It has been estimated that 85% of engine troubles can be traced to tank and fuel line issue. The fuel tank should be placed so that the tank center line is placed vertically within 5 mm of the spray bar when the aircraft is in its flight attitude. The fuel tank needs to be protected from vibration by loose fitting foam in the fuel tank compartment or use some form of bladder (bubbleless) tank.

Now what often trips up the sport pilot is the fuel line and its hardware. In the old days we tended to use brass or aluminum tubing to carry the fuel through the tank stopper or to splice the fuel tubing. These metal tubes often had a sharp burr that would cut very small pin holes into the silicon lines. Even if there was no burr the fact that the metal line ended with no radius would often result in cuts to the fuel lines. To solve these issues one should use polypropylene tubing for glow fueled set ups. Polypropylene can be flame polished to remove any burrs, it can also be formed ,by just keeping it in the heat a little longer, into a radiused retention barb. This keeps the fuel line on securely even with most pressured fuel systems, and eliminates the source of most cuts in the fuel lines. I hope the attached photos help make this clear.

One can follow the discussion here
https://www.rcgroups.com/forums/show...7#post15716519

Now we will avoid what causes the other 15% OF ENGINE PROBLEMS

Friends don't let friends fly nickel,
Konrad

As a former journeyman machinist and plater allow me to add my two cents (or is that nickels) to this discussion.

Lets look at the properties of chrome and those of nickel.

For our toy engines chrome offers the following advantages:

Chrome is very hard which gives it very good wear characteristics. This hardness also results in a very low coefficient of drag. This keep the heat build up down as the parts rub against each other.

In the plating process it develops micro-cracks. These cracks offer a means to relive thermal stress (both in the plating tank and in service). This result in good bond performance over the life of the plating. In our application it allows for lubrication to collect. This collected lubrication can weep out of these micro-cracks and offer some “last chance lubrication” should the equipment be subjected to lubrication failure (lean runs).


The disadvantages of chrome are mostly in the manufacturing process.

These disadvantages are:
Hexavalent chromo sulfuric acid is very toxic. This means that there are a lot of costs associated with it to meet environmental concerns.

It is what is known as a very inefficient process. This means that the chromic solution is susceptible to contamination.

It does not plate evenly. This means that to control dimensions it must be machined (ground). This lack of precise plating thickness control means that part features that don’t need to be plated must be masked to maintain their dimension.

...Continue Reading

Here is a picture essay on how to balance a spinner.

Tools needed:

A High Point balancer (the only way to balance cheap plastic spinners) . Poor quality spinners do not have a center mount. This necessitates the need to do a cantilevered balance.

Dremel tool with burr

Sharpie marker to index the back plate to the cone

How;

Find the heavy spot. Spin the spinner and allow it to stop on its own. mark the 6:00 position. Spin it again. If it stops in the same position this is the heavy spot. Note the photo shows the "X" at 12:00 but this is just for the picture.
Mark it (x).
Grind on both sides of the heavy spot (o)
re-check, repeat

A balanced spinner will stop at any point 360 degrees (just as a prop will). If it constantly repeats a location it is not balanced. (FYI; a prop that always stops with the blades horizontal is NOT balanced)

You can follow the discussion hear:
https://www.rcgroups.com/forums/showthread.php?t=587540

All the best,
Konrad

Sub Piston Induction (SPI) is the introduction of outside air to the crankcase from the exhaust port under (sub) the piston as the piston reaches Top Dead Center (TDC). The purpose of this is to try to regain back some of the pressure lost to the inlet venturi in the crankcase. This might add some extra power to the top end of the rpm band.

But it is very detrimental to the operation of an R/C throttle. This is because it effectively bypasses the throttle barrel by allowing the introduction of air into the crankcase. This is exactly what a throttle is trying not to allow.
Now if the engine is equipped with an exhaust system any gain on the top end is lost as the exhaust in the muffler of pipe will contaminate the crankcase.

This was a design flaw with the first (if not more) production run of the OS 91 ducted fan engine. To clear the rear drum housing OS over cut the piston allowing the piston to expose the crankcase to the exhaust system. This wreaked havoc with the performance and tractability of the OS 91 ducted fan engine. Unfortunate I wasn't able to get warranty from OS, or her agent. As they would not cover this under warranty claiming that because of the high performance nature of the engine there was no warranty. And this was for an engine that wasn't even run! Ok, I had mounted it in the fan unit. If looking for a performance engine, avoid the OS. Look for one with real Chrome plating such as the Rossi or Picco ducted fans. All one needs to do is read the warranty disclaimer to see that OS doesn't think their engines are very good!

Please note the disclaimer under the tech notes:
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXBZ02
Again another fine OS nickel plated product! NOT

Friends don't let friends fly nickel,
Konrad

Often one will read about the 4 cycle to 2 cycle break. This can be very difficult for a beginner who has little or no experienced help to understand. I have also seen many instruction use the terms but offer no explanation as to what it is. What follows is my attempt to explain the phenomena.

