CEF speed contest Design Discussions

Richard, across town for me is Tammie's.  The small local shop is Hillsboro Hobby Shop.  Tammie's has just about everything you need for R/C, but they have almost nothing for C/L.  What they have for C/L is just stuff that's been on their boards for 15-20 years, and as I buy it, they don't re-stock. So, if they have something I want, I just buy three or four of them, which is usually buying all they have.

I have a question for everyone.  I'm still trying to decide what size of wedge tank I want to use.  Either a 1/6 or a 1/4 ounce tank.  The 1/6 ounce is roughly equivalent in volume to a 5cc Babe Bee tank, and the 1/4 ounce equivalent to an 8cc Black Widow tank.  Is a 5cc Cox tank is going to be enough volume to make the 10 timed laps plus a couple of unloading laps?  

Assume a lap takes me 3.5 seconds for calculation purposes. If it takes 3.5 sec to complete a lap, and assuming it's going to take at least 13 laps to get a good run, that's 45 seconds.  Is a 5cc tank good for 45 seconds on a hot Reedy?  I never tried to time the tank or count the number of laps when I flew my Baby Ringmaster using a Babe Bee tank.  I'd go out and try timing some runs, but it's below freezing out there right now.  

The Cold, Calculating Mark

My fastest Black Widow with an 8cc tank and a 5x3 prop ran between 90 - 105 seconds on 8cc if that helps. It was turning over 20k on the ground.

RknRusty wrote:My fastest Black Widow with an 8cc tank and a 5x3 prop ran between 90 - 105 seconds on 8cc if that helps. It was turning over 20k on the ground.

Good.  Then the 1/6 tank should be fine for the contest.  But, I have to wait for it to come in.  Ordered it last night.  I can't proceed with any more building until I have the tank to mount, so I know how to locate everything else left to install.  So, since I'll have to wait, here's how she'll sit for the next few days:





The Waitin' Mark

Mark, The plane looks FANTASTIC! I LIKE it! The tank(s) I'm building, work out to be 7.7cc's... (.26 oz.) I thought that would be "plenty"... It's anyone's guess; as to what type fuel set-up will work the best... and "why" it worked the best. (so many variables)

Phil's "Crop-Duster" uses a similar out-board engine-mount to yours. I see a lot of 1/2-span elevators in use too... I know there must be a reason for this elevator style... possibly helps with less control sensitivity?... I have a "full-span" split-elev. on my F8F-2... but will choose the "least sensitive" control-throws. I'd have to cut through a 1/16" music-wire "joiner" in order to make that modification now. It was a lot of work to make, so it's gonna stay as-is.

Your one-piece gear looks as solid as your fuse... and it's design looks like it will strengthen the wing too. Nice approach!

All the best,
Roddie

Anyone care to discuss "lines"... seeing that the only restriction is the length? It would seem that most of us (contestants) haven't been flying "speed" exclusively or even ever... I'm curious about opinions. Some may plan on stranded stainless... others braided polymer... solids... mono-line  

If I'm out on a thin limb here... I'll digress.  


Has anyone thought about their line-choices' resistance to the wind? It's obviously less at the handle, than at the lead-outs... correct? I think this factor is where a race could be won... by a "significant" amount; given 2 equal performance models... using different lines... (and lead-out-connections...)

Steel or spectra are the only real choices. Dacron is extra draggy.

Speed requires a heavier pull test than stunt. The AMA rules indicate a 48G pull test, 10 oz maximum model weight (should be no problem for anybody to be lighter than that) as opposed to 10G for sport and stunt.

So for a 10 oz model that is 480oz pull test or 30 lb. This also means a minimum line weight of 15lb test for spectra.

(I will be running 20 lb for some safety factor, and also I run 20lb spectra for sport as it is.)

I don't expect anybody to spring for special length steel lines.

How the system is measured has not been discussed. I expect it is from the center line of the model to the center line of the handle.

The "ref" and rule writer gets the final say on this though.

