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Old Oct 24, 2012, 03:59 PM
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jjmelo's Avatar
United States, CA, Burbank
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70mm BAE Hawk maiden flight and crash. What happened?

Hey guys!

I bought a 70mm BAE Hawk, made by TFmodels, here on rcgroups. I put it together and flew it this weekend, but the maiden flight ended in a crash.

Check out the video here:

http://www.flitereport.com/bae-hawk-...t-crash-video/

The instruction manual said to set the CG at 85mm behind the leading edge, but the seller said it was wrong and it should've been set to 65mm. The manual for the E-Flite version (which this TFmodel seems to be a clone of) says 80 - 90mm.

I set it to 65 mm, I even stuffed a 1000mah 3-cell in the nose to balance the plane at that point, but after I crashed it, the very helpful gentleman that was helping me out with the maiden said it seemed too tail heavy (the guy flies turbine-powered planes).

To me, it seemed like I had way too much throw on my ailerons, even though I lowered the throw to 70% with 35% expo, per said gentleman's recommendation. When we were doing a pre-flight check, he recommended that I lower the throw on aileron.

You can see I'm over-correcting on ailerons, causing me to invert at some point, lose orientation and eventually hitting planet earth. What do you think happened?
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Old Oct 24, 2012, 04:29 PM
"Take Off" eh!
vettster's Avatar
Canada, ON, Beeton
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Looks tail heavy.

Oversensitive control surfaces is a bi-product of a tail heavy situation. When in doubt...always go with the nose heavy CG.

A nose heavy plane will fly poorly..but a tail heavy plane wont fly long.
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Old Oct 24, 2012, 04:31 PM
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Looking at the videa I don't see how the experienced rcer could say it was tail heavy. It showed no signs of purpoising or tail stalling. Did you have to put a lot of down elevator to keep it level? I think it's clear from the video that too much aileron throw/expo was the issue. You over-corrected and that led to the crash.

Also I'd be weary of your plane actually being too nose-heavy, sound like you have a LOT of weight up the front. If the plane starts to pitch up at speed because you have to put trim, you'll likely have your CG set too far forward.
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Old Oct 24, 2012, 04:42 PM
"Take Off" eh!
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Do you see when he's climbing out to the left how the tail is also to the left?

Was he pulling up to climb or was the plane doing it for him.. I dont know. But over sensitive ailerons are for sure a biproduct of a tail heavy situation. With an experienced turbine pilot next to him, I highly doubt he let him take off with an inch of throws.

Comon Pav...get with it

The instruction manual said to set the CG at 85mm behind the leading edge, but the seller said it was wrong and it should've been set to 65mm. The manual for the E-Flite version (which this TFmodel seems to be a clone of) says 80 - 90mm.
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Old Oct 24, 2012, 05:21 PM
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GWS A-4 will balance on right on and seem tail heavy if there are too much throw in elevators and ailerons....really weird.

Seems like it's the same here....too much throw in controls...

Plane looked like it took off pretty good and got wild afterwards...I would make it nose heavy also and go from there.
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Old Oct 24, 2012, 05:54 PM
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Planes that fly dead level but have too much aileron sensitivity are NOT tail heavy. As I said, I asked the OP if he had to do much elevator correcting during the flight, which would certainly indicate imbalance.
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Old Oct 24, 2012, 06:29 PM
"Take Off" eh!
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You may have asked...But he did not reply...

Where in that video did you see it flying dead level? He was climbing the entire time until it dropped a wing on the bank due to tail heavy. The rest was for sure over compensation. But in the bank the plane Stalled

Here's another question for him. Where DID you set the CG

See ya Pav got to go
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Old Oct 25, 2012, 05:20 AM
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According to the website with the video (linked in the orig. post), jjmelo set the CG at 65mm behind the leading edge. If it was supposed to be 85 mm behind the LE, that means he flew it with a CG that was 20mm forward of where it was supposed to be. Still sound like it was tail heavy??

