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Old Sep 09, 2009, 06:38 PM
waynemia is offline
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A trail of smoke is GOOD!
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USA, TX, Springtown
Joined May 2008
7,233 Posts
Prop Load Factors,Servo convert from Metric to Oz/In,convert deflections,ST, CA Hinge

These spreadsheets help select props and convert the servo data from metric to oz/in. There is a table to convert deflection angles and a table for mixing fuels.

OK - some explanation stuff -

Prop Load factors: I got the formula from a book by Gerry Yarrish, "Getting Started in Radio Control Airplanes". Chapter 13 has about 12 pages on props. I just entered the formula into a spreadsheet so I could have reference values. The unit of measure is just PLF, Prop Load Factor.

The formula is PLF = D^2 * P where D is diameter and P is pitch.

Example: The manufacturer recommended prop is 13x6. This has a PLF of 1014. You try it and the engine is running great. and turning 11,000 rpm. Now you decide you want a little more speed. So you need to increase the pitch. You look at the table and 12 x7 plf is 1008, 11x9 is 1089, and 11x8 is 968. All three of these props should give you about the same load on the engine but they will give you different performance.

This at least gives you a good starting point for selecting a prop.

One of the things I found was my Saito 1.25 was the Horizon page says the prop range is 15x7 to 17x6. The problem with this is that there are props in this range which under prop the engine and cause it to over rev.

The manual gives:
15x6 to 15x8 1350 to 1800 Sport
16x6 to 16x8 1535 to 2048 Scale
17x6 1734 Aerobatic

Ok the engine likes 1800 to 2048 loads. I was using a 16x4 on it which is 1024. This was over revving my engine at WOT. It was in the "range" of 15x7 to 17x6 but this does not work. I could have continued to run the 16x4 but would need to manage the throttle or reduce the end point to keep the RPMs down.

Since then, I look at the manufactuer recommendations for more specific prop ranges. Once you know the PLF range, you can play with props within that range without getting into a lot of trouble.

The servo stuff is just converting Kg to Oz. I am not good at metric measures.

You can quickly go from Kg to Oz by multiplying the Kg value by 13.89.

There you go.
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Tuning Super Tigres

My ST is running the stock muffler. On the test stand, it would run with the pressure tube off. I was really surprised since there is all the emphasis on pressure. If you run a Pitts you just close off one of the pipes. I also did not see a big deal with tank position on my test stand. I moved it around a bit while trying to tune the carb.

I have the ST mainly to save some cost and on his recommendation. I was not able to get it to run right until I followed these steps after burning about 3 tanks at about 3,000 RPM:

1. Start the engine and set if for high RPM minus about 300rpm.
2. Put a piece of fuel tubing on the carb and the carb just closed, close off the low idle screw while blowing in the tube until no air was escaping.
3. Restart the engine and it should run pretty well.
4. Adjust the high speed needle again.
5. Now adjust the low speed again. ONLY TURN THE LOW SPEED NEEDLE HALF THE WIDTH OF THE SCREWDRIVER AT A TIME!!! This needle setting is extremely sensitive.
6. Continue adjusting the high speed and the low speed until you get it they way you want it.
7. If you continue to have problems with the mid-range, you can try rotating the spray bar. There is a small screw that holds the spray bar in place. It should face straight down the carb barrel if you look in from the bottom. I did rotate mine but ended up putting back to center.

After I discovered this technique, it tuned up pretty quickly. I was ready to send it in to service! And the low speed sensitivity is a big key. You can't just give it a spin like you can an OS engine. Also, if you change the high speed setting, expect to need to adjust the low speed. This is the same information I received from other ST owners.

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CA, Hinging

Stick stuff here! :P

Here is a link on CAs including Insta-flex

A link on installing CA hinges

Robart page on glues. Notice the ZAP Hinge Glue. This is also known as Pacers. This is water based for easy cleanup.

Uhu Por for Styrofoam

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Battery Help

Need help on batteries?

Check out this website:

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Rule of thumb, get OS plugs.

Type F for ANY 4 stk
#6 (A3) for .10 to .60 -- standard plug for the OS 46AX
#7 a little hotter than the #8, I plan to try these
#8 works for nearly anything, I use this on all my 2stk engines except the 46s.
#10 (A5) plug for .60 and up, classified as cold. I plan to try these.

Glow starters -- battery powered

They have NiCd or NiMH batteries in them. They come with 10 hour wall wart chargers. Some have removeable batteries. These are best since you can replace the batter a little cheaper than buying a new one (most of the time). You can usually find them cheap at the swapmeets but don't expect the batteries to be any good. If it is a NiCd, put them on a cycler for 3 or four charges, they may come up to full capacity.

I carry two to the field to be sure.

Some have meters. This is good because they are an indication the glow plug is working - not foolproog though. It is based on current in the plug. If the plug has all the platinum burned off, it still won't work.

Some have a long reach which is nice for some cowl mounted engines.

