Amokka Race Plank - Page 3 - RC Groups
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Oct 21, 2008, 04:21 PM
Deniable plausibility
Shedofdread's Avatar
Instead of using a hinge, make the section of the trailing edge rotate. Very similar to the diagrams in MattyB's post but at the point where a hinge is, use a rod and pivot the section about that. This rod can also be used as a torque rod to drive the airbrake. This was a common way of acheiving braking in the 'pre - crow braking' era. The linkage needs careful design to ensure that it stays shut at speed.

S

PS
Here's a piccy of my new airbrake!
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Oct 21, 2008, 11:02 PM
trying to kick the habit
Matty, given how sensitive planks are to elevator input, I imagine that the split second it takes to go from "elevator up" to "airbrake" mode would cause some general badness. Maybe not though if the lower part is the correct length/angle to compensate for this. Requiring that much elevator travel would really mess up the resolution in elevator mode, too. If you used a cam in the linkage to correct for this (causing the last bit of servo travel to cause a lot of deflection) the servo would have to be crazy strong. Pretty cool if it would work though. Definitely a tidy solution.
Oct 21, 2008, 11:22 PM
Where's the wind?
the_canuck's Avatar
One solution I found with crow on a plank (48" carbon LJ and 48" foam LJ) was to deploy slower and allow the plane to gradually slow down. If you hit the crow hard while the plane was moving fast it would pitch hard up or down. The direction depending on initial pitch position. If you applied slowly you could eliminate the pitch problems with crow. Once the ship is slowed down you can then fly around with full on crow and not have pitch issues. Tweaking the timing of the deployment of flaps vs ailerons helps some as well to eliminate one surface from being applied before the other causing pitch issues.

The fun is getting close on setup for the first few flights. If you don't get it close enough landing can be a handful. I think once you get some time on the sticks and get the setup worked out a plank can be reliably slowed and landed with acceptable risk.

Andrew
Oct 22, 2008, 06:08 AM
Registered User
Dear Matt and Ed and so on

thanks for all your comments. And thank you for the picture of the flap arrangement....I was actually looking for one, but couldn`t find it. It is almost correct, if you just take the top picture and the last one. So the flap was more stiff, because there was more material. On the other hand I couldn`t use it for elevator or aileron purposes. Stiffness is maybe very critical to achieve (or very heavy). On the Amokka the flap is at its maximum just 4 to 5mm thick!!!!! Even the airfoil (main) is rather thick (8,6%). So there is at least a challenge here. The good thing about this flap configuration was that it almost didn`t produced any changes in pitch.

The split flap design, I think will produce some pitching moment, at leasts according to Abbott and Doenhoff. So there will be no gain comparing to a normal camber changing flap, in my opinion.

The Split open flap on the Zipper, here in the forum, is a very nice idea, as it can produce som positive pitching moment, which can be compensated with down trim, therebye increasing lift. Very nice! Backdraft is probably that you make the fin more prone to flutter, especially with a sweep back fin and you will add some weight at the back of the plane, increasing inertia, and will it break enough?

So at the moment I would still go with the same arrangement as the Amokka has, but the extend of the inner flap would be less. But it would be very interesting to hear more about the Zipper fin design.

So far the settings of the crow of the Amokka is that I added so much inner flap deflection that there is no up or down pitching moment when you are flying slow, and when you are flying fast and open the crow, the Amokka will try to take its nose down. This can easily be compensated by holding some elevator. In my opinion this works. This may change, when I have to land a fully ballasted Amokka with wind from the back, but that is also not a lot of fun with a conventional plane.

I will measure the crow settings and post it.

The Amokka is a no commercial project, and I have not decided yet, wether I will make some planes for people that are interessted in getting one, as I have to built them myself. On the other hand, guessing from the very good coaching advises about my F3F flying style , it would probably very interessting to give an Amokka to a more experienced F3F pilot to hear his opinion. This will for sure boost the development of F3F planks. There is a lot to catch up, and a lot to try out.
The airfoils, which are by the way different from the Retox, will not be public. Maybe some time. The full blown version will again have different airfoils, as the Amokka main airfoil is rather thick (8,6%). The newer ones will be thinner to increase the potentials at lower speeds, while maintaining or even increasing lift.

Yours Peter

P.S.: Next time I will try to videotape crow breaking, landing and maybe some special flight situations.
Oct 22, 2008, 08:20 AM
Taranis Tyro...
MattyB's Avatar
Quote:
Originally Posted by Crashaholic
Requiring that much elevator travel would really mess up the resolution in elevator mode, too.
From Peters psot it sounds like pitch change is not a problem when applied slowly, but I hadn't thought of the resolution issue - I agree that would be a significant problem. I suspect having a small section dedicated to braking alone as Peter has dione is probably the way to go, and abandon the elevator bit - just too difficult to get right without a whole series of prototypes and a lot of construction effort.

