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Aug 19, 2004, 01:25 AM
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Derek_TX's Avatar
Quote:
Originally Posted by Trikster
Its definately the ESC causing the surgeing. I have tried different Rx's, different radios (+/- shift as well)... I am wondering more and more if the switching frequency really isn't high enough for two larger motors.

Put flights 10 - 13 on 'er tonight. Have been trying different mixing and still think all that is needed is about 20% A/R mix.

You may have hit on a key clue: what if the two motors are creating a small beat effect due to superposition of the demand on the esc by two devices?

You should be able to find a similar pattern with more than 2 motors, with a different beat rate.

Just a late night guess after thinking about the switching frequencies as periodic phenomena.
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Aug 19, 2004, 02:28 AM
Always right
Hovertime's Avatar
Trickster-what happens when you reach LVC?
Your symptoms sounds like soft LVC cutoff, when its reached ESC reduces power, and amp draw by pulsing throttle, to keep voltage from going below programed LVC.
Your batteries may be bad...
Aug 19, 2004, 10:36 AM
Zoom, zoom...
Trikster's Avatar
I think I have hard cutoff set right now. The motors have pulsed with the LVC set to soft, hard and off. I have only flown down to LVC once and all it did was slowly cut power until the motors no longer spun. I usually fly 2 10 minute flights per charge with a rest period in between. On my TP 2100s, I usually put back in about 1200-1500 mAh of juice. My packs are new (I have two of them bought at different places) and charged on an AF 109. They hold voltage well (Gen 2 packs) and rarely get much hotter than ambient temp. I have tried other packs as well as hooking up my power supply to the ESC. One thing I did notice is that when I lost a prop in flight, I no longer heard the pulsing. I am thinking its because one motor no longer has any load on it and can sync up a little better with the other one. I am thinking about putting a schotkey diode across the terminals to see if that helps. I used to in my old R/C Cars.
Aug 20, 2004, 10:12 PM
Always right
Hovertime's Avatar
Maiden flight report:
Flew it first time today, using 6 cell AA 1400mah CBP pack.
CG was set at 55mm, (factory recommended 50-55mm) First thing it did-nosed over on taxi Thats because when using recommended CG it is right behind the landing gear.
Anyways-next liftoff was batter-held the elevator up until it accelerated. Lifted off at half power.
Flew excellent without rudder servo, so this answers my question finally

Could not trim it as I like-I usually trim for power off glide, but my C-47 wanted to dive... all was good for medium power , at full power it would go in a stall, if not corrected. This also tells me that recommended CG is wrong...

Flew for a while-flies very fast, possibly due to heavy batteries.
Made 3 more underhand running lunches, on the last one noticed reduced power, made a circle, aborted landing, another circle , got nervous, and while i tried to turn to land against the wind it nosed in , elevator did not help, was flying too slow, there was not enough power

So latest tips are-
2 servos as aileron/elevator works very good, no need for rudder

Don't know why, but recommended CG is wrong. Although it looks like it should be right-CG is usually located just behind the highest point on the wing??? Design mistake? I'll need to find CG that will make a nice glide with centered elevator power off.

Looks like LIPO is the way to go for this airplane, with AAA's-batteries are way overstressed and flight time is short, while AA makes it very fast airplane due to high wing loading.
If I will be using AA, I'll need to add some weight to the tail, especially after repairs
Aug 20, 2004, 11:12 PM
Zoom, zoom...
Trikster's Avatar
A CG of around 68-75mm from the LE of the center section of the wing seems to be just the ticket. With the layout of my radio gear, I was able to use the stock location for the 2s 2100 without having to shift anything and add weight.
Aug 20, 2004, 11:15 PM
Zoom, zoom...
Trikster's Avatar
Also, adding rudder makes your turns nice and flat. I did try and see if the DC-3 could fly as a rudder/elevator plane... It can, but it isn't pretty.
Nov 29, 2004, 08:26 PM
Always right
Hovertime's Avatar
Well my poor C-47 is still sitting on the bench after that minor incident, everything is glued back together thought...
I need to find some light spackle and fill up the holes that foam safe CA ate in it! (funny but it worked good on a few seams and few-not so good, go figure.)

Now that anticipation is over and C-47 is released a while ago, and real world use experience is known, sadly it looks like GWS C-47 did not turn out a very popular airplane...

I still question the need for rudder of most GWS airplanes (apart than selling more servos )-look at the Alpha models, they are much higher quality, and see no need for rudder for their war-birds?
Nov 29, 2004, 08:56 PM
Registered User
Hovertime, the CofG is 70mm from the LE centre for my DC3 which seems to be the best compromise. with the CofG at this setting and low speeds require flat turns or tip stall results.

