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  #11  
Old 02-26-2020, 08:02 AM
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blackshire blackshire is offline
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Quote:
Originally Posted by ghrocketman
About 75% were Powr-Prangs due to lack of thrust and about 25% due to total instability.
Thank you--this could serve as a guide for PMC modelers, for which pitfalls to watch out for, and the probability of getting "stung" by each one. The F-104 is one of the possibly few fighter/interceptor designs (due to its small, rearward-positioned wings, its ventral strake [or strakes, in the case of the Aeritalia-built F-104S], and its tail assembly) that can be made stable about all three axes for vertical rocket-powered flight *without* requiring a ton of ballast up front. (With the exception of the Cox RTF [although mine flew okay for me], the X-15 kits and RTF models, such as Estes'--and the X-15 isn't very different in general layout from the F-104--flew/fly very stably, so an F-104 PMC model should, with relatively little or possibly even no forward ballast, fly equally well.)
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  #12  
Old 02-26-2020, 09:09 AM
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Quote:
Originally Posted by blackshire
A 1/32 scale (and just maybe even a 1/48 scale) PMC F-104 model should also have enough internal space to accommodate micro-R/C equipment.


My PMC building days are pretty much over, but if I were tackling a new project, I'd be doing everything possible to cut mass out of the model. Most PMC builders push the thrust to weight ratio on these birds pretty close to the minimum, and if there's any wind at all, the flight goes south pretty quickly.

My $0.02. WMMV.
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  #13  
Old 02-26-2020, 10:15 AM
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100% agreement with Mark above.
With the C5-3 returning, one should be able to use BP SU power in 18mm PMCs.
I definitely would NOT try r/c conversion.
It's enough to get one to fly in a stable rocket/chute configuration.
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  #14  
Old 02-26-2020, 07:53 PM
zog139 zog139 is offline
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(flew/fly very stably, so an F-104 PMC model should, with relatively little or possibly even no forward ballast, fly equally well.)

I respectfully disagree. I have built four F104 models and each one if them required a significant amount of ballast to get the CG where it needs to be. I used another modelers CP calculation that was derived from the cardboard cutout method. Each model flew very well. YMMV
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  #15  
Old 02-27-2020, 11:14 PM
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Quote:
Originally Posted by ghrocketman
100% agreement with Mark above.
With the C5-3 returning, one should be able to use BP SU power in 18mm PMCs.
I definitely would NOT try r/c conversion.
It's enough to get one to fly in a stable rocket/chute configuration.
I wouldn't try adding R/C capability either, myself (and I also agree with Mark's "minimum-weight maxim" for PMC models). I just mentioned it as a possibility for novel flight capabilities with larger-scale (and higher-powered) PMC scale modeling subject kits. (At the time, I was thinking about Clem Sohn [1910 - 1937, see: https://www.google.com/search?sxsrf...i10.imPDhg53VqM ], a "bat-man of the original barnstorming days" who jumped out of airplanes and then flew for seconds to minutes using his 'wingsuit,' before opening a conventional [round] parachute to land safely [a parachute failure in 1937 ended Sohn's career and life].)
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  #16  
Old 02-28-2020, 12:43 AM
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Quote:
Originally Posted by zog139
(flew/fly very stably, so an F-104 PMC model should, with relatively little or possibly even no forward ballast, fly equally well.)

I respectfully disagree. I have built four F104 models and each one if them required a significant amount of ballast to get the CG where it needs to be. I used another modelers CP calculation that was derived from the cardboard cutout method. Each model flew very well. YMMV
Depending on how many forward interior detail parts there are, especially in larger-scale (1/32 and 1/48 scale) F-104 kits (the ejection seat(s), pilot figure(s), the cockpit's/cockpits' instrument panel(s) & side panels, the radar dish and its mechanism [under a removable nose radome], etc.), the more likely forward ballast would be unnecessary, or nearly so, and:

The version of F-104 that is modeled for PMC flying can also make a difference. For example, the XF-104 and YF-104A, F-104A, and F-104C had/have shorter (from front-to-back; that is, smaller-chord), and thus somewhat lighter, vertical stabilizers than other F-104 variants (and the YF-104A also lacked the centerline ventral strake that later F-104 variants have, which would delete a bit more tail mass, in a YF-104A PMC model). Plus, some F-104 variants (the F-104B, F-104D, TF-104G, etc.) have two seats--and definitely noticeably longer cockpit canopies--which add more mass well ahead of the wings, which would benefit PMC models of these Starfighter variants. Also:

The Cox and Estes X-15 RTF models (particularly the latter) flew/fly well, and they didn't/don't need ballast. Their wings' and tail surfaces' relative sizes and locations (with respect to each other, and to their fuselages' widths, lengths, and fineness ratios) were/are similar to those of the F-104. In any event, of course I concur with the wisdom of determining the location of a PMC model's--or *any* non-kit model rocket's--CP (Center of Pressure) with respect to the model's Center of Gravity (CG), and adjusting either (or both) to ensure stability in vertical (or nearly so, for launch angles up to 30 degrees "down" from the local vertical), rocket-powered flight. But as with the RTF X-15 models, F-104 PMC models need not always require added ballast up front.
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  #17  
Old 03-03-2020, 04:56 PM
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Blackshire.

I downsized a Fat Cat F-104 Starfighter in 2011.
I included my yorf post.
Been flying it for years.

Daniel

https://forums.rocketshoppe.com/sho...104+starfighter

https://www.rocketreviews.com/fat-c...hobbs-2054.html
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  #18  
Old 03-03-2020, 11:18 PM
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Quote:
Originally Posted by dlazarus6660
Blackshire.

I downsized a Fat Cat F-104 Starfighter in 2011.
I included my yorf post.
Been flying it for years.

Daniel

https://forums.rocketshoppe.com/sho...104+starfighter

https://www.rocketreviews.com/fat-c...hobbs-2054.html
Thank you for posting both of these links! (For anyone who hasn't opened them yet, the first one also contains a link to a launch video...). While the wings look "over-spanned" for scale appearance, this need not be the case, as the three "keroperox" (JP-4/hydrogen peroxide) AR2-3 rocket engine (and RCS thrusters)-equipped NF-104A aircraft (see: https://www.google.com/search?sxsrf...i10.zJKT9DrqVXI [NF-104A plastic model conversion kits are also shown here]) had extended-span wings. (An NF-104A model rocket--or PMC--would make an interesting clustered-motor model [with two--likely different-sized--motors mounted in the GE J79 *and* the Rocketdyne AR2-3 exhausts]. As long as the model's CG point and the AR2-3's thrust line were properly lined up, so that the thrust line passed through--or very nearly so--the CG, it should fly straight, although the motor in the angled AR2-3 section might make it "walk" sideways ["downward," with respect to its wings] through the air.)
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http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
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