CEF makes another visit to Fort Jackson - good discussion

It did have a destine sound to it , getting the job done and Ron looked like he was having a blast with the shoestring . Thanks Rusty bee waiting for the rest of the report , Glad ya'll could get together and have some fun , and Ron can have that job I wouldn't want no part of it even in my younger days getback

I think that was the first flight and it was a tad rich, but when the fuel was getting low you can hear it 2 stroke when it's pointed into the wind and 4 stroke on the other side with a tail wind. You get that with a forward pointed open uniflow vent. That's an interesting thing I only learned recently since I usually run muffler pressure, which eliminates that little phenomenon. I have some footage of another flight where the break is tuned more accurately. I always try to get my FP engines to do it, but they aren't as reliably repeatable as this. I suppose a Fox with an ST Needle valve runs like the Max... or visa versa.
Rusty

That wasn't the first flight, the first one I landed inverted...

After that I was really conservative on the bottom half on the tank and flew a lot of level laps to avoid that happening again.

The Shoestring was much more fun to fly this visit after a longer control horn was installed and the addition of the .35S

Thanks for the writeup and for allowing me to fly the old girl.

Ron

Looks like "The Official CEF Moderator Fun-Fly!"

Cribbs74 wrote:That wasn't the first flight, the first one I landed inverted...

After that I was really conservative on the bottom half on the tank and flew a lot of level laps to avoid that happening again.

The Shoestring was much more fun to fly this visit after a longer control horn was installed and the addition of the .35S

Thanks for the writeup and for allowing me to fly the old girl.

Ron

You're quite welcome. The old girl needs the exercise. After all the carnage I've created since I started flying bigger planes, I'm really happy the SS is still with us, and relatively pretty. We were blessed with a jewel of a day to fly, considering how crappy the weather had been. It was great to get together. Btw, I meant to mention while you were there, Jim is the one who gave me the Baby Streak-II.

Admin wrote:Looks like "The Official CEF Moderator Fun-Fly!"

Haha, I didn't think of that. The bandits coulda' run wild with the forum police out to play.

I'll try to do another report installment tonight.
Rusty

I'm not an expert on running engines with a 4-2 break. I never flew older engines except for one Fox 35 and it still has the flat faced needle in it, and I hear that it's a poor design, and ST needles are usually the way to tune for a well timed stunt run. That is, 4 stroking while flying under a light load, and 2 stroking when demanded to climb and perform horsepower maneuvers.

In fact I've learned that the RPMs don't vary much, if at all, between the two modes, because even though it's firing on every TDC in 2-stroke, the extra load keeps the engine speed from significantly increasing. Then diving back out of a climb, the 4-stroke mode takes over with less torque, and still turns the prop at about the same speed with the reduced load. I learned that from a conversation I read between Randy Smith and Brett Buck on Stunthangar. Interesting, and to me unexpected, but not hard to understand. Maybe some of our older-engine aficionados can add to that, and either confirm or deny it.

In any case, as far as I can tell, the video I'm posting of Ron flying the Shoestring demonstrates a pretty well dialed in 4-2 break. I'm interested to know because this engine, once tuned right for the day appears to be capable of repeating it without having to fiddle with the tach and needle like I've had to do with some of my other engines. The closest I can compare with this is my 35fp, but it's a much less distinct break.

Also in this video, is me flying the Cardinal after adjusting the elevator throw at the horn, to try and achieve the same shape on inside loops as I do on outside loops. Outsides always seem to come easier to me, and insides are always a struggle to bottom out at the correct height. This is true of all planes I fly, and I don't know why. Time seems to slow down on outsides and I can put it where I want it. Strange that insides are more difficult.

So those are the subjects of the two flights in this video.
Thanks for watching and commenting,
Rusty
https://youtu.be/sND8GnmHz2o

U guys R havin way too much fun!! I'm shoveling snow outta the driveway and you're flyin airplanes. You certainly had a great day for flying. Whomever did the finger in the viewfinder reminded me of my Mom taking 8mm movies of us as kids. Most of our family vacation movies had her finger in the view. Heh, heh! Thanks for sharing the fun!

