AcroWot Foam-e setup - Always climbing

[PatMc]

Forget the down/up thrust nonsense it's not going to make much difference. Get the cg sorted using the dive test. Then just use the throttle & elevators properly.

[Stevo]

OK PatMc

The thrust angles are worth checking out anyway and I'll look at this later tonight... But in retrospect I can offer this information..

100' up. rolled her onto her back and pulled some up in to get her to drop vertically, with power all but off. She stayed vertical, but.. remember I've got 2mm of down on the elevator to make ot all manageable, so assuming I feed a little up into it so that the elevator is now level, it would have climbed right out of the dive.

Does this qualify as a dive test? If not I'll see what I'm doing tonight, or even tomorrow AM and go to the field armed witha hacksaw, double sided tape tape, a church roof, a small aubergine and endless patience

let me know PatMc if the above qualifies...! Thanks

Edited By Stevo on 08/08/2013 08:14:10

[graham dewis]

Stevo

Did you check the COG with it inverted.

It's not making sense.

Graham

[Stevo]

Hi Graham,

Yes, it sat on the Great Planes balancer inverted as a low wing thingy should do.

[Stevo]

CoG

Just out of curiosity, I put the figures into a CoG calculator, and 75mm gives me 35% ( I wouldn't think that Mr Foss would have got it wrong or even Ripmax published the wrong figure !!) http://www.friendlyflyers.org/cg-calc.html

 The range 25 - 33% gives me 55 - 70mm, however if tha manual says 75mm (35%) that  is what hundreds of others are setting it to. Enough Maths... It balances at 75mm on the nose, (inverted!) however a couple of posts ago suggests that when it drops vertically, it stays there - but it already has down trim set so will climb out if this is removed, indicating nose heavy.

A conundrum.

Edited By Stevo on 08/08/2013 09:05:53

[Chris Bott - Moderator]

Stevo have you looked at the trimming guide here ? There might be something useful.

[graham dewis]

Stervo

My Acro Wot COG is at 75mm inverted, elevator level with tailplain, 4mm dia washer on bottom motor screw, t's also got 25 gram of lead on the tail but thats due to all the wood & epoxy that has been added to the front end due to the 2 prangs with the concrete. Flys great on 13*6.5 ACPE prop

Graham

[Stevo]

Hi Chris - printed off and studied.

Graham, that's exactly what I have, minus the ply and epoxy of course but that will be inevitable . 75mm balance inverted, 25g on tail. however - still 2mm of down needed.

I'll say that once Ive added the 2mm of down it's very flyable

[Stevo]

Right - a little further!!!

Took it the field with some quite experienced bods... We took a punt and removed weight off the tail, and put onto the nose.

Took her up... not so much down needed now!! Climbed under full chat, but that was into a strong headwind. With a tail wind of course it was not quite so marked.

CoG at recommended, was 75mm = 35%, with weight now on the nose it comes in at 60mm, which equates to 28%. May just add a litte more, and make it secure in the cowl somewhere. However another guy at the club apparently had the same thing, but the weight fell into the motor and it... exploded.

Thoughts...?

 

Edited By Stevo on 08/08/2013 18:46:58

[PatMc]

The further forward the cg is the more the nose will pitch up as the throttle is opened.

The practical most rearward cg will result in the least difference in pitching between low & high throttle. There's bound to be down elevator trim with a rearward cg compared to forward cg.

Forward cg with bags of downthrust is OK for trainers but spoils the performance of aerobatic models.

[Rich too]

Why is that Pat? Surely with a more forward cog, it will be nose heavy and pointing downwards? Having said that my Pulse 125 is definitely nose heavy (Zenoah up front - I am going to move servos etc to the rear at some point) and needs lots of up elevator trim - but when its going at WOT it climbs quite rapidly! Rich

Edited By Dickster on 09/08/2013 06:57:42

[Bob Cotsford]

Posted by Stevo on 07/08/2013 22:50:51:
Btw.. all incidenes are spot on with nothing trapped or misaligned!

this is the one that interests me, what are you matching the incidences against? Are they specified in the instructions? If you the recommended CofG didn't make the model over responsive and you need down trim to get a flat power-off dive the I would have thought that the tailplane incidence is wrong. Could your fuselage be bowed up a degree or three?

I think Pat is saying that a nose heavy model needs more up trim, which will have an increasing effect with airspeed and cause the excessive climb on high power.  Moving the balance point back allows a zero incidence on the TAILPLANE (note, not just the elevator!) which will have a more constant effect over a larger speed range.

Edited By Bob Cotsford on 09/08/2013 08:15:32

[Alan Randall]

This is the same problem that many of us suffered with the Parkzone Extra 300, and David Ashby covered it in his review of the model. A couple of washers behind the top motor fixings cured it.

[graham dewis]

Hi

if you look at this **LINK** the COG problem is not new

Graham

[Stevo]

Hi All.!

Apologies for not replying yesterday and thanks for all replies.

I flew it again yesterday (note: my flying skills are jst a little away from 'trainer' !) and it was quite a different model. The rear stab was a little cocked (but the incidnce was OK) and I removed it all and reassembled it OK. I also drilled out the U/C for 5.2mm, drilled and tapped the fuselage bracket for 5mm nylon bolts too..

Anyhow, the flight. I'm still flying with a touch of 'down', but nothing too drastic. I rolled her over and pulled her down into an almost vertical dive, and it had no tendency to tuck under or climb out. As my last post, into wind and full chat, needs a little down to stop it climbing, but no violent pitching upwards anymore. With the wind it simply gets.. faster. Loops and rolls were fine...

So, happy Bunny, but as I get used to it I will experiment more with that CoG. PAt, perhaps it being trimmed a little like atrainer may suit my (lack of) flying skills???

Thanks all!

Steve