F-20 Tigershark - Tim Hart Plans - RC Groups
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Aug 19, 2012, 12:45 AM
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Build Log

F-20 Tigershark - Tim Hart Plans

Okay, I guess it's about time for another build. This time I'm doingTim Hart's F-20 Tigershark, scaled down 38%. This gives you 10.8" WS and 18.5" length. I had originally cut a 9" WS (33% scale) for B.I.M.'s 22mm NDF, but don't have the gear on had that fits. So, had to up size her a bit. I'll be trying to get the following gear in:
B.I.M. 25mm MDF, thinking cut down GWS w/ 6 blades
Leaning towards the E-flite BL 180 (10mm long can)
BA 2.5g Servos
Turnigy Plush 6a ESC (If I can keep it under 6a on 3S)
AR6300 Rx
Host of 3S bats

I'm going to try a couple of things with this build. Attempt to get better airflow to the EDF unit. I'm also looking to go with an airfoil on wings and stab. Depending on how everything squeezes in, I may try to have ailerons and elevator. Otherwise, I'll just go with tailerons. Here's a few pics to show what I'm working with. I'll post more pics as I start loading gear in.
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Aug 19, 2012, 12:56 AM
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Freddie B's Avatar
Now that is going to be really cool. Should fly real nice too. I love your metric cutting mat too BTW. I think you will find a way to fit all the gear in and that fuselage should help with lifting area. I'll be watching and enjoying your efforts. Thank you so much for doing a build log on this! Best of luck and I'm sure it will be beautiful!

Aug 19, 2012, 01:04 AM
corsair nut's Avatar
im on board! sweet project!!
Aug 19, 2012, 09:24 AM
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Waltjg's Avatar
Great, watching this one! w
Aug 19, 2012, 11:36 PM
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Thanks for the encouragement. I had hoped to get some building done today. But the Misses wanted to go to the beach. So I wind surfed in 15mph - 20 mph winds. That's with my Gripen, F-22, and T-50. Yes, that little sucker can surf with the best of them. Then it was off to the movies. The new Bourne movie is pretty good. Then had to spend time at Borders Book store. So, not much done.

But I think I have settled on how to do this. I'll use 1mm depron to make a ramp from the inlets to the wing. Then I'll use some 6mm Aero Depron to transition to half circles, like I did for the T-50. From here I can use index cards for inlet tubes to the fan face. Trying to keep it simple, but need to contain the air flow. The servos, ESC, control linkage, and wiring will be beneath and beside the inlet tubes. I'm also going to try and keep the taileron linkage internal. I have some 2mm square CF tubing, that's just the right size for piano wire to run through. Lay 4mm long CF tubing, flush to the outside fuse wall. The piano wire will run from the taileron, through the CF tubing, and be bent 90 deg vertical. I'll run the 90 deg bend, into a cutoff servo control horn. I have to credit NC with that set up. I think I should have the clearance around the EDF/exhaust. I just don't want exposed linkage, if I can help it. Now that that's out, I just have to make it happen. More to come.

Aug 19, 2012, 11:42 PM
Addicted to building...
Freddie B's Avatar
Please take lots of picture during the build if you are so inclined to do so. It would be really cool to see it come together one step at a time. We all learn cool things from each other and you linkage setup sounds really neat! Good luck getting some building time!

Aug 22, 2012, 09:40 AM
it wasn't me flying that plane
Hover or die's Avatar
When you start your ducts make your template parts make them 1 or 2 mm bigger than you need..This will give you room to sand them smooth and fine tune the turns..
Remember the spackle(to fill small imperfections),primer and paint will add a little to the overall thickness..
I have some other things that may help..
Do you have a small hotwire cutter?
I can point you to a nice handheld model that is great for small stuff if ya need...
Shoot me a pm or ask in either thread if you need anything..
Take care................Chris
Aug 22, 2012, 11:40 PM
Registered User
Okay Gents, here's an update. I've talked with Hover Or Die (Micro Viperjet) about making glass ducts. I managed to get a good plywood template cut out. I plan on doing the first hot wire cut tomorrow. Then we'll get to the next step. I will post pics of the process as I go. If you haven't looked at Hover Or Die's micro build, please do so. I'm doing my ducts the same way. It's crazy how there's no time when you REALLY want to do a project. More to come...

Aug 24, 2012, 01:27 AM
Registered User
Okay, this evening has been a bit frustrating, to say the least. It started out, my hot wire "Styro Cutter" would not heat up. Yes, you get what you pay for. Next, I turn to a "Hot Wire Foam Factory" table top model. It cuts, but I'm not sure it's hot enough or I'm just trying to cut too fast. Check out the pic below. At any rate, I'M NOT GIVING UP. Stubborn I guess.

I did have one bright spot. My nephew wanted to a model plane together. Real simple model, snap and screw. We managed to get it together and it doesn't look to bad.

Attaching pics of tonights efforts. Hover Or Die, you can send that pm now.
Aug 24, 2012, 03:40 AM
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Freddie B's Avatar

I feel the pain. I too had moments of frustration when I started trying hot wire cutting. I only now am getting much better results. I know the wire only needs to be in the 400 F something degree range. Yes you can easy try to cut to fast. Let the wire do it's work. I am also getting better at keeping the wire in contact with both templates at the same time. The wire will stretch some, but it should not look like a bow and arrow, drawn and ready to be released. I sure wasn't there when you were cutting, but the ridges and humps sure look like possible lost contact with template, and or the wire catching on rough edges on the template. Last with cuts they must stay parallel to the area being cut or you will get some weird tapers.

