Archive for the ‘RC’ Category.

Model Aviation Wowness

I’m starting to think about model aviation again. It’s been a long while. I had promised Ma’at that I’d get her in the air at Burning Man 2006. It still seems like a great challenge. There are two big challenges I can think of. First, finding the right plane to put her on. The Trick 1000 didn’t work very well for a few reasons. The second challenge is safety. I want to fly her over the heads of Burners at night. What I want to do is put her on a platform that can (in a worst case scenario) hit a person and have it not hurt. I’ve been hit by my Zagi a few times and the EPP foam and rear-mounted motor made the strike a non-issue. I think it’s possible to make a crash-safe plane but it’s going to take some effort to get such a plane to be able to carry the 12 oz payload of Ma’at and her batteries.

My apartment is strewn with playa-dusty airplane parts as I begin to get things together. While I was looking online for some answers to my questions, I ran across an inspiring video. Give it a view and then tell me flying isn’t uplifting and beautiful.

(Article with video link)
(Video link), Mark Leseberg at Tucson Shootout 2003.

(local version) (26megabytes)


Lee’s Flying Page

(Originally from my flying website from 2005 or so. The original publish date is lost)

Lee’s Flying page


My setup:


Bought from (I broke 1 of the 11×5.5 e props prop, and I can’t be without props for Burning Man!

  • 4 props  11 x 5.5e  $3.50 * 4
  • 6 zagi props  $12
  • 0.5 oz CA Super Gold +


Bought from 4 10-cell CBP 1050 2/3A NIMH packs


Bought from

Wingspan 39.95 in.
Wingarea 384 in²
Weight 32 oz.
Wingloading 11 oz/ft²
Airfoil Symmetrical
  • 4 Maxx Products MPI MX-50 servos (14 oz/in, 0.09 sec/60 degrees, 0.86″ x 0.43″ x .78″, 0.32 oz, Teflon bearing)
  • Phoenix 45 ESC
  • Axi 2814/12 (Weight (gms) 131, Diameter (mm) 35.5,  Length (mm) 48.5, Shaft Dia (mm) 5mm, Stator Dia (mm) 28,  Rotor Length (mm) 14, Efficiency 80%.   Kv(rpm/volt) 1270, no-load current 2 amps, Rm (milliOhms) 67, battery cells 7-10) full specs
  • Electron 6 receiver (yes, a second one)
  • 5mm prop adapter
  • 2 APC 11×5.5e props


bought from


  • Kavan Projeti electric flying wing (32″ wingspan, 240 wing area, 21″ long, for 3 channel control – elevons and motor control. Flying weight about 20 oz. Wing loading about 12 oz/sq. ft.)
  • Mega 16/15/4 motor
  • 2 APC 6×4 “e” props
  • APC 5×5 “e” prop (untested as of 7-12-04)
  • Thunder Power 3s 2100 (11.1v) 2100mah, 14X, 4.7oz. 6C LiPoly battery warnings
  • Castle Creations Phoenix 25 speed control manual
  • Electron 6 receiver manualspecs
  • 2 small servos
  • Great Planes Triton charger manual

Previous equipment

  • Zagi 400x acrobatic electric flying wing  –  Zagi 400x instructions from Trick R/C (48″ wingspan, 480 in2 wing area, 19 oz w/o motor & battery)
  • Zagi Speed 400 6v electric motor (3097 rpm/volt, 0.437 InOz/amp, 0.269 ohms, 2.6 oz. according to P-Calc) (spins about 14,500 rpm with 8 cells. Draws about 12 amps from an 8 cell 1700mah NiCd)
  • Promax 7.2v electric motor – (added 6-20-03)
  • Zagi 20 amp electronic speed control (0.4 oz, / soft brake, can’t be disabled. BEC rated at 1 amp or 1 watt. We recommend that no more than two servos be used with the Zagi-20 controller although three low current servos have been used successfully with adequate cooling)
  • Gunther No. 302 125mm x 110mm (5″ x 4.3″) prop
  • 1 “Zagi” Sanyo KR 1700 AU Ni-Cad battery pack  – Battery specs  Battery size guide (9.8 oz, 8 cells at 17 mOhms and 1.27 oz apiece)
  • 1 WattAge 1100mah 9.6 volt Ni-MH battery pack (6.0 oz, made with 8 2/3A cells (I think) .63oz, 1.1″ tall, .67″ diameter each. Bought 6-4-03 from Kenvil Hobbies)
  • 1 more WattAge 1100mah 9.6 volt Ni-MH battery pack (bought 7-22-03)
  • 2 Hitec HS-81 servos
  • 2 servo savers
  • 1 Hitec micro 555 receiver on channel 42
  • 1 roll of white Oracover, 1 roll of blue.
  • A lotta Deans Ultra connectors


  • Astroflight 110D charger datasheetinfo
  • Hitec Laser 4 transmitter on channel 42  –  Hitec Laser 4 Manual (Installing the Acrobat Asian Fonts pack (or whatever it’s called) will stop the error, “There was an error processing a page. The encoding (SMap) specified by a font is missing or corrupted.” They use a tiny bit of Korean in the footers. Hurumph)
  • Cosel K150A 12 volt, 13 amp power supply (bought used eBay for $30 7-9-03 :-)  –  specs
  • 4 old 6v 4ah lead-acid batteries from my APC Smart-UPS 400 computer uninterruptible power supply.


