Gday again to all you good Slow Flyers have you been following your mission people?? You remember the one: to fly slow and prosper!?!?
I have received several requests for information on the suitability of cells other than Nicads for our SlowFly applications. Presented this month is part one of a round up of information from experienced users on alternative power sources to nicads. There is also an update on the Duration Competition, a follow up from Leon Wolfe on modifications to the Twin Turbo radio, details on how to fix those BEC jitters when using 9g servos, more pictures and news from around the SlowFly globe, as well as Marlin Mixons blue foam construction article.
The end of the financial year is almost upon us in Australia, but fortunately reading The E Zone is one thing the tax man hasnt pinged us for - so, read on and ENJOY!!
The first thing I am going to do this month is hand over the controls to Marlin Mixon so he can explain how to construct models using blue foam. See you on the other side of Marlin's piece!
How To Build Flying Model Aircraft Using Blue Foam - By Marlin Mixon
Carving blue foam is a remarkable technique for modeling scale subjects, especially of any modern monocoque/aluminum/stressed-skin airplane from WWII on forward. It opens up new realms of possibility. Have there been any scale subjects that appeal to you but would be difficult to build using traditional covered balsawood frameworks? Maybe your dream airplane has compound curves or frustrating details like faired gun blisters or large faired fillets where the wing and fuselage meet. If so, read on. You've come to the right place because these types of subjects become easy and even pleasurable when carved out of foam.
Let's compare blue foam to typical balsawood construction. Scale blue foam subjects can be made every bit as light as their balsawood counterparts. It's possible to hollow out a foam fuselage to a 1/32" thickness and still maintain decent structural integrity. Even small subjects like peanuts and pistachios can be constructed to fly competitively against balsawood counterparts. Foam looks better for some scale subjects because foam can be carved to form a continuous smooth surface with no ribs, stringers or bulkheads to disturb the scale appearance.
What about plans? Don't you need special foam plans to build a foam airplane? No. I build my planes from plans intended for balsawood construction. At a minimum, you need a full-sized three view as a guide. Cross section information is helpful to give you information about the precise fuselage shape, but not required. You can create a "plan" by simply getting three views from a book and using a photocopy machine with good quality scaling capabilities to enlarge the plans to the size you want to build.
What tools are needed to carve foam? You need a different set of tools to work with foam. For example, a hot-wire which is simply an electrically heated wire is useful for rough cutting shapes. I use a used electric train transformer for this, which is nice because I can adjust the power output to effectively adjust the temperature of the wire. (See Figure 1.)
The hot wire consists of a wooden frame that serves to keep the cutting wire taught. I made the frame out of a thin base board and I screwed in some shelf brackets that support the wooden vertical members. For wire I used to use nichrome wire, but it's kind of expensive. Lately, I have been using the smallest music wire available in hobby stores or 0.015" diameter wire. For carving the foam, I use a highly sharpened pocket knife, sharpening the blade often as I carve. For hollowing out the interior, I use a dremel tool with a carborundum drum which is a small cylinder wrapped with sandpaper. (See Figure 2.)
Are there any peculiarities to working with foam? Yes, foam has a low melting point and when it is heated or melts, it tends to shrink and get denser. This is noticable when you cut foam with a hot wire. After cutting you may notice that a tough skin forms right where the wire has passed. This is a particular concern when you are trying to cut thin light sheets. What happens is you get thin sheets, but since the foam has been melted, your sheets are heavier than expected. This also occurs when you use a high speed rotary tool to carve foam. As the friction of the tool heats up the foam, the foam starts to densify, melt and spall. The solution to these problems is to cut or carve slightly thicker than you need to and to sand away the denser foam by hand. Also note that the foam sheet coming from the factory is not of uniform density. It too has a denser skin right near the edge. If you are trying to keep things light like you always should be doing, then be aware of these density considerations.
How do you carve foam?
