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Rktman

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Mine weighed closer to 8oz (I tissued only the vertical stabilizers and the canard). At that weight they flew well on D12-3s. But I think with your 20-25% extra weight I'd stick with E12-4s.

Regarding frozen pistons: well, they do get awfully sticky from the ejection crud. Maybe even stuck. Before each flight, I make sure the piston is free to move:
  • Push the piston into the tube (to boost position)
  • hold the glider vertically nose down
  • drop a 1-2 oz weight down the motor tube, knocking the piston forward
  • rinse, lather, repeat as necessary
After a few times, this knocks the crud loose, freeing up the piston so it moves fairly easy -- but it's always a bit "gritty" and never friction-less. As you know, (and this is mostly for any future EC Thunder flyers reading this), the piston wants (and needs) a bit of friction to hold itself firmly against the canard actuator after the ejection charge has fired.

I like your idea of coating the aft end of the piston with JB-Weld. I'm adding that to my build!
I've got a long bottle brush that I`m thinking of using to clean up the worst of the build up. I like your idea of using a weight to knock crude loose where the brush can't reach, though my problem would be freeing up the piston when it's stuck in the open (deployed) position. There's not much room to get leverage against the front of the piston when it's jammed in the forward position (especially with my smaller 13mm Ecee).

Looking forward to your build. I agree with Dave, I'd definitely recommend using a 1/32" or thicker plywood disc in addition to JB Weld on the ejection end of your balsa piston, or consider substituting a 'glass coupler in place of the balsa, as I'd think it's way more heat resistant and less problematic in the long run.
 

Ez2cDave

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I've got a long bottle brush that I`m thinking of using to clean up the worst of the build up. I like your idea of using a weight to knock crude loose where the brush can't reach, though my problem would be freeing up the piston when it's stuck in the open (deployed) position. There's not much room to get leverage against the front of the piston when it's jammed in the forward position (especially with my smaller 13mm Ecee).

Looking forward to your build. I agree with Dave, I'd definitely recommend using a 1/32" or thicker plywood disc in addition to JB Weld on the ejection end of your balsa piston, or consider substituting a 'glass coupler in place of the balsa, as I'd think it's way more heat resistant and less problematic in the long run.
Eric,

Another possibility might be a coupler, mounted on a dowel rod, peeled or sanded down, with wrap of sandpaper around it . . . Get all you can with the brush and then "hone" it with the "abrasive coupler".

I have been thinking about "un-jamming" a jammed piston . . . What about securely mounting a Screw Eye or a Wire Loop in the base of the Piston ? You could reach it with a heavy wire "extractor" ( Made from a wire coat-hanger, for example ), inserted from the aft end, and pull it back.

Dave F.
 
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Rktman

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Eric,

Another possibility might be a coupler, mounted on a dowel rod, peeled or sanded down, with wrap of sandpaper around it . . . Get all you can with the brush and then "hone" it with the "abrasive coupler.

I have been thinking about "un-jamming" a jammed piston . . . What about securely mounting a Screw Eye or a Wire Loop in the base of the Piston ? You could reach it with a heavy wire "extractor" ( Made from a wire coat-hanger, for example ), inserted from the aft end, and pull it back.

Dave F.
We think alike. In both Ecees I inserted a needle into the balsa piston on its outward-facing side to make it easier to grab and slide it back into launch position, and also to limit how far back it could move into the MMT (didn't want it sliding all the way back to the motor end).
IMG_3973.JPG

Glad I did too because I used it to free up the piston in my 113mm Ecee by jiggling it and then rotating it side to side as much as I could. That broke off enough of the encrusted crud so that I could move it just enough to get a small round file in there to sand the balsa piston.
 

Rktman

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Eric,

Another possibility might be a coupler, mounted on a dowel rod, peeled or sanded down, with wrap of sandpaper around it . . . Get all you can with the brush and then "hone" it with the "abrasive coupler".

I have been thinking about "un-jamming" a jammed piston . . . What about securely mounting a Screw Eye or a Wire Loop in the base of the Piston ? You could reach it with a heavy wire "extractor" ( Made from a wire coat-hanger, for example ), inserted from the aft end, and pull it back.

Dave F.
I just realized what you meant (forehead slap). Must be developing Attention Deficit Disorder or something. Yeah, I like that idea of a loop or screw eye! If the piston gets seriously jammed and I have to surgically remove it, I will definitely go that route. Thanks, that's a really inspired solution.
 

Ez2cDave

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Glad I did too because I used it to free up the piston in my 113mm Ecee by jiggling it and then rotating it side to side as much as I could.
Eric,

Going for LEVEL 3, eh ??? ( " 113mm Ecee " )

LOL !

