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Post  batjac Mon Sep 01, 2014 2:14 am

Well, I did it this time.  No, I really did!  I built a plane with minimal time involved so it can crash away with no emotional involvement at all.  Really.  I don’t care.  Not in the slightest.  It’s nothing to me…

Presenting the BTC-4.  I didn’t put the absolute minimum time into it, but I put very minimal time into it.  It took an afternoon/evening to draw it out, cut the parts for two airframes, and glue one airframe together.  Then I sprayed it this morning with four light coats of flat clear LustreKote to fuel-proof it.  This is the second plane I’ve done in flat clear, and I’m really coming to like it.  It looks just like bare wood.
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I built it with a 20 inch span, four inch chord.  Five to one aspect ratio should make for a good looper/figure-eighter.  Especially with the ridiculous amount of elevator I gave it.  I just used the Brodak radial mount because it was the way to finish the nose with the least time/effort invested.  Simple thread hinges (which I’m coming to like also), and a surplus Carl Goldberg bellcrank.  I’ll weigh it tomorrow to see what the final weight is, but it should come out between 6½ and 7 ounces.  I pulled out a new-in-the-bag product engine and a 3/8 ounce tank from Bernie.  Because of what I’ve read here and elsewhere, I pulled the engine apart and checked it out.  The piston ball had excessive play, so I reset it with a few light taps in the reset tool.  And, I cleaned out the metal shavings that Estes left in there.  Should be good to go now.
The Incomparable BTC-4 DSCN2270_zpsfb0992f6


I balanced it at the 20% point.  On the following picture you can just see the two small marks I made at the 20% point.  
The Incomparable BTC-4 9956c509-32d2-4c37-b310-f4ce1da64258_zps50ba2cbf

And here is my novel balance fixture.  I bought a big bag of assorted safety pins at the Dollar Store Friday.  I used the largest size for the pushrod guide, the smallest size for the tail skid, and the medium sized pin I glued to the end of the fuselage. I tried various sizes of crimp on fishing weights until I found the size that would balance the plane at 20%, then firmly crimped it on with some pliers.
The Incomparable BTC-4 DSCN2268_zps5a7228ef

I’ll try the plane with no wingtip weight for now, as when I balance it fore-aft on the prop shaft and tail, the outboard wing drops quite positively.  I’m calling this one the BTC-4R, as it’s got the radial mount.  The other wood I cut has a longer snout for a beam mounted Medallion.  That’ll be the BTC-4B when I finish putting it together.


The Carefree Mark
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Post  ian1954 Mon Sep 01, 2014 3:53 am

I like the shaping of the wing tips.
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Post  Kim Mon Sep 01, 2014 7:32 am

Absolutely Great !!!!!!  You should offer kits!  

"It's NOT just a plane...It's a Batjac!"


Not sure how much money you'd make, but how cool would it be to have your namesake kits traded, sold, and fussed over on Ebay and at Swap Meets??!!!!

"FOR SALE":  Original "Batjac BTC-4R"...NIP...Excellent Condition: $575.00.

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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Post  roddie Mon Sep 01, 2014 1:31 pm

Hey Mark.. I just LOVE your BTC threads!!! and I LOVE the BTC-4R!! It encompasses your original "vision" entirely. I hope it fly's well for you. I like the natural wood finish too. The pin/fishing-sinker on the tail for balancing, is a great idea! Who wouldn't want an airplane that assembles quickly.. is cheap to build.. and flies well?

I think that the BTC-4"R" is the way to go though.. You'd be MUCH more carefree about tossing-around and tearing-up the sky with a reedy.. than you would with a more expensive and harder to replace rotary-valve engine. Two Cents
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Post  RknRusty Mon Sep 01, 2014 4:37 pm

I'm a fan of the BTC concept to. This is what I need to do so I have something to put in the hands of kids or curious neighbors. Or my son. Lol. The above reasons are why my 1/2A fleet is depleted to a state best described as rickety.
Rusty

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Post  roddie Mon Sep 01, 2014 9:24 pm

RknRusty wrote:I'm a fan of the BTC concept to. This is what I need to do so I have something to put in the hands of kids or curious neighbors. Or my son. Lol. The above reasons are why my 1/2A fleet is depleted to a state best described as rickety.
Rusty

I LOVE Mark's whole inception of a BTC (built to crash) model. So many "would be"/ beginning aero-modelers are turned-off to the hobby.. because of the lack of knowledge and/or "tutoring" associated with it.. and end up crashing the fruits of their "hours-worth of labor".. because of a lack of knowledge... and give up in frustration. This is a hobby that is "ripe" with new ideas and concepts to be explored. I applaud Mark for his "spirit" in introducing the BTC concept!
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Post  RknRusty Mon Sep 01, 2014 9:42 pm

Hey Mark, in your BTC-4, the picture looks like the pickup(or narrow edge of the tank) may be a tad lower than the venturi center. If you have any trouble cranking, cutting off early or inverted, it may be worth checking. Maybe the picture is just giving that illusion.
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Post  batjac Tue Sep 02, 2014 1:31 am

RknRusty wrote:Hey Mark, in your BTC-4, the picture looks like the pickup(or narrow edge of the tank) may be a tad lower than the venturi center. If you have any trouble cranking, cutting off early or inverted, it may be worth checking. Maybe the picture is just giving that illusion.
Rusty

Yeah, after looking at the photo, I double checked. It's just the camera angle.

