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Old Oct 23, 2012, 12:09 AM
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Knoll53's Avatar
United States, CA, Marina
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Here's a better example of the "tail assisted" short landing.

Plank 101 - Short landing (0 min 54 sec)
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Old Oct 23, 2012, 02:07 AM
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Kent, UK
Joined Nov 2004
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Herk's right about the PW51, from what I understand all the plank boys fly around with a touch of up trim in.

I've noticed that my lighter slope wings are happier with a larger static margin, I'm guessing the heavier they are the more inertia they have so they're less prone to getting upset by rough air. Probably be less of an issue for you on your coastal site though Kent (I do most of my slope soaring inland).
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Old Oct 23, 2012, 03:12 AM
the answer 42 is
Switzerland, AG, Lenzburg
Joined Jan 2006
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Well if they are flying the PW with trim up they are basically nose heavy :P the CoG range on planks is veeeeeeeeeeeeeery sensitive and sometimes we end up being very conservative, 1 or 2 mm can make a huge difference on planks so the people will often go nose heavy.

the PW series is a nice one but I always prefer to use the HS130 series. We build couple of planks using both airfoils and the HS (http://static.rcgroups.net/forums/at...8-DSCF3148.jpg) has wider range than the PW, I mean it can fly faster and slower than the PW making very good planes for slope racing. That being said the PW performs better in low lift and thermal conditions (at least that is my experience) but again the HS130 is a better package.

I am really thinking to build one of these without the fuse and vacuum bagged. It will be a good platform to fine tune my CNC foam cutter. BTW if ti works CNC cut cores will be available for friends and and RCG palls but this might take some time :P anyway

http://static.rcgroups.net/forums/at...4-DSCF3156.jpg

regards

EZ
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Old Oct 23, 2012, 07:58 AM
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Kopenhagen
Joined Apr 2005
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Dear Kent

You are wondering about the uptrim you use.
Yes it right, that the PW51 needs some uptrim in levelflight.
I designed the PW51 as slope airfoil and lowest drag at CL=0, which means straight down :-)
So no flap deflection on the PW51 means swoop. The reason for this type of design is, that profildrag is biggest contributer to total drag in this flight condition. Therefor it is normal to fly with some uptrim at levelflight.
On the other hand are plank airfoils very sensitiv on small changes at the rear end of the foil or changing thickness or camber...so this will always lead to a different uptrim. Very accurate (moulded) PW51 wings need also some uptrim (about 1 degree) at levelflight, as it is very difficult to predict cm from Xfoil or other programs..even a fuse will change it.

Concering this, I was quite pleased how the PW51 turned out and is in fact NOT very sensitiv i this regard....thats why it is till flying with this thickness :-)
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Old Oct 23, 2012, 09:33 AM
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United States, CA, Marina
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Quote:
Originally Posted by Peter Wick View Post
plank airfoils very sensitiv on small changes at the rear end of the foil or changing thickness or camber...
Thanks Peter. That explains a lot.

Clearly my little plank has a highly modified PW51 so it is any bodies guess as to what my airfoil is doing. Due to the covering sag between the ribs I have not only changed the thickness of the airfoil, but it's shape too.

On the first day of flying, I've flown it with a wide CG range with good effect. I'm so happy with this version of the PW51 that I'd like to know what a real one flys like. My next plank will be a slope machine with an unmodified PW51, solid foam cores and full span elevons. That should get me a little closer.

Kent
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Old Oct 23, 2012, 10:12 PM
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Moved the CG forward a little today and dialed the elevator throws way down...Still twitchy on the elevator. No complaints on the elevator response. Better than anything I've flown. Since it didn't make a noticeable different, I'll move the CG back.

Flew inverted today, although with this tail design, it looks the same.

The paraglider pilot said the winds were 15mph today...felt like 10.

Plank 101 - 15 mph (0 min 0 sec)
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Old Oct 25, 2012, 10:04 PM
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Ballast !

Tried flying with ballast today for the 1st time. Bolted on 17oz of external ballast for a wing loading of 17.1 oz/s.f....Not surprisingly, it moves out even better and flys with more authority but still floats when needed. This little plane really carries weight well. It could carry more. Stall behavior is still gentle. Winds were moderate. Maybe 15 mph. The le Fish is a pig compared to this plane. At least my le Fish is.

