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2015 Design Contest - Airrow Two

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2015 Design Contest - Airrow Two

Old 06-26-2015, 07:57 AM
  #26  
MJD
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The little balloons sold for water bombs might be ideal - I have some at home, I'll grab a syringe and measure volume next time I'm in the dungeon.

CrossCheck.. don't forget we gotta go fly the Profi Toucan together sometime. I'm comfortable enough with it now I'd fly it here in the village, at the community center. It totally floats on the glide so landing here no prob.
Old 06-27-2015, 03:21 AM
  #27  
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Is this a swept wing design?
I'd expect it to be easy to keep the
CG forward if it is. I bet it would be
pretty fast with an ace tapered wing,
and even faster with a thinner built-up
wing

Jenny
Old 06-27-2015, 05:15 AM
  #28  
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Jenny there is still time for you to sign up for the competition
Old 06-27-2015, 07:25 AM
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I would sign up if I had time.

Jenny
Old 06-27-2015, 08:30 AM
  #30  
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Hi H6605,

Awesome 'Peanut Gallery', Interested, in your project !

Do your own thing... it is Fun!

I helped underhand launch a Do335 (.25 OSFX front/ .15 OSLA rear) at a scale combat Match.
Took some 'field modifications' to make an 'air scoop' aimed, at the head of the rear engine overheating problem.
We got it going, it was awesome ! The sound of 'miss matched' engine sounds, at speed, are friggin...

A pair of .049s 'in sync' will be even more awesome!

Cheers,
Dave'crosscheck'Fallowfield
Old 06-30-2015, 06:06 PM
  #31  
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Originally Posted by Cross Check

I seem to remember a TD pusher design, the Shockwave from RCM perhaps.
The article covered pusher props and tank setups. It had sweptback wings for CG reasons. Looked cool.

Cheers, Dave'crosscheck'Fallowfield
I had to look it up as I remember it too... It was the RCM January 1979 issue. He used a Tornado 5.5x3 pusher and plans only show a hard tank with pickup curled back to stopper end of tank.

Here's some stills from a video of the original Airrow equipped with the Ace constant chord foam wing. Everything except last pic is both engines running. Last pic shows slight nose-up attitude with power-off prior to touchdown.

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Old 07-01-2015, 06:37 AM
  #32  
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Originally Posted by MJD
The little balloons sold for water bombs might be ideal - I have some at home, I'll grab a syringe and measure volume next time I'm in the dungeon.
Ok, maybe not - 2cc!
Old 07-02-2015, 08:39 AM
  #33  
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Originally Posted by Jennifer Curtis
Is this a swept wing design?
I'd expect it to be easy to keep the
CG forward if it is. I bet it would be
pretty fast with an ace tapered wing,
and even faster with a thinner built-up
wing

Jenny
In terms of aesthetics, I think it would look best with a tapered planform but I'm planning a constant chord, no sweep wing at this point like the original.


What means is used to mount a bladder - I'd feel a lot better if there was some way to immobilize it by securing/supporting it at the neck of the balloon around the stopper - or is this not necessary? Should the space occupied by the bladder be confined to restrict movement of the bladder? Perhaps I'm over-thinking this whole thing.
Old 07-02-2015, 12:41 PM
  #34  
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Yes you can pin it at the neck, so long as the reservoir itself is relatively unfettered. Soft foam around it as protection and a movement limiter does not hurt. But don't restrict the volume of the full balloon, leave a cavity sufficient for the filled volume. The watchword is that the bladder should always be at ambient pressure - no squeezing or you're affecting head pressure, right? Like you suggest, don't overthink it, common sense will go a long way. No sharp things to nick it, some support for the neck so it stays there if you wish, or just some gentle containment around the whole perimeter, don't pinch the fuel line - as long as the engine can drink from the straw smoothly without restrictions/variations, yer good to go. If it flops around under flight loads and folds over on itself or kinks the fuel line.. then the results are predictable.
Old 07-02-2015, 05:20 PM
  #35  
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All right; thanks on that MJD.

BTW, cardinal sin spotted in the video still adjusting mixture on rear engine - nose should be down - tail up!

Last edited by H5606; 07-02-2015 at 05:36 PM.
Old 07-06-2015, 11:55 AM
  #36  
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Hi H5606,

Those 'in air' photos are cool...
Any chance the top fin could be somehow mounted to a tank hatch?

On my .049 engine test wand, I just used a cut down cardboard 'end of toilet paper' tube to the dia of the filled bladder.
Wad of paper towel end stop. Slide filled bladder in, tack in place 'loosely' with another paper wad. Worked great..
Even in severe 'flightGs' I could simulate. Did not crash test it.
Making me think about CPs idea of a fuelproof hole to retank and fill... being lighter and more practical....

MJD,
Your previous post said it all about bladders, just adding to it.
I'll see the Toucan go...
When I get you to test launch the Go-Fer ...

Cheers,
Dave'crosscheck'Fallowfield
Old 07-07-2015, 04:48 PM
  #37  
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CC, I may yet consider a hatch like you said - on top. Makes me think a "Y" tail config in place of the cruciform tail would have been even better...

