Re: 049 Black Widow tuning

--Oz-- Tue Aug 27, 2019 11:38 pm

I did a little measurments today on stock and modded motor.

The exhaust port opening is 0.109 high, the stock motor on exhaust port opens ~90%, and close to 0 spi opening.

When I dropped my cylinder 015" past the standard of my other two motors of 078 (down to 063 deck height), here is what happened.

SPI I could not measure on the stock motor, but I could just see the opening, 005 feeler gauge would not fit in (guessing 003 or less).
But with my modded motor, spi higher was 026 lol (at least ~9 times more gap), get a good laugh at the amount of spi!

black widow venturi - 049 Black Widow tuning - Page 3 Modspi10

I also created a side by side stock motor and mod motor with the same magnification to show the cylinder drop.

black widow venturi - 049 Black Widow tuning - Page 3 Crankc10

With the mod, my piston TDC was 016" higher than the cylinder shoulder where the head gasket rests, not close to even as most I have read (with 4 head gaskets, total 020 gasket height) and stock glow plug.

black widow venturi - 049 Black Widow tuning - Page 3 Standa10

As with any fuel motor, it's a "air pump" (fuel is easy to get in, EG: easy to put too much in), so the better you can get more air though it the better. I truly believe intake is more important that exhaust, why, pressure difference, the low vacuum pressure vs exhaust pressure, exhaust is relatively easy to exit motor, while intake is relatively much harder, so I am guessing the ~9 times spi helps my theory. (only god knows, lol)

Some pilot(s) stating my mods are the "timing duration is almost nothing" (with my small changes), I believe is completely wrong comparing my modded vs stock motor. When i get conrod length, some more numbers will be posted. 7K increase is pretty amazing for one simple mode. I wish I had my 051 TD to try, or will it just break the crank pin, lol?

Surfer_kris Thu Aug 29, 2019 4:09 am

--Oz-- wrote:
Some pilot(s) stating my mods are the "timing duration is almost nothing" (with my small changes), I believe is completely wrong comparing my modded vs stock motor.

I guess that refers to me...?

What I have said is that the changes to the timing of the exhaust and intake durations are very small, and that your gain is likely dominated by the increase of SPI and compression ratio.

Just put a degree-wheel on it and measure the timings and the SPI, then you'll see what I've been trying to get across...

aspeed Thu Aug 29, 2019 10:28 am

OK, so now you need to set the head space to .006" with the lowered cylinder and the stock setting. Get a degree wheel and write down the total open exhaust degrees each way. A round protractor is cheap at a stationery store, drill an 1/8" hole in the middle. I use a piece of solder wrapped on the engine lugs and bend the end to the zero on the protractor. Check the SPI too. Then run it both ways with whatever shims it takes to get that .006" headspace. You will need a base shim (.020" maybe) too because it should be the same motor. Use the high compression head. My theory is your gain was mostly higher compression gave you the big gain. I would guess "too" much SPI will eventually give you no base compression at all for getting the fuel mixture past the bypass ports. What too much would bee IDK. - The next step if you have a mill, would be to raise the exhaust port on the cylinder maybe .020" after checking every which option shimmed up and down using the tach. At least doing it that way will tell you if it is the exhaust timing or the SPI that gave you the gains. Of course you may have a scrap cylinder. Enquiring minds need to know these things so share the results.

Surfer_kris Thu Aug 29, 2019 11:32 am

The other way to get SPI is to remove a bit from the piston skirt. That way all the timings and the compression ratio stays the same, but you can increase the SPI by as much as you want/dare to.

Here is a "free" degree wheel, just print it out and glue it to a suitable card board:

black widow venturi - 049 Black Widow tuning - Page 3 Degree10

1/2A Nut Thu Aug 29, 2019 11:33 am

Yes timing wheel check will for sure help, looking forwarded to the results.

Small Cox Logo

black widow venturi - 049 Black Widow tuning - Page 3 Cox_0411

--Oz-- Thu Sep 05, 2019 6:51 pm

rex f. wrote:Hi oz have just measured 4 new cases they are
1 .073
2 .073
3 .078
4..084
As you call deck height
To the best of my knowledge .073 is correct for black widow
Giving 132 degrees or exhaust duration and approx 40 degrees
Spi iwould take a further 10 / 15 thou off the piston skirt to achieve 70 degrees
Of spi adjust head clearance using galbreath merlin if you have any
Or cox 1702 head to 15 / 20 thou using 35% nitro ( 1 shim for every 10%)
You wont go wrong with this setup but will still need to play a bit
As all engines vary evev killer bee cranks can vary in stroke by .001
Hope this helps
Rex f.

Thanks Rex.

