'Jemima' vintage model from RCM&E plan - build log

[Stuart Eggerton]

Well I have away for a few days, so sorry for the delay in replying to you Stewart.

First up is the cowl, I have not added in the balsa below the window area yet, but will do in due course. I tacked the hatch on with a couple of drops of cyano to allow the hatch to be shaped and blended into the cowl / fuselage. I decided to fix the cowl and not have it removable. My motor was quite long so I needed quite a large diameter circular hole in the front of the cowl, this is big enough to allow motor extraction I hope! if I need to remove it for any reason.

 

 

The the wire undercarriage bound with string and pva, unconventional, but hey ho!

The covered and hinged tail feathers

Tail wheel installed and bound into rudder

 

 

Edited By Stuart Eggerton on 26/03/2013 22:22:18

[Stuart Eggerton]

The model so far, and rigged up

[Former Member]

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[Stuart Eggerton]

Hi Stewart, I got the snakes from Slec, the hinges I had in my tool box and are the square plastic ones joined with a small brass pin, you can use mylar hinges if you like, it's not critical as long as the control surface can move freely without binding or snagging.

The size of the hinges is 27mm x 11mm (assembled), look around online and you should find something suitable.

I bought some M2 threaded rods from Blackburn models and the threaded end screws into the snake inner (yellow). I cut the threaded rod to size and slid a nipple clevis on to the end, these can be adjusted for length by a small brass screw. These were also from Blackburn models.

I made oblique holes at the exit point for the snakes. These were a bit big, so after fitting and checking controls work I tend to tack glue with cyano and then fill and gap around the snake / fuselage interface with some wood / epoxy/ filler? it's up to you.

I used plastic control horns from Blackburn models as well, these seem OK, for a model of this size, metal are the best though

Above are M2 threaded rod, typical hinge and joiner and nipple clevis. There is always more than one way to skin a cat (poor cat!) and loads of different ways to do the control runs. As long as the end result is slop free, no binding, is accurate and no double neutral. Remember your servos must be big enough to move the surface and deal with expected flight loads!

The rudder linkage, showing where the blue snake outer exits the fuselage, inner yellow snake inner is just visible, this is screwed a length of m2 threaded rod.

The m2 threaded rod is cut to length and slid into the end of the nipple clevis. Remember to leave enough room between the end of the blue snake and the start of the nipple clevis to allow full deflection of the control surface, note my rudder is fully deflected to the left and has not reached the snake.

You can see the plastic control horn in the shot too.

Above you can see I have installed my servos, I decided to get them really close up to the front, but remember to make room for your battery lipo pack and esc and rx etc!

I have yet to fit threaded rods to these snakes. Try to make your snakes run as straight as you can if possible as bends and curves accumulate friction with each curve added.

Hope this lot is helpful!

Oh and just a quick piccie of the battery pack mounting plate. I mounted it at an angle like Jim did to get the battery at an angle and hence more weight further forward.

Just shout if you need any more pics of this installation. I am off after today and back to forum on Tuesday.

[Stuart Eggerton]

Coaming and cowl shaping

The next step I took was to add in the 1/16th balsa sheeting to make the curved part which the bottom of the clear canopy rests on. The hatch slips underneath this part as shown in the picture below.

The hatch and fuselage were blended together as well as the coaming to make a pleasing shape. A Jim say's it's probably not critical to follow the design to the letter but put your own interpretation on it.

I attached a piece of balsa under the coaming so I can attach my ESC with velcro. Rub some cyano into the wood before adding the velcro strip as it helps the strip stick better.

You can see I have added the battery carrier. This was not a box so much as a strip of 1/16th ply just wider than my battery and with a couple of balsa stringers added each side for strength.

This is glued at an angle which allows the battery to just fit inside the hatch and just miss the bottom of the fuselage, thus getting the maximum amount of weight forward. Again I glued this in with cyano and added velcro strips to battery and battery holder.

