Sport_Pilot

The exit area should include the cutout for the engine, minus the area the engine displaces. With that it may be close, though it is difficult to determine how much area the engine is blocking from photo's.

flhyr

Oh.. well if you look at it like that, its probably pretty close now.

I still have this inkling that its going lean in the air from aerobatics, especially with the tank setup the way it is and 8 inches from the carb... whe I take the temperaure measurements, I'm going to see how much the tank presure there is using the manometer method. If it doesn't push the fuel at least 8 inches up, then thats a problem that a perry pump will fix.

kochj

I hope you have better luck with a perry pump than I have had....

flhyr

Uh oh, care to elaborete?

PacificNWSkyPilot

My Feedback: (19)

Virtually ALL name brand fuels now come with anti-foaming agents these days, which is why most ARFs simply provide bulkheads cut to the shape of the tank and tell you to slide it in and glue something across the back to keep it in place. In fact, this exact point was recently covered in an article in one of the last one or two Model Aviation mag. Foam is no longer needed for tanks.
Don't get me wrong, I'm as anal as the next guy and yes, after 30 years of this in most of my planes my tanks still inexplicably sit wrapped in foam. In others they don't and it doesn't make a bit of difference.

So, if you need a little nose weight, what's the harm? Otherwise, it's got little to do with overheating. Supertigers like low Nitro content. I think that's a great place to start.

Jim

freakingfast

My Feedback: (3)

I's usually a bad idea to use any pump on a carb not designed for a pump. This is why Perry sells pump(ready) carbs and non-pump carbs.
On a standard carb, the metering is set up for very little pressure. You can adjust the high speed and the low speed but the mid range will be rich. Reducing the pump pressure does not to cure this problem and defeats the purpose of the pump. The pump pressure is unstable at these low levels.

You can use an "on demand" regulator like an Iron Bay or Cline regulator on a standard carb.

http://www.billsroom.com/pcfs/produc...uelsysdesc.htm

Tip; keep the regulator close to and the same height as the carb for best results.

iron eagel

By the way the way you were told to calculate your inlet is erroneous. It is a common error that many people make you do not subtract the area of the engine in determining you inlet area. All of the opening facing forward counts as intake despite the engine blocking that area. That is why my original comment regarding the possibility of an overpressure situation regarding your cowl. Any and all of the frontal area open to air in the front of the cowl should be considered intake area and you exit area should be calculated based on that. Granted you may be having additional problems with fuel mixture as well but from everything I have read the design considerations for cooling. For most sport models you should size the area of the intake to the amount of finned area on the cylinder. What shape it is does not matter but rather that it is sized properly... Now you may be confused after having seen pylon planes or high speed airplanes with tiny slits as inlets, this is only because of the air speeds that the operate at that, such a tiny opening allows more than enough volume of air to pass over the motor for cooling. Looking at your photos as you originally posted them I would estimate that the actual opening (inlet area) is 3-4 times the size of your exhaust. The photo I had posted showing one of my cowls is on a sport aerobatic aircraft not intended for speed so the opening is sized using the finned area as a basis. Now just to give you an idea of what the proportions of the whole system are I have included a picture of the outlet area for the same airplane which also contains the exit nozzel and expansion chamber. The name for the type of cooing system is ducted cowl, it incorporates baffles ducts and diffusers to maximize cooling.
Now as far as your tank mount and fuel flow issues. I like TexasSky still use foam mounting for my tanks, not because you have to (because of the anti foaming agent in most fuel), but rather out of habit and just to be sure it isn't an issue.
Before you go through the nightmare of trying to use a pump with your airplane install a uniflow setup. I know it will eliminate any issues that you are having with the mixture due to the planes attitude during flight. The uniflow system was developed to prevent changes in fuel flow/mixture at all attitudes during flight, and was originally pioneered by the CL stunt guys many years ago for that very reason. Many guys flying aerobatics have adopted the system and I myself have made it a standard in all fuel powered planes I fly, like I have said before it does seem to help with many issues as far as fuel delivery. If you like take a look at http://www.fraserker.com/heli/uniflo...flow_works.htm for info.
I would try that before using a pump and regulator you would be amazed at how many problems it will cure, I know I have been.
Hopefully when you get a chance to take some temperature readings you will be able to tell if cooling or mixture is an issue.
I would take a look at the cylinder and case temperatures as well to see what is going on.
Either way you are on your way to finding out exactly what is going on so hang in there and good luck.

flhyr

Thanks, I've seen that article already and found it quite useful, however the way I understand it, the uniflow will alleveiate fuel supply issues strictly related to changeing fuel levels in the tank and will not help with fuel delivery when the plane is pointed up and the fuel is fighting to get up an eight inch column.

