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Today was a good day!

skeplin

Senior Member
#1
The rained cleared enough today to take my scratch build FTFlyer out for a maiden flight. Aside from a minor problem with the landing gear not clearing the prop, IT WORKED!


So now that I've had a flight that didn't end in bits of foam blowing across the field, it's time to adjustments. First and foremost, I had the rudder on the left with the throttle and on this particular airplane, I'm not sure I liked it there.

Second, I felt that the plane was very "touchy". There was a bit of wind (<5 mph) but it seemed that minor stick adjustments translated to major actions.

Question: Do I just set the dual rate to 40% or do I add some expo?

Advice is appreciated!
 
#2
Learning to fly rudder on the left stick is commonly suggested. I learned early with my Super Cub with the rudder on the right stick, and it has been tough to relearn muscle memory.

The large wing surface area makes the plane twitchy when faced by wind. You can soften this up by setting a softer dual rate (70% throw) and/or setting a deading of the expo (30%). Just be mindful, while softer controls help when you're into the wind; they give you less authority away from the wind. Find a combination that suits you.
 

FlyingMonkey

Stuck in Sunny FL
Staff member
Admin
#4
First and foremost, I had the rudder on the left with the throttle and on this particular airplane, I'm not sure I liked it there.

Advice is appreciated!

Keep the rudder on the right side, until you have ailerons. For now, with a 3 channel dihedral plane, the rudder is acting as ailerons. It creates more roll than yaw.

In a 4 channel plane, you use the rudder in cooperation with the ailerons. You rarely use it alone, except for when you're taxiing on the ground.
 

FlyingMonkey

Stuck in Sunny FL
Staff member
Admin
#5
Question: Do I just set the dual rate to 40% or do I add some expo?

Advice is appreciated!

You can set dual rates, and then you can switch between high and low rates.

Chances are you put the control rods as far to the outside of the servo arm as possible, and or you put them low on the control horn, this will give you the maximum throws. Which would give you a very sensitive feeling plane.
 

skeplin

Senior Member
#6
Thanks for the advice -- I just got back from taking it out a second time with some adjustments and it flew OK. Unfortunately the wind had picked up and it was harder to keep it under control. However, I still brought back a whole airplane so...WIN.

Now I need to buy some more batteries.
 

earthsciteach

Moderator
Moderator
#11
According to the HK site, looks like you can go with a 7x3.5 with a 3 cell battery and get 420 g of thrust. They don't rate the 8x4.3 for 3 cells, only two.
 

skeplin

Senior Member
#12
Can you elaborate on what that means? What happens if you run an 8x4.3 on 3 cells -- Is there a danger of burning up the motor? Where did you find that information?
 
#13
When you look at the page for the motors, there is the common specs of Watts, Amps, Weight, and Size. It lists a recommended max draw of 9 amps. Right below those specs is generally (but not always) test data of thrust with different props and voltages. Here is the test data for the 1600KV Park300:

Test Data:
7.4v - 8x4.3 prop - 8.5A - 355g Thrust
11.1v - 7x3.5 Prop - 7.2A - 420g Thrust

7.4v = 2 Cell (2 Series), 11.1v = 3 Cell (3 Series)

The 8x4.3 prop on a two cell is already tapping on the recommended max current draw for the motor; if you're running it on a three cell with the same prop, you're likely looking at 13.5 amps +/- 1 at full throttle. Certainly stress to the motor, but the small 500mah battery limits how long the motor runs for and limits how quickly it could "burn up."

From the test data you can see the 7x3.5" prop is comfortably under the current limit of the motor and still produces a good amount of thrust. Stepping down the one prop size will still give you plenty of power and potentially almost doubles your flight time with less draw on the small 500mah three cell.

The 30A ESC is also a bit over kill. Not that having too big of an ESC is a bad thing; but it might be something to keep in mind when you plan a second build. For example, get a 12A Plush ESC for this motor and 7x3.5" prop, then use the 30A ESC on a bigger plane that pulls more power and swings a bigger prop.
 

earthsciteach

Moderator
Moderator
#14
Mustang said it well. A bit of a rule of thumb for esc's is to size them based on about 125% of expected amp draw. For instance, if your motor is pulling 7.2 amps, then the esc would be 7.2 A x 1.25= 9 A. Just round up to the next largest esc.
 

Toddy

Junior Member
#16
I love dual rates. Like yourself I enjoy flying and bring the plane back in a semi fly able condition. Heheh. Like flyingmonkey said the rudder is best left where it is until you get ailerons, just set your rates back and put in lots of expo. I started back at fifty percent with 43% expo on one and 74 with 43% expo on the other just in case 50 wasn't enough. As I got use to the plane and my abilities grew so did my rates, it doesn't take too long before you find the sweet spot and then really start enjoying flying your plane.
 
#17
Mustang said it well. A bit of a rule of thumb for esc's is to size them based on about 125% of expected amp draw. For instance, if your motor is pulling 7.2 amps, then the esc would be 7.2 A x 1.25= 9 A. Just round up to the next largest esc.
Thanks, Teach :).

Mustang, earthsciteach, thanks for the explanation! That is a tremendous help. That would be a great Flitetest episode.
There was a video the guys did about two and a half years ago about using a watt meter. It shows how to read amp draw for a given motor and prop combination, which will help you to ensure you're running a good setup. Using published information will get you in the ball park when making the purchase, but doing your own measurements to ensure you're in spec will protect your "investments".


This video, from a year ago, also applies to the discussion at hand as well.


Glad I could help.