Servos

You can see the servos have been installed now, two standard sized ones. Mounted on balsa rails, I did add a strip of ply on top of the balsa rails to give the screws something to 'bite' into. We don't want those servo's coming loose, oh no!

Control snakes and fittings

For the controls rods I used plastic snakes, threaded wire and plastic nipple clevises.

[Stuart Eggerton]

You can see the servo installation in the picture below. I used a blue plastic outer snake, with a yellow plastic inner snake within this. Screwed into the yellow plastic inner was the threaded part of an M2 rod. The m2 rod was cut off at the correct length and inserted into a plastic nipple clevis, which goes to the servo arm. Metal clevises are always better though!

I spaced the servos so that the servo arm would be quite near the sides of the fuselage, so I could run the snakes near to the sides of the fuselage. Small locating pieces were used to hold the snakes against the fuselage at various points along the snake length.

You can see the exit points in the tail of the aircraft where the snakes emerge. Including the threaded rod, nipple clevis and horn.

Below you can see the finsihed hatch, dowel is to provide a grip for fingers for hatch removal!

Undercarriage is shown below with saddle clamps, I need some proper screws for mounting it though.

 

Next stage is to fill in around where snakes emerge from tail and then cover the fuselage. I need to cut and fit the windscreen too.

Edited By Stuart Eggerton on 02/04/2013 22:53:04

[Stuart Eggerton]

I have not posted on the forum for a while as someone has made an offer on my house and I have accepted and now running around getting it ready for the surveyor!
I have just about finished Jemima and have actually flown her! she flies well, although I need to look at double neutral problems on the elevator. I will give a full update and video when time permits. Why can't they buy my house in the winter argh!

[Stuart Eggerton]

Hope the other Jemima builders are doing well, it' s a great model and well worth the build I flew into a dust devil/very strong thermal with Jemima and she leapt up fifty feet in a second, the fill in breeze was about 25 mph and models on the ground were picked up and whirled about. =-O

Edited By Stuart Eggerton on 09/04/2013 23:00:14

[Jim Newberry - Nuviation Ltd.]

That's brilliant Stuart, well done! Pleased to hear the maiden went well and you enjoyed the build!

Jim.

[Stuart Eggerton]

Hi Jim thanks yes it's been a nice build, good traditional construction, strong, well thought out.
The motor I have used produces about 250 watts which is more than adequate. I was having a bit of a problem with a pronounced dutch rolling tendency, this was traced back to a very bad double neutral on the rudder! the elevator suffers too, so I need to tweak these. I had mounted the snakes too close to the servo arms making too much friction hence the double neutral problem.
When I get time I will make the adjustments and re-fly the model.

Edited By Stuart Eggerton on 11/04/2013 14:59:33

[Stuart Eggerton]

Here is the first flight of my 'Jemima' model is almost finished

Model was flown by ace test pilot Tom Wright. I did the video, sorry for the shaky start.

 

Edited By Stuart Eggerton on 11/04/2013 21:46:11

Edited By Stuart Eggerton on 11/04/2013 21:46:55

Edited By Chris Bott - Moderator on 28/04/2013 17:49:54

[Jim Newberry - Nuviation Ltd.]

That's brilliant, well done Stuart! Really enjoyed watching that, hope you have lots of fun flying the model!

Jim

[Stuart Eggerton]

Thanks Jim, yes it's a nice model to fly mine came out a shade over 4 lb which is a bit heavier than yours, I do have a tad more wing area than your model so I supsect the wing loading will be comparible with yours

Edited By Stuart Eggerton on 12/04/2013 14:47:22

[Jim Newberry - Nuviation Ltd.]

Well I used very soft balsa for mine - but it was designed to have wing loading to spare, as it were, to allow it to carry things like cameras, floats, bigger batteries etc and also to allow for other builders to use denser grades of wood (in my experience, most builders over spec their wood) as you said, your model has the recon wing which will not only add a little more weight but also allow it to carry more weight. The next Jemima variant (working name at the moment is Jocasta) will have the 60" wing like yours but will also have ailerons and a sheeted D-box, both of which will add weight. The fuselage will also be a little longer so I reckon the final weight will be closer to 4.5 - 5 lb. Now that you have flown yours, I would really appreciate your thoughts about things that could be improved in the design - any aspects you liked or disliked? Any feedback, positive or negative is greatly appreciated!

