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BBA/Winter Build 2017/18 - Top Flite Corsair

Joker 53150

Mmmmmmm, balsa.
Mentor
#61
Ah, the joy of fixing another guy's work! :) Good thing you saw the problem and knew enough to fix it before sending up for a (very short) first flight.
 

willsonman

Builder Extraordinare
Mentor
#62
Yeah, I guess I never spoke about the issue here. You can clearly where the carbon went that the wood is butt-jointed. It should be dove-tailed per the plans AND instructions. I went back and forth on this for many days trying to decide on whether or not I should do a folding wing. I opted not to. It is a bit much to take on, maybe if I had another year.
 

willsonman

Builder Extraordinare
Mentor
#64
In reality, the wing center section is keyed together and would not be that hard to build. The outer panels are assembled separately and then epoxied to the center section. Really the hard part is making sure the outer sections are epoxied in at the correct dihedral angle.

Moving along I need to get going on proper mounts for the aileron and flap servos. I'll study the plans and, more than likely, cut out new ply mounts for them. Originally, this is to have a single aileron servo with bell cranks. With how the corsair usually flies, I would like to be able to program my own aileron differential rather than make mechanical differential. this will make rolls much more scale and rudder coupling will not be nearly as dramatic or sensitive. I also will be using smaller, lighter servos but with sufficient torque. The effort is to save a bit of weight, if possible.
 
#65
Pretty sure that weight will come back in scale detailing. With some of the great small servos available these days, there's no reason to not save some weight with servos.

I love the new radio gear out there! I'd love to have another crack at a Carl Goldberg Ranger 42' like I had as a kid, and see how it would fly with modern gear! In 83 I had an OS .10 on the nose with three full size servos inside and an AA alkaline receiver pack. It was probably close to warbird wing loading. Looking back, it's no wonder I didn't learn to fly with that plane....

BTW, I love Corsairs!!
 

willsonman

Builder Extraordinare
Mentor
#66
Every gram saved in construction gives me another gram to play with in details. It is a skill acquired over building many many models.

Wrapping up the retracts a bit, I referred to the retract section on page 39 of the instructions. I found this builder's note:

"Robart Robostruts were used on the prototypes. These add to the appearance of the Corsair and smooth out good to moderate landings. They cannot, however, absorb the huge amount of energy that wire struts can. For example, a fast or
high sink rate landing on rough grass will put a huge backwards bending force on the gear. Wire struts will handle this well; Robostruts are not designed to cope with this situation. The prototype Corsairs were flown off of pavement and grass through good to moderate landings while equipped with Robostruts
with no failures."

This is sound advice and I went digging through a reference build over at RC Scale Builder. I found that I had been thinking the same thing. Why not have the best of both worlds? Rather than use a robostrut (oleo) alone, use a sprung wire as well. I used the wire supplied in the kit and used my dremel to cut the hardened steel. Grinding the flat spots took quite a while to get right as they are not true to the front/back or sides. The rotating gear's grub screw is offset so it took a lot of trial and error of fitting. This was compounded further by the loop in the wire not fitting between the case of the retract so it had to be rotated just right for a perfect fit.
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At this stage I am more or less on page 15 of the instructions. I need to install my servo mounts still as well as the hinge blocks on the TE of the wing for the flaps and ailerons. I will also need to run my tubing for the pneumatics. I am making the call to follow the instructions closely and will not be doing fully-hidden linkages. While it is a nice commodity, it takes a lot of time and effort and usually introduces slop that I am not willing to accept.
 

rockyboy

Skill Collector
Mentor
#67
That's a killer mod on the retracts! Very excited to see it in action.

I wonder why Robart hasn't offered this as an option before (or did I just never see it)? Would it just cut into their replacement part sales too much? :p
 

willsonman

Builder Extraordinare
Mentor
#69
What is interesting is that the opening pages of the instructions call for the 100-degree robart retracts. Later in the installation of the retracts, it calls for the 90-degree ones. The only flaw I have found so far in the instructions.
 

willsonman

Builder Extraordinare
Mentor
#70
Had a couple of hours last night so I forced myself to get back on this project. I'm buttoning things up for the wings to be sheeted.

First up is the aileron servos. These are metal geared digital mini servos that will do the job just fine. I had to cut away the stock bell crank mount and make this tray. There is a platform that the servo screws onto and the platform is screwed into the tray. A hatch will be created in the bottom of the wing to make the servos accessible. I also want to note that this is the 4th rendition of this mount. 3 other failed attempts were made so there was a lot of work involved here.
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Two pieces of balsa on the ribs for support and one cross member to stiffen things up as it is pretty thin ply.
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Next up was the flap servos. Stock location and there was plenty of room for full size servos. There is a Y-harness that has a reverser built in so the arms move the same direction.
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A shot from the top.
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Time to plumb the retracts. One of the perks of working in the biotech industry is expiration dates. Something goes bad and it simply gets tossed out. This PharMed tubing from Masterflex is one of those salvages. This tubing is resistant to pretty much anything chemically and is UV stable as well. It should last a good long while and is much more flexible than the standard tubing used in pneumatic retracts. Cable ties secure the tubing at the barbs and I am using standard T connectors from DuBro. The system was pressure checked for leaks and I left the system pressurized at 80psi for an hour. I only lost 1psi over that hour and afterward I got 37 full cycles of the gear into the locked position. I did not use cable ties at the air valve so I'm pretty sure that the slight leak came from there but overall... yeah...I'm confident that this will be a very robust setup.
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WIth all this work now done I can go over the shaping instructions carefully and prep the structure for sheeting.
 

willsonman

Builder Extraordinare
Mentor
#71
Well, here we are again.