The Angled Mark
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Post  batjac Tue Sep 02, 2014 1:34 am

Cool! Weight ready to fly came out at 5.25 ounces.  The product engine should have no problem pulling this thing 'round the circle.

The Incomparable BTC-4 DSCN2273_zps3cee5470

The Lighter Than Expected Mark
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Post  RknRusty Tue Sep 02, 2014 2:42 am

Is she ready to maiden?

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Post  batjac Tue Sep 02, 2014 1:36 pm

RknRusty wrote:Is she ready to maiden?

Yup. But the engine is designated for a special purpose. I think I'll swap out this engine for a product engine from another plane to do the maiden this weekend.

The "Special" Mark
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Post  batjac Sat Sep 06, 2014 7:53 pm

Well, since it was too windy to fly, I decided to glue together the BTC-4b.  I left gear off of this one, as it would have taken time and effort to install.  Also, I fly over grass, so gear just catches on landing and flips the plane over anyway.  Medallion .049.
The Incomparable BTC-4 DSCN2278_zpsd2975b18
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I’ll shoot this one with flat clear also.  Maybe I’ll get to test fly on Wednesday.  I’ve got a backlog building of planes to test fly…

The Put Off Mark
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Post  Waffleman Sat Sep 06, 2014 8:27 pm

Send it to me and I'll test crash fly it for you. Very Happy
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Post  pkrankow Sat Sep 06, 2014 8:28 pm

Medallion powered!  Very nice.

I hope you have the deflection on that bar door set pretty small. 1/2 inch total travel might be too much with that whopper!

Got basic measurements of this bad boy?

Phil
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Post  batjac Sun Sep 07, 2014 3:21 am

pkrankow wrote:Medallion powered!  Very nice.

I hope you have the deflection on that bar door set pretty small. 1/2 inch total travel might be too much with that whopper!

Got basic measurements of this bad boy?

Phil

Phil, the basic measurements are:

Length, firewall to rudder end - 10"
Wingspan - 20"
Wing Chord - 4"
Stab span 8"
Stab Chord 1"
Elevator Chord 1½"
Fuse height - 1½" firewall to wing T.E., tapering to 1" at stab L.E.
LOA - Firewall to elevator T.E. 11.5"
Elevator deflection ~25° up/down
Weight 5.25oz./149gm

The Basic Mark
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Post  pkrankow Sun Sep 07, 2014 7:46 am

Thanks.

I might have to build one as a test bed for some different engines I now have.

Phil
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Post  batjac Sun Sep 07, 2014 11:33 pm

Woo-Hoo!  After two full coats of clear, and 2 grams of tail weight, the BTC-4R weight ready to fly is 4.9 ounces!  The Medallion should pull it around quite nicely.

Final specs are:

Length, firewall to rudder end:  BTC-4R is 10", BTC-4B is 11.25"
Wingspan - 20"
Wing Chord - 4"
Stab span - 8"
Stab Chord - 1"
Elevator Chord - 1½"
Fuse height - 1½" firewall to wing T.E., tapering to 1" at stab L.E.
LOA - Driveplate to elevator T.E.  13.5"
Elevator deflection ~25° up/down
C.G. - 20%
Weight RTF: BTC-4R is 5.25 ounce, BTC-4B is 4.95 ounce

The Finished Mark
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Post  Theo Kleynhans Mon Sep 08, 2014 3:28 am

Hi Mark

Both these planes looks great. I think that medallion is going to haul that plane quite fast!!

We are waiting on the edge of our seats for the flight report and maybe a video.

Theo
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Post  roddie Mon Sep 08, 2014 7:14 pm

Mark, If I may make a suggestion.. I noticed that your BTC's "high-wing" mounting uses braces underneath; that tie-in to it's profile fuse.. but; your rather LARGE tail-plane doesn't have any bracing.. other than the fin/rudder on the topside. There's only .25 sq. in. of fuse material supporting 20 square inches of stab./elev. (assuming your fuse is 1/4" sheet).. Where the BTC-B required some tail-weight to balance... I figured you could make it "functional".. by adding similar basswood(?) bracing.. and remove the fishing sinker? If the BTC-R balances satisfactorily without any tail-weight.. then you might want to add lightweight balsa tail-plane braces. I'm just thinking of the integrity of the tail-plane bracing; in the event of a less than perfect landing.. or even less than careful handling.

