Peter Fundarek
Aug 01, 1996, 01:00 AM
<html>
<head>
<title>Lessons from the Electra</title>
</head>
<body bgcolor="#FFFFFF">
<p>The art of building and flying model aircraft consists of a considerable amount of
trial and error as various options are pursued to determine which ones will provide the
best flight characteristics. Since the main aim of a club is to share information, I would
like to present some of the information that I have gained from building and flying the
Goldberg Electra. </p>
<hr>
<h2 align="center">Part 1<br>
The Power System </h2>
<p>The Electra comes complete with an "05" ferrite motor and a prop which is
meant to be installed as a direct drive system. This is a mistake. The Electra is a slow
flying glider which is designed to operate in a speed range of about 15 30 mph. A simple
equation for calculating the approximate theoretical flying speed is pitch x (RPM/1000).
For a 7x4 prop spinning at 13,500 RPM, this translates to about 54 mph. This means that at
best, the prop is cavitating and you are chewing up valuable battery capacity just trying
to get it to move. I first tried the Electra with a direct drive prop and often I could
simply not get any altitude at all. A better way is to use a gear drive to reduce the
speed of the prop thereby allowing a larger prop to be used. The gear drive allows the
motor to operate at high speeds which is more efficient while allowing the power to be
applied to moving the larger prop. This past summer I experimented with a 2.5:1 gear drive
running a Graupner 11x7.5 prop at 5400 RPM. This translates to a flying speed of roughly
40 mph. I have decided to slow the plane down even further by installing a 3:1 gear drive.
This should give me about 4500 RPM and I am going to try a Sonic Tronics 13x7.5 prop.
Although this will draw about 17 18 amps, the motor will only be on for a short run at any
time and this will give me improved climbing power. When you use a gear drive, be sure to
lubricate it well (I use a mixture of Molyslip 'E' and white lithium grease) and use a
speed controller. The simple on off switch supplied with the Electra will easily chew up
the gears when starting it due to the inertia from the large prop you need the soft start
supplied by a speed controller. </p>
<p>Replace as much of the wiring as possible with Astro 13 gauge wire or equivalent and
remove any unnecessary switches or other connections. I mount the fuse holder on the
outside of the plane and use it as the arming switch. The only connectors that I have in
the circuit are for plugging in the battery. And speaking of connectors, use Sermos
connectors instead of the Tamiya connectors that are supplied. Sermos connectors have much
lower resistance and are easier to use. Don't eliminate the fuse! It is vital to have it
there and best installed on the negative wire immediately after the battery connector. </p>
<p>The motor could be replaced with an 05 or 035 cobalt motor but for this plane, I do not
believe that the extra expense is warranted. The motor is not on long enough for it to
make a difference. Save the cobalt motor for a plane with more performance requirements.
The motor supplied with the Electra is sufficient but be sure to break it in properly and
lubricate the end bearings at least once per season. </p>
<p>Whatever the prop that you select, spend the extra amount and get one that folds.
Graupner are good but expensive. Sonic Tronics are a good alternative. Master Airscrew put
more of a current drain on the batteries and are less efficient. Not only will the folding
prop prevent damage to the motor on landing, during the flight when the motor is stopped
it will fold back and minimize the drag associated with a wind milling prop. This will
translate to increased flight times and more flying satisfaction. </p>
<hr>
<h2 align="center">Part 2<br>
The Structure </h2>
<p>Build light. This is not a gas powered plane and not subject to the kinds of vibrations
that you get with such an engine. Therefore, use less glue and reinforcement as you want
to minimize the amount of excess baggage that the motor has to haul around. </p>
<p>I have made some modifications to the structure based on my experience and some less
than perfect landings. I found that the front bulkhead ('former A' on the plans) tends to
get beaten up quite badly. I have replaced it with a copy made from plain printed circuit
board and this has proven to be quite good. It is almost as light as lite ply but is
stronger and more resilient due to the lack of grain. In a hard landing, this former will
just pop off the front of the plane, minimizing the damage to the rest of the structure.
