Focke Wolf Ta 154 Laser

[John Stainforth]

Chris,

 

Looking at the pictures of the plane, the wing seems to be very far back: short tail moment and lots of aeroplane (engine nacelles, long nose) in front of the wing. Some of the drawings of the full-size appear to have the wing further forward. Also, watching your video of the model in flight, it almost looks as though some weight may be shifting about. I am wondering if you have long fuel tanks that, if not full, could be shifting the CG quite a bit as the fuel moves back and forth in flight.

[Martin Harris - Moderator]

On revisiting your video, the model certainly looked less stable after undercarriage (rearward?) retraction which would reinforce C of G issues on that flight - but it seems that had been addressed for the second attempt.  No video of this one I suppose.  However, your statement that it seemed better when slower (I'm assuming you meant throttled back?) might suggest a thrust line issue.  The forward position of the underslung engines would suggest it may pitch up with power.

 

Just throwing in points to ponder...

[Jon H]

I have to admit my money is still on the elevator itself not responding as expected with resonance or a structural problem being the likely candidates in my view.

[J D 8]

 I sometimes wonder how much flying of their prototypes some designers actually do.

My TDM I16 Rata was a right handful and in the end it was the fitting of a working rudder that made it flyable, not that anything was said on the plan  [ See Thread " Rata by name rat by nature" ]

    With the 154 what was the reason for the full size having an adjustable tail plane ? And at what angle is it set on the model ?

 

  p.s. Rata is still airworthy, last year I gave it to a friend who fitted an Enya 15 and it now goes round on some control line wires.?

[Chris Walby]

Thanks guys and replies in order

 

JS – As mentioned previously the Ta154 full size and model does have long nacelles and tricycle UC + a short TE to tail compared to the DH Mosquito, but then again there are lots of other differences like wing area and wing cross section. Although I can’t say I have see any with the wings further forward and I have a book dedicated to the Ta154 including lots of digital 3D images and I would say mine was as scale as the model designer could get it with the variations within the mark. Please PM me with the detail if you can out of interest.

 

C of G was 90 mm with gear up and tanks dry. The tanks (SLEC) were full and sit behind the engine so if anything on take off the actual C of G would have been close to 70mm. Flight was 25 seconds and the tanks recovered were +95 % full. Nothing had become dislodged or had moved to cause a shift in C of G.

 

Martin – UC down to retracted made about 20mm difference and as it was balanced with gear up at 90mm then anything else would have been forward of that. Yes it was videoed and I’ll see if I can post it, but it’s a very small image due to the distance. When I said slower I meant airspeed not throttle and looking at the video and how it flew it seemed far more prone to pitch up with increased air speed, although the throttle setting would have been higher as I was trying to increase airspeed. Not sure about the thrust line theory, but I’ll add it as a possible. I was using a RX with 3 satellites (one in the nose, RX midsection and two in the tail) all correctly orientated and at no point did I think I had a TX/RX issue.

 

Jon,

 

Elevator servos (big ones in each horizontal stabilizer) had short slop fee linkages from two different RX outputs so I think we can rule that out. However that still leaves a couple of elevator/horizontal stabilizer questions. Firstly on both flights I took off on mid rates, started running out of down stick so switched to high rates (on the first flight only), but still ended up with a lot of stick in (gentle movements) before it snapped with the down pitch. Second flight I didn’t really have enough height to play the snap down pitch game and was losing orientation. There is a public path on the far side of the woods and I was not going there. This leaves the issue of wing/tail incidence and where the original model had a fully adjustable tail on a big screw and locknuts.

 

JD8

I take your point and bearing in mind that this is a 1976 plan and I have not see many models about (2 others) it may be a tough one to crack. IIRC drawing says +2 degrees on the wing and horizontal stabiliser on fuselage centre line, but this was a real bugger to measure a set up.

 

 

I was conscious of comments regarding over controlling the elevator with travel so took off with mid rates, in hindsight that may have been a mistake on the second flight.

 

Another nugget of information that has just dawned on me is that the original model flew with fixed UC (plans were published circa 1976) so in being clever and having retractable UC I may have caused an issue.

 

Autopsy found nothing wrong apart from the missing engine, fuselage in front of the LE of the wing missing and a bunch of holes the size of your fist punched through wings and fuselage from the tree removal pole. Oh and the impact damage of falling 30 ft out of the tree.

 

Anyway back to the point.