Fuselages and Engine Nacelles I usually start construction with the fuselage because carving the fuselage offers the biggest challenge when working with foam. To carve one of these structures I start out by hot-wiring a blank from which to carve. To do this, I first cut out full-sized cardboard templates of both the top view and the side view. I cut a pair for the top view and a pair for the side view. I then use a hand saw cut two rectangular pieces of foam that are slightly longer than the maximum fuselage length and slightly taller than the maximum fuselage height. I then tape the two rectangular pieces side by side with double stick tape so that the blank looks like the one shown in figure 1. The final step prior to hot-wiring is to pin the top view template to the taped blanks as shown in Figure 3,
then pin the other top view template to the bottom of the blanks. Make sure, when you do this, that the center lines of the two templates match up to the separation line of the two taped blanks. Now you can hot wire. When you are done you will have a shape like that shown in Figure 4.
The next step is to pin the side view templates to the freshly cut blank. It's not critical where you locate them on the blank just so long as they match up left to right. This is shown in Figure 5.
Now it's time to hot wire as shown in Figure 6. Remember when we taped the two blanks together? Do not worry where the tape falls because the hot wire cuts right through the tape almost as easily as it cuts through the foam.
Figure 7 shows the completed blank ready for smooth sanding prior to exterior carving.
Once the blank is sanded so that the top, bottom and sides are smooth you then have a perfect carving guide. the top view centerline (where the two halves separate) delineates the highest point of the fuselage.. Material below this point will be removed, but no material will be removed exactly at this center line. To aid the carving, I also draw a line with felt marker along the fuselage representing the high point of the fuselage side view. This line like the top center line marks the high point of the side of the fuselage. Again material will be removed up to the high point line, but no material is to be removed right at the line.
I start by using a sharp knife to cut away the corners so that I can start to carve a rounded fuselage cross section as shown in Figure 8.
Figure 9 shows the fuselage after roughing out the basic exterior.
The final step for the fuselage exterior is to smooth sand the exterior with 100 grit sandpaper. Sanding with finer grit sandpaper is done but much later in the process. Figure 10 shows the final exterior form ready for hollowing out. Notice the engine nacelles. These are carved just like the fuselage.
The next step is to hollow out the fuselage. I use a rotary tool for this. Be sure to wear eye protection and a face mask to filter the dust. Hollowing out the fuselage and engine nacelles is a simple but somewhat lengthy process. Your goal is to make a shell that is as thin as you dare without punching through to the exterior. Bold strokes are used in the beginning and light paintbrush like strokes are used towards the end. (See Figure 2.) One trick is to use a light to back light the work as you go. This helps you see the thicker parts because they are darker blue. This is depicted in Figure 11.
Please take care when using this backlighting technique. At one point I touched the fuselage to the light bulb and it left a 1/2" dent that required patching later.
After hollowing out both sides of the fuselage, it's time to glue them together. I use white glue. I smear both sides with glue and tape them together with masking tape and set them aside to dry. I duplicate the technique with the nacelles.
You will most likely need to cut away portions of your fuselage as needed for wings, stabilizers and canopies. A sharp single edged razorblade works well for this. At times, however, it can be a challange to mark exactly where cutouts are to be made, especially with a rounded fuselage and nacelles. Figure 1 shows preparation for cutting out the canopy area. I am carefully referencing the plans as I do so.
Pins are great tools to help you in positioning slots to be cut in rounded fuselages. Figures 12 and 13 show how pins can be used in figuring out where the wing slot is to be cut. Sighting down the pins, you can see if both sides of the wing slot are parallel or not. If not, move one of the pins slightly so that they are parallel.
Once the pins are aligned properly, you can use them as a guide for a straight edge. Use a marker to draw the base line of the wing as shown in Figure 14.
Wings. Wings are relatively easy to build. I cut my wings using a hot wire. I make root rib and wingtip rib shapes out of balsawood. Then I make a right and a left wing, one at a time. I start by cutting a foam blank for the right wing that is half of the total wingspan in length. Then I pin the root rib to one side and the tip rib to the other. Once this is set, then I drag the heated wire through the foam using the rib templates to drag the wire against, which forms the airfoil. (See Figure 15.)
Typically, I'll only cut the upper surface of the wing with the hot wire and carve and hollow out the underside of the wing with a rotary tool. For any wing, I'll carve to 1/8" thicness. If I'm building a super light model for indoor flying, I'll leave it undercambered. For outdoor flying I take the same wing but make the wing three dimensional by gluing a thin sheet of foam to the bottom of the wing. Sometimes I'll also glue a spar spanwise along the thickest part of the wing to add extra strength. This spar can either be made of foam or balsawood.
Figure 16 shows some warping trouble I had in cutting the wing.
