FTFC23: Build-ruary by Inq: Inq'd F-8 Crusader with Training Wheels

[Inq]

I'm probably deluding myself again, but the FTFC23 Focke Wulf Ta 152H is taking way too much design time for it to get done this month. And... I've been following @telnar1236 's F-104 and Mig 21 builds. I have a couple of cheap 70 mm EDF's that I got on sale several years ago that have never been out of the box. All these thoughts have conspired to drive me to attempt to build and more ominously fly an EDF. My first thought was to just slap the EDF between two foam boards with the silhouette of the Crusader, pop on a FT style fold over wing and build it in one day.

Although @telnar1236 says the f-8 has some nasty habits in model form, I kind of have to... this is the plane my father flew in the Marines.

Well... famous last words. I then thought... I've been learning to curve the foam boards, let's try to at least round the body and still have a boxy silhouette nose. Then that gets into having to have some sections to hold the rounded shape. But, I can't put those in since that's where the air has to flow through. So... the project grew some more... 3D printed, aerodynamic formers. I started this morning at 9:00 am and this is where it stands now.

It turns out I can get pretty close to scale with one strait tube that does neck down, but it a basically a conic so only a 2D curving is required. I also can get the egg-shape cross section pretty close. I've designed the four fuselage stations to hold the proper cross sectional shape and have streamlined them inside to minimize duct drag. They're printing now.

From front to back, the first one will mount the nose. I may make the nose removable. It'll depend on where I need to put the battery to get a proper CG. The second and third stations will have the wing mounts for a removable wing (more in a moment). The last one mounts the EDF and tail cone. I'll take a stab at a 3D Printed nose as its got way too many 3D curves for my skills with foamboard. The jury is still out whether the tail cone will be foamboard based or 3D Printed. Likewise on the vertical stab. I plan on making the flying wings fly, but I'll make them elevons even though the F-8 only had them as an elevator. I hope not to need wing mounted ailerons.

Training Wheels
The wing will actually be two wings. I'll make one to scale of the F-8 with the 5° anhedral. But I also think I'll make a lot bigger one with less or no sweep and probably include some dihedral to help me transition to a faster EDF airplane. I'll make it so that the A.C. is in the same place on both wings so I don't have to change the C.G... and I'll use the same fuselage mounts. If I can get away without putting servos, ailerons and such... is should be a 10 second swap for when I get brave enough to use the F-8 wing.

Oh... no real wheels. Trying to keep it light, and simple for the FTFC23. It'll be a belly lander.

 

[telnar1236]

I'm probably deluding myself again, but the FTFC23 Focke Wulf Ta 152H is taking way too much design time for it to get done this month. And... I've been following @telnar1236 's F-104 and Mig 21 builds. I have a couple of cheap 70 mm EDF's that I got on sale several years ago that have never been out of the box. All these thoughts have conspired to drive me to attempt to build and more ominously fly an EDF. My first thought was to just slap the EDF between two foam boards with the silhouette of the Crusader, pop on a FT style fold over wing and build it in one day.

Although @telnar1236 says the f-8 has some nasty habits in model form, I kind of have to... this is the plane my father flew in the Marines.

Well... famous last words. I then thought... I've been learning to curve the foam boards, let's try to at least round the body and still have a boxy silhouette nose. Then that gets into having to have some sections to hold the rounded shape. But, I can't put those in since that's where the air has to flow through. So... the project grew some more... 3D printed, aerodynamic formers. I started this morning at 9:00 am and this is where it stands now.

View attachment 234913

It turns out I can get pretty close to scale with one strait tube that does neck down, but it a basically a conic so only a 2D curving is required. I also can get the egg-shape cross section pretty close. I've designed the four fuselage stations to hold the proper cross sectional shape and have streamlined them inside to minimize duct drag. They're printing now.
View attachment 234914
From front to back, the first one will mount the nose. I may make the nose removable. It'll depend on where I need to put the battery to get a proper CG. The second and third stations will have the wing mounts for a removable wing (more in a moment). The last one mounts the EDF and tail cone. I'll take a stab at a 3D Printed nose as its got way too many 3D curves for my skills with foamboard. The jury is still out whether the tail cone will be foamboard based or 3D Printed. Likewise on the vertical stab. I plan on making the flying wings fly, but I'll make them elevons even though the F-8 only had them as an elevator. I hope not to need wing mounted ailerons.

