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P13 Reverse Spins

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Old 05-21-2012, 12:33 AM
  #1
Malcolm H
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Default P13 Reverse Spins

I'm currently flying an Oxai Asyuler fitted with a Neu powered Brenner Sharp Contradrive.

Its trimmed using the Hebert method and is hands off neutral in knifedge, vertical up and has a tiny amount of down elevator throttle mix for down lines. Trimmed this way it needs some aileron to spin as per Bryan's notes.

The problem is that when reversing the spin direction, the model "walks" forwards as it changes direction. I can reduce this tendency by reducing the elevator throw in my spin flight mode but I get to a point where further reduction causes the model to unstall and hesitate before starting to spin in the second direction. The "walking" and the hesitation when reducing elevator throw is the same no matter which spin direction you start with. I'm running braking on the motor so normally the props are just about stopped when dropping into the spin but I have tried a flight idle setting in the spin mode which seems to make the "walking" worse.

Anyone have a cure for this?

Malcolm
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Old 05-21-2012, 12:41 AM
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Default RE: P13 Reverse Spins

Hi Malcolm, I have the same set up with my nuance and it does the same in the spins. It would be nice if there is a solution. I would like to know also.
Also Malcolm on a different subject
, how did you make the carbon fibre insert for between the model and contra?
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Old 05-21-2012, 12:48 AM
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Default RE: P13 Reverse Spins

Hi Malcolm,

What throws have you got on rudder and elevator?

Cheers,
Jason.
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Old 05-21-2012, 01:06 AM
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Malcolm H
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Default RE: P13 Reverse Spins

Rudder is currently as much as I can get within the mechanical limitation of the hinges but previously it was around 45 deg. Didn't notice any real difference with this change.

Elevator was approx. 30 deg. but as I said I have been dialing this back.

Malcolm
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Old 05-21-2012, 01:12 AM
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Jason Arnold
 
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Default RE: P13 Reverse Spins

Hi Malcolm,

Rudder seems fine but 30 degrees of elevator seems like 3D type throws! I use about 18 degrees on my Spark.

When reversing the spin, what inputs are you giving the model?

Regards,
Jason.
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Old 05-21-2012, 01:38 AM
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Malcolm H
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Default RE: P13 Reverse Spins

Remember this is a separate spin flight mode not normal flying elevator throw. It is now much less maybe 20 deg. Best success input wise has been to keep the elevator in and reverse rudder and aileron simultaneously. I've also tried letting off elevator as the other controls are reversed and then re-applying it but that was worse.

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Old 05-21-2012, 02:06 AM
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Default RE: P13 Reverse Spins


Quote:
ORIGINAL: Malcolm H

Remember this is a separate spin flight mode not normal flying elevator throw. It is now much less maybe 20 deg. Best success input wise has been to keep the elevator in and reverse rudder and aileron simultaneously. I've also tried letting off elevator as the other controls are reversed and then re-applying it but that was worse.

Malcolm
Yes, I realise you have a spin flight phase. You shouldn't need 30 degrees of throw to stall the model or get it to spin. You may need less than 20 degrees....

Will the model spin without aileron? Using opposite aileron to stop the spin and reverse it is perfectly normal.

When in the spin, is the nose pointing down or is it fairly flat?

Would be great to see a video.. :-)

Cheers,
Jason.
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Old 05-21-2012, 05:33 AM
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Malcolm H
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Default RE: P13 Reverse Spins

Hi Jason,

Have you used the Hebert trimming method? Models trimmed this way have a very forward CG and require more elevator throw than conventionally trimmed models. They will also need aileron to spin.

My model spins nose down but I'm afraid I don't have any video.

Malcolm
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Old 05-21-2012, 06:12 AM
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Default RE: P13 Reverse Spins

Hi Malcolm,

Your airplane wants to keep flying, so CG seems to be far forward, how is your snap doing?

Best regards

Alejandro
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Old 05-21-2012, 06:26 AM
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Malcolm H
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Default RE: P13 Reverse Spins

Snaps are very good, the plane keeps on line extremely well compared to a rearward CG setup.

