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Old Aug 11, 2007, 07:52 PM
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Charles, I am just looking around like you. From what I have seen it appears to be a decent combination in the 60mm size range. There are different versions for different diameter motors. Looking at the EDF forum the 60mm Alfa fans seem to be popular, and I think you might have trouble reaching the same performance level using a smaller fan unit. What size and weight model are you planning to use it in?

This thread contains some info about the performance using the Alfa fan and also some others such as GWS 64mm. In most cases the RPM is measured rather than the thrust, since the idea is that you can relate the two using a graph such as the ones from www.alfamodel.cz or the one posted here.
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Old Aug 12, 2007, 05:04 PM
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John235 your posts were informative and the work looked so sophisticated. I believe the easy way out for me is to consider the Alfa 60/25 with 4 cells and the 5 turn Mega. It would be a starting point to try for the 21 ounces thrust and try to keep the weight down to 21 ounces. The wide and long fuselage would be the worst part but it would be a challenge just to have it work. This idea is still small but also different which makes it interesting. Charles
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Old Aug 15, 2007, 06:10 AM
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Some build progress

My little canard project is just getting underway. The wingspan will be only 32". There is more background on the project info in post 889.

I just realised my justGoFly 300DF motor isn't suitable for pusher application. I am trying a low cost outrunner from Welgard - its the A2208/12 with kv=1800. I am planning to use a 6x4 propellor which will probably draw around 10A on 3S. To get plenty of prop clearance for hand launch, the motor will be mounted on the tail fin just a few cm above the shoulder mounted wing. For the control method I am keen to try simple elevator/ailerons as well as elevons mixed with canard elevator.

Comments are welcome.
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Old Aug 15, 2007, 06:28 PM
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John235 Canard

John, Congratulations on your design. Please continue to post the details of your build here. We are having pollution and a heat wave here which prevents the testing of my new Delta but I do enjoy having it around to enjoy while I wait. I did take it to our local field for taxiing but the surface is rough with clumps of coarse grass. At quarter throttle the nose was bouncing up due to the long springy nose gear. At near flying speed, the nose bounced up which gave the main wing enough positive angle of attack to lift the model into the air. The canard probably was not moving fast enough and dropped as I cut the power. I repeated the taxi with the same results except a gust of cross wind caused a left turn rough landing which could have been a tumble or cart wheel. I must find a smooth place with good conditions for more testing. I am looking forward to Fall temperatures well below the triple digits we have had for two weeks. Charles
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Old Aug 16, 2007, 02:27 AM
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Charles, I somehow recall that you are in Atlanta.. is that right?
Is the pollution just smog due to lack of wind?

On the topic of nose wheel bounce, have you considered moving the nose-wheel further back? It occured to me that for planes using a conventional layout, the nose wheel is generally closer to the center of gravity. Anyway I think there are a few of us looking forward to hearing of the D^2 maiden flight.
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Old Aug 16, 2007, 03:26 AM
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Tricycle gear:

If the plane bounces the nose up and causes premature liftoff and stall... shorten the nose strut SLIGHTLY.

The AOA will be less... and it will be harder for it to bounce the nose up.

If that causes problems with rotating for lift off... move the mains forward slightly so less elevator is needed to overcome the weight being ahead of the wheels.

Its a ballancing act... litterally

And... the further FORWARD the nose gear... the more separation form the mains...... the more stable the plane is on the ground. (just as wider main spacing improves stability on the ground)

The closer the nosewheel is to the CG... the smaller the rock needed to bounce the nose up. The rock essentially can apply infinite force to the model, so it doesn't matter that it has less leverage. (softer tires reduce the effect....)