Dave F.
 
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Ez2cDave

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Hmm . . . Back in the day, we called that a "Power Prang", when a Glider looped violently and struck the ground under power . . . Yes, it was UGLY !

Dave F.
 

ed-n-eddy

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Would aluminum foil tape help with the heat issue? I'm thinking of the stuff used on HCAV systems.
 

Ez2cDave

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Would aluminum foil tape help with the heat issue? I'm thinking of the stuff used on HCAV systems.
That's an interesting idea . . . My only question would be how the adhesive would hold up, under the heat from the ejection charge.

I did a little search and found that there is also Stainless Steel, high-temperature tape ( only up to 250 deg F - same question about adhesive ) . . .

https://www.amazon.com/High-Tempera...63011,p_n_feature_seven_browse-bin:5485702011

I have no experience with with the Aluminum or Stainless tape in this application.

Dave F.
 

Massrokit

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That's an interesting idea . . . My only question would be how the adhesive would hold up, under the heat from the ejection charge.

I did a little search and found that there is also Stainless Steel, high-temperature tape ( only up to 250 deg F - same question about adhesive ) . . .

https://www.amazon.com/High-Temperature-Tape-Stainless-Steel/s?rh=n:256163011,p_n_feature_seven_browse-bin:5485702011

I have no experience with with the Aluminum or Stainless tape in this application.

Dave F.
How about the paint used to refinish/repaint bbq grills to coat the end of the piston. It's high temp.
 

Rktman

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Someone elsewhere on the Forum used a thumbtack for his Holverson Swinger (another glider that uses a piston). That might be a good solution for protecting the ejection side from erosion, plus a coating of epoxy over it (there are 1" diameter thumbtacks that could easily be ground down to fit the ETs 7/8" diameter piston). I still feel a 24mm fiberglass BT cut down to the piston's length would be the most heat resistant way to go. Definitely wouldn't swell up from heat like balsa.
 

Ez2cDave

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Someone elsewhere on the Forum used a thumbtack for his Holverson Swinger (another glider that uses a piston). That might be a good solution for protecting the ejection side from erosion, plus a coating of epoxy over it (there are 1" diameter thumbtacks that could easily be ground down to fit the ETs 7/8" diameter piston). I still feel a 24mm fiberglass BT cut down to the piston's length would be the most heat resistant way to go. Definitely wouldn't swell up from heat like balsa.
Eric,

Reading your post gave me an idea . . .

A fiberglass piston with a "ground down" thumbtack on its aft end would be "bulletproof" . . . Thoughts ?

Dave F.
 

new2hpr

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There's also the foil-lined 24mm tubing from Balsa Machining. It holds up very well to ejection heat.
-Ken
 

Rktman

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Eric,

Reading your post gave me an idea . . .

A fiberglass piston with a "ground down" thumbtack on its aft end would be "bulletproof" . . . Thoughts ?

Dave F.
Absolutely. It would likely outlive the glider. In the event of a really bad crash, it definitely would be one of the things left intact, like an aircraft's flight recorder.
 

Ez2cDave

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Absolutely. It would likely outlive the glider. In the event of a really bad crash, it definitely would be one of the things left intact, like an aircraft's flight recorder.
Just clean it up and re-use it in the new glider !

Dave F.
 

Rktman

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There's also the foil-lined 24mm tubing from Balsa Machining. It holds up very well to ejection heat.
-Ken
After seeing it on their website three years ago, I've been trying to think of a way to use it to its best advantage.
 

TDSapp

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Eric and Kevin... You guys are killing me. Saw this thread show up and started to read it. I have been working mostly with High Power recently but in the past I have built quite a few gliders. (Not near as many as some guys on here though...) I decided that I needed to see what I have in the stash to fly and to build.

I started going through my built rocket boxes first and found 11 built gliders and 10 of them are in flying condition.

20191204_182451.jpg


Most of them are Rob Edmonds designs. So these I can fly at our next launch but I enjoy the build just as much as flying. So I started to search my build pile. I had recalled buying a few of the Edmonds rockets a long time ago. Turns out I still had 11 of them sealed in their bags. Plus I found a Squirrel Works Mega Baron.

Here is a list of what I found...

Deltie Airshow
Twinsee
Geminee
Ecee
Tinee

DeeCee Thunder
Ecee Thunder
Giminee Thunder
Arcie Thunder

And the Mega Baron

20191204_182458.jpg




So now here is my issue... It's hard to tell in the photo, but there are actually TWO Ecee Thunders and TWO Arcies. I am thinking I would like to build them all. But then I think that having two of them might be a bit much... Maybe I should sell the extra ones... Maybe I should sell them all... Maybe I should keep the Thunders and sell the small ones that I have already built.