Malcolm
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Old 05-21-2012, 09:55 AM
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Default RE: P13 Reverse Spins

Hi, I have experienced exactly the same with my Valiant, which was also set up as per Bryan's incidence and CG recommendations. I tried all sorts of things to get rid of it, but it was noticable especially in light wind conditions. I know of some pilots that will do the second spin as a negative spin, whereby there is no jump forward as the spin direction changes. Only a really sharp judge will pick it up, but if they are looking for that cheat then it's a sure zero. Certainly less elevator helps reduce the tendency to jump forward during the direction change, but you still need enough elevator to enter the spin, especially in calm conditions.

I've only just started to fly a Peridot, and I was pleasently surprised to find that it has less of a tendency to jump forward during the reversal. I don't think it has quite as much +ve incidence on the main wing and CG is a little further back than the Valiant (my Peridot has a small tuck to the wheels on L rudder KE).

Regards
Clint
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Old 05-21-2012, 10:09 AM
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Default RE: P13 Reverse Spins

Malcolm and all, I was doing the negative second half spins and I got scores for them. But when it was pointed out to me I decided it should be done the correct way. At our 4 round comp just gone I averaged 7 for my spins which isn't too bad. I think my problem may be the entry, putting the nose up too high and not quite stalling a wing as the judges would like. I will work on this.
The best one can do is minimize the kick back and get the stops right and the judges must ignore the movement backwards as the plane is in a stalled condition.
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Old 05-21-2012, 12:49 PM
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Malcolm H
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Default RE: P13 Reverse Spins

Hi Paul,

Just checking you got the PM and the email?

Malcolm
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Old 05-21-2012, 02:11 PM
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Default RE: P13 Reverse Spins


Quote:
ORIGINAL: Malcolm H

Hi Jason,

Have you used the Hebert trimming method? Models trimmed this way have a very forward CG and require more elevator throw than conventionally trimmed models. They will also need aileron to spin.

My model spins nose down but I'm afraid I don't have any video.

Malcolm
Hi Malcolm,

Yes, I also use the Bryan Hebert timming triangulation method. It works well for me. A more forward CG should actually improve spins & snaps.

I'm finding it hard to picture what the problem actually is to be honest. It almost sounds like the model is flattening out when you stop the first spin.

Have you tried e-mailing Bryan? He's very helpful.

Cheers,
Jason.
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Old 05-21-2012, 03:23 PM
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Default RE: P13 Reverse Spins

Hi Malcolm, I did thanks. It went to an old email.
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Old 05-21-2012, 05:14 PM
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Default RE: P13 Reverse Spins

At this point I will suggest to start high and change the elevator input while in the spin, then you will notice what is the elevator appropiate setting for the spin, the airplane will tend to fly out if it is not fully stalled, use ailerons only if the airplane ask for it. I only use ailerons to change direction.

Regards

Alejandro
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Old 05-21-2012, 06:52 PM
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Default RE: P13 Reverse Spins

Same issue here. What has worked for me is to reduce elevator input to almost zero very briefly when you reverse directions before going back to the regular spin rate throws. It is not easy to be consistent using this method though.
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Old 05-21-2012, 08:27 PM
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Default RE: P13 Reverse Spins

Try to apply ailerons fisrt anf then, in a half a second rudder when you change direction of rotation. This way you will stop rotation fast and the plane won't hung leaving the line.
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Old 05-21-2012, 11:14 PM
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Malcolm H
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Default RE: P13 Reverse Spins

Thanks guys for the suggestions. I did leave a post on Bryan's website so he might get back to me or even better post here.

I will report back if he gets back to me.

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Old 05-22-2012, 07:38 PM
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Default RE: P13 Reverse Spins

I have an additional issue:
The first spin has a fairly slow rotational rate.
When I put the sticks in the opposite corner, the plane does the 2nd spin rotation much faster.
Thoughts?
I use a high idle and some extra elevator throw to get the spin entry better.
I should get a video.

Thanks, Dan
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Old 05-24-2012, 08:19 PM
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Default RE: P13 Reverse Spins

Hi Dan

Probably you use too much ailerons. Try to reduce aileron rate after changing direction. E.g. I use ailerons just to reverse rotation and then remove it completely. In this case you may want to adjust your rudder and elevator rates to make spin look more realistic.

Cheers
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