Pond Skipper

Thank you CP always great info!

4p prop is part of the limit only way to beat it is lower the weight and size so 55 Sq in. - RTF 6.5 to 7oz will allow props like a 3.5 x 6
at 24.6k rpm 140+ is possible. At this time even the 88sq.in Skorch wing looks like more than plenty at 11oz.

In retrospect I should note I have a 28in plank wing from about 7yrs ago looks kinda like the Skorch wing done from 3/16th - RTF at 5.7oz on 2S 860mah on a 4x4 elect. prop.motor is heated up to perhap 65-70w and it rockets straight up on a custom wound 12T 8pole 22g wire -level tachs out about 115-20mph ish./ static is does about 27.6k loaded in the hand. I would love to do the same with a stock cox engine. ref. 3.5 x 6 at 140

Sourced a prop that may have a chance to be useful a glass 5x5 cut to 3.75 x 5 full size when opened.

combatpigg

My Feedback: (3)

I see the method to your madness now..!!
I'm just stuck in a rut because I've never come up with a power to weight ratio that could make use of a massively over square prop.
There used to be a free online calculator that would spit out "load factor" for any prop you plugged into it. It would also give you the HP generated.

Pond Skipper

lol ty ty yes its all about taking advantage of the new gear.
The Lil Speedy ply fuse plane let me see what weights are possible with IC how the micro servo's would respond to engine vibrations and confirm there was enough torque to motivate the surfaces without being forced to size up. Really has opened up the door with a strong simple platform to hide the gear without having to make anything too elaborate in carbon or fiberglass.
Limitations:
- fuel tank size must be at least enough fuel for 3 min runs or it will all stop too soon and be frustrating.
- engine weights thus far the cox is the winner and can be modded as I did with a small prop and plane load you can push the rod and socket and crank pin with nothing but rpm. We have all heard them scream when a prop spins off and nothing breaks so min load can still yield a long lasting engine with just socket resets every 20 flights or so. The weight and power of the performance engines force you to beef up. I only need 80w of power at 26 to 28k unloaded beside more engine means more fuel. The micro servo has to stay in perspective and on the plate or you're forced to up the battery size not going to happen I have flown up to 8 flights on my 260mah cells with three micro's and still had only used about 120mah when recharged.
- prop choice I wish I could just make a phone call and special order narrow high pitched carbon props such as a 4.5 x 7 but thats not in the cards anything with a 7 pitch that could be chopped down and reshaped would still have a hub suited for a 10 or 15 engine.
Lucky for us the electric world is now making a few props that can be used. The trend is having a flared out high pitch section near the hub this doesn't work with IC engines they need constant pitch. Very few I have seen will work the one in the pic is new from Cermark and has a chance. The hub is right material is doable just down to trying the 5p and 6p options there are a lot of 4.5p but that doesn't make enough of a jump and would force damaging rpm. I would like to stay under 28k it is not just about stress its about wear and fuel consumption too. 6p at 28k could yield 160mph. these new black glass props seem to hold their pitch and don't flatten out. I know now with the lil stinker at 5.3oz a 3in dia prop is the limit as it starts flying like a ducted fan from the Y2k days no fun not worth the extra speed if its lost in the turns. So I think 3.7D has a chance at max limits of 7oz. I have been tempted too many times to cut off an inch from the nose of the Lil speedy to slap on a .049 knowing the frame can handle the power and extra speed but then would ruin it as a nice .020 plane so it forced me to move up to the Skortch which I already know will make a better .09 plane the fuselage is so tough it could handle a 15 if I glass the wing. Nice narrow fuse with ample room as a 5ch.could have gone 6 with retracts as that 10mm thick foil on the high side could hide the gear. The Skorch will show some new doorways for 6 to 11g class of servo's. I will have two 7.5g servos in the wing and 5.4g in the belly which is plenty plenty. More about continuous service than having enough torque. If this was a 200sq wing with balance size surfaces in the tail I would want a min of a 8 - 9g servo on the elevator.
I remember being happy just to use 21g micro servo's from futaba FP S133 back in the 90's was a big leap forward for 1/2A flying and a must buy to be on track.

note the spec 77oz of torque wow lol overkill my lil speedy uses 4.8v / 11oz torque 4.5g servo's no prob. Now with the 7.5g servo's for Skorch at 20 to 30 oz at 4.8v to 6v more than plenty.

