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Author Topic: Boston Bonxie  (Read 3228 times)
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Yak 52
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« Reply #25 on: October 17, 2013, 07:01:30 PM »

Thank you Richard, the wood is nothing outstanding. Light strip wood from Balsa Cabin (http://balsacabin.webs.com/bwstrip.html) and sheet wood picked out from my local model shop, selecting the light bits from a sheet. It's probably SLEC or Seagull (via Ripmax).

I was going to see if I could use it to analyze my No-Cal models
I did try modelling No-cal airfoils in XFLR5 but the program doesn't deal well with the square LE and TE's on a single covered wing. The best approximation is a thin curved plate section. What exactly were you hoping to analyse? Xfoil is really for airfoil optimisation. XFLR5 has a few other features but it has it's limits. I'd be happy to help if I can.


Here's a few final bones shots. I'm afraid it looks more like a small pig than a sea bird  Undecided
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rgroener
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« Reply #26 on: October 18, 2013, 01:50:38 PM »

Jon, it looks great, no idea where you see a resemblance to a pig Roll Eyes
And I am sure, it will fly much better than any pig. (at least the pigs I know).
Cross my fingers that you get your desired flight time with your new plane.

Roman
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Russ Lister
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« Reply #27 on: October 18, 2013, 06:33:33 PM »

Looking good Jon ... and looking , not wanting to detract from your design input at all, very much like a Bostonian.
With a 'tightish' set of rules like Bostonian rules, the difference is in the details .... look forward very much to seeing how your details contribute in practice  Smiley

Looking a bit too late for me a to start a new Bostonian for Impington now ... but stranger things have happened!
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Yak 52
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« Reply #28 on: October 20, 2013, 09:10:42 AM »

Well I managed to get the Bonxie covered in time to trim it this morning at Bushfield. This was the first time I've covered entirely with UHU and annoyingly the tissue has started slipping off the fuselage. Perhaps I didn't use enough.

The airframe weight before the prop was 11g but in spite of the heavy prop I used it still needed a bit more nose weight. The final weight before rubber was more like 15g so I've missed the target. If I get time I will convert some of that into a spinner.

However the model flew 'off the board' the second flight was over a minute and the 4th was best at 72 seconds (10 second improvement on the Beagle.) This was keeping the circle tight to get in trim for Impington. Motor used was 30" of 0.100" with up to 2800 turns. This was still a bit powerful on the climb so I'm hoping to use 3/32 and a shorter loop next time. The full length 'HtP' gives a tendency to stall if the motor bunches but I've already noticed the cruise section of the flight improve in length. So far so good...
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« Reply #29 on: October 20, 2013, 12:05:26 PM »

Hi Yak52,

I had this UHU problem of tissue sloughing (sp?) off on some indoor models. I found, I could mix up a little stew of UHU and water, which I applied by finger tip to the tissue contact areas (and later brush). After that dried, I used the UHU right out of the tube and the tissue seemed to adhere better. I did this in spite of fears that the water might cause warping.

Your model is beautiful,

Outofbalance
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« Reply #30 on: October 20, 2013, 01:34:07 PM »

I have the same problem, which I cured by running a thin bit of highly thinned dope along all the seams that I can get at, smoothing it down with my finger before it dries.

Lately, I've been using the new "Blue" UHU stick.  It seems to be much softer than the pink and adheres better.  No info yet on how it stands up, but the high humidity that we've been having lately hasn't caused any grief.

Pete
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« Reply #31 on: October 20, 2013, 04:32:03 PM »

Enjoyed the meeting at Bushfield today Jon .... the Bonxie looks a real winner  Smiley
I missed the longer flights, but you could certainly see that the potential was there. 
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Russ Lister
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« Reply #32 on: October 20, 2013, 05:43:14 PM »

.... I have still not seen the 'commercial plastic' props rule for Impington in writing anywhere BTW.
Was it Gordon Hannah that mentioned this? (failing memory again)
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Yak 52
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« Reply #33 on: October 20, 2013, 06:31:02 PM »

Thanks guys. Russ, yes it was GH via email, but I've never seen it on the IVCMAC rules page. As far as I know you can trim a bigger prop down (to give more pitch) and balance them but that's it. Some more clarity would be good - I'm sure I remember a balsa propped model won or was placed in the March event?