I cut a few of these, but I could not seem to get rid of this unwanted spanwise warp. The solution was to tape the wing down to a piece of wood with negative warp and throw it into a 175 degrees F oven for about a minute. That worked very well, so well, in fact, that soon I hope to build a Corsair with the inverted gull wing baked in! Be careful when using this technique--I ruined a nearly perfect fuselage trying to remove a slight bow. I think that the safest course of action is to turn off the oven prior to putting the foam into it. Also try some scrap first so that you can be certain that your oven is not too hot.
To finish up the wing, do some final sanding on the wing to achieve the desired airfoil shape. Next carefully sand both wing roots for the appropriate dihedral angle. As you sand the dihedral, test fit the dihedral joint often to make sure of the following three things: 1. That the dihedral angle is correct. 2. That the any gaps in the joint is minimized. and 3. That you are not sanding in inappropriate sweep back or sweep forward of the wings. After sanding, you are now ready to glue the two wing halves together. I have had good success simply butt gluing the wings together with white glue. This type of joint seems to be plenty strong for foam wings.
Tail surfaces. You may choose to build the vertical stabilizer integrated into the fuselage as clearly shown in Figures 5-10, if this is consistent with the subject you are modeling. Otherwise, you can construct the tail surfaces out of thin sheets of foam. Thin sheets can be cut with a hot wire, but, as mentioned before, be careful about the weight associated with hot wired sheets. After hot wiring a thin sheet, you can simply cut out the shape of the desired surface with a knife or blade. Next the denser foam can be sanded away leaving a light tail surface. Additional sanding near the leading and trailing edges can give the tail surface a scale airfoil cross section.
Preparing the surface for painting. Nicks, bumps, and gaps can be patched with light weight Model Magic or Red Devil spackle. Smear it on, smooth it out and wait for it to dry, then sand it smooth. I have even built up entire wing fillets in this manner, though this is not the lightest way to make a fillet. A better way might be to carve a fillet out of foam, hollow it out, then glue it into place and use Model Magic to fair the foam fillet into the wing and fuselage.
Finishing. Flat finish is easiest and lightest--simply spray acrylic paint directly to the finely sanded and prepped foam. A glossy finish can be achieved by prepping the surface--In the words of Doug Wilkey: A neat finishing trick for foam is to mix white glue, Knox gelatin in water and talcum powder. Dissolve the Knox gelatin in water according to the instructions then add equal amounts of white glue, and then add unscented talcum powder. This partially fills the grain and also gives a hard shell to the foam. When the water evaporates from the solution, very little weight is gained. It becomes a very light weight sanding sealer. You can then airbrush a light coat of any of the acrylic hobby paints to get your final colors. Poly S is my favorite when thinned with Rubbing alchohol. Add a drop of liquid detergent to a bottle of mix to keep it from beading up.
Resources: Publication: "Indoor Foam Scale Flying Models, How to Build and Fly Them" by David Deadman, Peter Smart and Richard Crossley. Available mail order from Hannan's Runway.
Well, that man Bob Wilder has been at it again. Im sure you all read Jims report on Bobs performances in a previous Ezone article. The model featured in that report was powered by Nicad cells. For his latest success, Bob switched to lithium cells, and boosted the flight time to over 2.5 hours.
I have received some correspondence on the rules, or lack thereof. I dont propose to go into that discussion any further here, other than to say (again) that the intention behind the competition was to encourage people to have a go at indoor r/c. By tackling the task of duration flying posed by the competition, competitors would improve their r/c slowfly designing, building and flying skills.
I received a series of emails from Palo Lishak <palo(at)kosice.telecom.sk> in Slovakia, with news of his first attempts at the duration challenge posed by the EZone competition Palos efforts encourage me to believe that we were right in promoting the "Duration Competition".
From: Palo Lishak ( palo(at)kosice.telecom.sk )
My name is Palo Lishak. I live in Slovakia (at Middle Europe) and for many years I have been building Electric Powered Models with Speed 400 motors.
Your column on The E Zone inspired me to try new experiments. I am attaching some photos of my first Slow Flyer. Standard flying time is 8-12 minutes. Best flight so far has been 18 minutes. I think I will be able to do even better.
