apalsson

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All,

A few days ago, I received a 1/5 Pepsi Chipmunk from Apache Aviation is the UK. Having already built their 1/5 N13Y Super Chipmunk, I pretty much knew what to expect in terms of quality and and inclusions.
The reason for buying another Chipmunk was that I wanted a good quality kit for a G38 that I had lying around new in box.
My other Chipmunk has a Moki 1.8 in it and I wanted to try out a gas engine (as recommended by the designer of the kits).

I also opted to buy an optional two piece wing kit rather than the 81" single piece wing that my Super Chipmunk has.

The Chipmunks from Apache are pretty much a rework of the old Ohio Chipmunks (someone correct me here if I'm wrong) and have retained the same excellent flight characteristics and strength.

Upon opening the box, I found that pretty much all hardware was included. I ordered as an optional extra items like a secondary muffler for the G38, Robart Strut Covers, Robart Hingepoints and an optional wing fairing.

All contents of the kit were packaged in bundles for each major assembly.
The two piece wing is based around a 3/8" plywood joiner that is epoxied into one wing half but slides into a socket between the main spars in the other wing.

The first tasks to be done are to laminate ribs 3 and 5 together with plywood doublers and thicker plywood pieces that form a part of the landing gear mount. Ther gear mount itself is laminated from 3 plywood parts that interlock into the rib structure and the spar web.

All ribs are of 1/8" plywood and have some substantial lightening holes in them. The spar web is also plywood and is glues on the front of the main wing spars and interlocks into the ribs. Designed like this, it forms a very strong but relatively light wing.

I will post photos as the build progresses which might be fairly slow due to heavy work commitments.

Regards

Ari

apalsson

My Feedback: (1)

I have just started framing up the wings. As per the instructions, I have laminated ribs 3 and 5 and added the landing gear anchors to rib 3. Also laminated the langing gear block (shown in the photo below).
The lower spar is glued to the spar web before adding the ribs. The next photo shows the ribs and landing gear block dry fitted to the spar web.
Everything fits well so far and the only sanding I have had to do was some minor adjustment of the landing gear block to get a good sliding fit for ribs 2, 3, 4 and 5.
The end of the spar web acts as a dihedral guide for rib 1.
The last photo shows the spar web with the lower spar glued onto the front.

I have decided to use Robart hinge points rather than flat pin hinges. The plans have a good cross section showing where to drill and notch for hinge points.
Ailerons and flaps are built as a part of the wing and then cut away and separated, leading edge caps added to the flaps/ailerons and a capstrip to the trailing edge of the wing. Finally, the flaps are separated from the ailerons by cutting at around rib 6 and both ends capped.

Regards

Ari

apalsson

My Feedback: (1)

I have made some more progress.

Much of the left wing is now framed up with all of the ribs in place, top and bottom spars, shear web and the top stringers.
Also the trailing edge sheeting.
It was quite easy to align the ribs because of the tabs on the trailing end being pinned down (they even left holes in the tabs for the pins).
The sparweb has slots to slide the ribs into, so everything comes together straight and true without too much effort.
The root rib was slightly warped but I clamped a straight piece of aluminium profile onto it while I glued in the stringers. This gave me a perfectly straight root rib.

The manual is quite detailed and isometric drawing of many of the more complicated steps.

Only thing that was a bit tricky was to align the trailing edge sheeting so that it glued tight to the rear tips of the ribs. This is because the alignment tabs are very close to the edge and hard to get clamps on the ends.
Suggestion to Apache is to move the tabs 1/2" or so forward.

One of the steps in the build is to cut a slot in the root ribs between the main spars and epoxy the 3/8" plywood joiner into the pocket that the spars and sparweb make.

Regards

Ari

PlaneKrazee

My Feedback: (14)

Looking good.

What do they use for spar material?

apalsson

My Feedback: (1)

HI Brian,

The spars seem to be spruce.
The leading edge sheeting is on now, I'm waiting for it to dry.


Ari

apalsson

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A bit more progress today.

Today, I finished sheeting the top side of the wing.
This allowed me to take it off the board, cut off the alignment tabs of the ribs and start fitting the landing gear mount etc.

