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

Mid7night

Jetman
Mentor
No Fair! Slingshot is certainly guaranteed to get that wonderful sound and I'm the 5 blade guinea pig! :)

Made good progress last night and the EDF may be here today so I hope to have it installed tonight. I like the way the inlets are done with the forward pieces creating the bifurcated inlet and the rearward piece pushing out into the nascelle to guide the air into the EDF. Clever and tidy.

As always, a couple of questions- numbers refer to the pic

(1) Looks like an angle gauge, smells like and angle gauge, but I am not sure what angle it is supposed to be used for
(2) Simply do not know what this is or where it goes.

(3) (not on pic) - is there any additional support needed for the vertical stabilizer?
(4) (not on pic) - any chance you could post a pic of your battery installation?

All in all, I am enjoying this build. The plans work well and the fitment seems good all round.

DamoRC

View attachment 87388


LOL... Well, I confess, in the midst of my replying to anyone and everyone, I got you two confused ... :-S

1) It IS an angle gauge. Figure it out.


Just kidding. It's for setting the angle of the outer-flaring part of the inlet. The part that pokes out into the nacelle. The gauge is just suppose to help you glue it in the right ballpark before putting the nacelle on. Because when you put the nacelle on there's really no way to hold that piece out against it as you push the nacelle on.

2) That is the 'floor' of the inlet. It slides in from the side, under the bifurcation pieces. The little dot/mark in the middle is supposed to line up right under the 'point' of the bifurcation. The line on it is a score/crease line, as you will notice it needs. The wider end goes forward.

3) I had doublers at the base on my first (prop) version, but I left them off on the EDF and it seems fine. If it bothers you, add some doublers. :p I always reinforce joints like that with a fillet-bead of glue along the whole seam anyway. That seems to be enough. Just don't lean on it. ;)

4) It basically goes right under the fan. I'm working on an update to how it goes in from the front, instead of thru the belly. I PM'd you. Call me and I'll explain what you need to do.
 

SlingShot

Maneuvering With Purpose
Ah. LOL. EXACTLY the same one I had flying in mine at FFWest. :cool:

Yeah. I'm not very adventurous in that respect. I want what works.

I do really like the sound though, and I'm hopeful that we'll be able to replicate it here :)

From Wikipedia:

In December 1974 the Navy Flight Demonstration Team downsized to the subsonic Douglas A-4F Skyhawk II and was reorganized into the Navy Flight Demonstration Squadron. This reorganization permitted the establishment of a commanding officer (the flight leader), added support officers, and further redefined the squadron's mission emphasizing the support of recruiting efforts. Commander Tony Less was the squadron's first official commanding officer.[citation needed]

220px-A-4Fs_Blue_Angels_Fleur_de_Lis_1984.JPEG

The paint scheme is no-brainer for me.
 
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DamoRC

Elite member
Mentor
Quick Update - finished the build last night.

IMG_2603.JPG

A big shout out to Ben for taking the time during the week to discuss the build, CG, battery placement etc. It was a huge help.

Maidened her this morning and she flew great. I was particularly impressed with how she handles slow flying - really stable.

Unfortunately - the 6 blade EDF doesn't produce that wonderful sound that Ben's original 12 blade version makes. I think Ben is going to try to see what could be done about this.

All in all, great design with some really nice features in the plans (the guide for making the thrust tube were excellent and made it really easy), nice build (lots of cutting), and flys great. Thanks Mid7Night!

Diamond has a new EDF friend to hang with.

IMG_2602.JPG

Video of Maiden


DamoRC
 
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Mid7night

Jetman
Mentor
Woohoo! There are two Skyhawks flying!

Bummer that the sound doesn't hold ...but with fewer blades and a higher Kv I guess it is expected. I've got a similar fan on order, and I will investigate if there are any little tweaks I can make that will help to shield that "whine".

Damien: what size battery did you use? And what is you total flying weight?
 

DamoRC

Elite member
Mentor
Woohoo! There are two Skyhawks flying!

It won't be long before there are more I'm sure - ball is in your court Slingshot!

I am using Turnigy Nanotech 2200mAh, 4S, 35C. AUW is 31 oz.

DamoRC
 

Mid7night

Jetman
Mentor
It won't be long before there are more I'm sure - ball is in your court Slingshot!

I am using Turnigy Nanotech 2200mAh, 4S, 35C. AUW is 31 oz.

DamoRC

Awesome. That's a good weight. Probably why you have better low speed handling. I think mine weighs more than 40oz, but I'm also using a 3000mAh 4s.

I'll be excited to see if Slingshot gets the same sound with the same fan, or if I somehow just got stupid lucky! :p
 

SlingShot

Maneuvering With Purpose
It won't be long before there are more I'm sure - ball is in your court Slingshot!

I am using Turnigy Nanotech 2200mAh, 4S, 35C. AUW is 31 oz.

DamoRC

I'll pickup the hardware over Memorial Day weekend. I was looking at the sheets of foam I have and allocating them to projects. (2) B-25's , (1) DR1 (templates made), assemble the SK-3, (1) Baby Bugatti and (1) A-4. Somewhere in there I need to get a Super Chipmunk up and running.

I'm about to get motivated so I would expect to fly an A-4 in the first week of June.
 

jpot1

Elite member
Do you think this could be made into a pusher with a big enough battery up front to balance it out?
 

F106DeltaDart

Elite member
Woohoo! There are two Skyhawks flying!

Bummer that the sound doesn't hold ...but with fewer blades and a higher Kv I guess it is expected. I've got a similar fan on order, and I will investigate if there are any little tweaks I can make that will help to shield that "whine".

Damien: what size battery did you use? And what is you total flying weight?

