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Build Thread; Mountain Models QF-2 DLG

Old 07-08-2008, 04:47 PM
  #26  
buzzbomber
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Nice to see a build of this kit. I've been toying around with the idea of trying a DLG for a while and have narrowed it down to this kit or the DL50, since most of the composite airframes are either expensive or regarded as junk. This type of construction is more what I'm accustomed to, though I have done foam wings before. Do you see any areas that would be difficult for anyone who's built laser/die cut balsa and foam kits previously?
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Old 07-09-2008, 02:32 AM
  #27  
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Default No Problem!

Hi Matt,
The build so far hasn't presented any problems that a reasonably-experienced builder couldn't handle. There are a few newer techniques like the F/G cloth over the tail surfaces and the carbon-reinforced dihedral braces. But these are really a good entry point for composite construction and are so well-explained with both text and photos that it seems unlikely that an "unfixable" mistake would be made.
The one suggestion I'd make (and this is recommended in the instruction booklet, but not everyone does it!) is to read the whole booklet before starting. I found a few areas that caused a little head-scratching upon first reading, but as I got to later chapters, it all became clear.
Since I'm one of those who likes to know the "why" of things, this was a little disconcerting until I got to the section that answered my questions. Then came the "Aha" moment and all was well!
So, a long way of saying "Yes", great intro DLG, with some good new ideas thrown in.
Ron
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Old 07-09-2008, 04:10 PM
  #28  
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Cool! Thanks for the feedback, Ron. I think I might have my birthday present to myself picked out.
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Old 07-10-2008, 02:30 AM
  #29  
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Default Wing Work

Hi Matt,
Yes, I hope you get one, you won't be sorry!
Here's the ribs glued to the spars (only) and the trailing edges.
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Old 07-10-2008, 12:12 PM
  #30  
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Default More Wing Work

Here's the next stage of the wing construction, and should clarify why the ribs were glued to the bottom spars only, not the sheeting. This was one of those "Aha" moments I mentioned.
The airfoil has Phillips Entry, a slight upsweep on the lower leading edge.
(1) Front of ribs before gluing to sheet.
(2) A 1/16" shim is placed under the leading edge of the sheet, or you can lift it with your fingers, pressing down on the spar at the same time. It may sound tricky, but the instructions explain to quite well. I ended up using a full-span (half-span, actually) scrap from the rib material. Each rib is then glued to the bottom sheet as the upsweep is held in place.
(3) Right wing done.
(4) Both wings done, you can see that I've moved the shim to the left wing.
(5) Added rib "1A" to center.
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Old 07-11-2008, 07:44 PM
  #31  
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just pulled the trigger - will be watching this thread for tips.
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Old 07-12-2008, 01:55 AM
  #32  
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Default Vertcal Webs, 2 Methods

Way to go, Matt! Hope you enjoy your QF II.
In addition to the sheeting, the spars have front and rear webs, which form a "box" spar, one of the strongest structural elements used on wings. When the top sheeting is added it will form a "D" tube leading edge, another very strong technique.
Here's the web installation. The instructions have a somewhat hard-to-follow method that uses pins to mark alternating rib bays, so that you only glue in every other web, and the pins hold the spar (and the rest of the wing) flat on the board. Once you read it through, it makes sense and insures a warp won't be built in. Then you remove the pins and add the missing webs.
I understand that any kit must be made to be as foolproof as possible and Mountain Models is one of the best at this. They know that their kits will be built by modelers with a wide range of experience (or inexperience, as the case may be) so great care is taken to avoid the common pitfalls.
Having said that, I prefer to install all the webs at the same time. I know there's a possibility of warping the wing this way, but by using "medium" CA and holding the wing down with my thumb while also holding (each) web in place has worked for me many times. This is what I did.
Sorry if this is a long post, but there may be newer builders watching this and since I deliberately deviated from the instructions, it seemed important to explain why, and what the consequences might be.
I'm not saying one method is better than another. It's a choice, a personal preference.
(1) Wings with webs in place, not glued yet.
(2) Webs glued in, took about 30 minutes.
(3. 4, 5) Close up of webs, glued in.
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Old 07-12-2008, 01:03 PM
  #33  
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Default Next Step, Sanding

