Robrow

I am considering retrofitting flaps to my A4 Skyhawk and was wondering if anyone had any experience in this area. Would they function the same even though the A4 has a delta wing ?

Rob.

maverick

My Feedback: (12)

The full scale A4 Skyhawk had split flaps, like this:

Robrow

OK, thanks for that, maybe trickier to make than non-split.

Rob.

elmshoot

My Feedback: (6)

Rob,
I helped a buddy about 10 years ago with a Yellow A4. From what I saw I don't think adding flaps will give you much. Add lightness not weight will work better. High Alpha approaches didn't seem to work well despite the delta wing. The ground handeling was always a challange, just like the full scale which I got about 200 hours in. For takeoff and landings it was stick forward and into the cross wind.
Sparky

Vincent

My Feedback: (61)

Elmshoot,

I agree with you on the Y/A Skyhawk, add lightness. I built three of them over the years and it was the lightness that made them fly good and able to get out sticky situations. I moved up to the larger Planes Plus turbine A-4 about three years ago and still fly it today. The old saying bigger is better applies to the A-4, this one loves flaps and is not at all "snappy" like its little Y/A brother. You are right on with the cross wind / ground handling too. Pedal to the metal and steer into the cross wind!! I ended up cutting down the long struts a bit to help on the cross wind landings and ending up on a wing tip. Not sure about the full scale but mine will pitch the nose down when flaps are deployed but once corrected the jet will land slow and easy every time.

Vin...

Johng

My Feedback: (4)

Vin or elm - did either of you guys actually add/use the split flaps to the Y/A A-4? I've spoken to and watched a few guys at fly-ins who said they really liked what the flaps did for them. I intend to do it to mine.

Robrow - Adding split flaps should be pretty simple. Draw the outline of the flap on the bottom skin and remove with a dremel cut-off wheel. Cut/melt out the underlying foam and add a sub-spar to the front of the flap bay. Cut a rectangular piece of 1/8 ply to be the flap. Hinge it to your new sub-spar so it sits flush with the wing skin.

The pushrod can be run convetionaly from a servo, mounted forward of the surface. It could also be run completely inside the wing with a little more work. The flap servo could also be conveniently mounted inside the landing gear fairing, I think.

Robrow

I have added a pic of my A4 to the Jets photo gallery, just tap in A4 Skyhawk on the search. It was originally a German d/f kit which was built from the outset with a turbine powerplant. She still only tips the scales @ 18 pounds wet. I think the flaps should add an interesting addition.

Rob.

EddieWeeks

The book "Theory of Wing Sections" indicates
that they similar in performance to plane flaps.
This book is one of the most widely know and most
referred to in the world of Aerodynamics.

The Isobar has had split flaps its whole life and
they are very effective at producing drag and lift.

Great pics of Rocketmans Isobar with split flaps.

http://home.bellsouth.net/p/s/commun...upid=61192&ck=

The main reason I use split flaps is because they are
so easy to install and they can just scabbed on the bottom
of the wing. The wing is never cut and 4 big hinges hold
the 1/8 inch plywood flap.

The Isobar flaps are bigger than a scale A4 flap, but if I
were you I would still put them because I think creating drag
while landing is more important than people think.

Hope this helps.

Eddie Weeks
http://www.corpcomp.com/weeks1/

Robrow

Thanks for that input Eddie, theres no substitute for experience. The split falps sound like a fairly easy add-on and probably well worth the extra work.

I'll see if I can track down a copy of that book.

Cheers, Rob

Johng

My Feedback: (4)

I have a tendency to want to add too many features to a plane before I just go fly it. But, I must say, that the next step is to put on the (semi) scale leading edge slats - THat's what will really allow that nose-high approach.

Way, way more complex than adding split flaps though. I think it would start with making a female mold of the wing LE.....

bradders

SO SHE'S A BIT QUICK ON THE LANDING EH? MATE,
MANY THANKS FOR ALL YOUR HELP AND STUFF DURING THE LAST FEW WEEKS. I AM OFF TO PUNITZ IN THE MORNING AND THEN ON TO FLY IN HUNGARY WHICH I AM SURE WILL BE INTERESTING UNFORTUNATELY THE HOT SPOT IS NOT YET FINISHED BUT NO DOUBT THERE WILL BE LOTS TO SEE. I WILL TAKE MY CAMERA AND WILL PUBLISH SOME SHOTS ON THIS SITE ON MY RETURN AND WILL BE IN TOUCH THEN IN THE MEAN TIME;

TJT'S RULE O.K!
CHEERS BRAD.

Thud_Driver

My Feedback: (1)

I added flaps to my Yellow A-4 long ago just like Johng described above except I ran torque tubes inside the fuselage for the pushrods. I did it as a mod after the plane had flown a number of times.

I took off with half flaps to give lift. The OS.77 and a Dynamax with the original ducting didn't give a ton of performance and I was using all of a 400 ft runway to get off (mostly).

Full flaps gave quite a bit of drag and getting them down full too early, particularly on a dead stick, could be a big impact.

I'd use them again if I had an A-4.