Two basic types, one you pull a sleeve back and the other is a press and twist. I have had the first one fail after about a year of use. It can't hold the plug any more. I have never had a press and twist fail but it is sometimes a bit testy getting it on the plug.

There are also plug ignitors with a cord to connect to a field box and power panels that allow you to adjust the current flow. I don't use the corded ones. I am afraid they will get tangled in the prop. I don't care for the current adjust models. Just apply 1.2V and go.

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Multiblade Props

Here is Zinger's take on it and a nice table:

Here is Master Airscrew:

To convert from 2 blades to 3 blades you want to decrease the
total blade area and increase the angle of attack (or pitch) to
overcome the increased drag of the third blade.
The general rule is to DECREASE propeller diameter by 1-2”,
and INCREASE by 1-2” the propeller pitch. It is all right to keep
the same pitch when going from 2 blades to 3.

Set the Date on a Keychain Cam

Go to this post
All things keychain cam:


RealFlight Sim Twists

RealFlight downloads

Another TT40
TT60 (low ratings)


Regulators - Warning Technobabble

All switching regulators generate noise, they have to by design. The issue is does the noise get out. This requires shielding and filtering. High-end (usually means expensive) may do a better job than a super cheapie. The efficiency of a switching regulator is usually reasonably high. This just means more of the power in goes to the power out, but not all of it. Everything uses something so nothing is FREE.

Linear regulators have to waste voltage to get to the regulated voltage. The more current you pull in the regulator the more power must be wasted (P=IxE). The power is dissipated through a heatsink. The more power, the more dissipation, the bigger theheat sink. Look at an older power supply and you will see one or more transformers mounted on a big heatsink. These are the pass transistors at the output.

Nearly all modern receivers and servos will run on 4 to 6V. That is why you can use a 4cell or 5cell Nicad/NIMH or 2cell A123 battery pack. This means you only need a battery pack and a switch - simple.

Components can fail. In our sport, our equipment is exposed to a lot of vibration. This makes the chances of failure on a wire connection or circuit board component greater.

We are seeing the newest receivers and servos comeout that can accept 7.2V. This opens the door to Lipos without regulators.

A lot of this is personal preference when you make the final decision. I look at cost. I can put a Nimh in for $25. Can I put in an equivalent lipo and reg for the same price?

A redundant system has nothing to do with battery choice, you just have to use two of what ever you choose. (Note that you need something that will control current from the two power systems.)

Pick your poison and have fun. I like to keep it simple. I only use Lipo kind of batteries (including A123) when I have to have the high currents that only they can provide, I.E., electric motors.

One more thing, I would NEVER use a regulator on my ignition. JMHO

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Servo Reversing

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When you use one servo for the elevator, the elevator halves must be connected together and driven on one side. This is OK when the elevators are relatively small.

When the plane gets larger and you want to do more agressive maneuvers, you need both elevator halves to be equally responsive. The tortion bar that connects the two elevator halves, like on the Twists, would have to be very strong and creates a situation where the non-driven half can lag behing the driven half as the tortion bar twists. The distance from the driving servo also amplifies the load.

You can't just use a Y connector like you do on the ailerons. On the ailerons the servos move in the same direction. This is what you want since you want one side to go up when the other goes down. Elevators must both go up or down at the same time.

The Flaperon settings on radios allow the transmitter to reverse one servo to make the ailerons both go the same direction, up and down, so you can simulate flaps or add reflex. The 9C and other transmitters have a function similar to flaperons to allow you to have two servos on the elevator and reverses one of them. Futaba calls this Ailevator.

If you don't have the feature in your transmitter, you can use an electronic device that goes in-line with one of the servos, usually the left one, to reverse the signal. You use a Y connector on the two servos and put the reverser between the Y and the servo you want to reverse.

This also means that you can use lower torque, less expensive servos on the elevator halfs.

There are some ways you can do to avoid this without reversing one servo but the ARF makers assume you will reverse one of the servos when they design the planes. Example: On the ailerons on your wing, assume that both servo arms point to the wing tip. If you just reverse the servo arm on one side so it is pointing to the fuse. The arm is now pulling when it was pushing before you changed it. Now the ailerons will both go in the same direction.

The two servo elevators mount the servo in the tail. One technique is to have room to mount the servos so one arm goes up and the other goes down. You have to get all the symetry correct of course. Apparently, conventional wisdom is just reverse one side.

With two elevator servos, you can also program some kewl stuff like making the elevators work as ailerons. This can give you some additional roll when both the ailerons and the elevators can roll the plane!

Gas:Oil Ratios

Gas Fuel mixtures by ratio

Gal = 128.0

Ratio (Gas:Oil) Oil (oz)
20:1 6.1
25:1 4.9
30:1 4.1
35:1 3.6
40:1 3.1
45:1 2.8
50:1 2.5
60:1 2.1
70:1 1.8
80:1 1.6
90:1 1.4
100:1 1.3

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Last edited by waynemia; Aug 17, 2010 at 08:38 PM.
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