MPC Flat Cat (twin-tail dimensions?)

[blackshire]

Hello All,

I'm working on building a Quest Flat Cat boost-glider as the original MPC version of the kit that had twin vertical stabilizers.

The scans of the MPC Flat Cat instructions on JimZ's web site (see: http://www.dars.org/jimz/mpcr216.htm ) do not directly give the dimensions of the balsa parts, but there are black rectangular "inch markers" on the scans of the wing & tail assembly balsa sheets. I was unable to print the plans at full size (it only prints at a larger size, at least with my computer), so I printed them up and manually divided the oversized "inch marker" for the tail assembly balsa sheet into 1/16ths using a drafting compass, then measured the parts using it.

Due to the thickness of the parts' black border lines, measuring the dimensions of some of them was difficult. The rectangular horizontal stabilizer has a chord of 2", and its span *appears* to be 5 + 3/32" (the thick border lines make this rather uncertain). The two vertical stabilizers' dimensions are more uncertain due to very thick border lines. Their height could be 1 + 1/2", or 1 + 9/16", or perhaps even 1 + 17/32". Their root chord looks like 2" and their tip chord appears to be 1".

Does anyone have accurate measurements of these twin-tail parts on the MPC Flat Cat? Many thanks in advance to anyone who can help.

[shockwaveriderz]

According to the original FlatCat BG dimensions shown in the 8/69 issue of MRm the fin root is 2"; the fin span is 1.5" and the fin tip is 1".


see http://ninfinger.org/rockets/ModelRocketry/ModelRocketry.html

hth

terry dean

[mrhemi1971]

See now....You guys are gonna make me build another Flattie.....I HATE (haha) when that happens...... :chuckle: :chuckle: :D

[blackshire]

According to the original FlatCat BG dimensions shown in the 8/69 issue of MRm the fin root is 2"; the fin span is 1.5" and the fin tip is 1".


see http://ninfinger.org/rockets/ModelRocketry/ModelRocketry.html

hth

terry dean

This is perfect--Thank You Very Much! In addition to building my own MPC-style Flat Cat, I'm working on helping a local school group that is using model rocketry, and the teacher (actually, a local college professor) is very big into *constructing* model rockets rather than merely *assembling* near-"Ready-To-Fly" models. Stine's Flat Cat article will be perfect for scratchbuilding (no pun intended, given the model's name).

For the pop-pods, while BMS can make the 1 + 3/8" long balsa ogive nose cones, I'm not sure if he can order T20 tubing, the "internally telescoping" motor tubes, and the thin motor clips from Quest as separate parts anymore (they don't appear to list parts on their web site or in their catalogs). If necessary, BT-20 tubing, BNC-20A or -20B nose cones, original Estes-style motor clips, and BT-20 mylar motor clip lock rings (sleeve tubes) can be substituted to build the pop-pods.

[Bob Kaplow]

One modification I'd suggest to the Flat Cat or any "Piece X" BG design:

The notch cut into the boom creates a weak point, and the glider really likes to break there. And when it does, it's virtually impossible to fix and still have the pod come off without binding.

I have a simple rule: NEVER cut the fuselage in front of the wing, or any where that it is not reinforced with something glued to it.

My suggestion on the Flat Cat is to invert the hook, so that the piece is cut out of the pod. The pylon is reinforced by being glued to the motor tube, so it's not going to break.

[o1d_dude]

What Bob said.

Never cut into the fuselage of glider. You can sandwich a cut with thin thin thin ply or CF but it will probably still break there regardless. I used to drill a hinge hole in the fuselage and Hot Stuff a length of aluminum tubing into the hole for strength. The wing was attached at that point via a hinge to pop the wing up as a dethermalizer. That was also the point where the fuselage would eventually fail but it was easier to replace a fuselage than a whole glider.

Gliders "auger in" quite a bit and it's usually a compression break rather than a side to side or lateral one although "cartwheeling" a glider along the ground can do that, too.

I've rarely been able to find the mythical "long grass" that is alleged to protect against flying model damage.

[Bob Kaplow]

If the standard Flat Cat pod design is what was called "Piece X" then this is the "Reverse Piece X" or "X-Piece" design that I suggest as an alternative. Forward is to the left.

[blackshire]

Bob and Kit,

I thank you both for confirming what I've always suspected. I've never flown a pop-pod B/G, but to me the fuselage notch point always looked like it would be a weak point. Besides, the balsa "slab sides" that are cemented on both sides of the notch generate drag, perhaps more than the "reverse X-piece" protruding from the top of the fuselage boom.

Bob, thank you for the drawing. I will pass it along (with acknowledgement to you) to the local model rocketry educational group. Having fewer broken gliders means more flights and less frustration!

[Bob Kaplow]

Bob, thank you for the drawing. I will pass it along (with acknowledgement to you) to the local model rocketry educational group. Having fewer broken gliders means more flights and less frustration!

FYI, this is NOT what I use on my competition gliders. My pods are a bit more complicated, and not something I'd recommend to a beginner. The idea of the X-Piece hook was to stay as close to the original, both in design and in skill level, while fixing the weakness. And while it may not be clear from the drawing, you still need the balsa side plates, but now they are on the pod instead of the glider.

For serious competition, I'd recommend something like the Apogee / Gassaway molded hooks. They have the neat feature that they are symmetrical: exactly the same piece is used on the glider and the pod, you just reverse the direction.

[Shamous]

I've rarely been able to find the mythical "long grass" that is alleged to protect against flying model damage.
It's called the Kansas Tallgrass Prarie. ;)

[o1d_dude]

It's called the Kansas Tallgrass Prarie. ;)

Thanks for pointing that out.

I've placed the Flint Hills of Kansas on my short list of places to visit when I my show on the road. Too many times I've seen the flatlands of Nebraska instead.

[blackshire]

FYI, this is NOT what I use on my competition gliders. My pods are a bit more complicated, and not something I'd recommend to a beginner. The idea of the X-Piece hook was to stay as close to the original, both in design and in skill level, while fixing the weakness. And while it may not be clear from the drawing, you still need the balsa side plates, but now they are on the pod instead of the glider.

For serious competition, I'd recommend something like the Apogee / Gassaway molded hooks. They have the neat feature that they are symmetrical: exactly the same piece is used on the glider and the pod, you just reverse the direction.

These models are for an educational program, so ease of construction and durability outweigh absolute performance in this case. I know that either the glider or the pod's pylon has to have the balsa side plates with the Flat Cat configuration, but I'd rather have them--and their drag--leave with the pod. :-)

I've always been partial to the maple dowel/balsa shim "hook" and launch lug "socket" with short-span balsa fins/mount stabilization plates, as used on the Estes Orbital Transport. (The plates should be on the pod or the large parasite booster rocket to minimize the glider's drag.) The "hook" and "socket" can be either on the glider or on the pod. While not as aesthetically neat or low in drag as the molded hooks, they're easy to make from scratch.