and it fits awfully tight. The space that Clancy designed for the tank is just too small. The tank fits so tightly that the foam compresses and even the tank even contacts the nose in the front corners. Yep, got a fuel foam problem at <1/3 tank.

I've got the tank removed and plan to cut away the parts of "dashboard" (the rear bulkhead of the tank compartment) so that the tank does not need to be crammed into that space. I don't know if a smaller/narrower/thinner tank is available, so I needs to make do with what I gots.

But, I may see if there a flex tank that could fit, or maybe a bladder tank or an Ernst tank.

n553302

Bill, would not hurt to double check your propellers balance, this can churn up the fuel.

BillHarris

The prop was balanced, the problem was that the tank was virtually in contact with the firewall and fuse and fuel foaming was guaranteed.

I removed the tank and re-did the tank compartment so that I could use lots of loose foam around the tank. I haven't run it yet, but it has to be better.

And, yes, I'll double-check the prop balance....