Even if I decide to sell them I would have no idea what they should sell for. I have never sold a rocket kit and tend to keep them forever in a box until I decide to build them. I saw that Kevin said he found his on EBay but I can't find any on there now.

Now after doing a quick google I am thinking about building both Ecee Thunders, one as suggested in this thread, and the other build it as an RC glider.


Tim Sapp
 

Rktman

Eric
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Eric and Kevin... You guys are killing me. Saw this thread show up and started to read it. I have been working mostly with High Power recently but in the past I have built quite a few gliders. (Not near as many as some guys on here though...) I decided that I needed to see what I have in the stash to fly and to build.

I started going through my built rocket boxes first and found 11 built gliders and 10 of them are in flying condition.

View attachment 400145

Most of them are Rob Edmonds designs. So these I can fly at our next launch but I enjoy the build just as much as flying. So I started to search my build pile. I had recalled buying a few of the Edmonds rockets a long time ago. Turns out I still had 11 of them sealed in their bags. Plus I found a Squirrel Works Mega Baron.

Here is a list of what I found...

Deltie Airshow
Twinsee
Geminee
Ecee
Tinee

DeeCee Thunder
Ecee Thunder
Giminee Thunder
Arcie Thunder

And the Mega Baron

View attachment 400146



So now here is my issue... It's hard to tell in the photo, but there are actually TWO Ecee Thunders and TWO Arcies. I am thinking I would like to build them all. But then I think that having two of them might be a bit much... Maybe I should sell the extra ones... Maybe I should sell them all... Maybe I should keep the Thunders and sell the small ones that I have already built.

Even if I decide to sell them I would have no idea what they should sell for. I have never sold a rocket kit and tend to keep them forever in a box until I decide to build them. I saw that Kevin said he found his on EBay but I can't find any on there now.

Now after doing a quick google I am thinking about building both Ecee Thunders, one as suggested in this thread, and the other build it as an RC glider.


Tim Sapp
Tim, If you decide you'd like to sell any of your bagged kits, I'd gladly buy the (in order of preference):
Ecee Thunder
DeeCee Thunder
Geminee Thunder
Arcie Thunder
Twinsee
Geminee

or all 6 iof the above listed, at whatever you feel is a fair price. I've been an Edmonds fan ever since I stumbled across them online about 2 years ago. I'm not a collector and would rather build and see these magnificent gliders back up in the air where they belong.
 
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Rktman

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It seems I have another somewhat serious problem: one side of the ET is seriously heavier than the other (enough to probably put it into a death spiral). No idea why and never noticed it until now. The glider is a tad nose heavy so I had to add 5.05g of trim weight to the tail. Moving it out to the very back tip of the glider's lighter wing helps with the roll imbalance but because the wings are swept back, doing so pushes the CG too far back. It's kind of a Catch 22 problem; if I reduce the trim weight to put the CG back where it ought to be, then it no longer counterbalances the heavy wing. And I've tried moving the trim weight all over that lighter wing to no avail; there is no compromise location that works.

So now I'm faced with trying to find an aerodynamic solution, but I'm pretty much flying blind here. Maybe adding a downward angled flap to the heavy wing to try to compensate? How big a flap, and how much of an angle? Any suggestions?
 

kjm

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HI Eric --

Here my experience (FWIW): All but two of the three that I built had left/right (roll) imbalances. They flew fine -- completing two or three wide turns around the launch site before landing.

One of them was perfectly balanced and would head out for the far hills and a long walk at Snow Ranch. I read a suggestion by Rob Edmonds to add weight to the tip of one wing to get it to circle. Worked great, but I (like you) had to also add weight to the nose compartment to trim it out. Unfortunately, I don't remember how much weight. I was using these little 1/4 oz stick-on lead weights and I know it was not more than one of those on the wing.

At any rate, some roll imbalance is a good thing. Perhaps the thing to do on your bird is to try half the weight (2.5g instead of 5g), thus ensuring it circles but also cutting down on the nose weight needed for re-trimming.

Kevin.
 

Ez2cDave

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It seems I have another somewhat serious problem: one side of the ET is seriously heavier than the other (enough to probably put it into a death spiral). No idea why and never noticed it until now. The glider is a tad nose heavy so I had to add 5.05g of trim weight to the tail. Moving it out to the very back tip of the glider's lighter wing helps with the roll imbalance but because the wings are swept back, doing so pushes the CG too far back. It's kind of a Catch 22 problem; if I reduce the trim weight to put the CG back where it ought to be, then it no longer counterbalances the heavy wing. And I've tried moving the trim weight all over that lighter wing to no avail; there is no compromise location that works.