 

Don’t knows

·        What the designer ended up with regarding horizontal tail incidence adjustment

·        The designers actual C of G point

·        Aerodynamic effect of retracting the UC, the mossie does a pitch down with gear down, but I counter that with flaps down position 1 so didn’t really thing about this. Plus the Ta154 has a nosewheel to cause a bit more drag

·        I can’t say 100% if the wing and tail incidence are right + once set my tail incidence was not adjustable although I didn't have enough flights to adjust it anyway

 

 

On the plus side

·        I have a nice pair of Laser 70’s and a hole lot of spare servos

·        If there is ever a next time, don’t put the gear away and take off away from the wood!

[Chris Walby]

For those interested in a flying Ta154

 

Big IC version, there is a second video if you search

Focke Wulf TA 154 - YouTube

 

about same size as mine but electric, but I don't think it was the same set of plans

FOCKE-WULF TA 154 "MOSKITO" TWIN EP GERMAN NIGHT FIGHTER - TEST FLIGHT - 2020 - YouTube

Edited May 8, 2021 by Chris Walby

[J D 8]

 Just been watching the same video's out of interest in the type. [ no plans to have one ] not many about and some were not exactly scale.

 How about a 189 for those Laser's ?

 

[Jon H]

Im not questioning the strength of the servo or linkage, i am questioning what happens to those servos if they are suffering some sort of resonant vibration. 

 

I have seen it before where a servo is being hit with a certain frequency and becomes paralysed by it. The poor old servo is so confused it simply stops responding to commands. The only time they do respond is when the commanded input is so large it takes the servo out of that band where the vibration is screwing it up and it is able to hold the commanded input. This is what causes the all or nothing feel on the controls. 

 

It could also be that only one servo is being impacted by this vibration so you have this unpredictable elevator depending on how many servos are joining the party at a given moment. If a large elevator command brings the 2nd servo out of this resonant paralysis you can all of a sudden have double the elevator control you did before. Assuming the model isnt finished i would definitely take the time to try and check the operation of the servos with the engines running and the model supported such that any airframe vibration is not damped out. IF it seems fine but still fails in the air, chop the engines and see if its any more controllable. 

 

If it was incidence, as i suspect the SG Hurricane was, it would still fly. It might do odd things but should not be totally uncontrollable. The moments are not the same as a mosquito but i do not see why that matters. Many aircraft have short moments but still fly. My P39 has a short backside but i dont have these issues. 

 

The BF109 also had an adjustable stabiliser and we dont see 109's behaving this way so i would say that can also be discounted from the running as a likely cause. . They used adjustable stabs instead of elevator trim so its not a big issue. I think the lysander does this as well, but it might have both. I cant recall. 

[Tim Flyer]

Hi Chris I just came across this post . I’m really sorry to hear that it crashed . You did an amazing job building such an impressive model . I’m afraid I’m not expert enough to be able to cast any light on why it exhibited such bad characteristics in the air. Unfortunately it seems some full size planes make very problematic models. 

[Chris Walby]

Well it sat in the naughty corner for a couple of weeks and I stripped all the wiring out. Basically holes from the poking stick to get it out of the tree and lots of damage from the 30 ft when it descended out of the tree.

 

With the the nagging questions still unanswered I enlisted Richard Wills and his boys, plus club and forum members with two goals. Firstly what was wrong with it to make the way it did and secondly how to get it to fly?

 

Following a lot of gluing, but not as much as building a new one it is now back together again with period combat damage/repairs!

 

The maiden part 3 was with

• Gear down for the entire flight
• Not flap at any point
• C of G at 90mm forward
• More travel on the elevator

 

 

Notes

• Take off needed a big dollop of up to unstick it as opposed it leaping off itself 
• The pitching up seems to wipe a lot of airspeed off, nothing new but if I hold the nose down its okay
• Still seems to hold its tail down
• A bit of rudder in the turn produces a pitch down effect
• Throttle servo settings need adjusting as its not much up to half stick and everything after that

 

Thanks again to all those that helped out.

 

Up to the club with it tomorrow and see if I can get some improvements and what happens when the gear goes away (I think it will need a lot of down elevator mix, but that's just me!)

 

 

 

The sky was complete rubbish for filming, but the wind was in the right direction and good for flying the Focke.

 

 

 

Focke Wolf Ta154 Maiden - again - YouTube

[J D 8]

Well done, got the devil to stay in the sky.? As you say difficult conditions for video and not easy to see what was going on in the flight. Landing approach looked good and steady though. 

[RICHARD WILLS]

Well Chris , as the corporal in charge of the firing squad, said about Black Adders upbeat banter " I do admire your balls sir ". 

That was a brave flight and you certainly kept it in the comfort zone compared to its earlier behaviour . 

We all agree that a forward Cof G will help . but as we discussed , the drag of the undercarriage also has a significant effect on pulling that nose down despite its attempts to buck up . 

