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rtfm

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Hi,
After two unsuccessful attempts to bond the turtledeck to the rest of the fuselage, I've decided that it I'm experiencing these issues, so will any subsequent builders. So I've dropped it. The new FleaBike will have a minimalist look, which I like very much.

Pictures on the website, if you are interested.
 

Hot Wings

Grumpy Cynic
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How does that move the trust line to center of the prop hub and stop the airframe shake .?
We are getting pretty off topic..................

By replacing the fixed mounting point at the crank flange with a pivot eliminates the torque about the crank from the offset lift/thrust of the single blade.

The average lift of the blade is still around 42% of the prop blade span but we have now introduced a 'coning angle', just like in heli and gyro blades. The centrifugal force of the blade, due to the coning angle, now introduces another force vector aligned with the crank axis.

Imagine a static prop blade hinged at the root. Pull on the blade to simulate thrust and it will pivot with no force applied to the crank until it is at 90 degrees to it's normal position. In between if you also pull on the tip, to simulate centrifugal force, there will be force on the crank.

The coning angle will constantly change with each change in thrust or RPM and leads to per/rev force variations due to those changes - making a static counterweight a less than perfect fix.
 

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Protech Racing

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Thats a poor test.
First; We know that the optimal single needs to be larger than the 2 blade. So the single blade was never optimized.
My point is that the optimal single blade shakes the airframe due to the thrust line being down th blade of the prop. Not centered on the hub , like any multi blade prop .

Hot wings . thanks, yes , that would improve it .
 

rtfm

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Question:
I think I may have built the fin slightly off-true along the fore/aft line. It's bonded on solidly now, so there's no removing it. Any advice on how to compensate for this?

Duncan
 

Topaz

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Question:
I think I may have built the fin slightly off-true along the fore/aft line. It's bonded on solidly now, so there's no removing it. Any advice on how to compensate for this?

Duncan
Depends on how badly it's out of line. In fact, if it's a only a degree or so in the correct direction, you've unwittingly compensated for P-factor in climb. ;)

If it's not too bad, put a permanent trim tab on the rudder and call it a day. You'll be living with a slight rudder deflection all the time, but that's the price you pay.
 

rtfm

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Beginning to plan the construction of the wings. The wings will be built in 1.25m sections. On the front wing, the two inner sections will be fused, to make a single 2.5m section, with the outer 1.25m panels connected with hinges, so that the panels can fold up and over the top to meet in the middle.

1615769609516.png

I'm not that flash with 3D CAD, but this is the view from the top:
1615769690131.png

My issue at the moment, now that the fuselage is complete, is how to build the wing sections. What sort of jig do guys use? Since my sections are only 1.25m long, it ought to be relatively simple - but I'm struggling to get my mind around how to line things up.

I have 1.25m long spars, the ribs are cut from 25mm Dow blue foam in 3 pieces (leading edge, middle, and tail sections).

I was going to thread the leading edge section of the ribs onto two 25mm stainless tubes I happen to have in the shop. The tubes run the length of the section, and terminate in two sturdy end-pieces. Then I planned to bond the pre-bent plywood onto the ribs and onto the spar cap.

Once done, the middle section would be threaded onto two more SS tubes to fix their position, and the middle section of the plywood skins bonded. Similarly for the tail section.

Mmmm Not sure about this methodology - how do other builders do it??

Duncan
 

rtfm

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After some hours of thinking, here's what I think I might do:
1615791313464.png

  • Use the cnc router to cut our recesses for the spars and shear web.
  • Also cut out a recess for a 3mm strip to bond the pieces (nose/body/tail) of the foam ribs together
  • Bond the joining pieces to the foam (use a jig to ensure alignment)
  • Bond the spar caps to the shear web (19mm x 19mm either side)
  • Cut a jig in order to sand away the excess on the spar caps
  • Slide the ribs onto the spar, and bond in place

Basically create single piece foam ribs just like the chopstick ones, and bond them all together.
 

Victor Bravo

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If you bond the top joiner strip to the front and rear rib halves, and let this glue set, then you can spread the "partially completed rib" slightly apart and slide it over the spar, then squeeze the rib back together to clamp together onto the spar. This could help prevent misalignment, and speed up the assembly process.

By contrast, if you glue two separate rib halves on the spar, you will have to come up with some kind of jig or holding system. With the "partially completed flex-rib" trick, you will only need two nails and a rubber band to close the ribs around the spar while the glue sets. Then you go back and put on the remaining wood joiner strips all in one operation, just holding them on with masking tape.
 

rtfm

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Question:
I think I may have built the fin slightly off-true along the fore/aft line. It's bonded on solidly now, so there's no removing it. Any advice on how to compensate for this?

Duncan
Well, as the saying goes, "Seeing is believing". Not true! One's eyes are terribly deceptive.

I was convinced that my fin was off by an uncomfortable margin - so I unearthed my trusty DeWalt line laser level from under piles of half-forgotten piles of wood and other detritus - and turned it on. Batteries kaput. Armed with fresh batteries, I was able to confirm a slight misalignment, which over the length of the plane amounted to about 10mm at the nose. I think I can live with that.
 

rtfm

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If you bond the top joiner strip to the front and rear rib halves, and let this glue set, then you can spread the "partially completed rib" slightly apart and slide it over the spar, then squeeze the rib back together to clamp together onto the spar. This could help prevent misalignment, and speed up the assembly process.
Victor Bravo - that's an excellent suggestion. I'm so pleased I asked the question, because I certainly wouldn't have thought of your flexy trick.

Thank you,
Duncan
 

rtfm

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Another question for the Flea-bitten brigade:
I was planning on using Richard Fraser's F5Fras15 airfoil, but am now thinking I might go with a more "mainstream" airfoil. Question: What is the currently preferred airfoil for Fleas?
 
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