SU-27 40" WINGSPAN

also at http://www.rcgroups.com/forums/showthread.php?t=413554

Yet another exploration into the magnificent world of the SU-27, a flat foam jet. This time, I am going XXXL. I saw the Ikarus XXL model (videos and photos , ikarus-modellbau.de) and said to myself: "Eduardo, go for a bigger one".

I am still using the Foam from Staples (r), and my brushed 400 motor. I will, eventually, get a brushless and LiPo batteries. In the meanwhile, here are the specs.

You can buy it from Ikarus here: http://www.ikarus-modellbau.de/

or from hobby Lobby here: http://www.hobby-lobby.com/

You will need a V-Mixer: http://www.ikarus-modellbau.de/ and here http://www2.towerhobbies.com/

1ST TRY

Specs:

Weight Distribution: (1 oz = 28.35 grams)

Rational Deduction - Hypothesis: The weight to trust ratio is still 46%. Same as on the 24" model. However, the wing load decreased by 2 grams per square decimeter. In theory, the plane should have an equivalent of 100 more grams of trust than the previous 24" model. Or, in other words, the plane is 100 relative grams lighter than the 24" model. It should perform better. We will see...

PLANS

su27scalegrid.pdf

I modified Stringfly's plan. It's a jpg image on top of a PDF with the right size. When printing, make sure to print in several pages without borders nor any reduction. The vertical, horizontal and diagonal grid lines I added will guide you when putting the thirty-some pages together. It is a very low quality plan, but it is enough for the creative mind.

Note: Note, in order to reinforce the structural integrity, I added a carbon rod at the wing, where the control surfaces mount. I also added another piece of depron to the tail (identical to the one under the CG). The tail is too wobbly if you do not add this. I also put a piece of fiber tape under the stabs and socked it with thin epoxy.

When mounting the servos, you might want to put them in between the ailerons and the elevators. I put the receiver back in the tail. I used an extension for the ESC/BEC and the battery which is below the cockpit.

The CG is 7 1/4 inches from the trailing edge of the main wing. I believe it can even go further ahead, up to the V joint of the wing and front fuselage. This is a wild guess. I have no certainty about the location of the CG. I am not familiar with delta wings.

Both control surfaces, stabs (elevators) and ailerons move in the same direction (weird!). They should oppose each other when attempting to change the attitude up or down, but in the case of this plane, they don't. I gave very little dynamic range to the ailerons by means of the control horns. The stab has more degrees than the ailerons. Let the tail do the work. Avoid the ailerons from  getting too involved. This is a wild guess. I do not know a lot about the dynamics in delta wing planes. I must add that I am not completely satisfied with the configuration. I might add another set of servos for the ailerons once I get a brushless.

PHOTOS

40" wingspan

One servo for stab and wing, same direction.
The aileron control horn is on minimum drive, the elevator one on max.

Added another piece of fanfold/depron in the tail for structural support. The receiver in the tail. I also added another piece of depron to the tail (identical to the one under the CG). The tail is too wobbly if you do not add this.

Battery GPMP0310 NiCd 8 cells: 245 grams of weight, 300 grams of trust with 6 x 3.5

The aileron control horn is on minimum drive, the elevator one on max.

55" x 40" (140 cm x 101 cm)

Large!

This model was the inspiration of it all:

Please take notice how the two surfaces, elevator and aileron, move in the same direction. Common sense would dictate that the flaps need to move down and the elevator up to lift the nose of the plane. That is not the case in this configuration. Watch the video http://www.rcgroups.com/gallery/videos and photos. However, the elevators have 200% more movement than the ailerons/flaps.

http://www.knaapo.ru/
It is probably the most amazing airplane of the XX Century. America should bring Mr. Sukhoi, as it did with Herbert Von Braun.

August 12, 2005

I am very exited. It is Friday. I just got off work. I arrive home, mow the lawn and grab my plane to go to the field. I arrive at the field at around 1:30PM. The field is closed so I decided to call one of the members at the store to ask him for the combination to the lock. He tells me to call General Chuck. I call Chuck and he tells me that it is too dangerous to fly alone. He does not want me to fly by myself. He is afraid and concerned. I understand what he says, yet I want to fly. I thanked him and left the gates of the field looking for another place to fly my first flight on this awesome plane.

