Pond Skipper

Took the Skorch out today to try the pipe system - it needs pressure as the first three hand launches the engine would die as I tossed it.
Managed one launch with it running rich to overcome the fuel issue but that didn't have it screaming on the pipe. Will tap in a pressure
nipple tonight and try again Sunday.

Pond Skipper

Ok learned a little something through doing. The AP carb design like the Norvel both use pressure off their mufflers to achieve good running characteristics.
I didn't have a small enough 90 deg pressure tap so was reluctant to install a standard small nipple.

Tonight I tested the pressure line, the engine now idles down to 5700 constantly and transitions to the top end without any lag.
I installed the pressure nipple at the connector ring on the pipe in hopes for extra meat and to lock in the threaded pipe sections.
Will have to do some digging online for a micro size 90 deg. pressure tap.

Pond Skipper

Ok did the flight and vid

It flew for 5.18 mins then after multiple knife edge passes I snapped the vertical fin off.
The tank had about another 30 seconds of fuel. Set idle little high for throttle chops in the air - 7.8k rpm and still learning whats possible on pressure.
Noted so far 24,793 rpm on the pipe APC 4 x 4.5 / 94mph tuned length for 25k unloaded.
Passes where consistent it is locked in on the pipe (9.8in) from center of the convergent cone to the piston face.
I need to shorten a hair more to be in the 25.5k range about 9.2in might do it.
Needle set to running with a reasonable plume of oil out the pipe as it was hot today 91F / with a heat index of 96F
Didnt want to risk overheating the engine or a dead stick - needle was set make the pipe chime on the ground.
Winds about 8-9 mph small gusts to 13 mph. 20% castor 25% nitro. Two shims now as of last night for hot weather.

Note this is the only video of a 1/2A RC plane flying that has the engine boosted by a tuned pipe.
The only other vid has a pipe functioning as a muffler on a cox reed engine, the pipe length is way to short for
the best unloaded rpm of 13.7k - pipe would need to be 17in from the center of the divergent cone to piston face.
Published on Jun 28, 2015

Link to watch full screen HD
https://www.youtube.com/watch?v=oiLQfuQ4y64


https://www.youtube.com/watch?v=oiLQfuQ4y64

combatpigg

My Feedback: (3)

It sounded real good..!
The pressure tap works like a charm.
Keep rough track of how much use you get out of the AP [if you run it exclusively like this].
It sounds happy to be run with that prop / rpm / fuel.

Pond Skipper

Thank you CP using pressure solved the launch issues and made sense with this style of carb. The barrel rides the threads of the NV steam / as it rotates backed out of the carb body. Need to dial in the needle I was 3.2 turns from closed on that flight. I'm sure it will end up much less, couldn't get in any more dial in flights with the vertical stab failure. I have about 50 mins. on the engine right now with another new AP in the hanger when this one trashes out or could use one of the Norvels. The .061 is making good thrust with the 4.5 so will try the 4.2 next to see max speed hopefully without ripping anything else off the plane

The glue joint didn't break free, the thin ply footing for the vertical stab actually ripped out balsa from the horizontal stab. Over time the level of force on the vertical stable riding in a knife edge was stressing balsa grains. The ply footing was fairly wide so it took a good beating for many flights. Im glad I waited to fix this at the house so I can peel back some monokote and get a long lasting repair finished off with the hot iron.

combatpigg

My Feedback: (3)

That's a pretty good amount of wood that sheared off. It looks like it was good for any amount of flying you could throw at it..

If I have a failure like that, I'll dowel it with round toothpicks or bamboo skewers, followed with some 1.5 oz cloth saturated with medium CA.

Pond Skipper

Yea amazing the stresses on fast flying planes, when it failed It was on the ground in a heart beat.
I thought about the dowel trick during the design phase, but crashes would have them snapping in short order perhaps carbon rod would be the end all be all.

Instead I built a wide base sheet of thin ply over the horizontal stab and a narrow footing glued to the vertical stab the idea was to sheer the glue joint between the two ply sheets during crashes this actually worked twice and made for fast repairs. However I was stressing the underlying balsa grains with the base sheet. I should have selected hard balsa for the stab ah well the glue saturated in the balsa should make it tough enough to hold up to high speed knife edge flying.

Mr Cox

I would guess the rudder broke from tumbling over at landings, time to finally ditch that landing gear perhaps?
Looks like a good combination, although it doesn't really jump onto to the pipe like other piped engines do. Have you tacked it without the pipe?