I took a break from the engineering details to build a little: added a belly scoop - purely cosmetic at the expense of weight and drag. I did reduce it in size by about half and added some lightening holes FWIW; cross-grain sheeting is 1/16". Also fabricated ventral fin with tab in slot - this time it's swept to match the top fin. Landing gear is a remnant from the prototype and I believe it originated from a Sterling Minnie Mambo that for all I can remember - never flew under power.
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Last edited by H5606; 07-07-2015 at 04:59 PM.
Old 07-07-2015, 09:11 PM
  #38  
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It's taking shape nicely..!
Old 08-20-2015, 04:57 PM
  #39  
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Took a detour for a few moments to quell the razzing due to another project that was unfinished... Lost momentum but am back on it - hopefully. I wanted to build up the perimeter of the fuselage cheeks to 3/32" before adding doublers to the inside - hence the sheeting wetted with Windex, glued, and taped to dry. I finally settled on a stopper/bung to complete a bladder tank; I found a piece of 3/4" thick rubber block at work and cut 1/2" and 5/8" diameter slugs using brass tubing that I filed teeth into and chucked up in a drill press. After some deliberation, I opted to use the smaller of the two even though the neck of the balloon didn't fit as snug as on the larger one. One picture shows a bunch of stuff I was thinking of using for a stopper including a piece of Delrin I turned down and a Fultz nose gear spacer. Weighed the bladder and compared it to the tank I was going to install - am thrilled to eliminate five times the weight (1/8 vs. 5/8 oz.) as CP and MJD pointed out. Last pic shows airfoil I was talked into using by trusted source.
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Last edited by H5606; 08-20-2015 at 05:16 PM.
Old 08-20-2015, 07:05 PM
  #40  
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Interesting airfoil.. what is supposed to be magical about it I wonder.
Old 08-20-2015, 07:09 PM
  #41  
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Oh yeah, nice job on the tank. I wonder what rubber that is. Have you soaked a small piece in a bit of glow fuel for 2-3 days yet? Maybe make sure it doesn't gooey on you.
Old 08-21-2015, 04:12 AM
  #42  
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I was going to use TLAR to create my own airfoil thinner than the Ace airfoil and know that even a shoe size 9er or a flat plate would probably work. I'm also of the school of thought that more importantly than airfoil selection is that the wing be defect free - i.e. no twist, warp, excessive aileron hinge gap, etc. I work in an environment where I hear the term "Reynold's numbers" and one of 'em said that airfoil variances at that low a Reynolds number doesn't matter... Another says to use this airfoil for a good balance between low and high speed performance. I figured it wouldn't hurt and decided to give it a try. Thanks for the heads up on the rubber selection - no I didn't test it but I will.
Old 08-21-2015, 07:52 AM
  #43  
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Anybody know if Hobbico resolved a Cox fuel issue - some concern about all syn and no castor oil?
Old 08-21-2015, 02:58 PM
  #44  
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This is certainly a good design to try different wings with.
If you have a pair of easy to start engines, running twin .049s can be addictive.
Old 08-23-2015, 05:56 PM
  #45  
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Would like try to use the digital age resources at my fingertips to get some help as I don't have a good feel for numbers here - the original design flew with the constant chord Ace foam wing - it had a chord of 6" and span of ~35". I've decided I'd like to give a tapered chord planform a go after all. Does 187 sq" sound small based on an unknown weight at this point?

Progress is excruciatingly slow. Airfoil at the top - was told is used on the RV series of aircraft - surprisingly, tracing around the Ace airfoil matches nearly perfectly. The one at the bottom is planned templates - still need to remove a 1/16" perimeter for sheeting clearance... 2nd pic - more lightning holes and induction recess in firewall. Sorry - first go at Windows 10 - I can't get rotation task to go through.
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Last edited by H5606; 08-23-2015 at 06:10 PM.
Old 08-23-2015, 07:32 PM
  #46  
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Capt we need more rotation


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Old 08-23-2015, 08:12 PM
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If the wing loading is low enough, the airfoil isn't very important. I'd keep the airfoil simple, smooth and 8% to 10% thick. A thin airfoil will slow down adequately for dead stick landings. A fat airfoil produces more constant speed through the maneuvers. I see your plane having plenty of thrust for solid launches [regardless of airfoil type] if you stay on track and keep the weight low.
A 10% thick airfoil with a fairly small radius leading edge should be a good all around airfoil.
Old 08-23-2015, 08:32 PM
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Chucks spot on for RC planes, reduced thickness still "plenty of beef" and 187sq. in is plenty for a good mix of reasonable speed and slow flight.

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Old 08-24-2015, 06:20 AM
  #49  
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I think it is total bollocks to say the airfoil doesn't matter - that's stretching it too far. At the same time I agree that things behave differently at these low chords, low wing loadings and Rn - so traditional reasoning can be certainly be challenged.

That 23012 might be great, dunno. For 2% camber I'd probably end up using a 2410 to 2412, for symm 0010 to 0012 or E168.
Old 08-24-2015, 08:17 AM
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I built and flew dozens of 1/2 A RC combat wings that were all identical except for the airfoils.
36" x 7" and 12 ozs or so when new.
We flew hundreds of "combat hours" over a period of several years using identical power [AP .061s].
Flying side by side, rubbing wing tips, chasing through the maneuvers....
None of the airfoils we used were thin [for strength reasons they were about 14% or more] but we tried flat bottom, semi sym, full sym and variations of each type. We finally settled on flat bottom, since they were the easiest to build and keep trimmed after repairs.
Flying combat gave us a unique opportunity to do side by side comparisons during the dozens of all day sessions we had when there was a small group involved with this. There just weren't any clear cut advantages noted in performance other than the model's weight, or how many times it had been repaired.
In the case of the Contest Plane we're talking about here, I think you could build a few different symmetrical or semi-sym airfoil sections with the same thickness and I would challenge you to tell me which NACA number you were flying with this 10 - 12 oz plane.

Last edited by combatpigg; 08-24-2015 at 08:23 AM.

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