erbroens

Well guys, this is a new experiment. This is a 7 years old A-4 Skyhawk molded in honeycomb...
done by a Brazilian guy living in Miami . The problem with this kit, as far as I know, is
that it has the nasty habit of snapping at take off. ( the 2 other kits built here in Curitiba where lost
in the first flight) , so the original owner lost interest on it...

Having witnessed both crashes, I thought that it deserves a chance, as long some mods where built
on it. The problem is that I really like the A-4 ,and I want to stay as close as possible to the original ,
without changing too much its looks.

The full scale A-4 didn´t have this tip stall tendency at all written in the history books, I think that the
slats where part responsible for this, so I drawed a fixed slat / leading edge drop on the scale wing.
Mr.Patake worked so fast on it that I didn´t have pics of the early opened wing structure... also the
horizontal estabilizer where slightly enlarged too.

Let´s see what will happen with this scooter!


Rgds, Enrique

Vincent

My Feedback: (61)

I built one of those about 6yrs ago. I got the kit from Don Kanak and flew it many many times. IMO it was one of the most stable jets i have ever flown. I never saw any sign of this jet departing early in slow flight. Flaps were comfortable at 35d, any more it caused some severe nose down issues.
V..

erbroens

Hi Vincent, Let me tell you what I saw about this plane,,, #1, powered with a AMT pegasus. it rolled out straight, seemed to pick good speed to rotate, and as it rotated , it started to swing it´s wings
wildly at a high AOA ,( pretty much like the old f-100 sabre dance footage) . it flew at about 2 meter high 50 meters in this fashion until it hit the ground... # 2, AMT-180 powered: again rolled nicely, rotated, lifted off and again a single snap. don´t know what the pilot done but he saved it, and after winding up speed and trimming .
it flew nicely, until landing when it bounced badly,and tip stalled again.

I even not mentioned the smaller ducted fan models that had the same fate here.

Perhaps something to do with this is that Curitiba is over 3.000 feet above sea level, and planes here tend to have faster and less predictable stalls.

tschuy

My Feedback: (1)

Great Idea, but it looks to me that you might have gone a little overboard in the size. It seems that it should have been about half of what you added. Being too large with the wingtip extensions will cause some other adverse affects, like stalls at the root of the wing and poor aileron response. I guess first flight will demo this to you

Cheers,

erbroens

Tschuy, That's exactly what I want, the root of the wing stalling first! about the aleiron response i am not very concerned, 'cause the original A-4 has a outstanding
roll rate, and in my mind this mod didn't reduced at all the aleiron effectiveness.
and of course, I will post here the results of the first flight whatever the outcome.. after all
we are all here in this little planet to learn, right? [8D]

AsiaSRC

Nice idea, definitely lead to some interesting finding!

A much smaller one went in last weekend, might b due to those nasty habits too?

All the best!
Regards
Albert

erbroens

Thx Albert, I can't say if any model A-4 has nasty habits, but I can say that the only ones I saw
flying more than once, used sport scale wings, with about a 10% of wingspan increase... and this design is seldom seen in the jet meets either... so seems that something didn't work in the
scaling down of this plane.

tschuy

My Feedback: (1)

Yep that's true.....

Will be looking forward to your results being posted.


Cheers,

Jackjet

My Feedback: (1)

Make SURE the A4 is NOT tail heavy - this 95% of the problem with tip stalls.

Jackjet

erbroens

Well, I can't be sure now, cause I changed the wing lift distribution and the stab area...

anyway the 2 other guys followed strictly the cg instructions and they didn't had luck.

but yes, of course I will do my homework!

erbroens

Painting done.... funny how after so much work and guessing about it's colors it looked not very different from the primer stage. don't know what I will do now with the decals, perhaps
plotter cut vinyl markings, painted with a stencil or perhaps promark ones... read some years ago
in a magazine about a computer printer material that makes water decals. did somebody
has any experience with it? any input will be appreciated. thx.