I decided to go with the flaps that are designed with the kit.
This was really the only involved thing I have had to do so far.

The building procedure makes you sheet the top side of the wing before gluing in the supports for the flap torque rod and then glue in the torque rod bearings into the support.
Because of the shape of the torque rod and how it comes through a 1/8" hole in rib 2, I had to cut a hole in the top sheeting that was bigger than what I liked, just to get the rod into place.
I will fit this before top sheeting the centre bays when I build the other wing.

It is interesting to look at the airfoil. At the root, it's semi-symmetrical but the tip has washout built in. The airfoil gradually blends between the two. Hopefully, the photo below shows the airfoil at the tip. Without doubt, this contributes to the excellent slow speed handling of the plane.

There is also a photo of my other Chipmunk. It has a Moki 1.8 and it one of the best planes I have ever had. Hopefully, this one will be just as good on the G38

apalsson

My Feedback: (1)

Today, I got a chance to more or less finish the left wing and start framing the right one.
As mentioned above, I purchased the optional two piece wing kit.

Each wing half is built around two hardwood spars joined by a 1/8" spar web. This is quite a strong design and the spar web and ribs are slotted for an interlocking mechanism.

The wing joiner is a piece of 3/8" plywood that slides into the pocket between the spars. It is epoxied in place in the left wing and the spar web in the root rib bay is then doubled with another layer of 1/8" aircraft grade plywood, epoxied onto the spar web. A pair of 4mm bolts then screws through the doubled spar web and into a blind nut on the back of the joiner piece.
Access to the bolts is given by leaving the root rib bay in the right wing unsheeted over the bolts.

I suspect this will work quite well and be strong, as the joiner fits snugly between the spars and is pulled tight up against the doubled spar web by the bolts.

I will try to post some photos tomorrow.

Ari

apalsson

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These photos show the right wing frame and the opening in the root rib bay where the joiner bolts fit in.
The top of the wing has been sheeted and the trailing edge bottom sheet is on waiting to dry.

Wish I knew how to post photos and text in between them

apalsson

My Feedback: (1)

Finally got both wing panels fully framed up.
I'm not 100% sure I'm happy with the way the left and right wing panels are joined when you put them together.
I have bolted the joiner in place in the right wing panel and the other end slips snug into the pocket between the spars in the left.

The trailing edge is joined by a 1/8" screw that screws into a captive nut in a tab on the left panel. This is done by little tabs on top of the root rib.
Unless you are 100% accurate with the joining of the wing halfs, there seems to be a bit of tension and since the captive nut is only sitting in a small 1/8" plywood tab, this could easily break.
Admittedly, there will be very little stress on this, as the wing then bolts to the fuselage in the conventional way.

I am trying to think up a better way of doing this. One idea is to double up the rear end of the root ribs and put a guide pin that is glued in place on one side and slips into a hole on the other.

Failing that, I might simply epoxy the wing halfs together and wrap a band of fibreglass cloth around the join. This will give me a solidly joined one piece wing.

The photo below shows this little tab in the root rib. If you look carefully, you can see the captive nut inserted from the back.

Does anyone have better ideas on how the trailing edge could be joined?

apalsson

My Feedback: (1)

A bit more progress today.

Saturdays are normally my flying days but today has been very windy and no flying weather. Thus - I have been working on the Chipmunk.

I have now separated the flaps/ailerons from the wing structure. Earlier in the piece, two 5/8 x 3/32 strips were glued down into notches in the ribs, forming leading edge spars for the flaps / ailerons and trailing edge reinforcements for the wing. These strips are spaced approx 1/2" apart.

Next step is to cut away the sheeting between these spars and cut through the ribs and hinge blocks.
The hinge blocks are simply aileron stock that neatly slips between the spars. Later on, I will drill for the Robart hinge points into these blocks.

One of the photos below shows these blocks in place.

Once the leading edges have been glued on the ailerons and trailing edge caps on the wings, the aileron and flap are separated by cutting straight across at rib 6 with a razor saw. One end is then closed with some scrap balsa and the other is capped by the rib.

