Airsail - Dehavilland Chipmunk Kit

[Evan Pimm]

On a model as small as the Airsail Chipmunk, a standard servo is plenty for flaps.

Evan.

[Richard Duvall]

A bit more progress made. Skinned the wing centre section leaving a cut-out for the aileron servo. I need to open up a bay for the flap servo. Also drilled hole for wing bolt.

[Richard Duvall]

Completed one wing framework. It all seems to be taking less time than I expected; my aim was to have it ready for its maiden flight in the spring and with all the rotten weather lately I've not had any time in the air with my trainer to finishing learning to fly and get my A cert!

Although the kit seems to just have the airleron control rod just going through holes in the rib I've added a plastic tube for the rod. The instructions are a bit vague on things like this and leave you to guess when to install it. I took the view that it would not be possible to fit the rod later when the wing is at a more completed stage.

The aileron top sheet is on. At this stage the wing ribs are one piece through into the ailerons which are cut off later.

Test fitted the wing against the centre section. Seems a good fit and the wing tip is resting on a tin of sanding sealer which co-incidentally measures the required 75mm dihedral.

[Phil Winks]

a most interesting blog so far Richard. if you've not bought the engine yet I suggest a 4 stroke will certainly sound better and being a touch heavier might negate any need for ballast weight. on the subject of glass skinning try looking at this stuff  poly c is less messy lighter and possibly cheaper. and provides a finish comparable to glass fibre resin.

[Lew Weaver]

The alternative to pushrods would be a mini servo in each wing panel which is easier to set up.

It would fly well on an Axi 4120 and a 5S LiPo  

[Richard Duvall]

Phil,

Thanks for the suggestions. I will almost certainly be going for the Poly C solution.  As to engine, I've not made my mind up yet but thought that a 4 stroke might be a bit more complicated so am taking the view of one step at a time and sticking to a 2 stoke, which I am familiar with, on this model and then go for a 4 stroke in my next model which may well be the Tony Nijhuis Hurricane.

Lew,

Might consider the mini aileron servos. Stefane Savard took that option with his Chipmunk but ended up with an ugly surface mounting on the underside of the wing. Also can't see why he used such heavy "ducting" for the servo leads.

Richard

[Evan Pimm]

If you use a plastic tube bearing for the aileron rods, you will find that they will bind as the bellcrank moves. Best just to let them run through biggish holes in the ribs so that they can move fore and aft as needed. Hence the reason for just holes in the ribs, the support offered by the servo at one end and the bellcrank at the other is plenty as the actual rod length is not great.

Evan.

[Chinesespaceman]

spoke to the owner of the full size at Breighton and he has been really helpful, offering full access. He is even going to bring me down manuals and scale drawings. I think I will have to do a "mini me" and base the colour on Tony's G-BTWF / WK549.

Anyway, I'm there tomorrow morning to take some pictures and will post them on a web server and post the link here. If anyone needs anything specific that I haven't got, then please don't hesitate to ask

roll on tomorrow

Gav 

[Richard Duvall]

Progress has been slow over the last couple of days as I try and plug the gaps in the very sparce instructions. This build was always meant to be a learning experience for me but I did not expect to learn so much!

I did consider Lew's suggestion of wing mounted aileron servos, and it would have made sense to do the same for flaps. However, there is very little room in the wings so I have decided to go ahead as (sort of) specified in the plans and use control rods, with bell cranks, to the centrally mounted servos. Not as easy as it sounds in the instructions! Due to lack of height, the servos need to be mounted horizontally which means you can't screw them in directly. I have therefore made up some servo mounts to which the servos can be fixed and then the mounts fix into the bays.  Hope I've not added too much wood to add to the weight. Will add some photos later but the wife's away visiting her daughter and taken the camera with her!

As recommended by Phil, I am going to glass the plane using Poly C; ordered it yesterday and it arrived today can't beat that for service! Now I'm ready with covering, I may go back and finish the tail section but now I'm close to resolving the servo/ centre section  I'm close to being ready to join the wings to the centre - spoilt for choice!