Phil

Where this first contest is run "remotely" (individual flyer's choice of location) and the fact that there are no officials present (possibly only the flyer and his video camera)... lines could be "anything"... as long as they're the required 42 ft.

Pull-test... "if you want to perform one"... but not required by the rules.

One "could" opt to run very small dia. lines if they had them.. or... run 21 ft. of them from the lead-outs, and 21 ft. of "standard" line to the handle. The weight of an extra line connection would be negligible; compared to the benefit of decreased wind resistance at the outer (fastest) area of the circle.

Whomever has the fastest time, "should be" (IMHO) required to duplicate their models performance (within fractions of a second) in the presence of a CEF Speed Contest official; who will inspect the model for compliance and an "official" victory. This official "might" be the nearest CEF member "geographically" to the winner, willing to meet the contestant at a predetermined location, for an official flight.
or... the "official" flight could be in Pheonix at Jim's house... and Bernie could pick up the tab on the air-fare!

Since I wasn't direct on making this a question...

Line length is measured how?  What are the reference points?  

My assumption is center line of the model to the handle.  

Phil

pkrankow wrote:Since I wasn't direct on making this a question...

Line length is measured how?  What are the reference points?  

My assumption is center line of the model to the handle.  

Phil

The rules state "centerline of the model to the handle". I think for sake of accuracy lets say centerline of the model to center of the handle grip.

Jim

JPvelo wrote:

pkrankow wrote:Since I wasn't direct on making this a question...

Line length is measured how?  What are the reference points?  

My assumption is center line of the model to the handle.  

Phil

The rules state "centerline of the model to the handle". I think for sake of accuracy lets say centerline of the model to center of the handle grip.

Jim

I feel the egg on my face. I've read those rules a dozen times and glossed right over that part...but it reads what I expected it to read.

Phil

pkrankow wrote:Steel or spectra are the only real choices.  Dacron is extra draggy.  

Speed requires a heavier pull test than stunt.  The AMA rules indicate a 48G pull test, 10 oz maximum model weight (should be no problem for anybody to be lighter than that) as opposed to 10G for sport and stunt.

Phil

Phil, while I understand that Speed planes are faster with more centrifugal force, I doubt that any of the planes we're building will approach true "Speed Competition" velocities and associated compound forces.  That being said, I have a spool of 20# test yellow Spectra that I'm going to be using.  On my C/L planes I always use a ring at the end of the leadout that I clip the lines from the control handle to, but for this plane I'm going to forgo the attach ring and clip and have one continuous line, hopefully eliminating some drag.  I'll measure out the 42' from the handle, add another foot for wastage, and then tie directly to the bellcrank.  


Roddie, I thought about using a split elevator.  But after the speed contest, I figure I'll just use this plane for sport flying.  I have no illusions that I'll actually win, or even place in this contest.  I'm just in it for the challenge of designing something new.


Eric, I made the motor mount kinda conventional, but not really.  I designed the fuse with a ply/balsa/ply sandwich, not only for the strength laminations would give, but also because I initially wanted to try and recess the crankcase into the fuse if I could.  But by going to the thinner ply, my original idea wouldn't work as well for that.  I was able to strengthen the firewall attachment, though.  Since I used 1/8" ply for the firewall, I marked the fuse where the firewall was to be located, then cut a 1/8" slot through the outer ply skin and the center balsa.  This just left the inner 1/16" ply skin with no notch cut.  I then test fit and sanded the firewall for a snug fit into the notch, and then glued the firewall into the notch.  That way, the firewall was not flush mounted, and had almost 4 times as much gluing surface than if it had just been flush mounted to the side of the fuse (a total of 7/16"x1" glue area vs. 1/8"x1" gluing area).  I could probably have gotten away with 3/32" ply for the firewall this way and saved a few grams, but I'm still concerned with the plane being tail heavy.  After gluing in the firewall, I did the conventional balsa wedges behind it for support.  Then, test fitting the wing in the fuse showed that the wing butted up hard against the lower balsa wedge.  Hmmm....  To make more space for the fuel tank, I measured 1/4" overlap of the bottom wedge with the leading edge of the wing, and then cut off the remaining portion of the lower wedge.  You can see in the picture how I did that.  Now the wing serves as the lower bracing for the motor mount.



