HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Mar 22, 2012, 03:03 PM
Registered User
United Kingdom, England, Portsmouth
Joined Jan 2009
689 Posts
Discussion
cg help needed on kfm glider build? motor question added

ok here is a 'not to scale' but all measurements are accurate representation (all be it very crude) of a glider i have built.
i am having a prob with the cg location, i have gone for the thickest part of the kfm wing and the i get the cg at 75mm from leading edge, but it just dont look right?
i have tryed the online cg locator gives me a cg location near the trailing edge??
can someone please advise if they can.
Many thanks in advance RCT

wingspan is 1603 not 1630 sorry my bad
rcta15 is offline Find More Posts by rcta15
Last edited by rcta15; Mar 23, 2012 at 06:25 AM. Reason: wingspan fault
Reply With Quote
Sign up now
to remove ads between posts
Old Mar 22, 2012, 04:01 PM
treefinder
springer's Avatar
SE MI
Joined Oct 2004
9,545 Posts
It looks like it's about 38% of wing chord which would be too far aft for me if I was setting up a plane. I likek to start at 25%, Now that's just me, and lots of guys like cg at 30% of chord. This all for a conventional type plane like yours. I don't know why the calculator might say otherwise. Generally with a KFM2 or 3 and the 50% top step, cg will be foreward of the step.
springer is online now Find More Posts by springer
RCG Plus Member
Old Mar 22, 2012, 04:08 PM
Build straight - Fly twisty
Whiskers's Avatar
Australia, QLD, Little Mountain
Joined Feb 2010
4,206 Posts
OK. Going by the old Rule of Thumb the testing CG should be at 25% of the wing cord, that is 30mm from the leading edge. The CG can then be moved back to around 1/3 of the cord to 65mm.
Or: Using a calculator I get testing at 33mm and final at 52mm.
That'll get you going.
Good luck with it all.

Hah! My bro got in first!
Whiskers is offline Find More Posts by Whiskers
Reply With Quote
Old Mar 22, 2012, 04:11 PM
Registered User
United Kingdom, England, Portsmouth
Joined Jan 2009
689 Posts
thanks to you both that has helped loads, now to get back to building.
RCT
P.s. its a kfm9 foil
P.P.S. made a mistake in the wingspan it should read 1603 not 1630.
rcta15 is offline Find More Posts by rcta15
Reply With Quote
Old Mar 22, 2012, 05:35 PM
Up-Out-&-Gone
demondriver's Avatar
Charelston SC U.S.A.
Joined Mar 2007
15,604 Posts
Quote:
Originally Posted by Whiskers View Post
OK. Going by the old Rule of Thumb the testing CG should be at 25% of the wing cord, that is 30mm from the leading edge. The CG can then be moved back to around 1/3 of the cord to 65mm.
Or: Using a calculator I get testing at 33mm and final at 52mm.
That'll get you going.
Good luck with it all.

Hah! My bro got in first!
Bingo-correct! Whiskers hit the CG on the head!
demondriver is offline Find More Posts by demondriver
RCG Plus Member
Latest blog entry: Introducing The "Demon-Claw"...
Reply With Quote
Old Mar 23, 2012, 06:28 AM
Registered User
United Kingdom, England, Portsmouth
Joined Jan 2009
689 Posts
which motor would be good for this glider?

now AUW so far is 900g ish so i was looking at either of these two motors what do you think?


http://www.giantcod.co.uk/epower-gt2...-p-405956.html because i need some extra weight up front, still might need say 40g extra on the nose i think.

or this one...

http://www.giantcod.co.uk/221720t-86...-p-402409.html but will need to add extra weight for this one.

i am leaning towards the first one but not to sure, will want to put a nice big folding prop on it as well.
can i please ask for everyones advice on this matter please?
many thanks RCT
rcta15 is offline Find More Posts by rcta15
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Experiments with KFm airfoil on 'Elf' DLG glider JetPlaneFlyer Foamies (Scratchbuilt) 118 Jun 30, 2012 11:46 PM
Question Help with CG on Miss wind 50 Knysna4 F3A Pattern 2 Mar 21, 2012 02:25 PM
Discussion need help on cg for rotorshape djmd Auto Gyros 2 Dec 10, 2011 08:36 AM
Help! Need help on building a rc aircraft WildMaster Fuel Plane Talk 17 Sep 11, 2011 07:07 AM