I finally took one of my motors apart and what a castor gum-a-thon, lol. Also conrod needed a good reset (about 0.005" slop), this probably gave some errors in my last post (exhaust and spi feeler gauge measurements).

black widow venturi - 049 Black Widow tuning - Page 3 Stock_10

As you can see, the exhaust duration reduced 10%, but spi increases 255%! With 0.078 deck height, the spi did open, but just barely, so the small 22 degree duration plus the tiny gap was relatively doing nothing. So spi increase was not 2.5 times more the math shows using degrees, it was really like several hundred times more spi function. So going from 22 to 56 degrees spi shows no relative info imo, this is why I didn't really understand why most talk degrees. Need better math to show the difference of simply moving the cylinder down 0.015". Timing only added 24 degrees, but effectiveness (of spi) was exponential.

I did measure the conrod length (best guess from center of crank pin to center of piston ball) = 0.765"

When cleaning the motor, the intake screen just fell out, suggestions for holding it in place (its a plastic carb/tank back)?

What cylinder number does is this motor have?

black widow venturi - 049 Black Widow tuning - Page 3 Cylind10

EDIT:add a couple more pictures

black widow venturi - 049 Black Widow tuning - Page 3 Partia10

The solder point was a KISS solution, thanks!

black widow venturi - 049 Black Widow tuning - Page 3 Timing10

balogh Thu Sep 05, 2019 11:24 pm

I usually add screens even to the unscreened Killer Bee backplate. I take a screen sold by COX International and form a dome of it by pressing it with the blunt tip of e.g. a ballpoint pen against my forefinger. Then simply push it into the intake with a piece of silicone tube, having the convex side of the dome facing outside. When it hits the spraybar the small pressure applied will flatten the dome, i.e. expands its circumference and make its edge hold on to the intake channel.

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The screen then holds firm.

If your engine has 2 bypass ports like in the photo then it is No1 if only 1 port then No2

--Oz-- Fri Sep 06, 2019 11:09 am

On the BW, the intake screen is placed in a small hole that looked to be tapered (small entrance and slightly larger where the screen sits). I ended up slightly bending 4 of the wires at 90 degree apart to make it wider, worked like a champ!

black widow venturi - 049 Black Widow tuning - Page 3 Cox_bw10

black widow venturi - 049 Black Widow tuning - Page 3 Cox_bw11

black widow venturi - 049 Black Widow tuning - Page 3 Cox_bw12

black widow venturi - 049 Black Widow tuning - Page 3 Cox_bw13

1/2A Nut Fri Sep 06, 2019 11:16 am

So what plane are you going to use this engine on Oz any idea's?

--Oz-- Fri Sep 06, 2019 12:19 pm

Its a ultra low cost indestructible (or close to) U-control combat plane. Pictures are in the 1st post.

At the two parks I fly, they dont allow gas/nitro planes, so we usually fly them at abandoned schools.

--Oz-- Sat Sep 07, 2019 10:01 am

balogh wrote:If your engine has 2 bypass ports like in the photo then it is No1 if only 1 port then No2

Thanks, Its a number 1. There is a stamped number hidden in the exhaust port I didn't see, doh! It has a single mill pass transfer channel on each side of the cylinder.

I have seen the picture of the 4 types of cylinders, but cant find it now, can someone post it, tia.

I found another motor in my box (the red one), it has a dual mill pass transfer channels on each side of the cylinder, what cylinder number is this one? It this the TD cylinder? It also has the high compression glow plug, could this be a venom motor or?

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ian1954 Sat Sep 07, 2019 3:09 pm

https://www.coxengineforum.com/h23-cylinder-identification

--Oz-- Sun Sep 08, 2019 11:24 pm

ian1954 wrote:https://www.coxengineforum.com/h23-cylinder-identification

Thanks! That has more info than I seen before, but less in some aspects (not all cylinders are displayed)

So I get 25Krpm with a simple mod (lower the cylinder to 0.063" deck height and add 4 total head gaskets with low compression head and with 10% nitro with ~~6x4~~ 5x4 prop) all with a substandard old #1 cylinder (no extra bypass ports). Very Happy

When I cleaned up that motor, I noticed some good amount of piston/conrod slop (0.005) and the plastic reed looked well worn (so I flipped it over).

1/2A Nut Mon Sep 09, 2019 12:11 am

--Oz-- wrote: So I get 25K rpm with a simple mod (lower the cylinder to 0.063" deck height and add 4 total head gaskets with low compression head and with 10% nitro with 6x4 prop) all with a substandard old #1 cylinder (no extra bypass ports).

So static with a 6x4 / 25,000 rpm ?
Per thrust calc: .583hp - 428w / 95 mph pitch speed.

