Black Horse Pc-9 lost on take off

[MThemadhatter]

Hi guys, has anyone had their hands on the new 60 size Pc-9 from blackhorse ??

I ask as I have just lost mine on take off on its maiden flight and
was wondering if anyone else had an issue with this particular kit ?

Unfortunately we did not video the take off but this is what the bystanders. spotter and my self observed.

 

Take off run was good and the plane tracked straight with a tiny correction on rudder from me, at about 3/4 of the way across the patch ( about 100ft ) and at a good speed I started to rotate. Immediately the plane started to roll to the left and continued as the wheels came off the ground and it started to climb. I put in opposite aileron but the roll continued until i was inverted and nosed down and hit the ground.

 

All the controls were checked multiple times before and everything was moving in the right direction. The control throws where set as per manual, C of G at 70mm as stated in the manual.

 

One thing we all agree on is that it was going fast enough as I rotated. We then checked the ailerons again as it was suggested they could be reversed but they where not.

 

Now I am at total loss with this one, it felt to me that I had no aileron control ??

[winchweight]

Really sounds like a stall on take off. Identical to my leccy Seagull Sea Fury, also lost on its maiden.

[MThemadhatter]

I would agree but it started to roll the moment the nose gear came off the deck, plus it was as described by onlookers "honking along" and I have stalled a plane on take off before and it did not feel like that, and it was a gentle rotation rather than yanking it into the air.

 

If it had been me I would be more ok with it but at the moment I am mystified along with everyone else which is not a good feeling.

[Tony Bennett]

one of mine would stall and do the same on nearly every take off if i didn't have enough speed.

 

was one wing heavier than the other.

[Wingman]

Certainly sounds like a tip-stall caused by the drag of the down-going aileron and some adverse yaw hence no apparent aileron control.

[Biggles' Elder Brother - Moderator]

Was everything connected when you found the model? I ask because we had a similar incident at our club a while back. The concusion was that the battery had come disconnected whilst being "jiggled about" on the take-off run. Could that be the cause? You can never be sure of course because it could come disconnected in the imapct.

 

Did you have control of any other fuction right before impact; throttle, elevator, rudder? If not any it could be loss of power to Rx.

 

Was the Rx new? Was it rigourously range checked?

 

One that happens occassionally on our patch is dandilions catching in control services and preventing them from returning to neutral!

 

With it being a maiden some sort of new system failure has to be suspected, or a connector not quite fully pushed home?

 

BEB

 

PS Whats the damage? Totaled? Or repairable?

[MThemadhatter]

It had a redundant switch and battery set up, ie two of each, and where connected and still working afterwards.

 

Impossible to tell if anything had come unplugged as the wing came off the airframe, however I did a control movement and sense check before take off. We plugged it all back in afterwards to make sure I had ltagged the aileron servos correctly

 

Range check was done and I was almost into another field (Aurora 9) I also used the "test" function on the TX to run all the servos for a good 5 mins continuously on the bench to make sure all was ok.

 

It is repairable , but if it did tip stall then I would say it is un-flyable with the recommended 90FS, as it was going about as fast as it was going to get. In my experience and in the eyes of those watching it had all the air speed it needed to take off and some. It just kept rolling over even with full opposite aileron, and it was a constant rather than sudden roll movement from the moment the nose lifted off the ground rather than the nose lifting to high and then it snapping over.

 

Here is before and after. The damage is to the centre leading edge of the wing, and the formers and tail sections wich is split along the opposite side in the photo.

 

[Biggles' Elder Brother - Moderator]

That wing isn't that liable to tip stalling. Assuming you're right and the speed was up and the nose was not too high I find it very hard to see this as a tip stall.

 

At least it looks well repairable.

 

BEB

 

PS Which way did it roll? To the left? Could it be a massive torque reaction? But then why did opposite aileron have no effect? I know - I'm clutching at straws!

[Wingman]

Presumably the wing was true - no twist causing wash-in on the left wing?

[MThemadhatter]

Roll was to the left, and that was something discussed at the field, ie whether it had enough side thrust.

 

I had a good look at it now and the tail section is a mess internally. The tail section has split and peeled open like an ice cream cone with most of the stringers and formers damaged. The wing mounting plate came off with the wing and the wing seat formers are pulverised as well.

 

The wing looks true, but I need to get an incidence metre on to check. One suggestion was that the wing mounting plate had come loose during the take off run this might account for the wayward behaviour. No way to tell though

 

As it stands if this was a tip stall then the flying characteristics of this model are just plain nasty, which would surprise me for a BH models plane. Any faster on the take off run and you would be doing damage to the retracts. FYI dry weight was 8.8lbs exactly as stated on the box.

Edited By MThemadhatter on 19/08/2011 17:39:48

[Martin Bowman 1]

I had a similar problem on mine powered by an OS65AX, roll to left on take off fortunately into a corn field with no damage. Post incident assessment was insuffcient speed on rotation even though i was fairly sure the speed was sufficient .