So now I'm faced with trying to find an aerodynamic solution, but I'm pretty much flying blind here. Maybe adding a downward angled flap to the heavy wing to try to compensate? How big a flap, and how much of an angle? Any suggestions?
Eric,

How much difference is there in the left / right weight bias ?

I suspect that "wood density" is the culprit here . . .

Dave F.
 

Ez2cDave

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Tim, If you decide you'd like to sell any of your bagged kits, I'd gladly buy the (in order of preference):
Ecee Thunder
DeeCee Thunder
Geminee Thunder
Arcie Thunder
Twinsee
Geminee

or all of them, at whatever you feel is a fair price. I've been an Edmonds fan ever since I stumbled across them online about 2 years ago. I'm not a collector and would rather build and see these magnificent gliders back up in the air where they belong.
At the very least, make templates for all of them and make them all publicly available here, on the Forum . . .

Dave F.
 

Rktman

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Eric,

How much difference is there in the left / right weight bias ?

I suspect that "wood density" is the culprit here . . .

Dave F.
A LOT. Not sure how to quantify "a lot" other than to say that when I balance the forward and aft ends on dowels it instantly tips over to its port side. I agree it's a difference in wood density. Since I really don't want to pile on any more weight to an already heavy glider, I'm looking for an aerodynamic solution like maybe adding a down-facing flap to the trailing edge of the port wing? Or a small outward-facing flap to the starboard rudder?
 

Rktman

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HI Eric --

Here my experience (FWIW): All but two of the three that I built had left/right (roll) imbalances. They flew fine -- completing two or three wide turns around the launch site before landing.

One of them was perfectly balanced and would head out for the far hills and a long walk at Snow Ranch. I read a suggestion by Rob Edmonds to add weight to the tip of one wing to get it to circle. Worked great, but I (like you) had to also add weight to the nose compartment to trim it out. Unfortunately, I don't remember how much weight. I was using these little 1/4 oz stick-on lead weights and I know it was not more than one of those on the wing.

At any rate, some roll imbalance is a good thing. Perhaps the thing to do on your bird is to try half the weight (2.5g instead of 5g), thus ensuring it circles but also cutting down on the nose weight needed for re-trimming.

Kevin.
Unfortunately it's a really serious imbalance. I had the same thing happen to another smaller glider and gave up flying it because the starboard side was so heavy, it would always do an immediate death spiral and come down hard. At any rate, it's my bad for not weighing each wing while I was building it and could've fixed it then when it was easier.
 

Ez2cDave

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A LOT. Not sure how to quantify "a lot" other than to say that when I balance the forward and aft ends on dowels it instantly tips over to its port side. I agree it's a difference in wood density. Since I really don't want to pile on any more weight to an already heavy glider, I'm looking for an aerodynamic solution like maybe adding a down-facing flap to the trailing edge of the port wing? Or a small outward-facing flap to the starboard rudder?
Eric,



I give a warning about using "rigid" flap(s) . . . Perhaps, a "flap" that deploys at Ejection ?

Rigid flap(s) will, likely, almost certainly, induce spin during Boost. If that morphs / evolves into "Inertial Coupling", it will likely be fatal for the Glider.

Dave F.



 

Ez2cDave

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Eric,

Another theoretical "fix" might be to cut out sections in the heavy wing, until the desired balance is achieved, and then cover it with Silkspan ( like a "built-up" construction wing ).

Dave F.
 

Ez2cDave

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Eric,

An excellent explanation . . . by Richard Nakka.

https://www.nakka-rocketry.net/ep_lr7.html

QUOTE :

Inertial Roll coupling

Also known as Pitch-Roll coupling or Yaw-Roll coupling, Inertial Roll coupling is a "resonant divergence in pitch (or yaw) when roll rate equals the lower of the pitch or yaw natural frequencies", according to Reference 1. In other words, this term describes a phenomenon whereby dynamic instability of a rocket (or other flight vehicle) develops under certain flight conditions with potentially catastrophic consequences, if that vehicle has the mass and geometric configuration that makes it susceptible.

