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Old Oct 09, 2012, 08:03 AM
So I'M meant to be in control?
Colonel Blink's Avatar
Ilkley, West Yorkshire, UK
Joined Nov 2008
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Quote:
Originally Posted by Sundancer View Post
Bit more investigation of the trim needed maybe?.
Absolutely....!

This morning I was up at the golf course at 7am waiting for it to be light enough for another flight on my way to work. There was a little air movement, but less than a couple of knots in my estimation. I got another 10min flight in, giving 28mins total airtime so far. Manage a couple of T&Gs as well. With regards to the trim, I am now trying to analyse what the model is doing as opposed to what I am doing to the model.....

At this point I need to admit that my knowledge of trimming has been of the 'balance at the point shown then use the Rx trims' style - this being the first powered model that I have built (as opposed to assembling f0@m*$). I don't count the rubber powered stuff I did as a 12 year old, when often they would fly only a few more feet than I could chuck them. At that point in my life, trimming was what you did to the tissue which wouldnt stick down. So please be patient with me!

The glide seems pretty good - I may be able to lose a little nose weight, as I need to add a little power & up elevator to ensure a 'rolling' as opposed to an 'upending' landing from a glide approach from 50ft.

On a low throttle opening, the model flies beautifully - sedate and quiet, unflustered and unhurried. As soon as the throttle is opened above about a third, it climbs steeply and banks firmly left. This requires quite significant right and down stick, invariably leading to overcontrol and a hilariously drunken gait. From what I understand, right and downthrust is required to help tame the trim change with power. I was going to start with a washer under the appropriate mounting screw of the motor (I have the cruciform mount in 'X' orientation).

A bit of expo (negative) on the rudder would possibly reduce my overcontrolling also. What sort of figure should I start with? -10%? -90%??

I wont be putting any expo on the elevator for the minute, as it is surprisingly ineffective. Both rudder and elevator are very ineffective with power off - I expected this, but not to this extent. The elevator doesn't seem to do much power on or off - though its authority may be being overpowered by the current power on/off change of trim. If it is still weedy after I've changed the thrust line, I'll start by moving the elevator pushrod in to the closer hole on the control surface horn to increase movement and try that.

Feel free to tell me my logic is awry, or that I am simply a fool!

And finally, the motor seems reluctant to 'start' as the throttle is opened, stuttering at first. When it does start spinning, you can back it off to a lower opening than was required to get it moving. This got so bad at one point this morning that I needed more than half throttle to get it spinning, at which point it would come in with a bang, and up would go the nose and right wing. It does it a little bit at 0:50 & 6.05 on the video, but seems to be getting worse - anyone any ideas???
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Old Oct 09, 2012, 08:47 AM
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United Kingdom, England, Lancs
Joined Sep 2006
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[QUOTE=Colonel Blink;22952599
Feel free to tell me my logic is awry, or that I am simply a fool!

Neither Colonel. You've merely entered a most interesting and satisfying aspect of aeromodelling. You have built the Ajax not bought a bit of Chinese plastic! You've undertaken techniques that are new to you ie: tissue over mylar and done so most successfully. Now the matter of trimming. A bit of guidance I received many moons ago was "balance and trim." For every state of balance there is an ideal trim until one gets outside the model's "comfort zone." Nose heavy and it flies like a cowshed. Tail heavy and it flies once! Get it to a decent height, cut the motor and observe the glide. It is essentially a free flight model so aim for a free flight type glide. Slow, a little above the stall, gently responsive to the controls. Then apply power and watch what it does. It sounds as if it needs downthrust and some right too. Applying that will alter it's current power on trim at lower throttle settings. So, start again using the new trim as a starting point. The glide, however, will stay the same although you may want to re-trim to fly a little faster. Keep fettling the performance until it's right for you. Later you may wish to re-balance it slightly further back and tweak the performance again. There's a load of pleasure to be had from this procedure and it keeps ones interest alive. All the best.
ps I've just flow my Senator for the first time. Test glides only as yet as I'm short of a couple of grub screws for the prop extension. Hand glides were fine so looking forward to getting some power up front soon.
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Old Oct 09, 2012, 01:35 PM
I like real wooden aeroplanes!
Sundancer's Avatar
South-west France
Joined Sep 2007
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Very sound advice from Bob there Colonel. The word is - get the glide right, then all further adjustments to the power flight phase are thrust-line or airscrew changes. It sounds as if you definitely need some down and right thrust, add it a bit at a time. Don't overdo the downthrust, it is, after all, basically a rubber model so it SHOULD climb when you open the throttle, too much downthrust and it will hurtle around the sky in a most inappropriate manner with every chance of breaking something! At first reading it does sound as if you could cope with a slightly further aft CG, but only after you have sorted the thrust line out. BTW what prop are you using, changing this (reducing pitch) could help to sort out your "left turn with increased throttle" problem.

