Failure to launch..

[Nick Stock 2]

Hi folks,

got caught out on a take-off with my Seagull P-47 today, just as I’ve started to really get a feel for her flying characteristics in the air and on landing.

Lucky, on this occasion the ‘only’ damage was main retracts being ripped clean out of both wings and some minor tears under the wings and a slight dent in the lower front fuse.

I’m hoping some of you may be able to offer some advice on my take off technique:

I have to start my run up with full back elevator, otherwise the model will simply nose in when any power is fed in. My gear is raked as far forward as possible. Flaps set at half.

I was then adding a bit of power just to get the model rolling and then fairly quick on to full beans.
as I get to full throttle, I quickly release the amount of elevator I’m holding to balance the model on the main gear but doing my best to let it run for a bit to build up speed. I have been lifting off the ground early like this and have come dangerously close to tip stalling.

Today I tried feeding power in more gently and trying to ‘feel’ the elevator amount needed so that I was on the main gear, balanced, before smoothly progressing to full power.

The model lifted early, stalled, hit the deck and subsequently slid across the rough.

Has any one else gone through a learning curve with heavier tail dragging warbirds and have advice?

Nick

[MattyB]

Have you tried taking off without the flaps being deployed? That might allow for a smoother transition to the tail up position prior to takeoff. I certainly never used them on (admittedly lighter) electric warbirds at takeoff, they just exacerbated the nose-over characteristic inherent in most taildragger warbirds at model sizes.

[Jonathan M]

Nose-over tendencies of the model type aside, is your CG too far forward? (Is there a range or an absolute position specified?)

[Trevor Crook]

These warbirds can be tricky! If the model is prone to tip stall, it's probably unwise to move the cg back any more. It sounds as if you are doing everything right with your elevator and throttle handling, so I would try Matty's suggestion of taking off without flap. I've seen warbirds be more prone to nose-overs if taxied with the flaps down.

I use the flapless takeoff technique with my 1450mm Avios Spitfire and my 1400mm FMS 109, and that works fine. These models are quite resistant to noseovers though, P47s seem particularly susceptible..

[Graham Davies 3]

Hi Nick.

I feel your pain. My 55" Tempest is OK, but I have a smaller model that is a pig. It has reserves of power so stalling is not a problem, but nose-overs happen very often.

a method that worked for me is to set a 'take off' rate on elevator with quite high rates but loads of negative expo. It made it easier to transition from full up needed at the start of the run to just a squeeze as it got rolling. as soon as you are off the ground, click to normal rates.

Graham

[Tim Flyer]

Sorry to hear that nick. On my P47 (same model and engine) I never use flaps for take off. That allows me to attain the correct air speed before take off and I think also helps straight tracking as the model stays grounded longer and the wheels are less likely to slip sideways.. I also note on this model that I find it important also to retract the flaps soon after touchdown as I find that also prevents nose overs as it slows down. Tha flaps are quite close to the ground when fully deployed so there is a pressure tunnel effect which can lift the tail. 

Edited By Tim Flyer on 01/09/2020 09:19:43

Edited By Tim Flyer on 01/09/2020 09:20:48

Edited By Tim Flyer on 01/09/2020 09:24:39

[Bob Cotsford]

Flaps will also be adding drag and reducing the models acceleration. Maybe full size flyers could confirm but I thought take-off flap where used was generally only a small percentage and certainly much less than half? I've not yet come across a model that needs flap, but plenty that needed a good length run on grass in order to build up to a safe flying speed. On taildraggers the model should need very little if any elevator to lift off though trike undercarts can need a bit more of a tug on the stick to get into flying attitude.

[Cuban8]

Nick, we've all made the mistake of getting a warbird off too early because of not timing the up elevator. I did the same thing myself with my Brian Taylor Spitfire - a moment's inattention and slightly out of wind but thankfully no serious damage - very lucky indeed and all fixed now. Seen so many lovely warbirds wrecked this way, YouTube's full of 'em.