That was my finger Lol. I forget where the lens is on my phone, and I can't see a darn thing in the display, especially with my sunglasses on.

Very nice man can't wait to see the SS fly when I come over next month.
(Bandit)

Iv'e never flown a control line bigger then half a.Got a couple of shoestrings in the shop. That video makes me want to start building one.

Gardner, the Shoestring is great. It flies fun like a 1/2A, only tighter on the lines and turns corners at the pilot's will... note Ron just standing there flying it with his hand in his pocket. And he was taking it easy and safe. Best of all, at least I can say so for the Goldberg kits, it can take a lick. It's a very tough little bird. If you want to move toward bigger planes, the SS is a good one, not too big, not too small. Just put a tall control horn on it or it will fly like a slow combat plane. If you have one, put it on the table and let's get 'er built! It should build out to about 30 ounces, and any modern 25 will work nicely. I think they're beautiful planes except for the original colors,. which I obviously don't like.

Of course it's not scale with the stunt airfoil. Take a look at the razor thin racing wing. Jeez, where does that pilot put his legs...






And here's my version. Now I'm itching to fly it. I better be careful, Ron will kill me if I wreck it  


No one's offered any opinions yet on my thoughts regarding the 4-2 break. I'm curious to know if I'm right about what I said about the RPM, and how close to the desired classic run we had in that second SS video.
Rusty

I suppose that's why it's called a Shoestring Stunter as it wouldn't do so hot with thin wings.

Regarding the 4-2 I don't think the RPM is that close. The best way to tell would be to time level laps in 4Stoke and then in 2. From experience the speed is very different between the two as is the pull. So I doubt it's only a difference of a few hundred RPM

To be really honest I don't buy into 4-2 either. It should be called rich-lean as that's what is happening. For it to be really a 4-2 it would have to grow and shed a valve train in flight.

That should start a debate...

That second video is as good as it gets with a stock timed engine. Re-worked engines will 4-2 without fail.

Cribbs74 wrote:Regarding the 4-2 I don't think the RPM is that close. The best way to tell would be to time level laps in 4Stoke and then in 2. From experience the speed is very different between the two as is the pull. So I doubt it's only a difference of a few hundred RPM

Hmmm, I want to disagree, but let's see if I can express what I think happens.
It's doing two different jobs. I think the idea is, when it 2-strokes in a climb, the added prop load from the full weight of the plane resists increasing RPM, yet the additional torque/thrust maintains enough speed to fly. But in level flight, with the wing supporting the weight of the plane, the 2 would run faster because it's not doing heavy lifting, and the engine and plane do speed up. The 4, given the same job in level flight, would turn lower RPM than the 2. Does that make sense?

To be really honest I don't buy into 4-2 either. It should be called rich-lean as that's what is happening. For it to be really a 4-2 it would have to grow and shed a valve train in flight.

Yes, you and me both agree here, but I guess it's as good a term as any I can think of, since a perfect 2-stroke fires at every TDC while a 4 fires on every other TDC due to precisely tuned wetting of the glow filament when the fuel's pressure head changes with the attitude of the airframe.

That should start a debate...

I hope so

That second video is as good as it gets with a stock timed engine. Re-worked engines will 4-2 without fail.

It sure is, I think it's a thing of beauty. And I'm not sure anymore that I want a muffler on it.
Rusty

Cribbs74 wrote:
To be really honest I don't buy into 4-2 either. It should be called rich-lean as that's what is happening. For it to be really a 4-2 it would have to grow and shed a valve train in flight.

Not gonna debate it Ron, but I think the 4-2 description is appropriate as we are genuinely talking about firing on every second stroke (one up, bang, one down) as compared to every forth stroke (one up, bang, one down, one up, one down).  One in two = two stroke, one in four = four stroke.  Has nothing to do with valves.  Four stroke engines have valves, so do two strokes, whether be reed, piston, crankshaft or rotor/drum.

Personally, when flying as a kid, I wanted that thing to scream as hard as I could get it to go.  Four stroking meant reduced performance.  You wouldn't want your car misfiring like that, so why should the plane?  Lucky I used Enyas then because it never did them any harm.
On the other hand, running lean probably cost some significant stunting ability, and I had the wreckage to prove it.