 

Second attempt more speed and flat climb out with no problem. The model flies well with no tendancy to tip stall and landings with full flap are smooth & stable .

 

The nose gear is unfortunately complete rubbish as you will no doubt find out after a few landings, i spend more time modifying the gear than flying the model and in reality it needs changing for a Robart or something similar.

 

Good luck with the re-build

[James40]

Were you holding in rudder to keep the model tracking straight on the ground as you rotated?

[Gary Binnie]

I'll have a stab!!

 

The grass in the 'before' picture looks quite long (up to the wheel axles), is the runway like this?

 

Sounds like propeller effects at low speed.

 

The spiral slipstream hits the left side of the fin/rudder and will make it yaw left

 

On rotation the downgoing propeller blade (on the right) has a greater angle of attack than the upgoing blade, more thrust is being produced on the right which will make it yaw left. It's known as the 'P effect'.

 

Torque reaction will make it roll left and if the mainwheels are still on the ground it causes extra pressure on the left wheel and more drag (causing a yaw to the left).

 

Any yawing will turn into a roll in the same direction as the advancing wing has more airspeed (more lift).

 

Another effect present is gyroscopic precession but that is working the opposite way on rotation on this model.

 

It's quite common for high-powered electric models to roll left from a hand launch, I have to launch my Alfa Spitfire on low throttle and then feed it in as it picks up airspeed.

 

Everyone seems to say that it was moving fast enough at rotation but perhaps it wasn't quite. I don't think it stalled, just not enough airspeed for the stability of the fin and dihedral to kick in.

 

Hope you get it fixed and flying.

 

Cheers

 

Gary

 

 

 

[MThemadhatter]

Posted by Martin Bowman 1 on 22/08/2011 13:53:35:

I had a similar problem on mine powered by an OS65AX, roll to left on take off fortunately into a corn field with no damage. Post incident assessment was insuffcient speed on rotation even though i was fairly sure the speed was sufficient .

 

Second attempt more speed and flat climb out with no problem. The model flies well with no tendancy to tip stall and landings with full flap are smooth & stable .

 

The nose gear is unfortunately complete rubbish as you will no doubt find out after a few landings, i spend more time modifying the gear than flying the model and in reality it needs changing for a Robart or something similar.

 

Good luck with the re-build

Sounds the same as mine , so maybe I needed even more speed on take off, difficult to do on grass. I had ditched the shocking retracts the kit came with, and put some eflite 60-120 size retracts in. Just need to decide if this is a practical model for my patch. No harm in trying to fix it though.

 

I had used right rudder at the start of take off run but not at rotation.

[Biggles' Elder Brother - Moderator]

P-Effect? An interesting theory and well anything is possible - and yes it might lead to an initial roll to the left. But I'd be very surprised if it would be strong enough to continue to do this against the correcting aileron input?

 

BEB

[Gary Binnie]

P effect is just one of three effects happening to make it roll/yaw to the left, all the effects are more pronounced at high power and combined may well be not helping.

 

All conjecture and very difficult to analyse without being there.

 

If the ailerons were working correctly and the model was not responding it could not have had enough airspeed (or the ailerons are too small!). If it was not flying fast enough and was near a stalling angle of attack adding right aileron to correct the roll would actually make it roll further to the left by stalling the left wing. That's how I enter a spin in the Tiger Moth, slow down at one knot per second with the wings level to maintain a normal attitude, add rudder then opposite aileron.

 

The angle of attack is measured using the mean chord line (leading edge to aileron trailing edge), when an aileron is moved down (or up!) the angle of attack changes. If we are sitting at 14 degrees (typical stalling angle of attack) with the wings level and move the stick left or right we might have 13 degrees on one side (not stalled) and 15 degrees on the other (stalled). The stalled wing (and the unstalled wing on the other side) causes a roll and the aircraft will also yaw to that side because of the increased drag.

 

The PC-9 looks a fairly scale design with relatively small tail surfaces and a high wing loading, a real shame it has crunched on the first flight.

 

GB

Edited By Gary Binnie on 23/08/2011 00:02:25

[Ian Jones]

Could be P effect etc mentioned above and/or insufficient airspeed.

 

Take a look at the PC9A, PC9M and Beechcraft T-6 Texan II - all have different dorsal fins, the PC9M being the most obvious which amongst other things has an enlarged dorsal fin in order to improve longitudinal stability.

So depending on scale characteristics it may well be that there is a point where where the roll can be difficult to control. Not noticed it with my 71" Seagull PC9A though.

Edited By Ian Jones on 23/08/2011 02:33:35

[Tom Wright 2]

I do think Garry's theory could be the answer .I have observed the same effect when a model with minimal fin area is flown at high alpha and high power the result is a sudden loss of directional stability ,which when near the ground is uncontrollable .

In take off rotation situations the effect can be aggravated by the unequal loads on the u/c and even a small unfavorable cross wind components .