FalconWings

My Feedback: (57)

www.tailormadedecals.com

He can make anything for you, water transfer.

erbroens

Ok, well this is a old thread! To make the story short, this plane never flew to this date, was sold twice and I bought it again. I am curious to see if this 15 years old scooter will fly any good.

Since the start of this post, the years went by, and the a4 is still considered a difficult jet to fly by most. Now I am painting it with a new scheme and doing some hangar rash repairs..

By the way is great to show a A4 without usng ascII characters as seems that RCU is able to upload pics again.

Turbulence

My Feedback: (76)

I got one of those in the corner of the Garage too. Century Jet has the molds, I think. Anyway, they have a set of gear for it. Don't recall if the gear is full scale or just semi, but I got the set too.

Ralph

erbroens

Thanks for the info! I think that this could be a great flying jet presuming the "cheat" works out. I´ll keep you informed to wathever happens in the maiden.

In this days I would used some sort of slat instead, for a better scale appearence... and I don´t disregard this solution if the current mod doesn´t work as planned.



Best regards, Enrique.

Art ARRO

My Feedback: (5)

Enrique,
Ensure that you have some washout in the wing panels to prevent tip stalls. If the wings are already built you can raiseboth ailerons about 3 mm to provide some washout. I am currently building one of the original BVMA-4s, about 1/8 scale, and the plans for for 1/8" or about 3 mm washout built into each wing panel.
I am also going to add vortex generators, outboard of the wing to help prevent tip stalling. These can be made from G-10 material and inserted into the wing skins before the final finish. The full scale A-4 had about a dozen vortex generators installed on the leading edge slat and about 2 dozen midway between the slat and the aileron. The slat set were aligned with the airflow and the wing set were aligned with the airflow inboard and gradually aligned toward the root as they went out to the wing tip. Good luck with yourSkyhawk.

Art ARRO

erbroens

Excellent advice, thx! The wing extensions already make a washout effect at the leading edge kind like the F-15, but I will also rise the ailerons too when activating the flaps for landing and takeoff.

The BVM A4 was the first ducted fan flown this place, circa 1980 with a K&B 7.5cc.. it had the sport wing version but even so it stalled in a turn in the first flight.. not a fault of the airframe at all, but the lack of power of the setup as nitromethane fuel was simply unavailable those days. I am sure yours will not have any lack of power and will be a great flying model. also believe the vortex generators will help too.

pbusa1400

I've owned two of these models. Great flyers!!!!

erbroens

Hi Pablo, I saw the video of your SM one flying and IMO was the best flying r/c a4 ever. If this one flies anything like it I will be very happy.


By the way, congrats for the new girl!

erbroens

Painted this weekend the tactical bands.. this was used in the Falklands war as a way of avoiding friendly fire with Argentina´s flak. I am using them as visibility aid too! I feel somewhat proud for doing them without peeling out the white paint while removing the tape mask, lol.

erbroens

Getting it together.. masking the camo and matching the color wasn´t easy, even if it is a sport scale job. The good thing of not having a lot of painting skills is that the airplane already looks realistic, with many battle scars!

erbroens

On its feet for the first time and some rigging added.. I also departed from the "scale" offset landing gear to reduce the torsion loads in the main legs.

erbroens

Well, I took my time.. but it was well worth the wait! Today I flew it and it is a great jet.. seems that the mod worked very well, and the estimated CG was perfect. Very solid in the air, and viceless at stalls. The day wasn´t ideal, very hot and 90 degrees crosswinds, however everything went well!




and this is the maiden flight landing...

http://www.youtube.com/watch?v=bBSUcsLM3YI

uncljoe

My Feedback: (8)

Enrique
That one good looking Flying field you have there
Semper Fi
Joe

erbroens

Thanks U,Joe! This place is nice, but kind of unforgiving with jets. 600 feet of strip is plenty enough for normal operations but as it is surrounded with slopes , included steep ones at the headings is easy to break or even loose a plane if something goes wrong with the engine or a landing that isn´t well done. Anyway, I like it very much as it was the best we could do 14 years ago.

http://goo.gl/maps/VZDqi