#26 Model airplane build clinic... Astro Hog

[pd1]

Parts is parts
I'm building an old Sig Astro Hog kit. The kit I'm using is from 1983.

Almost ready to fly


This is a newer version of the original Berkeley kit. The construction is a little more complicated than a nice laser cut kit, but still a fun build.

Step one. Take an inventory of the supplied parts. All I was missing was the decal.


Start building the parts to make the plane. The ribs need plywood doubler's added, spars have to be reinforced and the wing tips have to be laminated.


I used a piece of left over spar to stack the ribs and sand them so they are all the same. Die cut ribs always have variations between ribs. A little sanding and they're nice and straight.


Wing tip parts

Spar pinned down and ribs glued to bottom spar. Hole in ribs were added to allow servo wire to pass through. I'll be using two servos instead of the single servo with torque rods.


I added the trailing edge sheet for the top and the wingtip.


The plans called for bending the 1/4 inch square spar to go over the end rib and attach to the wing tip. To relieve stress, I used a razor saw and made a small cut on the bottom of the spar at the last rib.

The spar bent easily and I've since sanded the tip and added the gear blocks. Some sheeting and I'll start the second wing half.

Second half same as the first.

[pd1]

The wing halves are joined and the leading edge sheeting and center section sheeting is almost finished.
I've started the pockets for the aileron servos.

The wing structure should be finished tomorrow.

The wing tips were a pain, the plans called for the sheet to be wrapped around the wingtip. I had to wet the sheet and wait a few hours for the sheet to dry and wait a few more hours for the glue to dry.


The sheeting used is 3/32 which is pretty heavy, the sheet supplied are hard sheets which are even harder to work with.



The leading edges and trailing edges were rectangular stock larger than needed.
After they were on, it was sand off anything that didn't resemble a leading edge. I used 80 grit sandpaper on a block after trimming with a knife to cut the excess off. The leading edge won, I used four sheets of 80 grit. usually I use one sheet per airplane.


Servo pockets. The plans called for a single servo driving torque rods to actuate the ailerons. I elected to use two servos, one for each aileron.
I am making a mount to bury the servo in the wing so only the arm protrudes from the wing surface.


Caps strips have been added along with center section sheeting.


Now to fit the wing to the fuselage.

[pd1]

I decided to change the fuselage sheets on the Astro Hog.
The factory supplied 3/32 sheet stock, while this might be perfectly fine, the stock in my kit was very light material.

I decided to up it to 1/8 sheet. I edge glued some 1/8 and transferred the printing to the new sides. I also changed the doublers from light ply to balsa.

Sides are together and formers have been added.


Without the torque rods for the ailerons, a new simpler and stronger rear wing mount was used.


Mount drilled and blind nuts added for 6x32 nylon hold down bolts.

Wing squared up to fuselage and front pegs and rear bolts added.


Firewall trial fit and then clamped and glued in place.
The ply pieces ahead of the mount are only there to help keep the firewall in position until the glue dries.


BLOCKS R US
Added the blocks to the front of the fuselage.
A cutout was made so the ESC cooling fins are flush with the outside of the plane.




This thing is built like a tank.
I roughly rounded the blocks on one side of the fuse. I'll do the other side tomorrow.

Did some work on the fuselage. Servo mounts and battery mounts are in.

Pushrod tube are installed and the bottom sheet has been started.

Stringers on top and the top sheets should go on tomorrow.


I finished the bottom aft sheeting.

I added the top aft sheeting and started the forward top sheeting.

I had to enlarge the battery opening so I had to loft a new former.

The rear part of the battery hatch is now the new former.

The second part of the forward sheeting is now on.

The darker color is because the wood has been wet so it bends without cracking.

Made the battery hatch and started final shaping of the nose.


The nose is only roughed shaped with 80 grit. I'll final sand everything immediately before covering.


The fuselage is finished for now, I'll put the fuselage and wing away for now.

The headrest on, makes it the Hog.

Fuselage covering..
Started prepping the fuse for covering...