If you care too, and it's totally your call, but you might look at my newer thread on the Yak 15/17, and mostly the first few pages. I covered some hot wire cutting on the thread, and showed the good and the ugly. I used some of the cheap foam cutters too BTW and they worked. The wings were a whole another chapter.

Be stubborn, it is the only way to get the 'feel' of foam cutting. I even have practiced on some cheap packing foam just to get some practice without ruining my good stuff.

Realise to that posterboard also works well as templates. I cut 5 cones yesterday, 4 1/4" tapered to 3 3/4" dia, and the templates were posterboard.It sure is easier than making wood templates and I just use scissors.For me, if I make a top and bottom template, run the wire across both at the same time, the cuts look pretty like "those other guys" we wish we had their talant. LOL.
Last edited by Freddie B; Aug 24, 2012 at 03:42 AM. Reason: spelling, spelling, and always spelling....
Aug 24, 2012, 07:02 AM
it wasn't me flying that plane
Hover or die's Avatar
Also be sure to take the time to sand the templates smooth..the wire will slide so much better....don't worry to much about little blemishes as they will sand right out and you can also spackle the plug to add back any material needed..
I also cut the plug into 4 pieces to make it easier to hold a template on the front and back of each of the 4 pieces..then glue them back together..be sure to number the pieces so you glue them back exactly the same so your turns stay put..just be sure to sand every wood part smooth so the wire does not hang up..
Will find some more detail pics as well...
Don't give up as you certainly have the skills to do this....Just takes some patience and practice...

Also in the case of your ducts I would cut to/6 or even possibly 8 pieces...
Take care........Chris
Aug 25, 2012, 01:54 PM
Registered User
Well, an itty bitty update. Got the first hotwire cut done, see pics below. Before I do the elevations, I'd like to ask a question. Would it be okay to have the inlet tube rise immediately, or run level for say 5mm - 10mm then rise? I'm wondering if having the tube rise immediately, will affect the plane like an unseen control surface. Check out the first pic. The EDF unit sits on the front edge (or further back) of the H stab. The next section is transition from 100% FSA to fan face. The next section 100% FSA above the wing. The next section is not drawn. This will be the rise section from the inlet face. And this is what my question is about. And before I forget, I'm trying to keep the rise to 6 deg up angle at most. This is to keep loses to a minimum on the inlet side. Comments are welcome.

Here's a few pics to ponder.
Aug 25, 2012, 04:52 PM
Addicted to building...
Freddie B's Avatar

I will answer best I can. I think you are worried about the angle of the intake ducting causing changes to pitch during flight, The transtion from zero to 10mm max within the ducts is very minimal, however covers a long distance. This could have a small effect on the pitch settings, however we must remember that the fuselage contours top and bottom of most aircraft would be doing the same thing, only usually more pronounced. Look at the side profile of most in-line engined prop driven planes, say a P-51, with the extreem angle of taper in the nose, especially the bottom ( of the wing to spinner location), yet this does not cause huge varying pitching motion in flight.

The horizontal tail could be set slightly angled to compensate, say no more than 1 degree, but I set my tail based upon wing airfoil, not so much the ducting. What is more important is the exhaust side of the duct. This is the real high speed air that you want to be exiting straight. I would worry most about getting the exhaust duct set to your intended thrust line.

My Yak-17 has a most extreem intake angle, maybe 10-15 degrees, and I still set the horizontal based upon the wing, plus 1/2 degree.

Beautiful work ther Sir, BTW! I will try not to clutter your thread so often, sorry if I have over posted so far.

Last edited by Freddie B; Aug 25, 2012 at 04:54 PM. Reason: Spelling, spelling, and grammer.
Aug 25, 2012, 10:11 PM
Registered User
Waltjg's Avatar
Inside ducts aren't going to effect your pitch, just so long as your thrust angle Is correct like Fred said... You want to try to keep any transitions in your duct work as smooth as you can without abrupt changes for maximum efficiency. Good luck, good build going. W
Aug 26, 2012, 08:36 AM
it wasn't me flying that plane
Hover or die's Avatar
A long straight edge will help draw a line from the bottom of the intake to the bottom of the fan former..and then draw a straight line across the top,from the top of the intake to the top of the opening in the fan former..this will give you your perfect taper of 10mm in rise..
I use a metal ruler that is flexible for my lines you may have to use a straight piece of trim (thin straight piece of wood).
Your hotwire ducts look great so far!!!!!

I also cut 3 pieces of wood,one for the opening(you mentioned yours were more squared)to cover the shape of the ducts opening and 2 cut in the half moon shape..
The first piece of duct I use my fingers to hold the squared piece on the front and the halfmoon shaped piece on the back and hotwire the cut.. this will get your from the opening shape to the shape to fit the fan.then use the 2 halfmoon pieces on the front and back of each piece you cut..then. glue all the pieces back together according to your numbers..then it is just a light sanding over the whole length to get it all smooth and make it fit to your liking..
Just make sure you glue the pieces back together well so it will not show cracks when primimg and painting..if you use 3m spray make sure its well glued..
Hope that helps some................Chris

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