SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old May 01, 2012, 09:34 PM
Registered User
Don Stackhouse's Avatar
United States, OH, Bradford
Joined Jun 2005
4,085 Posts
Careful, that's a violation of copyright law.
Don Stackhouse is offline Find More Posts by Don Stackhouse
Reply With Quote
Sign up now
to remove ads between posts
Old May 02, 2012, 08:36 AM
Registered User
Joined Sep 2007
526 Posts
Gents, please I need your help!

In post #5923 I gave you a link to my building thread in the Vintage Column for a double size Cunny Canard I have built.
I made and balanced my model exactly as suggested by the plan but, unluckily, the maiden was not successful!
I first taxied the model along the grass strip to see how she would behave and once I saw she was running smooth and straight, I made a second run increasing the power a bit farther than half throttle with the intention to have a short leap in the air.
As soon as I reached a sufficient speed I applied a gentle pressure to the elevator stick and the nose of the model abruptly arose vertically and I had my canard keeled over her back in no time and without lifting off the ground one inch!
Luckily the model suffered no damage but a rudder wing tip unstuck.
Initially I estimated that the problem was the stabilizer set at an excessive incidence (+5°) but checking C.G. position with the “Canard Center of Gravity Calculator”, I found that the C.G. shown in the plan was way too rearward than required being at 41.2cm instead of 29.6cm (assuming a static margin of 10).
Actually the stabilizer is an healthy 57% of the wing area but I wonder if my computation is right. Your suggestions are really appreciate!
Guizzo 17 is offline Find More Posts by Guizzo 17
Reply With Quote
Old May 02, 2012, 09:00 AM
Registered User
Don Stackhouse's Avatar
United States, OH, Bradford
Joined Jun 2005
4,085 Posts
No dimensions to check your calculation, but it does sound like having the C/G half an inch too far aft is probably a major factor.

If your MAC is about 3" (76.2mm) (a wild guess on my part), then that difference in C/G locations equates to about 15% of the MAC, which would put the C/G for your first flight about 5% AFT of the Neutral Point. That would definitely be statically unstable in pitch.

Having all the incidences set for a C/G at least that far in front of the NP, the plane would tend to pitch up violently as soon as the airspeed was high enough to lift the nose, which was exactly what you saw.
Don Stackhouse is offline Find More Posts by Don Stackhouse
Reply With Quote
Old May 03, 2012, 09:26 AM
Registered User
John235's Avatar
Sydney, Australia
Joined Mar 2006
1,315 Posts
Hi Guizzo, I've been watching your thread on the Cunny canard. I've been enjoying the photos of your beautiful work.

I'd expect the canard calculator to work for this style of small model, so my feeling is the CG needs to move forward from the one on the "canny canard" plan. Looking at my copy of the rubber plan from H.A. Thomas, the CG looks too far back on the plan. I admit it seems strange that the plan would be wrong if the CG location worked for free-flight. Just to be clear, did you mean to write the CG location should be 41.2mm in front of the main wing leading edge?

The 5 degree canard incidence may be too much as Charles posted on the other thread. However the model can still fly if the elevator is trimmed to compensate. I think the problem was most likely a combination of both too much incidence and rearward CG. If attempting to fly again, I'd personally be looking at moving CG forward, closer to the position suggested by the canard calculator.
John235 is offline Find More Posts by John235
Reply With Quote
Old May 03, 2012, 05:35 PM
Registered User
Joined Jun 2005
2,465 Posts
Guizzo, My model under construction has a 50% canard. The CG is 5.75 inches forward of the rear wing which makes it 26.4% of the distance between leading edges which measures 21.75 inches. I hope this gives you an idea of what your proportions should be. As the canard area increases, the CG moves forward.

Charles
canard addict is offline Find More Posts by canard addict
Reply With Quote
Old May 03, 2012, 05:59 PM
Registered User
Joined Jun 2005
2,465 Posts
Canard Twin Update

Here are a few pictures which show fuselage progress. About two hours per day has been spent on designing, documenting and building.

Charles
canard addict is offline Find More Posts by canard addict
Reply With Quote
Old May 04, 2012, 07:03 AM
Registered User
Joined Mar 2011
783 Posts
Not related but very interesting, hope link works

http://www.gizmag.com/perching-mav-u...m_medium=email

I've thought about manipulating dihedral for control for a while now but thought in a full scale application the aerodynamic forces on the controls may be too much.
captarmour is offline Find More Posts by captarmour
Reply With Quote
Old May 04, 2012, 12:42 PM
Registered User
Joined Sep 2007
526 Posts
C.a., John and Don, thanks very much for your replies. Definitely what you say is unquestionable! I rechecked the computation and I have to admit that my mistake was thrusting the plan! Worst of all I’m not a freshman!
No John, CG location should be 41.2mm from Canard L.E., that's the reference point for the calculator (http://adamone.rchomepage.com/cg_canard.htm), and yes as you correctly say, the canard incidence may be too much but definitely not the culprit for model instability! Thanks again to you all!