Re your motor starting problems; I suspect your throttle end points on the Tx need changing, certainly I have never had this problem with any of the (four) motors of this type I have currently flying. Try adding full trim in the "shut" direction and see if that helps. Exponential? I find that nothing much under 40-50% seems to have much effect.

Good fun though, all this tweaking, as Bob says. Sometimes it takes several hours of flying before I get a model EXACTLY how I want it, my Tomboy was one of the worst in this respect - sometimes (the Sportster was one) I don't touch a thing from flight one - but that's just blind luck! It is well worth the time and effort to get them just right. And aren't computer Txs with multiple model memories GREAT - once you get the thing right it STAYS right. I'm lucky enough to have a total of 64 memories spread over my three Txs (40,16,8) so I can build a lot more models yet!
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Old Oct 09, 2012, 08:03 PM
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Colonel, I don't know if your esc is programmable or not, but I can tell you I have had the exact same problem - twice. The reason for the problem in the first case was a used esc that I bought was programmed for heli throttle instead of aircraft. A quick programming change and what a difference! The second case was, as far as I could tell, simply a faulty esc.

What I know is, what you described above is just not right, so it's not something to live with.
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Old Oct 14, 2012, 05:01 AM
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mixer421's Avatar
United Kingdom, England, Kent
Joined Aug 2007
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Quote:
Originally Posted by Colonel Blink View Post
Wait no longer, Sir Sparks, for verily hast the Ajax defied the unseen tethers fastening her to Mother Earth.


And I shall describe it via the medium of dance.....oh alright then, video...

https://vimeo.com/49981366

Apologies for the video quality, but it was taken with a keycam velcroed to the frame of my glasses....
Hi Col. I am currently facing due North, on my knees, humbled by your achievement but also inspired. I haven't read the entire build log, after the first half dozen pages I skipped to the first flight video, so before I commit myself to a similar project I will study your progress in detail. Then there will be questions. What to build? Can I come close to your success? Will it all end in tears?
BTW, Dx6i with Orange RX is wonderful!
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Old Oct 14, 2012, 05:23 AM
So I'M meant to be in control?
Colonel Blink's Avatar
Ilkley, West Yorkshire, UK
Joined Nov 2008
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Hi Mike.... just on my way out, but thanks for the kind words. I will reply fully later, but suffice to say it has been a fantastic experience, and one which I will (am) repeating!!
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Old Oct 14, 2012, 06:32 AM
I like real wooden aeroplanes!
Sundancer's Avatar
South-west France
Joined Sep 2007
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Quote:
Originally Posted by mixer421 View Post
Hi Col. I am currently facing due North, on my knees, humbled by your achievement but also inspired. I haven't read the entire build log, after the first half dozen pages I skipped to the first flight video, so before I commit myself to a similar project I will study your progress in detail. Then there will be questions. What to build? Can I come close to your success? Will it all end in tears?
BTW, Dx6i with Orange RX is wonderful!

Hi Mike

If your interest is tending towards electric R/C conversions of vintage and nostalgia rubber models, you will certainly learn a lot from the Colonel's sometimes off-beat but always entertaining build log. There are also one or two more you might like to look at:
http://www.rcgroups.com/forums/showt...6#post21631890
http://www.rcgroups.com/forums/showthread.php?t=1645875
http://www.rcgroups.com/forums/showthread.php?t=1685597
http://www.rcgroups.com/forums/showt...0#post21535595
http://www.rcgroups.com/forums/showthread.php?t=1606834
http://www.rcgroups.com/forums/showthread.php?t=1591818

As you will see, electric rubber models are great fun and they fly very well.

As for finding projects; try http://www.outerzone.co.uk/vinplandex/

Have fun
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Last edited by Sundancer; Oct 14, 2012 at 06:45 AM.
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Old Oct 14, 2012, 09:24 AM
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Ajax, Ontario, Canada
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George, where does one purchase electric rubber? Surely it should be good for a 'Sparky' .....

Okay, okay...... 'bye
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Old Oct 14, 2012, 12:10 PM
I like real wooden aeroplanes!
Sundancer's Avatar
South-west France
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Originally Posted by Applehoney View Post
George, where does one purchase electric rubber? Surely it should be good for a 'Sparky' .....

Okay, okay...... 'bye
I have an AMPle stock of it Jim, so much I don't know WATT to do with it. I know there is a lot of RESISTENCE to the CURRENT trend towards electric power, in fact I guess some people find it reVOLTing
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Old Oct 14, 2012, 12:17 PM
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Ouch .....
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Old Oct 14, 2012, 12:54 PM
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United Kingdom, England, Lancs
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Originally Posted by Sundancer View Post
I have an AMPle stock of it Jim, so much I don't know WATT to do with it. I know there is a lot of RESISTENCE to the CURRENT trend towards electric power, in fact I guess some people find it reVOLTing
If you come out with much more of that stuff you'll be run to earth in a magnetic field and robbed of your joules!
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Old Oct 14, 2012, 02:03 PM
So I'M meant to be in control?
Colonel Blink's Avatar
Ilkley, West Yorkshire, UK
Joined Nov 2008
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Try as I might, I can't think of a decent pun using COULOMB......