Some detail for you:
- The power system consists of a small motor (probably type 280 ?) which through the 3,2/1 hand made gear drives a plastic propeller (cca 180 mm diameter)
- The model weighs 220 gr together with Aku 7,2V/320 mAh
- The leading edge of the wing is a carbon tube. That's why the model doesn't have any problems doing loops
- A landing gear is not necessary because the model takes off and lands in my hand!
- Aku makes a stick which is shifted into a balsa tube of the fuselage.
- There are two servos (2 x 9 gr) and the REX 4 micro-receiver fitted below the wing.
- An ESC from WES is fitted to the motor.
The model in the above pictures is not assigned for indoor flying. It's a "garden flier" only. I think it will lure some "heavy" electro -pilots from my country to the doors through which they'll see a wonderful "Indoor world".
With compliment, PALO LISHAK , Slovakia.
Twin Turbo Revisited
Following on from Leon Wolfs great article on the Twin Turbo last month, here are some more details from Leon on the micro-processor modifications offered by Sergio Zigras
A CLOSER LOOK AT SERGIO'S MICRO-PROCESSOR FOR THE TWIN-TURBO
by Leon Wolf
Last time, I gave an overall view of the TT system, with some modifications to enhance the operating parameters. This time I will try to explain the workings of the TT-Tx, the TT-Rx and Sergio's chip, and some modifications using the u-processor.
To keep things straight, I'll refer to the TT transmitter Integrated Circuit Chip as the TxC, the TT receiver Integrated Circuit Chip as the RxC and Sergio's micro-processor as the UC.
We'll start with the Tx and what happens there.
The TxC changes outputs in frequency and duty cycle (ratio of length of time on to time off) in response to the movement of the two sticks. With both sticks in the center, the output is a series of pulses that are on 50% of the time and off 50% of the time ( a 50% duty cycle ) with a frequency of about 100hz. With the LEFT stick forward, the frequency goes to 250hz with the duty cycle remaining at 50%. With the LEFT stick back, the frequency goes to 500hz with a 50% duty cycle. With the RIGHT stick forward, the frequency stays at 100hz but the duty cycle goes to 75% (on 75%-off 25%). With the RIGHT stick back, the frequency stays at 100hz and the duty cycle goes to 25%. With BOTH sticks forward, the frequency is 250hz and the duty cycle is 75%. With BOTH sticks back, the frequency is 500hz and the duty cycle is 25%. All these changes are decoded by the RxC into useful outputs.
The RxC decodes the varying width and frequency pulses of the TxC and changes the voltage level of pins 5, 7, 8, and 9 from a normally "high" state to a "low" state in response to these pulse changes. Pin 5 goes low in response to the Tx LEFT stick moved forward. Pin 7 goes low for LEFT stick back. Pin 8 goes low for RIGHT stick back. Pin 9 goes low for RIGHT stick forward. From the preceding you can see that you can get a combination of two pins low at the same time ( pin 5 and either 8 or 9-- pin 7 and either 8 or 9-- pin 8 and either 5 or 7-- pin 9 and either 5 or 7). All four pins are "high" with the Tx sticks in the center position, which gives no (or off) motor control. All four pins will also go "high" with a loss of Tx signal (out of range, or Tx not turned on). Pins 5 and 7 control the LEFT motor reversing bridge and pins 8 and 9 control the RIGHT motor reversing bridge by turning the PNP and NPN transistors thus allowing the motors to run.
On to Sergio's UC:
The UC is using pins 6 and 7 as inputs from the LEFT stick and pins 4 and 5 as inputs from the RIGHT stick, pin 3 as LEFT motor output and pin 2 as RIGHT motor output. UC pin 7 is connected to pin 5 of the RxC, UC pin 6 is connected to pin 7 of the RxC, UC pin 5 is connected to pin 8 of the RxC, and UC pin 4 is connected to pin 9 of the RxC. UC pin 1 is the power (V+) connection and UC pin 8 is the ground (common). Holding the UC with the notch (or dot) on the one end up and the pins away from you, pin 1 is on the top-left, and pin 8 is on the top-right. Holding the RxC with the dot up and the pins away from you, pin 1 is on the top-left, and pin 16 is on the top-right.