Since it is stronger, more air holes can be provided to maximize the air flow over the
speed controller and batteries. </p>
<p>Another problem with repeated hard landings is that the cowling seems to really take a
beating. I have minimized damage to this unit by holding the unit on with either tape or
hatch latches similar to that used on the battery compartment. In a hard landing, this
allows the cowl to slip off and therefore minimizes the damage. A fibreglas cowl is even
better and can take more abuse. Larger openings can be cut to improve the airflow
through th e motor and battery compartments. </p>
<p>Don't install the optional landing gear as it only adds weight and does not improve
landing performance. A perfectly satisfactory landing can be made without the landing
gear, just remember to pull up slightly just before landing. </p>
<p>When holding the wing on, use at least 10 elastics as the minimum of 6 that is
recommended is not enough. The elastics will still allow the wing to suffer minimal damage
in the event of a hard landing. </p>
<p>To balance the aircraft for the stated centre of gravity, do not add any extra weight
to the plane to make it balance. Instead, move the motor battery forward or backward as
necessary to achieve balance. I installed a strip of lite ply across the fuselage in front
of the servo actuators to protect them from the motor battery. Installing the servos so
that the actuators are as far toward the tail as possible provides a bit more room to
manoeuvre the motor battery. </p>
<p>I also locate my radio battery in front of the receiver, as opposed to the arrangement
shown in the plans. This prevents the batteries from crashing into the receiver on a hard
landing. To minimize weight even further, it is possible to replace the standard battery
pack with one that has a smaller capacity (for example, 250 mAh). The servos, if installed
properly, only require 250 mA to operate and most of the time they are not operating so
this battery pack will provide at least one hour of flying. Check your receiver pack
before each flight and you will be fine. I do not advocate using the battery eliminator
circuit from some of the speed controllers as they can be unreliable and I have heard of
too many crashes associated with this feature. I have found that 1/4" foam rubber is
sufficient to wrap the batteries and receiver as there is little if any vibration from the
motor to be concerned about. </p>
<p>The canopy typically gets beaten up a bit by regular use and replacements can be
expensive. A cheap alternative is to buy a sheet of clear polythene and cut out your own
canopy. Take what remains of your current one and press it flat on the new sheet. Trace
the outline onto the new sheet and cut it out. To achieve the proper curve, simply hold it
over the outer container from a 2 oz size bottle of Zap (or equivalent) and heat it with
the air gun used for shrinking the covering. The plastic will drape around the container
and give you a reasonably good canopy. I use a bit of electrical tape to hold the canopy
in place during a flight. </p>
<p>Make sure that the battery compartment hatch is always in good condition and that it
closes securely. The last thing you want is for the motor battery to drop out of the plane
during a flight. If the hatch gets damaged or broken, replace it rather than repairing it.
A new one can be fashioned from lite ply quite quickly and easily. Remember to cut the
ventilation holes though. </p>
<p>I hope that you find this information useful. Making the changes as noted above has
significantly improved the performance of my model and I hope that it will help you to
enjoy this plane and the hobby. </p>
<p>Peter Fundarek<br>
<a href="http://rcgroups.com/shared/nospam.php?u=P.FUNDAREK&d=utoronto.ca">P.FUNDAREK(at)utoronto.ca</a>
</body>
</html>
<head>
<title>Lessons from the Electra</title>
</head>
<body bgcolor="#FFFFFF">
<p>The art of building and flying model aircraft consists of a considerable amount of
trial and error as various options are pursued to determine which ones will provide the
best flight characteristics. Since the main aim of a club is to share information, I would
like to present some of the information that I have gained from building and flying the
Goldberg Electra. </p>
<hr>
<h2 align="center">Part 1<br>
The Power System </h2>
<p>The Electra comes complete with an "05" ferrite motor and a prop which is
meant to be installed as a direct drive system. This is a mistake. The Electra is a slow
flying glider which is designed to operate in a speed range of about 15 30 mph. A simple
equation for calculating the approximate theoretical flying speed is pitch x (RPM/1000).
For a 7x4 prop spinning at 13,500 RPM, this translates to about 54 mph. This means that at
best, the prop is cavitating and you are chewing up valuable battery capacity just trying
to get it to move. I first tried the Electra with a direct drive prop and often I could
simply not get any altitude at all. A better way is to use a gear drive to reduce the
speed of the prop thereby allowing a larger prop to be used. The gear drive allows the
motor to operate at high speeds which is more efficient while allowing the power to be
applied to moving the larger prop. This past summer I experimented with a 2.5:1 gear drive
running a Graupner 11x7.5 prop at 5400 RPM. This translates to a flying speed of roughly
40 mph. I have decided to slow the plane down even further by installing a 3:1 gear drive.
This should give me about 4500 RPM and I am going to try a Sonic Tronics 13x7.5 prop.
Although this will draw about 17 18 amps, the motor will only be on for a short run at any
time and this will give me improved climbing power. When you use a gear drive, be sure to
lubricate it well (I use a mixture of Molyslip 'E' and white lithium grease) and use a
speed controller. The simple on off switch supplied with the Electra will easily chew up
the gears when starting it due to the inertia from the large prop you need the soft start
supplied by a speed controller. </p>
<p>Replace as much of the wiring as possible with Astro 13 gauge wire or equivalent and
remove any unnecessary switches or other connections. I mount the fuse holder on the
outside of the plane and use it as the arming switch. The only connectors that I have in
the circuit are for plugging in the battery. And speaking of connectors, use Sermos
connectors instead of the Tamiya connectors that are supplied. Sermos connectors have much
lower resistance and are easier to use. Don't eliminate the fuse! It is vital to have it
there and best installed on the negative wire immediately after the battery connector. </p>
<p>The motor could be replaced with an 05 or 035 cobalt motor but for this plane, I do not
believe that the extra expense is warranted. The motor is not on long enough for it to
make a difference. Save the cobalt motor for a plane with more performance requirements.
