HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old May 12, 2011, 10:58 AM
or F, J, K, or even TD
FLY F3B's Avatar
Joined Jun 2007
2,914 Posts
Quote:
Originally Posted by gopherhunter View Post
Thanks, Tom... This quote describes what I expected to happen by shimming the stab (leave out the part about servo load), with the effect being a launch with a straight trajectory. The CX2s handling is superb and I didn't notice an obvious handling change by shimming the stab.

John
Yep, and this quote further translated means that you should shim only if you care how it looks, cuz aerowise, it just don't matter

M
FLY F3B is offline Find More Posts by FLY F3B
Reply With Quote
Sign up now
to remove ads between posts
Old May 12, 2011, 11:53 AM
Maurice
mpodder's Avatar
Bakersfield, Cal.
Joined Jul 2004
1,099 Posts
Now that 2 of the best and most respected pilots in US and the designer have told us and proven by their performance that it doesn't matter if there is a little down trim we probably should drop this part of the discussion. And no I'm not saying this just because Roland is not happy with me and still has another plane to build for me. - Yes I'm scarred very scarred :-)

Ive caused enough trouble, I'm sorry, I didn't mean it and I'm sure it will all be look different in the morning.

Maurice
mpodder is offline Find More Posts by mpodder
Reply With Quote
Old May 13, 2011, 05:23 PM
excelling at mediocrity
gopherhunter's Avatar
Franktown, CO. USA
Joined Mar 2009
3,095 Posts
Got it-undercamber

OK guys today I flew the CX2s with CG further forward with a little lead taped to the nose and no stab shims. This is the first time I've flown them at anything other than 86mm. The results were very good. Of course launching with reflex helped.
Now they climb out nice and straight on launch and handle the ever present wind better... I'm happy.
These planes rock... and roll...

John
gopherhunter is online now Find More Posts by gopherhunter
RCG Plus Member
Old May 13, 2011, 11:46 PM
Zeus
Wild East
Joined May 2008
291 Posts
Shim or not to shim

Thank you Maurice, just one word you forgot to mention.....Amen......:-) Never mind!

Well, about the shimming, there is still some words to say, even though it rather should be a fully fledged dissertation.... Still I can remember hot discussions about this issue from my old days in high level German F3B league.

Shimming actually is a relic from old days of free flight (now it is timer controlled) and the beginning of single channel (rudder) RC-planes, where the decalage could not be changed otherwise for flight / glide optimization.
Nowadays we have fast and powerful computers to calculate and even simulate, what was only possible before by measurements in wind tunnels and perhaps during real flight testing to even include the amount of down wash / Cl quite precise to set-up an almost perfect decalage for the desired flight mode.

On top of it, our modern planes are equipped with multiple control functions in any axis and additional camber settings to match the requirements of controlling high performance glider wing sections with multiple camber settings possible, hence controlling the decalage as well as a function of the respective camber setting, which would render any attempt of shimming obsolete, if not nonsensical.
For good, the CX2 is equipped with a dampened horizontal stabilizer, which is preset for best decalage at neutral (0) flap position to provide best performance at design Cl (coefficient of lift) in cruise mode.
For example, if one would shim to reduce this optimized decalage, the plane would fly at lower Cl numbers, hence increasing speed but loosing efficiency in circular flight, hence need more elevator throw in circular and slower flight conditions, increasing elevator drag over extended periods of time.

To gain highest performance level, it is desirable to have the plane flying as long as possible, at lowest possible drag over the total flight time. Of course, strategic changes of camber settings can virtually increase drag or reducing lift, but will provide advantages such as higher climb rate or higher velocity otherwise.

As a resume, everything can be controlled by the right camber- or reflex setting of your flap, in conjunction with some (slight) adjustments of CG location for matching the overall weather situation.......
Do you still need to shim?

Roland
KINETIC is offline Find More Posts by KINETIC
Last edited by KINETIC; May 14, 2011 at 12:44 PM.
Reply With Quote
Old May 14, 2011, 12:46 AM
or F, J, K, or even TD
FLY F3B's Avatar
Joined Jun 2007
2,914 Posts
Roland, that was beautiful! What a great description. I was just pondering the issue more today while powerwashing 100ft of 6' block walls. My thoughts were this.... if I were designing a DLG, and I had the design experience, I would want to be able to make a glider that had the stab set perfectly. I immediately recalled what is perfect to me may not be for others.... but if I did decide to, I'd have to pick a flight regime, and my thoughts were that cruise would be the best one to optimize... but if I did that, the trims would be different at.other airspeeds, or flight modes... I have always just trimmed it and flown it, and have always known that the little but of trim I carried didn't effect me negatively at all...