More speed and a gentle transition may keep the problem from occurring but if our theories are correct its likely the effect will jump out and bite again .

Interestingly my smaller PC9 is devoid of all bad habits ,unless the c/g is to far back then it gets very interesting indeed .

 

 

[Tim Mackey]

Posted by Ian Jones on 23/08/2011 02:25:58:

Could be P effect etc mentioned above and/or insufficient airspeed.

 

Take a look at the PC9A, PC9M and Beechcraft T-6 Texan II - all have different dorsal fins, the PC9M being the most obvious which amongst other things has an enlarged dorsal fin in order to improve longitudinal stability.

So depending on scale characteristics it may well be that there is a point where where the roll can be difficult to control. Not noticed it with my 71" Seagull PC9A though.

Edited By Ian Jones on 23/08/2011 02:33:35

 

Me Neither, and it has very little sidethrust incidentally. I know we are discussing the black horse PC9, but by default, they do look very very similar models to the Seagull.

[John Muir]

Can't resist a bit of postulation.

The description of what happened does not sound to me like a stall. It sounds like the model started to roll left on take off due to torque and propwash effects, which we would normally correct for with right aileron (rightly or wrongly, probably should be right rudder). The correcting right aileron command was given, but nothing happened. Ergo, the ailerons did not work properly.

I can think of three reasons:

The ailerons are not big enough or have insuffiicient movement - unlikely as this is a model that's been sold for a while and these are flaws which could have been corrected.

Airspeed was too low for the ailerons to have enough effect. Possible, but doesn't seem likely as the plane obviously had flying speed to get off the ground and once off the grass, would accelerate (unless the pull up was pretty steep, in which case I think you'd get a snappy stall).

One or both aileron connectors jiggled loose on the take off run. As both had obviously pulled loose in the crash, there's no way to be sure, but my money would be on this. Or an intermittent connection in an extension lead. I reckon one aileron not working would have been enough to cause the problem.

[Craig Spence]

Interesting problem, I think the P-effect is very interesting.
It was mentioned about the wing being true wasn't it?, I would make sure that it is.
I'm assuming that the wing you have comes in two halts and is then epoxied/ fixed into position. One of those wing halfs could be slightly warped and you would never see it unless you really scrutinise it.

I would defiantly think that could possibly be a problem.
Also take of speed on this model and climb, I have got the seagull PC9 and that likes to take most of my patch to take off, and when it does it tends to take up at a nose high angle to such an effect I have to sometimes keep in down elevator.

On stalling mine on a test it dropes the left wing and looses hieght rapidly, recoverable but not at a lower height plus.
I think, unfortunately this is another big factor, the flight characteristic of mine was to get sucked off the ground violently sometimes and go for a high angle climb, stall country.
I'm not sure if the model you have carries the same traits.


Hope it fixes up ok.

[Braddock, VC]

Did you use the flapperon function? Is it possible you connected the the wings to the wrong channels? As you said the wing came off you'd have had no way of checking this post crash.

The only reason I say this is that it the original post cried out aileron reversal. I mean if it's a stall the ailerons won't work will they?

 

Black Horse models are some of the better artfs, and I'd resist the temptation to blame the model until all avenues are explored.

 

Same thing happened to me on an arc cessna, though I managed to bung in opposite aileron then landed it rudder only which was difficult.

 

Edited By John Gibbs on 23/08/2011 11:25:22

[Martin Bowman 1]

The wing actually comes as a centre section & two outer panels which have predrilled dowel locators and an aluminium tube wing spar , Iagree with Craig's post in that at rotation the model does leap in the air and a dab of down elevator is needed to check the climb angle.

My current mod is to introduce packers between the nose gear & mount to give a slightly more positive angle of attack when on the ground ( cannot fit a bigger wheel due to clearance issues)

[Stephen Grigg]

Ive read this post with interest but am not sufficiently experienced to make any sort of comment.Im just into flying a Seagull Zlin 50 and have had problems learning to take off with the effect of side thrust.and my lack of being able to use my left thumb to steer with rudder on the ground.This post has made me realise how forgiving the Zlin is because my take offs are entertaining to say the least and yet th Zlin gets in the air with me following on a bit behind all thats going on.

[Craig Spence]

Hi Martin,

Id be very carefull adjusting the thrust line, as you know how the model can react. Go the wrong way and plane will lol.

I tried putting in down thrust and it didnt like it, the only thing I could really think of would be to adjust the CofG slightly each time and see what effect it would give on take off, but this will have an opposite effect on landing, dooh!.

 

So basically less chance of stall on take off but more on landing lol.

These little things can consume a whole flying session with me, I spent a whole day sorting out wing balance before and then realised the wing had an ever so slight twist in it and this is what I was trying to push home with the wing being true.

They sometimes look fine but once you start pulling rolls and the plane goes out of it or spirals it all becomes alot more aparent.

 

Theres very little you can do about it either apart from learn to fly with the fault.