Take off problems

[Winco Steve]

Good afternoon all,

I'm having problems with my Seagull Fairchild on its first maiden flights. I wonder, can anyone advise?

On take off, as per, model wants to yaw to left. Apply right rudder (needs full ) to set in straight line. On take off and on release of rudder (to zero) plane yaws (quite rapidly) left and dives. After rapid trouser change and getting safety altitude, trims out to nice level flight. No problems until next take off, does the same thing.

1. Engine is OS 46, running well, no problems

2. Propeller was 11x6 but changed to 12x6, 12x7. Awaits result on that one.

3. Rudder and tail wheel all checked, correct and aligned.

4. Engine mounted correctly as per instructions. Slight offset to right. Sufficient?

5. C of G correct, checked on Great Planes machine, spot on.

6. Longtitude balance?

After various trims, adjustments etc have run out of ideas. Probably a real obvious remedy but escapes me for the moment!

Cheesr to all,

Winco Steve, sunny Spain, 28 degrees! Brilliant flying weather!

[paul d]

Not familiar with the model but a few things spring to mind, is it the recommended engine? are the flying surfaces all square?

you could try more side thrust and check the down thrust.

A finer pitch prop could help as well (12x4 or 13x4).

[Winco Steve]

Hi Paul,

Engine size is that recommend ,flying surfaces are all square but haven't tried a finer pitch propeller. What baffles me is that it flies really well without showing any signs of design, manufacture or engine problems.

I chose to go up in length size in relation to propeller size rather than to decrease in pitch.

I will see what my prop store holds.

Cheers,

Winco Steve

[john stones 1 - Moderator]

Flies o.k once settled down ?

Sounds like it's close to stalling when leaving the deck, you got a handful on the floor and pulling off early ?

[Winco Steve]

Hi John,

Flat out, plenty of speed most of long runway taken up. It does give the “appearance “ of a stall but it isn’t.
So, quite happy that’s not the problem with other nods from the ‘team’. Pity they can’t come up with the answer too!

Thanks,

Winco Steve

[john stones 1 - Moderator]

I'm sticking with the stall theory Steve, too much elevator or too early.

My turb used to do the same, once settled it was fine, pilot hadn't got the knack of his model.

Cured my problems by shallower climb out, and gentle elevator.

Hope you get sorted.

Edited By john stones 1 on 30/09/2019 13:43:49

[Winco Steve]

Just to add, perfect in flight and need to throttle down to half so it doesn’t race around,

Winco Steve

[Winco Steve]

Just to add, perfect in flight and need to throttle down to half so it doesn’t race around,

Winco Steve

[Winco Steve]

Hi John,

Could be that setting on elevator is a bit high although it’s as per instructions. I will decrease throw a bit. I’m using about 30% exponential. Admittedly, low rate, in comparison to that of ailerons, does appear a tad much.

Im a bit concerned that it exhibits such a strong ‘yaw’ to the left on take off. I know the torque is responsible but it’s quite significant.

Will try out next time,

 

Thanks , Winco Steve

Edited By Winco Steve on 30/09/2019 13:47:40

[Peter Christy]

I assume this is a tail-dragger? Are the main wheels turning freely and are they correctly aligned? Ideally they should have slight toe-in to help keep it straight on take-off, but parallel is OK. They should NOT have toe-out!

Does it run straight on the ground without the engine (gentle push)?

--

Pete

[flight1]

Check the main wheels are tracking true with a slight toe in, this will help keep a steady track on the ground and maybe need less rudder.

When you release rudder on take off does the left wing drop? because your description sounds like the left wing stalling so check the washout on the wings (release the rudder more slowly next time) also check your c of g as as very forward c of g will exacerbate the nose drop in stall stall.

Also are the ailerons in the neutral position when it is trimmed for level flight? and check the lateral balance of the model too

[Winco Steve]

Hi Peter,

Yes, tail dragger. Main wheels turn freely, and no toe out. As best I can test it is free running when not under power.

I could try toe in? Because of the field conditions I have had to put slightly larger wheels on ( not too much ) .

Flying conditions were excellent, with only very slight wind down runway.

Regards, Winco Steve

[Winco Steve]

Hi flight1,

I will adjust to toe in. Need to check other points you make. I’m happy with C of G as checked on machine ( not fat finger balance). I am releasing the rudder reasonably slowly but can adjust this.

Thanks for your suggestions,

Cheers, Winco Steve

P.S. How do I check wing washout?

[Simon Chaddock]

Winco Steve

"Sudden" release of the rudder is a concern.

You are applying right rudder (lots) to stop the yaw to the left which suggests the left wing for some reason has more drag and/or lift than the right. Could be several reasons for this.

So soon after lift off a sudden removal of rudder will cause the plane to quickly yaw left. This means that briefly the right wing speeds up and the left slows down hence a bank to the left but if the plane is already close to the stall the left wing, most likely the tip, can momentarily stall as well so creating even less lift and more drag resulting in the symptoms you describe.

