Aerodynamics help

[Nicholas Booth]

Hi all

 Those of you who have seen my posts in the past know I have built and converted a Top Flite DC3 to brushless electric motors. The problem is not the electrics but the aerodynamjics of the plane.

The first flight consisted of applying a large amount of throttle and the plane lifting of early down to what I believed a lot of wrong triming on the elevators. This caused a premature take off and an instant wing drop. I managed to correct this as it was about 20foot high using full rudder and a lot more power. I went on to fly the plane and trimmed it in the air so all was ok.

the second flight was yesterday, not so succesful, I decided to have a smoother transition through the throttle this time but at just under half throttle and a short run it lifted off very prematurely but this time was too low when it dropped a wing and caught its wing tip and nose on the ground cart wheeling down the runway. The damage was not too bad, with the nose being destroyed and a few cracks here and there.

For information, I applied up elevator at the start of the run until the tail lifted in the air and then converted this to as much down elevator as I could apply without catching the props on the grass runway. The tip stall is very vicious and quick when it happens and as it is a twin and was at low speed had lttle rudder authority.

I am not sure of all the options I can use and what affect they would have. and am looking for help.

I did not use flaps on take off as they seemed to have a nose up affect and I am not sure of how this would affect the take off at this time,

I have seperate aileron servos joined with a Y lead but could seperate them and lose the landing lights and maybe configure them to be both in the up position on the training switch ( would take some serious manual reading I think) that could maybe be released when enough speed is gained for take off.

Would flaps help or could they worsen the condition?

I was hoping for plane with great landing and take off ability here so did not really want to tear away at full speed but just over 1/3 throttle is tooooo low.

Any help please otherwise I may never try to fly it again and that would be a real shame.

TIA

Nick

[Former Member]

[This posting has been removed]

[Nicholas Booth]

The model has only got into the air once and to be honest flew very nicely, it was set up with the recomended throws and did not overly react on elevator or ailerons. When building the plane you build in all sorts of angles and all were checked and double checked to make sure they were correct.

The tail lifts off the ground very quickly and is the same in some of the videos I have seen on the internet of the plane crashing in pretty much the same way as mine. Once I have rebuilt the nose I will re-check the C of G but it was checked many times before taking it to the field.

With only split flaps under neath I fear that applying them may give it a nose up attitude but try to lift it off even earlier but my knowledge of this is not too good.

When I flew her thew first time she was happy at about 2/3 rd's throttle although a little fast for scale flying. I need to find a way of keeping her on the ground for longer to gain more speed before take off.

[Nicholas Booth]

The kit has about 6 degrees of down thrust built in so don't want to mess with that too much. I will rebuild the front and try moving the batteries forward a tad and check the C of G again.

Cheers guys

[Simon Chaddock]

I would agree with JETSOME. Up elevator until the tail lifted  is way too long. If the tail lifts with up elevator applied you must be at flying speed so as you are asking the plane to climb - it will try to.

Watch a full size tail dragger take off. Any up elevator is taken off pretty quickly so as flying speed is reached the elevator is more or less neutral and the plane just "flies off" the ground.

[Terry Whiting]

NIck,

Was washout recommended in the build? as the DC 3 has one hell of a taper if it's true scale . I personally think you tailplane (TP) incidence is OK. Too much TP leading negative incidence would put her nose up in flight, but would not let the TP rise as quick as you say on take off,

I would recheck the balance point and go for at 25% of the mean chord as a starter.

[Terry Whiting]

Hello Jetsome,

Sorry if I have stepped out of line, I stand corrected,  I assumed that placing my thread  'Hi you guys'  in  Newbie Threads was the only requirement. Unlike modelling, this PC caper is totally new to me.

[Terry Whiting]

I have now added details to my profile

[Terry Whiting]

Well Jetsome it's an own design based on a  three view line drawings by Richard Ferriere obtained through Google Image. My scale I based on Air Power 700 units which gave me a  finished nacelle diameter of 105mm. That then become the basis for  the scale.  

The fuselage was built as two half shells, using the horizontal datum line as the devider, this enabled me to fit out with close loop, or as the Aussees call it a  pull, pull system which I think describes  the system well. No bellcranks were used to opperate the elevator, as  the pull pull passed throught fine PTFE tubing, and up through the fin. .                                                                                                                                                          

Narcelles were also built as the fuselage,( forgot to mention, the fuselage  and narcelles are  planked) The wing is all sheeted with two spars running parallel  130mm apart, had two 3mm mortice boxes made between ribs where the narcelles  were to fit, Two tenoned formers were incorporated in the build of the top nacelle halves, these were halves were part built, glued in situe, then completed.

The tailplane was made 12mm lower than scale, this  little more root chord and 50mm greater span, this helped to increase total area .

Span 150cm...Fuz length 115cm...Nacelles 41cm   finished model less electrics  2lb 4oz.  

[Terry Whiting]

Building, kits, Models & Plans as suggested,,,,,,see you.