I found an engine timing diagram on my computer, it was made by someone else on this forum (can't remember who). It looks like you could possibly do better by shimming under the cylinder to get rid of the SPI and gain a little exhaust duration too?

aspeed

According to that diagram, it has sub piston induction. I didn't know that would work well with a muffler or pipe. Usually the crank timeing is 40 60 for a piped motor. The closing tiime at 57 is pretty good.

Pond Skipper

I was doing a lot of full throttle knife edge flying Right and Left full rudder inputs. I had left rudder in a long knife edge pattern at full throttle the vertical stab popped and caused the plane to spin as I had some aileron mixed in when it happened. I only had time to chop the throttle before it went in. The engine is running great, temps where good and the plane was fast. Some of the Jett engines use SPI on a pipe along with some of the car engines.

combatpigg

My Feedback: (3)

I had to take a 2nd look at those numbers after a cup of coffee.
These engines are so small they aren't easy to check.

Pond Skipper

What did you see Chuck things can be a bit subjective at times. Did you put one of your AP engines on the timing wheel?
I dont get 162 deg.. more like 145 / 150 tops watching the piston seal off the exhaust port.

combatpigg

My Feedback: (3)

I've never checked a AP. Does your engine [with mild exhaust timing] have SPI...?
I wouldn't sweat it, unless another guy shows up with a .061 powered plane that is so much faster than your's that it makes you angry..!
You're already at a nice level of performance for this class of engine. Making them go faster [with Toad mods for example] just wears them out. At that point it makes sense to buy a Russian Combat engine and outfit it with a muffler / pipe and an engine kill. You'll be money ahead in the long run. They even have pressure tapped backplates if you make a point of ordering that option.

Pond Skipper

I hear you Chuck....Per post #635 "The engine is running great, temps where good and the plane was fast"

MJD

My Feedback: (1)

In my modest timing measurement exercises so far, I have noticed that when the eye says the port closes can be very subjective (easily off up to ?10 degrees?), but with bright light down the plug holes it becomes much more consistent.

Pond Skipper

I can feel it start to seal
Good idea with the light Mike, you can feed low pressure compressed air thru a modified glow plug installed to hear when the air seals off
or use a air gauge and watch for the needle to stop.

MJD

My Feedback: (1)

I take no credit for the concept of shining light into the cylinder, only for repeating someone else's good advice (CP I suspect). Some time when I am near a lathe I'll bore out a glow plug and epoxy in a bright LED. With no light leakage to distract the eye, the task of spotting port opening/closing should be pretty simple. Could also stick the end into into the crank opening from the rear for front intake measurements, I guess.

The air idea sounds pretty feasilble.. got a stethoscope?

combatpigg

My Feedback: (3)

The degrees of "dwell" the piston has at TDC needs to be measured and split in half when zeroing the pointer on the wheel. I use a flat bar of metal bolted across the top of the cylinder. The bar is threaded 4-40 so that a screw can be used to tap the piston either side of TDC. By changing the depth of the screw to allow the piston to just barely tap it either side of TDC you can take note of how far off the wheel is set from being perfectly centered at TDC.

Pond Skipper

Updated:

The Killer TD .049 - Cox RC carb
Breaking in the engine in the air
Galbreath / Nelson plug
#1 cylinder 2 bypass ports 1 boost flute per port
2nd flight APC 4.5 x 4
22,044 rpm in the hand static - 25% nitro
best pass at 24,160 rpm 3rd fastest set up -needle is set bit rich. 67 F. winds 6 to 9 mph

Killer TD .049 3rd flight
APC 4.75 x 4
20,873 rpm in the hand 25% nitro
22,287 rpm cross wind and 23.94k down wind
9 to 12 mph winds - temp 78 F Humidity 80%

Stock TD .049 - Cox RC carb - Cox High Comp plug
APC 4.75 x 4 (no data with the 4.5 x 4)
19,380 rpm in the hand 25% nitro
21.4k rpm cross wind 23.3k down wind.
Winds about 4 to 6 mph per hourly weather check. 74 F


TD .050 #5 cylinder- high compression head 1 shim - 1st flight test
performance crank non SPI - 140 deg exhaust timing 25% nitro 78 F
Tarno carb - APC 4.5 x 4
In the hand 21,237
unloaded 23,771 best pass / 90 mph theoretical
In a down wind high dive 24,9K 94.3mph

Bench Tests
Profi Tuned Pipe TD RC .050 non SPI - 1st bench test
Tarno Carb, Cox buggy header pipe with half moon 3/4th around brass shim to block 1 exhaust port
#5 cylinder 2 bypass ports and 2 boost flutes per port -1 shim HC Cox Plug - KK pressure tap
- Idle with Tarno carb 11.786 rpm APC 4.5 x 4
- vid static recorded 20,996 rpm on the pipe best noted 21,370 rpm 25% nitro


