Unstable Quinstar?

On TRF Les had an unstable Quinstar flight with a D12-0 engine.
Some thought maybe it got hung up on the launch rod, starting to spin on the way up. 

For anybody interested in a 24mm conversion, 
Here's my TRF response - 

I've launched my Quinstar with both C6 and D12 engines. My flights were stable.

I've attached a picture showing a D12 engine installed and how far it extends, 1/4" out the back.
Also shown is the 18mm adapter. The upper end slips inside the 20/50 centering ring used as an engine block.
With the 18mm adapter the casing extends 3/8" out.

To see the entire Quinstar build conversion from finish to the start: CLICK HERE

Estes Quinstar #7241 Build, Part 11, Finished

This was a fun build and turned out better than I thought it would.

With just the flat, upward facing pieces filled and smooth the model looks good.

The 24mm engine conversion was easy to do. Will it survive the boost or reach the Speed Of Balsa? Who knows.

It'll be flown with 18mm engines first and the D12 engine later.

For a lot of 1/16" thick balsa, the structure seems very strong.

Here's the views from the side with the launch lug and from the rear.
To keep the weight down, I didn't worry about getting paint in every nook and cranny. I just shot the flat surfaces and let the paint fall where it wanted. You can still see some bare surfaces if you really look.

Estes Quinstar #7241 Build, Part 10, Undercoat and Red Paint

The assembled model was hit with a light coat of gloss white. I wanted to use Rusto Red Metallic. It's a bit transparent and would need the white underneath it.

I thought I might get by with Titebond M&TG fillets on just the upper part of the model. But, the bottom areas really showed the open joints and seams.
I went back and added more fillets to the lower half.

Most all the surfaces got a light sanding before the red was shot.

All the flat upper surfaces were filled for three reasons.
The upper flats are the most visible on the finished model.
There would be less drag without adding much weight.
The decals would adhere better to the smoother surfaces.

TIP: Set the decals on the model (still on the backing) before soaking to get an idea how they will be centered.

Estes Quinstar #7241 Build, Part 9, Removeable 18mm Mount

The 24mm BT-50 tube and ring are glued into the center hole of the cage.
Glue was dripped down the side walls and the tube slipped into place with the centering ring (engine block) at the top.

Glue together the 18mm mount as shown in the instructions but the top 20/50 ring is left off. That ring is already inside the BT-50 now in the cage.

A rubber band was used to keep the split ring ends down and against the body tube wile the glue dried.

The open top of the BT-20 mount slides into the 10/50 centering ring at the top of the BT-50.
I had to rub down the burrs on the inside of the centering ring so the top of the BT-20 tube would slip in easier.




Here's the 18mm mount in the 24mm tube. It's not glued in, but slipped into the 20/50 ring already in the top of the BT-50 tube.
The rear notched ring is flush with the end of the BT-50 tube.

A small strip of tape would wrapped around the back end to keep it in place. The fit is pretty tight, it might not even need the tape.
The ejection charge would blow out the top, it might not kick out the engine mount.

Estes Quinstar #7241 Build, Part 8, Launch Lug and 24mm Mount

It's a blog post day - Free internet at the Starbuck's in Arruba!

One of the "L" pieces has a hole in it for the launch lug to slide through.
Apply a line of glue and slide the lug into place. Be sure that glue doesn't get into the lug.

The 24mm mount is actually pretty simple.
Glue a 20/50 centering ring (not the split ring) even with the end of the BT-50 tube. A D engine will be friction fitted or simply tape wrapped for retension. There isn't enough room on the sides for an engine hook.

The top hole in the bulkhead is sized for the 18mm mount.
It'll have to be widened to the inside diameter of a 24mm engine.

Wrap some 220 grit around a 13mm engine casing and widen the hole diameter.





Set the BT-50 tube into the cage with the centering ring up against the bulkhead.
Check to be sure the hole is slightly wider than the middle of the centering ring.
To protect the inside hole sides wall from the ejection charge, rub some glue into the balsa.

Estes Quinstar #7241 Build, Part 7, Star Points and Spin Flats

There's FREE internet in Curacao, so today - A build post!

The star points are glued next.

You probably could sand an angle so they fit without a separation line. That would shorten the width and require larger ones to be cut out.






The angled spin tab flats glue to the outside.

The structure is getting pretty strong now.






Flat center horizontals are last.
The tabs on the "L" pieces fit into the slots.
The outside ends didn't quite meet up with the cage sides.

Estes Quinstar #7241 Build, Part 6, Fillets and Bulkhead

Flip over the cage so it can be pressed down and even on the tabletop.