Full throttle on takeoff or touch and go does not need much elevator or the nose goes up and you will have a vertical climb to a stall, this could possibly be eliminated I believe with application of motor down thrust, unfortunately this needs the motor mounting sticks to be totally reset, a bit hard after initial build.

Flies at half throttle with a 2S polyquest PQ-2600 with an endurance between 20- 30 min depending on your throttle management.

Rudder is nice to have with a 25% A>R mix, stops the tail from hanging out on a turn.

Weight is not a big concern (mine 595 grams) just makes the landings a bit faster.
Nov 30, 2004, 12:57 AM
Go FASST or go home...
Ben_E's Avatar
Quote:
Originally Posted by Hovertime
I still question the need for rudder of most GWS airplanes (apart than selling more servos )-look at the Alpha models, they are much higher quality, and see no need for rudder for their war-birds?
Turning the c-47 without rudders is no problem - but if you are going to make nice scale like turns you need rudder input during the turn. Too many actually don't know how to fly with both tumbs Coordinated turns (rudder/ailerons) looks so much better!!

And for the warbirds that's supposed to be aerobatic (at least with a motor upgrade) needs rudder to do ie. stallturns etc!

Ben_E
Nov 30, 2004, 01:21 AM
Always right
Hovertime's Avatar
Quote:
Originally Posted by Ben_E
And for the warbirds that's supposed to be aerobatic (at least with a motor upgrade) needs rudder to do ie. stallturns etc!
Ah, that explains it. There are airplanes more suited for that sort of flying though.
Well, I guess "Whatever makes you happy ".
Nov 30, 2004, 02:09 AM
Registered User
Hovertime, the Alfa models may come without a rudder as standard but the FW180 I have came with the parts to convert to an operating rudder. After flying heli's for many years I now find I constantly use rudder when flying fixed wing, even when there isn't one there!
Nov 30, 2004, 06:19 PM
Registered User
kensp's Avatar
Quote:
Originally Posted by Hovertime
Could not trim it as I like-I usually trim for power off glide, but my C-47 wanted to dive... all was good for medium power , at full power it would go in a stall, if not corrected. This also tells me that recommended CG is wrong...

Don't know why, but recommended CG is wrong. Although it looks like it should be right-CG is usually located just behind the highest point on the wing??? Design mistake? I'll need to find CG that will make a nice glide with centered elevator power off.
The position of the CG on the C47 is complicated by the fact that the outer wing panels on the GWS model are tapered and have 11 degrees of sweep back, so the CG has to be further back than the high point at the center of the wing.

Ken
Nov 30, 2004, 06:38 PM
Always right
Hovertime's Avatar
Thats it!
How stupid of me-never thought of that!
Well, I was gonna find the perfect CG during flight tests anyway, but never got to it as my poor C-47 flew only for one charge
Getting CG perfect is also a bit complicated by its battery tray position, I like Cargo trans for its battery tray position-right under CG.....
Nov 30, 2004, 07:11 PM
Registered User
kensp's Avatar
Quote:
Originally Posted by Hovertime
Thats it!
How stupid of me-never thought of that!
Well, I was gonna find the perfect CG during flight tests anyway, but never got to it as my poor C-47 flew only for one charge
Getting CG perfect is also a bit complicated by its battery tray position, I like Cargo trans for its battery tray position-right under CG.....
My preliminary balancing before gluing the C47 has established that the battery needs to be in the nose or 3+ oz of lead would need to be carried to achieve correct CG.

I plan to use two AC World CD-Rom motors and APC 5.1x4.5 inch props. I have test run these on one Castle Creations Phoenix 10 Controller. See attached photo. The CD-ROM motors only draw a total of 5.2 Amps, on two cell LiPo, at full throttle but will give a top speed of 33 MPH which is 2 1/2 times stall speed.

The estimated total weight is 14 oz, plus any lead needed to achieve the correct CG. With a 1600 mAh 2S1P lithium pack I expect to have 19minutes of full throttle flying.

I have also reduced the size of the elevator to scale. I was going to reduce the ailerons size to scale but this would have required a new grouve cut in the wing so I comromiset and made the ailerons almost scale span and the GWS cord size. After reading of PC47 type manouverability and power I decided to make the C47 so that it will fly more scale like. I have made a CF elevator joiner and plan to make CF aileron torque rods.

The last photo shows my planned colour scheme

Kem
Last edited by kensp; Nov 30, 2004 at 07:35 PM.
Nov 30, 2004, 08:09 PM
MINE!
Mick Molloy's Avatar
Nice work Ken
Did i send my cad drawings for the adru stuf ??? i forgot.
I have attached what I had on my pc at work plus a little excel thing i started doing, its a bit rough....

How did you go about running the 2 cdroms of the one controller any mods or changes required to make it run ??

Do you think the size and aerofoil on the tail affect the C of G, I think it moves it aft be lifting the rear end in flight.


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