Ziroli F9F Panther enlarged by 10%


I had been thinking about a Ziroli Panther as a first jet project for a number of years. I figured with that straight wing, flaps, and generous wing area, I might have a prayer of getting off of the grass fields I fly from. I've also always liked the looks of the Panther and the Bridges at Toko-Ri is one of my favorite movies ("Where do we get such men?")

I'd been putting it off as I didn't really want to get into the hassle of ducted fans and the turbines were too expensive. Then a friend of mine in our club, Capt. Scott "Snack" Strimple finally got his HotSpot with a JetCat P-120 going. I saw it fly and it was great. It looked, sounded, smelled, and flew like a real jet, and operation (well taking off anyway) from a short grass field was NOT a problem.

Luckily, Scott was also a DEALER for JetCat and Planes Plus and got me a deal on a P-80, Kangaroo, and all the associated goodies (how CONVENIENT!). I got permission from the Klenke family CFO (I may be in Europe for a few weeks next summer - quid pro quo), and, thanks to a lot of help and encouragement from Scott, I was off and running as a certified jet jock! The 'Roo has been a challenge, a great, durable learning plane, and is fun to fly, but I'm really a scale nut, so it was only a matter of time before the Panther came up again.

I was reading RC Universe one day and came across a thread on building Panthers. Apparently Joe Huntley had digitized the Ziroli Panther parts templates and a fellow named Jesse at Laser Works in Texas was cutting the parts for a great price. In that thread was a response from a gentleman named Reuben Saliba from Malta, who had built a Ziroli Panther from wood and installed a turbine. I emailed Reuben and my subsequent detailed conversations with him via email (thanks Reuben!) convinced me that the Panther would be a good platform for a turbine. In one of his emails, Reuben mentioned that if he were to build the Panther again, he would blow it up by 15%. Also, in a previous phone conversation, Jesse mentioned that he was reducing the Panther parts by 80% for a customer who wanted to build an EDF version. A quick call to Jesse confirmed that he could easily enlarge the parts by 10% or 15% (although the notch sizes would also change, but that would be easy to deal with). I also called Robart to check and see if they could fit slightly longer struts to the Panther gear set they offer - they could. The only problems remaining were how to deal with the "plastic" parts like the tip tanks and canopy, etc. I figured I could make my own inlet ducting if its even required for the turbine version (it may not be). I also decided that I could modify the stock tip tanks by increasing their length by 10%. I could also possibly modify the stock canopy to look OK on the enlarged version, but I also may have to pull my own. With those questions answered, I called Jesse just in time to have him cut my Panther parts at 110% of normal size. I received the parts within a week and a half and they were very nicely done. A quick order to Balsa USA for a big box of balsa sheets and sticks and I was ready to begin.

I would also like to thank Harley Condra and Larry Nobel whom I met on RC Universe for their discussions of my Panther project and their experiences with Larry's Panther. They gave me a lot of good feedback and suggestions.


The following features are planned for the "Super" Panther:


Construction on the Panther has begun! I started by building the stab because it was easy and didn't require me to completely clear off my workbench to begin construction. Below you can see pictures of the stab construction along with my Raptor heli undergoing repairs (blown auto...) The parts from Laser Works for the stab matched the outlines on the parts drawing EXACTLY, but when construction started, it was found that S3 was about 1/4 inch too long and resulted in the leading edge not laying out straight. A few seconds with an Xacto knife and some sand paper fixed that quickly. You can actually see the result in the photos below by looking at where the modified S3 ends in relation to the leading edge vs. the other stab ribs. I've had a few friends who have built from Ziroli plans and have mentioned this type of problem. I will be sure to measure and trial fit everything as I go so it comes out straight and without any "dips" or "humps" in the lines.