Thanks for your post.

Mike
FLY F3B is offline Find More Posts by FLY F3B
Reply With Quote
Old May 14, 2011, 01:13 AM
Eggcellent...
tewatson's Avatar
United States, CA, Orange
Joined Oct 2006
2,451 Posts
Full-flying stab, anyone?

Tom
tewatson is offline Find More Posts by tewatson
Reply With Quote
Old May 14, 2011, 01:02 PM
Zeus
Wild East
Joined May 2008
291 Posts
Quote:
Originally Posted by tewatson View Post
Full-flying stab, anyone?

Tom

Tom, many thanks for your very interesting question.
Do you have any specific reason for this question in mind we should know about?
As I have mentioned before, the CX2, as any other top level DLG's have all in common a dampened stab installed for good.

Roland
KINETIC is offline Find More Posts by KINETIC
Reply With Quote
Old May 14, 2011, 07:51 PM
usaf3kteam
rcgeorge's Avatar
Joined Sep 2005
5,678 Posts
Roland I got John all set and he is happy with new set up. It snowed in Colorado so we did not go.
rcgeorge is offline Find More Posts by rcgeorge
Reply With Quote
Old May 14, 2011, 11:12 PM
Registered User
Joined Jan 2008
4,494 Posts
I read all the discussion about shimming and CG with great interest. It was what I was thinking about while I was assembling my own airplanes one day, and it lead me down an interesting path.

I have a Legend and two Taboos. Recently, all three got new tails: the original, glassed balsa sheet tails were replaced with a new generation of "wonder tails". The Taboos got Oleg's current kevlar feathers, and the Legend got a nice set from Shaper Dave himself.

The impact on all three airplanes was nice, beneficial, a learning experience, eye-opening and fun. Among other things I got rid of a lot of nose ballast, especially from the Legend. I heartily recommend Oleg's tails, and Shaper Dave's.

I was happy, or so I thought.

I was getting set to launch the Legend one day, and noticed I had noticeable up elevator for launch. It bothered me that the tail was not in least-drag position, so I wound up removing even more nose ballast, until the launch configuration had the tail at dead-zero deflection, for (I assume) minimum drag. Launches have always been good, but the payoff was a much more lively airplane; while still retaining overall speed, and good manners in windy conditions. I measured decalage, and both wing and tail are now at the same incidence, in launch condition. Nice! And note: no mention of shims. I proudly fly one of the few Legends weighing less than ten ounces. Whoopee!

But wait, there's more: when I go to cruise flaps, there is compensating elevator movement, which when combined with trim for cruise, still gives me ZERO elevator. I get minimum drag in cruise, too. Lucky me.

When I next flew one of my Taboos, I noticed the same thing: noticeable elevator deflection in launch condition. However, neither Taboo has any nose ballast at the moment. So, I started shimming the tail, until the desired launch behavior was achieved with zero elevator deflection. I finally settled on two pieces of masking tape under the rear tail bolt, and now the elevator for launch is zero deflection. I get a wee bit better launch, and they still fly nicely. What's also nice is that they are much faster, if I choose to speed up. There is some elevator deflection for cruise, but detectable only with a straightedge on the horizontal tail. I use launch condition for fast traveling when necessary.

Anyway, just thought I'd mention it. I'd like to try a Concept, hope to have one (or similar fancy bird) someday, but the Legend and two Taboos will be the tools for this season. Watch out!

George: Good luck in Sweden!

Yours, Greg
glidermang is offline Find More Posts by glidermang
Last edited by glidermang; May 14, 2011 at 11:22 PM.
Reply With Quote
Old May 15, 2011, 12:27 AM
Kevin Botherway
New Zealand
Joined Jul 2004
134 Posts
Fantastic model!!!!!!!

