Vintage Model Company cub 4 channel trainer.

[Denis Watkins]

JD8 is always right EGB

Set your bleed screw to cover Half the hole, and make sure the Hole is fully unblocked.

Double check your tank for pressure leaks at pipe joints and the dreaded flimsy centre screw on rubber gland stopper tanks.

Get a 4oz SLEC tank in it you can, Blue tank, 82mm 42mm x 42mm.

Edited March 28, 2022 by Denis Watkins

[EGB 953]

Thank you for the sage advice. How do i know when the airbleed screw covers half the hole? it is really small? I will take a look at the SLEC tank!

[J D 8]

 A good light and magnifying glass needed.

To get the slow running right first get the engine running fast and warmed up [ main needle set for full power ]  then slow to tick over for 15 seconds [ ish ] then open throttle. If the motor revs up slowly sputtering and missing then the air bleed screw needs to be opened  [ turn anticlockwise ] about half a turn and try again.  If the engine just cuts out when throttle opened then the screw is set too lean and needs to be turned in clockwise.

 It is always a good thing when in the air to get into the habit of steadily opening and closing the throttle and not slapping the stick one way to other.

[EGB 953]

4 hours ago, J D 8 said:

 A good light and magnifying glass needed.

To get the slow running right first get the engine running fast and warmed up [ main needle set for full power ]  then slow to tick over for 15 seconds [ ish ] then open throttle. If the motor revs up slowly sputtering and missing then the air bleed screw needs to be opened  [ turn anticlockwise ] about half a turn and try again.  If the engine just cuts out when throttle opened then the screw is set too lean and needs to be turned in clockwise.

 It is always a good thing when in the air to get into the habit of steadily opening and closing the throttle and not slapping the stick one way to other.

Thank you this is extremely helpful. I will have a go at tuning it this weekend!

[EGB 953]

So, following the excellent advice from the forum, especially @J D 8 I tuned the engine yesterday (opened the airbleed) and got vastly improved acceleration, while being gentle on the throttle.Had three really good flights, am going to mix in some down elevator with throttle now as at over 50% throttle she climbs very quickly.

 

Two remaining issues, on one flight, I tried ROG take off (instead of throwing) and the engine did not want to accelerate, it sped up slightly but not very quickly and I had to abandon, so i think i should possibly open another half turn. or possibly after idling so long I should have just opened throttle a bit to clear the motor as once int eh air she behaved very well.

 

Other issue is too much wobble in the wheels which i think adds to challenge of steering on the ground.

 

That aside, the sheer pleasure of having built the thing from scratch, converted to IC, taken the gummed up engine, taken it apart, cleaned and rebuilt it and the whole package now actually flies nicely. I couldn't stop smiling.

 

Many, many thanks to all who have followed my posts and offered advice, it is helped massively.

[Denis Watkins]

Just add tube bearings to your wheel and axle to take up the slack.

Keep biro tube, brass off cut fuel pipes and spray bottle tubes in your scrap box.

Otherwise, for larger I/C or heavier electric, plan to have brass bearing tubes available to make close fitting wheels as most operate in the 3mm - 6mm range and can be drilled as such or a bearing added from pre-prepared tube.

[MattyB]

1 hour ago, EGB 953 said:

So, following the excellent advice from the forum, especially @J D 8 I tuned the engine yesterday (opened the airbleed) and got vastly improved acceleration, while being gentle on the throttle. Had three really good flights, am going to mix in some down elevator with throttle now as at over 50% throttle she climbs very quickly.

 

Can you not add some downthrust, or maybe pack up the TE of the wing a tad? Nothing wrong with throttle to elevator mixing per se, but if the tendency to climb under throttle is as pronounced as you say it would be better to reduce that substantially through a combination of thrustline and decalage, then fine tune with a mix.

[EGB 953]

20 hours ago, MattyB said:

 

Can you not add some downthrust, or maybe pack up the TE of the wing a tad? Nothing wrong with throttle to elevator mixing per se, but if the tendency to climb under throttle is as pronounced as you say it would be better to reduce that substantially through a combination of thrust-line and decalage, then fine tune with a mix.

You make a very good point and I had forgotten I was going to look at this. the angle of attack (if that is the right term) of the wing is quite high in the design of the plane, I think to make it easier for the 3 channel version. I put a small degree of down and RHS thrust on the engine, but I was going to look at changing the wing angle slightly, so maybe i will experiment with the wing TE in small increments.

[J D 8]

 Packing the wing trailing edge a little at a time is a good way of getting the climb angle you want, less touchy than  doing adjustments at the tail. The model design itself harks back to free flight days when thrust and wing adjustments were common I recon.

      My old free flight Matador [ now RC assist ] is throttle, rudder control with a small trim tab elevator on a switch. throwing the switch gives some down which enables the model to penetrate into wind when if you just opened the throttle it would only climb.

[EGB 953]

56 minutes ago, J D 8 said:

 Packing the wing trailing edge a little at a time is a good way of getting the climb angle you want, less touchy than  doing adjustments at the tail. The model design itself harks back to free flight days when thrust and wing adjustments were common I recon.

      My old free flight Matador [ now RC assist ] is throttle, rudder control with a small trim tab elevator on a switch. throwing the switch gives some down which enables the model to penetrate into wind when if you just opened the throttle it would only climb.

Lovely model - what's the protrusion on the right wing? 

 

[David Davis]

46 minutes ago, EGB 953 said:

Lovely model - what's the protrusion on the right wing? 

 

It's a trim tab, bend it upwards if the model persists in turning left!

 

There's one on my old Junior 60 to compensate for a warped wing.

Edited April 5, 2022 by David Davis

[J D 8]

   As above. Just a bit of aluminium from a drinks can for the same reason, it is 50 years old and wing is still covered with original tissue and many original patches as well as some newer ones. Tail was recovered with silver lightspan when radio was fitted some years ago.