Update: 31 October, 2002

The construction of the stab is finished. It is shown below with the .75 oz. glass and one coat of epoxy. It will get a second coat of epoxy (I'm using Dan Parson's method for glassing) and be wet sanded before getting the primer coat. I added balsa blocks inside the hinge line at the location of the hinges and used Robart small hinge points - 5 per side. I also fabricated the joiner wire and drilled the holes for it, so the stab is completely ready to mount on the fuselage when its completed. The stab is shown over the original plans so you can see how big this plane is going to be. I think is going to be noticeably larger than the stock Ziroli kit, but not so large as to be difficult to move around (that's what I hope anyway)

I've started on the wing framing. There are pictures below of the wing framing in progress. Again, the pictures are over the original plans so you can see the relative size. The original method of mounting the wings is not adequate for a 30 lb. plane capable of 150 MPH, so I'm modifying it. Notice that the wing tubes extend an extra rib bay into the wings and are tied into the 1/16" plywood shear webbing. I also replaced the balsa spares with larger basswood stock. I think the slight increase in weight is worth it - I won't have to worry about pulling the wings off in high speed maneuvers. I'm going to modify the mounting of the wing tubes in the fuselage too, but I'm not sure how yet. The smaller tube in the wings is for the servo wire to the aileron servo. I don't think the mounting of the aileron servo at the root of the wing with a bellcrank linkage is necessary or wise with turbine power.

framed wing 1

framed wing 2

framed wing 3

Update: 19 November, 2002

The construction of the wings is completed. They are shown below slid onto the wing tube. The flaps and ailerons have been cut away and hinged. The wings are sanded and ready for glassing. I will be working on that and extending the tip tanks for the next few weeks. After the tip tanks are modified, they will be attached to the wings and glassed in place. Then I will weigh the wings and see where they came out. During the construction of the wings, I made the following modifications:
  • The wing tube extends one rib bay further into the wing
  • I replaced the 1/2" X 1/4" balsa main spars with 3/4" X 1/4" basswood
  • I used 1/16" plywood shear webbing between the main spars - the wing tube ties into this shear web
  • I used two pre-fabbed access panels from J&B Access Panels to each wing for the flap and aileron servos - the aileron servos are mounted outboard on the wing so that they have a short, straight linkage to the aileron surfaces
  • I didn't like the way the plans showed the flaps being hinged, so I just added 1/2" balsa hinge blocks inside the flaps and wing and drilled the robart hinges into them - it was much easier the the build-up "hinge channels" the plans showed
left wing

right wing

both wings

These pictures show the way in which the flaps come down. In the last picture, you can see the location of the flap hinges on the right wing.

left wing & flap

right wing & flaps

both wings & flaps

Last week the gear also arrived from Century Jet Models. It is the same gear they use on their Cougar kit, its just 1/8" longer. The struts are 3/4" SS, the axles are 1/4", and the whole assembly is very sturdy. I don't think it will be possible to bend this gear. Its so strong that I'm afraid that it will transmit a tremendous amount of force to the fuselage structure where they attach. I'm going to laminate all of the formers that the gear mounting blocks tie into with 6 oz.. carbon fiber to help transfer the loads to the structure. The gear is very nicely done and I am quite happy with it. Its major disadvantages, however are is weight (see the weight budget below - ouch!) and the $'s (ouch again!). I may as well trick this plane out to the 9's now, because its definitely going to be a Cadillac...

langing gear set

main gear

nose gear

Update: 2 December, 2002

The wings have been glassed. I am now currently stretching the ABS wing tip tanks by about 3" to make them a better fit for the larger Panther. When they are done, they will be mounted to the wings and also glassed. Then I can weigh the wings and see how they came out. I'm hoping they will be less than the 3 lbs. budgeted - I need to save somewhere!

 I've started on the fuselage construction. Like most Ziroli designs, that starts with building the crutch that temporarily holds the formers in place while the fuselage is built. The picture below shows the finished crutch on the board (notice my oh-so neat and tidy workbench!). Now I have to clear off the workbench (no small task!) to build the jig on top of it. I've cut 6" pine supports for the crutch. I'll temporarily glue these to the workbench at the proper spacing and then attach and align the crutch to it.

