sodbuster 1

Started out with a 24x 12 Biela WWII scale, beautiful looking prop,robbed too much RPM's for my liking.Best I could get was 5,500.Plane flew a little doggy.
Went to a 24 x 12 Mejzlik Sport. Not as pretty by far, but gained around 5-600 rpm putting the
engine in a better rpm range. Flew more than a little quicker too.

SJN

Thanks for the info.


Engine is a nice fit in the cowl.
With the ignighter on, you can almost slip on the cowl. So I will have to make a cutout for the cap.
I will probably make a hole in the lower cowl for cooling. I dont think the 2 upper outlets I have in the fusealge are enough.
Im going to close off the whole front of the cowl with my dummy radial, and then just cutout a srction the size of the cylinder.

sodbuster 1

Wow. The engine looks almost lost in there with all that room as compared to mine lol.
At least it allows you lots of options for all the lead you're going to need.

See the stack on mine? Wish that was silver instead

SJN

hehe.....thats a lot of lead

I better order som lead ballast from the diver shop.


The CG of the fuselage is spot on as it is right now.......

So adding the 2 tail fins. 6 servos, and part of the wings, and canopy and my tail retract behind the CG, is going to mess that up

SJN

Got the dummy radial installed.
Also did some baffling to force air through the engine fins......will see how that works out.

sodbuster 1

You should be fine on your cooling.
Did you open up the firewall area where you have your header going thru
to allow air to pass over the cannister and pass thru?

SJN

you can see the inlet to the fuselage in the first picture above in post 452.
Im going to make a duct around the cansiter, and lead air over it.
But I have to cut out the gear doors in the fuselage first, and make the wheel wells, and then determan the final location of all the bits and pieces

I hope my outlets are enough......of that the air will flow out of them quick enough.
There are the 2 large outlets on top of the fuselage. the 2 scale exhausts on the side, and the tail wheel well......but only testing will tell

SJN

Got my lead and battery shelf constructed in the cowl, and also mounts for my choke and throttle servo, and the ignition box holder.

Proceded to cut out my gear doors, and getting ready to make the wheel wells

I use some springs from 2 ball point pens as centering sprins for my tail wheel assembly, so it will not get stuck when retracted and extended once the steering slacken up in transition.

SJN

more pics....

sodbuster 1

Nice job on the gear doors!
Wish i would have thought in that direction when I opened up mine....
Instead I just opened up the belly and wing to allow free passing of the wheels.
Watching how you complete this carefully now [:-]

bignasdy

sweet. Nice work!

SJN

Thanks guys.

Got the new formers cut and installed.

SJN

Getting the gear doors finished.......but I will have to find a better matching paint. [:@]

Anyone found something that matches ?

sodbuster 1

Very nice job.
How do you plan on actuating them?

SJN

Thanks.

I have some air cylinders from hobbyking for it.

bob62

My Feedback: (28)

You do pretty work

SJN

Thanks Bob, I try my best


slow but steady progress

I mixed up some paint, and I think I have nailed it.....if you look at the picture with the cut out wheel well bins, I have actualy test painted the left one, and it is almost an exact match. (Havn`t painted the doors with the new mix yet )
I think I will add magnets to the corners of the gear doors to hold them shut tight during flight. The gear doors are quite large, and even though I have stiffened them with carbon, they still can flex a little.

rcpilotva

finally knocked out the gear in mine 2 weeks ago. minor cross wind, crabbing in, turned to set down, smooth and easy, the a gust just pushed her over  - kicked her feet right out and collapsed to port. Now to rebuild better - there was no - repeat no -  meat to hold the gear in place other than the soft balsa leading edge and two ply ribs, with holes cut out for whatever reason.
winter rebuil on both wings from underneath and do it right. getting rid of the borrowed gear and going with robarts, having my buddy mill me some new struts for the proper length for prop clearance.
will move the gear back slightly (very slightly) to allow for a better structural box around the gear....
and a repaint hopefully...

SJN

Yes, it is a shame that the gear mounts are so weak.
I hope mine will hold up a little better with the glass cloth I have added.