Josh
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Old Oct 25, 2012, 08:51 AM
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I think Vettster is on the right track. There may be more going on here like angles of incidence wing to tail, and the C of G has to be calculated to match.( Knock off kit?) If too tail heavy the ailerons become ineffective at lower movements and speeds
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Old Oct 25, 2012, 11:36 AM
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I think this is being super analyzed here. I think its somewhat clear he lost orientation and dumped it. Regardless of if it was a bit tail heavy or not. If he made it that far around the tail heaviness wouldnt be that big of a deal. To the op. This is your first edf im assuing?
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Old Oct 25, 2012, 11:48 AM
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Hey guys! Thanks for all the responses. Now to answer some of the questions that came up.

I set the CG to 65mm behind the leading edge of the wing. I was running it on a nano-tech 2650 mah 4-cell, which is lighter than the 3200mah battery other's have used. I stuffed a 1000 mah 3-cell battery to achieve the balance point.

I don't recall having to apply back pressure to keep level...maybe I did but the "flight" was very short.

This is my second EDF. My first one was the Hobbyking/Durafly D.H. Vampire. Its very gentle, forgiving and glides forever unpowered, mainly because its a foamy and because of the huge wing surface. I flown the Vampire a lot, and its the reason why I got bitten by the EDF bug. I've been flying for over 10 years, though.

I'm currently repairing the Hawk, fortunately I cut power and it landed in a soft spot. The nose is destroyed but very fixable (provided that I learn to fix fiberglass).
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Old Oct 25, 2012, 12:34 PM
BLANIK213
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I am at a loss to understand why most of you are in agreement that his setup was tail heavy when he stated that the CG was set at 65mm back of LE instead of recommended 80-90mm .65mm back would give you a biased nose heavy CG not tail heavy and at 20-25mm off from recommended CG and too much control throws that would create another type of stall situation in and out of a turn which is were the problem began and with over corrections he finished it.If not for the excessive throws he would have probably been able to get it back down in one piece to make CG changes and fly another day. Just my 2 cents sorry for your loss jimelo.
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Old Oct 25, 2012, 12:57 PM
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Quote:
Originally Posted by blanik213 View Post
I am at a loss to understand why most of you are in agreement that his setup was tail heavy when he stated that the CG was set at 65mm back of LE instead of recommended 80-90mm .65mm back would give you a biased nose heavy CG not tail heavy and at 20-25mm off from recommended CG and too much control throws that would create another type of stall situation in and out of a turn which is were the problem began and with over corrections he finished it.If not for the excessive throws he would have probably been able to get it back down in one piece to make CG changes and fly another day. Just my 2 cents sorry for your loss jimelo.
I completely agree with your thoughts, to add to it I think he also looked under powered and hawks like to tip stall or snap, so take off severely nose heavy and and probably holding up elevator to maintain level flight then he turns left and being nose heavy the nose will want to drop thus more elevator needed and BAM! high speed stall which is a snap roll to the ground.........I think the cg not being ideal was only a contributing factor to it being under powered, and yes it appears he was nose heavy not tail heavy. with jets, being overly nose heavy will cause you to crash also
my .02cents
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Old Oct 25, 2012, 01:59 PM
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over-contolling can cause a dynamic stall. rapid changes of AOA can cause a stall and the nose to tuck down as induced vortices are shed from the LE of the wing. based on what I saw in the video, it looked remarkably like the nose tucked after over-controlling while in the turn. combine that with the fact that the jet wasn't up to a decent speed yet and you got all the makings of the end result of the video. my two cents of course, but there's no doubt that the plane was over-controlled, which induce a nose down tuck and she stalled and hit the deck.
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Old Oct 25, 2012, 03:25 PM
Fremont, CA
United States, CA, Fremont
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sSorry about the crash, jjmalo. What do you mean by "back pressure"? First time I heard this term.
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