FTFC'18 WWII FH-1 Phantom designed by Namactual

[Namactual]

Why the Phantom:
Although I love everything flight worthy, there is something about turbines. I think it is the clean air frames that are possible with turbines. Lets face it, you don't see birds or even sleek sea creatures with massive swinging props on them. Lets not forget the absolute raw ground shaking power they project. Same goes for RC aircraft. I love my EDF's. So an EDF build was a must. That said, I wanted to make something that everyone could fly. EDF's have a bad reputation for being hard to fly, which I disagree with to an extent. You just have to fly using a little energy management.

This build is going to center around teaching energy management, but hopefully at a slower more forgiving speed. So an EDF trainer if you will. The air frame is going to need to be extremely light for my idea to work as I already picked out very modest power plants. Twin 50mm running on 3cells. Add that with my OCD must have scale appearance, this is not going to be easy.

I do love a challenge.

My low poly size mock up.

1/12 scale
40" wing span
37" long

(2) 50mm 4800kv EDF's (mfg claim 450g of thrust @ 18amps, I do not expect that. I hope for 300-350 static ea.)
(2) 20 amp ESC
(4) 9g Servos
(1) 3 Cell Battery (size TBA, I will cram the biggest one I can that will not hinder the flight performance)

 

[rockyboy]

Welcome aboard! :applause:

There seem to be quite a few EDFs in the challenge to get ideas from, but I don't recall anyone else targeting a low(er) speed capable one - will be interesting to see this develop!

 

[Namactual]

Thanks rockyboy!

 

[Erospace]

Sweet looking airplane!

Since you seem to be familiar with EDFs maybe you can help me out a little. My entry is going to be a 48" flying wing and I'm thinking about using twin 40mm EDFs. I'd like it to fly for 5 minutes. Do you have any suggestions on a good setup. I've never used EDFs before.

 

[DamoRC]

Mock up looks great!

DamoRC

 

[Namactual]

Thanks for the kind words all. Lets just hope the foam version looks like the model.

Ahoy Erospace!
I am by no means an expert, I am sure there are far more knowledgeable people out there on this subject. That said, they are not magic. They just use their power in a different way than a larger prop. Just like any other propulsion system, your thrust to weight ratio is going to be the key factor. The more thrust you have available, the more forgiving and easier the aircraft will be to fly.

Hopefully the manufacturer gave you some information about the EDF you are looking to use. They like to give you unrealistic numbers, but if its pulling a lot of watts chances are your thrust will be good. I like to take the manufactures numbers and reduce the output by 25% right from the start.

I have never used a 40mm. Past experience with 70's through 50's makes me kind of cringe at the thought of a 40mm, but if you throw enough watts at them and I am sure it would work. Do you have some picked out already? I did a quick search for 40mm EDF's at my regular shops and I did not find anything. I found a few through google, but they were very sketchy on the details. My gut says stay away from those.

Static thrust is probably going to be REALLY low on a fan that size. Hand launches will be a bit tricky. You can always use some kind of assisted launch system. Once you get past the launch and up to speed you should be ok. The only other concern you would have is drag, but the air frame you chose should not be an issue there as you can not get much cleaner than that.

Keep your speed up and your altitude high. Gravity is a free source of energy you can use when you get into trouble. Until you hit the ground that is. ;P Try to keep your build light and as clean as possible. Stay smooth on the sticks and the acrobatics to a minimum and you should be good.

Sorry about the rambling on. I do that sometimes. Hopefully some of that information helps a little. If it was me I would go with a 50mm, but a good 40mm should work as long as the watts are there.

 

[HilldaFlyer]

Watching with great interest.

 

[rockyboy]

I foresee an increase in searches for bungee launch systems in the forums this year

 

[Namactual]

Lest just hope we don't see an increase of bungee assisted "landings".

 

[rockyboy]

Yeah, done that trick too :black_eyed:

 

[Erospace]

Thanks for the kind words all. Lets just hope the foam version looks like the model.

