Experimental EDF Jets and Other Ideas
- Thread starter telnar1236
- Start date
telnar1236
Elite member
I'm using this motor and an old 60A esc I had sitting around
telnar1236
Elite member
Yeah, I kind of knew that going in, but it looked so cool, so I though how bad can it really be - and the answer was very
Mr Man
Mr SPEED!
90ish mph is very good with that motor!
telnar1236
Elite member
I think there's a lot more speed in this design than 90 mph - that was on 4s instead of the 6s this is designed for and during the shakedown portion of the maiden when I wasn't trying to push it for speed much at all. This thing picked up speed so fast it was scary without even really trying.
Houndpup Rc
Legendary member
Maybe I could try printing it out when I get a printer and throw my 3536 on it! 😁
Houndpup Rc
Legendary member
Would PLA+ be better?
telnar1236
Elite member
Might be a bit big, but it would be cool to see a really high performance motor on this thingMaybe I could try printing it out when I get a printer and throw my 3536 on it! 😁
telnar1236
Elite member
Definitely, or even normal PLA - the new print won't look as fancy but it should hold up a lot better
Houndpup Rc
Legendary member
That's why I would do it! JK
telnar1236
Elite member
Based on the abruptly curtailed flight of my pylon racer, I've been able to revise a couple of things in my jet design. While I didn't really get the chance to test the wing at high speeds, I did get the chance to see if the very thin tail mounted almost in plane with the wing resulted in a stable aircraft. Since it did, that lets me move the horizontal stabilizers from a T tail position down to a more conventional position. This is in turn, lets me reduce the thickness of the vertical stabilizer dramatically and change it to a better airfoil since I don't need to fit servos with the end result of about a 10% total decrease in drag relative to the original design.
I've also started to look at what a potential single 80mm EDF design might look like. This design incorporates a couple more lessons from the pylon racer in terms of shaping the fuselage to reduce drag. The result is a slightly better optimized design that should have a slightly lower stall speed and a slightly higher top speed. However, this comes at the cost of needing to use a 6s power system and potentially a reduction in flight time due to the larger size of the 6s batteries making it harder to find a way to fit two of them.
I'm pretty confident either of these designs will be able to meet the requirements I set out in my original post with a bit of tweaking so I now need to choose between them.
I've also started to look at what a potential single 80mm EDF design might look like. This design incorporates a couple more lessons from the pylon racer in terms of shaping the fuselage to reduce drag. The result is a slightly better optimized design that should have a slightly lower stall speed and a slightly higher top speed. However, this comes at the cost of needing to use a 6s power system and potentially a reduction in flight time due to the larger size of the 6s batteries making it harder to find a way to fit two of them.
I'm pretty confident either of these designs will be able to meet the requirements I set out in my original post with a bit of tweaking so I now need to choose between them.
quorneng
Master member
One solution to this sort of problem is to simply move the relatively heavy EDF back towards the tail.
There seems to be a feeling the weight must be concentrated close to the CG. This is true for a 3D aerobatic plane but for speed fore and aft inertia is not really an issue. Indeed it can be argued that the friction losses per unit length are greater in the exhaust duct due to the higher air velocity than it is for the inlet duct.
I have taken this principle to the extreme on several of my "own design" scale EDFs by placing the EDF right at the back to get the maximum possible performance where the installed thrust to weight was limited. Doing this means the batteries end up well forward, at least in between the inlets ducts, so completely avoiding obstructing the layout of the "sensitive" inlet ducting.
The only downside is the potential additional ohmic losses from the rather long ESC to motor leads it requires thus needing slightly bigger section wires.
Just a thought.
telnar1236
Elite member
Makes sense to me - part of my challenge with this design is the way the duct is so tightly tucked into the nose - it makes packaging both the retracts and the batteries tough since there is less space inside the fuselage than there would seem to be at first glance.
If I move the battery back it runs into the duct and there isn't space to add a second battery in front of it without running into the canopy. With the batteries this far forwards, it also doesn't let me trade flight time for thrust to weight ratio by flying with only one pack.
I'm debating moving to a design with more conventional cheek mounted inlets to allow me to do something like what you're saying since that would allow me to put the second battery closer to over the CG to make it optional.
Houndpup Rc
Legendary member
I should try a 2207 1900kv on 6s.....
telnar1236
Elite member
Not too dissimilar from what I'm flying now - it would probably fit just fine
Houndpup Rc
Legendary member
I have heard 2207 is slightly more powerful....Maybe I could squeak 100 out of it!
