Defiant Model 74 Flight problems

Defiant Model 74 Flight problems
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Defiant Model 74 Flight problems - 7/5/2007 4:42:28 AM

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Joined: 1/16/2007
From: Romeoville, IL, USA
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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!

RE: Defiant Model 74 Flight problems - 7/5/2007 7:47:30 PM

opjose

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From: Poolesville, MD, USA
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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.

< Message edited by opjose -- 7/5/2007 7:48:02 PM >

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RE: Defiant Model 74 Flight problems - 7/7/2007 2:28:10 AM

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From: Romeoville, IL, USA
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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.

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RE: Defiant Model 74 Flight problems - 7/7/2007 7:43:32 PM

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From: Whale Tail, RI, USA
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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

(in reply to kwiatkma)

RE: Defiant Model 74 Flight problems - 7/15/2007 6:41:58 PM

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From: Romeoville, IL, USA
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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.

(in reply to Rube Goldberg)

RE: Defiant Model 74 Flight problems - 8/7/2007 9:01:59 PM

wils

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From: , VA, USA
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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

(in reply to kwiatkma)

RE: Defiant Model 74 Flight problems - 8/7/2007 10:19:13 PM

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From: Romeoville, IL, USA
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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

(in reply to wils)

RE: Defiant Model 74 Flight problems - 8/7/2007 10:27:03 PM

opjose

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quote:

ORIGINAL: kwiatkma

Wil,

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.

< Message edited by opjose -- 8/7/2007 10:29:00 PM >

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RE: Defiant Model 74 Flight problems - 8/7/2007 11:21:45 PM

wils

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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

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RE: Defiant Model 74 Flight problems - 8/8/2007 3:35:39 AM

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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

(in reply to wils)

RE: Defiant Model 74 Flight problems - 8/8/2007 3:37:10 AM

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Oh yeah PS you can see pictures here of the plane: http://lisasimpson.homelinux.com/gallery2/v/model_airplanes/defiant/

(in reply to kwiatkma)

RE: Defiant Model 74 Flight problems - 8/8/2007 10:36:44 AM

wils

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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

(in reply to kwiatkma)

RE: Defiant Model 74 Flight problems - 8/8/2007 10:49:24 AM

wils

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

(in reply to wils)

RE: Defiant Model 74 Flight problems - 8/8/2007 5:28:24 PM

opjose

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quote:

ORIGINAL: kwiatkma

Wil,
I may be able to balance to the new CG by just moving the battery position in the fuse.

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.

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RE: Defiant Model 74 Flight problems - 8/8/2007 5:48:06 PM

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Wil,

I used inches.

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RE: Defiant Model 74 Flight problems - 8/8/2007 5:50:33 PM

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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.

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RE: Defiant Model 74 Flight problems - 8/9/2007 9:25:36 PM

wils

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From: , VA, USA
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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?

(in reply to kwiatkma)