Jim

[Peter Marsh]

Stuart, can I just jump in here and say that your excellent blog has inspired me, as a returnee to this great hobby, to have a go at Jemima myself.

I'm gathering together all the necessary, and I see that you refer to 'ordinary' servos.Can you give me a bit more detail regarding size etc?

[Stuart Eggerton]

Hi Peter, thanks for your kind comments, I used 41 gram servos from Giant Shark i.e. **LINK**

These are digital servos and more than adequate for Jemima.

Hope this is helpful?

[Stuart Eggerton]

Hi Jim, I will give a full review in due course. Just very busy at the moment trying to find a new place to live lol, so will add a few grey hairs I think!

The Jocasta sounds like a nice model, should fly really well

I was wondering if your Jemima suffers from any dutch rolling? I tend to get a bit on take off. I did fly Jemima in a 10mph + wind and she coped very well, but must line up exactly with the wind as the undercarriage track is quite narrow.

[Jim Newberry - Nuviation Ltd.]

Hi Stuart,

i find the Dutch rolling tendency for rudder/elevator models can be overcome with a good dose of exponential. Did you use any? I always use plenty and find it helps. As it understand things, with a model lacking ailerons a good amount of skid is required before the dihedral comes into play and starts a roll in the direction of turn. Once it starts, however, it keeps going beyond the amount required and then has to roll back to a point of equilibrium, by which point you've countered with opposite rudder and the process continues. In my experience, the solution is to start the turn quite gradually to give all the forces chance to keep up with one another. One way to achieve this is with a feather touch on the rudder control until the turn is established or to use plenty of exponential to limit the sensitivity around the stick centres. Let me know if this help.

Jim

[Former Member]

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[Former Member]

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[Eifion Herbert]

The undercariage does indeed look tough, I was quite surprised how thick 8SWG is in the flesh when it arrived. Won't fit in my wire bender, think it's going to be a vice and hammer job!

[Geoff French]

Just finished my Jemima, an interesting build - very 'chunky' construction, a million miles away from my first electric model which was powered by a brushed motor and nicads and only then managed to stagger round despite its flimsy light build. Thanks Jim for prompting me to get a balsa stripper after my years dithering, it was so nice to be able to cut a LE strip exactly to size required instead of substituting an oversize strip and whittling down. I too has the problem of fuse side cracking at the joint so have re-inforced it with extra gussets. Will now attempt to attach a couple of pictures.. Also I made a few changes (as you do) in that I created glazed cabin side windows, put on slightly larger wheels and a tail skid since our grass flying field is a bit rough., put on slightly larger wheels and a tail skid since our grass flying field is a bit rough.

[Peter Marsh]

stuart

I'm at the point of attaching the motor, however I see from your pic that there seems to be only a tiny length of prop shaft poking through the cowl,

It seems that in order to attach the prop, the cowl would have to be sanded down to make it much thinner. Or have I got it all wrong?

[Stuart Eggerton]

Hi everyone, I have been pre occupied with all sorts of things!. Wow Geoff your Jemima looks great, nice colour scheme and nice touch with the windows

Peter, yes I had to sand the front face of the cowl a bit to stop the prop catching on it.

A couple of weeks ago I managed to get a bit of flying in with the Jemima, the video is below.

It was a bit choppy on that day but my girlfriend Suzanne did a sterling job at videoing.

 

I did stall it in quite hard through the wind gradient but no damage one

 

Edited By Stuart Eggerton on 12/05/2013 09:31:31

[Stuart Eggerton]

Thanks Jim for the Dutch rolling advice, now I have sorted out the double neutral problem the dutch rolling is not as pronounced. I will try that exponential in due course.