I'm planning to use it because I do see the value in it and its ingeniously simple in its principals of operation.

I'm really dreading trying to close the openings I've created.... this is my first cowl, proving that everying is a learning experience.

As far as the case and cyclinder temps... I only have one channel on my data collecter so I guess I'll neet to pickthe best place to put it. I'm still thinkin the head is where I'll put it but it may end up where ever I can actually get it on.

iron eagel

No problem...
Glad to help!
I know that the Uniflow will not fix everything but it will actually help a lot more than you may think. Keep in mind that it equalizes the pressure regardless of which way is up maintaining an even flow. Now just how much this will help when dealing with an 8 inch column of fuel I can not say for sure... But it will help a lot.
If you do go with a pump be sure to use a regulator as suggested.
Now as far as the cowl goes look at it this way, when you look at it from the front any opening you can see is an inlet. Scan it up and down keeping it level in front of you raising it and lowering it
only the openings you can not see is an outlet. And if you notice your opening for exhaust will be partially visible, only a small air dam in front of the opening will create an area of low pressure to actually make it a true exhaust into a area of low pressure.
What happens is as your plane moves forward in flight or air is pushed in by the prop air move into the cowl though any open are facing forward. The air which hit your engine is not blocked but rather diverted from side to side and over the head. This air enters the cowl and is bottled up in the space behind the engine in front of the firewall building up an area of high pressure. Some of this is blasted out the bottom of the cowl through the rear opening but only to the extent that it can overcome the air that moving toward the rear of the plane diverted by the cowl. So at that point your cowl has stagnated airflow that starts build up pressure and forms a bubble that actually blocks air from mowing past the engine and cooling it.

From the outset I knew that your cowl was not set up properly for optimum performance, however I did not catch on to you fuel supply issues till much later.
At least now from a consensus you know what may be a issue, and there may be few problems or combination of them that actually may be all have been working against you.
And it is these types of things that can really make you pull your hair out.

Oh, and as far as detonation, you would know something is wrong, I can remember saying to myself what the heck is that rattling noise just before I blew a hole in the top of a piston. It goes from a weird metallic rattling type of noise, to a popping or even a pinging rattle. Not good for the engine and you may recall hearing something that is a bit off when it has happened.
Rule here if it does not sound right it probably isn't. Yes I know it is a generalization...
As far as getting a temp the head is as good a place to start as you can hope for followed by the area where the exhaust joins the engine. I would try for the head if possible because that will also give you an idea of how hot your glow plug is going to be. The 200 degree F figure is one that the heli guys have mentioned to me in the past and it sounds about right for most internal combustion engine. And all you may have to do to fix any issue you may have is go with a bit richer high end setting who knows... Granted that will limit your top end, but running them a bit rich makes them last longer, even after breaking them in, but there are trade offs involved even then.
But just to give you an example just looking at you plane I know I would have stuffed a 90 in something that size even if it meant building the firewall back a bit to get it to fit, or balance the airplane. Then I have even resorted to mounting servos and batteries in the rear of the fuselage before I resorted to adding any weight it make it work.
It's not a hobby it is an obsession we just have to admit it.

lol

Sport_Pilot

That is only partially true. The uniflow will help with fuel level with a change ion attitude, however it cannot help once the carb spraybar is above the top of the fuel tank.