The UC is an 8-pin, 8-bit CMOS microprocessor that can 'sink' (direct to ground) or 'source' ( output a voltage and current) from pins 2 thru 7. The current is limited to 25ma on any pin, with a total UC current of 100ma, and voltage limits of from 2.5V to 5.5V. Anything over 5.5V will "stress" the UC, and at voltages under 2.5V the UC will just shut down. Using the 6V batt. for the TT might be OK, but I haven't used that setup, I'm still using the 4.8V packs.
There are small 5V voltage regulators that can be used to power the UC when you are using higher voltage batteries. In fact, Sergio uses them in his IR Tx's with a 9V supply.
The effect of Tx off or out-of-range is that the UC will not respond to Tx signals, it will just stay where it is. That means that if the UC is giving full throttle and you get out of range, the UC will just keep giving full throttle until the batteries go dead. OOOOPs, fly-away.
You can use only part of the UC if you wish. As in using the throttle part from left stick, and bang-bang rudder from right stick. In this case we'll hook up pins 7 and 5 of the RxC to pins 6 and 7 of the UC respectively, UC pin 1 to V+, UC pin 8 to ground, and use UC pin 3 as the control for the motors. ( refer to the diagram that comes with the UC) We should also connect the unused UC pin 5 to V+ through a 1K-ohm resistor, otherwise the UC will see the pin as an input signal for speed-control. UC pins 2 and 4 may be left unconnected. We will use the right output of the RxC as is to give the reversing current for the rudder actuator, hooking it up as we did the original motors. We will also have to parallel the output transistors for the left motor reversing bridge, by jumping both bias resistors together (the ones marked 128) and both collectors of the NPN transistors together. The PNP transistors are removed from the board. Now V+ will be connected to the plus side of the motors (in parallel) and the other side of the motor will be connected to the collectors of the output transistors, turning on the motors when the transistors conduct. The UC will give the output transistors a pulse that varies in duty cycle from 0% to 100% resulting in speed control for the motors, the same way other ESCs work. This set-up has about a 20-step control range for speed. It also changes in response to the left stick by looking at pins 5 and 7 (pins 7 and 6 of the UC) of the RxC and changing the output pulse width in response to a "low" at either of these pins; increasing the width if RxC pin 5 goes low and decreasing the width if RxC pin 7 goes low. The UC also looks for RxC pins 4 and 5 but these are not connected to the UC pins 8 and 9 so right stick inputs have no effect on the motor speed.
As you know if you read the 1st article, turn control with this UC is done by varying the speed of both motors at the same time, one faster, the other slower. This is the reason we have to disconnect the right stick input from the UC, we don't want that input to vary the motor speed.
Still with me????
Another subject is increasing the current carrying capability of the TT Rx. This can be done by using the UC output to drive a MOSFET that can handle the current we want (in the tens of amps, if need be). MOSFETs have the characteristic of a very high input (gate) impedance (in the megohms, sometimes) that demands only a few ma of current to make them conduct, and a very low internal source to drain resistance ( in the 10ths of ohms). They do, however, need a gate voltage of at least 4 to 6 V. This rules out any battery pack of less than 4.8V, taking into account voltage losses and drops through the various components. Remember that each PN or NP transistor or diode junction will drop 0.6V, not to mention cold solder joints, small wire diameters and/or lengths, etc.. The UC can only source or sink 25ma, so keep this in mind when looking at the gate current requirements of the MOSFETs. Even though the MOSFET may be rated at 5 amp, you may not be able to use that much current if the power (Watt) rating will be exceeded at the voltage you are using.
International Rectifier has a HexFet in a TO-220AB package that is rated at 10amps with a 36 watt rating and 0.2ohms DS resistance. It may need a heat-sink at this power, though.
An alternative to the high current MOSFET is a parallel arrangement. Connecting two or more MOSFETs in parallel can give you all the current capacity you need, keeping in mind the total gate current needed.
One very important detail is the need for a diode rated at least 1amp across the motor terminals when using MOSFETs as switches. Connect the diode with the negative end to the positive side of the motor. (you can do the connections on the board) This shorts the back EMF (voltage) spike from the motor when the switch (MOSFET) is opened. Without the diode there is the real risk of destroying the MOSFET.
The other UC offered by Sergio that gives two servo-compatible outputs or the one that gives one speed control with a servo-compatible output use basically the same input-output terminals. The biggest difference is in the software used.
