Britkit Build Off 2012 - Mercury Mars - Plans Published, see post #90 - Page 6 - RC Groups
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Aug 27, 2012, 05:30 PM
SB-28 UK Display Pilot
GeeW's Avatar
I'm betting George (Sundancer) does something by Elite?

I hadn't heard of them before, until recently, but am seriously considering having a go at one of their designs (No1).

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Aug 27, 2012, 11:54 PM
I like real wooden aeroplanes!
Sundancer's Avatar
Thanks Brian. Not quite right Gordon. The next "serious" build will be an R/C electric version of the KK Stunt Queen, I am currently mulling over the plan and trying to work out how to get all the gear in, where to put the battery hatch, whether to stick with the original wing thickness and such issues. However, there will be no wood cut on that one until after I've had my knee replacement operation on 11th October.

In the meantime I have the "proper" plans for the 1.8 Sportster to draw up for Kevin at Q&EFI, and after a long run of building R/C electric scale-ups and conversions with all the complications of fitting equipment and control surfaces in, I feel the need of a simple build, and decided to build a small vintage glider that I can give to my nephew who is showing aeromodelling tendencies (poor kid!), but which can also be a "Britkit" entry.

I did give the plan for the Ron Warring's Elite No. 2 a good looking at, and the Airyda "Manx Cat", an appealing tailless model, but thought something more semi-scale would appeal to the lad more, so then got out the Frog "Fairy" and "Diana" plans. I like the 36" Diana a lot, but would probably prefer to build this as a two channel micro slope-soarer for myself, so the very pretty 30 inch Fairy has got the nod, and should provide a few weeks of pleasant diversion. It will be entirely as per plan except for the addition of an auto rudder, essential if it is to be a practical performer.
Aug 28, 2012, 04:20 AM
I like real wooden aeroplanes!
Sundancer's Avatar
As you might note from the time on the last post I was up early this morning - no, not quite THAT early we are an hour in front of BST here - when the sun came up it was beautifully calm so I hobbled up to the field for another flight with the Mars, along with one with the Sportster. I have reduced the rudder throw yet again and added some exponential, it is amazing how little movement models like this really need, and enjoyed a 22 minute flight which included a couple of leisurely 2/3rd throttle climbs to the visibility limit upwards (still checking the range of the Turnigy 9x Tx/Rx combo - it performed perfectly). I still had power to spare on the landing approach so the average power consumption during the flight must have been in the 25-30 watt range, these vintage type models will fly on next to nothing.
Aug 28, 2012, 04:32 AM
Registered User
Guizzo 17's Avatar
Fantastic model SD, a beauty among beauties! Small, electric and bipe, a mix I definitely love
Aug 28, 2012, 05:35 AM
I like real wooden aeroplanes!
Sundancer's Avatar
Thanks Guizzo. How is the Radian progressing? Must be getting close now.
Aug 28, 2012, 07:23 AM
Registered User
Nice job again on the Mars George and congrats to Ali too on another fine set of in flight shots. The wing configuration certainly makes for a very distinctive (and strangely attractive) shape in the air.

Aug 28, 2012, 07:27 AM
So I'M meant to be in control?
Colonel Blink's Avatar
Nice looking model, George - and glad that it sounds like it's a nice relaxing and economical flier (now)!!!

Originally Posted by Sundancer
In deciding where the CG had to be I had referred to the marked position of the original F/F rubber plan, then worked out where it should be for an R/C model as if it were a normal biplane. Clearly this isn't going to work for this layout, which is really more of a sesquiplane, so I recalculated it on the basis of a high wing cabin model, ignoring the lower wing and setting the position at 35% of the top wing chord.
It may just be my sun-addled brain, or it may just be a stupid question that I'd have asked anyway, but....

I'm struggling a little with the logic here - does the CG need to be so different from the FF version? I can understand perhaps a little rearward of the FF point in order to take out some of the excessive stability required for FF, which would fight control inputs for RC. How does the final RC CG compare with the FF CG???
Aug 28, 2012, 09:17 AM
I like real wooden aeroplanes!
Sundancer's Avatar
Hi Colonel. Hope you have been wearing a shady hat, can't do with you being sun addled.