SERVO FP-S133 HIGH-QUALITY MICROSERVO_

• Futaba hybrid custom 1C provides high starting outputtorque, narrow dead-band, and excellent trackability.• Thick film gold plated connector pins insure positive contactconnector shape increase reliability against shock and vibration.The connector housing has a reverse insertion preventionmechanism.• Adjustable (splined)

neutral position.• Despite being a microservo, operating speed is a fast 0.21

sec/ 60° and output torque is a high 2.2 kg/cm.


I use this for fast ref. to pitch / mph

http://www.rcpro.org/rccalc/PitchSpeed.aspx


times have changed.

aspeed

I wouldn't worry about the weight of the motor so much. It is the overall weight of the plane's power to weight ratio. A heavier motor that puts out double the power of , say a TD is still going to be much faster. Maybe a bit slower acceleration with a heavy plane on a hand launch. We made basswood planes with aluminum pans to hold the motor, they went very fast. It is mostly the motor, not so much the weight. A speed flyer I know always used a 5" pitch on his home made 1/2A motor, 'Just in case' things would hook up. He used single blade props even back then. There used to be a 4 1/4" - 7" wood prop available for speed. Maybe Revup? Most .049 motors could not pull it. Maybe one of the more modern .06 motors would. I made a mold of one, but can't seem to find the top half of it now. Maybe it broke years ago. Good luck finding an old original. There is an electric 4.75 x 4.75 that seems to be the thing for mouse racers. A TD may not break it. A stronger motor may.

Pond Skipper

Hi Aspeed thank you for checking in and your info!

I have the APC 4.75 x 4.75 it has an aggressive pitch near the hub then fans out ok if you cover it up with a spinner otherwise it dogs a cox engine.
The jest of the idea a 6.5 to 7oz on a light cox engine will have enough power and the parts are cheap to replace keeps the wallet from stressing out lol.
I could go the hardwood route with more engine but want some nice landings and avoiding having to use stronger bigger servo's.
Those rare wood speed props show up from time to time on ebay most are beat up (being wood) and so tend to move on. 4,25 x 7 seems reasonable
I had figured a 3.75 x 6 could work with a narrow cord on a cox engine. If you find that other mold half do tell- what did you use for the mold material?

MJD

My Feedback: (1)

Since it is not a big deal to spin a good 1/2A motor 35-40k it seems to me no more than 4.0" - 4.5" pitch should ultimately be needed to achieve 1/2A's potential. Maybe 5". I guess if you're limited in rpm by mechanical constraints, i.e. the engine can't, then who knows what could be achieved with modest engines turning little oversquare props, interesting. I can see it now..

2015 Online Sure Start RC speed contest

MJD

My Feedback: (1)

Here's the highest pitch stuff in Eliminator's lineup.


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[h=1]E-7 4 1/4 X 5 1/4[/h] [h=2]$5.00[/h] E-7
4 1/4 X 5 1/4
This Prop is was based on a Tornado/Grish, cut down, blade area reduced & repitched.
1/8" Shaft hole






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[h=1]F-6 - 2 5/8 X 5 - 1/2A Single Blade Speed Prop[/h] [h=2]$5.00[/h] F-6
2 5/8 X 5
1/2A Single Blade Prop designed for 1/2A Speed 049 with a tuned pipe.
This Prop is based on Bob Fogg's 1/2A Speed Prop.

combatpigg

My Feedback: (3)

When I first got into the hobby, Bob Fogg's name was next to 90% of all the 1/2 A records it seemed.

Pond Skipper

Thank you for the posts gents

Taking the E7 to scale then reshaped to 3.5 x 5.25 here is what I get.
Bare in mind a stock .049 /.051 cox engine can not spin at 35-40k in gen. the idea is to build a plane based on known weights of the Lil Speedy and what I learned thus far on the Skorch build to obtain a 6.5 to 7oz plane that can for the price of a cheap replaceable cox engine that all can obtain or already have on hand undergo a project that does not break the bank or require any special speed tricks or skills to exceed typical known speeds to date as a RC 2ch or 3ch plane. For me I would want to control throttle so would put a small 4.2g servo onboard.
I wish I knew a prop maker the only choice is to buy for now what's on the shelf and mod to suit.