EDIT: Isn't that your Sorta Senator (with a clem prop!) on the Impington rules page? Smiley

I seem to have sorted the uhu problem by soaking the tissue edge with thinned PVA. Looks rubbish but it stuck.
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« Reply #34 on: October 20, 2013, 07:02:41 PM »

Yes ... that's what confuses me, with the club showing that as an example. It is only the Sorta Senator that I have entered with a 'Clem' type I suppose ... the rest have been plastic, Peck usually.
I won with the Clem prop though ... and they're not taking  the wine back!  Roll Eyes
I suppose if we all use commercial plastic props it's not a problem, but I wouldn't exclude anyone while the published rules do not state them as a requirement.
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Pete Fardell
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« Reply #35 on: October 21, 2013, 04:05:08 AM »

Looks great, Jon!

I do like the colour. Which tissue is that?
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Yak 52
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« Reply #36 on: October 21, 2013, 05:42:17 AM »

...I wouldn't exclude anyone while the published rules do not state them as a requirement.

Exactly. The reasoning was that props were the main area experts could gain duration and the aim is to keep it beginner friendly.

Thanks Pete, it's the new esaki light blue (not doped or oiled.) It's very blue! It changes shade a bit depending on the light. It was a bit duller indoors. I want to check the weight of it. I have a feeling it's heavier but that could be my being rusty for indoor building. I've been doing bigger stuff for a while and it's funny how your perspective shifts.
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Pete Fardell
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« Reply #37 on: October 21, 2013, 06:48:21 AM »

That's interesting. I was thinking of using it for my Aerographics Albatros, but it looks too green for me on your photos.
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Russ Lister
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« Reply #38 on: October 28, 2013, 04:43:54 PM »

I enjoyed the usual trip down to Impington yesterday ... a little down on numbers due to a combination of the weather and the Shawbury meeting.
Even though I wasn't flying, I didn't get myself into action with the camera.
I did however grab half of a flight of Jon's Bonxie .... I set the phone camera up quickly and didn't notice my finger in the corner  Roll Eyes

http://www.youtube.com/watch?v=A_hAgD9YnnI&feature=youtu.be
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Yak 52
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« Reply #39 on: October 28, 2013, 06:10:49 PM »

Thanks for that Russ, didn't know you'd taken it.

I came second in the end, to Pete Adams who did some great times. The Bonxie was flying on 3/32 so I'm happy with it but it needs some trimming. I got one 63 second flight but then broke it  Roll Eyes

Ho hum. I actually had a lot more fun with my Frog Speedy  Smiley
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Russ Lister
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« Reply #40 on: October 28, 2013, 06:45:42 PM »

Where's the fun in having fun when you have a new model to wrestle with?! Wink

The break was just one of those things ... the model itself was coming along very nicely.
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lincoln
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« Reply #41 on: October 28, 2013, 11:02:08 PM »

As far as the 15 grams goes, maybe it's time to make a heavy spinner or prop hub for your plane? I'm guessing you could get down to 14 grams that way. Or you could always move the peg.

Do you back off turns after you wind as hard as you dare? That's what I do with a lot of indoor models that have too much climb, and I think it works much better than using a thinner motor or putting in fewer turns in the first place. My rule of thumb is it's working correctly if the turns left at the end are about the same as the number of turns I backed off. Another rule of thumb, which I guess may be somewhat dependent on the rubber you're using, is that if you wind up all the way and back off half the turns, the rubber is the correct size if it cruises in level flight when released.

Seems like with some good wood picking, you could make an all sheet or all foam Bostonian that would still be down at 14g. I've never seen it done in person, though Bob Bienenstein had a design which appeared in Model Builder in September, 1984. It was called Boston Beany. Is it bad for charisma points or something? Mr. Bienenstein used 1/16" for the wing and sides, and 1/32" for the top and bottom, except for 1/16" planking in front of the windshield.

Can't run Xfoil right at this moment, but I seem to recall an "optimized" airfoil from a paper on very small UAV's that had an airfoil which had a bend of maybe 12 or 14 degrees at 15 percent and another one at 85 percent, although of course it was smoothed a bit. Wondering how that would compare with yours?
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Yak 52
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« Reply #42 on: October 29, 2013, 07:16:04 PM »

Hi Lincoln,

The cruise with the 3/32 (0.093") could have been better, it was more of a steady descent as you can see in the video. The climb on full turns was still too much for the ceiling height so I was backing off about 150 turns and when I got it right I was getting about three circuits in the climb. It did 57 seconds on one flight in spite of a proper clang on the rafters and loss of 20 feet or so.

