Glow plugs, hot or not.   

 

 

 

  For many of us Nitro fans, glow plugs are a mystery. They need to be lit to start the engine but after that we really don�t know anything about them, other than they work. As soon as we have problems with an engine that has run reliably for a few seasons we start fiddling with carb adjustments or fuel. Not to say they aren�t possible problem areas, but there is another possible problem you could have overlooked because you didn�t know how, or why it worked. It�s your glow plug.

 

  How they work

 

 

   Glow engines are often referred to as 2 stroke diesel model engines. This would be incorrect. Although they do not have a dedicated stand alone ignition system they do have a �chemical reaction� ignition. Where diesels work through compression, glow engines operate through a chemical interaction that causes the element to �glow�. That�s how glow engines got the name glow engines, easy enough. What happens is the element in your glow plug is coated with platinum, the platinum has a chemical reaction with the methanol which is what our �glow� fuels are based on. Without this chemical reaction our engines would not run.

 

Glow engine timing   

 

 

    I am asked from time to time if �glow� engines can have their timing adjusted. I always tell people, yes, that�s easy. Buy higher nitro fuel. Our glow engines have their compression ratios set by the manufacturer based on what fuel the manufacturer believes the prospective buyer will run. It�s not good to deviate from that to much unless you don�t mind buying a new engine soon. The compression, and fuel �nitro content�, work together to achieve the correct ignition timing. The basics idea is simple. Most European engines are higher static compression engines due to nitro being so expensive. They expect their consumers to run FAI or 5% nitro.  Most engines destined for the US market have lower compression ratios because the manufacturer is expecting 5% to 15% nitro to be used. Higher nitro advances the timing as well as higher compression ratios. Run an OS max FP on 30% and you most likely won�t have it as long as you would running it on 10%. The reason is you have advanced the timing and the power output to a level above what the manufacturer intended.

 

 

 

 

 

Glow plug types

 

  There are as many glow plugs out there as there are opinions. My old stand by for many years was always the K&B KB1L. It always worked so I used it in everything. Then came my first tuned pipe engine and suddenly my KB1L would only last about 3 flights and sign off. I learned my first lesson about glow plug heat ranges and application. Stick with what the manufacturer tells you and you should be fine. Once you start modifying engines and exhausts you will get a quick education on how well your airframe glides unless you are smarter than I was and install a cold enough plug to deal with the �hot set up� you have put together. There are other solutions like head shims but that�s a different discussion. Dead sticks will be common until you learn the lesson. Below I have some guidelines.

 

Enya   #3 Hot, for sport flying and 4 strokes  #4 slightly cooler for sport flying  #5  Medium heat for stock sport engines with higher nitro. #6  cold plug for high nitro and tuned pipes

 

K&B   KB1L hot for sport flying under about 20% nitro. KB7300 is for 25% nitro and higher. They also make an idle bar plug but I don�t care for it.

 

OS MAX   F is long reach 4 stroke, A5 is a medium heat sport for .60 and up, #8 medium heat for general sport flying A3 is hot for engines up to .60

 

Rossi    Rossi makes a line of plugs from R1 to R8. R1 being �very� hot and R8 being �very� cold. In my experience they are one of the best plugs on the market that money can buy, period. The R2 is the most common �sport� plug. The R4 is the cold plug that I use in piped engines.

 

  There are many other plugs available but these I have experience with. Fox makes a plug that many people use and have luck with. I have no use for them and have never had luck with Fox plugs. I have replaced many fox plugs in peoples engines with KB1Ls just to hear people say � wow, my engine actually idles�.

  For 4 stroke engines of any make I have always used OS Max plugs. Even in my YS engines I use the OS Max plugs. They work.