Having come this far I think any changes should be tiny steps . It still has a strange stance in the air which for me points toward wing incidence . That may also explain that as you accelerate, the plane claws itself up and yet the glide path throttled back looks normal . 

Thrust line has been checked I guess ?

One good thing about the model is that it seems very stable in roll considering that it spent most of the first flight prop hanging . We would have expected most models to tip stall out at that angle of attack and yet it hung in there to the point of ridiculous . Surely that fact alone would imply the C of G is within its design limits . 

I dont know what the rest think but as its a high winger how about a little shim under the back of the wing to reduce the incidence ?

The model looks great and its upsetting to see you put in so much effort . I dont think its anything you have done wrong . 

 

[Ron Gray]

I agree with Richard to reduce some of the incidence and try it again.

[Chris Walby]

Thanks guys for the continued interest and advice as it all adds to the overall analysis and ultimately the plan of what to do and when.

 

With comments so far, plus club members who have contributed the plan will be to fly it again with the goal to trim it with the gear up but first as Richard points out a few things need to be checked.

• Measure the C of G with tanks full and gear down to see where the C of G actually is (90mm dry and gear up), could be as far forward as 55mm as flown
• Measure the engine alignment as both bulkheads were disrupted in the second crash
• Recheck the wing incidence as its been reduced from +2 degrees to close to zero

Plan for the next flight

•  Add a little down thrust assuming its not incorrect (if incorrect then just set it to where it should be)
• Set a mix up on a switch with gear to elevator on the TX knob, I have a feeling its going to pitch up when the gear goes up (same a the ballooning with flaps, but more of that later)

If this does not help then packing plate under the TE of the wing and take a bit more incidence off (to a definite zero, only concern is the wing does have washout and not forgetting it effectively drops the thrust line as well). give that a go and see what it flies/looks like

 

 

 

  The take home is that its now just about flyable which allows hopefully many more flights to sort it out

 

The great Eric "Winkle" Brown only flew the Ta 154 with the gear down due to hydraulic issues and the rescaled plans flew with fixed gear, hence I think there could be a lot of work in progress before its fully sorted.

Still pleasantly surprised it take off with no flap, lands like any 17lbs warbird would and the UC stood up to the side thrust  (drifting test!). That was all my fault as I wasn't on the ball with the rudder once the wheels touched !

[RICHARD WILLS]

The thing is Chris , if we dont keep pushing the boundaries , as painful as it is , how can we know what we are capable of ?

Whatever happens , you've learnt a lot . 

[Chris Walby]

Thanks Richard and after a spot of flying this morning it was shed time with the Focke this afternoon. Actually the shed does not have enough space to have the wings on and sit on the C of G stand so I have to use the kitchen worktop. Sue's very tolerant after not fancying the cold workshop to build her Ohmen during the winter build so I have have a special exemption.

 

Anyway results are in!

• Measure the C of G with tanks full and gear down to see where the C of G actually is (90mm dry and gear up), Very surprising with gear down and tanks full the C of G only moves 7mm forwards. I am going with Richards UC drag theory as a significant factor.
• Measure the engine alignment as both bulkheads were disrupted in the second crash. The engines already have 1.48 degrees of down thrust compared to the wing 
• Recheck the wing incidence as its been reduced from +2 degrees to close to zero. This came out at 1.25 degrees

Plan for the next flight

• Add a little down thrust assuming its not incorrect (if incorrect then just set it to where it should be). Thinking I'll leave this where it is
• Add a packing plate to the TE and bring the wing down to 0.25 degrees as this was the last change before and seems to have made the biggest difference + it will effectively change the thrust angle anyway. 
• Set a mix up on a switch with gear to elevator on the TX knob, I have a feeling its going to pitch up when the gear goes up (same a the ballooning with flaps, but more of that later)
• If the above helps then I might try moving the C of G forwards say 4 mm at a time and see what happens

Tomorrow looks like another reasonable day for weather and wind direction...report due post flight!

[Chris Walby]

Todays flight reports, that is if anyone is interested? I enlisted Dave B one of our very experienced flyers/instructors to wiggle the sticks as he can fly, assess, decide best course of action and trim all at the same time! 

 

Flight 1

• Wing incidence set to 0.25 degrees up at LE
• C of G unchanged at 93mm
• No flap
• Gear down for entire flight

Flight 2

• Moved the C of G forward another 4mm
• Rate switched the rudder with a 80% travel and 60% expo
• Took off with flaps 10 degrees and changed to no flap as speed  built on climb out
• Inflight retracted gear, no massive pitch change

Post flight notes

• Turns right with aileron only with little pitch down
• Turns left with rudder and a bit of reverse aileron or it rolls in with a pitch down tendency
• Pulled the nose wheel retract out (as Richard predicted !), but an easy fix 

We seem to be taming the beast and video to follow

 

Next on the agenda is to move the C of G another 5mm forward as take off and landing are good and still good elevator authority is available.

