Enerjet Pterodactyl help

Anyone know what thickness balsa was used for the fuselage of the old Enerjet Pterodactyl? I'm trying to clone one and the plans don't specify. Thanks for any info you can provide.

Hi, Eric !

I believe the fuselage is 3/8" hard balsa . . .

www.oldrocketplans.com/enerjet/Enerjet_KE-6_Pterodactyl.zip

Dave F.

Ez2cDave said:

Hi, Eric !

I believe the fuselage is 3/8" hard balsa . . .

www.oldrocketplans.com/enerjet/Enerjet_KE-6_Pterodactyl.zip

Dave F.

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Thanks Dave, I believe you're right.

Curious how you arrived at 3/8" since it's not shown on the templates? Would I be correct in assuming you traced a known thickness from something in the drawings (like one of the pylon mounting plates, which is 1/8" per the plans) and then compared that to the mount spacer drawing (which is the thickness of the fuselage). Anyway that's what I did and came out with that same thickness estimate, though whatever method you used might be a whole lot more accurate than mine.

Eric,

It was a combination of the memories of building several original ones 45+ years ago, remembering the "fun" of sanding the "V" profile into the fuselage, and looking at the drawing showing the top view in the area of the Canard.

Dave F.

Ez2cDave said:

Eric,

It was a combination of the memories of building several original ones 45+ years ago, remembering the "fun" of sanding the "V" profile into the fuselage, and looking at the drawing showing the top view in the area of the Canard.

Dave F.

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Thanks Dave, can't ask for any better credentials than first-hand experience. 3/8" it shall be!

Rktman said:

Thanks Dave, can't ask for any better credentials than first-hand experience. 3/8" it shall be!

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Eric,

Be sure to us "hard" balsa for the fuselage !

Dave F.

The fuselage thickness is 2/8 inch hard balsa. I have a original kit and it measured at 2/8 not 3/8. Otherwise quarter inch thick.

The fuselage thickness is 2/8 inch hard balsa. I have a original kit and it measured at 2/8 not 3/8. Otherwise quarter inch thick.

Thanks for the information. I'm toying with cloning the Pterodactyl. I have to wonder if the plans at JimZ were full sized or around 95%. Although I wouldn't be surprised if I was tripped up by a quirk of my computer or printer.

Doug Holverson said:

Thanks for the information. I'm toying with cloning the Pterodactyl. I have to wonder if the plans at JimZ were full sized or around 95%. Although I wouldn't be surprised if I was tripped up by a quirk of my computer or printer.

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All the laser cut flying surfaces are available from eRockets except the fuselage. https://www.erockets.biz/semroc-las...yl-set-of-4-sheet-a-b-1-18-balsa-sem-fej-ke6/

I'm going to order those and fab my own fuse and pop pod. You could go that route if you're unsure of the JimZ templates.

Does Semroc include the boom?

Doug Holverson said:

Does Semroc include the boom?

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No you'll have to make your own. Not a difficult shape so should be easy enough. Talked to Randy about it several times but it doesn't seem to be a priority with them right now.

Doug Holverson said:

Does Semroc include the boom?

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You can stitch pgs. 5 and 6 together from the plans to get a template for the boom. Use the nose block pieces from the Semroc balsa sheet to check for size. Up or down scale the template as needed.

I'll likely order a couple of Semroc Pterodactyls when I get home. $18 doesn't seem too bad for four big sheets of laser cut balsa.

I mean, it takes time to draw that stuff up in CAD and time to wrestle with the temperamental laser cutter that's down more than it's up at OMG.

Posted this on another thread.

Just an update. Finished the build and several things become immediately obvious.
First the size: for something designed to use E and F motors I expected a somewhat larger glider (my initial impression came from a 1995 Sport Rocketry article that incorporated the templates but didn't mention its size).

Second, it's ruggedly designed. All flight surfaces use 1/8" balsa, and the fuselage is 1/4" hard balsa. Moreover, per the instructions, I strengthened it with tissue/dope. It's pretty much bulletproof now.

Third, it's just a tad weighty for its size/shape IMO (26 grams or just under an ounce). And that's fine with me. I reason that with its mass, I can feel comfortable using a C motor and it'll come down fast enough that I won't lose it in a moderate size field. It should also handle breezy days better as well. And I always have the option of stepping up to a D or E motor at a larger launch site.

Just a final note: don't use the templates printed in the '95 Sport Rocketry magazine. It doesn't scale up correctly. Instead use the templates from the JimZ site (https://www.spacemodeling.org/jimz/ke-6.htm), it's accurate.

Nice job, Eric !

Dave F.

Rktman said:

Just an update. Finished the build and several things become immediately obvious.
First the size: for something designed to use E and F motors I expected a somewhat larger glider (my initial impression came from a 1995 Sport Rocketry article that incorporated the templates but didn't mention its size).