Before adding glue, the BT-50 was slid into the center cavity so the pentagon shape would be even. One of the centering rings was slid into the compressed BT-50 to keep it round.

A line of glue was applied and smoothed with Q-tips. Some areas are hard to reach with your fingertip.

There are three pentagon pieces. The two smaller "H" pieces are glued together to make a thick stop bulkhead.

Mine was too small and slipped right through the center of the cage. I probably sanded off too much of the burnt laser edge.
A wrap of card stock strip was glued around the outside to increase the diameter.





The instructions have you glue the H pieces into the cage and then glue the "I" piece on top.
I glued the I piece to the Hs then glued the assembly into the cage top.

The top pentagon bulkhead is glued in place.

Estes Quinstar #7241 Build, Part 5, Dry Fit Cage

Look close at the picture to the right.
Where the outside ends cross, the holes on the outside (left of center here) should be smaller.
If you have two outside holes the same size, it is assembled incorrectly.

Try a dry fit first, no glue should be used until you are sure of the assembly.
Pieces 1 and 2 are slid together.
Enlarge the picture and you can see the numbers 1 and 2 are inside and facing each other.

Part number 3 is added.
The numbers 1, 2 and 3 are facing the inside of the structure.

Part 4 is slid in.

Part 5 finishes out the cage and forms a star and pentagon at the center.
Check the outside cross intersections. The right side will be higher than the left so the flat "K" pieces will end up at an angle.

Estes Quinstar #7241 Build, Part 4, Don't Make A Mistake! TIP

Be ready, the balsa is thin!
If it breaks, just glue back together with some CA.







Here's all the punched out girder pieces.
There are a lot of them. They are probably too small to be re-used.



Two different forum posts mention errors made when gluing together the wide center "cage" pieces. It's a complex interlocking structure and easy to get wrong.

As the instruction NOTE says:
"Numbers must face inwards toward the center of the model."
This is important. Dry fit and double check before using any glue.



Here's the numbers they are talking about.
The numbers 1 - 5 are only burned on one side of the balsa sheet.
The numbers should be at the top and all face inward when the girder "cage" is assembled.

Estes Quinstar #7241 Build, Part 3, Balsa Prep

I usually sand off some of the burnt laser cut edges.
Don't take off too much, the fit of the parts might end up too loose.

When the center pieces are removed, there are many hold down "ticks" left along the sides.






It takes a while (there are a LOT of cut-outs) but they can be smoothed off.
Some 400 grit was wrapped around a dowel and the hold down ticks removed.






Here's an after shot showing some smoothed cut-outs.

Estes Quinstar #7241 Build, Part 2, Balsa Prep

The instructions have you make the engine mount first.
I'm going to wait as there will be some changes to adapt it for both 18mm and 24mm flights.

I'm not going to fill all the balsa, that could make an already draggy model too heavy. I decided to fill just the flat surfaces you will see looking down from the top.

The balsa sheet is 1/16" thick. CWF was brushed on while the perimeter pieces were still attached to the sheet.
Notice the number "3" on the center of the large center piece. I only brushed filler onto one side of the sheet, the side with the numbers on them. These will end up being the top side of the horizontal pieces.

The instructions have you sand the pieces while still attached to the sheets.
TIP: Sand up and down, not side to side as shown in the instructions. If you sand side to side you'll hit the vertical slots. Look at the top picture, you can see they are lifting.

Here I'm sanding up and down with 400 grit.
Sand enough to smooth the balsa, you don't want to thin it any more than it is.

Estes Quinstar #7241 Build, Part 1, Parts

This should be fun!
Here's another kit that shows what can be accomplished using laser cut balsa.
"Quin" is named for the five point star saucer. No nose cone on this one, it's much larger than the Blenders.
Blenders use 13mm engines, the Quinstar is made for 18mm engines, the B6-0 and C6-0. The C6-0 altitude is only 150 feet.
I just might convert it for 24mm engines. It should be strong enough, the 1/16" balsa is well supported with all the interlocking struts.

The face card is actually a picture of a finished model, not redrawn or smoothed out using photo editing. You can see balsa grain pores. The horizontal flat piece "M" has the hole for the launch lug. There is no lug in the face card picture.

Parts of interest: 

There are five laser cut sheets of 1/16" thick balsa.

A small sheet of silver decals.

A standard 20/50 engine mount with Mylar retaining ring.

The BT-50 tube was flattened a bit. Not creased, but flattened.
This was like some tubing found in the STM 012 kit. The kit bag isn't big enough and compresses down on the tubes.