With a stock Cox engine unloaded would need:
30.17k for 150
28.16k for 140
26.15k for 130
24.14k for 120
Speeds less then above are mute.

combatpigg

My Feedback: (3)

With the old HP THRUST CALCULATOR, you could take a known, upper limit performance number [like 25,000 with a 5x3 prop], then take note of the load factor and the HP that was required to do the deed.
Armed with that data, you could test the feasibility of hypothetical prop ideas. If you set your imaginary prop's specs within the load factor and HP required, then you could be reasonably sure you weren't on a Wild Goose Chase.
A stock Cox .049 will reliably disintegrate at 25,000 + within X minutes of being run like that.
A KillerBee with lightened piston seemed happy at 28,000+, but I never heard how long it lasted.
A DIY lightened piston is in my book mandatory equipment if you are willing to spend at most an hour to get set up to crank one out.
If you don't allow revs into the upper 20's, then I don't think you'll extract as much power as you can.

Pond Skipper

So 25k with what prop causes it to disintegrate:
- spinning mass in weight
(what improved odds if with a dramatic loss in weight and drag such as a 3.5 to 3.75in prop)
- load static or unloaded
if launched at 20k then opened up could it survive.
A cox engine that throws it's prop screams over 30k (I would imagine) till its stopped.

APC 4.2 x 4 - 3.5g
Cox 4.5 x 4 - 3.1g (plastic)
Cox 4.5 x 4 - 4.1g compitition dark grey new to cox

cut down mod prop
3.5 x 5.25 - 2.7g (just a guess)

Assume most will not be able to mod their piston what is next for most?
For me this all came up for a need to save weight with the Lil Speedy to slap on a 049 for a slight weight gain to the 5.3oz RTF plane making it a .049 3ch 5.833oz plane
Weight shown with this 4.5 x 4.5 stiff glass plastic prop TD Cylinder If cut to 3.5D perhaps 37.5g
If at 25k with it cut to 3.5 x 4.5 unloaded flying a (5.83oz plane 21in span) 107 mph.


per Bernie in Canada -4.5 X 4 in grey or yellow. 20,000+ RPM on a .049 reedie
On the bench so fig. 22.6k for 86 mph

combatpigg

My Feedback: (3)

The "Gold Standard" for competition flyers who ran TD .049s around here was 23,500 to 24,000 with a rubber 5 x 3 or that engine didn't make the road trip to fly combat or pylon.
To gain performance above that the 5 x 3 was cut down until the model's performance suffered in combat. With the models we typically flew [120-150 sq in @ 6 or 7 ozs] droping down to 4.5 x 3 was "about it".
The pylon racers @ 200 / 20 needed the full 5 inches of diameter, so they aren't comparable to what you're doing here.
Anyway, the engine would run fantastic above 25,000 with the stock weight piston until the ball socket crumbled from work hardening or the other end of the rod would go oblong and break.
I never failed any cranks, or recall seeing anyone elses' fail. If we were using wood props or just a circular flywheel, I believe the red line would improve, but even when APC props first arrived the Cox engines still died predictably at 25,000+.
Shaving the piston...I think anyone who sees Dickeybird's thread about the Poor Man's Lathe will be able to decide whether they want to try it or not. The Leadloy material shaves so easily with the back edge of a #11 Xacto blade, it's amazing. I dared myself to shave them down somewhere between typing paper and playing card thin and never had the piston fail. They DO wear out faster though, but shaving them really improves the red line and buys the engine more time.

Pond Skipper

Thank you CP this helps set a baseline to go by I need to run the engine on the ground at 22k and in the air at 25k n hold my breath to see how long the engine will last. I have a 20% castor blend fuel that may help.
Combat with lines adds some drag this is good solid info;
CL [120-150 sq in @ 6 or 7 ozs]
If no line drag and if say 60sq. in to help reduce drag further with no abrupt flying style shall and will not twang the load numbers as much lol.
I dont need sharp turns or have punchy bang on lift just fast tracking and turning with some vertical.
I dont want to have to reset the ball socket every other day in the field as it thins the metal I feel over time.
Where you shave the cylinder to reduce load / wear I can imagine the route with a small rc plane will allow an alternative.