 

 

 Glow plug life span

 

 

  The life span of your glow plug varies greatly depending on how you treat it. Lean runs are the quickest way to burn the coating off of your plug and render it �glowless�. I hate it when someone tells me the reason their engine quit has nothing to do with the plug. They pull the plug and politely (not really) show me how it glows with a glow starter attached. I would like to say �Dah, it�s got 1.5 volts telling it to glow, how does it work in the engine Einstein????� But I haven�t ever said that yet. My point is just because it glows with a driver doesn�t mean its going to glow through chemical reaction in your engine. I have read that a plug treated well and not abused will last somewhere around 30 to 40 flights. I have to tell you I have more than that on some of mine but I don�t try to set lean needles either.

 

 

In the end

 

 

I guess I hoped to shed some light on an often mysterious part of our model engines. Don�t forget to check your glow plug if you have an idling or running problem and remember that just because your glow driver makes it glow that doesn�t mean its working in your engine the way it should. Try to stick with what the manufacturer of the engine tells you to run if your engine is stock and you are running the recommended fuel. If you are modifying your engine in any way take notes on what works and for how long. Remember that higher nitro and tuned pipes will most likely demand a cooler plug if you want the plug to last more than a few flights. I hope this was helpful.

 

 

Contributed by: Rusty Scott, Guildhall Fun Flyers 3/8/2007

                                                                                                                                                              

Choosing a prop for your airplane the right way..   

 

 

 

A propeller is nothing more than a thrust generating RPM governor for your engine. Don�t overcomplicate it. With the incredible selection of props we have available to us today there is no logical reason I can think of for not testing different engine / prop combinations. Remember it�s a hobby, have fun�����..

 

A. Tools needed.

 

  1. Tach
  2. Tach
  3. Tach
  4. Test journal
  5. prop selection

 

      I can�t stress enough to �tach� your engine. When your done, �tach� it again and enter the combination and results into your journal. Remember to note temp and fuel used. Higher temps or higher humidity will result in lower RPM settings and corrupt your test data. Cooler temps will raise your RPM as will lower humidity.

 

B. Flying style

 

     You really need to know what type of flying you are going to do and what you are expecting from your airplane. Ask yourself, � What is the number one thing my airplane needs to do well?� No one propeller will give you speed while providing �3D� performance. A good rule of thumb is, Aerobatics demand low pitch blades with the greatest possible diameter. Speed demands high pitch blades with smaller diameters. Sport flying often is a compromise that lies between. Remember that both increasing the pitch and increasing the diameter lowers RPM. Decreasing pitch or decreasing diameter raises RPM.

 

Aerobatics      4 / 5   degrees of pitch     Prop for the top of the RPM range

Sport flying    6 / 8   degrees of pitch     Prop for the middle of the RPM range

Speed             9 / 14  degrees of pitch     Prop just under peak RPM

 

 

Another factor that is harder to predict is blade width. Keep this one in the back of your mind. Wide blades lower RPM with more bite while narrow blades bite less and have a higher RPM value.

 

 

 

 

C.  My experiences

 

  1. Most people tend to �over prop� an engine. This results in poor performance and can overheat an engine
  2. Under propping is much less harmful to an engine than over propping and overloading.
  3. You must know the manufacturers �peak HP� RPM.
  4. Generic prop charts �DO NOT WORK�. They may be a place to start but more times than not huge improvements can be made with a tach and testing.
  5. Props do �unload� in the air. Higher pitch props in my experience unload more than lower pitch props.
  6. Lower pitch props give better throttle response than larger pitch. Sport props are best in the 6 / 7 degree pitch range.
  7. Experiment and ask others who have experimented. Just because you have the right RPM does NOT mean you have the right prop for your application. Having the correct RPM is only half of the equation. The other half is weather or not it performs for you the way you want it to. Remember rules are made to be broken so don�t be afraid to experiment within reason. We all know a 1.20 wont work very well with a 9x6 prop.

 

 

D. Pitch experiences

 

1.      4 pitch gives instant throttle response, but cuts down on top speed.

