Stealth SB-X

 Flew and landed my COX SB-X Stealth Bomber this morning.  I was able to modify the plane and used my stooge set for tricycle.  Slow and lumbering would best describe the flight

1975 control line guy wrote:
Slow and lumbering would best describe the flight

Is the original 3-blade propeller on the model? If so; could you check the size marked on it near the hub and note it here? I'm just curious.. because the instructions don't specify the size.. only the part# 58061. The original propeller looks to be a smaller diameter than Cox's standard 3-blade left-hand prop.. which is a 5" X 3.5" (#7508) but I could be mistaken.

I'm wondering if mounting a different propeller might provide a bit more speed.. but you'd have to make sure that there's sufficient ground-clearance if the diameter is larger. If the existing prop has a 5" diameter.. you could try running a 5" X 4" 2-blade right-hand prop by mounting it "backwards".

I like your pit arrangement. That's an interesting glow-driver. Is a voltage inverter powering it?

Roddie,

The one I m flying (I have 3) I picked up used and and it has a Thimble Drome 5D 3P prop mounted backwards and spinning clockwise as you look at it.

You have a point about the prop, this is a pusher and can use a steeper pitch.  Most likely COX used what was readily available.  I wouldn't go larger than a 5D prop for this plane.

The vertical stabilizers are mockups made from a black plastic waste paper bin using the curve of the bin to steer the plane outward epoxied in place.  The stock vertical stabilizers are flimsy and would never hold up to real world use.   After this last fight I had to reinforce the underside of the plane around the front landing gear mount with JB Weld since the top of the plane has developed white stress marks on the top near that mount.

I have not had good results with double D battery box and made my own very reliable glow drive system.  I use a small portable AC portable power station powering a Nice Power DC power supply.  I  have found if you set the power supply up to 2.6 volts DC (I know 1.5 volts is the maximum   ) the engines fire much more readily.

I have found that knee pad indispensable too.

Flight of the COX SB-X Stealth with a 5-4-3 prop (thanks Roddie) on 25 feet 10 pound test spider wire.  Other than the rubber spinner popping off on the "landing" it went well.  Even though the elevator only has 2 settings "up" or "crash land" I will always have this plane in my lineup.

Nice!! So it's a 5" diameter X 4" pitch 3-blade? What make/brand propeller is it?

Roddie,

It is a no brand black nylon prop with looks like a 1/4" arbor.  I went into my eBay purchases and couldn't find a specific purchase; so it must have been in a parts lot that I picked up along the way.  I have 5 more though if this one fails; or I want to expand my squadron.

Regardless the plane now does about a 4.75 second rotation where before is in excess of 6 seconds.  The rate of fuel consumption has increased so I may change to a larger fuel tank to get at least a 2 minute run.

Is the prop a 2-blade or a 3-blade? Tractor or pusher?

3 blade:

Well I have figured it out.

I went into the box I found R and unmarked props in the same packaging.  Doing an eBay search I learned what type of prop it is.

I have installed and successfully ran a polycarbonate high performance racing drone propeller on a 1987 COX pusher plane  

I believe that the "R" designation denotes "Reverse-Rotation".

I have bench-ran drone props without incident.. but have been warned that they can fracture when used on a petrol engine. I've been told that this is something having to do with the piston's reciprocating-action transmitted to the crankshaft.. which is a non-existent with an electric motor.

Safety goggles should definitely be worn when running an aero-engine/motor regardless. Better to be safe than sorry.

Note the photo below which compares blade-root cross-sections. The one with the "RED BOX" is a drone (electric) prop.

Point taken.

For example, when powering a 2300KV motors with a 3S LiPo battery (12.6V), the motor would spin at about 28980 RPM.  This COX service engine will do about 12000 RPM.

All planes undergo a preflight inspection including flexing and inspecting the props for defects.  So far this prop has 3 flights and 4 bench runs and looks good.  I will keep experimenting with caution and let you know how it goes.

Just for fun I did try to break one, and couldn't.  

1975 control line guy wrote:
Point taken.

Just for fun I did try to break one, and couldn't.  

That's pretty convincing.. Were you able to trace the manufacturer/brand?

Bad comparison Roddie lol, not all E props are that weak at the hub - clearly a biased photo

APC E props are the same material in grey with some being a carbon blend
in black. I have flown E many sizes without ever throwing a blade .010 thru .09.
Can recommend that brand there are others that are worthy. Just good common
sense to do a strength test and judge the material / design prior to use.

Example this high pitched APC E prop can handle 3 to 4 times the output of this TD.
There are speed vids on youtube with on board data loggers pushing over 500w with this 5.5x6.5  E prop!
Modified for the power of a .051 TD APC E prop cut to 4.22x6.5N


Example:
EFXTRA 6S APC 5.5X6.5 Carbon prop version.
Massive power to the small prop: 1450mAh 70C 6S


I did IC test the prop with a powerful Picco .05 engine prior to using it with the TD:

Picco .05 / Profi 1/2A Tuned Pipe / APC 4.22 x 6.5N E / 164 mph prop pitch speed
Perfect size load for the TD, the Picco engine kicked it's butt in a fully loaded static state.
Static power per calc: 26,566 rpm / 10.3oz thrust / .278hp - 205w
Est. unloaded state + 6.4k rpm / 32,566 rpm / 203 mph prop pitch speed est. 190mph 1/2A

1/2A Nut wrote:Bad comparison Roddie lol, not all E props are that weak at the hub - clearly a biased photo

APC E props are the same material in grey with some being a carbon blend
in black. I have flown E many sizes without ever throwing a blade .010 thru .09.
Can recommend that brand there are others that are worthy. Just good common
sense to do a strength test and judge the material / design prior to use.

I'm actually glad that you commented to that effect Brad. Because of the popularity of drones/quad-copters; replacement propellers for them are plentiful.. as well as economical. What's more; they're almost always offered in "sets" with a R/H and a L/H.. (reverse-rotations) whether buying one or several.

Replacement OEM "pusher-props" for our Cox engines have been increasingly difficult to source. Modelers with Cox Prop-Rods and Shrikes have lots of options for running them now. One could also run a TeeDee engine in a "pusher-configuration" if desired.

Roddie,

I did an eBay search and this what I found:

HQProp 5X4X3 V1S 5040 5 Inch 3-Blade Propellers Set (2x CW / 2x CCW) Poly Carbon $6.99

SpeedyFPV

I am very sure this the supplier's prop that turned by SB-X into a 4 second roaster.

1975 CLG