F-20 Tigershark Makeover

Nov 09, 2012 3 Comments by

This makeover article comes to us from Rick Mitchell (white-wing F-20) and Mike Oser (red-wing F-20).

In the real world, there are propeller driven aircraft as well as those powered by jet engines. Both also exist with radio control models, but the cost difference between the two can be substantial. As a result, RC has a separate, in between class of model airplanes. These models look like jet planes but are powered by standard reciprocating engines, all at much less cost. These are today’s radio controlled propjets.

Years ago I built a propjet Phoenix Models F-20 Tigershark, but I only had two flights before it was destroyed. I had the ailerons set up much too sensitive, and the model tended to float on landing. On my first flight, my F-20 would not settle down on landing, and it overshot the runway and severely damaged its wing’s leading edge when it ran off the runway. On my second flight, the overly sensitive ailerons caused me to over control the model and it crashed. All of this was with hundreds of prior flights on other models under my belt.

When I got back into RC in 2012, I often thought about what went wrong with my F-20, and how could I correct that and maybe build another one? After all, this model has been available for many years and others are successfully flying it. I read several forums and looked at YouTube video about this F-20. I soon found that others had similar concerns as I did years ago, but had still achieved success. This touched off numerous pages of discussion on the forums about how to make the F-20’s basically good design into an outstanding aircraft.

One of the individuals who contributed many great ideas for improving the F-20 was Mike Oser, and I soon made contact with him. He added many modifications to his F-20, and I later saw YouTube video about flying his modified F-20. All of this encouraged me to order another F-20 and try again!

After reading the forums and emailing with Mike, I settled on the following changes for my second F-20: shorten each wing and ailerons by 4”, add wing fences to improve the low speed handling, add dummy rocket rails instead of wingtips, reduce aileron throws, re-calculate the CG and add a dummy jet engine exhaust tip to improve my model’s looks. My F-20 is powered by a Thunder Tiger .46.

Since I already had to recover the wing after clipping it, I decided to change my color scheme to resemble the first prototype Northrop F-20 Tigershark that had a beautiful red and white color scheme with black striping. This also meant recovering the tail surfaces and part of the nose section. The result was quite a nice looking model airplane, and the shorter wingspan made the model look more like the real jet.

Mike assisted with most of these changes, but the F-20 that he built before me was modified much more extensively than mine. Mike installed an OS .55AX with a Macs muffler, added retracts, and he moved his landing gear mains forward which also meant moving his fuel tank and adding a Perry pump.  He also made some structural improvements, added a dorsal fin, and arranged for his ailerons to droop slightly as flaps for even smoother landings. Mike recalculated his CG using a software app based upon the new dimensions on his F-20. Mike later ran these calculations for my F-20’s CG, too, something I had never seen before in RC. Very impressive!

The results of these modifications are two nice looking and great flying modified Phoenix Models F-20 Tigersharks. Because this ARF is all balsa and ply, the changes are easy to make while improving the F-20’s looks and performance. These models look like they are jet powered but are available at a fraction of a jet’s cost as this ARF is reasonably priced and uses a two cycle engine. The modified F-20 can fly a full slate of aerobatics and make high speed passes yet has smooth landing speeds. Mike said that even with his retracts and clipped wings, the F-20 can be slowed to a crawl for landing, and I have seen the video to confirm this!

The Phoenix Models F-20 just may be one of the best propjets available today with its low cost, easy modifications and great performance. Text & Photos By Rick Mitchell and Mike Oser

RICK MITCHELL’S PLANE:


Strip all covering from the wing halves with the exception of the wing tips as they will be cut off. NOTE: All control surfaces are pre-hinged. You will have to break them and re-hinge after recovering this model so purchase additional hinging materials ahead of time.


Cut off the last 4″ of each wing panel just outside that rib.


Add a 1/8″ balsa sheet or plywood dummy rib on the outside. Sand the edges slightly. Add 1/4″ plywood inside the old rib to use to attach the dummy rocket rail with screws.