If not, then I also will rebuild it properly when they have torn out

bignasdy

I used a micro servo for my rarebear gear doors , simialr setup to yours but I used ca hinges instead. You do good work. Thanx for takin the time to share!
d

sodbuster 1

How about posting pics of the mount rebuild as it goes along?
Would be greatly appreciated.
Don't have a lot of experience with retracts and am sure mine will tear out again....

rcpilotva

plan to start that next month or so - my buddy andrew will be doing the 'heavy lifting' on this...

rcpilotva

complete aside - carb questions for zenoah 26's, venturis and airflow -
been trying to get my ziroli b25 to stay in the air for more than 2-4 minutes. new engines, broken in.
thought the tanks were too small (16 oz). thought the carb(s) were bad/poorly set.
one or both engines would lean out in flight, or burble and quit. (the sucking sound heard was my you-know -what sucking in air after repeated 1 engine landings. turn into dead engine several times - no choice with tree line - that will grow hair.
went back to standard clunks. test run on the ground, tethered 12-14 minutes at 3/4 throttle, 9K rpm at full. APC props.
did high speed taxi runs to find that one engine (never the same one) was slow on coming up.
fuel gone in 6 minutes.
4 experienced gas drivers, and what we learned/saw - airflow over the cowl was literally sucking fuel out the carb(s). whichever engine was on the leeward side of the wind stayed, windward side leaned out or went rich and burbled or died accordingly.
we put a hand in front of  the venturi , it would go rich, put your hand behind the venturi, it would lean out.
any of y'all had this before? didn't find anything on the build sites....
here's what we are going to try - going to 3 blade props to reduce prop speed (and power, which will make it harder to save the plane on flameout). also thinking about removing the venturis and putting a blister on the cowl to enclose the carbs, so they take air from inside the cowl. or building a deflector, sim to a hood scoop, with the opening to the rear.
ideas, recommendations, thoughts would be appreciated.

sodbuster 1

You need to baffle the cowls/ engines so there is no direct airflow over the carbs venturis.
One thing you can try is hose clamping some tubing over the venturis and running the tubing back into an
area that doesn't have turbulent air.

rcpilotva

here's what we've learned:
1) the venturi stacks on the carbs stuck out into the slipstream around the cowls (on my B 25), causing the suction over the open end of the venturi to suck fuel from the 16 oz tanks out the venturi in about 4 minutes of flight. 16 oz at 3/4 throttle on the ground gave abt 12 minutes. - the filter clunks i was using exacerbated the problem, by only allowing about 2/3 of the tank to be used before air was pulled. went back to heavy clunks. in the tanks now is the brass tube through the stopper, a small section of tygon fuel line, a 1 1/2 " section of brass tubing, another small section of tygon and the then the clunk. there is no way the clunk can twist or vibrate around - it can only move up/dwn/side to side as it needs to.
attached are photos of the baffle box my buddy and i built to cover the end of the venturi stacks.we cut the flare off the stock zenoah venturis,and glued this lite ply box on with the holes facing to the rear. a little bit redneck looking, but solves the problem of keeping steady air into the venturi tubes without having the wind blow across the opening. we lost about 50 rpm off the 2 blade props. with this. and the size/number of holes does make a difference - we actually adjusted engine speed by increasing the hole sizes on the slower engine.
2) the max speed (9200+) on the 2 blades was also part of the problem. ver-r-r-y senstitive on the carb adjustments, even though it was the brute power that has saved the plane from the engine-outs. we are going to 3 blades to reduce the sensitivity of the carb, even though the risk of plane death is a bit higher. the 3 blades are turning about 8400, but a hair less pull - the needle settings are much more forgiving.
3) using a leaf blower while the engines were running to blow in and around the cowl and venturi shroud to simulate flying condition (other than having the prop unload in flight) - wow. proved another weak point, which was an old fix. the little hole into the diaphragm on the carb. it's right behind the false cylinder heads on the starboard engine, and right in the opening on the port engine (lost a fake cyl head somewhere). the flying speed actually causes the diaphragm to not work, and kills the motor. I was able to stall either motor in about 10 seconds or less. 2 weeks ago, we flew her on a very breezy day. the wind coming down the runway would cause issues almost immediately, or on the 1st turn to change the wind direction - either into the venturi or into the cowl. 4 flights, 4 engine outs.
my buddy is going to silver solder a 2" piece of brass fuel tubing and bend it so that it faces to the rear between the carb and the cyl head. I had this on my C-47, an another's P 38, and why we didn't do this first - old time brain fart. make sure the tubing is bigger than the hole in the diaphragm plate.


Mike