cap3Der

My Feedback: (9)

CG location is correct, it is 15 cm(150mm) from a front edge of wing at close location to fuselage, fuel tank should be dry(NO fuel). It might sound like you have a problem with elevator surface, also called "trim". When you turn radio on, make sure that elevator is on the same level with a horizontal stabilizer flush(not pointing UP or DOWN), and also make sure that that elevator have movement at least 1,2cm(12mm) UP, and 1,2cm(12mm) DOWN! Let us know if the problem is still there, Good Luck!

cap3Der

My Feedback: (9)

Sygy00, thanks for doing this build, I can hardly wait for the results and flight report.

Sygy00

Flew the F20 last Friday to see how it handled the remote tank. Took a few flights to get the pump, low speed needle and high speed needle all aligned with the planets and stars that govern such things. Seems like it was running pretty good, so I'm proceeding with main gear. Couldn't find a plastic cap of any kind that was the right size for a wheel well, so I rolled some 1/32 ply around a vinegar jar!

What do you call a plane with two wheels that is not a tail dragger? Seriously handicapped (see pic). One more to go!

BIuehawk

Nice job!!!!!!! ::applauding::
On a sad note...I haven't started building mine yet after what...over 2 years?? It's still sitting in the back room in it's pretty new box...but not lonely...it has many other planes (completed) back there with it to keep it company!

Sygy00

Got all the retracts in and flew the F20. FANTASTIC! Looks great and flies great. The remote tank was no problem at all once I got everything adjusted. My Jackal (now a hangar queen) can't compare at all with this. It's very fast even without a tuned muffler, and will turn at full speed on a 15 ft radius. Pulling full up at full speed results in a 180 deg turn in just over 1 second. Total weight is now 7.5 lbs and I did not feel the extra weight at all, even on landing. I think the airfoil speaks to this, but I did add about 10 deg flaperon, which just made landings even sweeter.

I can wholeheartedly recommend an OS 55AX with 11x6 APC prop, Macs muffler, and Perry pump for this airplane. Even with the extra weight vertical climb was incredible.

I've included some photos here, and you can see 6 HD vidoes on YouTube at the links below. Got me a new fav airplane...

Mike

http://youtu.be/SdPq3zL84s8
http://youtu.be/3L5v5GEnIQc
http://youtu.be/hQDxfJiFEYc
http://youtu.be/40jlwJk4eiQ
http://youtu.be/cW5OdVJMlec
http://youtu.be/Gia-l31-pBo

tdcombat

Well, that looks like one heck of a plane! Seems very fast and solid. I've got my main gear detracts half done, but it's a project severely neglected. Any chance you could clock that setup??? I have a Jett .60 rearing to go, I'd think it would likely outperform the OS. At some point that airframe is gonna shudder though. Was there any flutter at all that you noticed?

TXKflier

http://www.youtube.com/watch?v=3L5v5GEnIQc

Using the doppler frequencies I've measured in the video above, I estimate its ground speed to be about 100 mph. The approaching frequency is about 291 Hz and the departing frequency is 255 Hz. Of course, there's a headwind that's slowing it down some.

More info here:

http://www.supercoolprops.com/articl...rdrdoppler.php

Sygy00

That calculated speed sounds just about right, I estimated it wouldget near120 mph, and I had about a 15+ mph headwind at the time. Also most of the vids were done using a 12x5 prop since we were testing for max climb. I switched to an 11x6 laterand definitely got more speed. You can hear me say in the vids" I think it is slower"at one point with the12x5. Later in the day I retuned the engine and it was just plain screaming and even faster. Yet the engine was not running hot! I'd guess it wasgettingover 120mph at that time (I know how to estimate speed better that most). One of my flying buddies has a radar gun, so I'll see if we can clock it.

Keep in mind that this is not really a plane designed for high speed. The fake intakes are a big drag item as well as the blunt tail. However, I am QUITE pleased with the speed AND manueverability, and it looks nice in the air - especially with the retracts. It is a slam-dunk over my H9 Jackal in terms of just plain fun and ease of set up.

No apparent flutter was seen or felt. However, I have a Jett muffler thatwillallow this engine to turn a 10.5x6 apc at 16,000 rpm. That same engine/muffler made the H9 Jackal really haul. I want to try it on this plane, but I think I will have to re-do the tailplane servos for shorter more direct links. I put a lot of work into this plane and I don't want to risk it.

With the Jett 60 and tuned muffler you will definitely be fast, but without retracts your top speed will be limited. If you do this you should consider making sure you have short, direct, heavy duty links to the elevators and rudder. This will probably mean re-installing the servos closer to the surfaces if you can get in there to do that.

TXKflier

That 12x5 prop explains why it wasn't going as fast as I thought it should have been. Also, the rpm's weren't as high as I would have expected on an 11x6. The in-flight rpm I calculated from the doppler frequencies was 15,200.

I have a Phoenix F-20 that's partially out of the box. The first thing I did was build a new horizontal stabilizer out of 1/8" x 1/2" sticks and sheeted it with 1/16" balsa. I'm afraid the stock stab will flutter and blow off above 120 mph. Maybe one of these days I'll finish it.

BillS

SYGYOO,

Great information on the tweaks.

Kougar has approximately the same size and type of wing and might benefit from a wing fence. It appears the fence is about half way out the wing. Did you find information about the size of the fences or was it all experimental? Did you find information about the size of tip plates? If you had not put tip plates on would you have used more than one fence per side? Would you mind sharing the dimensions of the fence?

I like the changes.