So.. get the nosewheel FORWARD and slightly get the nose down (shorter nose strut) to prevent that bounce that stalls the plane.
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Old Aug 16, 2007, 05:41 PM
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Canard Landing Gear Discussion

Yes, I live 12 miles north of the center of Atlanta which now has 4 million population. We have had several unhealthy air days and it is over 100 degrees again today. The thin air, the heat on my body and the rough field are delaying the maiden flight. Last year when I had the 380 Long EZ which had similar ground handling problems, I took it to Tullahoma Tennessee where there was a paved runway and Gary Wright, an expert pilot, who tested the model for me. I flew it one time the next week in Alabama from a smooth surface. Later, when trying to get it airborne from our rough field, it bounced up from the nose gear and left main wheel and rolled onto it's back. This Delta, with it's light wing loading, will get airborne easily within 20 feet and once it is tested and trimmed, it can be flown from a smooth section at my field near the pits but with a short space ahead before trees. The Delta's main gear is 3" behind the center of gravity which makes the nose gear load only 4.5 ounces. The nose gear is 17" forward of the CoG. The main wheels are 13" apart on the 36" wing span. The gear was set up with the flat bottom wing parallel to the ground. The nose gear is about 5" long and is made of 3/32" spring wire with a 3/4" single coil at the top. I have never had this type gear to distort. The main gear is 3/32" wire torsion type which plugs into the fuselage at W1 rib. The torsion part is over 5" long. On take off run, the main wing depends on the canard to lift the 4.5 ounces UP which gives the main wing the angle of attack needed to lift the rear of the model. as it rotates and the speed increases, the canard must take on it's proportion of the ships total weight and will drop down a bit. I have attached a picture of a canard that failed due to being set up wrong for good rotation. Charles
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Old Aug 16, 2007, 06:55 PM
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hmmm my edf canard was very similiar...
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Old Aug 16, 2007, 07:13 PM
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Balancing act of:
good wheel base for stability on the ground...
ability to rotate to lift off...
Keeping the prop out of the dirt when it rotates...
Preventing premature lift-off...

Check the Canard surface incidence... it may be a smidge too positive and causing the nose to JUMP up. ( Same as holding full up the whole take-off run with a conventional trike gear model) That can cause the plane to do 3/4 loop coming off the ground. (Straight into the ground)
CG too far back would magnify the effect
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Old Aug 16, 2007, 09:21 PM
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The canard incidence is 3.5 degrees which is the same as the Egret and is what the chuck glider needed to just fly level. I have confidence in the CoG which was taken from the Calculator and has been right on for all previous designs. On my taxi runs, the nose just bounced up and gave the main wing the angle for high lift. The model probably was not up to flying speed. Thanks for the comments and please keep them coming. Charles
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Old Aug 16, 2007, 09:48 PM
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my newest design is undergoin construction starting in a few minutes. Also a EDF canard but with a Wattage Sabre fuse and Ultrafly f-16 wings and canards made out of the tailerons and the orig. F-86 elevator as wingtips. Using a Vasa 65mm fan internally with a GWS brushless inrunner or Razor 2500 on 5s,not sure yet,need to test the gws first
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Old Aug 16, 2007, 11:01 PM
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Ability to rotate and a tendency for the nosewheel to bounce too much are both related to the horizontal distance between the MAIN wheels and the C/G.

C/G needs to be set in accordance with in flight stability and control issues. Once the C/G is determined, then the main wheel location needs to be determined (relative to the C/G location) by ground handling requirements.

In order to have some load on the nosewheel (so it doesn't bounce to much), the mains have to be behind the C/G by a sufficient amount. However, the further aft they are, the more additional weight there is on the nosewheel, and therefore the more difficult it is to lift the nose on takeoff. The plane will have to accelerate to a higher airspeed during takeoff roll in order to get enough additional elevator authority to lift the nose. If the mains are too far aft of the C/G, such as in the example of the Sai Ambrosini SS4 above, it may not be able to get enough airspeed on the ground, and simply cannot rotate for liftoff. At the very least, it can result in unusually long takeoff distances.

Unfortunately that's not the end of it. In flight, the plane acts like it is pivoted on a frictionless ball joint located at the C/G. On the ground, it pivots around the main wheels. The C/G is in front of and above the mains. As the airplane starts to rotate, the C/G swings aft, reducing the horizontal distance between the C/G and the mains, and reducing the amount of extra force needed to further raise the nose. In addition, as the plane starts to rotate and the angle of attack of the wing starts to increase, less weight is carried on the mains (and more on the wing and canard), which also reduces the amount of force needed to raise the nose.

