Hello all. has anyone successfully balance and flown the rutan defiant from nitro planes? I have had two unsuccessful flights, waiting for a CG verification from NM, as I am suspect of the numbers in the manual (we all know about the manuals) Instead of the 40 2 cycles I did put in the OS 70 4 cycles..First flight plane was extremely nose heavy...wouldn't lift off ground. Rebalanced to spec and now extremely tail heavy, will try in between for next flight but that takes me out of the CG range specified in the manual...again.

Anyone out there with a flying one please let me know your setup and where it balances out to!

THANKS!

Canard planes and pushers need to have the gear set up so that the plane has a positive incidence compared to the runway.

Often people will correctly set up the C.G. and overlook this.

You may have everything right but with the wing canted down, the plane will not lift off.

Try adjusting the gear if the leading edge of the wing does not point up a bit.

Interesting take...I will make that mod and report back. I may have to extend the nose wheel a bit and make the main gear slightly lower...great thought.

You can find an online CG calculator for canard aircraft here:

http://adamone.rchomepage.com/cg_canard.htm

I suggest you measure the required dimesions in millimeters and run it through the calculator to see if the specs are close.

Remember also, the elevators on the canard deflect downwards when you pull back on the elevator stick on the transmitter to go up. Positive incidence in the nose gear is a MUST. Otherwise it will probably "leap" off the ground with insufficient airspeed when you input too much up elevator on the take off roll to try and get it to rotate. It shouldn't be too much different than the Long-EZ which when set up correctly will rotate and lift off on its own.

Good luck!
Rube

WOW I wish I had this two flights ago....I need to do some measuring and will get back if the CG in the instructions match what this calculator comes up with.

Just finished assembly on my Rutan. The cg according to the instructions was 4" from the leading redge of the wing. It took 29 0zs. of weight in the tail to balance. I will try to fly sometime this week. Let me know how you fare with yours kwiatkma...Wil

Wil,

I did all the calculations from the link to the canard calculator in this post. The "new" CG location is only 1" from the LE of the wing, instead of the plans called out ~4.1".

I could not get my model to fly with added weight in the tail...like you are doing. Maybe you will have better luck. I have 2 OS70 4 cycle engines in mine. Did you do with 2 cycle? If so which kind?

I am so glad to have another builder on here! Let's keep this thread going...we can help each other....I've already had 2 crashes on mine, hopefully my information can prevent you from going through the same frustration. Another thing is that these canard planes need a lot more ground roll to get in the air. I'm going off a grass field...I'm wondering if these airplane designs are better on a asphalt strip? Anyhow, I'm keeping tabs on this.

My plan of attack is to rebalance at the "new" CG from the calculator above and try another flight. AFTER I'm done with the minor repairs!

-Matt

Yeah pushers do far better off asphalt. There is less of a nose down tendancy due to rolling resistance from grass.

In a tail dragger the rolling resistance helps to lift the tail. In a pusher it helps to keep the nose from lifting.


Don't forget to change the plane's attitude at rest as well. That positive incidence helps a lot.

At the very least being nose heavy may cause the plane not to lift off, but if it does it WILL fly.

Just allow enough space past the end of the runway to stop in case you have to.


If you have G3 you can play with the different C.G. and incidence combinations to give you an idea of how your plane may fair.

Hey Matt, I'm Running a pair of OS 46 ax's I'll show your info to my RC guru I'm glad to talk to some other pilots before putting this plane in the air. I;d hate to trash it first time out

Wil,

I have to ask for clarification did it really take 29 oz to balance? That's an extra 1.8 pounds of weight if my calculations are correct! What is your A/C final weight? It should be around 8~9 lbs. By the way it took 18 oz. to balance mine (which is an extra 1.1 lbs.). for the plans CG. I am not sure I need any weight to balance to the "new" CG. I think I may be able to balance to the new CG by just moving the battery position in the fuse. I should have a flight in the next week or two. If I have success I'll let you know...If you have success let me know! I just want to let you know that I think to find the correct CG on this model may be through trial and error. So far I have two errors! HA HA

Oh yeah PS you can see pictures here of the plane: http://lisasimpson.homelinux.com/gal...lanes/defiant/

Yeah Matt 29 ozs. I couldnt believe it! Thats why I wanted to talk to others before I put this thing in the air, maybe save some repair time.I havent weighed the whole plane. I would like to fly this weekend. I'll stay in touch here and let you know what happens..Wil

Hey Matt What type of measurements did you use in the CG calculator...Inches/fractions/decimals/Metric/mm/cm?

As a point of comparison, I would have needed to use an equal amount of weight to balance my Bobcat .50 due to employing an oversized engine.

I ended up stuffing a slightly larger and purposely heavier battery pack in the very tip of the nose.