Second, it's ruggedly designed. All flight surfaces use 1/8" balsa, and the fuselage is 1/4" hard balsa. Moreover, per the instructions, I strengthened it with tissue/dope. It's pretty much bulletproof now.

Third, it's just a tad weighty for its size/shape IMO (26 grams or just under an ounce). And that's fine with me. I reason that with its mass, I can feel comfortable using a C motor and it'll come down fast enough that I won't lose it in a moderate size field. It should also handle breezy days better as well. And I always have the option of stepping up to a D or E motor at a larger launch site.

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Eric,

The Enerjet Pterodactyl was designed to fly on Progressive Burn composites motors, ranging from the E24 to the F67 . . . It had to be built strong, especially if flown with a "Pop-Pod", rather than as a Parasite Glider on the Aero Dart !

Dave F.

Ez2cDave said:

Eric,

The Enerjet Pterodactyl was designed to fly on Progressive Burn composites motors, ranging from the E24 to the F67 . . . It had to be built strong, especially if flown with a "Pop-Pod", rather than as a Parasite Glider on the Aero Dart !

Dave F.

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Wish those Enerjet motors were still around. That E24 has a nice thrust curve when compared to a D12 or comparable Aerotech motors. Quick spike to get the model off the pad and then an even power increase instead of a quick drop off. Bit gentler than an AT motor. Because of its small size it'll be hard to keep eyes on it so I'll probably limit motors to C6s or a D12 at most.

Eric,

The big difference, other than being composite motors, is that they are NOT "end-burners" but, essentially, "core-burner's" . . . As the motor burns, more and more fuel area is exposed, progressively increasingly thrust, accordingly.

In a BP motor, like an FSI F100, this was the general configuration and performance . . .

https://www.rocketreviews.com/fsi-f100.html

I really miss core-burning BP motors . . . Estes, are you listening ?

Dave F.

I'm back with trying to clone this. eRockets isn't currently accepting orders. Are the plans at JimZ about 104% oversize or am I suffering a printer quirk? The balsa sheets seem to be 3-1/8" wide instead of 3".

Never mind. They're taking domestic orders. I finally bought the two sheets four years later. Too bad most of their SemRoc Centuri fantasy kits are all sold out. Now to lick the scaling thing. Is the boom 13-5/8" long?

I received my sheets. Can anybody tell me exactly how long the boom is and how tall it is on each end?

Doug Holverson said:

I received my sheets. Can anybody tell me exactly how long the boom is and how tall it is on each end?

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It looks like Dave's post #2 has a lot of information. I have an old Energet catalog. It shows the overall length from the nose tip to the tip of the tail (rudder) to be 14.9" . The wing span is 9.3". The canard is 3.3" wide. Glider weight is 1.6 oz. Unfortunately, I don't have the boom length.

Hope this helps . . .

Dave F.

I had printed out a full scale Pterodactyl plan a while back to the published 14.9" length.

Measured the length of the boom by itself from the top view and it worked out to be 14.2" long.

The thickness of the boom measures right at 1/4".

The cool thing about the basic Pterodactyl design is that it is infinitely scaleable up and down.

Okay, going from the JimZ plans and the Semroc pieces. I'm going to make the boom 14.2" long, 1.4" thick, 3/4" tall in front and taper it to 1/10" or 3/32" in back.

Doug Holverson said:

Okay, going from the JimZ plans and the Semroc pieces. I'm going to make the boom 14.2" long, 1.4" thick, 3/4" tall in front and taper it to 1/10" or 3/32" in back.

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Will we be (hopefully) seeing a build thread?

Ez2cDave said:

Eric,

The big difference, other than being composite motors, is that they are NOT "end-burners" but, essentially, "core-burner's" . . . As the motor burns, more and more fuel area is exposed, progressively increasingly thrust, accordingly.

In a BP motor, like an FSI F100, this was the general configuration and performance . . .

https://www.rocketreviews.com/fsi-f100.html

I really miss core-burning BP motors . . . Estes, are you listening ?

Dave F.

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Remember how reliable the cored BP motors were (or weren't) esp. after storage? This is a very strong clue as to why you don't see them in mass production by Estes. They have been prototyped, in fact I have couple of C core burner prototypes in my collection. The B14 was just a B4 with the core post-drilled manually. That operation is why those are no more, the B8 being a measly machine-formed half filled C5.

Rktman said:

Wish those Enerjet motors were still around. That E24 has a nice thrust curve when compared to a D12 or comparable Aerotech motors. Quick spike to get the model off the pad and then an even power increase instead of a quick drop off. Bit gentler than an AT motor. Because of its small size it'll be hard to keep eyes on it so I'll probably limit motors to C6s or a D12 at most.

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Why would you want progressive thrust? It is the most stressful thrust profile for the airframe and results in lower acceleration off the pad. Once manufacturers figured out how to do segmented grains more easily these went by the wayside. The D12 actually has a nicer thrust curve IMHO.