Most make 75w on a good day Shocked

Surfer_kris Mon Sep 09, 2019 1:19 am

Yes, on a 6x4 prop that would be some serious power from a .049 engine... Rolling Eyes

In another thread/post the prop used was the soft cox 5x4 prop. These are really about 4.8" in diameter and they start flexing around 20krpm, loosing both pitch and bending forward. Balogh has had similar issues on the TD .051 engine.

I've used one on a Norvel .061, the engine "loved it" but the plane didn't go very fast...

1/2A Nut Mon Sep 09, 2019 1:35 am

If a 5x4 at 25k per calc would be 206w
4.8x4 / 175w

5" dia. prop can put out some thrust as long as the plane is low weight / slick in design
no problems getting the most out of 4" pitch. I prefer modified APC props in my case.

Surfer_kris Mon Sep 09, 2019 5:38 am

My point is that the rpm value doesn't really mean anything as that specific prop will not hold its shape. To me the rpm limit seems to be below 20000rpm.

The APC 4.7x4 is a heavier load for instance, and it will keep it shape at higher rpm. Together with the power data that APC provides one can in principle get an actual estimate of the needed power for a specific rpm. I don't know how they measured their data though, it might simply be the needed power supplied to an electric motor, rather than the power that goes to the prop....

gkamysz Mon Sep 09, 2019 7:48 am

Surfer_kris wrote:Together with the power data that APC provides one can in principle get an actual estimate of the needed power for a specific rpm. I don't know how they measured their data though,

It's not measured, it's also an estimate based on geometry and prop theory. You can compare to Selig's windtunnel data and it doesn't match.

fredvon4 Mon Sep 09, 2019 11:40 am

Hey Oz

Try this Wiki for a good Cylinder chart and other great info

https://en.wikipedia.org/wiki/Cox_model_engine#Cylinders

Surfer_kris Mon Sep 09, 2019 12:19 pm

gkamysz wrote:
It's not measured, it's also an estimate based on geometry and prop theory.

That's a pity, they should have enough resources to use a simple torque vs rpm set-up. Sad

I know that the APC 7x4 is way off at higher rpms, but the other props that I have looked at seem plausible at least.

--Oz-- Mon Sep 09, 2019 6:08 pm

I miss wrote 6x4 in that single post, it was 5x4 as I have said from the beginning, I corrected my typo post above.

As some are saying, the prop flattens out, that maybe true, it is a soft flexible prop and great for combat, but going from 18 to 25K with the same prop tells me something, the motor is making more power than before the mod. The 25K maynot be relative to any other prop, nor have I compared it to any other prop, I basically stated what little mod I did to gain 7K rpm (werther is was from 10-17K or 18-25K, the rpm increase was key), even if it was 1 or 2K gain it would still be worth it. Someone mentioned their reedy motor did 25K, it was 5x3 prop and something like ~30 nitro.

When I was sponsored for a decade in rc on-road cars, my sponsor would dyno test a pallet of motors (~1500), the team drivers got the cream of the crop (top 5%), there was a huge difference in preformance from the pallet. There was two different flywheels (loads), ALU and steel, the heavier one was for modified motors, 50Krpm was scary with that much momentum, if a winding flew and jammed the arm, the whole motor would rip a new one. The dyno would plot out torque and HP (torque X rpm) over rpm with input current also on the graph.

black widow venturi - 049 Black Widow tuning - Page 3 Rsr-br10

Surfer_kris Tue Sep 10, 2019 1:20 am

The soft props can not be used as reference props, they are simply all over the place in terms of engine load. It even changes from the beginning to the end of a single flight....

The APC props are better as reference props as they are stiff enough to stay the same between engine tweaks.

1/2A Nut Tue Sep 10, 2019 2:59 am

Hi Oz,
Can you run that engine up on a rigid prop and vid it lets see what it's doing. Very Happy

Kris,
Did you cover the VA .020 Mini Zipp? If so please post some pics in my speed thread
on RCG. Thank you, looking forward to that one getting up and running.

RC Plane

--Oz-- Tue Sep 10, 2019 7:19 am

fredvon4 wrote:Hey Oz

Try this Wiki for a good Cylinder chart and other great info

https://en.wikipedia.org/wiki/Cox_model_engine#Cylinders

That's the one I was looking for! thanks!

--Oz-- Tue Sep 10, 2019 7:34 am

1/2A Nut wrote:Hi Oz, Can you run that engine up on a rigid prop and vid it lets see what it's doing.

Maybe, I have another box of cox stuff I need to find, then that comes to finding a prop and the 20+ year old fuel. At this point, I am not going to buy anything for it as I am not planning on flying it now and I am heavy into electric quads/planes.

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