  • Firebird beginner trainer electric plane kit (discarded 6-04)
  • Schumacher PRO-SERIES 612-A-PE lead-acid battery charger – to charge the lead-acid batteries to power the Astroflight charger to charge the nicads at home (I don’t know why I swallowed the fly, I’ll probably die). 7-02-03 When charging my dad’s (6 volt) Packard battery it made the awful smoke of electronic doom. We don’t know why… but it did. R.I.P.
  • an Ikarus Bleriot III electric slowflyer that caught a nasty microburst at the Bergen County Silent Flyers field. The day was too windy but we really wanted to fly. It was hovering in the wind against a 10 mph headwind about 10 feet in the air and then it suddenly went down. It didn’t nose-in, it was as if the air around it got tired of holding up the plane and it went down. It hit gear-first, which would be good except that it hit hard and the thing was way to delicate… driving the gear into the struts into the basket into the servos into the motor into the frame into 5,000 pieces. c. 10-01.


Zagi Tips

(Originally from my flying website from 2005 or so. The original publish date is lost)

Here’s several Zagi making hints I’ve found online. Most of them came from and The best reference is the Zagi Manual pdf from Mike’s Hobby Shop. Cliff at Atlanta Hobby has been my pleasant & responsive pushe… Zagi dealer. Those sites have a lot more tips than I list here. Check ’em out. I’ve rewritten these hints with my own comments.

Zagi Manual – good

Use Shoe Goo or other silicon based adhesive to attach the motor to the plastic pod this keeps it from coming out on hard impacts with the ground.

Use the old 3M 77 spray adhesive. It was discontinued in 2002 or so. But don’t use the new stuff in the purple and black can!! They changed the formulation to be better for the environment but the new acetone formulation eats the foam. I don’t know what you should use instead, sorry!

Add a strip of plastic to your batteries so they will be easier to find when they eject from the plane on impact. My strip is only about 4″ (a lot shorter than the photo)… that’s easier to tuck in for flying.
When the speed control is put in the plane, loop the wires around itself and put a zip tie on them so that when the battery is pulled out of the plane in the event of a crash the strain is on the motor not the speed control.
Cut the nose back a little from the leading edge of the plane. This will let the foam absorb some of the impact not the plastic. This ultimately didn’t save my tip from cracking, but what are ya gonna do?
Use the extra foam that is in the kit to make a landing and launching skid on the bottom of the plane. I haven’t done this yet. I used the extra foam for other little things. Oop!
The props have to be turned around were the lettering is toward the back of the airplane as shown in the picture.
We found that the lexan tips that it comes with cause the plane to wonder find some coraplast sign material and cut your own wing tips this will help stability in flight. Use 2 mm coroplast… most roadsigns are 4 mm.
When installing the receiver in the Zagi 400 X the instruction call for it to be placed in the nose of the airplane. Don’t put it there! Mount it in the wing on either side of the electronics pod this will protect the receiver in a crash. Also note the servos are laying down in the wing not standing upright.
Note receiver is half way under tray with xtal on the outside for easy changing if necessary. The receiver will be covered by the colored tape when the tray is taped on. (Zagi 400X)


When you examine the wing core, you might notice strands or “hairs” of glue and hard plastic. Gently remove these with your fingertips or gently pry up the tip of one strand with a knife to get it started. If your kit included a small block of EPP foam, this can be used for gently rubbing off all of the excess foam “hairs”.
You might find some fairly thick pieces that wander across the wing. This is a normal side effect of the hot wire used to cut your core. Gently pry them up. The truly large ones might leave a small indentation in the foam after you remove them. The foam will slowly expand out again over a few hours so try not to worry about them. This is normal.


Use a coat hanger to hang it on the wall.




put strapping tape on the inside of the battery tray, top and bottom. To keep the tray in one piece.


When you get your first roll of Monocote, know that before you try to stick it to your plane, you should peel off the very thin, transparent protective coating. My first time, I didn’t catch this important point and just cranked up the iron… it stuck, but crappily.


Hinges and Tape

If your elevon comes off during flight, exciting things are bound to happen.  The Mylar hinge tape provided with the kit is fine, but there is a better solution which can be applied to all of your aircraft.  Winter flying plays havoc with the stock hinge tape as too many fliers have discovered 300 feet AGL (above ground level).  Strapping tape does not seem to be as susceptible to thermal weakness as the Mylar hinge tape is.  If you originally used the hinge tape, check it during the winter if you fly during cold weather, and certainly before the first flight after winter.  At some point, replace it with strapping tape.

Before applying your hinge tape, make sure you mask off the elevon and lightly spray some Super 77 on it.  Let it dry before applying the tape.  Although S77 is not required when applying strapping tape, it should be done regardless to ensure that your hinges will not come off until after the aircraft is destroyed.

The best example of this has been done by Andy Willetts and is show here.

  If you have 3/4″ or 1″ width strapping tape, you can use the over-under tape hinge method.You will need at least two “sets” per elevon and should do three if you can afford the weight.

If done correctly, it simply does not fail.

(click for a slightly larger picture)

A compromise is to do 3 sets with only 2 hinges per set.  Over 100 flights have been done with these particular hinges and they have never come loose or needed to be replaced.(1600×1200 large picture warning)

Some have used the over-under hinge, then extended their Ultracote or a film covering over and around the elevon for additional strength and clean looks.  If you do this, make sure that you have not added a tremendous amount of resistance that your servo now has to overcome.

Buzzman has a great picture that shows an alternative method for hinges that you can view here.


General Electric Flying Tips

(Originally from my flying website from 2005 or so. The original publish date is lost)

Tips I’ve gleaned from sites and experience. These are notes I’ve created for myself so they’ll be a little rough. But you’re welcome to look over my shoulder!

