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Keith Evans 328/09/2020 10:23:35
426 forum posts
268 photos

After my last build ""The Kamco Kadet" I was looking for something new .

I was struggling ,until I came across the plans and short kit of the "Arup".

They were hidden away and only came to light during a major tidy up of "The Play room" as Sarah calls my work shed .

I must have purchased this about 6 or 7 years ago but was put off it as the wing is built vertically and I had never done this before .

I've actually started this about two weeks ago and as the build is "different " I thought some of you may be interested to see how I'm going about it .

For those who do not know what the Arup I'll add some photos taken from the build article . .

Keith Evans 328/09/2020 10:49:11
426 forum posts
268 photos

This is the Keith Humber plan and was featured in the "Model World " magazine Feb 2010 .

Before starting a build I study the plan , the laser cut parts and build article very closely .

A few issues I've found so far .

The wing rib spar notches are not correct .

The centre rib spacing does not correspond to some of the former dimensions .

Some of the ribs are longer than others .

I've also modified the plan .The fuselage is lengthened to accommodate a larger tank .

the engine will be side mounted .

I'll do away with the glazed cockpit and make the whole top front a removable unit

I'll also re rout the ail. snakes to do away with the bellcrank system .

I'll remove the ail pivot mechanism as it was designed out in flight development .

The engine beams will be replaced by an engine mount .

That's all for now .I'll be back with some build photos later and some of the issues I encountered .


J D 828/09/2020 12:19:06
1626 forum posts
87 photos

Pre war very low aspect ratio aircraft I think it had the nickname " the flying heel". Of similar layout the later Chance Vought " flying pancake."

Recently I came across a video of a modern home build of similar lay out in Aus I think but can not find it again.sad

Edited By J D 8 on 28/09/2020 12:19:29

Martin_K28/09/2020 13:27:14
206 forum posts

I am on the Sarik Hobbies mailing list. They have sent multiple promotions featuring this model in the last few weeks. (You may not be the only person in the country building one).

Keith Evans 328/09/2020 13:43:32
426 forum posts
268 photos

These are the two very large plans I'm working from.

You can see where I've marked where the removable cockpit will be and the lengthened front nose .

I read on one review that the builder actually built the plane on the floor with large wooden supports .My shed isn't big enough for that .! !

Before construction started I marked the centre lines of all the end ribs ,the L.E. and T.E. and all rib positions .

During the build I found it a help to notch the T.E. to allow for rib length variations and to keep things straight .

If i was doing it again I would do he same for the L.E.

While doing the centre lines I marked the position of the ail. snake runs .These were determined by laying the snakes over the plan and seeing if there was free movement . I also worked out what if any snake supports were needed for these and those for the rudder elevator and throttle .

I checked the servo positions and changed these on the plan .


Keith Evans 328/09/2020 14:33:59
426 forum posts
268 photos

Here goes the build.

You will notice the use of clamps ,rubber bands ,pins , straight edges spacer blocks etc to try and keep everything straight and square .The mark one eye ball is problematic for me as I wear vari focals , and for those who know , every thing comes out as a curve ! ! ! I was quite pleased as only a few ribs needed adjusting before the T.E. was added .

One thing that is not too clear on the plan are the gussets .They are masked by the T.E . in the drawing .If I had noticed this earlier I would have added these to the T.E. before adding it to the ribs as it acts as a good support for the end ribs .

The spars were made up of three laminations of 1/16" ,1/16 "and 3/32 ".This combination made up the right size for the slots in the ribs . It was either this or recut every rib slot.

The first lamination was of 1/16" used straight .I completed one side of the wing with one lamination and then did the other side .I repeated this procedure for the remaining 1/16" and 3/32" but pre bent using water and a thumb nail ! I

I used C.A. for the L.E. joints and aliphatic everywhere else with a little bit of balsa cement if there was any slight gap filling to do .

I can't emphasis too much the need for constant checking . The centre lines were a great help .

Later I found it far better not to bend the rear most spars but to cut them off and replace with 1/4 shaped balsa .This will help with the tip snake runs and mid spar gusset fixing .

Yes two sets of hands would make a difference but wit patience it can be done .

I'm awaiting a delivery from the Balsa Cabin to complete the wing . It should be with me in the next few days .

It's mainly for the L.E. sheeting the cap strips and the T.E. Note that near the main spar the T.E. is in plan view and needs to be adjusted for the true dimensions .I'll probably use some card board to develop this .

In the mean time I'll crack on with bits of the fuselage and the elevator .