I was looking at the photos and see that my workshop is a mess! Must clean up tomorrow

PS: I found a slight problem with the kit here.
The aileron leading edge stock and the wing trailing edge cap are approximately 1/2" too short.
The aileron / flap cutout is one rib bay longer in the flap version of the wing than the aileron only configuration. I might send a note to Apache about this. Anyhow, this is not a big problem as the gap can easily be filled with some scrap material.

Ari

ronaldh

Hi Ari,
Am following your build progress with interest! Have started my RCAF version but progress is slow. Still recovering from major surgery.

One point. Should you not have glued the wing tip block on and sanded to shape before cutting the aileron/flap from the wing?

In your Pennzoil version with the Moki 180 did you:

a) use engine vibration eliminators sold by Apache and use the special Moki radial mount?
b) use separate servos for each elevator half? Servos mounted in the tail or up front using the long metal pushrods supplied.

Keep up the good work

Regards
Ron

apalsson

My Feedback: (1)

Hi Ron,

Thanks for the kind words. Since the last posting, I have built the horizontal stabiliser and elevators and will try to post some photos in a couple of days.

I agree that maybe I should have glued the wing tips on before separating the aileron / flaps from the wing but since I had some problems with my last build (read careless with glue), I decided to leave the tips off till last. This way, I have to do a bit more careful sanding but the upside is that now I can accurately match the countour of the tips with the ailerons once the Robart hinge points are in.

On my last build, the wing tips came out slightly shorter than the combined wing / aileron width due to the hinges and a slight hinge gap, so I had to shape the aileron tips a bit to compensate for it.

The Pennzoil has the Moki 1.8 on a Moki radial mount with the vibration isolators from Apache. Frankly, I don't see much benefits in the isolators, even though they are good quality because the Moki runs quite smooth and has very little vibration.

I did use a single servo for both elevators on the Pennzoil but didn't quite like the joiner and made one slightly thicker and longer. I will probably use a separate servo for each half on the Pepsi and then some pull-pull for the rudder.

I know the rear mounted servos offset the heavy nose, especially because I will be using a G38 in the Pepsi (the Pennzoil balanced exactly with everything in stock position) but I am willing to put a bit of lead in the tail to compensate for the servos being inside the fuse. I don't like the look of the rudder and elevator servos exposed, so I will most likely take this approach.

Good luck with the RCAF - maybe it will be my next Chipmunk.

Best regards

Ari

apalsson

My Feedback: (1)

A few more details on the progress so far.

Since I got a bit tired of working on the wings and had already framed up both and separated ailerons/flaps from the wings, I only rough shaped the wing tip balsa blocks and glued them on.
Prior to separating the ailerons, I traced the outline of the tip onto the wing tip blocks and then hollowed the blocks before gluing them on.
Since the tips are quite soft and lightweight, I don't think I will save much weight here though.

The wings are now ready to start shaping the leading edges of the ailerons and mount the hinge points.

The tail feathers have been built for the most part. Elevators are ready, so is the stab and fin.
Only thing so far that I'm not too happy with is that the skins for the stab and fin is 1/16" balsa and is quite soft.

Fin and stab are built from a 1/4" thick frame sheeted with 1/16 balsa while elevators and rudder are 3/8" open frame construction. Nothing unusual here.

The elevator have 1/8" plywood pieces recessed into the balsa where the joiner is inserted. These plywood pieces also double as strong points where you mount the control horns. Since I will not be joining them, this is probably not necessary but I figured I'd fit them anyway for added strength and also for a solid surface to screw the control horns into.

The rudder frame is pinned down on the board at the moment drying.
The plans show a similar plywood reinforcement of the bottom front corner where the tailwheel wire is supposed to slot into between the plywood pieces.

I will not be using the stock tail wheel setup because I don't like the direct coupling between the tail wheel and the rudder. Nor will I be using the stock rear mounted rudder servo. I am planning to try to come up with some sort of a pull - pull arrangement for the rudder and spring couple the tail wheel to the rudder.
I still haven't worked out how this is best done because the rudder sits completely above the tail section of the fuselage and I don't like the rudder pull-pull wires and control horns to be exposed there.
I suspect some sort of control horns can be soldered onto the stock tail wheel wire and sit underneath the stab / rudder.