 

 

 

[RICHARD WILLS]

Sounds like you are getting there Chris . Have a good look at the motor alignment from the side and from above . The diving to the left on a left turn may be that motor having excessive down thrust .

I know its  difficult with Ic motors , to run them slowly , but it does seem that most of the issues disappear when throttled back on the glide path . If you feel it sort of glides comfortably , then perhaps there is a motor alignment issue going on . 

 

[J D 8]

                    Having fought a few almost unflyable types I find this thread interesting.

Wrong incidence, flexible structure, sloppy controls and CG position the usual suspects.

Some you win some you loose. An aerobatic depron model type I just gave up on last year as no matter how much stiffening was added it still remained unpredictable as once one bit was sorted other bits flexed more. It was probably best left as original.  Made a fine bonfire though.?

[Chris Walby]

JD8, Depends on how many hours you have spent building it and how much you want it to to fly. I agree as I have a little depron model with 3 micro servos and fully operational elevrons and canards and rudders (yes can be done!) its a pig to set up. Worth all the effort, not really however the Focke Ta 154 is very different as its a scale up from an old plan.

If you read the thread you will have picked up that the original design had many features mine does not for whatever reason (different wingspan, fixed UC, adjustable tail incidence, one piece wing etc) and the article said it flew ok. Flight performance is a matter of opinion and Dave B can fly stuff I will never be able to, but he has more experience and far better technical skill than me. I can't see how you can be critical of a design and model you have not flown.

• The incidence may have been correct for the original model, just not suitable for mine
• Its 1980's IC design and at 17lbs there is not much flex in anything
• It does not have sloppy controls, servos are in the wings and horizontal stabilizer with very little play
• C of G may have been in the right place for the original, but again just not suitable for mine

So far every change made with the help of Richard and all the others have improved the flight performance. Perhaps it will never fly as well as other designs, but its way ahead of the SG hurricane (take a look at that thread if you want to see a real dog in action) that can only really be sorted with major surgery and an electronic stabilizer (some ARTF that is).

 

I fully appreciate there is a massive risk with using a plan from 40 years ago and changing lots of things on the road to building it, but one of the great things with this forum is that there are people willing to give their time to help and offer their expertise. 

[GrumpyGnome]

Sounds like you are winning! Good news.

 

As someone said, we need people like you to push the envelope - otherwise we'd all be flying the same planes....

[J D 8]

      HI Chris, I have been following thread all the way, just noting my interest.

I spent a whole of time getting my Polikarpov I 16 Rata to fly half decent a few years ago see [ Rata by name rat by nature ] thread.   Looking more like the 154 will be a usable model now. Cheers John.

[Chris Walby]

Last Friday having glued the nose UC back in (Richard predicted this!) form a heavy landing we had another go. This time the wind was in a different direction and we we caught out by the long grass infield and ended pulling the front nose UC out again. Not a problem as its 8 inch high grass so it will stop anything model related and it just pulls the mounting plate off the bulkhead so an easy fix.

 

Saturday the wind was around to a northly, hence a right to left take off with C of G another 5 mm forward (about 85mm) and flaps at 10m degrees. Once up Dave circled and did some passes with flaps at 10 degrees and UC down/up with little pitch change. Up to a better height and then full flap with a notable nose up and continuous climb  even if power was reduced to 1/2 throttle. Flaps back to 10 degrees and steady decent across the back of the filed and started a left turn on full power.

 

It started to drop the left wing which is usual however this almost instantaneously developed into a near flat spin about 40 ft off the ground. It continued the flat spin until the ground rushed up to meet the fuselage and nacelles. Its completely destroyed the fuselage from nose to TE of wig + structurally damaged the entire tail section and broken the main spars in the wing center section across to both nacelles.

 

All rather disappointing as we though we we getting somewhere with all the changes making slow but steady progress to the flight performance.

 

Only main observation was that it spun almost completely flat which was commented on that the C of G could still be too far back, possible issues with thrust lines as it right turned ok but left would drop its tail and try and roll in unless with rudder and reverse aileron.

 

Any ideas or suggestions from anyone else before I contemplate a new home for a pair of Laser 70's? 

 

 

Final flight although I stopped filming as everything seemed to be going OK!

 

 

 

[GrumpyGnome]

Ouch. I feel for you.......

[J D 8]

     Would have been nice to get it to fly well, but as you say time for a new home for Laser's.

     The info about flight handling of the 154 is very limited and those I have seen on the tube do not look as scale as yous did.