Keith Evans 328/09/2020 18:36:21
426 forum posts
268 photos

Here are more photos of the wing build

I've shown the end and side wing gussets . Note the rear gusset is larger than that on the plan as I thought this may be a potential weak area .

Both snakes are now in position but not yet fixed . This is so I can better determine their relationship with the servos and snake support bulkhead .

A fair amount of the central wing rib has been removed to make way for the new servo tray ,This is made from 1/8" ply with 1/4"x1/8" hard wood servo screw supports to the rear .The whole mount will be fixed to 1/4"x1/4" balsa rails fitted to wing ribs W2 .

The snake exit point is lead through a slot in the 1/4" sheet tip . This will be filled in when the snakes are permanently installed .

You may also notice in one of the photos how the width of former F3 has been widened ---the one with the beam cut outs .

Hey Ho onwards and upwards .


Max Z29/09/2020 08:53:39
559 forum posts
248 photos

The Arup....yes I did consider that a couple of times. I did build a scale model of the Grumman V-172 "Flying Pancake" many years ago, twin electric drives and all, but it would not fly (except for one very tight looping, straight from the launch surprise).

I am wondering about those snakes driving the ailerons, it seems to me that those 180 degree half-loops will give you a lot of play in the movement of the control surfaces. Can't you install the servo's close to them with a more or less straight linkage? Plenty of powerful yet light servo's around these days.

Keep at it, I like it.


Edited By Max Z on 29/09/2020 08:55:01

Keith Evans 329/09/2020 13:02:34
426 forum posts
268 photos

Hi Max and thanks for your observations .

When I came to modifying the Arup ,ail. control was near the top of the list .I do not like bell cranks ,apart from those in my control liners ,because of potential slop over time from both the main pivot and the holes for the wire rod connectors .

I looked at small servos fitted close to the exit points around about between the third and fourth outer ribs .

A torque rod system running along inside the L.E. operated by a single servo in the centre bay .

The long curved system I've shown .

I went for the curved snakes because I have at least two other designs with similar layouts .In practice they are pretty much slop free and work well .I fly very sedately with no violent aerobatics where slop could be a killer .I also had them available and no mini servos to hand . If I do experience any problems then I'll consider the mini servo route .

Please keep coming up with suggestions as it will certainly help me and other possible builders .

On another point I lengthened the nose for two reasons .

The write up article suggested a lot of weight was required in the tank bay area to get the C.G. in the right place .and that only a small tank could be accommodated .So I sacrificed scale looks for something more practical in the weight distribution department.

The removable ,planked , top canopy is to allow for easy access to the tank and servo bay .Yet again it was a practicality issue and the canopy glazing went out of the window (pun intended) .

Right ,back to the elevator .

Keith Evans 329/09/2020 18:26:54
426 forum posts
268 photos

Here goes with the elevator .

Same principle as for the main wing. This was a lot easier ! !

The T.E. was added by holding the assy .in my hands .

The cap strips were added and it is all done .

The shaping of the L.E. will be carried out by spot gluing the elevator to the T.E. of the main wing ,when that is complete , using a mini plane and sanding block .

Going back to the use of ail. servos ---it may be possible to fit them into the front ail. stubs and connecting with a straight push rod .Whatever you do though ensure servo lead holes are made before building the main wing .



Keith Evans 330/09/2020 19:00:07
426 forum posts
268 photos

Slowly plodding on .

Wing stub and aileron construction .

Same as elevator .Centre lines and straight edges .

I will profile the L.E. when I start doing the same for the wing itself .Hope to make a start on the fuselage soon .



Keith Evans 301/10/2020 17:19:05
426 forum posts
268 photos

Started on the fuselage today .

Joining the supplied parts before modifying .

The next shows the shortened nose cut at the down thrust angle and trimmed bottom edge .

I've marked out the doublers onto 1/16" ply .As there is a sheet of 1/16" ply for laser cut ply redundant pivot reinforcement ribs still included in the short kit pack ,it would have been better to have included the doublers instead .

Marked out the former positions .

Drying out under weights .! !



Keith Evans 302/10/2020 18:39:20
426 forum posts
268 photos

As I have decided to use a commercial engine mount and to mount the engine on its side I did not require the beams themselves apart for alignment purposes . I've made up a sacrificial jig as shown out of 1/2" square balsa .

As I have made another solid engine bulkhead I did not fancy making "beam " holes and re filling them where the captive nuts and bolts will be positioned .So the balsa beams will act as a good guide for alignment along with the guide lines marked on the ply doublers .