I will check out his thread but the idea is to stay stock for the every day joe to slap the concept together for a cheap fast 1/2A that gives predictable speeds from the design in gen.

Pond Skipper

Product 8/12

[h=1]K-12 5 X 6[/h][h=2]$8.00[/h] K-12
This Prop is based on a Tornado Presswood.
1/8" Shaft hole


Could try a 3.4 x 6
25k for 142mph

at 3.4D I would have to be at 6 to 6.5oz.

aspeed

Lots of posts here when I was gone for a day. The second top is the 4 1/4 - 7" bottom mold. The two bottom pics are a 6-6 or 6-7 IIRC. The top is an old 5-5 Tornado presswood. The Eliminator ones look good and are reasonably priced. I would just get those, and would have if they were available back then in the '70's and 80's. The FAI props were $15 then, and minimum wage was around $2 an hour, so we made our own. I used plasticine to shape the first half, the Bondo for the second, then Bondo again for the top. At one time I used a better epoxy steel filled molding material but have no idea where to get it now. Since then I usually split the top part of the mold in the center to ease the mold separation as in the top pic. Maybe you can see the air bleed holes that need to be drilled out in the top half in the bottom part, and the clearance at the prop tips for the fibers to go through.

Pond Skipper

Nice work on the molds A Speed!! 15 bucks good gravy and min wage 2 bucks so around 1974 of course you could buy a soda for 15 cents then.

Well I did up the tail feathers as all that speed talk has me wanting to finish this one up to see what she can doo..9.6g is what the tail feathers came out to.
Dubro nylon pin hinges for the rudder and will just monokote in the elevator. All up weight less monokote for the flying surfaces and epoxy on the fuselage, two 1/2A horns and some piano wire torque rods: 9.96oz leaving 1.04oz to work with. Should I need to save weight I will nix the 280mah 4cell nimh at 23.2g for a 2S lipo 12.2g 260mah. giving me 1.40 oz to work with to stay at or under 11oz.

Mr Cox

What voltage reduction do you use for the LiPo?

I have fiddled a bit with LiFe batteries lately, but unless they can be used directly (at 6.6V) there is not much weight to save in practice.
They do save a bit in terms of handling though, with low self discharge and faster charging etc.

All this talk about weight and speed is very interesting, but to me the landing gear needs to go first of all...
Are there no good fields around that you could fly off, or simply make it a high wing instead?
These small planes barely touch the ground if there is some nice grass to land on.

MJD

My Feedback: (1)

I'm taking the plunge and going to use a 200mAh LiFe directly with the Toucan.. it seems to work fine on the bench with the Rx and HS65's. Dunno what trouble I am walking into but we'll see.

Pond Skipper

Hey Kris I have looked at the 6v LiFe batteries have you found them in 350 mah range yet? If so please post a link.

My thoughts on the matter and what works for me:
For LiPo example my Lil Speedy 4ch 2.4ghz RX can handle up to 16v my analog servo's have (less voltage pulses 50 cycles a sec. than digital 300 cycles per sec. and are less power hungry) micro servo's are rated from 4.8v to 6v max in order to be rated for long or reasonble duty life - a fully charged lipo is hell on a small brushed motor arching the carbon brushes on the armature will take them out in short order. Note when you arm the servo at startup they jump prior to centering waiting for a signal from the TX with 2S lipo the servo's screech into position at FULL voltage this is bad and for now the nature of the electronics. Once the servo is centered by a now binded RX with the TX the voltage pulses are on standby allowing the servo travel fast or slow depending on how you use the TX controls. Most speed flying is done with smooth consistency least if the power band is marginal sucha as the TD .020 and you want to keep the speed up in my case or its very fast plane and your steady on the throws all the same. You can get away with what i'm doing with my Li Speedy on 3 micro 4.3g servos this way. If I was flying acro not so much. Note I am using analog HS-35HD ultra nano servo's for that plane with 3 Karbonite gears combo where it counts. The Skorch has 5 larger servos and will absorb the voltage jump during the binding process with less stress to the coreless motors. I recommend HV servo's whenever possible to take advantage of the light weight lipo cells that pack more mah. such as;JR DS285MGHV High Voltage Digital Hi-Torque Sub-Micro Servo (Metal Gear) 11g.