Quote:
Originally Posted by Peter Wick
The Amokka is a no commercial project, and I have not decided yet, wether I will make some planes for people that are interessted in getting one, as I have to built them myself. On the other hand, guessing from the very good coaching advises about my F3F flying style , it would probably very interessting to give an Amokka to a more experienced F3F pilot to hear his opinion. This will for sure boost the development of F3F planks. There is a lot to catch up, and a lot to try out.
Don't be too harsh on yourself - I've only ever competed in two F3F comps, but I saw every different type of style used dependent on hill, model, pilot and lift conditions. Yes, you probably could have been a bit more aggressive in those high lift condions (employing more of a full reversal style), but the video was plenty good enough to show the potential for a competitive F3F plank for use in good conditions. A back to back test would ultimately be useful to silence the cynics , but that won't be a fair test until you have a 3m machine.
Quote:
Originally Posted by Peter Wick
The airfoils, which are by the way different from the Retox, will not be public. Maybe some time. The full blown version will again have different airfoils, as the Amokka main airfoil is rather thick (8,6%). The newer ones will be thinner to increase the potentials at lower speeds, while maintaining or even increasing lift.
Shows what I know - I'd have thought the airfoil had to be thicker to improve low speed performance, and that increasing the lift coefficient with a thinner airfoil was impossible! Hey ho - I guess I still have lots to learn!
Oct 23, 2008, 06:53 AM
Scorpian 60'' 2012
BMtech's Avatar
Peter

On my 2mt plank I was going to make the inner flap the same area as the outer but now with what you have said I will be making them some what smaller

Have you thought of using a pop up blade type spoiler set on the cg at all ?

Rick
Last edited by BMtech; Oct 24, 2008 at 04:59 AM. Reason: spelling
Oct 23, 2008, 08:41 AM
Twisted and Confused
flyonline's Avatar
Quote:
Originally Posted by BMtech
Have you thought of using a pop up blade type spoiler l set on the cg at all ?

Rick
I've been waiting for someone to do that. My only concern would be that it might blanket the tiny throws of the surfaces being so close to them.
Oct 23, 2008, 08:50 AM
Registered User
ENGINETORQUE's Avatar
what about a canopy brake - this one works great
Oct 23, 2008, 08:55 AM
Deniable plausibility
Shedofdread's Avatar
Another solution would be a braking 'chute. Not really advocating this though - tried it once and it certaily worked if you got it right but it's a one shot device. Spectacular though!

S
Oct 23, 2008, 08:58 AM
Twisted and Confused
flyonline's Avatar
Steve
can you give a photo of the servo/linkage from the inside? I'm interested in how you actuate the arm.

thanks
Oct 23, 2008, 11:00 AM
Registered User
Marc10's Avatar
it is a pleasure to have Peter's contributions in this forum. The ammoka looks fanctastic to me. Looking forward to see the full size monster in action.

I am planning to make a 2m plank and this plane is very good inspiration. I hope that Peter will keep on providing new plank airfols for the enjoyement of the community.

I was wondering about a different aproach to slow down the beast: a wide central flap (2x the width of the elevons) but very short (<5% of the span) that will pop up to create drag.

It will create a up pitching moment that will be compensated with down trim, a similar effect to the split fin, but probably more robust to hard landings on trees and bushes.

Will this setup create a stability problem?
Has anybody tried this solution before?

Marc
Oct 29, 2008, 03:45 PM
Registered User
I promised to post my settings for the crow break of the Amokka. Her they are:
The inner flap deflects 20 degrees downwards and this is compensated by 16 degrees upward deflectet flap of the ailerons.

Yours Peter

P.S.: I think I will try to built a new fuselage with a split fin. Let`s see how this works.
Oct 29, 2008, 04:08 PM
Crikey never leave beer behind
steve wenban's Avatar
Peter you have just got to DS this baby its just made for it.
SteveW who does'nt care about slowing down
Oct 29, 2008, 05:22 PM
Deniable plausibility
Shedofdread's Avatar
Peter,

Interested to see how the split fin works out. Inspired by your design, I'm thinking of building a 'plank' but instead of a split fin airbrake I think I'll use an airbrake like the one pictured in post #31. It started as a feeble joke but actually, it makes sense as a solution.

Will a split fin cause a significant pitch up moment? The 'Bucanneer' style solution should result in zero trim change, I hope...

Please post more pics.

S
Oct 29, 2008, 05:42 PM
Registered User
ENGINETORQUE's Avatar
Quote:
Originally Posted by flyonline
Steve
can you give a photo of the servo/linkage from the inside? I'm interested in how you actuate the arm.

thanks

Not sure If we exchanged PM's - anyway it's dead simple - long extension on the servo arm - servo on it's side and a similar length link to the canopy

Cheers


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