The bottom was covered first so the edges of the seams won't show.
All the junctures had a strip of covering added so overlapping joints are easier.


Finally the side is covered and I just have to trim the edges and iron the edges down again.


Orange is nearly done

I've covered all the fuselage and stabilizer. Vertical fin on one side is covered and control surfaces are hinged.


All that's left to the orange is battery cover and half the vertical fin.


Now some trim.

Added some white to the top of the wings and stabilizer. A little on the fuselage too.

White needed on the leading edge of the vertical fin and maybe some checkers on the bottom of the wing. Running out of white.

The plane on the box has a black section on the top of the fuselage ahead of the windshield, haven't decided if I'm going to do that too.


Added some checkers on the bottom of the wing to help me with orientation.
The sheet of paper is for locating the checkers. Also a good straight edge.

Started adding the black pin striping too.

[pd1]

Started the stab and vertical fin today.
I photo copied the stab plan so I didn't ruin the kit plan.
Am I glad I have power saws.


Cut out the stab tips and made the spars.
Started gluing the parts together.


Sanded the fin flat.


Added the top and bottom spar and center section sheeting today.


After sanding check fit of stab to fin.


Now to check fit to fuselage... Oops...


One cut with the saw and now it fits


All the structures are done. All the parts from the kit fit well except for the little dorsal fin to fuselage fit.
A small cut fixed that problem.

Now final fit and finishing.. One big question.. what covering?
I like silk but I would like to use the Towercote I have before it goes bad.
I have four rolls of orange... decisions, decisions...

I have adjusted the incidence to where I want it and now have glued the stab to the fuselage.

The plastic square on the table was used to get the fuselage vertical before leveling the stab.
elevator has to be covered and hinged before fin can be glued in place.

The toothpick is to hold the hinge. Cut off and lightly sanded til flush with the surface and then cover.

The fin has been glued in place.
Alignment had to be checked so it would not be tipping left to right and so it didn't get a built in offset rudder.

And a check of the fit of the rudder before covering and hinging.

[pd1]

Started covering.

First up I like to balance the wing just before covering, the wing needed 10 grams to balance. I drilled a few holes in the wingtip, added B B's and then put a sheet of balsa over them.


Start covering.. I like to cover the trailing edge of the wing and wing tip parts before the main cover.


I like Du Bro pinned hinges, I hold them in with a wooden toothpick.

I cut the covering large enough to do both sides of the aileron with one piece. After attaching the covering to the leading edge of the aileron, I added the hinges. then ironed down the bottom side of the covering.


The trailing edge was trimmed and then the top side of the aileron covering was ironed down. I use as low a heat setting as I can to just get the covering to stick and not shrink at this time.
After the aileron was covered, I hinged the aileron to the wing with toothpicks. After the wing is covered they won't show.
If the control surface ever has to come off, it's easy to just punch the toothpick out and remove the surface.


Covering the lower half of the wing. I lay the oversized sheet on the wing and using the lowest heat setting.

I tack the highest part of the root of the wing. I then pull the covering tight and tack the tip then the leading edge and trailing edge. By only tacking in small places at first, the covering can be re positioned until most of the wrinkles are out and it is tacked all around the perimeter.


Once the perimeter is tacked I like to seal around the perimeter to about the width of the iron, I use a little higher temp setting for this.

Then I trim the edges and iron them down.

Last, the heat gun should get the remaining wrinkles out. One weird part is once the heat from the gun is applied, the covering slackens up a lot. Keep the gun moving and keep heating the covering and the covering will start to shrink again.


Wing covering finished
I finished the orange base color for the wing.

The tip of the top wing has a pronounced compound curve in it, much more the the bottom of the wing.
I did the tip first so that I would be working with a smaller more manageable size of covering. Also if I messed it up, less waste.
Also the seam at the tip will not be very visible because there will be a sunburst white over most of the tip.

