Large Model Association Forum

Went to test fly an aircraft yesterday but was getting radio glitches when engine was running. For CoG purposes I have the two Rx batteries, the ignition battery and the ignition unit just behind F1, along with at least a couple of pounds of lead. Could this be the cause or does anyone have any other ideas? I would like to keep the batteries where that are or I will need even more lead but I will be led by the experts! BTW it's a Thor 45cc engine with the stock ignition.

Any advice most welcome, as always.

Steve

check you've got the right spark plug with a r in it

Will check that out Arthur.

Thanks!

Steve.
Correct spark plug is BPMR6F plug.

Its internal resistance should be checked - 5000 ohms or could be a bit more.
Meter reading between spark electrode and metal plug top.


The screened lead should have good continuity with the plug cap.

The receiver batteries and ignition batteries should be kept well apart.

The ignition unit if room should be in the engine housing.
battery too if possible.

The ignition switch should be as far forward as possible

Receiver as far rearward as possible.

Always let a freshly charged receiver battery settle for a while to enable

the very high full charge peak to normalise.

Tony

I have had this with a faulty plug lead. Also make sure the aerial(s) on the Rx are clear of the engine and not blanked by it.

Tony Collins 1073 wrote:Steve.
Correct spark plug is BPMR6F plug.

Its internal resistance should be checked - 5000 ohms or could be a bit more.
Meter reading between spark electrode and metal plug top.


The screened lead should have good continuity with the plug cap.

The receiver batteries and ignition batteries should be kept well apart.

The ignition unit if room should be in the engine housing.
battery too if possible.

The ignition switch should be as far forward as possible

Receiver as far rearward as possible.

Always let a freshly charged receiver battery settle for a while to enable

the very high full charge peak to normalise.

Tony

Tony,

Many thanks for the pointers, I will attempt to address all of them but some will be easier than others due to the short nose on the aircraft. I might need to extend the nose or alternatively, source a lead propellor.

Steve

Bob Thompson1894 wrote:I have had this with a faulty plug lead. Also make sure the aerial(s) on the Rx are clear of the engine and not blanked by it.

Bob,

Thanks for the reply, I'll check the plug lead but the Rx should be OK as it is well out of the way.

Steve

[quote="Steve McDonald"][quote="Tony Collins 1073"]Steve.
Correct spark plug is BPMR6F plug.

I have just checked the spark plug and it is a BPMR7A which differs from the one quoted above. Will this make a difference? Haven't measured the resistance as yet.

I wish I had kept the old plug but was sure I cross referenced it to the BPMR7A, unless of course it was the wrong plug to start with!

Steve

it is still a resistance plug thinking outside of the box could you mount the ignition unit on the engine side of the firewall

From the NGK site, the R6F is 5,000 ohms and the R7A 10,000

arthur barlow wrote:it is still a resistance plug thinking outside of the box could you mount the ignition unit on the engine side of the firewall

Not as it is at the moment but I could extend the nose by fitting a box that I could mount the ignition on. I might allow me to shed some of the lead I'm using to balance it!

Steve

Steve Perry wrote:From the NGK site, the R6F is 5,000 ohms and the R7A 10,000

Thanks Steve

Quite a difference! With the resistance being higher, I assume that less current will be drawn by the spark plug giving a weaker spark. Although it runs, would you advocate changing it for the R6F?

Steve