Test fit the rocket rail. Its height is the same as the last rib. Mark off the center line of the rail and the center line of the rib for alignment. Locate four spare screws to attach the rails to the last ribs for later. Drill the rails and last rib and test fit the screws.


Finished rocket rails and wing fences ready for covering. The rails and fences are my designs based on pictures from Mike.


The shortened wing halves recovered in Monokote Jet White to resemble the prototype F-20.


Strip all tail surfaces of covering.


I recovered all tail surfaces in Monokote Missile Red as it is a very close match to the original red Oracover.


Test fit the wing and begin adding red and white Monokote and contact Monokote trim as needed. Later the model will be pinstriped in black.


Close up of my F-20 nose color scheme with reference photos nearby. There are many reference photos of the first F-20 on the Internet.


The finished wing with red trim added, Air Force markings and fake aileron, flap and lead edge slats added with pinstripe. These will stand out later in the pictures.


The underside of the wing minus the belly pan.


The prototype F-20′s tail markings added.


My F-20 when 70% completed. The wing fences are missing as are the rocket rails. The attaching holes for the rocket rails are seen on the recovered wing tips.

Routine installation of Thunder Tiger .46 showing detail of the red and white covering with black pinstripe.


The plywood wing fences epoxied to the leading edge after removing minimal covering.

 


Finished model with dummy jet engine tail cone. The cone is actually a 1-3/4″ diameter wooden flower pot from a craft store painted silver with a black disc added over the bottom, and then 30-minute epoxied.

MIKE OSER’S PLANE:

Installing the main gear retracts was not as difficult as the nose gear, as there is plenty of room.  3/8″ x 1/2″ hardwood rails were added on the same ribs used by the fixed gear (seen cut away farther aft), and reinforcing ply and hardwood strips added for strength.

1/64 ply was rolled to make wheel wells, balsa sheet used to fill in around the main gear rails, and the covering replaced.

The main gear fully installed.  This location is almost 2-1/2 inches further forward than the original fixed gear, but this is actually closer to the ideal location relative to the CG.    Note the tape reminder to re-balance the plane!

The E-flite nose gear was laid on the bottom of the fuselage and cutouts made for the wheel and strut.  Space was needed to fit the nose gear and leave room for a Perry fuel pump.  1/32 ply doublers were installed on both fuselage sides to support the gear mounting plate.

3/8″ square hardwood glued to the fuselage sides at measured locations.  The gear mounting plate will be laid on these.  This avoids having to trim the mounting plate to exactly fit the tapered width of the fuselage and provides additional strength.

The gear mounting plate checked for fit.  The mounting holes are drilled and tapped, then the plate is glued in place.

The nose gear and fuel pump being installed into the nose section.  Fuel lines will be run both under and over the gear mounting plate.

 

The nose gear fully installed with cover plates.  There wasn’t quite enough room to get the steering arm under the cover plates.  The original steering pushrod was perfectly suited for this as the eflite gear uses a pushrod linkage rather than pull-pull cables.

Since there was no room left up front for the fuel tank, it was moved back to the wing area just under the canopy.  The Perry pump suffices to bring the fuel to the engine.  One advantage of this arrangement is that there is no change in CG during the flight.

The completed model, ready to fly!

 

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3 Responses to “F-20 Tigershark Makeover”

  1. DENNIS says:

    THAT DOES NOT LOOK LIKE A REAL TIGER SHARK JET…. AT ALL,,,

  2. Mike says:

    Of course not. It is a Phoenix F-20 Tigershark ARF and is only intended to somewhat resemble the F-5 / F-20. The mods are intended to make it look a little better and fly a little better than the stock airplane. It is, however, about as close as you will get with any prop jet kit or ARF.

  3. Allen B says:

    Great make-over. Very interesting that the aerobatic performance was changed so much using the fences. I know some arfs could stand to have their wings shortened a bit.
    I had this but lost it due to a rxr link loss.

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