The concept of roll and pitch is shown in Figure 6. If a rocket rolls, it will rotate about its own principal axis, the line of least resistance, rather than the flight path (geometric axis), as illustrated in Figure 7. The position of the principal axis is determined by the particular placement of items of mass that make up the rocket. If the angular difference between the principal axis and the geometric axis is sufficiently large, and if the rocket rolls sufficiently quickly, the destabilizing moment from the inertial forces will overcome the stabilizing aerodynamic moment provided by the fins. The centrifugal force due to the roll will cause the nose and tail to try to swing out perpendicular to the rotation axis.The rocket will become directionally unstable, with the pitch angle continually diverging, developing a wobble or coning motion, to the point where the vehicle's structural limit is exceeded, leading to break-up. In order for the rocket's principal axis to be different than the geometric axis (dynamically unbalanced), the distribution of the various components that make up the mass of the rocket would have be uneven, with respect to the centreline of the rocket (geometric axis). Components of the rocket such as the fuselage, fins, nosecone, and motor are generally symmetrical about the rocket's centreline axis, and would not contribute to dynamic imbalance. However, certain items of mass, typically payload items, may have a centre of gravity (CG) that is not in line with the centreline of the rocket. It is these items that offset the principal axis and lead to dynamic imbalance and the potential for inertial roll coupling.

What makes a particular flight vehicle susceptible to inertial roll coupling? The most obvious condition is the presence of roll. For a rocket, roll may be produced by fin tabs, asymmetrically airfoiled fins, or even misaligned fins. Another condition, as mentioned, is the configuration of the vehicle that leads to dynamic imbalance, such as offset items of mass that result in non-coincident principal and geometric axes. A second condition is the existence of a large difference between the roll moment of inertia and pitch moment of inertia for the vehicle. This is typically the case for rockets , which have all the mass contained within the fuselage (low roll inertia) and have long fuselages with heavy motors, payload, etc. (high pitch inertia). From reference [1], this susceptibility can be expressed in terms of a coupling inertia ratio given by (Ix-Iy)/Iz for any flight vehicle, where Ix is the roll moment of inertia about the geometric axis, Iy is the pitch moment of inertia about the geometric axis, and Iz is the yaw moment of inertia about the geometric axis. Coupling tendencies increase as this ratio approaches a value of -1. For most rockets, the pitch and yaw moment of inertia are equal, owing to symmetry, and the roll moment of inertia is usually written as IR. The coupling ratio then reduces to IR/IL-1, where IL= Iz = Iy (longitudinal moment of inertia).

END QUOTE:

Dave F.
 

Rktman

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Eric,

Another theoretical "fix" might be to cut out sections in the heavy wing, until the desired balance is achieved, and then cover it with Silkspan ( like a "built-up" construction wing ).

Dave F.
I'm leaning toward a pop up flap on the lighter wing vs my mauling the heavier wing full of holes that might structurally weaken it. Pondering location at the moment: close to the root edge = a larger flap at a higher angle and a shorter burn string with less chance of jamming. However, mounting the flap further out at the wingtip = a smaller flap at a shallower angle (because of increased leverage) but having to route the burn string the entire length of the wing.

I'm favoring the first location because I'm reasoning that if the flap angle is off (I'll have to guess at what it has to be at least initially), it'll have a less severe impact than if the flap were at the end of the wing.
 
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Ez2cDave

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Eric,

This might be a "crazy idea" to help adjust the necessary angle on your flap . . .

Insert a loose-fitting rod ( a 3/8" - 1/2" dowel ) into the aft end of the airframe . . . Use an electric fan to simulate "glide speed airflow" . . . Point the glider into the air-stream and adjust the flap angle until the glider is behaving as desired.

Not a "perfect solution", but it does give you a "working theory. A "real" Wind Tunnel would have a cluster of tube to smooth out the airflow from the fan.

https://apogeerockets.com/education/downloads/Newsletter252.pdf

Read TR-5, at link below . . .

https://estesrockets.com/wp-content/uploads/Educator/2845_Classic_Collection_TR-TN.pdf

Alternate idea : ( Maybe consider a pair of deploy-able Ailerons, one on each wing, to correct problem. )


Dave F.

TR-5 - 1.JPG



TR-5 - 2.JPG



TR-5 - 3.JPG



TR-5 - 4.JPG



TR-5 - 5.JPG



TR-5 - 6.JPG



TR-5 - 7.JPG



TR-5 - 8.JPG
 

ed-n-eddy

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How about some modeling clay (non-hardening) on the tip of the light wing? If you like it, seal it in with some c-a or replace it with small slugs of lead solder (cold; drill holes, press the solder in and c-a in place). Removing weight is most desirable, but adding weight where you want it is often easier. This also lets you zero in on the problem by eliminating lateral imbalance as a contributor.
If you've built a warped, or twisted, wing, then it can take some work to get it straight. Ya, maybe cut or break it and re-glue. Then fill and balance again.
 
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