No, it isn't a stupid question, but I think it is all about tailplanes. Some of my other conversions - for example the Bantam and the Witch fly happily as radio models with the CG dead on, the free-flight position. The Tom Tit flies with it a little forward of the F/F position However, all the three models mentioned have big tailplanes, and in the case of the Witch and Bantam, positive cambered tailplane sections. Figures are:

Tom Tit - tailplane 20% of total (biplane) wing area, flat plate
Bantam - tailplane 35% of wing area, positive cambered
Witch - tailplane 34% of wing area, positive cambered.

Now look at the Mars

Tailplane 17% of total (as a biplane) wing area, flat plate. 25% of top wing only.

The CG position on the original Mars plan is 75% of the top wing chord back from the LE. Obviously, regarding the model as a biplane, and allowing for the 3" stagger and the fact that the bottom wing is only 37% of the total wing area, this equates to more like 60% of the total wing area, which is still a long way aft for a 17% tailplane.

I probably didn't express myself very well, but basically I think the bottom wing, set at a lower angle of incidence and only just over 1/3rd of the total area is along for the ride. If we look at it as a monoplane, the F/F CG is 75% of the top wing chord and the tailplane is 25% of the top wing area - not likely to be a stable set-up. My model balanced originally at 65% of top wing chord, which still proved to be too far aft with a 25% tailplane. It is now at 40% of the top wing chord and seems just right.

Regarding the Ajax; I think that has a pretty large percentage positive cambered tailplane, but personally I would want the CG somewhat forward of the F/F position, certainly not aft of it! You are going to be asking it to fly in a somewhat different regime to the rubber powered one.
Aug 28, 2012, 01:56 PM
Registered User
marksherlock's Avatar
George, Another charming creation from you there sir! She looks lovely..
Aug 28, 2012, 02:19 PM
I like real wooden aeroplanes!
Sundancer's Avatar
Thanks Ian, Blinkie, Mark, glad you like it. I did think this one might come out a bit ungainly - as you know that can happen particularly when you scale a model up - however my fears were groundless and although it is a strange looking bird, it really looks the part in the air and now handles very sweetly. This is another one that may well find it's way into the mag as a free plan.

I also mentioned I flew the Sportster this morning, and the more I fly that little bug the more I like it. I was really wringing it out this morning in the nice calm conditions, most of the flight was zipping around at low level "control-line" style and it is really good at this - a sort of high speed park flying reflex sharpener!
Aug 29, 2012, 03:51 PM
Sic itur ad Astra
sparks59's Avatar
Hey George, I read your submission on the Mars to Stick and Tissue today, nothing new to followers of this thread of course, but a pleasant piece anyway.

I like to read some of the contributions that are posted there, although some of them do go rambling on a bit, off topic, around it and with a bit of luck back on it again. The only thing I find irks me, which is refreshingly better here on RCG, is that you can't send a direct and immediate comment to the author. But still great to see it thriving.

Aug 29, 2012, 05:41 PM
I like real wooden aeroplanes!
Sundancer's Avatar
Yes Sparks, S&T is always good for a bit of nostalgia.

Latest on the Mars is that it will be appearing as a full size plan in Q&EFI, that is when Kevin has caught up with the others, he has the Mamba which should be appearing fairly shortly and I am just in the process of sending him the Sportster, which I guess will appear some time in early 2013, so the Mars should follow on after that, unless he decides to change the order for some reason.

When the Britkit build off is over I really must get down to doing some original designing again, I've got several ideas running around the brain, some of them to do with model aeroplanes
Sep 02, 2012, 02:13 AM
I like real wooden aeroplanes!
Sundancer's Avatar
Just to round off on the Mars; it will eventually - sometime next year as the Mamba and Sportster are already in the queue in front of it - be a full-size plan feature in Q&EFI.
Sep 02, 2012, 04:28 AM
Sic itur ad Astra
sparks59's Avatar
Well done George,
Maybe they should give you a salary and give you a job on a more permanent basis
Mar 18, 2013, 09:59 AM
I like real wooden aeroplanes!
Sundancer's Avatar

UPDATE March 2013 - Plan published

Just to wrap this thread up; the Mars was published as a "free" full size plan in the April 2013 issue of RC Model World.

My prototype is still performing delightfully.

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