PacificNWSkyPilot

My Feedback: (19)

Before you get too far into the science of uniflow, most of the time all you need is to make sure you have FLOW. There are a few brands out there that I have found I can make run much better simply by finding the largest drill that will slip into the exhaust barb (pressure tap), and then take the next drill size up and ream out the barb fitting just that much more. Pressure to the tank increases, which can help which a tank that's positioned a bit further back away from the firewall. It's a tiny modification that takes 30 seconds and which simply increases fuel-flow overall.

I've taken engines that were just adequate in power and increased their power simply through better fuel delivery that way.

Aftermarket pumps and carbs are all great additions, and they have their places and their uses. But they're also expensive solutions to a problem that sometimes, even often, CAN be solved simply and easily. I guess that's a holdover from the days when few of those things were available and we still had to find a way to make our engines and motors run well. Sometimes there just wasn't the extra money around.

Jim

jaka

Hi!
The worst problem with your set-up is the distance between the tank and the engine.
I cannot see the problem of moving the tank forward!?

All you have to do is take a Dremel with a tungsten carbide cutter and carve away enough plywood so the tank can be moved forward.

Forget any temp meters!!! Our engines can be run completely cowled in without any intake or exit holes as they are 75% licquid cooled by the methanol in the fuel. All we have to do is set them a little rich and they will run all day long.

An engine which is run on too much nitro is nearly impossible to set! The high speed needle gets very sensitive and the engine will cut out before reaching max rpm despite you being careful with high speed needle.

Everyone who has been into this hobby long enough knows that the Uni-flow tank set-up system is the way to go if you want your engines to run good. But few, other than pylonracers , seem to know that a Tettra "Bubbleless " tank is even better.

PacificNWSkyPilot

My Feedback: (19)

Wow, I didn't think that he was here looking for the VERY BEST of everything.

And he's not. For a thousand bucks I'll drive to his house and make it run perfect without half of the junk people are talking about here. But it's not about money or the very best stuff. He's just trying to get it running well.

The ST's don't like high nitro contant. That's the place to start, LONG before bubble-less tanks and the long list of stuff here. I too think his cooling holes are probably sufficient, and some simple steps can go a long ways toward straightening it out.

Jim

PacificNWSkyPilot

My Feedback: (19)

Gee, even I can see the problem with moving the tank forward. If the tank is near the CG then it affects the CG when it is moved forward. Or backward.

Fuel line is cheap, having a tank a little further back is of no consequence. Many guys add extra rounds of fuel line to alleviate certain issues. That's absolutely no different than the tank being further back.

In at least HALF of my planes, my tank sits on the CG. Sometimes that's over a foot away, and often 18 inches of fuel line or more. They all run great. And even if I took them all to say, SWEDEN....I'm pretty sure they would all STILL run great. If you have pressure, you have fuel flow. Even without big-dollar tanks!

So, As long as we're giving our opinions on where the fuel tank should be, I'm going to say that where he has it is absolutely FINE. He can ream out his pressure tap with a small drill bit and increase pressure in 30 seconds. The tank could be in the tail and still work.

Also, His cooling cutouts appear to be quite adequate, so they are fine.

Now, the nitro content.....THAT could be a smoking gun here. Also, eliminate any fuelers from the system for test purposes JUST IN CASE they might be allowing it to suck air into the fuel...

Sincerely, stick with the simple, straightforward stuff before you get into all this other gear and special pump-carb systems and .....bleaah... you'll be pulling your hair out if you don't stick with basics to eliminate what it is NOT.....

Have a great weekend....I'm going flying at our local float-fly here in San Antonio!!! Better put the old girl on the charger for the night....

Jim

freakingfast

My Feedback: (3)

Uhhhhhh.....Wow!?!

Must be dang cold in Sweden. That literally wont fly here.

Keep it simple, change one thing at a time.

jaka

Hi!
I'm not saying a Tettra tank is necessary! Just informing that they exist!

It's well known fact that the tank should be placed as close as possible to the engine. Having it placed some decimeters behind the engine is asking for trouble.
Moving the tank forward is so easy so why not give it a try!? Just carving away some wood with the Dremel...

As for running our glow engines with no air intake and exit...well give it a try and you will see that it works. Our glow engines is partially liquid cold...remember though that you cannot set the engine at max rpm if you run it in this way.