I got the shop table cleared off so that I could create my sheets of balsa. Quite a bit of time was spent blending the leading and trailing edges to the ribs. The curves in the bends were the trouble spots as you want to make them even but you cannot really use a sanding bar. like a traditional flat wing. The skins are made from 4 planks of 3"x24" that are glued end-to-end. They are then sanded flat with a bar sander. Skins are cut with 3/16" overage and dry fitted to make final fitting cuts. I tack glued them into place with thin CA and followed up with a cotton swab and wood glue. I use this method as a means to push the glue into spots without using too much to save a bit of weight. The tips are separate pieces on the bottom.
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Next up will be the top of these areas as one sheet. Before I do that, I need to use a #11 blade to cut holes for the servo hatches. I will glue in a ply plate from the inside, or at least corners, for the hatch to screw into. This is one extra step that is NOT in the plans as they call for a bell crank system. This will take a bit of time since I will need to make the hole and make sure I can remove the servo and mounting plate... then cut overage for the ply plate. Once one is done, the other will be a mirror image.
 

willsonman

Builder Extraordinare
Mentor
#73
Its really not that hard.

If you can cut a piece of foam from a large piece of foam, then glue it to another piece of foam... you can...

cut a piece of balsa from a large piece of balsa, then glue it to another piece of balsa.

:p
 

PsyBorg

Fly Angry
Mentor
#75
The Corsair is on my top ten list probably top five if I think about it. Gonna be so nice to see this baby in person at FFE (if you plan to bring it hopefully) Now that you are starting to covering process have you thought about the colors squadron markings or anything like that or is it too soon to think that far yet?

Setting my lack of fixed wing piloting skills aside I would love to do a balsa build if I had the room. Barely enough room for my quad stock pile of parts and stuff in this little mouse size apartment though so that will sit in the "One day" pile still.
 

willsonman

Builder Extraordinare
Mentor
#76
I have thought about markings a bit. I'm leaning toward a Marines unit. Mostly because it will make the paint and marking s easier AND by keeping the paint simple, it will help the details, line panel lines and rivets, stand out. In all honesty, I've had the original parkzone corsair and orientation is pretty easy to keep with the silhouette this thing makes. So colors on the top and bottom will not make much difference for me.

An yes, I have every intention of bringing this to FFE this year.

Moving along...

I did get the aileron servo hatches done. The hatches are balsa scrap from the skinning process and some light ply was used as a support for it.
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I also installed the pitot tube and sensor for air speed.
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The port side top wing skin is curing out currently and I hope to get the starboard side done before the end of the day.
 

willsonman

Builder Extraordinare
Mentor
#77
Last update for the day...

So the top skins I used a combination of CA and my default... gorilla glue. I put the GG on the spar and inner ribs while leaving the outer ribs, LE, and TE bare for CA. I positioned the cut skin over the wing and slightly adjusted until happy. I glued the root rib and then the tip rib. The LE and TE were then glued and the whole thing was laid out with sand bags for curing. This is MUCH faster than using wood glue and worked amazingly well.
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Here is a completed outer panel.
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After it was all dry, I used my razor planer to get rid of the excess on the leading and trailing edges. The #11 blade and sanding bar too care of the ends. I still need to clean up the root rib a bit as the top gets the sheeting before the bottom on the inner panels.
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PsyBorg

Fly Angry
Mentor
#78
Ahh. Was wondering if maybe you might be going with the silver n black or the all black and not traditional Pappy scheme.

Do you have to treat the sheets at all to form them or is just working with the wood grain in the proper direction enough to shape this type wing enough? I know before you guys had talked about spraying wood with water and ammonia I think it was or am I confusing film covering with the wood methods?
 

willsonman

Builder Extraordinare
Mentor
#79
Yeah, so these parts it is all about working with the grain. It is honestly the same as working with foam board... it has a grain too. The center sections are the difficult bits where you use the wood grain at a 45-degree bias as well as wet it out to conform to the compound curve. Exciting stuff ahead.
 

willsonman

Builder Extraordinare
Mentor
#80
More progress. Not as much as I would have liked but still good progress to keep me motivated.

Just follow the instructions... one piece at a time. Believe it or not, this was the HARDEST piece to trim right. One side soaked with water on a paper towel and the dry side is glued in place. Worked perfectly.
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A few more pieces and BAM!
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Rinse and repeat for the other panel.
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