Training Wheels
The wing will actually be two wings. I'll make one to scale of the F-8 with the 5° anhedral. But I also think I'll make a lot bigger one with less or no sweep and probably include some dihedral to help me transition to a faster EDF airplane. I'll make it so that the A.C. is in the same place on both wings so I don't have to change the C.G... and I'll use the same fuselage mounts. If I can get away without putting servos, ailerons and such... is should be a 10 second swap for when I get brave enough to use the F-8 wing.

Oh... no real wheels. Trying to keep it light, and simple for the FTFC23. It'll be a belly lander.

Looks good. It's always cool to see more scratch-built EDFs. The F-8 can be nasty if tail heavy, but so long as you keep the CG forward you should be fine.

Looking at the design there is only one thing that looks like a potential issue. You probably want to keep some anhedral even in the trainer wings although you should be fine to reduce it a bit. Too much lateral stability can cause as many problems as too little. I would expect the high wings to provide enough lateral stability by themselves while adding dihedral could result in a dangerous Dutch roll mode and potentially spin instability. Also, with a pure taileron setup, you don't want too much stability since you still need to be able to roll the plane.

Overall, it looks really good and like a great first foray into EDF design.

 

[Inq]

Progress

All four stations are printed. The 3D Print of the fuselage forward of the main foamboard tube is designed. I'm trying it as single-wall "vase" print. Even though it has continuous curvature, being such a large print, it may oil-can. I'm hoping to not have to add stringers to it. Another experiment. It is on the printer now. The Radome is also designed.

Definitely in need of some tail feathers.

 

[luvmy40]

Take this as a completely uneducated observation.

I think you will need to cut some "cheater" intake into the main fuse. That intake mouth just doesn't look like it will supply enough volume for the EDF. Especially on launch. Do you have the resources to run any kind of fluid dynamics prediction or model?

 

[Inq]

Take this as a completely uneducated observation.

I think you will need to cut some "cheater" intake into the main fuse. That intake mouth just doesn't look like it will supply enough volume for the EDF. Especially on launch. Do you have the resources to run any kind of fluid dynamics prediction or model?

Oh certainly! I've been following @telnar1236 's threads on building scale planes with EDF's. He discussed it in his threads and I've asked questions. I just assumed that was standard practice here on the forum. He actually uses CFD to test for fluid dynamics. Me... I'll just use a knife and cut a bigger hole. But... yes, the inlet being 3 feet away from the EDF and about 1/3 the cross sectional area of the EDF... I'd say we get a near perfect vacuum chamber in there. @telnar1236 also mentioned cleaning up his inside duct work on his latest, so I've gone to some effort to have a clean path. Basically the entire cross sectional area is usable as duct. Even the four stations keeping the F-8 shape are streamline inside to minimize abusing the air.

Actually, that was just a mental waste of time as the ESC and battery will be sitting in the airstream and make a far bigger nuance to the air. BUT they will be cooled. Considering in my short tenure I have fried one motor and actually caught another ESC on fire, I am prioritizing cooling over aerodynamic efficiency.

Here is the station at the leading edge of the wing. I don't know if the picture shows it, but the foamboard tube will be wrapped around this. It has lots of surface area for bonding, and note that the leading and trailing edge of the station itself is knife edge, barely disturbing the flow.

But more to your point... I'm new to the foamboard rolling thing. I'm guessing it would be best to roll the DTFB on and get them glued solid and set... then make the big holes for the wing and inlet. I plan to put the primary inlet just in front of the EDF and between the ventral fins so they will hide it somewhat.

Obviously, your seeing the design process unfold real time. I haven't even come up on the first 24 hours of opening the browser to find an F-8 blueprint. Scary... seeing inside the cluttered mess of the old noggin.

Inq - Designer of @#%* good looking lawn darts.

 

[Inq]

I was unpleasantly surprised with what was (and wasn't) on my printer this morning. After reflection... I'll consider it a blessing... kind of. Just last month, my 3D printer's SD slot stopped working. The poor thing has gone through 81 kilometers of ABS filament. Anyhow, I found out I could directly USB it to my computer. Unfortunately, the USB plug is in a peculiar place on my printer. As the Z head moved up last night (unattended) it pulled the cable out. The print was about 80% done... but turns out there was some major oil canning going on anyway and I'll need to head back to the CAD and add some internal stringers. Maybe, I can place them where there are panel seams anyway.

 

[Inq]

This really was intended to be a silhouette plane made up of all foamboard. Hmmm... I'll just make one piece in plastic to make it easier to form the foamboard. I'll just do one little piece here to make it look a little better. Oh! What if I make this in plastic...