The Challenged Mark

Looks awesome Mark!

Shot some orange, and put fingerprints in the white due to impatience...

Phil

Any idea how fuel-proof fingernail polish is? The label says "nitrocellulose" right on the bottle...

Phil

pkrankow wrote:Any idea how fuel-proof fingernail polish is?  The label says "nitrocellulose" right on the bottle...

Phil

Not sure how fuel-proof it is... but you could have a beautiful "creme" no-chip finish... you'll just have to buy 20 bottles and a bigger brush!  

roddie wrote:

pkrankow wrote:Any idea how fuel-proof fingernail polish is?  The label says "nitrocellulose" right on the bottle...

Phil

Not sure how fuel-proof it is... but you could have a beautiful "creme" no-chip finish... you'll just have to buy 20 bottles and a bigger brush!  

  
I am using it for the black trim and lettering. 1 bottle should be plenty, at $2 it is relatively cheap if it is.

I have some samples prepared to test tomorrow (overnight cure should be long enough right?) I painted the ends of some wood skewers (about 3 inches.)

Nail polish is usually nitro cellulose in a butyl actetate or more commonly ethyl actetate solvent.

I think it should be fuel proof but it can become quite brittle. It can be removed using its solvent - butyl or ethyl actetate - but even more rapidly with acetone.

ian1954 wrote:Nail polish is usually nitro cellulose in a butyl actetate or more commonly ethyl actetate solvent.

I think it should be fuel proof but it can become quite brittle. It can be removed using its solvent - butyl or ethyl actetate - but even more rapidly with acetone.

Sounds like it will be perfect, depending on my fuel bath test tomorrow with my test sticks.

Phil

Question for Phil and Mark ---

Since you both have chosen a similar approach in mounting the engine, I'm sure there is a viable reason.

With the engine mounted to the right of the centerline, it seems that it would have a tendency to turn the plane into the circle. Aside from simplifying fuel flow, was there a particular reason for outboard mounting rather than inboard? I don't know how much impact outboard vs. inboard would have, which is why I'm asking.

andrew

pkrankow wrote:Shot some orange, and put fingerprints in the white due to impatience...

Phil

Looking good!
I decided to try the Polycrylic method on my sons mouse racer. After three coats all I can say is wow! It's like a plastic coating for the balsa. I like it so much I just started it on my corsair for the contest. Best part is I did the corsair and the final coat on the mouse at the kitchen table with the windows closed and was able to clean the brush with water from the kitchen sink. Pretty amazing stuff.

Jim

pkrankow wrote:

ian1954 wrote:Nail polish is usually nitro cellulose in a butyl actetate or more commonly ethyl actetate solvent.

I think it should be fuel proof but it can become quite brittle. It can be removed using its solvent - butyl or ethyl actetate - but even more rapidly with acetone.

Sounds like it will be perfect, depending on my fuel bath test tomorrow with my test sticks.

Phil

I assume the nail polish won't react with the Polycrylic?... If it reacts with fuel... maybe you could "mist-it" w/a few coats of Lustrekote (fuel-proof clear) after trimming... especially if it's a "hard-to-match" perfect color you've found. I've got lots of trim to paint too... and I'm not sure how I'm gonna' do it yet... I hope this works for you.

Roddie  

p.s. My "wife" uses this nail polish called "Out the Door"... or "Express Finish"...so you can image how quick that stuff dries... I don't know the chemical make-up off hand though... I'll tell you what I "do know"... If we spent as much money per month on hobbies; as the average woman spends on beauty/cosmetics... do the math. "not that I'm complaining"...

just sayin'...   

I think Ian is right, a friend of mine uses clear nail polish to seal numbers and sticker to dope finishes. works good for him.


Ian, you sound like a chemist.   A laymen would use nail polish remover to remove nail polish though.