After getting the CJM landing gear, it became immediately apparent that the landing gear mount area was not going to be strong enough. Those gear are so stiff that any stress, especially fore-aft stress, is going to be immediately passed onto the mount structure. There is now way those 1/8" lite ply formers would have taken the stress. To reinforce them, I laminated some 4 oz. carbon fiber cloth to them. They are much stronger now, and I think that they will take the loads OK.

laminated formers

Update: 9 December, 2002

The fuselage construction continues to progress. After I laminated the formers in the landing gear are with carbon fiber, I decided to construct the F-9, F-10 assembly before they were added to the fuselage crutch. I elected to do it this way for two reasons. First, I felt that I could get the overall assembly straighter if I did it separately, and second, by doing it separately, I could take the entire assembly out into the garage to work on the carbon fiber reinforcing. The carbon fiber is nasty to work with and doing it out in the garage is safer for all concerned. The pictures below show the completed assembly with the temporary bracing attached to keep it straight until the fuselage sheeting locks it in place. All joints have been reinforced with carbon fiber patches. Note that part of the forward landing gear mount block had to be removed to make room for the larger 1-1/2" wing tube. I do not think that this will adversely affect the strength of the gear mounting as the blocks are maple hardwood and still quite substantial.

The picture below shows formers F-11 and F-12 also with temporary bracing installed to keep them straight while they are installed on the crutch. These braces will be removed once the top fuselage sheeting is in place to hold them straight.

The crutch was aligned on a temporary jig built on top of my workbench. The formers have all been added to the crutch and the vertical fin has been built. The stringers are starting to go into place. I put a piece of plastic between the hatch formers and the main fuselage to keep them separate while the stringers and sheeting are added. I believe that I will cut the hatch loose as the sheeting is applied as it will be easier to do that then to try and cut it out once all of the sheeting is in place. I plan on sheeting the top of the fuselage before removing it from the jig. I will then mount and align the wings before sheeting the bottom and completing the fuselage. Again, note the extremely neat and tidy workbench!

Update: 20 January, 2003

The fuselage planking process has started. I began with two parallel planks, one on each side, placed right at the edge of the canopy opening. I made these two planks the full 3/4" width to both ends. The result, with the first tapered plank below it,  is shown below.

Next, I started filling in the planks on both ends. These planks are tapered on both ends, towards the nodes and tail, to compensate for the decreased diameter of the fuselage at both ends. To determine the amount of taper, I take an untapered plank and tape it to the fuse so that it is butted against the previous plank in the middle of the fuselage - that section is close to being perfectly round and serves as the "datum." Then i hold down each end of the plank so that it lays flat against the fuselage. In doing so, it will overlap the previous plank at the ends. I mark the place where the plank just starts to overlap the previous plank near the middle, and the point where it overlaps the pervious plank at the end. I do that at both ends and take the plank off and cut it in a straight line between the two points at both ends. Then I take a sanding block and round off just a bit, the transition from the straight edge of the plank in the middle, to the taper at the ends. Then I fix it to the fuse butting up against the previous plank. With a bit of pressure holding it against the previous plank, you can usually get a pretty good joint, and filler takes care of the rest.

Here is the result of a week end's worth of planking. Additional planks will be added up the vertical stabilizer until the horizontal stabilizer cradle is reached. The sheeting above this point is added after the horizontal stab. is mounted and is 3/32" sheet. The planking down to the stub wings will then be added. At this point, the planking will be sanded and I will mount the wing tubes in the fuselage because I can get to them easily and the fuse is perfectly aligned with it on the jig. I will then make a new jig in which the fuse. can be mounted inverted and the planking will resume. The planking looks a bit rough now, the the B-17 looked the same way, and with sanding and a fair amount of filler for the joints, it came out very well.

Update: 3 March, 2003

Finally, another update! I've been working on the Panther off and on, but between going to Forida Jets and work commitments, I haven't been able to post any updates lately. The planking of the top of the fuselage was completed. When this was done, I took the entire fuselage, in the jig, into the garage. There I rough sanded the planking and also used the flat concrete floor to align the wings and epoxy the wing tubes into the fuselage. Then I popped the fuselage off of the jig and cut out the top hatch. This must be done at this time because it involves cutting the fuselage formers inside the fuselage and would be very difficult with the entire fuselage planked, to say the least.

