Ripmax ARTF Wot 4

[Alan Matthews]

I have just finished building my artf WOT 4 which was very easy - I've been flying (mostly gliders ) for 30 years and am upgrading from a Super Air with an Irvine 53 to a WOT 4 with the same engine.

 

One last thing is final location of the fuel tank provided.

 

I feel that for best location the "bung " end of the tank should perhaps be pushed thro' the hole in the engine bulkhead - but it will not quite go through - is it meant to, because if so I will have to enlarge the hole in the wood a bit.

 

I'm sure it will probably be OK either way, but if the bung end of the tank does not locate in the hole, then there may be a possibility for the pipes to be pulled off the tank tubes.

 

All advice gratefully received ( the closed loop rudder seems to work OK but is a bit of a fiddle to adjust and I feel that the threaded bar is not really long enough to match it with the servo throws properly.

[Biggles' Elder Brother - Moderator]

HI Alan,

 

I am not familiar with the ARTF WOT4 - but I have been the proud owner of the old original kit version. In some models it is intended that the bung section of the tank pokes through a hole in the firewall and us usually located there with, say, silicone adhedsive.

 

But its by no means essential, what is essential is two things and one recommended;

 

1. that the tank can't move around. If its fixed in then there should be no danger of the fuel pipes coming off the pipes.

 

2. that the tank centre line is in line with the engine carb

 

3. I'd suggest that the tank has a bit of padding to gaurd against vibration induced fuel frothing 

 

Sorry but I don't quite follow your second point about the threaded bar on the closed loop system - can you try to explain it a bit more?

 

BEB

[David Ashby - Moderator]

Hello Alan 

 

Good advice from BEB re the tank there.

 

I've built the ARTF WOT4 and flew with the threaded bar supplied. I'd suggest you fit and fly, see if the rudder throw afforded is enough for you and go from there.  

[Martin Harris - Moderator]

Best set-up is a true parallelogram with the servo arms and horns having equal (effective) lengths and the horn's holes being on the hinge line.

Other than a lack of mechanical nicety, as long as the servo arm is shorter than the horn arm then it should all work OK as the "dead" side will slacken.  Airflow should prevent any untoward effects in any normal forward flight condition.

[Alan Matthews]

Thisis a reply to Biggles elder brother which was on an email to "alerts at modelflying" but for or some reason was not accepted so is probably not in the correct chronological sequencwe- but thanks to the others as well for the advice.

 

 

For the closed loop system on the ARTF, a length of threaded rod is passed thro' the rudder with a nut and washer on each side. Then nylon parts with a small hole in are screwed onto the threaded rod on each side for the connections for the closed loop to go to.

 

The rod length is not very big so that quite small movements of the closed loop cables result in large rudder deflections.

 

Mechanically this is never good because then even with very short servo arms one has to run the transmitter at about 50% to achieve reasonable control for fairly gentle flying.

 

Also it must always be best to use longish arms at both ends of any system to reduce the effects of any backlash in the system and the short length of what are in effect cranks on the rudder makes its operation more sloppy than necessary.

 

Does this clarify the situation a bit.

 

It is however not easy to set up the closed loop with the system provided with the ARTF so that all the transmitter settings are at zero (including trim), servos in the centre etc. which is where I like to start.

 

[Biggles' Elder Brother - Moderator]

Hi Alan,

 

thanks for the clarification. I remember seeing this on a WOT4 ARTF now. I would go with David's advice on this - i.e. build it as is for now. On a model like the WOT4 you want to hiae lots of available rudder movement - you almost can't have too much! If you find it a bit oversensitive for S&L dail in some expo. but it unlikely that you'll need it.

 

In my experience I've never see back-lash or slop in a taut closed loop system, and I've done loads - including closed loop ailerons. I'd say they are the ultimate in "slop-free" configurations. So I'd go for it and try it out before changing it. The original kit had a closed-loop rudder and in my opinion it was one of the best points in a very good kit. Mr Foss knows a ting or two about designing model planes

 

BEB

[Martin Harris - Moderator]

Most plans/build instructions show quite small rudder movements but full size almost invariably have much more angular deflection. 

 

I tend to set the maximum movement to parallel with the inner ends of the elevators on scale models which is usually around 45 degrees either way and the same for fun-fly type models.  The one exception is my Panic where the rudder goes as near to 90 degrees either way as I can get it - but it is a silly thing!

 

  I can't say I've ever felt the need to reduce the movement and as BEB says, there's always expo. Spins (and recoveries!) are enhanced and the main benefit is in ground handling at taxi speeds.

Edited By Martin Harris on 18/08/2010 23:44:43