One thing you could try to get some better sound is to add a "cheater" intake somewhere. The only really good sounding, low blade count EDFs that I've flown (like the Durafly Vampire) have a cheater grate right in front of the fan. The theory over on RCgroups is that the turbulence from the cheater helps give out that jet woosh sound. It's not exactly scientifically proven, but it might be worth a shot.
 

Mid7night

Jetman
Mentor
Do you think this could be made into a pusher with a big enough battery up front to balance it out?

I'm certain you could make that work. My first version was a tractor-prop up front and it also worked great.


One thing you could try to get some better sound is to add a "cheater" intake somewhere. The only really good sounding, low blade count EDFs that I've flown (like the Durafly Vampire) have a cheater grate right in front of the fan. The theory over on RCgroups is that the turbulence from the cheater helps give out that jet woosh sound. It's not exactly scientifically proven, but it might be worth a shot.

I've thought of doing something similar. A coworker and I did some math regarding RPM, blade count, stator count and tone frequencies...and we've come up with a couple different things to try, which I will be experimenting with on this latest build.

I've also just wrapped up recording my first build-video for the latest version... SHEESH that's a lot more work than just building the thing! And I haven't even edited it down yet! ;)
I've got even more admiration for the FT Crew after doing this myself... I know I'd sure like to have an editing team to hand this footage off to! :D
 

Mid7night

Jetman
Mentor
Side-by-side; v1 and v2:

IMG_3634.JPG


Testing continues!!

I discovered that my as-built nozzle was not as big as I had intended it to be. This results in too much back-pressure, making the fan work harder for no gain. I will be increasing the nozzle area appropriately (yes I've done the research :) ). Version-2 already has the bigger nozzle, so I will test and compare data and report back. This SHOULD result in more thrust for at least the same current. But we'll see. :)

WOOHOO!
 

SlingShot

Maneuvering With Purpose
Side-by-side; v1 and v2:



Testing continues!!

I discovered that my as-built nozzle was not as big as I had intended it to be. This results in too much back-pressure, making the fan work harder for no gain. I will be increasing the nozzle area appropriately (yes I've done the research :) ). Version-2 already has the bigger nozzle, so I will test and compare data and report back. This SHOULD result in more thrust for at least the same current. But we'll see. :)

WOOHOO!

That's an interesting development.

I'd like to see a big loop or half loop, pulling from level flight :)
 

Mid7night

Jetman
Mentor
DATA! I just wrapped up the last thrust test after modifying the 12-blade installation, to have larger exhaust area. Now both of my Skyhawks have about 83% FSA exhaust nozzles. I won't bore you with EVERY graph, but here is the summary comparison between the 6-blade, 12-blade, and both the too-small-exhaust and the new-larger-exhaust:

70mm_EDF_thrust_compare.png

Increasing the nozzle area saw a 40% thrust increase for the 6-blade installation, but only a 15% increase for the 12-blade installation. The bigger gain was obviously running the 6-blade on a higher-C battery. :p

It's possible given the additional blades, possibly moving more air, that the 12-blade installation might benefit from a larger nozzle still. But it's still a thrust increase, with a marginal power increase.

The really nice thing to note is that the thrust dramatically increased for the 6-blade, but its power-draw did not increase proportionally. The Watts/lbThrust ratio got better with the larger exhaust area. The efficiency ratio also got better for the 12-blade EDF, just not by as large a margin.

Alright, enough geeky typing, here's my latest vlog where I show you the two aircraft, and their sound comparisons:


Also, the updated EDF plans are attached here, as well as added to the first post of the thread.

View attachment FT_A-4_EDF_v4_PDF_Plans.zip
 
This looks great. I posted on your twin 50mm edf build that I wanted to make one, but I prefer the idea of building this.

I think I'd build it using a 6s capable fan.

Is there plenty of lift with from the wing as I would probably be using a 6s 3000. Together with the edf that's a lot of mass. Do you think the plane could handle that or would it be a bit of a brick dart?

You can use a viggen for reference as I have a heavy viggen running a 4s 3000 and extra rocket motor in the back
 

Mid7night

Jetman
Mentor
This looks great. I posted on your twin 50mm edf build that I wanted to make one, but I prefer the idea of building this.

I think I'd build it using a 6s capable fan.

Is there plenty of lift with from the wing as I would probably be using a 6s 3000. Together with the edf that's a lot of mass. Do you think the plane could handle that or would it be a bit of a brick dart?

You can use a viggen for reference as I have a heavy viggen running a 4s 3000 and extra rocket motor in the back

I think it would handle it, especially considering you'd have a big performance bump running a 6s fan. I flew it once on a Graphene 95C 6000mAh 4s, to see if I got better performance. It flew, not great, but it flew. But now with the nozzle properly sized, and on 6s, I think you'd be fine.

FMS actually makes a 6s version of the 12-blade fan I have. Same rotor and shroud, just a different motor capable of running 6s: https://www.banggood.com/FMS-70mm-6...850KV-Brushless-Inrunner-Motor-p-1115122.html
 

Mid7night

Jetman
Mentor
Hmmmmm........6 blade more powerful.......

Well, a static run only tells one story, and all of these thrust numbers are based on calculations of efflux, air density and exhaust area. All that to say, there is room for error. However, on a comparison basis, there still is evidence that the 6-blade has a better punch. But I don't think that's NEWS in the EDF realm.

And even if the 6-blade has more thrust, I might still be inclined to fly the 12 for its sound. :cool:

Only way to know is to fly em! I'll report back when I have comparison flights for both.
 

SlingShot

Maneuvering With Purpose
Yeah. I can tell by the relative speed that the A-4 had with other planes that it will do well. The most important thing for me will be how well it will carry energy from a dive. It's going to be a nice foray into the EDF world.