What I did not want was everything being square on the fuselage but not with the wing itself .

For those who may go down the full beam mounting route be aware that all the beam cut outs need to be checked ! !

The jig is only glued to one former and rigidly held in place .The rear former will be removed and assembled into the wing .

The fuselage will be constructed by inserting the jig into the wing from the front ,engaging with the former now placed into the wing and the fuselage sides slid over the wing .Again a lot of alignment marks will be made .

The balsa jig parts in the tank bay will be removed at a later date .

Note ,as I have modified the fuselage in certain areas I have been modifying the supplied formers to suit .

This build takes a lot of checking and re checking .




J Moyler02/10/2020 18:58:33
154 forum posts
56 photos


I built one a few years ago. See attached link. I used 4 cells and about 600 watts. Flew quite well. Following with interest.


Keith Evans 303/10/2020 18:05:37
426 forum posts
268 photos

p1040223.jpgp1040224.jpgHi JM. Thanks for the link . I now have something to look forward to . When ,

I do not know but I can dream .

Started on the T.E.'s

I've used a cardboard template to arrive at the true shape for it , particularly around the main spar area .

As you can see I'm having to be a bit inventive . I'm now out of 1/16" sheet .



Keith Evans 305/10/2020 18:30:43
426 forum posts
268 photos

Balsa supplies should be arriving tomorrow .

In the meantime I'll carry on with the elevator .I spot glued the elevator to the T.E. of the main wing with balsa cement .I find this works the best for me in this application .

I've protected them both with masking tape and strips of 1/16" balsa to make sure I do not plane into the ribs and cap strips .

After a pile of lovely shavings and some swipes with my Permagrit block I've ended up with a nicely matched pair .

The next step will be to chamfer the L.E. edge of the whole elevator assembly to arrive at the 3/16" reflex required .

Only when this is done will I separate the elevator out .The elevator will then be shaped to allow for hinging .

Later on I will glue the outer portions to the main wing .



Keith Evans 306/10/2020 19:14:35
426 forum posts
268 photos

Continued with the elevator etc.

I made up a simple jig so I could sand the L.E. of the assy .to get a reflex of approx .3/16".

I did not split the assy. at this stage in an attempt to arrive at the same angle at both ends .

If they were different then I suspect it may have an adverse affect on the flying characteristics .

I continually checked with a set square .Sorry about the flash . Both reflexes looked the same when I had finished .

The elevator was then chamfered .

The last shot shows the outer tips being fitted along with the positions of the snake supports .

The balsa arrived today .So it will be back onto the main wing .






Keith Evans 308/10/2020 19:22:58
426 forum posts
268 photos

Began L.E. sheeting

Using some water and the mark one finger nail along with some slitting where the bend was going to be I prepared the 1/16" sheet .

I started the sheeting in the centre of the wing and worked my way out to tip .

With a tremendous amount of pins aliphatic ,'P.V.A. and cyno . I managed to curve the sheet out and down to the wing tip . A little bit of filler to cover the slits and the job was done These few words do not convey the difficulty at bending the sheet to the tips . If I were to tackle this again I would either use foam or balsa block between the two end ribs and carve to shape .

I've laid out the top fuselage formers again to show the under size dimensions .Again it would be worth considering re positioning ribs W2 to allow for this .

I'm in the process of trial fitting the sacrificial jig to check for alignment .It all looks good so far .

Gluing up the rear beam mount in the servo bay .













Keith Evans 310/10/2020 18:44:11
426 forum posts
268 photos



Just a few things done today .

The new bulkhead with captive nuts .

I've started on the wing snake outlets . This is not shown on the plan but I thought it was necessary in this area .

This is the1/32" ply cover .

It is fitted at the wing tip and both ends are recessed into the T.E. and rear of the L.E. sheeting .

I used 1/32" ply for its flexibility to try and cope with the complex shape in that area .

Once fitted I glued a similar cover of 1/32" balsa .

Any remaining gaps in that area will be filled later .

Although only a small part of the build it did take some time to develop the cover shape itself .





Edited By Keith Evans 3 on 10/10/2020 18:44:58

Keith Evans 311/10/2020 19:00:35
426 forum posts
268 photos

Some more work on the wing today.

The innermost four bays appear identical in height so I thought I'd make a little sanding block .

I roughly planed and sanded the L.E. but left the centre two bays square . I did this to ensure the former at that position would get a lot of support .

Just a little more tidying up and then its onto the underside sheeting and cap strips .



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