A4HawkPilot

My Feedback: (3)

I hardly use my flaps. I can pretty much float it in anyway with the sport wing. I have noticed though that when I do use them it just makes it a LITTLE pitch sensitive. They sure look cool too.

mlevings

My Feedback: (14)

Thud_Driver, do you have any pics of your installation. I have a Yellow A4 that wants to land way faster than I do. I have it all apart right now for repair (spun it in on final) so it should be pretty easy to modify.

Thanks,

Mark

Jackjet

My Feedback: (1)

Pilots ,
I am installing flaps AND spoilers AND leading edge slat(s) on a Byron A 4 -do I need all this -no -BUT I like the way it looks-plus a FULL set of gear doors too.

Jackjet

Johng

My Feedback: (4)

Jack:

Have you got a design for the leading edge slats? I've rolled one around in my head, but I'd like to see what you have. The design ofthe tracks/rollers/whatever to allow the correct movement of the slat while not jamming, and having sufficient strength is what interests me. Can you post some details?

rcav8tr

Hi Jack

Keep me updated with your progress. I've got a Byron A-4 waiting patiently for my SimJet 2250. Plan to use it as a scale project.

Ed

Thud_Driver

My Feedback: (1)

mlevings,

No, sorry, I don't have any pictures. That airplane was one of the very original Yellow A-4's (late '88 or early '89). In fact I got it before the manual and plans were finished, they had to send them later. The inlet/exhaust duct efficiency back then was bad (4" exhaust outlet on a Dynamax) and I didn't know any better, so I used the flaps to help the takeoffs mainly. They also helped a bunch on landing too as I had the scale wing and was flying at an elevation of 3000' in the hot desert.

I just outlined roughly a 2"x8" (whatever the distance from the fuse to the aileron was) and cut out the bottom sheeting. Cleaned out the foam and ran wood around the edges. Then I used flat pinned hinges into the wing and a ply/balsa plate for the flap. Ran a torque tube (ala sport ailerons) into the fuse and ran a servo linkage to it. Took only a day or two to do it. Since the servo links in the fuse were probably the hardest part, putting a servo in each wing is probably the easier way. I wasn't real concerned about looks back then, but if you have a flat white finish or thereabouts on the bottom, matching the paint won't be hard.

mlevings

My Feedback: (14)

Thud_Driver, thanks for the info. Actually right now, my wings are stripped down to the wood. It should be an easy mod it sounds like. My A4 is also a very old yellow kit. I have the sport wing though. How much flap throws were you using?

Thud_Driver

My Feedback: (1)

I used about 25 or so degress for half and around 60 degrees for full. The full setting was pretty dramatic for slowing down - I got them down full too early on a dead stick once and ended up short. You may want a little less throw if you want lift only or as much as I did if you want lots of drag. In the previous post, I think I said 2" wide, but they could have been more like 2.5" of moveable surface.

I also ended up using a flap-elevator mix to trim out the pitch change. You may also want to use a servo slow setting to slow down flap extension and reduce the impact of the pitch change. On a go around you will want to get them up to half pretty early in the process.

This mod isn't hard, particularly if the jet is stripped down. So I would suggest you go for it.

mlevings

My Feedback: (14)

My main concern right now is weight. I was at 12lbs before I stripped it down. i assume it will be at least that heavy again before I add the flaps. It has an OS .91/ BVM fan setup. It's fast but too heavy to slow down without stalling.

Mark

Thud_Driver

My Feedback: (1)

As I recall, my Yellow A-4 was about 10 3/4 pounds new and was probably 11 1/2 after the multitude of glass/bondo jobs on the nose. Back then, this all seemed a pound to a pound and a half heavy as everybody else was claiming under 10 on their DF airplanes. Today, I don't worry about the weight as much.

smokinT

My Feedback: (6)

Bob Boswell had a nice article on the "newest" version of the Yellow A4 several years back in Flying Models mag. He reviewed the scale wing version and put scale split flaps on it. It looked really simple. He placed two metal-gear mini servos in the aft end of the landing-gear pods and cut the pods aft end to rotate with the flap. Looked cool but his opinion was that it made it quite sensitive and unstable feeling but did slow it down some. I also have this particular aircraft on video and it landed very fast w/o the flaps. Unfortunately it was lost some time later to the dreaded A4 low high bank high speed snap.

Todd

Shaun Evans

Hi,

The flaps aren't hard to do. They do help on landings. I've flown it both ways, and I notice a difference. I agree that the weight is a thing with this plane, but I've also flown it at 14.5 pounds. My latest one was built by my nephew with split flaps, BV wheels and brakes and operable scale speed brakes. That one came in at 12.5 pounds dry. With a BVM .96 and Viofan, it was pretty fast.

With a little nose-heaviness, the plane takes longer to rotate, but the high-speed stall is a lot harder to enter.

Jackjet

My Feedback: (1)

Johng and Ed,
what I will do is just make the L.E. droop instead of actual slats -untill I can figure out a way to do it scale-that way each wing will only have 4 servos in it.

Jackjet