I want to fly an A-4 at Flite Fest...

SP0NZ

FT CAD Gremlin
Staff member
Admin
Moderator
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...Out of curiosity, how much does a sheet of water-resistant weigh?

I measure all 50 sheets of the first box of production foam I received back in early 2016:

Average weight is 111 grams [3.9 ounces] /sheet.
 

SlingShot

Maneuvering With Purpose
I measure all 50 sheets of the first box of production foam I received back in early 2016:

Average weight is 111 grams [3.9 ounces] /sheet.

Thanks!

@Mid7night

It's a big difference in the weight of the foamboard.. But 1200 gms AUW is a proper weight like you say, and not at all excessive.

Good job jet boy! A combination of the 80 amp ESC, the intake ring on the fan and over-driving the throttle endpoint, and the Acme EDF Bench Tester yields a robust 700 gms of thrust. Round 2 is gonna be a lot different. Thanks a lot!

tester.jpg data.jpg
 

Mid7night

Jetman
Mentor
Woohoo! Glad you got some thrust back! That should be a much better thrust ratio, and should accelerate nicely. :cool:
 

DamoRC

Elite member
Mentor
the Acme EDF Bench Tester yields a robust 700 gms of thrust

That's more like it! Check that you are still getting that when you re-install into the fuse to confirm that you are not suffering from any restrictions that are starving the fan.

DamoRC
 

Mid7night

Jetman
Mentor
Wait. 2.2"?..... like 2 3/16"?

:D:D:D

I trimmed my taper down close to that. 980 gms of thrust! :cool:

That's awesome! That's also in line with what I found when I first opened up the nozzle area from the first build.

Since your thrust tube is now shorter, in order to connect it to the exit hole I suggest you detach it from the fan and make a new constant-section (if possible) as an extender. That was advice I got from a coworker of mine, who is an actual propulsion engineer.

Or you could just make a new tube with the larger diameter. :)
 

SlingShot

Maneuvering With Purpose
That's awesome! That's also in line with what I found when I first opened up the nozzle area from the first build.

Since your thrust tube is now shorter, in order to connect it to the exit hole I suggest you detach it from the fan and make a new constant-section (if possible) as an extender. That was advice I got from a coworker of mine, who is an actual propulsion engineer.

Or you could just make a new tube with the larger diameter. :)

That's a great idea. But I´m building a whole new plane (less wing) with a new tube. For the record, I think that the modeler needs to know that they are building for that 2.2" ID. I just "sized" it with the tail butt piece and ended up with what I ended up with.
 

Mid7night

Jetman
Mentor
That's a great idea. But I´m building a whole new plane (less wing) with a new tube. For the record, I think that the modeler needs to know that they are building for that 2.2" ID. I just "sized" it with the tail butt piece and ended up with what I ended up with.

Dually noted. Things like that are always built a little different from person to person - I thought providing a tail piece and those four size-rings would help get everyone in the same ballpark, but knowing the dimension helps too.
 

SlingShot

Maneuvering With Purpose
Dually noted. Things like that are always built a little different from person to person - I thought providing a tail piece and those four size-rings would help get everyone in the same ballpark, but knowing the dimension helps too.

Yup. And pencil marks and all of that. I found the rings helpful as a jig. All I know is yesterday I knew nothing about "birthin' no thrust tubes!" Today thanks to you all I'm an expert in, "Nozzle Diameter: It's pretty Important".

Since your thrust tube is now shorter, in order to connect it to the exit hole I suggest you detach it from the fan and make a new constant-section (if possible) as an extender. That was advice I got from a coworker of mine, who is an actual propulsion engineer.

Back to this idea. This might be a good strategy for building a consistent product. Tune the pipe and then connect it to the fan with an extension. In my case, with my treated, glossy posterboard, I have to use two pieces anyway. A 3D printed nozzle might help to idiot proof the process.

Regarding the constant-section, I'm curious about the effect of our relatively slow velocities. Wouldn't that tend to negate the benefit?
 

SlingShot

Maneuvering With Purpose
Sling Tube.jpg

The Sling-Tube 1000 has been dialed in. A solid 1000+ gms of sustained power and 1130 with "afterburner" on takeoff.
 

Mid7night

Jetman
Mentor
That's awesome!! Is that your own creation, or is "Sling-Tube" by "Tru Thrust" a product somewhere? I couldn't find any info on it.

Either way, you should be in business now!

Related: I should be receiving a new ESC for Jester today. I plan to install that later today, do a static run test (with Wattmeter), and re-maiden tomorrow.
 