Make My Own Battery Packs


Here’s just a couple notes I made to myself about making my own packs.   A big thing: If you buy or build a battery pack, make -2-. That way, you can charge them together by making a Y cable.

look more on google: “HR-4/5AUP” buy
shrink wrap!

make a battery pack

look on google: “how to build a battery pack”

check out

for cheap batteries?

compare to Radio Shack braid:
Copper Braid (narrow)
Flat copper braid 1.9mm (.075″) wide x 0.3mm (0.0120″) thick. Equivalent to 18 gauge wire. Up to 10 amps. Per inch.

Doculam covering material


I haven’t tried it yet but the creators of the WagMax Zagi mentioned that they use it. You can buy it here. From what I gather, here are the pros and cons:

  • Way cheaper than Oracover, Monokote, etc..  Oracover costs $11 for a 26″x76″ roll while a 27″ by 500 ‘ (yes, that’s 500 feet) roll of Doculam is $25. Oracover is 40 times more expensive.

  • Doculam is transparent and paintable

  • It shrinks less than the other major coverings.

  • You have to buy it in $50 packs


The covering supplied with the combo deal is called Doculam. It’s a clear (after heating), light weight material. It is actually a document laminating material that works well for a model covering. It is about 1.5 mils thick, weighs about 1/3 as much as MonoKote, and has it’s own heat sensitive adhesive. The adhesive activates at about the same temperature as MonoKote (325-350 degree F.). It doesn’t shrink as much as MonoKote, so try to keep the wrinkles out as you install it, rather than trying to shrink them all out later. Tom points out that because it is a light weight material, and is not as strong as MonoKote, it should only be used on a slow flyer. The adhesive worked well, and I found the covering fairly easy to work with. Even though it doesn’t shrink as much as MonoKote, I still managed to warp the structure in different areas. A little re-heating and careful twisting straightened out the problem.

I wanted to add a little color to my wing tips, rudder and elevator to make the model easier to see in flight. Tom’s instructions say that the Doculam can be painted on the outside, but says that painting it on the inside actually works best, and ends up more durable. Doculam’s adhesive is not adversely affected by most fast-drying enamel/epoxy/acrylic paints. I was a little skeptical, but I taped a ten-inch square piece to some cardboard and sprayed it lightly with a transparent red Testors spray enamel (on the adhesive side), and allowed it to dry overnight. I used this piece up to cover the top of the wing tips, both sides of the rudder and both sides of the elevator. It really worked great and ironed on just like the unpainted material.

Comparing Doculam and other covering materials

from 6-15-03

Covering Material
Supplier Type Wt (g/m^2) thickness (mil) Comments
IMS Polimicro-Film 1.3 0.035  
WES-Technik 0.002mm mylar(x12in) 2.2 0.08  
IMS 0.012oz condenser paper 3.7    
Office Depot waste can liner 5.8   frosy clear
IMS 0.020oz condenser paper 6.1    
WES-Technik 0.004mm alum mylar (x24in) 6.8 0.16 good for hot air envelopes
WES-Technik 0.005mm mylar (x24in) 7.0 0.20  
Saran Wrap colored 11.9    
Sig light silkspan 12.0   17.0 doped
Saran Wrap Cling+ 12.1    
JCI Jap tissue 13.4   19.0 doped
Reynolds Plastic wrap 13.9   crystal blue
  mylar 17.8   rescue blanket coghlans
Tony Avak 0.013mm alum mylar 19.0 0.50 good for helium envelopes
  mylar gift wrap 19.4    
Solarfilm lite 20.0   approx
Dow Saran wrap 20.2    
Sig heavy silkspan 20.7   29.0 doped
  Airspan 22.0   light colored
  gift wrap 24.0    
  Mylar gift wrap 26.3   irridescent
  Litespan 28.8    
  colored micafilm 35.0    
  Doculam 41.5 1.5  
  Solarfilm 68.0    
TopFlite MonoKote 126.0    

Lithium-Ion Batteries

I haven’t heard of anyone using li-ion on a speed 400 yet. I’ve seen some amazing deals on eBay for computer batteries (i.e. $50 for 50 li-ion laptop batteries) and I’m curious. But I haven’t tried yet. So let’s see…..

A li-ion battery provides 4.2 volts, max of about 3 amps. So to get my Zagi to fly on li-ion, I’ll need 8 cells. 4 parallel packs of 2 cells. That’ll give me 7.2 volts, 12 amps. Or maybe… hmmmm.


LiIon discharge limitations rates their LiIon batteries as having a max discharge rate of 2C. Their Li Polymer batteries have a max discharge rate of 1C. I’m thinking that this is going to be too much of a pain to do. I should probably just stick with NiCads.

LiIon defining limitations

from on 6-16-03

LiIon has great energy density but poor power density

Defining Terms

Energy density: the amount of energy a battery stores per unit volume at a specified discharge rate; also called volumetric energy density; usually measured in watt-hours per liter.

Power density: the amount of power a battery can deliver per unit volume at a specified state-of-charge; also called volumetric power density; usually measured in watts per liter.

Specific energy: the amount of energy a battery stores per unit mass at a specified discharge rate; also called gravimetric energy density; usually measured in watt-hours per kilogram.

Specific power: the amount of power a battery can deliver per unit mass at a specified state-of-charge; also called gravimetric power density; usually measured in watts per kilogram.

State-of-charge (SOC): the percentage of its total ampere-hour capacity stored in a battery.

USABC: United States Advanced Battery Consortium, a government/industry effort to encourage the development of batteries suitable for electric vehicles.

Wing Loading

from on 6-12-03

Calculated Wing Loading = weight ÷ area = 25 oz/sq ft. (A little higher than desired)

Using “Cubic Wing Loading” better compensates for aircraft size: – – Cubic Wing Loading = 11.3 oz/cu ft. (A little high) Between 9 and 10 oz/cu ft would be better.