[Chinesespaceman]

Evening all,

Got over to Breighton this morning and met with Tony, who couldn't have been more accomodating and helpful. A few things I noted:

• the wings are fabric from the main spar backwards and sheeted fore of that.
• Note the elevator trim tab on the rh elevator
• ailerons, flaps and rudder are  fabric
• The stitching on the fabric is pitched at 2" for the length of the rib caps, then covered with tape and painted. I suppose this could be replicated with thread or similar layed on top of the covering, then painted

See attached the link to the photobucket folder containing loads of pics

http://s132.photobucket.com/albums/q28/chinesespaceman/DH%20Chipmunk/

Cheers for now

Gav 

 P.S. the insruction booklet with the Airsail kit is a joke - it presumes all builders are clairvoyants - a lot of time spent guessing, wondering and head scratching

[Richard Duvall]

Gavin,

Interesting set of photos - a lot of detail. In my wildest dreams I don't think I could replicate much of that in my model!  It would appear that the kit deviates from scale so much that it would take too many changes to correct it. That said, I've more or less decided to deviate from scale even further by fully sheeting the wings as I think I can handle that better than playing around with fabric, and I'd already ruled out using any form of plastic film. It might be possible to add some stitching effects over my sheeting. The photos show a lot of rivits and again it may be feasible to replicate them, but if you do one, you've got to do the lot!  I'm not too happy that the kit contains so many plastic parts and I may look at making some wooden alternatives.

I'm working on finishing my elevators at the moment, so hope to be able to update progress soon. I've got some Robart hinge points for the flaps as specified in the additional instructions. Having seen these I'm inclined to use them all round as they seem so much better than the plastic ones supplied in the kit for the elevators, rudder & ailerons. I also think they'll be easier to fit as they simply need a hole drilled rather than a slot cut.

Richard

[Chinesespaceman]

Hi Richard,

Yeah, I think one rivet will lead to another..........

The bits I want to make sure to add on are the inspection hatches and trim tabs. Also there are quite a few protruding instruments such as the ASI on the underwing, navigation lights etc that I want to include in my build.

It was also interesting for me to understand where some items are positioned relative to rib positions etc.

I've used the robart pin hinges on several models now. I would advise making dummy parts first and testing the hinge position to make sure you get full movement and that there isn't a big gap between the leading edge of the control surface and the trailing edge of the supporting structure. I am considering adding a female semicircular section to the rear of the stabiliser and wings to create a realistic and functional interface.

The standard joint might end up looking like an ugly wedge found on an ARTF?

I think we need to start a self help support group over the airsail destructions Cheers for nowGav

[Richard Duvall]

Gavin,

Your idea to improve the interface sounds good in principle, but how far can you cover the gap without restricting movement?  From your drawing it would appear to work only if you could get a true rotational turn from a central pivot.  The additional instructions for flaps at least do something like that for the top edge but flaps only need to hinge one way.

I've gone with the standard hinges for the elevators now as I didn't have the forsight to add the blocks that would have been needed for the Robarts. Turns out it was not too difficult to cut the slots.

Any other candidates for a self help group?

Richard

[Chinesespaceman]

Hi Richard,

I proceeded by gluing 2 pieces of 6mm sq balsa along the vertical spar of the fin, then formed a radius using a dowel wrapped with abrasive paper. I will reinforce the rudder spars internally as I have removed a fair bit of material in creating the male radius. Would have been a much nicer job had I considered it prior to building - I think that goes down to lack of experience.......... 

[Lee Burke]

Great set of detail photos, Chinesespaceman.  Quite daunting to consider reproducing that amount of detail.  It would have been super to see some cockpit shots but there are a few knocking around on the web, not many, but a few. 

I wish I could join in the self-help team but my build is stalled (I have only finished the tailplane - and I may remake that as I built it a bit heavy) as my workshop (Spare room) is temporarily closed for this purpose.

I like the modification to the rudder post and am curious to see if the rudder turns okay like that once the hinges are installed.