I wouldn't use flaps for take off and I disagree with using expo on the elevator of a warbird - it can lead to all sorts of other unintended problems IMHO but this will be a matter of personal preference.  My advice is to try to squeeze a bit more forward rake to the undercart if at all possible, this might mean making a few changes to the mounting and the u/c geometry might mean that the wheels don't sit in the existing wheel wells, so a bit of mod needed there. It's a sports model for everyday use and it needs to be fettled to make it that way. My Hanger 9 P47 (changed to servoless retracts) has the wheels raked forward so they're almost half showing when looking down on the wing in plan view. Only the slightest touch of up now needed at the start of the take off roll and that can be taken off almost immediately the model's moving.  Not Scale appearance , but doesn't nose over any more. When tucked away, you'll never notice - Needed to take out the wheel l well linings, enlarge the space and reline with balsa to suit. Not a difficult job and she's so much more easy to handle on the deck at take off and in the landing roll out.

Most warbirds are very elevator sensitive, so using rates/expo needs great care as it's so easy to forget whether you're in take off/flying/landing mode even with modern talking radios or hit the wrong setting when in a stressful landing situation e.g windy and dealing with flap setting as as well.

Good luck, all part of the challenge I suppose.

 

 

 

 

Edited By Cuban8 on 01/09/2020 10:53:19

[Martin Harris - Moderator]

A very experienced friend flies a 1/5 scale Z62 powered P47 and swears blind that his taxies better with full flap! I don't think he uses flap on take off though.

As for Spitfires using flap on take off, as far as I'm aware, the only ones that did were being flown off a carrier to Malta and had wooden wedges trapped under the flaps to provide some extra lift - the wedges being dropped by cycling the 2 position (up/down) pneumatic flaps once safely airborne.

Edited By Martin Harris on 01/09/2020 10:51:27

[Peter Jenkins]

Nick, sorry to hear your sad tale. I would agree that you don't need to use flaps for take off. The Spitfire only had a2 positions as Martin has pointed out and they never used flap for take off apart from the Malta example.

Reading your account it would appear that you are not letting the aircraft accelerate sufficiently to get to a comfortable airspeed before you start to climb. The other issue is engine torque when flying close to the stall and at full power. That will tend to cause the aircraft to roll left (assuming the normal rotation of the prop) and using aileron to correct can cause a tip stall on the down going wing i.e. the left or port wing. So more speed and keep a shallow take off climb to allow airspeed to build up.

Good luck next time.

[Jon H]

Hi Nick

Were you at North London? If so I saw the incident and one of the main factors was a lack of rudder input.

I noticed on both of the takeoff's i saw that the engine torque was left to drag the nose to the left quite substantially on both occasions. On the final takeoff, while the model did leap into the air a bit early it was the yawing motion that caused the left wing to begin to drop, at which point you throttled back. In all honesty, you were committed to the job by that point all you needed was to relax the elevator pressure a bit and give it a fair shove of right rudder with a small amount of right aileron. This would have unloaded the wing (preventing a stall) and got it flying straight which would have stopped the roll.

I agree with the other guys who have suggested going flapless for takeoff. I never use flaps on warbird takeoffs as the additional drag is not helpful and neither is the added lift.

What i recommend is you try a fast taxi down the length of the strip with the tail up just to get a feel for how much rudder you need to keep straight. Remember that you need to hold this rudder in once off the ground and slowly release it as the speed increases.

It might also be worth looking at your radio setup as large movements with high expo gives a real lack of precision around centre stick and that is not helpful.

I think there is a plan afoot to fly on friday so if that comes together we can take a look if you like.

[Trevor Crook]

Yes, until recently I used a lot of expo (30%) on elevator for take-off and landing to help keep the tail down, but reduce sensitivity around neutral. However, I found I kept getting the landing flair wrong, and decided it was due to the non-linear response of the expo. I tried reducing it to 20%, and that works much better for me so I've left it at that.

Good points made about the torque as well. The Avios Spit is putting more than 1kW through a scale 3-blade prop which has lots of torque reaction potential. It has power to spare, so all my take-offs are at half throttle which keeps things pretty straight. As said, Spits never use take-off flap anyway, but leaving the flaps up on any warbird should mean it lifts off at a higher airspeed, so the aerodynamic surfaces have more of a chance of keeping things straight.

[Denis Watkins]

Ditch the expo on elevators, or

If you cannot be weened from dialling in expo, then 10% max

The model has no clue about expo, just your thumbs

[Jon H]

Posted by Denis Watkins on 01/09/2020 22:00:48:

Ditch the expo on elevators, or

If you cannot be weened from dialling in expo, then 10% max

The model has no clue about expo, just your thumbs

yep. expo is the last thing you add, not the first. If the model is set up correctly on the rates most dont need it, especially warbirds.