AP .061 Profi pipe with Sportwerks Header pipe
Static 25% nitro:
APC 4.2x4 / 25.63k
APC 4.5x4 / 23.47k

APC 4.5x4 Unloaded 1st vid flight 24,793 2nd fastest Skorch setup 93.91 mph
91F winds 7- 10

July 12th AP .061 on Profi Pipe
2nd Field Testing APC 4.5x4 in flight "rpm is locked on the pipe"
*Needle peaked - minimal oil on tail run time 6.35 mins. 1oz tank
Unloaded 26,324 1st fastest multiple passes all 26k ish / 99.71 mph
94F winds 8 -13 mph

APC 4.2x4 lots of screaming but thrust wasn't cutting it.
Would be good on 9-10oz RTF SWR for a faster plane.
Prop blade width is more narrow scrubbing off enough thrust
to climb fast at 11.8oz plane dry / with fuel 13oz guessing.
I will need the Norvel to use the 4.2 x 4

Pond Skipper

July 12th - AP .061 on Profi Pipe

2nd Field Testing APC 4.5x4 in flight "rpm is locked on the pipe"
Needle peaked - minimal oil on tail run time 6.35 mins. 1oz tank
Unloaded 26,324 1st fastest multiple passes all 26k ish / 99.71 mph
94F winds 8 -13 mph


APC 4.2x4 lots of screaming but thrust wasn't cutting it.
Would be good on 9-10oz RTF SWR for a faster plane.
Prop blade width is more narrow scrubbing off enough thrust
to climb fast at 11.8oz plane dry / with fuel 13oz guessing.
The Skorch would need the Norvel at 27.5k to use the 4.2 x 4

combatpigg

My Feedback: (3)

The 100 mph mark with a AP .061 is not something I would have imagined. By "locked in RPM", this must mean that the prop is just about a perfect mesh with all the other factors.
You're at a point where scraping some thickness out of the prop blade's airfoil can be tried for an extra MPH.

Pond Skipper

Yea I really milked the most rpm out of the needle on this round of flying as the engine was still needing some break in time in the air on the first day. The engine idles great and pops right back on the pipe keeping a steady instant top peak. Minimal goo just a spot on the right side of horizontal stab and a mist on the vertical stab. The front is drip free so far it has been a great change from the original front goo setup. I have gained a whole oz in weight but worth it.

I plan to try a Nelson head adapter next to eek out another 400 ish rpm. There is some half A fuel line that is a tad bigger then what I'm using on the pressure line should order some to eek out a better peak. The AP carb really needs the help and is poor on suction, the engine is getting good run time. The 4x4.5 prop is the way to go with my current weight - perhaps some shape work could happen to milk another 300 + rpm. 35% nitro would be another move forward and lastly could try a Norvel for another 1,200 rpm + I do like the APC props if I break one there is no winching when popping on another. Perhaps some carbon graphite pricey props would be on the menu if I start seeing a rarity on snapped blades. Some days are 0 loss like last weekend.

MJD

My Feedback: (1)

Some days are $16 a flight..

Pond Skipper

There you go Mike is why I havent pulled the trigger on them yet. APC you can buy a bag of them on ebay for cheap and fear not of running out for awhile.


Skorch II - 1cc to 1.5cc class engines:

I started a 27% increased version of the Skorch for the more heavy race.06 engines CS, Fuji, Sportwerks the Norvel .074 and Cox.09 engines.
Engine weights from 82.4G to 113.2g with props and spinners. RPM from 20k to 36K static / opens up the use of 5 different brands of engines.
I have been looking forward to trying these out for some time. I will go with a 3 to 4 channel plane a mix of speed and acro flying on 2oz of fuel.
The planes percentage jump comes from the limitations of a 24in sheet of ply. The original Skorch has 17.5in of ply fuselage.
With the right props these engines should have no problem getting the longer narrow fuselage past 100 mph. Span will be 32in / 120sq.

You would think ahh the .10 to .12 class traditional all aluminum framed engines too but heck no their weights start at 170g with prop spinner - in my collection.
Those and the .15 size engines can be bundled for use at a later date with the Slim V project.

Pond Skipper

This one will get some extra treatment in the tail area to support the additional loads and speed.

Looking for these numbers:
4.2 x 4
Fuji 27.6k static should do 29.8k on the pipe unloaded 114 mph.
CS 36.4k on pipe 138 mph

5 x 5.5
Norvel .074 22k / 115 mph
Cox TD .09 24.3k / 127 mph

Here is a pic just scissors and a exacto blade to nip out the wing saddle and horizontal stab seat.