...well, other than COULOMB down, Applehoney, the WATTer's lovely.

...and that's rubbish!!

Quote:
Originally Posted by mixer421 View Post
......before I commit myself to a similar project I will study your progress in detail. Then there will be questions. What to build? Can I come close to your success? Will it all end in tears?
Mike - I can honestly say that building the Ajax is the most modelling enjoyment that I have had in many years. Sure, there were frustrations, mistakes and the occasional 'after all this effort, how will I feel if it flies like a cowpat/crashes vertically in flames' - but as soon as the first hand glide, I knew that it had been worth it.

If you have the time and you have the desire, I suggest that you do it. I am sure that the good chaps around here will give you ample assistance and advice - and then you can be a 'remould' like me!!!

EDIT: Mike: Just sent you an IM
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Old Oct 14, 2012, 02:35 PM
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Quote:
Originally Posted by Colonel Blink View Post

Mike - I can honestly say that building the Ajax is the most modelling enjoyment that I have had in many years. Sure, there were frustrations, mistakes and the occasional 'after all this effort, how will I feel if it flies like a cowpat/crashes vertically in flames' - but as soon as the first hand glide, I knew that it had been worth it.

EDIT: Mike: Just sent you an IM
I endorse those comments absolutely. I've never enjoyed a build so much as the Senator. And to have it fly "off the board" as the saying has it and in much windier conditions than I'd any right to expect it to was magic! So I say go for it.
There are people posting on here who will be only too pleased to give you any amount of help and encouragement so you will be well looked after.
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Old Oct 15, 2012, 06:43 AM
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Joined Aug 2007
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Thanks to all for the encouragement and I will surely take advantage of the offers of help and advice. I have built many models over the last 60 odd years but of late have been tempted along the path of the, probably unmentionable on here, electric foam devices. Rather busy with household projects devised by Mrs Mixer at the moment but a bit of balsa bashing will be an exciting Winter project. One of my favourite Keil Kraft models was the Dolphin glider, perhaps an electric version (Pylon mounted?) could be quite an unusual challenge!
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Old Oct 15, 2012, 06:50 AM
So I'M meant to be in control?
Colonel Blink's Avatar
Ilkley, West Yorkshire, UK
Joined Nov 2008
3,281 Posts
Stage 2 in the trimming....

Based upon the advice I have received and because it is good engineering practice to make only one change at a time, I have:

a) Temporarily removed the noseblock and introduced a couple of degrees right and downthrust
b) Programmed in -40% expo on rudder, and
c) Increased the elevator throw.

Since the last flight, I have also managed to find an area of grass c250 x 250m, (with a completely flat area 120 x 120m) which is admirable for flying a small electric Vintage job; what's even better is that it is only three quarters of a mile from my house (by road; as the crow flies it's only 630m)! Only time will tell as to whether I get chased off...

So as the sun came up on Saturday morning (7:15am now ), I was there, Ajax in hand for the next test flights. I may fly it again in the current trim (or then again I may not) to confirm my impressions, which are:

a)The thrust line changes have definitely made a significant difference - I can now put in full throttle without having to add panic overcorrections. It still climbs and banks possibly too much - full throttle makes it pitch up to an unsustainable climb angle - ie it climbs, hangs on the prop and then stalls. Presumably correctly trimmed it should be in a sustainable climb, with a bank angle such that it continues a spiral climb, with no attempt at a spiral dive?? I think that a little more shimming is required.

b) I have already backed off the rudder expo to -25% as I felt too 'distanced' from the model at -40%

c) The increased elevator throw seems to have done nothing. In s&l flight, putting in full elevator seems to change model's attitude very little indeed! I think it acts more as a speed control than an attitude control. Is this due to the inherent FF stability, or should I have made the elevator larger? Where it does seem to help is stopping altitude loss during turns, and a big handful on the flare to land. Other than that, I truly believe that this model would fly happily on rudder and motor only (a configuration that I believe someone on here was championing).

Finally, I have cured the 'stuttering motor on tiny throttle openings' problem - by removing the noseblock. The bell of the motor was obviously rubbing on the block, but not enough to feel by hand. Being effectively a high speed stepper motor, I would think that very light throttle openings were not giving the armature enough of a kick to get it onto the next segments, hence it stuttered about where it was. The evening that I flew in the cold and damp, the problem was worsened because the block may have swollen and caused more friction.

'Learnink all ze time, learnink all ze time....Sieg Heil!' as Nanny used to say before we found she was an illegal alien. Bless her - she always had me in such a smart uniform on Sundays.
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