I think the longer 0.100" motor was better on the cruise so I may go back to that. It maybe needs the CG moving back a scratch (too fast!)

I have looked at banana foils in the past - the rules require a minimum thickness of 1/16" so a light sheet wing would potentially do very well. My recollection of the banana foil was that it really comes into it's own at slightly lower Re, around Re10k as opposed to 22k for Bostonians.
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« Reply #43 on: October 29, 2013, 07:30:07 PM »

Thats flying very nicely Jon. It looks like it has the potential but may need custom sized rubber to suit Impington which looks like more than a challenge.
Do you score a refly if a passing head walks into the model while its flying Grin Just another problem.
John
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Russ Lister
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« Reply #44 on: October 29, 2013, 08:07:30 PM »

Quote
Do you score a refly if a passing head walks into the model while its flying Grin

Thankfully you can fly as many times as you like and it's the best three to count!
I have had some meetings at Impington where I have barely been able to record a complete flight ... it's all part of Impington though.
My last competitive Bostonian was dragged along between someone's feet for a couple of paces  Sad
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« Reply #45 on: October 29, 2013, 08:43:22 PM »

Hi Lincoln,

snip

I have looked at banana foils in the past - the rules require a minimum thickness of 1/16" so a light sheet wing would potentially do very well. My recollection of the banana foil was that it really comes into it's own at slightly lower Re, around Re10k as opposed to 22k for Bostonians.
What kind of Cl do you think you're getting? I ran the  numbers for a Cl of 0.7 and got more like 18k or so. I have an idea for a Bostonian that is sorta like a Caproni Pensuti*  which might get down around 12 to 14k! So far it's just an idea. I have to keep it under control or it will look like the Caproni nine winged flying boat**.


*i.e. triplane like in Russ's signature picture, avatar, or whatever they call it.
**http://homepage.ntlworld.com/ccbrown/Cheshire%20falcons/Caproni.jpg
--------------
Russ,
That's too bad about your Bostonian. We fly in a site which must be about the same size as Impington looks in the video, but we don't have anywhere near as many people. However, at our previous site, I once saw a plan fly under someone just as he was sitting down. It was so funny and perfectly timed that even the guy who built the model laughed. It was just a stick and tissue pancake after that.
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Yak 52
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« Reply #46 on: October 30, 2013, 05:48:15 AM »

Thanks John, actually this is pretty quiet for Impington  Shocked  The video was just a trimming flight to check the cruise (hence the catch and not timing) At Bushfield the week before using the slightly thicker 0.100 I got better times without trying so hard  Undecided I will take it to Oundle and see how it goes there.


What kind of Cl do you think you're getting? I ran the  numbers for a Cl of 0.7 and got more like 18k or so.

I based Re22k on a typical Bostonian with CL 0.5, Wing area 48in2, Weight 18g (4g of rubber)

From empirical testing of similar sized models I would say a CL of 0.5 is typical for a 'normal' 9-10% flat bottomed airfoil at this size. I think these thin airfoils I've been using fly at more like CL0.6-0.7 (I've based the spiral calculations on 0.7 for safety) but in practice it's hard to trim them that slow with the CG shift problem of the long motor. I would be surprised if they achieve CL0.7 in reality. I will have to do some more speed measurements.
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lincoln
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« Reply #47 on: October 30, 2013, 11:26:07 PM »

You could probably get close, if you have a way to play the video back at a known, slow speed on a big screen, by seeing how many fuselage lengths it traverses in a second or two.

I tried it on my computer but I don't think it was terribly precise. Still, taking the fuselage length as 1 foot, I got a velocity of 13fps, which I think gives a Cl of about .5. I should probably stop while I'm ahead.  Of course, 0.5 is the Cl for the wing as a whole, so maybe 0.5 is more reasonable anyway.

I really ought to be working on something else.
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Yak 52
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« Reply #48 on: October 31, 2013, 05:41:40 AM »

I did do time over distance glide tests on my Frog Raven once (long dark evenings  Roll Eyes)

Jon
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« Reply #49 on: November 01, 2013, 06:13:01 PM »

The hall is 50' wide and the model flying in approx. 30' circles. It circles 3 times in about 21 seconds, so approx. 7 seconds per circle.
PI x 30' = approx. 94 feet ... divide by the 7 seconds and you get 13 or so FPS .... confirming Lincoln's estimation by another method  Smiley
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