The take-off crash

[Vecchio Austriaco]

Something which I know -as I had several cases- but it still happens from time to time to me. It's the typical " I will make it " situation. There are 2 Variations -

1) Pulling the model up when it is still too slow to avoid a crash into an obstacle or into the field at the end of the runway. This I managed with my Extra last year - it answered me by dropping a wing and I had 2 days of repair work...

2) changing direction during the take off because of wind or bad set up.

Example: Managed to fly in a fence post last Saturday with my Webbit. The fence post is always there as it was once part of the security fence for the pilots. I had the old problem not to terminate the take off in time - the plane went to the right - and as it has no steerable tail wheel it was not so easy to correct as long as it was slow. It took of finally but I didn't manage to avoid the metal fence post.

 

It took away the last 10cm of the right end of the wing and also the engine got its part. Shaft bent - new engine... And the firewall was crushed - I made a surgical operation to get it out and replaced it by a new one made by better quality ply So the fuselage is almost finished,

The weather forecast for tomorrow is bad - so I plan fixing the wing. May be on Sunday the Webbit is in the air again.

 

And I will try to take off in an area away from the fence posts so it runs into the high grass if it doesn't run in a straight line.

[Tom Wright 2]

The runway sounds more like an obstacle course VA .Sorry to hear you have so much repair work to do.

[Chris Bott - Moderator]

Bad luck Veccio!

 

I think it's all down to experience, the more you fly, the more chance there is that these things can happen.

But also the more you fly, the earlier you will see a problem arising.

Also the more you fly, the more automatic the appropriate action becomes.

An accident like this really concentrates the mind on safety over "it'll be alright".

[Josip Vrandecic -Mes]

Hi Gerd, I'm sorry but I know you will solve a problem....

 

Cheers Jo.

[Flanker .]

Sounds to me as though you have power issues. If you have to yank a plane off by up elevator. Long grass is often the problem here too. If you don't want to buy bigger engines then you could try the "short field takeoff" method that I use sometimes that I learnt while getting my PPL.

 

Flaps one third. You DO use flapperons I hope, makes landing sensible instead of the stupid long flat flappless approach. -

 

1/3 flap. Brakes on. (hold the tail or get helper to) Full power. Release brakes. You will shorten the run by about a third.

 

Finally an aborted take off will usually cause less damage that getting airborne and stalling.

 

The Webbit sounds underpowered. Perhaps a hand launch ?

 

Eitherway very frustating and I am sorry for you. May your luck improve. There are "bad patches" I am in one right now. The plane that is finally destroyed seemed jinxed for along time.

 

go well F

[Vecchio Austriaco]

The Webbit is in one piece again. Unfortunately a bit multicolor as I didn't have the right color of solarfilm. Thanks for all comments and tips.

Underpowered: measured 430W - I think this sufficient for prophanging

Flapperons: I heard and experienced different things. Some aerobatics react odd to flapperons and tend to drop a wing. Happened also to me...Was expensive as not only the model was a rightoff - also the batterie (4S4000) and the ESC (80A) - reprogrammed quickly all other models to get the feature out....

The model is not very stable when on the runway - may be shorter grass or hand launch is the solution. I fly from the same strip since almost a year and never had contact with the fence posts. All other models follow the rudder quite well or they don't need it.

[Flanker .]

Flapperons should not cause a wing drop as they will lower stalling speed. BUT the drag goes up (good) so we need more power. Getting the habit of using pitch to control speed and throttle to control hight is the key here. Use your flaps and TRIM to set a nice safe speed and then use the throttle to control the hight.

 

I think the greatest error we make as pilots is not understanding the stall. Flaps are are reall must - but under used due to misconceptions ; like "some aerobats react oddly" ; they will if there is too much flap, or the drag of the flaps is not balanced with power. I have tried flapperons on ALL types with no problems ; but I set them up and get used to the speed range good n high!

 

A full size course would benefit many of us lets ask the govenment for a grant !