(Note: Cubic Wing Loading is an empirical formula that takes into account the affect of aircraft size on wing loading. As a general rule, larger aircraft can handle higher wing loading than smaller aircraft. Cubic wing loading = weight of aircraft in ounces divided by the wing area in square feet to the power of 3/2. [Scientific calculator required!])

Power to weight ratio for a standard Astro 40 power system in this aircraft =
425 – 450W/8Lbs = 53 – 56W/Lb. (Acceptable)


Since this airplane is on the large size for a 40, I also decided a little more power, say 60 to 65W/Lb would be nice

so the cell count was increased to 20, with an anticipated power in increased to 470 – 520W depending on the propeller used.   [i.e., 25 watts per cell(?)]

from on 6-12-03

[Everything he says here is right on. I was going to write my own list of tips but he says it just perfectly]

Nicad Care and Handling

by Rod Wooley

Keep your batteries in shape!

There’s no doubt that the one subject guaranteed to raise a heated discussion amongst modelers is nicad care and handling! However, we all need to be expert at battery handling for our radio gear and glow ignitors etc, not to mention it’s useful knowledge with the modern day prevalence of camcorders and portable power tools etc. For the electric-flight enthusiast good battery management is a vital to continued success and happiness, and so this month I will dare to say a few words on the subject.

To cut the verbiage I’ll use point form:

1. Charge new nicads and ones that have not been used for many weeks at a low current of C/10 for 15 or 16 hours. e.g. Charge a 600 mAhr cell at 60 mA. Continuing to charge fully charged cells at C/10 for another day or two will not harm them (except it does slowly reduce their usable lifetime due to cadmium migration into the separator.)

2. Cycle cells or batteries four or five times from new, or after three months or more of storage. This can significantly increase the capacity of a battery up to the rated value. (NB ratings are derived at relatively low discharge currents. Don’t expect the same capacity on heavy loads!) Once cells drop below 80% of rated capacity they should be replaced.

3. Overcharging cells at currents much above C/10 causes overheating and venting and rapidly leads to cell failure.

4. Nicad cells can be stored charged or discharged. It is safer to store them discharged as any nicad can deliver a very high current if shorted. Discharged cells can develop internal shorts but this is unlikely.(I had a pack that was discharged for most of ten years and it still worked fine.) It is not good to leave a load on a nicad battery as it will eventually cause damage once one or more cells are discharged. It is wise not to make a practice of discharging receiver or transmitter batteries by leaving them turned on.

5. Rx and Tx batteries can be managed as follows. Blank off a 15 hour period on a plug in wall timer. (E.g. duct tape) Remove all “on” and “off” plugs except one “off” one at the end of the 15 hour period, and one “on” one 15-20 minutes before. Plug in the C/10 transformer that came with your outfit. A full charge from “new” or “flat” is set up by manually turning on the timer and setting it at the beginning of the 15 hour section. Once charged, the short boost each day will make up for the small self-discharge, and the batteries will be full and ready for flying at any time. (Check voltage “on load” before flying if you do this!) Leaving Rx and Tx permanently connected to the charger is not recommended. (see 1 above)

6. After flying some people estimate the percentage usage of their Rx and Tx packs, add a bit, and charge accordingly. (E.g. 500 mAhr is good for say 100 minutes, 40 minutes of use represents 40% used: charge for 7 to 8 hours) It is also acceptable to provide a full 15 hour charge at C/10, but this is time consuming! Personally I find this too “hit and miss” and slow, and prefer to peak-charge at 500 mA and then put the packs back on the 15 minutes a day “maintenance charge”. ( Use of peak chargers also means that you need to “top up” the charge at C/10 every two or three charges. It is easy to wind in 2 to 3 hours on the timer to compensate for cell imbalance and bring all cells up to a full charge.)

7. Try to avoid discharging a battery below about 1V per cell. (Actually 1.2(N-1) V! This is to avoid cell failure: deep discharges cause a few cells to reverse charge.) A single cell can be taken to a lower voltage and even be shorted (once its voltage is below 1.0 V!), but should not be left in a discharged state for long periods with even a light load.

8. For electric flight applications many modelers have found Sanyo cells -provide unrivaled performance. SCR cells are a fast-charge type of cell and have a low internal resistance and so are ideal for high-current applications. E.g. a 1000 SCR can be charged at 5C or 5 A in 15 minutes, and can be discharged at 50 A (or more!)

9. Small motors, e.g. speed 400, only draw 10 A or less, and to keep weight down cells like the KR600AE are used. These should only be peak charged at just 2.5 C (1.5 A) and used once, followed by a 15 hour C/10 charge (60 mA in this case), or can instead be peak-charged and topped up at C/10 for two or three hours to bring all cells up to full charge.

10. Nicads are damaged by heat and overcharging at higher currents. Use of a good peak charger is recommended, but beware of the “mis-matched cells problem”: usually Sanyo SCR’s are well matched, but for example with camcorder nicads, repeated peak charges gradually leads to a low capacity. This is because some cells are empty before the others, and the effect is accumulative. Eventually the lower efficiency cells will fail. A good long charge at C/10 will often bring such a battery back to full capacity if things haven’t gone too far.

11. Nicads typically maintain a very level voltage over the 10 to 90% portion of the charge discharge cycle. A fully charged cell on charge can be as high as 1.6V. In use, this voltage quickly drops to 1.2 V and then slowly sinks to 1.0 V. After that it drops off quickly during the last 10 % or less of discharge. (On a very heavy discharge the cell voltage can drop immediately as low as 1V as a result of the cell’s internal- resistance, e.g. 4mohm x 50A = 0.2 V).