2.      5 pitch gives excellent throttle response with better speed for sport flying

3.      6 pitch gives good all around throttle response with a slower build to peak rpm but has good sport flying speed

4.      7 pitch will tend to build in a dive to peak RPM and may sag a little on an upline. Good speed with thrust starting to suffer.

5.      8 pitch is usually not a good sport prop pitch for smaller nitro engines (.25 to 1.20 ) this is where the speed props start in my experience.

 

E. Diameter experiences

 

1.      Diameter is thrust. Low pitch propped engines have their RPM limited with diameter when selecting a fun fly or aerobatic prop.

2.      This is my favorite way to prop an engine. Low pitch / large diameter. I like throttle response, good vertical performance and the ability to have a strong prop wash over control surfaces at low air speeds.

3.      Large diameter props have a beneficial braking effect during a downline maneuver.

4.      Smaller prop diameters work better for speed. .45 DF engines have been run with 8 inch diameter props with 10+ pitch angles to obtain insane speeds in delta airframes. The small disc offers less resistance at speed while rpm is maintained with pitch. Remember pitch is forward speed.

 

 

F. Engine RPM

 

  1. Remember there is no rule of thumb. 2 strokes vary widely in their output. Ball bearing 40s with high ports and large bore carburetors can turn in the 21,000 + rpm range. Plain bearing .40s with lower porting set to start easily, and equipped with a small bore carb for good fuel draw and atomization, may only turn 13,000 rpm. Turning the plain bearing .40 any higher in the RPM range will only overshoot the powerband of the engine and result in a loss of power. Try to pull a High Performance Ball bearing engine too far down in the RPM range and you may damage it on top of loosing power.
  2. Know the manufacturers peak RPM / HP specification. Without it you are shooting in the dark.
  3. The same �no rule of thumb� is true of 4 strokes. They vary widely. Use a tach and know your peak RPM. I have seen a YS .91 outrev a Saito 1.00 using the same exact prop and the same exact fuel. Yes a .91 may need a larger prop than a 1.00. Again use a tach and test, test, test.

 

 

G. Tuned pipes

 

  1. Once you set a pipe length to a prop size don�t change the prop size unless you test it first. The results could be catastrophic if the engine won�t come on the pipe because you have over propped.
  2. Tuned pipes tend to have a narrower RPM range than a canister muffler. Test, test, test.
  3. Prop to the top of the RPM range with your tuned pipe. It�s better to go over the top than to never �get on the pipe� when testing. If you can�t get to the minimum RPM the pipe starts to work at you may cut your engine power by ���.. Not a good scenario to be in

 

  H. Fuel

 

1.      Don�t overlook fuel. The Fuel you use in a Nitro burner can have an impact on your set up. In extreme cases it can have a huge impact. Test with whatever it is you are going to run. A change from 5 to say 20 percent nitro will have an effect on engine RPM.  

Contributed by: Rusty Scott, Guildhall Fun Flyers 2/26/2007

                                                                                                                                                                          

 

    

Tips & Tricks

From May 2007 Issue of AMA Insider

(Nat AMA Newsletter)

Measuring Washout 
Washout, the downward twist in wingtips that improves low-speed flight, is sometimes used in airplanes with flat-bottom wings. A good way to make sure each wingtip has the same amount of washout (or any at all) is to get two straight dowels or carbon rods. Tape each to the bottom of the wing near the tips. 
 
Set the wing on something so you can see both rods, and sight down the wing so you can see each rod in relation to the other. The rods magnify any angle that might be present in the wing.  
 
Correct the wing twist until you have the angle you want. This doesn’t work too well with wings that are rounded on the bottom, but is an excellent way of making sure the flat-bottom wings are true


GLAD Press ‘N Seal plastic wrap makes a great masking medium for spray painting. It is sticky on one side and will stick to itself, or the item you want to paint. It is much easier to work with than paper because it clings to the surface without lifting the paint off when removed. 
—From Flightline, Casper Airmodelers Association, Casper, Wyoming