Flying heavy is the only way to go....next time it will be a big internal ballast box.

Kent

Plank 101 - Laps w/ Ballast (0 min 0 sec)



Plank 101 - 1st Flight with Ballast (0 min 0 sec)
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Old Oct 26, 2012, 07:03 AM
Herk
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Virginia USA
Joined Jun 2007
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Wow - Kent - that simple little model is a blast.

I see that you don't feel the need for a bungee - that sure makes things simple. Will be fun to see what it does at the thermal site.

I'm guessing that you like the super simple construction method. Doesn't seem to suffer any aerodynamic deficit does it? That's been my experience too.

Congratulations - a real success.

Just to satisfy my curiosity, I'm interested in the ratio of fin area to wing area. What is the area of the fin and how far is it from the CG?
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Old Oct 26, 2012, 09:44 AM
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It IS a blast, even in a light wind. Really like the pointy lost foam fuse. Dork landings take on a whole new meaning. I wanted to test the new bungee hook yesterday but snapped off a control horn on the balsa elevon, so flying was cut short.

Hope to bungee launch and thermal fly it this Sunday down in Big Sur.

@ Herk: the drawing is at 1:4 scale. BTW, tried the Discuss Launch and it did not work at all. It just tumbled.

Kent


2 days ago at sunset, there was no wind.
Plank 101 dork landing (0 min 27 sec)
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Old Oct 26, 2012, 09:57 AM
Herk
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Quote:
Originally Posted by Knoll53 View Post
BTW, tried the Discuss Launch and it did not work at all. It just tumbled.
Hmmm - that's a surprise. Did you keep your arm straight all the way through the launch - i.e. move from the shoulder?????
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Old Oct 26, 2012, 10:12 AM
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yes I tried every variation I could imagine. Hard throw...Light throw. Got about 6 tumbles on the hard throw. Tried to avoid any wrist snap at the release to lessen the induced yaw. All to no avail.

video is of very light throw. Just trying to toss it into a gentle glide. Never even came close to controlled flight.

I could side arm launch the Alula no problem.

I think the main problem for all throws is that I am launching into a stall which is the exact opposite from normal javelin type launch. Those always go down.

D L (0 min 11 sec)
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Old Oct 26, 2012, 01:10 PM
the answer 42 is
Switzerland, AG, Lenzburg
Joined Jan 2006
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Hey Kent nice to see how much fun you are having

I still would like to try this plane as DLG, I just wanted to ask you, do you have any experience with DLG before?? just to make sure if it is something wrong with the design or just the pilot needs more DLG training

EZ
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Old Oct 26, 2012, 01:58 PM
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I am on record as having no DLG experience. I am learning as I go. That is why I have not sawn off the throwing peg yet. I am assuming that I'm doing some thing wrong.

I DID have good success with SAL the little Alula, so I have some experience. So now I've got a throwing peg to hang on to. Should be easier than pinching the wing as was done with the Alula.

I on the hard throws, I attempted to throw the plane UP. Just tumbled.

Although I am quite convinced that this plane cannot by Discuss Launched, there will be a next time. Next time, when the sand looks particularly soft, I'll try setting the elevator trim to "fast glide" and see if that helps.

Any suggestions on technique ???

Also, I wondering if a more forward peg location might help. It seems nose heavy while I'm swinging it.

Kent
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Old Oct 26, 2012, 02:10 PM
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Kent, maybe a few visual aids to spur you along...

DLG Launch High Speed video (1 min 41 sec)


F3K Starts (2 min 18 sec)


I've found that throwing more out than up and pushing the wing tip forward as I release the peg really helps. Get more speed on that bird and if you have any reflex at all in the control surfaces, that speed will give an upward pitch at release, so more throw out (more level than up) with excess velocity should work well for you. Keep at it, it should go.

Mark
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Old Oct 26, 2012, 02:41 PM
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Thanks Mark. More out than up... I'll try that. And push the peg forward at the release. That sounds like the tricky part.

Any comment on the throwing peg location in relation to the CG???

Kent
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