• RCaero4.jpg
  • RCaero5.jpg
  • RCaero3.jpg
  • RCaero.jpg
  • RCaero2.jpg

Engine Will Not Run At Idle. (Cylinder wear & Glow Assist)

 

Causes: As a glow engine ages and wears, it's ability to sustain good reliable idle runs decreases and as a result the risk of Deadsticks on landing runs increases. In particular two things occur.

1. The reduced compression due to increasing wear, makes cylinder head temperatures fall, which reduces the ability of the glowplug element to stay lit.

2. Reduced combustion at idle leads to unburnt fuel in the crankcase which again leads to glow plug element cooling, i.e. wetting the element with excess unburnt fuel.

Fix 1: Fit On board Glow

Fix 1: Fit On board Glow

On Board Glow.

Typically On Board Glow uses a 1.2 volt, 3800 mAhr Nimh baterry as a power source to light the glow plug element only when needed. Feedback sensors of various types, e.g. throttle position, glow plug element temperature etc., determine when and how to light the glow plug element. The purpose of the feedback sensor approach is to minimise battery useage, making it possible to use smaller cells and thereby reduce the weight impact to the aeroplane.

The method used to control the level of current through the plug is typically an electronic switching circuit. This allows for less current to flow at medium RPM and maximum current at idle, i.e. when it is needed most.

Fix 2. Fit PermaGlow

Fix 2. Fit PermaGlow

PermaGlow.

Permaglow lights the glow plug element for the entire flight.

The Pros and Cons of each system are listed below:

Glow Assistance Pros Cons
No Glow assistance fitted. Zero Cost Risk of Deadsticks on the landing run.
    Risk of safety consequences due to Deadsticks on the landing run.
    Risk of property damage due to deadsticks on the landing run.
    Particular risk of deadsticks while running in an engine, in the air.
    Needs nitro based fuel to minimise the risk of deadsticks.
    Use of cold plugs, with their associated advantages, is ill advised due to the risk of deadsticks.
On Board Glow fitted Risk of idle run related Deadstick events reduced / eliminated. Can be a little fiddly to fit.
  Reliability is good. Additional electronics that could fail.
  Because of the electronics, which only provide glow plug power when needed, circuit is very efficient and allows the use of alternative smaller batteries, with less weight impact.  
  Does not need a glow starter.  
Perma glow fitted. Risk of idle run related Deadstick events reduced / eliminated. Needs a 1.2 v., 3800 mAhr Nimh as a minmimum power source, with associated weight disadvantage.
  Very easy to fit. Need to monitor battery state during the flying session, and replace or field recharge as needed, based on field measurements.
  Circuit is super simple.  
  Reliability is excellent.  
  Monitoring the charge state through the flying session is easy.  
  Use of cold plugs with their thicker and therefore more robust elements is perfectly good, even advised.  
  Does not need a glow starter.  
  In all the cases of this method of glow assistance that we are aware of, there is no evidence of plug burn out. We have seen plugs in use that have seen hundreds of flights.  
  Operates during the whole flight so there is no possibility of getting the power to RPM discrimination wrong  

 

 

Details
Category: Power: Piston
Hits: 2430

You have no rights to post comments. We want to encourage wide participation in RC Aerobase, unfortunately there's people out there that will abuse an open system. Please register by following the link below the login fields and after your registration has been accepted you will be able to add your comment.