couple of drill number sizes, too.
If the engine does not have a minimum of
running time and the problem persists, you
might want to consider one of the Nelson’s
Hobby Products (Jerry Nelson) glow drivers.
These differ from the other glow drivers on
the market in that they sense the plug cooling off and apply heat to the plug regardless
of throttle position, which not only helps
the idle, but the mid-range as well. See the
sidebar for more on this product.
larly useful when adjusting the mixture on
a twin-cylinder engine with dual carburetors. When involved in Giant Scale Pylon
Racing with Bob Smith (the glue man), I
always matched the mixtures on our 8.8ci
A3 engines by noting the exhaust gas temperatures. Generally, though, cylinder head
temperature is a better indication of
whether the engine is running too hot.
Good luck with your project.
U I am interested in checking the in-flight
power of various fuels in a helicopter, with
instrumentation, using a quick “look-see” test.
The test will consist of hovering a helicopter at
wide-open throttle and adjusting the head temp
to something desirable, using an in-flight mixture control. The rotor speed would then be
noted. The second part of the test would be a
time-to-climb to certain altitude using the various fuels. The questions I have are:
1. What head temp would you recommend
for a .90- and .50-size engine?
2. What would you recommend as the maximum head temperature to keep from
hurting the engines?
3. It’s possible to monitor the EGT as well as
the head temp. Would that data be useful
versus the head temp?
PERRY PUMP FIX
U I read your piece in Model Airplane News
about the K&B . 61 and wonder whether you
could answer a query for me. I have a K&B with
Perry pump and carburetor that I picked up just
before I left Saudi some years ago. There was no
box or instructions. I ran it in 1996 and it gave
12,200rpm on straight fuel with an APC 11x7.
I tried it recently and lost the settings of the carb
and pump (finger trouble), so I put on an Irvine
60 carb, which has the same size spigot, and
blocked off the pump. It now gives 12,200 on a
similar prop, but with 10-percent nitro fuel.
As the designer specified the pump and carb,
I would like to refit them and use them, but
while I can set up the card (disc counter-clockwise for lean on slow running), I do not know
which way to turn the hex brass nut on the back
of the pump and hesitate to take it as far as it
will go lest I damage something. Presumably, I
should turn it too lean then back off for half a
turn, but which way is this, clockwise or
counter-clockwise? It is a nice engine and represents the best of its time, so I would like to use
MIKE HAWKINS, BANGKOK, THAILAND
Mike, turning the pump mixture adjustment in (clockwise) will richen the mixture
and turning out will lean it. The pressure
adjustment should be set with about
Any of your ideas and recommendations
would be appreciated.
Paul, different makes of engines will have
different operating temperatures, depending on the cooling fin area, amount of
lubrication in the fuel, mixture setting, etc.
Generally, you want an engine to run with
a cylinder head temperature no higher than
360 degrees F. Many of your synthetic oils
have a flash point of 390 degrees F, which is
the point where the oil goes up in smoke.
Castor oil has a flash point of 430 degrees F,
so a castor-based fuel can tolerate higher
As far as exhaust gas temperature, this
should always be taken at the exhaust port.
Normally, when using the Methanol-based
fuel, we see this in the 650- to 750-degree
range. However, this can vary considerably
with mixture setting. This can be particu-
THINGS YOU NEED TO KNOW ABOUT
I have a nifty product to bring to your attention this month mentioned in the first letter that
not too many of our readers are aware of: the Nelson Hobby Specialties (Jerry Nelson)
Intelligent Glow Driver. I first brought the Nelson Intelligent Glow Driver to the attention of
the readers of the now defunct R/C Modeler Magazine back in the January 2003 issue. As
five years have passed, I’m sure many of those new to the RC hobby have not been aware of
this great product.
Although there are quite a few glow drivers
on the market, they all work on the same principal: turning on the glow plug battery heat at
a set throttle position. What makes the
Nelson unit different is that it works independent of throttle position by sensing the glow
plug resistance via a micro computer and
turning on the battery heat only when
required at any throttle position below full
throttle. If an engine is idling fine with no tendency for the plug to cool off, the unit does
not turn on, saving battery life. The unit is particularly beneficial when doing those partial
throttle maneuvers that often result in the
engine loading up and dying on application of
the throttle. The Nelson Hobby Specialties Intelligent
Glow Driver is available in single-cylinder
The unit, which is actually made in and twin-cylinder (shown) versions.
England and imported by Jerry, is available in
single-cylinder and twin-cylinder versions. Pictured is the twin-cylinder version, which is particularly useful for those twins that have a tendency for one of the cylinders to flame out.
Individual adjustments allow tuning each cylinder independently of the other. Naturally, if
the cylinder flameout is due to a lean mixture setting, the Nelson unit is not going to help.
However, if it’s due to loading up then the Nelson unit will help or end the problem.
The single-cylinder version sells for $59.95 with glow-plug connectors and $52.95 without; the twin cylinder for $99.95 with connectors and $85.95 without, and they come prewired for Futaba, JR and Hitec receivers. The units can also have special connectors for the
O.S. and YS plugs for $71.95 and $114.95, respectively. These prices do not include the