Guys,

I think we can agree that an OS, Fox and even a Cox etc. is a 2 stroke engine. Regardless of valve configuration and yes valves do exist in 2 strokes, albeit different than a conventional 4 stroke.

That being said, what actually changes when going from 4-2 stroke operation? As I see it nothing. It's not like the spark is timed. The glow plug is always lit once started. Nothing changes internally inside the engine or the way it mechanically operates. So therefore it is not firing on every other stroke. It's just running rich or running lean.

The reason this happens is that on level flight the fuel is being drawn level with the intake and when the nose of the plane points upward it is harder to pull the same amount of fuel. So in essence what is happening is it is set slightly rich on the ground and it leans in manouvers because it is struggling to pull the same amount of fuel as in level flight. This is also the reason it is touchy to get it exactly right.

We can call it whatever. But a 2 stroke is always a 2 stroke.

That's my thoughts anyway

To add to the issue is plug temp, a hot glow plug will change the 'timing' of the ignition, making a engine 'break' earlier.

Mark Boesen wrote:To add to the issue is plug temp, a hot glow plug will change the 'timing' of the ignition, making a engine 'break' earlier.

Which would be a good statement to back up this:

RknRusty wrote:...a 4 fires on every other TDC due to precisely tuned wetting of the glow filament when the fuel's pressure head changes with the attitude of the airframe.

If I'd only added the phrase: "which retards the timing."


EDIT: I do, of course understand that 2 and 4 stroke engines are two different machines. And like Rod, when I was coming in from 1/2A I couldn't figure out why all these morons wanted to run their engines wet.

i think it goes back to the poor metallurgy of those fifties era engines, as they wouldn't live very long running in a two cycle and then pulling lean on vertical. Setting them up to run 'rich' then go 'lean' on vertical kept the engine healthy.....maybe instead of calling it 2-4-2, we should say rich-lean-rich!


....other things that effect 2-4-2 is compression, oil content, venturi, prop size, etc..
I can't remember how much time i'd spent in the past trying to get a modern engine to run like a Fox, when all was really needed was to run it the way it was designed, small pitch and let'er rev. That or re-port and drop compression, which it was kinda fun setting up FP's or LA's to 2-4-2.

Competitive Stunt weight/sized planes, and keeping a very controlled attitude is imperative vs fun flying, speed flying, combat flying, carrier flying where max RPM and changing, plugs, nitro, oil, tank position props is normal to find MAX RPM/Performance.....

Stunt flying is a bit more refined as the pilot wants/needs consistent lap times, and once engaged in a maneuver, needs the aircraft to NOT bleed off speed, wallow about, or stall and fall, OR fly the down line so fast that the bottom corners are exaggerated and sloppy because of too much speed

A history of the 4-2-4 break is out there, and I (like many others) do NOT think Duke Fox invented it...the 4-2-4 break was an anomaly that JUST HAPPENED to be exactly what a good stunt flyer needed..... consistent lap times with enough power to go vertical and NOT end the maneuver at super sonic speeds

Up right mount Fox 35s vs side mount Fox 35s added the development of the famous Fox burp in some over head maneuvers.... a totally different discussion

The 4-2-4 cycling was so desirable that MANY MANY users of OTHER THAN FOX engine users actually ruined a lot better engines that were designed properly for a particular HP and RPM with a range of propellers

I have read up on so much of this and find a lot funny because I am a typical engine guy and NOT a "perfect stunt run" guy.... That man would be (IMO) Brett Buck)..... Perhaps Howard Rush and certainly Igor Berger must be read about for their thoughts on the subject...

The physics of why a 2 stroke engine will run as a 4 stroke has a lot to do with the fuel, plug, needle setting, and relative Head of the fuel load AND design of the internals of the engine in question...