Ahoy Erospace!
I am by no means an expert, I am sure there are far more knowledgeable people out there on this subject. That said, they are not magic. They just use their power in a different way than a larger prop. Just like any other propulsion system, your thrust to weight ratio is going to be the key factor. The more thrust you have available, the more forgiving and easier the aircraft will be to fly.

Hopefully the manufacturer gave you some information about the EDF you are looking to use. They like to give you unrealistic numbers, but if its pulling a lot of watts chances are your thrust will be good. I like to take the manufactures numbers and reduce the output by 25% right from the start.

I have never used a 40mm. Past experience with 70's through 50's makes me kind of cringe at the thought of a 40mm, but if you throw enough watts at them and I am sure it would work. Do you have some picked out already? I did a quick search for 40mm EDF's at my regular shops and I did not find anything. I found a few through google, but they were very sketchy on the details. My gut says stay away from those.

Static thrust is probably going to be REALLY low on a fan that size. Hand launches will be a bit tricky. You can always use some kind of assisted launch system. Once you get past the launch and up to speed you should be ok. The only other concern you would have is drag, but the air frame you chose should not be an issue there as you can not get much cleaner than that.

Keep your speed up and your altitude high. Gravity is a free source of energy you can use when you get into trouble. Until you hit the ground that is. ;P Try to keep your build light and as clean as possible. Stay smooth on the sticks and the acrobatics to a minimum and you should be good.

Sorry about the rambling on. I do that sometimes. Hopefully some of that information helps a little. If it was me I would go with a 50mm, but a good 40mm should work as long as the watts are there.

Thanks for the input! Is it better for an EDF to have its inlet and exhaust tubes the same size as the fan? I'm sure I could fudge the dimensions to go up to 50mm if it will make a big enough difference. As of right now I'd planned on using a tricycle landing gear setup, either fixed or retracting (depends on what my Tx can do).

 

[Namactual]

Main airfoil is done.


@Erospace
As long as your inlet is as big as the fan face, you are good. As your inlet gets farther from the fan face you will want to open it a bit. What that ratio is I can not say, but you won't need too much in level flight. Once you start to deviate from forward flight, (add AoA) your inlet shape will effect the amount of clean airflow you get to the fan face. Ideally your inlet should not "starve" or block airflow to the fan at normal flight AoA. If your fans are going to be recessed a long way into the fuse, consider using cheater holes on the bottom of the air frame as not to starve the fans at high AoA's. At our little foam aircraft displacements, this is pretty much a non issue though. The faster and heavier your aircraft is, the more this will matter.

The nozzle is a touchy subject. Some swear they get more thrust by shrinking the nozzle a bit smaller than the fan face, but all your doing is forcing a larger volume of air through a smaller hole. You will loose static thrust but gain a higher efflux speed. If your motors can not overcome the extra back pressure you are actually going to hurt yourself in the long run. It might be a rocket if you can get up to speed, but it might take a while to get there. You may never get there if your air frame has too much drag.

It's never that easy though. There is a lot involved in fluid dynamics. Most of it is beyond my level of knowledge. If you really want me to make a fool of myself, I can try to explain what little I know, but for our application I think we are splitting hairs.

As a general rule, when thinking nozzles, the smaller your nozzle is compared to your fan you are trading static thrust for speed. Kind of like changing the gearing in your car. You always have the same horse power, you are just trading acceleration for speed. You can use this to tune your EDF's for your air frame. If you seem to have plenty of power during hand launches and you want to go faster, shrink the thrust tube a bit. I am sure there are some fluid dynamics experts out there that could calculate the perfect thrust tube for us. Unfortunately, that is not me.

If you do find one though, send them my way as I have some questions for them as well.

 

[Namactual]

Ok, wings are done.



Now for the fun part. Those engine housing/wing/fuse thingamajigs. <----(huh, that's an actual word according to spell check) Anyhoo, this is going to be the hardest part of this build by far. The rest will be a cake walk. My plan is to keep the entire wing a single object I attach the fuse to, rather than attach two separate wings to the fuse.