This brought the C.G. almost perfectly into spec once everything was in place w/o the need for all of the added weight.

Remember that shifting a bit of weight around to an extreme "leverage point" as I did, can have a rather dramatic effect on the C.G.

This is one reason that those rather light 2oz spinner weights are so effective in correcting tail heavy planes.

Wil,

I used inches.

Wil,

To clarify I don't think it matters what you use for measurement so long you use the same unit for all your measurements. I noticed that his wing area calculation is done is sq. in. so I used inches.

Hi Matt, I used the CG calculator and came up with a CG 1 5/8 inches from the leading edge. It takes 5 ozs of weight in the tail to balance. This sounds more realistic. Is this close to what you came up with?

Also , after a little experimentation I found I could move the battery( its a little heavy) to the rear and add 3/4 oz toward the front to get balance. I think I'm going to go with this set up and fly Saturday.

Wil,

Yes this sounds about right..I will have to admit I haven't done a final balance yet as I am not done with the repairs yet. I don't want to re-balance until I have my canard piece back on! I separated the left canard panel my last flight. I'll get you specific weight numbers when I do the balance. It seems that the calculator allows you to put in a fudge factor by giving the modeler a choice of how they want the airplane to fly. My CG measurement is very close to yours at 1.5 inches.

Hey Matt, Got to fly yesterday. !st flight balanced to 4" CG as per instructions, it went 20' down the runway nose lifted and flipped over. We moved the CG to 1 5/8 as per theCG calculator, got flight but still very tail heavy, had to make a "U" turn and emergency landing damaging the landing gear. Made repairs to the landing gear moved some weight forward and tried again. The controls between the transmitter and the plane were way to sensitive, I ended up in the most perfect flat spin I have ever seen....I wowed my buddies at the field! I could not get it out of this spin and was lucky that the cotton field provided a good cushion, damaging only the landing gear again. So back to the drawing board and I'll probably have it back at the field wed. or thur. I'll let you know what happens then.

Well Those flights sound very much like my flights....ARGH. Even with the CG at 1 5/8 it still flew bad? What can we do? Move it more forward? Now that you have seen the airplane fly (it seems from your description it flew better with the CG moved forward) do we dare move it MORE forward or is it a plane that will never fly right?

I am wondering if the plane is getting off the ground before the main wing is "flying"...or if there is a more serious problem like a design flaw. What are your thoughts moving forward. Now we are even on flights! If you can call them that! I was really hoping you were going to say that the forward CG fixed the issue. It seems it made it better but the AC is still in some sort of "stall".

Okay Matt, We are going to try this again! CG is 2" from leading edge of wing, no weight, battery mounted over the landing gear, slightly nose heavy.....I'll let you know when I fly

Hey Matt! Well good news and bad news. I acheived balanced flight with my Rutan! With a setup of being slightly nose heavy, the plane took off well. It tried to nose down on me a little, but I had one of my buddies with me and he adjusted the elevator trim a little while I was flying. I flew for about 6 minutes doing large ovals with smooth turns, totally under control. Suddenly I had some sort of radio problem, the plane went nose down and spiraled to the ground. I had no control what soever. The fwd firewall was broken off, the aft motor continued to run, I could not even shut it off with the radio. When I got to the plane all the controls seemed to work fine. The next pilot flying after me experienced some sort of radio problems as well. So, to sum it up, its to the body shop for this Rutan. We will get it back in the air, it may take a little while as I am dealing with other planes as well. Lets keep this thread going and let me know how you fare with yours. Wil

Wil,

Sorry to hear about the radio problems...May I suggest that the reciever crystal may be messed up from the previous crash. It may save some frustration to purchase a new crystal to see if it clears up any radio issues. The crystals don't hold up well to shock.

A couple of questions as mine is ready for another CG/flight test!

What was the magic CG point you used for your successful flight, was it 2" from leading edge of main wing?
What degrees of throw are you using for the canard/elevator?
How long was the takeoff roll and what field surface did you takeoff from(grass/asphalt)?

This is good news to hear that the plane actually flew!

We never reallyacheived perfect balance. We held the plane 2" from the leading edge of the wing, and moved the battery fwd to make it slightly nose heavy.We did this using our finger tips at the field. The instructions called for 20 deg. of throw but this made the plane too sensitive, so I went with 10 deg. and backed off on the expo so my "sticks" on the transmitter were not so sensitive.I rolled down 150' of asphalt and went through another 50' of grass I really wanted to build up some speed before I pulled up on the elevator. Also the model came with small diameter foam wheels. I replaced them with larger rubber wheels for better rollout. The damage is not to bad, this model is really tough, it will be in the air again! I will change out the crystal. Are you flying this weekend? Let me know how well it does.