I made a basic diagram, traced from a scanned image of the board, of the pin, trace, and component locations that should make it easier to follow the text. The image is of the TRACE side of the board. The callout of the pin numbers will be correct, though.
To mount the UC I made a small (about 1/4 x 1/2 in.) PC board to mount the UC. Take your Dremel tool with a cut-off wheel and groove the board so you have 8 separate copper traces, 2 across the 1/2" side, and 4 across the 1/4" side. Mount this to the Rx board with double-sided tape. Solder all the connecting wires to the board and then the UC.
By the way, here's a shameless plug for Sergio's IR system: It works great!!!!!
Hopefully, other TT users have gained some understanding of this unique system from my dissertations. I can try to answer any other questions.
Contact me at wolfie(at)centuryinter.net
Once again Leone thanks for the effort in compiling this information and your willingness to share it with us.
Nicad alternatives part 1
From Eric Parsonage <ericpa(at)mpx.com.au>, (via the Slow Flight Mailing List) comes information on Nickel metal hydryde cells. Eric uses 7 x 550mah NiMH cells with a speed 300 drawing 6A that have lasted for over 100 flights.
He uses an ACE R/C Smart Charger" - it is a delta peak charger intended for nicads. He charges the 7 cell packs on the transmitter output which will do 4 to 8 cells. The charge rate is about 0.9A. They do get quite warm in the last couple of minutes charging and also if he flies full throttle for the whole flight, which is when the model is drawing 5A-6A.
The speed 300 powered plane is geared 4.2:1 - it will fly at full throttle for 5 1/2 minutes with the 7 x 550mah NiMH pack and produce around 300g of static thrust. That thrust is enough to climb vertically in the 280g model. Thanks Eric for that info.
In case any of you are wondering what the differences in charging are, I did a little research. Technically, NiMH cells should be charged at constant voltage and the charge terminated when the voltage "peak" levels off, BEFORE it starts to drop off. Nicads should be charged at constant current and disconnected when the voltage starts to drop after levelling off.
A quick email to David Lewis <dlewis(at)usginteriors.com> on his latest efforts with cells yielded the following:
From: David Lewis - dlewis(at)usginteriors.com
I have the NiMH batteries in stock, the same ones Bob Wilder used to set a world record:
1.2v 550mAh, 12g, US$3. Recharge just like NiCd. Made by GP Battery (Hong Kong)
Will be getting in lithium rechargeables in a few weeks - 3v 800mAh, 17g, US$12. Made by Tadiran (Israel). Will withstand approx 600 charging cycles. Walter Scholl has been testing these out and is pleased with performance. He also has 100 on order.
David then snail mailed me some more info on the Tadiran lithium cells (data sheets, etc) Ill save that for next month!?!
Surfers Succeed (catch a wave??) in Internet Land!!
Here is some of the latest electro-spondence I have received that I know will interest you. Remember to tell us what you have been up to (or what you would like to get up to - as long as it relates to modelling that is !?!?!).
Leon Wolfe, <wolfie(at)centuryinter.net> who wrote the Twin Turbo article, sent in some pictures and 'specs' of his friend Floyd Richard's latest indoor model.
From: Leon Wolfe - wolfie(at)centuryinter.net
Here are two pictures of Floyd's latest Indoor-proportional-RC plane.
The Specs are:
- wingspan: 45"
- chord: 10"
- weight: 10 oz.
- motor: RS cheap 3V. motor with 4/1 gearing swinging a 7X7" hand-carved prop
- radio: Cannon/ rudder/elevator/and jeti 05 ESC
Flight is stable, but a little fast. Floyd says the plane is going to get the lipo-suction treatment.
I've been working on a .25 powered auto-gyro, and haven't had the time to get my indoor rc stuff completed. I just took the autogyro out this morning for the maiden flight. I'm glad to report that all went well, after a little cartwheel on the first take-off attempt. No damage other than a scraped wingtip. Putting it away 'till the meet. (.25FSR;3-1/4#; 46"rotor)
Yes, I know its a horrible, smelly, oily 2 stroke powered flying machine, BUT it is different! has anybody made a SlowFly ELECTRIC or CO2 version of such a machine??
Talk to you later, Take Care. Leon.