[Chinesespaceman]

Hi Lee, with a big enough servo anything will turn

Seriously though, I think getting these fitted up properly is gpoing to take some time and patience - the sort of work I need to be in the right frame of mind for. I am going to have a really hard think about the wing before I start cutting balsa and won't be surprised, if like you the tail plane doesn't get remade............

As for the cockpit, the number of instruments and controls in these things is incredible. I think the cockpit will be made in sections and then fitted into the airframe, although I will have to draw the line somewhere. I can nip across and get photos as and when needed, so the cockpit will wait for a while.

Richard, I'm glad you are a few steps ahead of me, just keep posting the snags (and solutions)

Cheers

Gav

[Richard Duvall]

Gav,

The trouble with being a few steps ahead of you means that I'm not able to benefit from your bright ideas!  However, I'm not convinced your nice curved elevator interface will work unless you can come up with a means of rotating it round the centre of your curved elevator leading edge. The movement from the hinges will produce an amount of up and down movement which will limit the extent to which your curved tailplane trailing edge will be able to extend.

Now I've got my camera back I will post some pictures of further progress.

Richard

[Richard Duvall]

I explained earlier the need to find a solution to mounting the flap servo in the limited space available in the center wing section. My solution was to fabricate a servo mount that could slide into the centre section and be fixed.

Photo's a bit blurred but this is my mount!

With servo in place .............

......... and mount in centre section!

Maybe not the neatest solution but it works for me! Now I need to do similar for the aileron servo where there is more space but not enough to mount it so that the horn is central - I'm working on mounting it diagonally - watch this space.

[Richard Duvall]

Might seem a lot of progress in a short time but I mentioned earlier that my camera had been borrowed!

I've now skinned the elevators and completed the end block carving.

and hinges temporarily attached to tailplane.

Work in progess completing the rudder.

[Phil Winks]

on the issue of the curved rudder tailplane interface you could try some pin hinges I think the're called and let them into the LE of the rudder/elevator/aieron sufficiently to get the pivot point in the centre of the LE radius if you see what I mean

[Chinesespaceman]

Hi Richard / Phil,

Yeah the plan is to use robart pin hinges, but as Richard pointed out I need to position the hinge line about 5mm inside the leading edge of the control surface. I'll have a go at it this weekend and see how I get on.

Richard, the flap servo housing looks great, really neat, I expect when I get as far as the wing it will make sense.

Keep her lit

Gav 

[Phil Winks]

In my humble opinion the easiest way to fit the hinges is to cut a reccess in the LE just wide enough to accomodate the hinge section and deep enough to allow it to reach the req hinge line before drilling the hole to take the pin hope this aint teaching you to suck eggs

[Bionic]

Hi Richard, I have been flying the Chippie, for 14 years now and it is the best low winger that I have ever flown, I fitted a Saito 65 FS and it punches holes in the clouds, also you have to be an animal to stall it.

Happy flying, Bionic

[Chinesespaceman]

Hi Richard, just getting through the middle wing section. I am finding that the laser cut pieces are nowhere close to accurate according to the plan. Lots of the laser cut parts are a tad short (the outside spars) and the slots are in the wrong position on the main spar, i.e. they don't match the plan.

Have you come across this?

I am just building to the plan and using triangulated braces where the 2 pieces of wood don't meet properly. I think for this model we have to be prepared to make a lot up as we go along - might as well build from scratch.................

Regards

 Gavin

P.S. got the rudder / fin hinges to work well. It means that the hinge pin line is 7mm back from the fin trailing edge - I'll post some photos later 

[Richard Duvall]

Gavin,

If you look back earlier in this post you will see a photo where the centre section did not match the plan. I thought I would have to make some modification, such as padding out the wing rib so that the short spar would reach . However, it seems to mate perfectly with the wing as prepared to the plan. My conclusion is that the spar is correct but the plan of the centre section is wrong.  I'm waiting to be sure I've got the aileron and flap controls sorted out before I join the wings to the centre section.

In the meantime I've been "glassing" the elevators and rudder before connecting them. This Poly-C stuff seems quite user friendly but needs lots of coats.

Richard