12. Nicads can be soldered without damage, but clean the terminals well e.g. with a slow Dremel tool using a flexible disc-sander. Avoid shorts due to solder “blobs” around the positive terminal. (Homemade masking tape seals are good). Tin the cell and connection. Use a light smear of flux and multicore solder, and a good powerful iron with a clean flat bit, so the joint is made very quickly before the cell heats up internally. ( Take care! Its easy to damage the nylon seal on the positive terminal!)

13. An accurate digital voltmeter, battery discharger and capacity tester and are very useful equipment for checking batteries. Keep a record of the voltage at the end of a charge and battery capacity. Capacity tests and voltage checks will quickly detect a battery that is starting to fail by detecting shorted cells and cells that are no longer holding a full charge. A good test is to measure capacity once immediately after charging, and then measure capacity again 3 or 4 days after a charge. Any pack that shows a marked drop should be replaced. A drop of 10% in capacity is the most one should consider safe after this time. (Obviously if a pack has not been used much in recent weeks it’s worth cycling the pack 3 or 4 times before checking capacity) A good test of an individual cell is to take it to zero volts and then short it out for 24 hours. Remove the short and see if the cell will re-establish some voltage greater than zero. If it does this it means it is free of any high-impedance internal shorts.

14. On electric models it seems to be best to store the propulsion batteries discharged until just before use, and then to peak-charge them. Land as soon as the pack starts to drop off so you still have control, and then run the battery down until there is not much “umff” left. Thus full charge, full discharge seems to work well and provide maximum capacity, although I am not sure why it is superior. It may be because it helps to avoid the mismatch problem mentioned above, perhaps because empty cells can’t self-discharge at different rates and get out of step!

Rod Woolley (Ottawa RC club)

Selecting the right electric motor, battery, prop, and gear ratio combination

from on 6-12-03

After much pondering, I have concluded that the biggest problem most people have is in selecting the right battery, motor, propeller and gear ratio combination. To do this right, you need at least a tachometer, an ammeter and a bit of common sense. If you don’t want to understand how to use these simple tools, at least find someone who does, and get them to do a quick check on your setup. It will immediately tell you what is happening and how your plane could possibly be improved. If you throw up your hands in dismay and say “I don’t know nuthin’ about that technical mumbo-jumbo!”, you missed the point! You don’t need to be a whiz-kid. You just need to know a couple of simple facts and how to apply them.

The first fact is that the speed at which a propeller will want to fly is approximately its pitch in inches times its RPM in thousands! i.e. MPH = pitch X rpm/lO00. Now you know what use a Tach is! You can work the thing out in your head once you have the RPM! In the air, the prop will unload a little, so add about 10% to its static RPM to get its flying RPM. Now you know why a 12 X 6″ prop turning at 4,000 RPM will not give a sparkling performance to an aerobatic sport plane that has a stall speed of 25 MPH. You also know that a 12 X 8″ folder turning at 6,000 RPM on your 25 MPH sailplane is just eating up batteries and cooking the motor.

The second fact you need to know is that power is amps times volts. At the current levels we use, we can assume that there is about one volt across each nicad cell in the battery pack. Therefore, power = amps x number of cells. This will tell you how much electrical power is being converted in your motor into mechanical energy and heat. Now you know the use of an ammeter! Again, you can do the calculations in your head! In the air, the motor will draw about 20% less current as it unloads, so flying current = 80% of static current. Now you know that if your IOOW can motor is drawing 25 amps on seven cells, you know it is not long for this world! You also know that if your Astro 40 is drawing 10 amps on 16 cells, you need a bigger prop or you might as well use an Astro 05! You must admit, none of the above really strained your brain and you didn’t even have to find batteries for your calculator! When you put the two simple facts together, you can find the right sized prop to match your motor and plane. If you can’t guess roughly how fast your plane will fly, ask someone with experience. You will know if they have experience because they will ask you what the wing area is and how much the plane weighs. If they can’t see your plane, they will also ask you how thick the wings are and what shape the aerofoil is, as well as what kind of performance you want. Then all you need to do is borrow a few props if you don’t have any and check the motor current and the RPM for each until you get the results you want. Then you can go out and buy the right sized prop and confidently join me in the clouds.

Propeller Diameter and RPM

from 6-14-03

The most important variables affecting the thrust a propeller can develop are its diameter and rpm. Thrust increases when either of those go up — in proportion to the square of the rpm, and the FOURTH POWER of the diameter. If you should speed up an engine-driven prop from 10,000 to 14,142 rpm, its thrust output would double. And if you spin a ten-inch prop at the same rpm as a geometrically-similar 5-incher, the thrust developed will be SIXTEEN TIMES as great.

… [large props are more efficient and quieter than small props]…

… [it’s very important to have a very stiff blade]…

Here’s a handy “rule of thumb” concerning propellers. The maximum speed a propeller-driven aircraft can attain is roughly equal to the prop pitch in inches, times its rpm in thousands.

Example: An 8-4 prop at 10,000 rpm can’t pull its model faster than 40 mph. (4 inch pitch times 10K rpm = 40 mph maximum.) The airplane can fly a lot SLOWER — particularly if it’s a high- drag design. But even in a dive, it won’t go faster than this “rule of thumb” limit.

The Best Propeller Tip Speed

from on 6-14-03

An interesting point in understanding power absorption is that propeller power varies as the cube of the rpm. Consequently, twice the rpm requires 8 times the power.

Tip Speed is measured in feet per second and a formula is provided below to find this measurement.

For model airplane purposes, the best tip speed for efficiency and noise requirements is 600 feet per second. This is due to compressibility losses and the fact that subsonic airfoils do not work well in transonic/sonic speeds with required sound levels.

Feet Per Second (ft/s) = RPM x diameter in inches x .00436

For example, to find the tip speed of a 10×6 on a .40 size engine running at 13,500 RPM, the equation would be 13,500 x 10 x .00436 = 588.6 ft/s.

