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Wayne young

Help needed for dlg build thread

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blancmatter

Hi, hope this is the correct thread, as I just got a Flipper 1.25 from hyperflight. (Similar to Smile DLG)

I'm concerned about the suitability of the elevator for spring and pullcord (the kit came with pushrods, with quite a bit of slop in the outer). The picture shows the top of the stab, with the open side of the hinge.

The opening of the hinge is on the top side of the stabiliser, and opposite to where the control horn needs to go underneath the stabiliser. Can I still fit a spring, or does the opening need to be on the same side as the control horn (as in all the other pictures I've seen of spring pullcord setups)

I can't invert the stabaliser as the sunken holes for the screw heads are on one side.

Thanks!

20200412_160612.jpg

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MikeDLG

Fitting a spring with the hinge opening opposite the horn would be difficult. You usually open the hinge (up elevator for above boom tail) and fit the spring in the untorsioned state so as you close the hinge the spring opposes the movement. 

To fit a spring in that hinge gap, you would have to fit the spring in the torsioned state (down elevator). I guess it’s possible, but will be tricky. 

I usually just push the spring legs into the foam, but if you fit tubes (cut from the pushrod outer?) for the spring legs to fit into , it might not be to bad. 

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Paul Gleeson

That seems all wrong and a manufacturer defect. Maybe you should ask for a replacement part?

how about filling the counter sunk holes and drill through when it has set hard. CA and baking soda / micro balloons will set rock hard in seconds but easy to drill out. Fill the hole bit by bit to ensure the surface of the stabiles is still flat
 

Go with a smaller dril first then use the right size drill ( if the hole is centred) or a fine found file.  then replace the counter sunk bolts with cheese head screws. Job done. 
 

I guess this depends on how much of aerofoil camber the stabiliser has. Whole think about. 
 

I would ask for a spare if this is a defect part

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Mark Evans

The kits comes with pushrods so you’d have to mod the holes like Paul says to convert it pull spring. 

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Paul Gleeson

Or try a push rod with fine wire or 1mm carbon running in a ptfe tube along the fuse. 

there is a knack to do this by using strong magnets with piano wire in the tube to hold the tube against the wall of the fuse. Then run thin CA down the outside of the tube. Cut the tube longer than you need to avoid any CA getting into the tube. Then trim to length. 

page 34 from here http://olgol.com/Flitz2/flitz2_instructions.pdf

just another idea 

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blancmatter

Hi, thanks so much for the helpful replies. I have contacted hyperflight and see what they say. If its is apparently 'in spec'  i'll  flip the stab using CA and Bicorbonate as a filler.

 

Another quick query. The horns for the stabs are slightly different lengths (distance normal from the hinge). I'm guessing the shorter one is for the rudder, as this should have more throw on a DLG?

Thanks

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blancmatter

 

20200413_180206.jpg

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Dave H

It’s an Underslung stab, the horn goes on the top ie on the closed bit where it should go , the cut is on the bottom , same as my falcon , all looks good.  
 

The top photo the model is upside down, the second it’s on its belly the control horn is just about visible in the middle of the h stab

 

hope this helps

 

dave h

4E48220B-3657-4F2D-9C63-CD4361A58579.jpeg

395C72F1-E95C-4A5E-BF5F-C430A4612080.jpeg

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Dave H

Ok just rechecked the hyper flight website, seems it may come in 2 versions. On the main photo it’s underslung on the insets it’s top mounted ???

if yours is top mounted then that’s the wrong h stab. Neils normally very good about issues like this

might be worth seeing if there’s a build thread on rc groups

The difference is on top the pull string gives up elevator , if the spring ever breaks you only have down available.

if the stab is underneath the pull string gives up , this not only gives a more solid connection in the high speed (launch) Phase but if the spring were to break you’d still have up control and may be able to still land safely

dave h

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blancmatter

Thanks so much for the advice on my build. Managed to build the Flipper 1.25m with AUW of 208g, so not too bad.

Just been having an issue with cracks in the pod. Have had a couple of hard landings each time I've been out (nothing severe) and a couple of small cracks in the thin pod, that I've already repaired with CF and finishing epoxy (added around ~1g) have gone and reappeared.

Any tips (other than learning to land softer, which will come) on repairing in a more sturdy way?

Thanks!
 

cracklocation.png

rearcrack.png

frontcrack.png

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MikeDLG

I guess because of the size of the hatch access, those are weak spots.  What I would say is that when I repair similar damage is that I use the cloth on a bias.  In your repair, the fibers running vertically are doing nothing really.  If you put the cloth on a 45 deg bias then all the fibers are helping to bridge the damage.  I would repair again with the cloth biased and try not to doink it! :)   It may be worth an extra layer of cloth as well.  

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Dan p

I had crack on my flipper exactly the same spot!

like the point about having the weave Crossways, wish I have done that.

I did use One Direction carbon for strength as well.   picture you can see my repair job. Hope she stronger now. 

I did find 50mm c g  seems bit nose heavy what are other people cg 

Thanks

 

20200522_225220.jpg

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CTR

Problem with carbon is that it’s very poor in compression (but great in tension). That top edge of the cutout is in total compression when the nose hits the deck!

That particular spot, just where the hatch starts, will only have a fraction of the compressive strength of the full hoop section of the fus’.  Probably not helped by the servo mountings starting at the same place along the bottom too.

My suggestion would be to insert a piece of 2mm carbon rod each side, just under the lip of the hatch. Make sure it starts maybe 50mm in front of the opening, and continues back the whole length of the hatch cutout + 30mm. This will add a few grams but will give resilience where needed.

Carbon tow could be used but the ‘rod’ will be much better in compression than flat tows.

May be worth a try.

Neil P

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mikef

It's the thin section that makes it weak in compression - it buckles and fails in local bending.
The locally thick additional member will be less likely to buckle so it will be stronger.  Taper the ends so as not to move the stress concentration from the lip of the cut-out to the ends of the rod.


(A carbon section that's thick enough not to buckle overall will have similar strengths in tension and compression,.  Compression is weaker due to the fibres bucking inside the epoxy!)


Signed, pedantic aircraft structural engineer.

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CTR

Further good advice from mikef as usual, thanks Mike 🙂

I kept it brief, but it’s always good to taper any strengthening as Mike stated.  I had thought that after adding the rods, impact likely to cause a failure in the ‘full hoop’ front sections of the fus’ would be the least of your worries 😬

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blancmatter
22 hours ago, Dan p said:

I did find 50mm c g  seems bit nose heavy what are other people cg 

 

 

Yeah I found the recommended 48mm too nose heavy and required a lot of up trim. I think I've moved it back to about 50mm, but still might go a bit further back.

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