Care free Park Jet -- Our 10 oz Durable Screamer

April 2008

Well I finished it up yesterday. I made sure everything was straight and it came out well. I maidened it with a 15 mph wind and it was fine. Should be a lot of fun. I call it the angry pumpkin.

Thanks for your help
Cas Kaditus
Stroudsburg, PA

July 2007

Joe,

I'm 82 yrs old. Been building models since I was eight. Went thru freeflight, control line and into radio in 1950. I'm a ham operator.Lived in Memphis for 14 years in the fifties and was charter member of the club there. I started in Electrics back in 82, and went full electric about ten years ago The foam you are using in your models is far superior to any I have used in the past. I'm basically a scratch-built modeler, but I am enjoying the Stingray immensely. The guys at the field can't believe how smooth it flies.

Robert Wick
Hendersonville, NC

May 2007

Hey Joe -

It turns out that the balance point I has was slightly behind the Spar - two nickels and some masking tape has solved all of my issues. I'm used to fast flying wings where slight balance issues aren't as big a deal - I keep forgetting that my batteries used in my other wings weigh about 10oz, and the Stingray weight 10oz, battery in!

I finally got it flying today in a light wind, and the performance is excellent - a little mixing and expo adjustment is still needed, but it's nice to finally have a "flying wing style" plane that I can fly in a small space and have so much fun with.

A new nice touch for me is that it will fly nice & slow - landings are a breeze

Thanks for making my new toy a cool one - it flies wonderfully, and it's a blast to fly in a small schoolyard!

Ryan in Toronto

February 2007

Hi Guys,

For your info, I have fitted new night lights to my sting, and its great. The idea is brilliant and extremely light. You might have seen / heard of it, but here goes. All you do is get 2 LED’s and stick them into a drinking straw on either side. Obviously you can use different colors etc. I then fitted these straws on the leading edge of each wing and a 1" straw on the trailing tip of each aileron for when you are flying away from you. The key is to get very bright LED’s. The one’s I have bought is 70,000mcd, each cost +-15 cents each, and weighs nothing! Let me tell you what, its great and extremely bright.

One last comment, I guess it might be obvious, but maybe not. You can connect the LED’s in series as well. So, lets use the Green LED as an example. They each run at 3.6V, so in series, they would need 10.8V. Now if you run a 3 cell lipo pack, you don’t need any resistors as you can see from the LED spec sheet they can run up to 4.2V. So you are getting maximum efficiency.

For the Red’s, you will need some, as you need to "waste" some voltage because there is still not enough resistance when you put them in series. I had to use a very small 44Ohm resistor to balance it.

So overall, a Very efficient lighting system, no power wasted on green and Very little wasted on Red.

One other comment, I have to date not found a glue that sticks to these drinking straws properly. I tried CA, but that is to brittle for a bendy straw. I then tried something like what I think you call goop. Much more successful, but still comes off. So, I was going to use clear office sticky tape. I have used this on many of my other plains and works 100%. I used some of it on the underside of my sting for the Receiver / Speed Controller. This way, you will also be able to change the straws should they become damaged.

I managed to find a scale that is capable of weighing these very light items. I borrowed a Lab scale from a friend of mine that works in a Cancer research laboratory. It unfortunately only weighs to 0.1g, but I guess this will be better than nothing.

So, here is my parts list as well as their weights. I have attached a diagram of where I have attached what, hope this helps.

6 X LED 0.3g each 1.8g total 3 inch wire (116inch total) 0.1g 3.9g total 4 X Straw (7&1/4inch each) 0.3g each 1.2g total 2 X Straw (1&1/2inch each) 0.1g each 0.2g total Heat Shrink misc 0.1g total Power Connectors What you can find variable Total 7.2g total = 0.25oz

So, the total of all the wire, straws, LED’s and heatshrink I have used comes to a total of 7.2 grams or 0.25oz. As you mentioned before, if you can find lighter wire, this will make the biggest difference.

Depends on your size of LED, but will generally be a 5mm and you therefore have to find a 5mm straw.

The only thing I have found is that you have to put the straw right on the leading edge or even embed it into the leading edge otherwise you really mess up the aerodynamics. But it works treat and is very light. It is SO much lighter than the glow-wire is was using with the 12V to 110V inverter that drives the wire.

I bought my LED’s from http://www.rapidonline.com/

I have attached a screenshot of the part numbers of the LED’s I bought. You can find these on the website by simply imputing the part number. The key is to look for the "mcd" figure and angle. The higher the mcd number, the brighter.

These LED’s do not have inbuilt resistors, so this needs to be calculated, which is very easy. However, this means wasted power, but, for I think my RED led’s, I wasted no power, thus needed no resistors. I connected them all in series which all added up to them running at 11.1 volts. For the Green, I had to insert a Very small (44Ohm) resistor, but still very efficient.

I have attached the spec sheet for the LED’s I have mentioned. It gives all the technical data for each of the LED types.

Here then the calculations on how to build the LED configuration. (Formula Calculations Courtesy of Andrew Foster-Borman)

What we need to do is 'waste' the voltage we don't need in the resistor. Therefore we need to work out what size resistor 'wastes' the correct voltage at the given current

Lets use the 3.6V 30mA LED as an example

We know the current (I), it's (30/1000) 0.03 Amps

We can work out the voltage (V) we DONT need, the voltage to be 'wasted'

7.4 - 3.6 = 3.8V (7.4 is a 2 cell lipo. Use 11.1 for a 3 cell)

Then we transpose the standard formula V=IxR to give us the resistance (R) required.

V/I=R

3.8/0.03= 126.66 Ohms

The standard resistor scale gives us the values 120 and 130. I would use the 130 Ohm and run the LED slightly under.

Power 'wasted' in the resistor can be calculated using P=VxI

3.8*0.03= 0.114 W

so you need a resistor with a power rating of at least 0.125W, the ones you have are

probably 0.6W so no worries.

You can use resistors in series to increase the resistance,

100R +47R = 147R

Or you can use them in parallel to reduce the resistance the formula is

1/R + 1/R = 1/R

So for example

(1/10R) + (1/10R) = 0.2 = 1/0.2 = 5R

1/10R + 1/10R + 1/10R = 0.3 = 1/0.3 = 3.33R

If you are really clever you can do both series and parallel….

(1/ ((1/10R) + (1/10R))) + 47R = 52R

Basically if you want 130R you would use a 100R and a 47R in parallel + a 100R

(1/((1/47)+(1/100)))= 31.97 + 100R = 132R

Hope this makes sense and will help you to calculate your configuration. It is actually very easy once you’ve done it once or twice. I have attached my Excel spreadsheet in the event that you find it usefull.

Best regards,
Charl Van Den Berg
Wilmslow, Cheshire
United Kingdom