Some photos below:

apalsson

My Feedback: (1)

Oops! You can onlyattach 4 photos per message.
This photo shows the stab and the fin fully sheeted:

apalsson

My Feedback: (1)

Interesting what you find when you start researching the Net.
The photo below shows the original SkyDancer and it's obvious that the wingtips should not be rounded as shown on the plans.
The other photo is from Apache and shows the underside of one of their demo planes. The difference is fairly obvious.

Admittedly, the kit is only "sport" scale but this is fairly obvious. I wonder what effects (if any) on flight characteristics it would have if I trimmed the tips down to be flat like on the full sized plane.
I might send Apache an e-mail and get their opinion.

Any ideas ??

PlaneKrazee

My Feedback: (14)

It looks like the wing tips have larger ribs to help stop vortices. It would probably fly better that way. At least it would be more scale.

The only drawback could be that the wing would be too short for IMAA competition.

apalsson

My Feedback: (1)

Skypilot,

I think you are right. If you wanted to simulate this, replacing the wing tip block with something like a 1/4" balsa that is a bit bigger than the tip would be the way to go.
I have plenty time to think this over.

I don't really mind if the plane doesn't quite have the span for IMAA competition. I'm not a competition pilot.

Regards

Ari

rcav8or

My Feedback: (5)

IMAA is based on NON-competition. It's just a big gathering of large planes, over 80" wingspan for monoplanes, and 60" for bipes. The exception is a 1/4 scale, of a plane, that comes in less than 80" true to scale, as in the case of my 31% One Design (DR-107). It comes in at 74" at 31%, since the scale plane has a very short wingspan, at 19'. 4".

I see you are in Oz, but for someone in the US, it would make sense to make sure the wingspan is 80", to allow it to fly at an IMAA meet. I am an active member, and it's a lot of fun to go watch a lot of "giant" scale planes, without worrying about the competition side of it.

Competition is good, in it's own right, and I will be competing next year in the IMAC, but it's also nice to just go and fly!

My $.02 worth...

My Ohio RC Chipmunk is still sitting gathering dust. Hopefully, it will be my winter project this year. Looking forward to it!

What motor are you going to be using on yours? I didn't see, but perhaps I overlooked it...

R

apalsson

My Feedback: (1)

HI Roger,

Thanks for the details on IMAA. I admit I wasn't quite sure about these.
As far as I'm aware of, we have no similar event here on Oz with requirements for 80" wing span.

I was going to mount G38 in the Pepsi. I have one floating around that has never been used and according to Apache, they work quite well in this plane.

My other Apache designed Chipmunk has a Moki 1.8 and I'm interested in seeing how the two compare. You will see that the Apache kit is very similar to the Ohio kit in many ways.

Regards

Ari

apalsson

My Feedback: (1)

Quite a bit of progress has been made this weekend.

I finished the tail feathers and have rough sanded the leading and trailing edges and dry fitted the robart hinge points.

The wing has been set aside for now. I still have some work to do there but as I like to work on several parts the same time, I decided to leave them for now.

The fuselage is now on the board.

The construction begins by measuring the exact length of the engine and making up spacers to that will give you the right length from firewall to the prop driver face.
A Moki 1.8/2.1 or a ST3000 will be the right length if mounted on a radial mount but the G38 is quite a bit shorter.

I ended up cutting 34mm long spacers from a 1" hardwood dowel and drilled through the centre. The mount pattern from the motor is then transferred to the firewall and mounting holed drilled accordingly. I still need to get proper size bolts and captive nuts, so having glued the stand-offs on the firewall and brushed it with thinned epoxy, I have set it aside for now.

The sides are made from 1/8" plywood at front and 1/8" balsa sheet rear end, "fingered" together.
Once this has been done, the instructions tell you to glue 1" and 1/2" tri stock along the edges of the fuse sides. This gives you material to sand away when you round the bottom corners of the fuse.
This tri stock is then sanded down at the tail end to give the proper fuse width, while being glued together for strength.