From Eric Parsonage <ericpa(at)mpx.com.au>, a fellow antipodean aviator (antipodean? I thought you were from Australia! -ed), comes a challenge to all you indoor aces lurking out there in internet land. I spent quite a while talking to Eric on the telephone one Saturday afternoon about a lot of SlowFly stuff including indoor aerobatics, then found this posting on the SFML that night. My suggestions/comments come after Erics email
From: Eric Parsonage - ericpa(at)mpx.com.au
I am thinking of building a new slow fly model. My main interest is aerobatics indoors. So I have to be able to roll whatever I build. I have built a couple of models that I do fly indoors but are not really slow flying (The adrenaline really pumps when I do a roll)
So having gained that experience it is time to build a slower model that will roll and fly well inverted.
Anybody got any good ideas ?
My experience shows me that as soon as you stick ailerons on the back of a wing you need a stiff wing, a stiff trailing edge, and a stiff aileron all adding up to a heap of weight. My best attempt so far has given me a 1000mm x 300mm wing that with ailerons attached weighs 64g. (some people fly aircraft that weigh about this)
I have the idea that much of the weight associated with putting ailerons on a model could be lost if I used fully moving wing panels. Has anyone seen this done before ?
If I where to follow this line of thought then I could probably do without an elevator by using pitcheron mixing.
Please let me know your thoughts.
Regards Eric Parsonage
Briefly, our conversation went along the lines of utilising very broad ailerons (about 25% chord) and mixing them with the flap function ala control line stunt fashion (flaps go down when elevator goes up and vice versa). Also, I believe that mixing in about 2 3 degrees of flap for normal straight and level would allow a thinner symmetrical (bi-convex) profile to be used with good results. Model size would be about 600-800mm span, mass about 120g and "full house" controls.
What do the rest of you think??
From Alexander Van de Rostyne" <alex(at)staf.planetinternet.be> comes news on his newest Pixel
From: Alexander Van de Rostyne" - alex(at)staf.planetinternet.be
Wayne, For your info, I am now building Pixel IV (building is done, still need to mount the electronics though). I will get it airborne at around 70 grams (2.5 ounces). I do not know where I saved the 30 grams compared to Pixel II but substituting 'stuff' with air seems to work rather well. I did not fly it yet but I keep you updated.
How does he do it?? (maybe he's antipodean -ed)
Fixing the BEC jitters
Many of you have experienced or read about the apparent glitches (I hate using that word its been done to death in modelling magazines!?) some radios experience when using a BEC with several of the 9g servos (FMA-S80, GWS Naro, etc., etc.).
The problems arise when the servos momentarily draw more current than the BEC is able to deliver in a stable manner. Typically, maximum current draw happens when the servo first moves as it accelerates and overcomes its motor inertia and gear box drag. The voltage from the BEC drops and when you are using an FM Rx, this is BAD. Modern FM rxs, while great for interference rejection, are not tolerant of voltage fluctuations in their power supply. The result is the glitches or jitters. Interestingly (to me at least!!) is that the older style AM rxs are not as sensitive to the problem of power supply fluctuations.
The cure is relatively simple. Place a 4.7 ohm resistor in SERIES with the servo motor between the servo amplifier and the servo motor. This increases the motors resistance which reduces the current drawn as the servo operates. Theoretically there is a power reduction, but I have not noticed any in the slowfly applications I have utilised this modification in. The servo is VERY SLIGHTLY slower.
Two words of caution though.
- Such modifications will void any warranty on your servo.
- Dont attempt this if you are uncertain of your soldering skills or basic electronic knowledge. Enlist the aid of someone who is!!
I took some pictures of how I modified my servos and fitted the resistor into the small space available. Unfortunately, they were not back from the processors before the column deadline, so youll have to make do with this diagram and wait till next month for those pictures sorry!
This modification was suggested to me by Walter Scholl from WES Technics thanks Walter, it works!! I have now done four of my servos without any problems.
Next month how about a "Kolibri" update, with hints, tips and pics on how to build and fly one of these great little aeroplanes (OK Kolibri owners send me your pictures and details for inclusion); there will be part 2 of our "Nicad alternatives as well as more from around the Slowfly world.
OK its that time again. Take your time (have a month if you need it!?) digesting all this months good info, do what Andreas said - Fly slow and prosper! and Ill Seeya next month. Hoo roo from Down Under ...
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