To find the correct diameter at 600 ft/s, use this formula:

Diameter in inches = 138,000   /   RPM

Using a .40 engine running at 13,500 RPM, the equation would read as follows:

138,000/13,500 = 10.22

Rounding down, the correct diameter is 10″

Comparison of different speed 400 motors (especially brushed vs. brushless)

from on 6-12-03

MOTORS – Cheap, Light, Powerful. You Can’t Have It All
by Stefan Vorkoetter

Ferrite “Can” Ferrite Car Cobalt/Neo Brushless
Cost Low cost – $10..$30 Medium cost – $20..$50 High cost – $125..$600 Very high cost $400 +
Quality – Low quality
– Brass bushings
– Carbon brushes on leaf springs
– Cheap ferrite magnets
– Large armature-magnet gap
– Medium quality
– Bushings or ball bearings
– Copper or silver brushes
– Brush holders and separate springs
– Better ferrite magnets
– Some have adjustable timing
– High quality
– Ball bearings
– Thicker output shafts
– Large brushes (usually silver)
– Brush holders and separate springs
– Powerful cobalt or neodym magnets
– Adjustable timing
– High quality
– Ball bearings
– Thick output shafts
– No brushes
– Powerful cobalt or neodym magnets
– Adjustable or self-adjusting timing
Weight Heavy (~2.3lb/HP) Heavy (~2.3lb/HP) Light (~1.5lb/HP) Very light (~0.5 to 1.2lb/HP)
Efficiency – Narrow efficiency curve
– Maximum efficiency about 70%
– Typically about 60%
– Narrow efficiency curve
– Maximum efficiency about 75%
– Typically about 65%
– Wide efficiency curve
– Maximum efficiency about 80%
– Typically about 70%
– Wide efficiency curve
– Maximum efficiency about 85%
– Typically about 75%
Power – Maximum power at about 50% efficiency
– About 140W out for a 7oz motor
– Maximum power at about 55% efficiency
– About 140W out for a 7oz motor
– Maximum power at about 60% efficiency
– About 220W out for a 7oz motor
– Maximum power at about 65% efficiency
– About 280W out for a 7oz motor
Advantages – Cheap!
– Readily available
– Can often be found surplus
– Wide range of sizes
– Low cost is great for multi-motor models
– Fairly inexpensive
– Readily available
– Brushes replaceable
– Some have ball bearings
– More efficient than “cans”
– Brushes replaceable
– Ball bearings for long life
– More efficient than car motors
– Low maintenance
– Wide voltage and current range
– Zero maintenance
– Ball bearings for long life
– More efficient than brushed motors
– Very wide voltage and current range
Disadvantages – Difficult to maintain
– Brushes not replaceable
– Loses power at high temperatures
– Difficult to find specifications
– Limited selection of sizes
– Fairly expensive
– Harder to get
– Very expensive
– Requires special speed control
– Not usually in stores
Examples – Graupner Speed 400, 600, 700
– Great Planes Goldfire and Thrustmaster
– Master Airscrew
– Kyosho Magnetic Mayhem
– Trinity Speed Gems (Ruby, etc.)
– Leisure Model Electronics
– Astro Cobalt
– Cermark Cobalt
– Graupner Ultra Neodym
– Astro Brushless 020 and 05
– Aveox
– MaxCim
– Kontronik
Effect on Power
– Sailplane with 12×8 prop and 7×2000 cells, geared for 4 minute run
– Graupner #1793 Speed 600 7.2V
– 2.65:1 gearbox
– 25A input
– 123W output
– Kyosho Magnetic Mayhem
– 2.7:1 gearbox
-25A input
– 128W output
– Astro #605 Cobalt 05 Sport
– 2.5:1 gearbox
– 25A input
– 146W output
– Aveox 1406/3Y
– 2.4:1 gearbox
– 25A input
– 159W output
– Effect on Run Time
– Sailplane with 12×8 prop and 7×2000 cells, geared to give 138W output
– Graupner #1793 Speed 600 7.2V
– 2.2:1 gearbox
– 32A input
– 138W output
– 3:12 run time
– Kyosho Magnetic Mayhem
– 2.3:1 gearbox
– 31A input
– 138W output
– 3:19 run time
– Astro #605 Cobalt 05 Sport
– 2.6:1 gearbox
– 23A input
– 138W output
– 4:24 run time
– Aveox 1406/3Y
– 2.55:1 gearbox
– 22A input
– 138W output
– 4:44 run time

Graupner #1793 Speed 600 7.2V
[So to read this chart…. this motor is most efficient when drawing 15 amps. At that draw, it’s delivering 80 watts of power. You want to keep the draw somewhere between around 7 and 35 amps to keep the efficiency reasonable.  The easiest way to tell what the amperage draw is with a particular propeller & battery combination is to sit it on a workbench and crank it up with an ammeter. Then fudge the draw amperage down 20% to simulate real flying conditions. When you’ve got a good combination, you can calculate how fast the plane would fly by the amount of twist in the prop (see the previous article). If that lines up with how fast you really want your plane to fly, you’re golden. – lee]


Kyosho Magnetic Mayhem

Astro #605 Cobalt 05 Sport

Aveox 1406/3Y

Prop Diameter to Pitch Ratio

from on 6-12-03

The diameter to pitch ratio is important. 12×6, 11×8, and 10×10 props absorb about the same amount of horsepower. Trainers and biplanes should use a diameter to pitch ratio 2:1 (i.e.. 12×6). Very draggy planes like a tripe might be better off using 3:1 (i.e.. 14×6). Sport planes can use a 1.5:1 (i.e.. 9×6). Fast planes racing planes might use a 1:1 ratio (i.e.. 10×10).

from on 6-12-03

Measuring Lead-Acid Battery Condition

Connect a voltmeter and measure the voltage across the battery terminals with the battery at rest (no input, no output) for at least three hours. These readings are best taken in the early morning, at or before sunrise, or in late evening. Take the reading while all loads are off and no charging sources are producing power.