Weather here is pretty warm..or has been, plus 27-30 centigrade the week before.

blw

My Feedback: (3)

That is 80-86 degrees Fahrenheit.

PacificNWSkyPilot

My Feedback: (19)

Gee, jaka, here I have been doing it wrong all these many years. Ironically, my planes are known to be the best running planes around, and when something needs tuning or tweaking they come to me. And I ALWAYS get them running right.

It's not a well-known fact, sorry to disagree with you. That thinking is obsolete, things have changed, and even back when that old wive's tale started there were ways to work around them. We used little things called science and physics.

Did you know that a contained liquid source can be pumped almost unlimited vertically in a pressurized environment? I work on these types of systems daily, we call them clean-water bottles and they were developed for use in Dental offices. It's a funny setup. It has a vent and a pickup tubing, and pressure is pumped in through a vent and the liquid goes anywhere you route the outgoing (pickup) tubing.

Does anything about that sound familiar? Today's more powerful engines through better porting (and other factors) typically have sunstantially more exhaust flow (Pressure) and the same percentage of that increased flow can be channeled into tank pressure (vent line). Liquid doesn't share your concern with its position, it goes where it is told to go. Like lightning and water, fuel will also follow the path of least resistance. A pump, or enough pressure (they amount to the same thing) simply delivers fuel to the engine/motor.

Old wive's tale-like concerns like tank placement don't stand up to scrutiny. A tank on the CG is actually subjected to LESS outside forces than it would be further forward or further backward. Even in a spin, the tank on CG is in the least affected place gravitationally or centrifically. On the CG, there is less splashing, less thrashing, less motor vibration. At the front (or back) of the plane, the tank is actually out on the equivalent of a long arm. Further forward, further out on the arm. Not that it creates any real issues that way either. On the CG, pressure is MORE effective since other forces are reduced.

A few inches of distance is no longer an issue, nor has it been for many, many years. Even a small amount of pressure from the muffler tap negates any possible issues. Todays motors....virtually ALL of them....provide PLENTY of pressure at the muffler tap. My drilling-out of the tap simply increases the VOLUME of that pressure. If it is not needed, no harm done. No paychecks spent either, there will be time for that later.

Throwing all the "cool" stuff at it before taking the time to apply REAL diagnostics to it and identify the problem is pure folly. Referring to unprovable Old Wive's Tales as well-known facts, well, that's more than folly, that just scarey.

I'm going to stick with that part of my engineering degrees that include the science of fluid physics and dynamics here. I use it every day at work. And I do so love my job.

Day after day, year after year I read about the latest and greatest methods for solving these kinds of problems. For the most part, they're an easier way to solve it, not actually better, and they're usually costly (hey, I'm Scottish, spending too much just goes against my grain!). It's nice to have them, we never did in the olden days when our RC planes were still horse-powered.... :^) But I still believe that when the problem is still cloudy and yet to be identified, the first...and BEST....course is to keep it simple and use the process of elimination.

I've done just that with this issue, and here are my conclusions;

The LAST thing that I would worry about right now is the cowling.

The FIRST thing I would address is the 2 fuel issues, the first being the delivery (pressure) and the second being the probable need for the reduction of Nitro content as an historical ST issue. I'd do both of these together. The ST nitro content issue is very well documented, and often in that case less is more.

The next (and very cheap) step is to use a cooler plug.

Then if the heating is still occurring then I'd trim out the cowl some more.

I'll be very, very surprised if you have to trim the cowl, unless I am underestimating by what I see in the photos.


Jim

PacificNWSkyPilot

My Feedback: (19)

So, Sweden has cold temps like Maine. It's 106 degrees here today in San Antonio. Fahrenheit, of course. And we're having a Float-fly! Well, as soon as I get off this puter and go there!

Jim

jaka

Hi!
Well in -95 when I was flying pylon in Muncie Indiana it was rather warm ( +40 degrees centigrade).

Sorry ! But tank placement has a vital role on how a glow engine react. This a common knowledge among all experienced modelflyers

Silencer pressure has nothing to do with having a modern glow engine or not. My old OS FSR .40 has the same silencer pressure as my GX .40 engine

Problem for us is that the our simple R/C carbs cannot tolerate too much pressure deviations. That's why a Uni-flo tank set -up is used by many of us, and has been used for 50 years or more among the CL aerobatic fliers.