Lovely model captarmour! Thanks for sharing!
Guizzo 17 is offline Find More Posts by Guizzo 17
Reply With Quote
Old May 04, 2012, 04:04 PM
Registered User
John235's Avatar
Sydney, Australia
Joined Mar 2006
1,315 Posts
Hi Guizo, I am confused now. Do you mean mm or cm. If you are talking in cm, then the difference between the two is 11.6cm, 116mm, or about 4.5 in - a VERY BIG difference! If you are using mm, then it seems much too close to the canard which doesn't make sense. I'd like to double check the numbers before going further.
John235 is offline Find More Posts by John235
Reply With Quote
Old May 04, 2012, 05:27 PM
Registered User
Joined Jun 2005
2,465 Posts
Guizzo It would be good to know the distance between the leading edges. Let's just say it is 40 cm. With a 57% canard, a reasonable position for the CG would be between 2/3 and 3/4 of the distance from the canard's LE or between 26 and 30 cm. To me, this is within reason for a guess. If the wings had equal area, it would seem that the position of the CG would be 1/2 of the distance between the mean aerodynamic chords. My impression is that your CG is too close to the main wing.

Charles
canard addict is offline Find More Posts by canard addict
Reply With Quote
Old May 04, 2012, 06:06 PM
Zombie flyer....
toffa's Avatar
United Kingdom, Huddersfield
Joined Mar 2010
137 Posts
I have read this thread more or less front to back, however, nowhere have I seen any mention to the phase3 squall. Standard delta design, no thrust vectoring involved, if I were to put canards on it ( al la typhoon, ef2000) could I realistically expect a far more manouverabe plane, and where would I put the canards? ( I have looked online, but no-one seems to have done this!)
toffa is offline Find More Posts by toffa
Reply With Quote
Old May 04, 2012, 07:08 PM
Registered User
Joined Jun 2005
2,465 Posts
Toffa, Is this the Phase Three you were referring to?

Phase 3 - Squall! HP EDF (Vectored Option) (3 min 37 sec)


It must have elevons as well as vectored thrust. The model Euro fighter has similar controls with a canard which looks more stable with good maneuverability as I see it. A bit of nose extension with a canard for the Phase Three might be a good flyer.This P3 rocks a little which calls for wing tip extensions and a bit less power IMHO. Could be material for more knowledgeable discussion.


Charles
canard addict is offline Find More Posts by canard addict
Reply With Quote
Old May 05, 2012, 03:21 AM
Registered User
Joined Mar 2011
783 Posts
What about a close coupled canard like the gripen. At high alpha it improves the flow over the wing which may help with the rocking. I would position it with the pivot above and forward of the strake root. I would first try setting their incidence where they orient themselves naturally as I see them in a level high speed pass to create minimum drag. I think as alpha increases at the same incidence their AOA relative to the wing increases as the upwash increases. I would use a planform close to that of the wingtip.

For a full scale the problem would be reduced visibility for the pilot. To improve visibility it could be mounted on the first half of the strake with anhedral, or last half of the strake with dihedral.

If I want to increase maneuverability without a canard the easy way would be to increase size of rudder and elevons.

The more invloved and interesting route would be to move fin and rudder back so that the bottom of the rudder would replace the thrust vector vane and extending the span of the pitch vane so it becomes a horizontal tail.
captarmour is offline Find More Posts by captarmour
Reply With Quote
Old May 07, 2012, 09:48 AM
Registered User
Joined Sep 2007
526 Posts
Quote:
Originally Posted by John235 View Post
Hi Guizo, I am confused now. Do you mean mm or cm. If you are talking in cm, then the difference between the two is 11.6cm, 116mm, or about 4.5 in - a VERY BIG difference! If you are using mm, then it seems much too close to the canard which doesn't make sense. I'd like to double check the numbers before going further.
Quote:
Originally Posted by canard addict View Post
Guizzo It would be good to know the distance between the leading edges. Let's just say it is 40 cm. With a 57% canard, a reasonable position for the CG would be between 2/3 and 3/4 of the distance from the canard's LE or between 26 and 30 cm. To me, this is within reason for a guess. If the wings had equal area, it would seem that the position of the CG would be 1/2 of the distance between the mean aerodynamic chords. My impression is that your CG is too close to the main wing.
Charles
John and Charles, forgive me for my late answer but I've been busy.
I made a mess in my previous post (#6113) so I give you more and precise information:

My model has 94.5cm wing span and the distance from canard and wing leading edges is 47cm.
Maximum canard chord is 13cm, which is the same of the wing chord.
Canard area is 670sqcm and wing area is 1230sqcm
Present C.G. position is 41.2cm from Canard L.E. and not 41.2mm as I previously stated, just 5,8cm from wing L.E. which, as Charles states, is too close to the main wing.
According to the Canard Center of Gravity calculator, the C.G. should be at 29.1cm ±0.7cm depending on static margin.
I guess I need to rearrange the position of battery, radio and speed controller and see if I may reach the correct C.G. position.
Guizzo 17 is offline Find More Posts by Guizzo 17
Reply With Quote
Old May 07, 2012, 10:43 AM
Registered User
Joined Jun 2005
2,465 Posts
Canard Twin Build

The fuselage bulkheads were built and installed to the left side.The sides were temporarily clamped together for a trial fit and alignment check of the wings.

Charles
canard addict is offline Find More Posts by canard addict
Reply With Quote
Reply


Thread Tools