Working on the tail cone... I can't imagine how you all make whole airplanes piecing portions of foamboard conics together to form such realistic semi-scale planes. I fell back to using the same technique, but in CAD and let the printer take care of the work.

Snowballs cause avalanches. Now, its starting to look so good, I won't be able to part with it!

 

[Inq]

MUCH BETTER...

A couple of stringers to fix the oil-canning and for good measure figured out how to add some panel lines so I could outline the canopy and still able to do a single layer vase print. Total weight of the forward fuselage and radome is 30.9 grams.

 

[Inq]

Pen Down

I believe... The CAD work for all plastic parts is complete. Might have some parts in the wings for mounting and maybe some Sidewinders, but otherwise the plane structure should be complete. Printing is about 80% complete and should finish today. Foamboard work is next.

Current plastic parts


Rendering of Fuselage

Cavern all the way back to the nozzle

 

[telnar1236]

Pen Down

I believe... The CAD work for all plastic parts is complete. Might have some parts in the wings for mounting and maybe some Sidewinders, but otherwise the plane structure should be complete. Printing is about 80% complete and should finish today. Foamboard work is next.

View attachment 235013

Current plastic parts
View attachment 235014

Rendering of Fuselage
View attachment 235015

Cavern all the way back to the nozzle
View attachment 235016

That looks great! What are you planning on doing for the thrust tube?

 

[Inq]

As I suspected, doing my first rolled foamboard is...

I don't see how you all do this and make it look so simple.

I'm all ears and will humbly take any advice, abuse or ridicule if it will lead to a better result... NEXT TIME!

It started out pretty good. This was my first batch of white DTFB. All other times all they had was black. The white paper on one side peeled off far easier. It came off in two pieces where the black often has a couple dozen. I drew out the lines of location and placed the station pieces using hot-glue and held them down for a good two minutes as advised in the videos.

It would have been far easier if I took advantage of the near flat bottom that the F-8 does have (note formers bottoms sticking up) to glue down to, but that means the seam would be on top. As much trouble as the seam looks now, it would have been a really ugly top.

I used the clear Gorilla glue to glue around the rest of the formers and a good thing... I must have spent a good forty minutes trying to get it all straitened up and I still didn't get it right. The bottom... I'm hoping I can go after this has set after the 24 hours cure time. I'm concerned I don't really have an accurate datum and won't know if the nose and tail cones will be pointing even remotely fore/aft.

 

[Inq]

Built a spreadsheet. Barely worth writing home for, but maybe the forum will be ok. It simply does the moment calculations to tell me where the battery needs to be placed so the CG will be right. Things were very malleable... Cura estimates one thing... it comes off the printer another and once I post process it, it's another. As I add pieces, the CG estimate gets better and better... or if its untenable, it'll let me know early so I can scratch my head (we'll go with that) to figure out what to do next. At the moment, the battery is still in a reasonable place.

Shooting for an AUW of around 700 grams. Hoping to have better than 1:1 Trust to weight ratio. Still not sure what this 70mm EDF will do. Should find some time to get it on the Thrust Meter. If for no other reason, than it would probably get some idea of power usage and how long my 1500 mAh battery will last.

 

[Inq]

Progress...

I'm really hoping to get this to a flyable state today! Not painted and pretty'd up, but flyable. Here is my morning's progress. Most all things are printed. Just a few little pieces left and if I need to make some joints for the wings. Here is the assembled tail section. The elevons are all flying and have even success retained the proper 6° dihedral.

 

[Inq]

So much for that goal. I did work on the foamboard fuselage, trying to get it all glued down. I had to resort to cutting off the two ends and just putting a flat floor on it. It' need some filler and sanding, but it might turn out ok if I get to the painting stage after the maiden flight(s). The main roadblock... I forgot that I wanted to quantify the thrust so I could incrementally modify the inlet and exhaust areas and see if I improved things or not. I had to 3D print an arm to hold the EDF on my test stand and running the tests took only a couple of minutes.

In free air (as shown) I tested it two ways. The inlet funnel is removable and I wanted to see the differences it made. I was thinking... ah... maybe 10%.

Specs

• 70 mm, 6 bladed EDF
• Motor QF2822D / 3000KV
• 80 Amp ESC
• LiPo 4S, 1500 mAh

Results

• w/o inlet funnel = 739 grams
• w/ inlet funnel = 1159 grams (+ 56.8%!)

 

[Tench745]

As I suspected, doing my first rolled foamboard is...

I don't see how you all do this and make it look so simple.

I'm all ears and will humbly take any advice, abuse or ridicule if it will lead to a better result... NEXT TIME!