Piotrsko
Legendary member
Yup they do that quite efficiently. Unsure if it's a design issue or a benefit
telnar1236
Elite member
Turns out the solution to all my problems is just to build a super saber.
More seriously though, it's actually one of two options now and while it resembles a super saber quite a bit, it evolved from my earlier designs on its own without setting out to design something that looks like a super saber. This is the other option - it has the same wing but retains the old fuselage design which might struggle to fit two batteries. I think it might barely be able to fit two batteries, but it would be a struggle and I'm not sure it will work for maintaining the CG.
I was doing a bit of investigating into different wing planform ideas, and a 360mm wing root chord with a 100mm tip chord with a span of 900mm seems to be the best option since it doesn't lose too much lift but significantly reduces drag - by increasing the Reynolds number a bit thanks to the increased chord, the wing is now very much in its happy place at high speeds and the flow remains very much attached and does not become turbulent till very late on the wing.
With the new wing, the second option has about 25% less drag than the original design which shared the same fuselage. The Super Saber look alike has about the same drag as the old version with the straight wing, but it has more internal volume, and critically, more usable internal volume - it is 4" longer and about and 1" greater in diameter. Both pay for the improved wing with a stall speed increase of about 1 mph.
I'm also a bit concerned about the flaps blanking the horizontal stabilizer at higher angles of attack. Based on how well the Freewing F-5 flies with flaps, I think it should be ok, and I'm not likely to want to fly at more than 10 degrees AOA with flaps down so it shouldn't be an issue most of the time, but it is a possible concern.
That said, the drag is getting into what I would consider truly low numbers now. Assuming constant thrust from the EDF, the second design should hit around 210 mph and the first around 187 - in practice, the thrust should actually fall off a fair bit by this speed, so I'm guessing more reasonable top speeds of around 170-180 for the second design and 140-150 for the super saber look alike.
In order to try and calibrate the speed/drag predictions, I'm thinking of trying to make a model of the Freewing Mirage 2000 - I have one I can take measurements on, it has a relatively similar EDF unit, and I know it is a 130-mph airframe so I can compare my predicted top speed to the actual value without needing to build my own design.
More seriously though, it's actually one of two options now and while it resembles a super saber quite a bit, it evolved from my earlier designs on its own without setting out to design something that looks like a super saber. This is the other option - it has the same wing but retains the old fuselage design which might struggle to fit two batteries. I think it might barely be able to fit two batteries, but it would be a struggle and I'm not sure it will work for maintaining the CG.
I was doing a bit of investigating into different wing planform ideas, and a 360mm wing root chord with a 100mm tip chord with a span of 900mm seems to be the best option since it doesn't lose too much lift but significantly reduces drag - by increasing the Reynolds number a bit thanks to the increased chord, the wing is now very much in its happy place at high speeds and the flow remains very much attached and does not become turbulent till very late on the wing.
With the new wing, the second option has about 25% less drag than the original design which shared the same fuselage. The Super Saber look alike has about the same drag as the old version with the straight wing, but it has more internal volume, and critically, more usable internal volume - it is 4" longer and about and 1" greater in diameter. Both pay for the improved wing with a stall speed increase of about 1 mph.
I'm also a bit concerned about the flaps blanking the horizontal stabilizer at higher angles of attack. Based on how well the Freewing F-5 flies with flaps, I think it should be ok, and I'm not likely to want to fly at more than 10 degrees AOA with flaps down so it shouldn't be an issue most of the time, but it is a possible concern.
That said, the drag is getting into what I would consider truly low numbers now. Assuming constant thrust from the EDF, the second design should hit around 210 mph and the first around 187 - in practice, the thrust should actually fall off a fair bit by this speed, so I'm guessing more reasonable top speeds of around 170-180 for the second design and 140-150 for the super saber look alike.
In order to try and calibrate the speed/drag predictions, I'm thinking of trying to make a model of the Freewing Mirage 2000 - I have one I can take measurements on, it has a relatively similar EDF unit, and I know it is a 130-mph airframe so I can compare my predicted top speed to the actual value without needing to build my own design.
telnar1236
Elite member
The much strengthened pylon racer design should also fly again tomorrow so I'm hoping to actually get to measure the top speed this time around without the wings falling off.
Mr Man
Mr SPEED!
Sweet!
Similar threads