PacificNWSkyPilot

My Feedback: (19)

Your post completely ignored everything I said. I made reference to my engineering degrees and my knowledge of fluid physics and dynamics, and you went right back to the "It's common knowledge among ALL experienced modelers..." Which means you'd rather die than admit you really don't have a clue about the actual causes of these problems... you're just not backing down. You have nothing to back up your position, you didn't take the time to explain in detail (as I did) what happens and why.

Just a little FYI, nobody in this entire thread has ever stated that silencer pressure has anything to do with HAVING a modern glow engine.

Let's review;

"A few inches of distance is no longer an issue, nor has it been for many, many years. Even a small amount of pressure from the muffler tap negates any possible issues. Todays motors....virtually ALL of them....provide PLENTY of pressure at the muffler tap. My drilling-out of the tap simply increases the VOLUME of that pressure. If it is not needed, no harm done."

Then I'm going to leave this thread. I'm also going to offer to drive up to Dallas and help flhyr to get this motor running right. Let's set a date, flhyr, or let me know when a Dallas, Waco or Temple fly-in is coming up and we'll get together. It would truly be my pleasure.

Jimbo

flhyr

Alright, finally got the inlaws out of the house, the lawn mowed, the kid to bed, and took the plane to an empty school lot and ran the engine. The plan was to run the engine without the cowl, with the standard muffler, and measure the heat on the head, and the tank pressure. Then repeat this with the Bisson inverted muffler.

So I was able to determine that there is a pressure difference of about 5/16" of fuel between the two mufflers, and the pressure was easily over a 12 inches of fuel, so I doubt that a pump would help me. I really didn't think I would have that much pressure, I though 5 inches would be normal but man, over a foot?

On the run with the standard muffler, the t'couple fell off the head. I had cleaned the head with acetone and then taped the t'couple to it with some tin HVAC tape. I though it would hold but was wrong so I don't think I can trust the graph for that run... I may have to do it again. I didn't realize it fell off till I had the standard muffler off so I just put the bisson muffler off and ran it again.

So.. I now think I can say definitively that the engine was overheating, not leaning. Why? refer to the graph... Max temp of 315F.... without a cowl. Yikes... that 100F over what I was told was normal....

I guess I'll have to go get some 5% or even some FAI and run it again.

After looking more closely at the data, it appears that the spikes are when the engine throttles back, and the temperature temporarily spikes, but the steady state running temperature is more along the lines of 245F or so. It shows that in 10 seconds, the head temperature went from around 245 up to 310, I'm guessing that was when I shut if off.

PacificNWSkyPilot

My Feedback: (19)

I'll be very curious to hear how it goes with the lower-nitro fuel.

Nice, thoughtful, thorough approach, by the way.

Jim

Sport_Pilot

That Brison muffler has more pressure than I thought, not surprised by the standard muffler though. This is sounding as though you need the 5% fuel. If you want to run 10%, consider a head shim instead.

I suspect that the engine slowing means the prop is not pushing as much air, and so the temperature spikes till the smaller heat load in the cylinder balances this out. I would think that is normal. Cars will do the same thing, they often over heat after a long stop at a light after some high speed driving.

flhyr

Thanks guys, I'll keep you posted on the results with lower nitro fuel.

What about compression? This engine has the worst compression I've ever seen (although this is my first ringed engine). That’s one reason I replaced the ring (not the only reason), hoping the compression would improve, but if it improved it wasn't by much. I can pretty much stick out my index finger against the prop and without much effort, turn it through a cycle. It actually seems like there is more resistance after the piston reaches TDC than while its traveling to TDC.

I gave up trying to hand start this thing and always go right for the starter, and it fires right up with the throttle 3 or 4 clicks above idle. I'm going to get a soapy solution to spray on the head to see if there is any kind of leak. When I drop some oil in the exhaust port, the compression gets much better but I think that’s normal.

So... how do I make a head shim or do you buy them?

Thanks!