I arrived at the College, but it was too crowded. I went to the lake, but they were charging the entrance (something they don't usually do on Fridays). It was 2:30PM and the wind was picking up with 15MPH gusts. I decided to come home and give it another try tomorrow early in the morning.

August 13, 2005

The plane flies. However, changes need to be made.

I made a couple of turns around the circuit. The plane had no difficulty taking off. With a trust to weight ratio of 46%, it is amazing it managed to fly. The thrust should desirably be at least as much as its weight (700 gr.), and preferable twice its weight (1400 gr.).

Problem: Plane too slow. Elevator, Ruder and ailerons too wobbly.

Cause: The wing does not have a profile. The flat configuration of the wing creates too much drag. I added a simple profile by means of putting another layer of Depron.  This layer should fix both the drag and the wobbly issues in the main wing. The drawback is that I lost all mobility in flaps. The tail should have all the features necessary to control attitudes. I also added a layer of depron in the tail (fin and stab) to prevent wobbling.

2ND TRY

The image shows where the depron was placed. The cost: 50 g. Do not forget to "shave" the edges to make them less resistant to airflow. 

NEW MOTOR

HACKER MOTOR WITH LARGE PROP. Please note I tried to make the slot for the prop aero-dynamical. It vibrated a lot with a rectangular slot.

The servo only handles one control surface: the stabs. The main wing is fixed.

The ESC with two sided foam tape.

The JR receiver with foam tape. There is a slot for the battery reinforced with carbon on both sides of the fuselage. It very well secured.

The big picture. Please notice reinforcements for wings and tail.

Servo setup

Motor Chart (click on it)

New Specs

Specs:

Weight Distribution: (1 oz = 28.35 grams)

Need to buy:

TOTAL COST WITHOUT RADIO AND BATTERY CHARGER: $160

If that is too much, you can buy a smaller 30" for $70 @ http://www.ikarus-modellbau.de/ or even a smaller 16.8" @ http://www.ikarus-modellbau.de/  

Other Jets @ http://www.hobby-lobby.com/electric_jets.htm

Motor Calculations (Disclaimer: I am not an engineer. Data might be wrong.)

Plane propellers and motors for RC.htm

August 27, 2005

It flies great! It climbs like a rocket.  It is extremely light. The stall speed is as predicted or even less. The max speed has not yet been tested. I flew the plane twice and made a couple of loops. It looks great!

Extremely stable plane. It landed exactly where I wanted it to land, even with 8MPH turbulent winds! It is a very docile plane!

On the next flight, I might move into aerobatics. I will need more responsive surfaces on the aileron axis to be able to do it.

I noticed two problems:

Lack of control in one of the axis. I do not have enough ailerons (the tail does not quite cut it as the only surface in charge). At the current rate, the plane needs a second or two to roll. I will have to do some changes. I might put another servo in charge ailerons restoring them as movable surfaces. As you recall, I was forced to sacrifice them to strengthen the wing.  Will keep you posted.

Another problem is the right push rod. It got stuck while flying. The plane kept on banking left. My response was not to fight it and let it turn when it happened. Thank God it got loose again. I suspected this could have potentially happened for my pushrod holder had an treacherous angle. I will be changing the pushrod rails.

3RD TRY

September 3, 2005

I have the ailerons installed. It flies great. I will put the pictures shortly, and maybe a video. It is fast and docile. I looks so real when it flies. I can also be so slow that landings are a controlled stall at 1MPH.  Looks great!

September 5, 2005

Another two flights. I tried some aerobatics. I rolled, figured 8's and loops. If I were a better flier, it would have looked much better. The plane flies awesome. It looks very realistic on the air. I will keep practicing until I become more skilled and able. I am a bit "dirty" performing the maneuvers. The plane is so forgiving and docile that it makes me look good, even though I am not an skilled pilot.

One guy at the field is building a balsa version with a gas engine. Another one asked me to make him one. I am going to share the plans and the ideas and let each one make its own.

I am trying to figure out a way of putting retractables. I would love to take off from the ground and land. I need to keep the weight extremely low. If anyone has ideas, please share.

LATEST PHOTOS

Monokote. Iron set on medium

I added Ailerons

Please notice reinforcement for tail

intranet video

- SURF -

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