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Looking for help in setting canard incidence and c/g for design in progress

#1
I am assembling a plane from various undamaged parts of previously crashed planes (every model aircraft has an expiration date). The configuration is an 80mm EDF mounted on a SUPER SCORPION wing complete with retracts, a reinforced foam board fuselage with a ME262 nose retract installed, and the SCORPION flying stabs installed as fixed canards. I am stumped as to the canard incidence setting and the proper c/g. Anyone out there have any help?? I am designing on the fly with no drawings, and it's been fun using parts saved, some several years old. My time on Florida's stay-at-home policy has been quite enjoyable.
 

mrjdstewart

Well-known member
#2
pics or it didn't happen. if completely stumped go to ecalc and use their wing designer to calculate CG. it can be a little fiddly at first but once you get the understanding of what they are doing it works quite well. that is were i always go when i am scratch building and need to check my CG numbers.

good luck,

me :cool:
 

Hai-Lee

Old and Bold RC PILOT
#3
I am assembling a plane from various undamaged parts of previously crashed planes (every model aircraft has an expiration date). The configuration is an 80mm EDF mounted on a SUPER SCORPION wing complete with retracts, a reinforced foam board fuselage with a ME262 nose retract installed, and the SCORPION flying stabs installed as fixed canards. I am stumped as to the canard incidence setting and the proper c/g. Anyone out there have any help?? I am designing on the fly with no drawings, and it's been fun using parts saved, some several years old. My time on Florida's stay-at-home policy has been quite enjoyable.
For the basic calculation of the CG point try the following site; https://www.ecalc.ch/cgcalc.php

As for the canard incidence angle it depends on the area of the canard, the distance to the wing LE and the overall plane weight.

I like to have a few degrees of positive incidence as a minimum so that the canard will stall before the main wing! If using undercarriage it is wise to have the nose slightly higher than the main wing when on the level ground so that the plane will be able to lift off without the need to attempt to have the plane rotate.

Taxiing trials should allow you to ascertain the exact CG point before the first flight simply by adjusting things so that the plane does not want to lift its nose or tail in isolation during high speed taxiing. It should just gently lift the wing and nose at the same rate at the same time without elevator input being required.

Just what works for me!

Have fun!
 
#4
I haven't used the ecalc tool, that is probably more accurate than what I'm about the tell you.

I would position the CG in proportion to the wing areas:
Calculate the wing areas for the main wing and the canard.
Then add the wing areas together and calculate what percentage of the total is the canard.
Put a reference mark at 25% back on each wing and measure the distance between them.
Figure how far forward of the main wing mark is that canard percentage and put your CG there.

For example, if the canard area is 27% of the total, and the distance between your marks is 14", I would put the CG forward of the main wing mark by 14x.27=3.8"

Now hold the plane there and go run around in the yard and see if it feels about right.

You might also want to add a few percentage to compensate for the incidence, but I think I'd rather my plane stall and tumble to the ground than nose dive into the ground like a dart.

On you first flights, move the CG instead of trying to trim out the control surfaces.
 
#5
Thanks for the useful info. I hope to meet or exceed the performance envelope of my FLITETEST VIGGEN, which is a hoot to fly. It can do a Harrier landing in a headwind of around 8mph. The canard on the Viggen is about 6 degrees positive incidence. Using existing pieces rather than designing from scratch has been more difficult. For instance the VIGGEN canards are flat plates, but my SCORPION sourced canards are a symmetrical airfoil. Also the wing planform of the SCORPION makes it hard to compute area and c/g point. Still a lot of fun playing around though. Been flying r/c since 1962, but this is my most challenging project.
 
#6
pics or it didn't happen. if completely stumped go to ecalc and use their wing designer to calculate CG. it can be a little fiddly at first but once you get the understanding of what they are doing it works quite well. that is were i always go when i am scratch building and need to check my CG numbers.

good luck,

me :cool:
Still a work in progress. No nose yet and canopy/hatch will be positioned when an approximate c/g with battery is known
 

Attachments

L Edge

Well-known member
#7
Food for thought:
Have you thought about having movable canards?

You stated that you enjoy Harrier type landings. Adding servos will realy increase your acrobatic abilities to that plane. I added servos to the canards of the Viggen build and a 2 D thrust vectoring nozzle. With the added weight aft, I was fortunate enough to reduce the + 7 or 8 degree angle to back to a zero setting. That will also allow you to explore what angle is best for you if you miscalculate. This was done by initally using a sliding switch to get it right while exploring.

Yon can fine tune the canards to get zero degrees by moving the battery fore or aft, fly, retune angle, repeat until throttle position always leaves you at same altitude regardless of speed.

My version starts on page 9 of the FT Viggen build.
 
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#8
Have indeed thought about it and am building so that it can be incorporated later, if the thing flies at all. That's one reason the photos do not have the nose attached. I am hoping to use a nose section that is crushable, like the Viggen and will give me access to modify the canards. I also am considering adding vertical and horizontal vanes in the exhaust stream later on for variable thrust.