The 4 cycle to 2 cycle break is a magical thing.

When a 2 cycle engine is running so rich the exhaust gas is traveling so slow that it can't all leave the cylinder. This leaves exhaust in the cylinder contaminating the inlet charge for the next cycle. This contamination is so bad that the cylinder will not fire on the upcoming power stroke. So on the next inlet cycle this contaminated unburned charge is pushed out by the next inlet charge. This inlet charge scavenges the diluted/contaminated charge enough that it will burn on the power stroke. This looks sort of like a four cycle (one power stroke for every other rotation of the crankshaft).

Now as one leans out the mixture the velocity of the exhaust gets high enough that it scavenges the cylinder well enough that the inlet charge will burn with each power stroke 2 cycling.

As an engine tuner this happens rather abruptly. Just by leaning out the mixture the engine will appear to suddenly develop a lot more power (rpm). It is usually best to break in an engine in the rich 4 cycle mode just prior to the 2 cycle break.

All the best,
Konrad

This is an open discussion as to the benefit of rear exhaust engines. I have often read that Rear Exhaust engines are more efficient than side exhaust engines.

I'd like to ask why this would be true?

I can’t understand why, in fact I find that the RX engine has some inherent problems with regard to internal gas flow. First the crankshaft pin and rod act as a vane pump. This biases one of the transfer ports over the other depending on direction of the crankshaft rotation. Also the rear bearing and crankshaft counter weight impedes the flow to the boost port.

This rod and crank pin action can be very evident in a twin engine set ups. The engine that is rotating in the counter clockwise direction will often be weaker (for engines with the exhaust on the right side). This is because the rod and crank pin are NOT adding (pushing) to the flow of the boost port.

I have also noticed that with the same timing values the Webra Speed (side exhaust) engine seems to have a little (very little) more output than the Webra Race (rear exhaust) engine. This was done open faced so as to eliminate the exhaust system interaction.

The only efficiency benefit I see to the Rear Exhaust engine is at the airframe level as the exhaust system can be hidden behind the cylinder or in the fuselage. Also the pressure pulse from the tuned pipe does not need to make the sharp bend in the adaptor header common with side exhaust engines.

All the best,
Konrad

P.S.
To follow the discussion please go to this link.
https://www.rcgroups.com/forums/show....php?t=1081375

I don’t mean to demoralize our friends on the east coast but here on the west coast we have been having great flying weather for the better part of two months. Visiting the flying fields I’m noticing a disturbing trend. That is that OS has been denying warranty coverage claiming that loose (stretched) head bolts and corrosion are a result of operator abuse.

While it is true that operator abuse can cause these issues it is more often than not an indication of poor design or material chooses by the engine manufactur. Now most of you know my issues with OS and her refusal to warranty “high performance engines” even those that haven’t been run. Now many discount my case claiming that this happened 15 to 20 years ago and with high performance engines (well high performance for OS). Ok, but these new warranty denials are for the current generation of sport engines the OS AX series. Now before I go into detailed analysis of what is going on allow me to preface this discussion by saying I have not seen the broken down (disassembled) engines. This is because OS has denied some of my warranty claims claiming that I disturbed the engine by disassembling the engine and therefore voided any warranty. As I was at the field sport flying when the discussions came up I haven’t seen the warranty denial notices.

At the flying field I have heard the term stretch head bolts. This is a bit of a misnomer, as the bolts themselves don’t usually stretch.
What is happening it that the...Continue Reading

Happy new year,
I'm spending my time bringing over my files to my new toy (a lap top pooter)I found this file I wrote many years ago Thought it might be dated but it is still valid today.
Sorry I found this after the christmas shopping spree.
Konrad

"Snake Oil"

One needs to look very carefully at advertising copy. A case in point is an engine manufacture has started a new advertising campaign with the buzz phrase ABL™. In this advertisement the manufacture is trying to claim that their new process has a new level of durability. You will note that they state that they ran their engine at full throttle and showed no visible wear after 3 gallons of nitro fuel.

Lets look at this statement first of all the new process of using two step plating process is not new it is used in most plating process (reference the American Plating Guide (APG)). During the plating process one can very the hardness or the bond strength of the plating by varying the PH level and/or temperature of the plating bath. Unfortunately there is a direct inverse relationship with these two properties in the platting bath. The higher the bond strength the softer to plating conversely the harder the plating the lower the bond strength. What they claim is that they use two alloys. The term alloy really is a bit of a misnomer in that what is really happening is that the manufacture is using two processes in the same solution on the same part. They are using the term alloy in a very exact term....Continue Reading

I have noticed that I'm often repeating myself in many of the RCG threads. This will be an attempt to consolidate many of my "pearls of wisdom" into one location.