The net result is a plane that rolls and rolls and rolls and rolls and rolls, then finally when it does rotate, it tends to do so very abruptly, like it wants to do a back flip. All tricycle-geared airplanes have the potential for this (not just canards), but it is usually negligible. Canards and pushers do tend to have more trouble with it because they generally don't have as much propwash over the elevators to help raise the nose. The full-scale VariEze has enough of this effect to warrant a fairly in-depth discussion of it in the pilot's operating handbook.

In extreme cases it could be severe enough to be alarming, and possibly even be dangerous. It also encourages PIO's (Pilot Induced Oscillations), where the pilot overreacts to the plane's sudden desire to (literally) leap into the air, and gives it a big jab of "down" elevator, slamming the plane back into the ground. There have been accidents due to this. In the VariEze POH, Rutan recommends that if the plane feels like it is "going over backwards", to just hold the elevator position fixed (do NOT apply down elevator!) and let the plane settle down by itself, without additional control input from the pilot.

The opposite problem is having the mains too close to the C/G, which is the likely cause of Canard Addict's bouncing nosewheel. In that case the nose is too easy to lift, and in extreme cases might even tip back onto its tail.

One other issue: the height of the landing gear is usually set by propeller ground clearance requirements. In the case of a pusher, that typically means a worst-case of either rotation on takeoff or flair on landing. The height of the nosewheel is then set so that the wing is near a zero-lift angle when the plane is sitting in a three-point attitude. In the case of a tailwheel aircraft, the three-point attitude is set so that the wing is at a stall angle of attack. In both cases, the goal is to put the wing in a zero-lift condition on the ground, to reduce its sensitivity to being upset on the ground by gusts.
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Last edited by Don Stackhouse; Aug 16, 2007 at 11:14 PM.
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Old Aug 17, 2007, 01:53 AM
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Thank you, Don, for a really interesting discussion! I loved every word of it. I wish the main gear on the Delta could be back a little further and I will work on it on future designs. I flew the Egret today and noticed the nose hop on return taxi and also that the steering was not positive. Down elevator helps on fast taxi or with a head wind. I can feel for the scale pilots if the canard and main wing leap into the air like my models do. A fast take off run for assurance that the canard will not stall will give the rapid elevation change. Charles
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Old Aug 17, 2007, 02:25 AM
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The Pusher Canard complicatees the main gear location...

You don't want to drag the prop in the dirt as you take off. Its bad for the paint.

The mains are most likely pushed back to try to reduce the ability to over-rotate, grind the prop to stubs as the plane starts to lift and promptly stall...

Thus my mention of the ballancing act.

Try a takeoff holding significant down elevator until it DEFINITELY has airspeed.. then gently head for neutral till it lifts off.

Use a LONG runway...

I'm still betting that your setup results in exess + canard incidence with all 3 wheels on the pavement. The above test giving a satisfactory takeoff is a "work around" that holds the nose down.
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Old Aug 17, 2007, 10:41 AM
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Canard Incidence

huber, I try to use the balancing act and agree with your thoughts except for the canard incidence. I do worry that it could be too much but had to go for the 3.5 degrees because it has worked on 10 of my designs and on Lennon's Canada Goose. Here are some considerations: The Delta weighs 29 ounces and from Lennon's equations,the canard will carry 9.9 ounces and the main will carry 19.1 ounces. The loading per sq. ft. for the canard is 14.6 and for the main is 8.6. On my first design the canard area had to be raised to 30% of the main area to carry the load and to stall when necessary.Using the chart for a Clark Y airfoil at 25 mph, I found that the lift on each surface was very close to the requirements. Again, Lennon's equations were used from his book. From looking at pictures of full scale canards, the decalage looks small on some and large on others. The 3.5 degrees seems to work on my light weight models with their thrust and drag configurations and slow speeds. I am very anxious to see the Delta fly but I want it to have excellent weather, surface and a good pilot which could even be me on a good day.Charles
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