Hi Guys
I would just like to thank Rolland for the great models in prep for the worlds. I have now flown my first one for about six hours now and great launch height (there is no doubt its launching heigher than any of my others) I will be checking it out soon with my Ram.The thermal indication and climb rate is right up there its certaily anthor leap forward.I have now flown in very strong wind and it comes home fine - no ballast All round a great model and fantastic finish and presentaion right down to the packaging!Thanks to Mike Smith who I have talked to on the CX2 for a little while and hes put me straight on a few questions.I have confirmed another order with Rolland - we may even get kiwis painted on these ones!

I would suggest that Horrizon or specktum need longer areials on their 6255 rx's probably 7" or 175mm though for them to clear the carbon leading edge.

Thanks again Rolland
happy Rowdy
New Zealand
rowdy01 is offline Find More Posts by rowdy01
Reply With Quote
Old May 15, 2011, 08:42 AM
usaf3kteam
rcgeorge's Avatar
Joined Sep 2005
5,678 Posts
Quote:
Originally Posted by rowdy01 View Post
Hi Guys
I would just like to thank Rolland for the great models in prep for the worlds. I have now flown my first one for about six hours now and great launch height (there is no doubt its launching heigher than any of my others) I will be checking it out soon with my Ram.The thermal indication and climb rate is right up there its certaily anthor leap forward.I have now flown in very strong wind and it comes home fine - no ballast All round a great model and fantastic finish and presentaion right down to the packaging!Thanks to Mike Smith who I have talked to on the CX2 for a little while and hes put me straight on a few questions.I have confirmed another order with Rolland - we may even get kiwis painted on these ones!

I would suggest that Horrizon or specktum need longer areials on their 6255 rx's probably 7" or 175mm though for them to clear the carbon leading edge.

Thanks again Rolland
happy Rowdy
New Zealand
Always great to here from you. CHEERS
rcgeorge is offline Find More Posts by rcgeorge
Reply With Quote
Old May 16, 2011, 10:20 AM
or F, J, K, or even TD
FLY F3B's Avatar
Joined Jun 2007
2,914 Posts
Awsome Rowdy! Really happy to hear you like the CX2 as much as I do. Hope all your preparations go well, and good luck in the Worlds.

Cheers,

Mike
FLY F3B is offline Find More Posts by FLY F3B
Reply With Quote
Old May 16, 2011, 06:25 PM
excelling at mediocrity
gopherhunter's Avatar
Franktown, CO. USA
Joined Mar 2009
3,095 Posts
Another Concept reality... 15mph wind, 9.3 oz AUW, CG at 80mm, no ballast needed.

The CX2's ability to turn airspeed into lift is remarkable!

Splendid work Roland!

And thanks rcgeorge!

John
gopherhunter is online now Find More Posts by gopherhunter
RCG Plus Member
Last edited by gopherhunter; May 16, 2011 at 06:33 PM.
Reply With Quote
Old May 18, 2011, 05:03 PM
usaf3kteam
rcgeorge's Avatar
Joined Sep 2005
5,678 Posts
Any New Concept pilots out there? Will be flying the Beat The Heat this Saturday will report back. Has been to windy here in AZ 25 to 35 no flying all week. Rowdy I have one at 12 OZ and it is the wind terminator.
rcgeorge is offline Find More Posts by rcgeorge
Reply With Quote
Old May 18, 2011, 06:32 PM
a.k.a. Matt Nelson
MattN's Avatar
North Tustin, CA
Joined Oct 2008
1,785 Posts
Funny you should ask, George. I just got a box in the mail this afternoon...
MattN is offline Find More Posts by MattN
RCG Plus Member
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
For Sale XPS Xtreme 2.4 Futaba module and RX $100 John Kim Aircraft - General - Radio Equipment (FS/W) 2 Mar 09, 2011 09:23 AM
For Sale Kyosho EP Concept 30 X 2 dhsmith1 Aircraft - Electric - Helis (FS/W) 0 Feb 14, 2011 05:34 PM
For Sale XPS Xtreme 2.4 Futaba module and RX $100 John Kim Aircraft - General - Radio Equipment (FS/W) 0 Jan 11, 2011 01:53 PM
For Sale XPS Xtreme 2.4 Futaba module and RX $100 John Kim Aircraft - General - Radio Equipment (FS/W) 0 Dec 26, 2010 02:57 PM
For Sale XPS Xtreme 2.4 Futaba module and RX $100 John Kim Aircraft - General - Radio Equipment (FS/W) 0 Nov 16, 2010 10:07 PM