At normal speed the flight the controls are well able to counter any inbuilt tendencies.

Sudden movements of any control anywhere near the stall can be dramatic and have unexpected results.

Some careful 'glide' stall tests would show if one wing (the left?) always dropped first.

I have a couple of planes that do this but otherwise fly well so forewarned I just take care near the stall.

[flight1]

P.S. How do I check wing washout?

do you have a wing incedence metere or can you borrow one from a mate? you need to check the wing tip trailing edge is up compaired to the root section basicly

here some links about it **LINK**

**LINK**

slso thread on here **LINK**

all good info

[Robin Colbourne]

Winco Steve, What happens if you loop the Fairchild dead into wind? If it winds out of the loop, the wing is likely to be the problem, and if it comes out off to one side of where it went in, then the rudder could be the problem.

When the Fairchild is sitting on the ground, measure the distance from the wingtip to the ground on each side. If one side is lower than the other, the model is already in a bank when its starts its take off roll.

The prop wash may be striking the left hand side of the fin. See here: Prop wash

Either adding more right offset on the engine, or accepting that you shouldn't use full power on take off may well be the solution. If it dives under power, but not when at idle or deadstick, then you may need some upthrust. At higher angles of attack when the wing is creating more drag, the need for upthrust would be more pronounced.

You can experiment with changing the thrust line by varied numbers of washers behind each corner of the engine mount and the firewall.

[Denis Watkins]

Winco, your prop is OK at 11 x 6, you say it is already ok in the air

If you need expo, then 10% is enough

Always use progressive throttle on take off

Up to half throttle then more if required as ground speed builds, let the wing lift it off

These models are very lightweight and will swing of you apply full chat right away

Edited By Denis Watkins on 30/09/2019 14:52:11

[Peter Miller]

You have not mentioned if the wings balance. You mention longitudinal balance but not lateral baalance. One wing much heavier that the other is never helpful

[Frank Skilbeck]

A clubmate built a Zero with a 35cc petrol engine and had a very experienced large model flier do the maiden flight, he noted that he had to hold in right rudder quite a while after take off. Once it had climbed and leveled off it flew lovely and was quite a pussycat to land, but needed right rudder applied during and the takeoff and climb out.

[Geoff S]

In the past I've had problems on take off caused by worn out tyres or those foam ones. This was on tarmac, I didn't try on grass. Onviously, as this is a new model the tyres/wheels are unworn but I'd try a different pair if you have them.

Peter Christie: Toe in or toe out - that is an interesting question. PDR (a very erudite conributor to the RCMF forum with a lot of full size design experience) always advocated toe out. His reasoning was that if a model veered (say) right on take-off, weight would transfer from the right wheel to the left. If there was toe-out then then the model would tend to move left and correct the deviation. Made sense to me.

Geoff

[Winco Steve]

Hi all,

Thanks to all for your comments, plenty for me to consider. I’ve been flying for about 15 years with various models and engine sizes but never experienced quite this problem. You never know everything!

Thanks again,

Winco Steve

[flight1]

One other thing I have seen a lot is that many never allow the tail to lift up and fly before lift off. Always holding up elevator until the plane yanks off the ground which can lead to problems like not reaching a safe airspeed before lift off and this is very much a bigger problem the more scale and heavier the plane is. mabe try this if you already don't

i think this will be a process of checking each thing off until sorted.

[Martin Harris - Moderator]

Any chance of posting a video?

[Jon H]

Posted by Frank Skilbeck on 30/09/2019 15:26:23:

A clubmate built a Zero with a 35cc petrol engine and had a very experienced large model flier do the maiden flight, he noted that he had to hold in right rudder quite a while after take off. Once it had climbed and leveled off it flew lovely and was quite a pussycat to land, but needed right rudder applied during and the takeoff and climb out.

My feeling is that Frank has nailed it.

If the rudder was keeping you in a straight line why let go of it? The sharp yaw left could easily change the lift situation from the wing and alter the trim. Its all to common for rudder neglect to set in as most only seem to use it on takeoff and once in the air they abandon it all together.

As in Frank's example i hold rudder on most of my models once in the air as they are still below their trimmed speed. All of my warbirds and other scale models need rudder held in on climbout after takeoff. I slowly let it off as the airspeed rises and im yawing in the direction of the control input. My sport models vary depending on wind conditions and that sort of thing.

By all means check the things everyone else has suggested, but my money is on a bit of torque swing rocking the apple cart.

[Winco Steve]

Hi,

Video, I’ll certainly try although I’m hoping for better things next time,!

I have run some checks as suggested. When pushed along ground, just about straight with a very slight turn to left. Such a small amount I can discount.

Wheels toe in v toe out? On the fence here, neither one nor the other.

One wing tip about 5 mm higher than the other ( left raised).

Everything else seems O.K.

Fin is vertical and in line. When trimmed for flight both ailerons equal.

Looking forward to next flight already!

Winco Steve