Parkjets

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Knowledge

WHAT IS FSA | FOR EDF LOVERS

KnowledgeParkJets
By Ed Waldrep

FSA (Fan Swept Area) is the area of the opening where the air goes through the fan. In other words, find the area of the entire face of the fan, the subract the area of the motor/spinner/hub, the result is the FSA.

Here's an example
WeMoTec Mini fan 480
Fan Shroud ID 2.715"
Motor tube OD 1.27"
Max Area 5.79 sq. in.
Motor tube area 1.27 sq. in.
Fan swept area 4.52 sq. in[U].
Tailcone diam. 100% 2.4"
Tailcone diam. 95% 2.28"
Tailcone diam. 90% 2.16"

The inlets may look quite small but if you measure and calculate the area you may find plenty of area. 100% of the FSA is the goal, a bit under you'll be ok, a bit larger is OK. You can go way above that and possibly improve static thrust, but too large and the scale looks begin to suffer (look at the huge nacelles on the GWS Me 262 and you'll see what I mean, they're way oversized) and there's increased drag at higher speeds because too much air is going in.

TRANSFER PLANS TO FOAM

KnowledgeParkJets

Transfering Plans to Foam ~ Sent in by Gene Cook

Fabric stores sell a spray that is used to temporarily bond patterns to fabric.  The spray works very well to hold plans onto foam and the plans can then be easily peeled off after the part has been cut out.  I also use the spray to temporarily bond two layers of foam together if I need two copies of the same part.

TORQUE ROLL RULE

KnowledgeParkJets
Prop Rule of Thumb to Minimize Torque Roll Tendencies

Whenever you are building a pusher prop, jet type plane, to minimize the effects of torque roll, always keep the prop diameter 1/3 (33%) of the wingspan or less. With a 28" wingspan, a 9" prop is 32% of the wingspan and would be a good choice. A 12" prop is 43% of the wingspan and will generate a large amount of torque roll.

MOTOR EFFICIENCY

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Calculating Efficiency of Electric Motors

(Example Motor)

Volts = 14.2
Amps = 28.0
Io = 1.1A (no-load amps at the operating speed)
Rm = 0.055 Ohm (internal resistance of motor)

Input Watt = V x A = 14.2 x 28 = 397.6 Watt

Copper Loss = Amps ² x Rm = 28 x 28 x 0.055 = 43.12 Watt

No-load Losses = Volts x Io = 14 x 1.1 = 15.62 Watt

Total Losses = 43.12 + 15.62 = 58.74 Watt

Output Watt = Input Watt – Total Losses = 397.6 – 58.74 = 338.86 Watt

Efficiency = Output Watt / Input Watt = 338.86 / 397.6 x 100 = 85.23%

Please note that we calculated the efficiency of the motor with a given prop.

INSTALLING MAGNETS

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Installing Magnets:(In Foam)

Locate and glue in all the single magnets flush on the fuse bottom. Cut small squares of saran wrap and place on top of them for a glue barrier. Now place the matching magnets on the ones you glued into the fuse with the saran wrap trapped between them.

Carefully place the fuse on the wing and make sure it is perfectly lined up.

MOTOR GUIDE

KnowledgeParkJets

MOTOR BASICS

R/C Electric Motors For EDF and Pusher-Prop Parkjets

If you have any Motor Information or if you would like to see a specific manufacturer's motor information listed here, please CONTACT PARKJETS.

Axi: The first two digits of the number are the stator diameter in mm: the second two, its length. The full designation of the motor includes the number of turns of the winding, found after a slash. For example, the 2212/34 has a 22mm diameter stator that is 12mm long, and it has 34 turns of wire.

Mega motors: Similar designations - Mega 22/30/3 has a 22 mm-diameter case x 30-mm-long rotor, and a three-turn stator.

Aveox: An Aveox 27/13/3 seems to use the following: 27-mm diameter of the outside of the motor (not the rotor!) and 13 mm is the length of the rotor while three is the number of turns of the stator.

Hacker: A Hacker B20-26S is 20 mm in diameter, with the “S” indicating short length (L is for long) and is a 26-turn stator.

KV ratings: Kv gives the rpms produced by a motor per volt applied, i.e . if the motor has a Kv of 2000 and you run it on 6V it will turn at 12000 rpm.

Number of Turns: Turns are much like gearing! The higher the number of turns, the larger the propeller you can swing, however, the lower the maximum current it can withstand. Brushless motors that come in 1-, 2-, 3-, 4-, and 5-turn varieties are usually the internal-rotor type (but not always like the Hacker!). Brushless motors with high numbers of turns (say 10-30) are usually the external rotor (outrunner as we call it) type like AXI, Nippy, PJS, and the new little Hacker Baby.

GETTING STARTED

Getting Started, KnowledgeParkJets

R/C flying is a really great hobby.

It's not as popular as some of the other forms of the R/C Hobby, however.  But since you are here reading this, I'll assume that you want to fly Jets, R/C Parkjets to be specific.

READ THESE FIRST:

R/C Dictionary 

Read Tower Hobbies R/C Dictionary to become acquainted with General R/C Terminology

A really good Tutorial for Electric R/C flying

R/C Groups Electric Flight FAQ

First, let’s take a look at you, and your experience. Do you feel that you are physically capable of grabbing a jet that is anywhere from 2-Ft. to 5-Ft. long and weighing several pounds, and giving that jet a mighty toss, like Brett Farve throwing a bullet pass for the winning touchdown, and then having enough wit's about you to grab the TX control sticks, and fly that jet out of what ever problem it has gotten itself into?

I hope you answered "Hell Yes!!" If not, then you may want to consider flying a more "Conventional" Airplane," one of those slow flying type's with the prop up front, and leave the ParkJets for when your older, and/or when you have more experience.

Things You Need to Do

You need to start reading all about the Electric R/C Hobby at the RC Groups E-Zone discussion boards. I HIGHLY Suggest you join the RC Group's and participate in the thread discussions.  The owners of the ParkJet plans found on this website deeply appreciate knowing there plans are being built, and they will gladly answer any questions you have about the construction, and flying of their creations.  Everything I know, I have learned from the great people at the E-zone :)

SENSIBLE SAFETY TIPS

Getting Started, KnowledgeParkJets

SAFETY BASICS

Most people enjoy flying ParkJets because they are not restricted the way that Fuel and Turbine Jets are.  They feel they can avoid the hassles and fees associated with flying fuel planes, by flying small electric planes in large open areas, or public parks.

However, just because you can do something, it doesn't mean that you should do it, if your not going to do it in a safe manor.  You need to follow a new common sense safety rules, which can save yourself and others from having needless accidents.  Finding the Right Place to fly.