Somehow, I am going to have to shoehorn a pretty stout wing spar in there without blocking to much airflow.

 

[DamoRC]

Still lookin' good! My only question would be why so much of the wing tip is undercambered. Looking at the wing section only, looks like a little under 50% is undercamber. Is this neccessary? Won't it just slow you down?

DamoRC

 

[Namactual]

I hope so.

Being a trainer, I wanted to keep it slow. There will be a lot of extra drag in level flight, but it will be worth it at low speeds. It should keep it nice, slow and under control.

You are right though, it might be a tad much. It won't be to hard to extend the foam farther out if it proves to be too much.

Nothing is written in stone. We will see how it maidens.

 

[PsyBorg]

Do the terms "Trainer" and "EDF" actually go together in our world? I always thought any edf was like 4th or 5th plane at the earliest in the chain of learning. I guess like anything that falls to the pilot and what skills and finesse they have to start and how fast they pick up on "soft" fingers to fly with.

 

[Namactual]

I put the stick time in on a simulator before I ever touched a real aircraft, but still learned to fly on an EDF. They are not that bad. They just fly different. I started flying two years ago and my first aircraft was a 64mm F22. Bank and yank, no rudder. I put probably somewhere in the order of 50 flights on that air frame. It still flies today. It's been through a few repairs, but still looks good and flies great so I don't have the heart to retire it.

But yeah, slow flying/forgiving and EDF usually do not go together.

They do now.
...well...

...that's the idea anyway.

 

[Namactual]

Good news, I got my parts in the mail today to start testing my EDF's. I busted out the old scratch built thrust rig and started the testing.

Of course things went sideways right from the start as I was having the strangest issues with my ESC and EDF. Something I have never experienced before and made no sense whatsoever. I did some searches online and others were having the same issue with the same ESC and the general consensus was a bad ESC.

But how can it be bad when it works for one second and not work the next? Having nothing to lose I stripped off the heat shrink and found the culprit pretty quick. A bad board design with the capacitor lead soldered in the board sticking out the other side like a lance...

...a lance which pierced the signal wire jacket which is soldered right behind and routed right over said lance. Once heat shrunk into place you have an intermittent ESC throttle control. Nothing a dremel could not fix, but still set me back a few hours all said and done. Time is one thing I do not have enough of.

Anyway, more bad news...
... I was right.
EDF Manufacturer claims: 450grams @18Amps

Test 1:
Static thrust no thrust tube:
325 Grams @14Amps

Test 2:
9" tube 5-20% reduction:
5% - 320 Grams @14Amps
10% - 318 Grams @14Amps
20% - 315 Grams @14Amps

Test 3:
5" Tube 10% reduction:
318 Grams @14Amps

Don't get me wrong, I expected this result. I was hoping I was going to be wrong and get a little more than expected, but I am not surprised. Maybe a little bummed, but not surprised. On the bright side, this is easily the smoothest running EDF I have ever experienced. Ear piercing sound, but smooth as silk.

So, its a little under 25%, but close enough. Expecting 600-650g of static thrust with two which is doable. My first EDF 64mm F22 ran about 550grams of static thrust and weighed in at about 750-800grams with a 2200mha battery. Hand launches were sketchy, but she flew great once up to speed. That was a very clean air frame with a VERY high wing loading.

I am hoping the Phantom will replicate the same type of flight characteristics at a much more manageable speed. The air frame will not be nearly as clean, but the wing area and lift should be much greater. I can always buy some FMS 50mm's if I have to, but I am going to go worst case scenario first and see how she maidens.

...oh, and did I mention the engine pod wing roots were going to be a pain to design? Yep, I have only been through 3 revisions so far and happy with none. They either look nice and would be a nightmare to build, or easier to build and not look scale at all.

I am still looking for that happy medium.

 

[DamoRC]

Which EDFs did you get?

DamoRC

 

[Michael9865]

Nice troubleshooting on the poor quality of your ESC.