[Dimeflyer]

your pics didnot come through guy ?
George

[gramps2161]

Originally Posted by Dimeflyer

your pics didnot come through guy ?
George

those posts are reserved for PD1 to post in when he gets to that stage of the build. That way the thread does not get cluttered.

By the way subscribed.

[stuart]

also subscribed pd1,lets see those pictures,we love pictures.

[pd1]

I borrowed an Astro Hog from a friend to check his incidence angle.

I first leveled the plane so the height of the stabilizer leading edge is the same as the trailing edge.

Measured at the center of the leading edge and the stabilizer in neural.


Next I measured the leading edge of the wing and the trailing edge of the wing. The leading edge is about 1/8th of an inch higher than the trailing edge. I measured the leading edge from the most forward part of the leading edge.


I will put my Hog on the jig and level the wing front to rear.
I will then level the stabilizer so the leading and trailing edges are the same height.

[rcers]

Originally Posted by pd1

Do the pictures in the first post not show?

I see them....

[Dimeflyer]

OK -I see the first post with your pics.
and I am thick between the ears but I got the idea about reserving the space now .
George

[pd1]

No problem George, just a senior moment.
We all get them.

[stuart]

pd1 those are great pictures........i was just saying i look foward to the future pictures of this build. i guess i'm a picture addict.....


it's a neat idea saving space for future pictures to be assembled together like that after the build is completed.[got any new pictures]jk

[Dimeflyer]

Thank you PD1
George

[pd1]

Second wing half pictures added to first post

[stuart]

pd1,the wing is looking great, just a thought on the pictures....if i follow the thread thru the process and jump to the last post typed each time to read your progress,it's strang to jump back to page one to see pictures. something new to me and i like the idea of all your picture located on page one for someone who opens the thread to take a glance and see all the photos. somehow it's going to take some getting used to since i like seeing pics as you go along on each new post,i guess i'm just a lazy sob. the pictures are great!!keep them comingand thanks for sharing.

[pd1]

Wing joined, see post number two.

[Dimeflyer]

Very interesting guy I think I may build one in a little smaller scale some day ?
Keep going we are watching closely !!
George

[Murocflyer]

Looking great Paul! You are speeding right along. Overall, how is the quality of the kit? Instructions good? Would you recommend it to others (like myself? )

Frank

[pd1]

Originally Posted by Murocflyer

Looking great Paul! You are speeding right along. Overall, how is the quality of the kit? Instructions good? Would you recommend it to others (like myself? )

Frank

Thanks Frank, I would recommend this kit. The build is more work than a laser cut kit, but I knew that going in.

The wood is a bit heavy in this particular kit, but there is always a variation of densities with balsa. My friend has an Astro Hog that has wood that is too light. Between us, we average out to perfect weight.

Instructions are easy and not many problems, other than the modifications I want to make to the plane.

My personal preference would be a slightly smaller plane. I keep hitting things in the workshop when I move the wing. My preference would be around a 50, plus or minus, inch wing.

The wing is done except for the cap strips, I'll wait on them until I have the fuselage done, one less thing to damage while moving parts.

I'll have a slight delay while I repair my Pulse. I flew it through a tree Sunday, broke the aft end of the fuselage off and tore the gear mount out.

The plane fared better than the tree, we cut the tree down to put it out of our misery.

[ENUT]

pd1 thanxs for building thread.I'm picking up this kit.
ENUT

[Murocflyer]

Copy that Paul. Thanks for the info.

Frank

[pd1]

Originally Posted by ENUT

pd1 thanxs for building thread.I'm picking up this kit.
ENUT

If you have any trouble locating this kit, RCBuyers Warehouse has one in stock.
No sales tax in New Hampshire either, plus free shipping.
http://rcbuyerswarehouse.com/sigastrohogkit.aspx

[pd1]

Started the fuselage. Pictures in post three.

[pd1]

Wing is ready for final sanding and covering. New pictures added.
Fuselage has been fitted to the wing and hold down mounts are in.
Firewall has been glued in. Now to pre mount some equipment.
Pictures are in fuselage post above.