The wings are off the board, now the front webs should be sanded flush with the top spar so the top sheeting will lay flat. But it's also important not to knock off the small "feet" that stick up and engage the slots in the sheet. Otherwise you'll be left with lots of unsightly (and sloppy) holes in the sheet.
So, out with the emery board, fits nicely between the ribs and is easy to control.
Test fit the upper sheet, no glue yet.
Here's the bottom, one wing sanded with 180, one not sanded. I use only a long sanding block for this, no low spots!
Ron
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Old 07-12-2008, 05:59 PM
  #34  
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Default Shaping Trailing Edges

Here's photos of the trailing edge shaping;
First a rough taper with the razor plane, with this I try for a 1/16" rear thickness and don't get too close to the rib ends, so I don't nick or chip the ribs. Mainly removing material from the "middle" of the T.E.
Close-ups after planing.
The instructions recommend a final rear thickness of 1/32" or more. Although composites can go to a finer edge, for balsa this is a good target, any thinner and it's liable to warp or split off.
To keep a constant thickness, I've placed 1/32" music wire behind the rear of the T.E. This will prevent the sanding block from reducing the taper too much. As you're sanding, you can feel the block reach the wire.
End views after sanding
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Old 07-12-2008, 10:46 PM
  #35  
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Default Trailing Edges, Both Wings

Well, after some Saturday chores, got in another short bit of work on the wings. Finished the other trailing edge, and finish-sanded both with 400 wet-or-dry. Wiped off the dust and here's the result;
(1, 2) View from center section
(3, 4) View from tip
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Old 07-12-2008, 10:52 PM
  #36  
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Really nice work Ron, looks great.
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Old 07-12-2008, 11:41 PM
  #37  
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I agree, looks good Ron. You're making some good progress. Can you take a photo of one wing panel when you get the chance?

Thanks,

Frank
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Old 07-13-2008, 12:37 AM
  #38  
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Default Wing Photos, Weight

Hi James + Frank,
Thanks for the kind words, this is sure a lot easier than the Corben Ace!
Here's more photos of the wing(s), each panel weighs slightly over 19 grams at this point.
(1) Both wings
(2) One panel from center section
(3) Same panel from tip
(4) One panel on plans, don't know if the ruler markings are legible but it's 23-1/4" from center to tip rib, plus another 1-3/4" for each tip.
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Old 07-13-2008, 01:55 AM
  #39  
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Oh yea, that's a good looking wing. Very similar in design to the Gambler but looks like it might be stronger.

Thanks for the photos.

Frank
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Old 07-13-2008, 03:25 AM
  #40  
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Default Dihedral Joiners

Hi Frank,
Yes, it's pretty stout and the top sheeting will make it even stronger. But the velocity of a discus-launch puts some teriffic stresses on the wing and they are transmitted to the center section. Hope it holds!
Here's the beginning of a multi-part wing joining process. Again MM has taken great care to make this as fool-proof as possible, even if it seems complex.
They supply a guide to sand each center to the correct angle. Then an addition 2-part dihedral joiner (not the same as the one with the carbon fiber center lamination) is glued together. This brace fits between the top and bottom spars. One lamination is slightly less tall than the other; The top spar sits slightly higher in front than at the rear, following the airfoil.
30 minute epoxy, clamps, an extra sheet of clear plastic, mixing cup, I'm ready!
Epoxy on the top + bottom of the brace, slide between the spars, wrap plastic around it, then the clamps.
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Old 07-13-2008, 03:06 PM
  #41  
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Default Joining Wings