It started out pretty good. This was my first batch of white DTFB. All other times all they had was black. The white paper on one side peeled off far easier. It came off in two pieces where the black often has a couple dozen. I drew out the lines of location and placed the station pieces using hot-glue and held them down for a good two minutes as advised in the videos.
View attachment 235026

It would have been far easier if I took advantage of the near flat bottom that the F-8 does have (note formers bottoms sticking up) to glue down to, but that means the seam would be on top. As much trouble as the seam looks now, it would have been a really ugly top.

I used the clear Gorilla glue to glue around the rest of the formers and a good thing... I must have spent a good forty minutes trying to get it all straitened up and I still didn't get it right. The bottom... I'm hoping I can go after this has set after the 24 hours cure time. I'm concerned I don't really have an accurate datum and won't know if the nose and tail cones will be pointing even remotely fore/aft.

View attachment 235027

View attachment 235028

View attachment 235029

That foam doesn't look too bad. I know you're past that step now, but if I had that situation I would tape or glue the one side down, strike a centerline on it and cut it on that centerline. Then overlap the other side and incrementally trim it down until it meets the first side nicely.

 

[telnar1236]

So much for that goal. I did work on the foamboard fuselage, trying to get it all glued down. I had to resort to cutting off the two ends and just putting a flat floor on it. It' need some filler and sanding, but it might turn out ok if I get to the painting stage after the maiden flight(s). The main roadblock... I forgot that I wanted to quantify the thrust so I could incrementally modify the inlet and exhaust areas and see if I improved things or not. I had to 3D print an arm to hold the EDF on my test stand and running the tests took only a couple of minutes.

View attachment 235095

In free air (as shown) I tested it two ways. The inlet funnel is removable and I wanted to see the differences it made. I was thinking... ah... maybe 10%.

Specs

• 70 mm, 6 bladed EDF
• Motor QF2822D / 3000KV
• 80 Amp ESC
• LiPo 4S, 1500 mAh

Results

• w/o inlet funnel = 739 grams
• w/ inlet funnel = 1159 grams (+ 56.8%!)

That is a ton of thrust. With the duct you will likely lose some of the 1160 grams, but still, you should have plenty of power.

 

[telnar1236]

Progress...

I'm really hoping to get this to a flyable state today! Not painted and pretty'd up, but flyable. Here is my morning's progress. Most all things are printed. Just a few little pieces left and if I need to make some joints for the wings. Here is the assembled tail section. The elevons are all flying and have even success retained the proper 6° dihedral.

View attachment 235079

It should probably be fine, but typically dihedral on elevons is a bad thing. If you look at it, dihedral elevons try to yaw the plane the opposite direction to the roll which can result in roll reversal, especially at high angles of attack. It's why more modern fighters like the F-16 have anhedral elevons and even slightly anhedral wings in many cases. You don't have much dihedral so you should probably be ok, but for stability it is definitely something to watch out for.

That said, the tail looks great!

 

[Inq]

That foam doesn't look too bad. I know you're past that step now, but if I had that situation I would tape or glue the one side down, strike a centerline on it and cut it on that centerline. Then overlap the other side and incrementally trim it down until it meets the first side nicely.

The white seems to hide the flaw in the image. I thought I had the board pre-rolled tight enough. I did have the average tight enough, but the tight curve leading into the flat bottom was way too tight, especially near the seam. I had to man-handle it too much and have wrinkles and finger compressions all over it. and I haven't even crashed it yet.

 

[Inq]

That is a ton of thrust. With the duct you will likely lose some of the 1160 grams, but still, you should have plenty of power.

Hmm... I thought you guesstimated around 1700 gram, but I assume you're probably used to the nice 12 bladed HO versions.. I was thinking I got what I paid for with 1160.

 

[Inq]

It should probably be fine, but typically dihedral on elevons is a bad thing. If you look at it, dihedral elevons try to yaw the plane the opposite direction to the roll which can result in roll reversal, especially at high angles of attack. It's why more modern fighters like the F-16 have anhedral elevons and even slightly anhedral wings in many cases. You don't have much dihedral so you should probably be ok, but for stability it is definitely something to watch out for.

That said, the tail looks great!

I didn't even pause to think... I was trying to be true to the scale drawings. And since the F-8 only had them as elevators, I see it was my doings and not the F-8. I'd hope not to add to my handling problems. All tail surfaces use NACA 7 Series since I needed some thickness back further to deal with the cross spar. Uses NACA 5 series around the cross spar.