. Digital servos are faster stronger as they pulse 300 cycles a sec. if with a coreless motor they spin up faster and stop faster. If you fly short range you can fudge along with 1S cell but must jump up in mah to make up the difference in efficiency. a digital coreless has great low end torque for small movements unlike a analog at 50cycles has a deadband of weak torque these ratings are only worth much during full throws. Most have to use a digital shunt to lower the voltage for normal heavy use / throws for sport or acro flying.
Note NiZn batteries are perfect cells at 1.6v nominal they charge to 1.9v for perfect light weight 3cell packs the bummer part is they only make small ones in AA size class if you see some AAA let me now I will try 3 for the 1/2A. I have 2,800mah 4cell NiZn in my TX great duration.

Per post 74#

( Based on the Lil Speedy at 5.3oz a 6.5oz - 2ch with a cox .049 reed engine at.55 sq in wing would be 1oz per 8.46sq in.
No landing gear the bare mins. I may try a no fuss build with my modified .049 at 35.7g with prop or 7oz with a TD. )

I have reasonable grass field to fly in, just like low wing planes.

Pond Skipper

The Life bats hold close to thier nominal voltage is a plus...FYI I think I can program my fancy charger to peak my Lipo's at 6.8v yet charge them up.

aspeed

http://www.hobbyking.com/hobbyking/s...gulator_5V_1A_ this may help. I have a similar unit from Hobby King that goes from a single cell to 5 volts. This one uses two LiPo cells so it would add weight overall. It will only go to about 1 amp, so it is not for a large model. I can't find the unit that I bought but it may still be in stock, and I just couldn't search properly. I haven't used it yet, so no review.

Mr Cox

Most of the servos, and receivers, I have are only rated up to 6V. Not sure how much safety margin they leave for a fully charged NiMh battery pack?
A fully charged LiFe may well exceed that undefined safety limit though.

So one would have to buy HV servos and receivers, or reduce the voltage. I have tried a voltage regulator that will give 5V on the output (so it would be fine even for 4.8V servos) together with a 2S LiFe of 700mAh. The net result is a similar total weight to a 700mAh NiMh solution, but the regulator doesn't manage to keep the voltage as stable as a NiMh battery can...

I have ordered some Si-diodes and will make a "step down" regulator to be on the safe side with a 2S LiFe.

In the mean time I'm flying happily with my NiMh batteries, they just have to be replaced after a few years as they go old and don't deliver the same amount of mAh as they used to.

Pond Skipper

The wee lil coreless motor can handle the voltage just a matter on how long they will last based on type of use.
Today I bought: 11.2g Smart Lipo 5V 250mAh 1S Battery regulator for 24 bucks off fleabay for the Lil Speedy as I really dont want to trash my 26 dollar ultra nano servo's.

Then I made this .8 ohm 1.4g voltage shunt for free lol.
Voltage drop across .8 ohm of resistance is dependent of the amount of current flowing through it -in the case of a few micro servo's the value is not much so there is very little worry the coil will burn down your plane.
.75-ohm amount of resistance can be around 1.5v loss so if you had a charge of 7.8v in a 2S lipo potential shunt to 6.3v good for start up loads prior to the TX binding to the RX I always have the TX on first to reduce lag time to bind.
This is a dirty way to reduce voltage results will vary (I want to make another one using 30g wire)and will waste some duration but worth it as you now can fly. Back in the day we had Nichrome wire wrapped around an insulator with a wiper arm driven by a servo as a cheap speed control for you RC motor - you can take a short piece of nichrome wire to reduce 1.5v. off a 2S lipo it does get warmer than using the copper coil shown in the pic.

MJD

My Feedback: (1)

I bought 3 of the HK step up regulators to investigate their use with 1S Lipos. On the bench they work fine, so far that is all I can say. A 350mAh 1S Lipo and one of these may be a smarter choice for me. I keep waffling.. no track record/experience with either in 1/2A's.

MJD

My Feedback: (1)

Wouldn't a simple diode on the LiFe pack at least drop some of the peak voltage out of the picture? Still flirting on the high side of 6v though.