Bill

Sygy00

Hi Bill,

I normally put wing fences at 60-67% of the exposed wing semi-span. On my F20 they ended up at 14 inches from the wing centerline. But remember I clipped the wings to 49 inch span (not including missle rails). The fences should be 5/8" high and about 4" long and start right at the leading edge. You will have to trial and error fit the fence to the airfoil. I just used some balsa and sanded it until I got a reasonable fit then transferred that to some .040 plastic stock, or you can use 1/16 ply. I glue 1/4" wide strip of plastic or ply directly on top the covering using CA (just sand the area lightly first) as a base for the fence, then glue the fence on top. This base strip is roughly aligned with the long direction then the fence glued on top using the trick below.

Here is a trick to get the fences aligned perfectly so you don't get any unwanted or unbalanced side forces. Place your wing on a stand in front of a wide mirror. Looking from behind, align the root centerline of the wing with itself in the mirror. Now place each wing fence on the base strip, and again looking from behind, aligning it with itself. I use very small amount of 5 min expoxy which is stiff enough to get hold the fence in place as you line it up, then if that is OK glue on permanently or remove and start over. You could also use tape to hold it, then go back and glue later.

As I mentioned above, I've put wing fences on several planes with slightly swept back wings. They all gained much higher angles of attack before stall or fall off. In fact, my fenced F20 goes to full up elevator with no stall or fall off, but will not do so without the fences.

Cheers,

Mike

BillS

Mike,

Your fence explanation is great and very easy to follow.

Looking at the fence in the mirror is a clever method of alignment. There are probably other places the technique could be used.

Thanks very much.

Bill

Sygy00

Yeah Bill - I do the same thing to align the vertical fin with the fuselage (for non-arfs).

avidflyguy

My Feedback: (48)

have an phoenix f-20 also, powered by webra 50 gt, problem i'm having is its impossible to get it to fly straight and level hands off, always wants to roll very very slowly (left and right depending on airspeed) no matter how its trimmed out, checked for wing twist with incidence meter and experimented with aileron reflex and droop and individual aileron adjustments. my kangke f-20 never had that problem, however it weighed too much and the phoenix is much lighter on the wing, anything i should be looking at that i'm overlooking?

BillS

I usually suspect rudder when a speed related problem exists. I put a loop of telephone wire on the prop hub and pull it across the stab and rudder checking both sides. The stab or rudder will sometimes not be in line with the prop at 12:00 o'clock. Other compensation (Ail) can correct for rudder at speed but the compensation is different at slower speeds. You will get a better answer from Sygy00.

After reading the entire thread I have some questions.

With a 10" diameter prop what is the prop to ground clearance?
I did not see the wing area anywhere. Does anyone have the wing area?
Can someone measure the cord at centerline?

Thanks.

Bill

BIuehawk

SYGY00 said:

Why is using the Rx battery not a good idea? How is the auxillary battery wired into the retracts from the Rx??
I'm confused...as always!

Sygy00

avidflyguy

I think I agree with BillS - look to the fin and rudder first. If you look a few posts up you'll see a mirror trick for aligning things like fins. Try that and see what you have and if you can correct it.

Also, warped wings and fins tend to have different response at different airspeeds. If something is warped (especially the wing) you may not get it balanced. I've sent back several ARF wings over the years as they do come warped sometimes.

Finally check the lateral balance and put some weights on the lighter wingtip. This is also a speed dependent effect that is difficult to trim out if one side is heavy as the weight force is constant but the trim force is not.

Hope this helps.

Sygy00

BlueHawk

Electric retracts can pull a lot of current when trying to operate against the airstream, and can actually cause your receiver battery voltage to drop to a critical level. The first time I tried electric retracts, using the receiver, battery, my receiver was actually cutting out for a few seconds in flight!! Also, if they stall they can draw a lot of current and drain your battery and drop the voltage.

If is very easy to wire in a new battery, see the attached image. I use a AAA 1000 mah pack for my eflite 25-46 gear and it works just fine. I can cycle the gear about 100 times on that pack.

Sygy00

BillS

I have a complete aerodynamic analysis for the F-20, well, for my modified F-20. I'll look for that and post it later. Once posted, if someone can post the dimensions of the original wing and tail I can adjust to match the out of the box aerodynamics. Note that this will include a calculation of the TRUECG which is not the same as the CG recommended by the manufacturer. There have been lots of issues with the F20 simply because the listed CGis too far aft for proper flight stability. Another is that the main landing gear are waaaay too far aft for easy rotation on takeoff or smooth landings (but that is a little harder to fix).

BIuehawk

4.8V or 6V? NimHi?

vicman

My Feedback: (10)

I was thinking lateral balance or warped wing myself. The other thing I thought of was is the wing centered properly to the fuse. Something is askew since these F20s should fly rock solid straight with such a thick wing and long tail moment.

Sygy00

Bluehawk
I use 6V for everything as the total battery energy for 6V battery is 25% greater than a 4.8V battery for any given mah, and the current draw is less. Simply more bang for the buck. I'm using a 6V 1650mah pack for my new plane that has eflite 60-120 retracts, but that is simply because I have one laying around and I can use the weight to balance my plane.

TXKflier

Sorry, but increasing the voltage by 25% also increases the current draw by 25%. Ohm's Law says so. You should increase the battery capacity by 25% to make up for the extra current draw.

BIuehawk

How does an increase in battery voltage and storage capacity increase current draw? The retracts will only draw what they need...if I remember my A&P training correctly. (A&P= Airframe & Powerplant licensed aircraft mechanic)
If I read it right, SYGY00 said he's using a 6V battery with a high storage capacity...correct?

BillS

Yes, higher voltage will draw more current. The servos will also work faster. You should be able to measure the current difference with a multimeter.

Greater capacity at the same voltage will not draw more current. At the same voltage the battery lasts longer which can be checked by counting the number of retract cycles before and after battery capacity change.

Bill