After the top hatch was cut out, the fuselage framework was very susceptible to twisting, so I fabricated another simple jig to hold it straight upside down so I could plank the bottom. Once it was in this jig, I mounted the removable former for the nose gear mount (I used the Century Jet Cougar former outline as a guide), and built the battery box between formers F-1 and F-3. Then I started planking the bottom as shown below.

Update: 18 March, 2003

Planking of the fuselage is finished. I've left the sheeting off of the upper portion of the sub-wings until I work out some of the structure in there. Next I have to rough sand the new planking, work out a nose-cone, get some of the interior structure done, and finish and glass the fuselage. Here are some pictures of my Panther on display at the club field along with my favorite copilot and one of my helis in the background.

Update: 8 April, 2003

Before I buttoned up the sub-wings, I wanted to get the turbine mounting setup while I had more room to work. Since the wing tubes would go right in front of the turbine if they were joined in the center, I needed some way to carry the load across the top of the fuse. You can see in the pictures of Larry Noble's Panther below, he use a removable piece to bridge the gap across the F-10 former to carry the load and keep the wings from "squashing" the top of the fuse when you pull G's. I wanted something a bit stronger and non-removable. I came up with the "ring former" you see below. Its 1/4 inch 5-ply aircraft plywood laminated with 6 oz. carbon fiber on both sides. Its quite stiff and strong. I epoxied it to the front of the F-10 former in line with the wing tubes and I'm going to lash the inner ends of the wing tubes to the ring former with kevlar thread. You'll also notice that I mounted the turbine (my JetCat P-120) farther forward than shown on the plans or in the Panthers below. I did that to help with the CG. Right now, my Panther balances on the CG with the turbine in and no extra weight in the nose. I hope to be able to continue this trend and totally eliminate the necessity to add any nose weight, thus saving about 2 lbs. over the stock Panther.

In the pictures below, you can also see the main and 2 saddle tanks built for me by Gary Muller at JetTech. The workmanship is excellent and they will hold a total of about 140 oz, with 48 oz. of it in the saddle tanks, behind the CG. This should help the plane rotate on our grass field better than if all of the fuel was up front.

Engine update: I just upgraded the P-80 that was headed for this Panther to a P-120, so I'm not as concerned as before about the weight - although I'd still like to keep it down to 30-32 lbs.

Weight Budget

I'm a bit concerned about the weight of the Panther, but not sure what I can really do about it. I have heard from other builders of standard sized Ziroli Panthers with turbines that they are at about 29 lbs. wet. I'd like to stay as close to that as possible, and I figure 32 lbs wet is a good goal. At 32 lbs. wet, the wing loading will be 58.05 oz./sq. ft. Not light, but better than the 67.63 oz./sq. ft. the stock Panther carries at 29 lbs. wet. With about a gallon of fuel, let's assume 7 lbs for fuel weight. At 32 lbs. wet, that leaves 25 lbs for aircraft empty weight. Here's an attempt to keep track of (and estimate) the weight:

9 oz.
(48 oz.)
(72 oz.)
JetCat P-80 turbine (complete with ECU, battery, etc.)
72 oz.
S.S. tailpipe
(10 oz.)
Wing tube
12 oz.
Fuel tanks (including full UAT)
(20 oz.)
Landing gear
48 oz.
Wheels and brakes
(20 oz.)
servos (10)
(15 oz.)
Receiver and batteries
(20 oz.)
Ballast (nose weight)
(32 oz.)
(20 oz.)
(398 oz.)

It looks like its going to be tight to meet the 25 lb. dry weight goal. Also, I'm sure I've forgotten something. I'll replace the estimated weights with actual as the parts are completed/arrive and I can weigh them.

Motivational Material

These are pictures of a Ziroli Panther built by Reuben Saliba from Malta (in Europe).

Here are some pictures of the Panther built by Larry Noble.

Here are a few pictures of Larry's Panther at the Fresno Jet Rally in September of 2002.





Here are some pictures of other Panthers in alternate paint schemes. Most of these are the same size as the Ziroli Panther, but are built from kits with fiberglass fuselages.