Now, the most critical step on the wing, or the entire airplane, for that matter. The instructions are very clear and I won't duplicate them here. Since I was running out of the right-size clamps, I adapted the "C" clamps with some scrap balsa, to apply pressure where it was needed.
First, these's several trial fittings (at least in my case, hopefully others have an easier go at it!) with a bit of sanding here, an increased bevel there, until it all fits.
The "C" clamps and balsa scraps form a cap on the top and bottom of the spars. This prevents the 2 carbon-reinforced dihedral braces from moving out of alignment vertically.
The 4 spring-loaded clamps squeeze the braces front-to-rear, pressing them against the spars and ultimately, the brace I put in last night.
So, the drill is, test fit the wings/braces, adjust for a tight fit.
Mix 30 minute epoxy, apply to top and bottom of the brace that's already installed in the right wing.
Slide the left wing onto the brace.
Put a coat of epoxy on the inside face and bottom of the C/F braces, place the 2 C/F braces in position, taller one at the rear of the spar, shorter one in front.
Use your 3rd and 4th hand to hold this together while wrapping everything in plastic.
Place "C" clamps to apply pressure to the top and bottom of the spars, here's where I used scrap balsa to distribute the load over all the braces.
Place the spring clamps to squeeze the front and rear braces inward.
While you're doing all this, the wing may shift a bit or seperate slightly. Once the clamps are in place, I wiggled and pushed the wing (back) together for a better fit.
Whew!
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Old 07-14-2008, 12:49 PM
  #42  
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Default Back To The Tail

While I was waiting for the dihedral joint to dry completely, I re-visited the tail section. The Minwax Poly has been dry for several days.
First I cut away the excess, in a couple of small spots the outside edges had lifted, I put a thin bead of fast-drying CA along the edge and rubbed it down with the poly sheet protecting my fingers.
I am sorely tempted to give the parts another coat of Poly, since the F/G weave isn't filled very well. It still has a "nub" or rough surface that just doesn't seem right.
But, the issue of WEIGHT rears its head. The instructions suggest a weight (at this point) of 9 to 12 grams for both pieces together. Mine came in at 10.87 grams. So, I'll leave them as is. If it balances OK and I have room to move the Rx battery forward, it may still get the top-coat later. If the C.G. doesn't have any latitude to add any weight rearward, they'll stay rough and I'll live with it. A gram at the tail means 3 or 4 grams in the nose!
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Old 07-14-2008, 01:52 PM
  #43  
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Default Ok, Ok, I Gave In!

Disregarding my previous advice and common sense generally, I gave in to the itch. A very thin top-coat of Minwax Poly somehow found its way onto the tail surfaces. Airplane finishes should be smooth!
This nit-picking will have a price, no doubt.
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Old 07-14-2008, 02:43 PM
  #44  
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Originally Posted by Sky Sharkster View Post
Disregarding my previous advice and common sense generally, I gave in to the itch. A very thin top-coat of Minwax Poly somehow found its way onto the tail surfaces. Airplane finishes should be smooth!
This nit-picking will have a price, no doubt.
Well, if it makes you feel any better SS I would have done the same thing. Nobody else will notice or care but it's one of those things that will be in the back of your mind every time you look at it.
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Old 07-14-2008, 05:37 PM
  #45  
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Default Thanks!

Hi Jim, Thanks for the support, you're right, it was already bothering me. Hopefully there won't be a big C.G. issue.
Ron
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Old 07-14-2008, 10:26 PM
  #46  
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FWIW Ron I have added baby powder to WBPU to smooth out the weave on a foamie before. It worked and smelled great when I was sanding it.
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Old 07-15-2008, 02:07 AM
  #47  
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Default Good Tip!

Hi James,
Thanks for the tip, I recall using talcum powder with my old dope + tissue coverings, it helped to fill the weave. Will try it next time.
The top coat tried quickly, especially after I put it near a window and the temp here was in the 90's all day.
Then I gave the surfaces a vigorous sanding with #400 paper, wiped off the dust and weighed' em. 12.2 grams! Not bad, and they are much smoother, I can almost live with it. Guess I'll have to!
Ron
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Old 07-18-2008, 03:11 PM
  #48  
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My QF2 kit came in the mail yesterday! Now to clear a spot on the building board...
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Old 07-18-2008, 04:49 PM
  #49  
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Hey guys,

Just a note on the current QF-2 kits. You'll need to scarf joint the spars to make them long enough. I was having problems getting some good spar materials, so I laser cut them from 24" sheets. So, being 24", they're not quite long enough, hence the scarf joint to make them long enough.

Sorry about not leaving a note in the kits that already shipped out after this change.

Brian
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Old 07-18-2008, 05:14 PM
  #50  
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Thanks for the heads-up, Brian.
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