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Old Dec 09, 2011, 09:18 PM
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toxic-trip's Avatar
USA, AZ, Tucson
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Het f-20

I am about to lose my mind, what is the C of G for the HET F-20. I cannot find it anywhere? I really want to maiden it Sunday morning but need some finalizations done first.
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Old Dec 09, 2011, 10:06 PM
Robert Wagoner's Avatar
Tucson, Arizona, USA
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Originally Posted by toxic-trip View Post
I am about to lose my mind, what is the C of G for the HET F-20. I cannot find it anywhere? I really want to maiden it Sunday morning but need some finalizations done first.
Here is a picture from the HET doc Carl Tulanko put together.

C.G. is 2.55" / 65mm from the leading edge of the wing root.

--RW
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Old Dec 09, 2011, 10:19 PM
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Thank you, do you know if that is from leading edge of wing or leading edge of triangle piece in front of wing?

I am almost done after two years of doing this project (I had lots of other projects come up)!!!
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Old Dec 09, 2011, 10:23 PM
AKA Terry Till
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Alexandria, VA
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From the LE of the actual wing where it meets the fuselage; not the extension. FWIW I had the CG at 67mm from the LE of the wing and found it very nose heavy. I moved it back to 80mm from the LE with no ill effects.
Unfortunately, my plane had a few mishaps, so I've put it aside for now.

Terry
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Old Dec 10, 2011, 12:02 AM
Robert Wagoner's Avatar
Tucson, Arizona, USA
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Originally Posted by toxic-trip View Post
Thank you, do you know if that is from leading edge of wing or leading edge of triangle piece in front of wing?

I am almost done after two years of doing this project (I had lots of other projects come up)!!!
Yes, as Terry mentioned. Nice looking F-20.

--RW
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Old Dec 10, 2011, 08:04 PM
To drive or to fly......BOTH!!
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Well I am the new owner of the Air Power version of this plane. Have out 5 flights on it so far but the setup it came with just doesn't put out like I expected so I am doing some power plant swap outs to try a few things. Will get some video once she is all dailed in.

Jason

P.S. My Air Power F-20 has the LE root extensions and my c/g is 115mm from the LE of the extension where it meets the fuse. Fly's great there. Not sure if that is in the ball park of the c/g's mentioned or not.
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Old Dec 11, 2011, 03:35 PM
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Maidened it today, almost planted it straight in to the ground, the CG of ~75mm from leading edge was nearly fatal (I was holding full up elevator entire circuit until I re-landed).

I then moved CG back to 85mm and HOLY $H!T it is FAST and stable!!! I never even hit past 3/4 throttle because I was too scared it would rip apart mid-air it was going so fast (it would compete with my 400 size pylon racer at these speeds)!

I love the HET 2w-25 6s 2200mah 30c w/ wemo pro fan!!!
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Old Dec 11, 2011, 04:42 PM
AKA Terry Till
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Glad it worked out for you.
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Old Dec 12, 2011, 09:00 AM
Aka: Tom Jenkins
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Palm Beach County, Fl.
Joined Aug 2008
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Leading edge root extensions (LERX)

This has nothing to do with the CG but thought y'all might like the info


LERX are small fillets, typically roughly triangular in shape, running forward from the leading edge of the wing root to a point along the fuselage.

On a modern fighter aircraft they provide usable airflow over the wing at high angles of attack, so delaying the stall and consequent loss of lift. In cruising flight the effect of the LERX is minimal. However at high angles of attack, as often encountered in a dog fight, the LERX generates a high-speed vortex that attaches to the top of the wing. The vortex action maintains a smooth airflow over the wing surface well past the normal stall point at which the airflow would otherwise break up, thus sustaining lift at very high angles.


Su-27UB with LERXLERX were first used on the Northrop F-5 "Freedom fighter" which flew in 1959,[1] and have since become commonplace on many combat aircraft. The F/A-18 Hornet has especially large examples, as does the Sukhoi Su-27. The Su-27 LERX help to make some advanced maneuvers possible, such as the Pugachev's Cobra, the Cobra Turn and the Kulbit.
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Old Dec 12, 2011, 12:18 PM
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That is really interesting, I had no idea they help with high alpha flight. It looks like on the new China J-10 (I think thats the number), the LERX can move about 30 degrees up and down, does this further help the performance of the aircraft?
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Old Jan 06, 2012, 04:54 PM
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Laziness dictated that i left the little triangle wing extensions off mine it still flies great in fact it flies surprisingly well, very stable and once you get used to it relatively easy to land.
It uses the HET motor and fan with a zippy 4 cell 5000mha battery, some people are using a lighter battery but it easily carries the weight of the 5000 mha and i get good flight times
This is my second one , the first was lost in a mid air with my mates HET Mig.
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Old Jan 06, 2012, 07:06 PM
deltas are cool
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Tehachapi ,CA.
Joined Apr 2006
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the lex and nose on the full scale F-20 are two of the things that made this a great plane ..the motor was awsome too! the lex should influnce the C/G a bit as the c/g is pretty far forward on most f-20 models
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Old Jan 07, 2012, 05:47 AM
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Lincolnshire, UK
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Quote:
Originally Posted by toxic-trip View Post
Maidened it today...
...I love the HET 2w-25 6s 2200mah 30c w/ wemo pro fan!!!
You are so right! I have the WeMo running the HET 2w-25 on 6s 3000mah 40C packs in my HET F16. Man that thing shifts! It's always a bit butt-clenching flying it because with that much power the fan can generate torque-roll which is not something I'm used to in EDFs. I cat-launch and bell-land on a tiny and rough grass strip so tailerons get replaced frequently. Using retracts on a tarmac surface sounds like real luxury: I'm envious!

You my find that with a bigger pack the motor will generate even more thrust as the voltage will sag less under load: you'll soon become used to the speed.

Si
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Old Jan 07, 2012, 05:48 AM
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Rupert - that's a damned pretty jet - pity the tailplane and elevator wouldn't last one landing at my field!
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Old Jan 07, 2012, 06:07 AM
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Rupert - that's a damned pretty jet - pity the tailplane and elevator wouldn't last one landing at my field!
Thanks, the tailplane seems quite strong (we have a grass strip with a few bumps and undulations)
If you judge the landing right the F20 seems to slow done well at a surprisingly high angle of attack until you are ready to lower the nose and let it settle onto the grass.
I have not had much experience with ducted fans but one of the appeals with these HET jets is that they sound fantastic, unlike some of the other ducted fans i have heard
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