The following table will allow conversion of the voltage readings obtained to an estimate of state of charge. The table is good for batteries at 77·F that have been at rest for 3 hours or more. If the batteries are at a lower temperature you can expect lower voltage readings.

You can see that when your voltage reading is about equal to
the battery “nominal voltage”your battery is about 60% discharged.

Battery State of Charge Voltage Table

Percent of Full Charge 12 Volt DC System 24 Volt DC System 48 Volts DC System
100% 12.7 25.4 50.8
90% 12.6 25.2 50.4
80% 12.5 25 50
70% 12.3 24.6 49.2
60% 12.2 24.4 48.8
50% 12.1 24.2 48.4
40% 12.0 24 48
30% 11.8 23.6 47.2
20% 11.7 23.4 46.8
10% 11.6 23.2 46.4
0% <11.6 <23.2 <46.4

The following chart reflects state of charge vs. specific gravity of the electrolyte in each cell.
A hydrometer is used to determine specific gravity.


State of Charge Specific Gravity
100% Charged 1.265
75% Charged 1.239
50% Charged 1.200
25% Charged 1.170
Fully Discharged 1.110
These readings are correct at 75°F


Lee’s R/C Shopping Guide

(Originally from my flying website from 2005 or so. The original publish date is lost)

In 2001, I was part of  a purchase of an Ikarus Bleriot III and related kit from Hobby-Lobby. The kit, which was put together by Hobby Lobby, contained a battery pack in a bad configuration (the batteries were in a squarish block but they should have been all in a row). We dealt with it, but it sucked.

I received a Zagi 400x and radio set from Atlanta Hobby in 2002. The motor had it’s wires attached incorrectly from the Zagi factory. Cliff from Atlanta Hobby was -very- quick and friendly when resolving the problem.

In May 2003 I bought an Astro 110D charger from Atlanta Hobby. It was performing a little strangely so I wrote to Cliff. He very quickly spoke with the manufacturer and got back to me with an answer to my question.

The Atlanta Hobby website and all my communications there have been very personable. :-)

I’ve been into Kenvil Hobbies a few times and bought a couple things. The owner is nice, he stocks a wide array of products, and although he’s not into flying himself (and doesn’t know that merchandise completely), he’s good in my book. My local hobby shop! :-)

I bought a set of 4 4amp/hr 6 volt batteries for my UPS from Battery Mart in May 2003.  They were cheap, shipping was very reasonable and the batteries are good.


I’ve been thinking about getting a lead-acid battery electronic desulfater. It sounded a bit like voodoo or fodder for a late-night infomercial so I asked around for a review. I got back this very positive response from one person about the Powerpulse. (he asked that I edit out his name and company)


Several years ago I persuaded the company to donate a set of the units to the Science Museum of [removed] for use in our electric car, but they never got installed. A couple of years later, the car’s new batteries sat unused and uncharged for about a year, and got pretty badly sulfated. We then installed the PowerPulse units and charged the batteries and checked them for capacity — the car’s range was about 10 miles. A week later the batteries would support a range of about 30 miles, and a couple of weeks after that they seemed to be back to full capacity. So I think the units work. It does seem like hocus-pocus to some folks, but I believe the theory of their function is logical.

Hope that helps.

Regards, Bob [removed], Science Museum of [removed]

Mostly flying the Trick 1000

That crazy plane.. I’ve had some trouble with it.

First I tried flying it with one 10-cell KAN-1050-knockoff pack. For the first flight, I tried taking off from the landing gear. Blech. It rolled. It went up, it twisted, it went down. I went to launch it again but when I held it in my hands and gave it throttle, it made a funny low buzzing sound. As I was turning it off, I felt something hit the side of my neck in my hair. It was a screw from the motor mount! That was kind of weird since I think the screw had to of hit the prop and gone in a giant arc up and then down into my hair. And I even caught it. Cool. Weird.

When I was putting it together, I had some trouble with the motor mount. See the drawing at the right. There is a mostly hollow rear motor mount (red) that’s glued to the fuselage, and a front motor mount (green) that holds the motor with the two inner (purple) screws. Trouble was (so I thought) that 1 of the 4 screws that holds the front mount to the rear mount (teal) didn’t go in tightly. I thought it would be alright. I was wrong. It is held in just with friction; the screws didn’t have enough bite, the hole was too big… whatever the problem, it didn’t stay in. So after my crash, I got out the CA glue!

It was suggested that instead of taxing, I should just toss it in the air. Gosh darn it if it didn’t work. Problem #2 & 3 cropped up. The center of gravity was way too far back and it was porpoising. Also, I only got 3 minutes of battery life out of it. But it flew!

I got it down in a hurried state, way low on battery (the problem might have been that the speed control was set to turn off at the wrong voltage. I haven’t had time to diagnose that yet… but I digress). It was a rough landing but in one piece. So I stuck 2 battery packs in parallel (I suspected I’d have to do this so I bought 4 packs, all the same :-) ). I brought it out to the field, got ready to toss it, reved it up and CRACK!