You're gonna' fly one of them this week... right? (no pressure.. Very Happy )
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Post  batjac Mon Sep 08, 2014 11:44 pm

roddie wrote:Mark, If I may make a suggestion.. I noticed that your BTC's "high-wing" mounting uses braces underneath; that tie-in to it's profile fuse.. but; your rather LARGE tail-plane doesn't have any bracing.. other than the fin/rudder on the topside. There's only .25 sq. in. of fuse material supporting 20 square inches of stab./elev. (assuming your fuse is 1/4" sheet).. Where the BTC-B required some tail-weight to balance... I figured you could make it "functional".. by adding similar basswood(?) bracing.. and remove the fishing sinker? If the BTC-R balances satisfactorily without any tail-weight.. then you might want to add lightweight balsa tail-plane braces. I'm just thinking of the integrity of the tail-plane bracing; in the event of a less than perfect landing.. or even less than careful handling.

You're gonna' fly one of them this week... right? (no pressure.. Very Happy )

Roddie,

I don't have the brace under the BTC-4R tail, but I did put triangle stock bracing under the tail of the BTC-4B. I'll leave the-4R as is for now. I'm much harder on the noses of these things than I am on the tail. And, if the stab does pop off, I'll just glue it back on. Quick and Dirty, not Quick and Sturdy... Still, I think that with a good glue joint and fillets, the stab is good for normal wear and tear. We'll see. But, thanks for noticing and prompting me on that. It's always good to have other eyes look at my hare-brained ideas.

I'm hoping to fly them this Wednesday if the weather cooperates.

The Hopeful Mark

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Post  batjac Fri Sep 19, 2014 11:19 pm

I finally got a little time to run out to the field with my son to test fly the BTC-4 planes.  I’m happy with the airplanes’ performance, but I need to do more engine work.  I also brought out my new table stooge to test out.  My first launches were shaky, but I’ll get the hang of it.  The videos aren’t the best resolution.  I’m still figuring out this video editing/posting thing.

Here is the BTC-4R.  It’s very responsive, and will be a great flyer once I get over my fear of running it into the ground.  My loops aren’t figure 9’s, they’re more like “@”.  After I get used to how this tracks, the loops should be nice and big and round. Then I’ll go into Figure 8’s and inverted.  I wanted to do some good wing-overs, but the sun was directly upwind of me, and when I went to do entries, I ended up flying right into the sun.  The balance on the plane is darn-near perfect.  When the engine cuts, it has a nice flat glide to it.  It even landed wheels down in the rough grass using the 1 ¼“ wheels.  You can see me doing a figurative “spike” at the end of the flight because of the great glide it has.  




The BTC-4B maiden wasn’t as successful.  The plane flew great. Then balance on this one is spot-on also. Great flat glide just before touchdown.  I just couldn’t get a good engine run off of the Medallion.  This Medallion has always been cantankerous and very, very thirsty.  The first part of the video, you can see the engine just go to hell after a couple of laps.  The second part the RPM’s are good, but the engine run is pretty dismal.  I think I’ll swap in a TD I just got off of eBay after I test run it and get it tweaked, and give it 42’ lines.



Anyway, I’m calling the BTC-4 base design a success.  The planes are responsive, and I think they are right on the money for the BTC concept.  Quickly built, cheaply built, and fun to fly.  Now to just refine parameters like line length and control throws.

The Un-Refined Mark


Last edited by batjac on Fri Sep 19, 2014 11:28 pm; edited 1 time in total
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Post  Cribbs74 Fri Sep 19, 2014 11:28 pm

Mark,

The first video came up as private.

I watched the second, what tank are you using?
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Post  batjac Fri Sep 19, 2014 11:32 pm

Cribbs74 wrote:Mark,

The first video came up as private.

I watched the second, what tank are you using?

Okay. Try it again.  Like I said, I'm still getting the hang of publishing videos.

I'm just using a Perfect wedge tank.  See the pictures on the first page.

The Perfect Mark
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Post  Cribbs74 Sat Sep 20, 2014 12:05 am

That works thanks Mark!

Sorry that I didn't look at the pictures first.

A couple observations, take it for what it's worth and consider the source.. Embarassed It appears that that tank is a little low. It might help to get it above the engine centerline.


It also seems that both launches were on the rich side and the engines are not unloading.

The Medallion should not be a finicky engine as it can only leak air in a couple spots. It just sounds like a rich run.

The plane you built looks like it performs well! Good job! I hope it does what you want it to.

Ron

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Post  RknRusty Sat Sep 20, 2014 2:16 am

I agree with Ron's observations. Also the tank on that Medallion is a long way from the engine, which might make needling difficult. A tee Dee would be worse in that case. Like Ron says, raise it a tad and get it as close to the engine as possible. Slice up a thin koozie or a mouse pad for some tank pads. If you're using a strap, you need to isolate it from contact with the tank too. Are you capping either vent while flying? I'd cap one and put a forward angled piece of fuel tube as a scoop on the other one. A fuel filter can smooth out the flow too, especially if there are any bubbles or foam(or dried grass bits) in the line. It really hauled ass whenever it did lean out though. Looks like you've built some successful planes. Good work.
Rusty

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