There are engines out there that will NOT 4 stroke...period.... and screwing with them to get the 4-2-4 is a waste of time, usually destroys the engine for it's intended use, and a lot of unnecessary effort

Glow engines for stunt will ultimately be relegated to VSC events as any sane competitor must move to fully proportional and timed control using electric motors

Pledge by Fred...I will never fly a C/L airplane with a Battery controlling any aspect of the flight

Interesting, IMO stunt engines are set up to be intentionally sensitive to being rich.
Ron is correct with his statement that all 4,2,4 is, is Rich, Lean, Rich. All 4,2,4 is, is an automatic Gov/throttling feature of the engine that is setup through the combination of plug, compression and port/valve timing.

How 4,2,4 works is simple, when in level flight, the engine is running in an unloaded state and fuel demand isn't extremely high therefore the engine runs rich (4 strokes) to control RPM and keep flight speeds consistent varying with head wind. When the model is suddenly put into a climbing maneuver now, load increases as well as fuel demand and then begins to lean out causing it to then Switch into a lean condition (2 stroking) and the power and RPM are then increased to help pull it through the maneuver and once the maneuver completes or the model enters the down side of a loop for example the engine then unloads again and fuel demand suddenly drops off and quickly goes into a rich state Switching again into a rich (4 stroke), This is the governing feature.

How quickly this happens or how precisely for that matter solely depends on how the engine is set up. and this is done through tailoring the three forces or process in the engine. Ignition, compression and fuel/air timing.

Compression:
Compression is one of the most important process in the engine, it dictates ignition timing in collaboration with the plug, determines fuel burn capability and starting ease without compression the engine would not run.
With a stunt engine the compression is intentionally kept low the reason why is to make it more sensitive to a rich run.
with low compression the engine is not as capable of burning off a rich mixture A two stroke has a threshold when once its starts to become rich, it will continue two stroking down to a point where the compression is not high enough to continue the current burn rate and then begins to transition over to alternate firing (4 stroke). the higher the compression the richer it can go before it begins to misfire. By tailoring the compression, one can dictate the point where it switches over from a two stroke over to a four stroke and back.

Fuel/air timing:
Fuel delivery timing is another factor, it dictates the amount of flow as well as how much fuel/air the engine can ingest (inhale) the more aggressive the timing, the more fuel/air the engine can take in and therefore the more RPM and power it can produce since it has the fuel/air present to provide such performance provided it has the compression to back it up.
Stunt engines are typically mild timed and are built more for torque. You want mild timing because due to the low compression setup, aggressive timing can make the engine critical to tune therefore unsuitable because of the increased amount of mixture being introduced which can cause drown out in extreme cases.

Ignition/glow plug:
Provides the bang to get things going and dictates if the engine runs or not, everyone knows that a glow plug works by a catalytic action between the platinum element and the menthol alcohol in the fuel. the richer it is, the less reaction (Less heat and glow) the leaner, the more intense the reaction and the hotter brighter the glow. A glow plug has an automatic timing adjust feature when the engine is running rich and slow the less of a reaction and the plug cools retarding the ignition timing towards TDC now when the engine leans out and RPM increases, the reaction is greater and the plug heats up causing the timing to advance away from TDC. Plug heat is also critical to tailoring timing and a med/hot to hot plug is needed to compensate for the low compression and rich conditions of a stunt engine. the extra heat helps the engine burn off the extra fuel in the mix.

Now a note on nitro:
When Extra nitro is used the engine not only gets a bigger bang and more power but the engine becomes more capable of burning in a two stroke at lower compression ratios Nitro reacts to compression not just the plug and is an ignition/power booster. the higher the nitro, the lower the compression. too much compression with high nitro is a recipe for detonation especially with too hot of a plug, put more than 15% in a Fox .35 the 4,2,4 is effected and an extra shim would be required to bring the engine back however that would cause too much pressure on it to begin with and was used as an example lol.

Sorry for the essay guys hope this helps! (this is just MO btw) (Bandit)

I have read more about 4-2-4 from chainsaw and motorcycle sources. It seems that those are pure load changes.

With a model airplane I think that going nose up reduces fuel pressure as it needs more power to climb.

Phil

Thanks for the replies, guys. I brought it up just because I thought it was an interesting subject. I may have cornered another LA for my Twister, so probably I won't be doing much 4-2ing except for when I play with my Yak and Shoestring.
Hopefully I can file another flight report this weekend. The forecast looks pretty nice.
Rusty