The foam forward of the motor mount (denoted in sad yellow) tore off! It wasn’t glued in well enough from the factory! So that was that for my flying day. I got it home, took out the fiberglass tape and epoxy and went to town. The nose ain’t falling off anymore! (See picture)
You’ll also notice in the picture that the bottom screws are larger than the top screws. Well, both of them had started coming loose so I went goofy on it. I drilled out the holes a little larger, cut down some long screws and screwed them in the holes and then I epoxied the shit out of them! The little circles in the fuselage are toothpicks (slathered in epoxy) I drove into it to reinforce. You’ll also notice the wear marks on the prop. It only got 1 more flight before cracking (I flew into a house… the house won)

Blah blah blah…. I got one 15 second flight out of it on Saturday morning. On board was 2 batteries, all the lighting, and the power module for the lighting. It’s a heavy plane! It took off and I couldn’t give enough right aileron to keep it up. I think the lighting was interfering with it. Nevertheless. It flew. Since I was out of time, I repaired the damage (House 1, Plane 0) and boxed it up for the trip to Burning Man. No wait. It didn’t fit in the box. I had to leave for the container in 30 minutes and I didn’t have a box big enough for the tail section!! ACK! The boxes I thought would fit…. didn’t I started driving toward the bike shop to make my own box out of a bike box…. then I turned around and started driving toward Hackettstown because it was closer, and “I would have to find something.” And I turned home with a plan.

I took a utility knife to the epoxied tail. I took a screwdriver to the landing gear. And darnit, I made the plane flat. I made it fit in the hard case I found at a junk yard in Vermont that I had gotten for this very purpose. (Well, I was going to use it for the Projeti, but the Projeti didn’t fit in it. It was only still in the garage because I didn’t have time to get rid of it (and I was secretly thinking that I had to find SOME use for it. Well I did!))

I put the Trick 1000 in a box. Projeti in a box. Tools in a box, supplies in boxes. bike in a box. I strapped the bike box to the roof of the Jaguar (finally, a good use for the Jag!) and I was Brooklyn bound!

My main piece of art, what I’ve worked on for 50 hrs+ MIGHT fly. It MIGHT light up in the air (only briefly tested!). Then again, maybe it won’t. Maybe it’ll melt in the heat of the container. Maybe it’ll rock.

Buying Last Minute Parts

Tuesday: I finished the plane! I put the batteries in. I tested the controls. ACK! One of the servos is bad! ACK! It takes 3 weeks for warrantee service! ACK! The nearest hobby store has recently proven that it regularly doesn’t have the most essential supplies (last week I asked for Deans Ultra connectors and Zagi props. No go.) I called him up and PHEW, he had them. Grumble, grumble, I had to drive 30 minutes each way just for this little 0.2 oz part on Wednesday.

Flaming Lithium Polymer Chunks

The guy at Zeppelin Hobbies told me why they don’t allow Li-Poly batteries at model car races. They don’t just burn, they throw burning chunks several feet. Cool. Imagine one battery blowing up and lighting all the neighboring cars on fire. Rinse and repeat. How’s that for adding an element of danger to models? Cool.

Making Ma’at in EL wire

She’s done! Take a look

How: I got window weatherproofing plastic (it’s lightweight and crystal clear. Thanks for the hint, oh my genius sister!) and 3M packing tape. As I’d go along, I’d shape the EL wire and then tape it to the plastic.

I ran into some weirdness when I tried to run some of the EL wires in parallel. Depending on how I did the positive and negatives, sometimes they’d light in parallel, sometimes not. Sometimes the brightness would be affected, sometimes not. I think the power supply didn’t like having 3 in parallel. I found one configuration that worked by putting some in series…

Projeti Coolness

I took her out today. It’s really a blast. My favorite from today was taking off at 3/4 throttle, taking a moment to verify stability and then giving her full throttle. She pulled out at an 80 degree angle until I told her to stop… about 400 feet. I’d have her go higher but I can’t see her any further away!I lost my 10 cell NiMH :-( I was practicing hammerheads (and getting moderately good, I might add!) when the battery fell out. I foolishly watched the big yellow plane fall all the way to the ground instead of following the tiny little battery. I looked for about 30 minutes but no luck. Well, I guess I’ll be getting a new matched set of NiMHs.

Wow, can build me a 10 cell generic 1050 mah pack with Dean connectors for $20/pack. That’s like 1/2 the price of my local hobby shop, with -exactly- what I’m looking for instead of whatever happens to be in stock.

I’ll wait to put together the Trick 1000 and see how it flies with the LiPoly pack. Then I’ll probably get a double set of batteries.

Cool Neon Order Placed

I wonder how I’m going to get all this stuff on the plane!







DBB 1 Big Boy Driver- Will power 50- 165 feet of Cool Neon wire.
$13.50 $13.50
ACPPC-W 5 Plug & Play Connectors- Wire Side
$0.45 $2.25
DF1 1 Fish Driver+ 1- Will power 5- 45 feet of Cool Neon wire. Cut the white wire to stop blink mode.
$5.25 $5.25
ACPPC-D 4 Plug & Play Connectors- Driver Side
$0.35 $1.40
DPS 1 Lights 4- 20 feet of Cool Neon wire.
Pipsqueak Driver: Original, smaller- add $2
$5.00 $5.00
WHBL_100 15 High Bright Longer- Life wire: 100-199 Feet
High Bright Colors: Purple
$1.20 $18.00
WHBL_100 35 High Bright Longer- Life wire: 100-199 Feet
High Bright Colors: Yellow
$1.20 $42.00
WHBL_100 27 High Bright Longer- Life wire: 100-199 Feet
High Bright Colors: Lime
$1.20 $32.40
WHBL_100 10 High Bright Longer- Life wire: 100-199 Feet
High Bright Colors: White
$1.20 $12.00
WHBL_100 13 High Bright Longer- Life wire: 100-199 Feet
High Bright Colors: Red
$1.20 $15.60
Tax 0.00
Total $147.40

(Actually, that’s 2 planes, a bike and some extra neon to round the order up to 100 feet.)