 

Lol F

[Martin Harris - Moderator]

Assuming we're talking strip ailerons, flaperons don't have the advantage of reducing tip stall probability as the advantage of the tips being at a lower effective angle of attack than the inboard flapped section doesn't exist. With a tapered wing (not the case with the Webbit as far as I'm aware) using strip ailerons, the effective AoA at the tip would actually increase were flaperons employed, increasing the chances of tip stalling.

 

On second thoughts, a typical strip aileron set up using torque rods might nullify some of the bad effects due to the aileron twisting and reducing its movement at the tip! 

Edited By Martin Harris on 20/06/2011 14:07:14

[Biggles' Elder Brother - Moderator]

One thing about the WebBit - its tail volume is quite small compared to the wing area. This may account for a slight lack of rudder authority on take off.

 

BEB

[Steve W-O]

Posted by Martin Harris on 20/06/2011 14:02:37:

Assuming we're talking strip ailerons, flaperons don't have the advantage of reducing tip stall probability as the advantage of the tips being at a lower effective angle of attack than the inboard flapped section doesn't exist. With a tapered wing (not the case with the Webbit as far as I'm aware) using strip ailerons, the effective AoA at the tip would actually increase were flaperons employed, increasing the chances of tip stalling.

 

On second thoughts, a typical strip aileron set up using torque rods might nullify some of the bad effects due to the aileron twisting and reducing its movement at the tip!

Edited By Martin Harris on 20/06/2011 14:07:14

 

 

 

This agrees with what I have found, if the flaperons are within roughly on chord of the tip, they increase tip stalling, at a lower speed maybe, but more vicious than the same plane without flaperons used.

 

An exception is the CH-701, where the ailerons are well below the trailing edge.

[Steve W-O]

Posted by Biggles' Elder Brother - Moderator on 20/06/2011 14:35:23:

One thing about the WebBit - its tail volume is quite small compared to the wing area. This may account for a slight lack of rudder authority on take off.

 

BEB

 

 

Perhaps we should make the tail out of 1/2" balsa, and double the volume?

 

I didn't notice any lack of authority of the rudder during my one flight, and it was fine on the ground, but all my planes are tail draggers, so maybe I just held the tail down more

[Vecchio Austriaco]

I fly tail draggers except one - and so I am quite familiar. What I did not do is a steerable rear wheel - Also on the edge 540 EP I had only a small wire at the tail - and with this plane I could go down the runway and turn around whithout the steerable wheel. Of course the rudder area of an Edge is somewhat bigger than that of the Webbit.

This was the reason (also the lack of the right size of wheel at the local shop) for leaving that feature out and replace it with a simple wire.

Edited By Vecchio Austriaco on 20/06/2011 15:33:57

[Flanker .]

Re Tip stalling with flapperons. As I said, keep the power on that is the whole point of flaps, MORE DRAG. It is obvious that the loss of lift on a stalling flapped wing will be worse. Folk stick the flaps down, up goes the drag, then they think, "oh I can fly slower with flaps" so they pull the nose up, fail to add any more power and wack a vicious stall, and then they blame the flaps of course !

 

The main benefit of flapped approaches is that they take up less room as you can come in steeper.

 

To get back to the point you can use them on take off to get a shorter run if you lack space.

However your elevator compensation must be programmed first.

 

A good way to test. Flapperons up. Feed in up till stalling. Note speed. Ad 1/3 flap Try again. The stall will come at a lower speed. Unless you have set too much droop, then you have a brake set up which could cause all sorts of trouble when deployed - esp at low speed near the stall.

 

All my aerobats with full span strip ailerons have flapperons and NONE tip stall unless STALLED.

 

Go well. F

[Mark B]

Why not a castoring tail wheel? It allows turning on the spot at any speed. as long as the main wheels are not binding one more than the other you should have very few problems other than at first while you are getting used to using the rudder more. (Adding throttle with rudder increases effectiveness.) I only used a fixed tail wheel on small models ie less than 40 inch wingspan.

 

Beware of crosswinds until competent!!!