The motor supplied with the Electra is sufficient but be sure to break it in properly and
lubricate the end bearings at least once per season. </p>
<p>Whatever the prop that you select, spend the extra amount and get one that folds.
Graupner are good but expensive. Sonic Tronics are a good alternative. Master Airscrew put
more of a current drain on the batteries and are less efficient. Not only will the folding
prop prevent damage to the motor on landing, during the flight when the motor is stopped
it will fold back and minimize the drag associated with a wind milling prop. This will
translate to increased flight times and more flying satisfaction. </p>
<hr>
<h2 align="center">Part 2<br>
The Structure </h2>
<p>Build light. This is not a gas powered plane and not subject to the kinds of vibrations
that you get with such an engine. Therefore, use less glue and reinforcement as you want
to minimize the amount of excess baggage that the motor has to haul around. </p>
<p>I have made some modifications to the structure based on my experience and some less
than perfect landings. I found that the front bulkhead ('former A' on the plans) tends to
get beaten up quite badly. I have replaced it with a copy made from plain printed circuit
board and this has proven to be quite good. It is almost as light as lite ply but is
stronger and more resilient due to the lack of grain. In a hard landing, this former will
just pop off the front of the plane, minimizing the damage to the rest of the structure.
Since it is stronger, more air holes can be provided to maximize the air flow over the
speed controller and batteries. </p>
<p>Another problem with repeated hard landings is that the cowling seems to really take a
beating. I have minimized damage to this unit by holding the unit on with either tape or
hatch latches similar to that used on the battery compartment. In a hard landing, this
allows the cowl to slip off and therefore minimizes the damage. A fibreglas cowl is even
better and can take more abuse. Larger openings can be cut to improve the airflow
through th e motor and battery compartments. </p>
<p>Don't install the optional landing gear as it only adds weight and does not improve
landing performance. A perfectly satisfactory landing can be made without the landing
gear, just remember to pull up slightly just before landing. </p>
<p>When holding the wing on, use at least 10 elastics as the minimum of 6 that is
recommended is not enough. The elastics will still allow the wing to suffer minimal damage
in the event of a hard landing. </p>
<p>To balance the aircraft for the stated centre of gravity, do not add any extra weight
to the plane to make it balance. Instead, move the motor battery forward or backward as
necessary to achieve balance. I installed a strip of lite ply across the fuselage in front
of the servo actuators to protect them from the motor battery. Installing the servos so
that the actuators are as far toward the tail as possible provides a bit more room to
manoeuvre the motor battery. </p>
<p>I also locate my radio battery in front of the receiver, as opposed to the arrangement
shown in the plans. This prevents the batteries from crashing into the receiver on a hard
landing. To minimize weight even further, it is possible to replace the standard battery
pack with one that has a smaller capacity (for example, 250 mAh). The servos, if installed
properly, only require 250 mA to operate and most of the time they are not operating so
this battery pack will provide at least one hour of flying. Check your receiver pack
before each flight and you will be fine. I do not advocate using the battery eliminator
circuit from some of the speed controllers as they can be unreliable and I have heard of
too many crashes associated with this feature. I have found that 1/4" foam rubber is
sufficient to wrap the batteries and receiver as there is little if any vibration from the
motor to be concerned about. </p>
<p>The canopy typically gets beaten up a bit by regular use and replacements can be
expensive. A cheap alternative is to buy a sheet of clear polythene and cut out your own
canopy. Take what remains of your current one and press it flat on the new sheet. Trace
the outline onto the new sheet and cut it out. To achieve the proper curve, simply hold it
over the outer container from a 2 oz size bottle of Zap (or equivalent) and heat it with
the air gun used for shrinking the covering. The plastic will drape around the container
and give you a reasonably good canopy. I use a bit of electrical tape to hold the canopy
in place during a flight. </p>
<p>Make sure that the battery compartment hatch is always in good condition and that it
closes securely. The last thing you want is for the motor battery to drop out of the plane
during a flight. If the hatch gets damaged or broken, replace it rather than repairing it.
A new one can be fashioned from lite ply quite quickly and easily. Remember to cut the
ventilation holes though. </p>
<p>I hope that you find this information useful. Making the changes as noted above has
significantly improved the performance of my model and I hope that it will help you to
enjoy this plane and the hobby. </p>
<p>Peter Fundarek<br>
<a href="http://rcgroups.com/shared/nospam.php?u=P.FUNDAREK&d=utoronto.ca">P.FUNDAREK(at)utoronto.ca</a>
</body>
</html>