I decided to use a slightly different sequence here.
Before gluing in the the tri stock, I glued in the formers and the servo tray. All these parts interlock into the fuse sides, making it very easy to build the fuselage straight. This structure also gives you the proper right and down thrust for the firewall.

Once the fuselage sides had been joined to the formers and servo tray, it was much easier to glue in the tri stock and get a snug fit with the corners of the formers. It was also much easier to properly shape the aft end of the tri stock for a close fit.

Wing hold down blocks can now be epoxied in and reinforced with tri stock.

At this time, I have a very strong structure that is straight and true. No turtledeck parts have been added, which allows me to work on the fuse structure upside down on the building board.

The firewall still isn't fitted. I carefully measured the thickness and marked back onto the fuse sides and glued in tri stock reinforcements there. This will allow me to align the firewall properly when I epoxy it in. First, I need to get these bolts and captive nuts and drill the mounting holed in the proper size.

Next thing is to check the alignment of the wing in the wing saddle, drill the hold down bolt holes and mount nuts in the hold down blocks.

I will post some photos when I get a chance.

Ari

jucava

Nice post. Keep the pics coming.

apalsson

My Feedback: (1)

All,

Here are a few photos of the fuse build.
I had to make up some spacers for the engine mount because I didn't have the cup mount for the G38. This is quite a bit cheaper as well, or approx 10" of 3/4" hardwood dowel that I paid $3.40 for a full metre (36") of.
I have brushed thinned epoxy over the firewall and stand-offs.

apalsson

My Feedback: (1)

And some more - one shows the size difference between the 81" Chipmunk and my other project

apalsson

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I have temporarily mounted the engine and it looks like the G38 fits quite nicely in the cowl.
The only thing I will have to cut is a small opening in the bottom for the spark plug lead and then where the cooling duct runs underneath the fuse. The photo taken from the front shows how well the width and height of the engine fits the firewall.

Connecting the throttle on these G38 engines is somewhat involved but as luck had it, I had a couple of ball link arms from my ZDZ80 that I wasn't using. When screwed on to the back end of the throttle shaft, it provided a straight (well, almost) run to a bellcrank that I mounted on the engine standoffs.

Next thing is to mount the wing on the fuselage, drill for the wing mounting bolts and hold down dowels and then make up the fairings where the wing joins the fuselage.

I am posting some more photos of the engine installation.

Ari

apalsson

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This weekend, I have been working on the fuselage and the outstanding items from the wing.

Having played with the wing a bit and thought about the join at the rear of the wing, I decided I didn't like the way it was designed and made the wing a one piece wing!! [>:]

I smeared 30 min epoxy all over the wing joiner and the joiner pocket where the joiner was bolted to the doubled joiner web and having aligned the joiner in the pocket, bolted the joiner back in. I guess this is the last time I see these bolts come out
I then joined the wing halfs in a conventional way, that is applied 30 min epoxy to the root ribs and the other half of the joiner and pushed the wing halfs together for a snug fit. Once the epoxy had cured, I put down some 4" fibreglass cloth over the seam. This will be a very strong wing!!

Next was drill for the wing hold down dowels and epoxy them into place. I then made up a fairing to the underside of the wing, to match the shape of the fuselage.

I then glued in place the fuel tank floor having fuel proofed the entire front compartment with thinneed epoxy.
Fuel tank is also in place now. This is only a 16 oz tank. I thought about this one a bit, as I like to carry as big a fuel tank as I can fit but since this is only a small-ish petrol engine, I figured 16 oz will do.
The smoke tank is also 16oz and if I carried more fuel than the combined 32oz, I would be adding a fair amount of weight.

The turtle deck formers and stringers go in in a conventional way.

At this time, I also cut a scrap piece of 1/8" ply to become the instrument panel later on.
The Pepsi is a dual cockpit plane (single canopy) and the divider of made up by shaping a balsa block and glue a piece of plywood on top. I'm not too sure how this will pan out but I made up these parts as prescribed anyhow. They can always be improved on later in the build.

A few more photos below show progress

Ari