SlingShot

Maneuvering With Purpose
That's awesome!! Is that your own creation, or is "Sling-Tube" by "Tru Thrust" a product somewhere? I couldn't find any info on it.

Um......we had a heck of a time getting the test pilot back into the cockpit. We had to tell him something (my creation) to convince him that we did in fact know what we were doing. Turns out ejecting 5 times in an afternoon can shake a guy's confidence in the program :rolleyes:

Good luck with Jester.
 

Mid7night

Jetman
Mentor
Sooo...Jester flew again today! buuuut I also fried ANOTHER ESC! >_<

I successfully flew two batteries, and on the second one I was flying with another jet, and we were chasing each other around the sky in a sort-of mock dogfight...and instead of throttling up and down as I usually do, I just left it at full throttle as a tore around the sky. It flew GREAT ... Until about 3 minutes into the flight; I was making another low pass and the motor just DIED. So I glided it in (again), and assessed the damage. No damage to the airframe, and no magic-smoke or smell, but the ESC shrink wrap was completely melted off. BTW, this was definitely not an over-current problem. A static test on the ground showed I was pulling 80A, and I was using a 125A RedBrick ESC. It definitely just overheated.

Conclusion: Vent holes are needed in the nose compartment. I worked out a way for there to be a vent exit at the tip of the inlet-bifurcation, but I didn't provide for any vent INlet. So I'll be adding two NACA inlets on the sides of the nose, as well as the cutout for the vent exit on the bifurcation. Look for those on the next release of the plans.

I've also got something in the works for this A-4 and my currently-in-development F-20 ... I haven't made a thread for that one, but I will... stay tuned.

:cool:
 

SlingShot

Maneuvering With Purpose
Conclusion: Vent holes are needed in the nose compartment. I worked out a way for there to be a vent exit at the tip of the inlet-bifurcation, but I didn't provide for any vent INlet. So I'll be adding two NACA inlets on the sides of the nose, as well as the cutout for the vent exit on the bifurcation. Look for those on the next release of the plans.

I'll bet you get more thrust also. When I buttoned my new one up, I took about a 250 gms of thrust hit. And it was pulling a vacuum through the hatch/canopy. I ventilated the hatch/canopy and got 120 gms back. Maiden tomorrow.
 

SlingShot

Maneuvering With Purpose
a4(2).jpg


I flew a jet today! The A-4 flew good. I did a dumb though. More on that later.

About 9 or 10 years ago I was in a well equipped airport bookstore looking for some magazines. One of them was a RC mag. That was my first glimpse into electric, jets, indoor, 3D, formation flying and the like. I never really thought about actually building and flying a jet. A recent perusal showed that you need at least $250 to $300 for a PnP 70mm EDF sport jet. Flash forward to today and there's Flite Test and guys like Mid7night and DamoRC that can put you into the cockpit with just some foamboard, a little work and an EDF unit. That's a pretty cool thing.

I learned a hard lesson today. With a big compartment to work with, a well secured battery is even more important. About a minute into a planned 3 minute flight, starting to warm up a little, I rolled inverted and pulled the nose down and the battery kept right on going into the nose, disconnected itself, and the airplane lawn darted on in from about a 100 ft up. The battery was totaled.

I was a little disappointed. But I am also very grateful that the experience was/is available to me. Disappointed, but not discouraged.
 
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DamoRC

Elite member
Mentor
My sincerest congratulations and condolences.

She looked great. Sounded like you had her flying well (based on you being at at least 100ft up before the incident).

Sorry for your battery loss - is the plane salvageable? Any gory pics?

DamoRC
 

SlingShot

Maneuvering With Purpose
My sincerest congratulations and condolences.

She looked great. Sounded like you had her flying well (based on you being at at least 100ft up before the incident).

Sorry for your battery loss - is the plane salvageable? Any gory pics?

DamoRC

wreckage.jpg

Thanks. Yeah it was moving fine. I had made 3 or 4 circuits.

The wing detached and was hanging by a thread. It's ready for one more go. The nose was demolished. The EDF/tube assembly broke loose from the cradle and the exhaust former and shifted forward about 1/2". It's fine also.
 

Mid7night

Jetman
Mentor
Congrats!! and... Yikes! That's quite an "after" shot. At least you got some successful air time though, that's something! And it looks/sounds like you can salvage most of it. You just need a new nose, mostly.

Oh yeah...and don't forget the Velcro! Or get a bigger battery... :p
 

KRAR

Member
How did you create the pdf?

I am looking to design a plane and wondering what exactly you did for the plans?