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Jul 08, 2013, 07:03 AM
Tony Audsley Retired Locksmith
Lockey's Avatar
Thread OP
Thanks Kadil, that looks like it will work, I like the 3rd one that Dr Kiwi did best

Lockey
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Jul 08, 2013, 07:10 AM
Tony Audsley Retired Locksmith
Lockey's Avatar
Thread OP
Think I like the twin booms best ... which one do you like?

Think I also like the more rounded top ... going fo a MORE rounded top next time .... Depron is SO easy to bend

Lockey
Last edited by Lockey; Jul 08, 2013 at 07:27 AM.
Jul 08, 2013, 08:09 AM
Retired CAD guy
birdofplay's Avatar
Tony,
About those motors:

the 2826-6 has a max current or 34Amps and watts listed at 342
the2205-34 has a max current of only "8" amps and no watts listed , but 12vx6a = 120W

It seems obvious to me that, just from the specs, the 2826-6 is going to HAUL !

I used to use a motor test stand when these motors 1st came out, as I was WINDING MY OWN from kits et al and needed a performance comparison for my efforts.

It was essentially DR Kiwi's 3rd design and worked out well.

I regularly use an onboard 100amp data capture board and
on the bench I use an HK Watt meter that they are apparently NOT selling any more.

It all helps TUNE IN the PAK/MOTOR /PROP combo - keeping everyone happy.

Bob
Jul 08, 2013, 08:41 AM
Registered User
Quote:
Originally Posted by Lockey
Thanks Kadil but the Aqua-Jet is a very similar configuration and they leave on the fin and it flies OK, BUT you may well be right mate

Lockey
The Aqua Jet is a good flyer but you do lose a lot of the things people like about the Polaris/Aqua Cat, namely low wing loading. You have to "fly" the AJ more and landings are trickier. The vertical fin is not a problem in terms of power loss. The EDF we use delivers 42 oz. of thrust and the plane weighs 32 oz. RTF. However, EDF's are very particular when it comes to inlet air interruptions and ducting.

One thing you will really need to plan for is the CG and battery placement. On the Aqua Jet, the battery needs to be pushed very far aft to get her to balance. With your fan location, this issue may be worse.

No doubt you will figure it out with your skills

Scott
Jul 08, 2013, 08:56 AM
Tony Audsley Retired Locksmith
Lockey's Avatar
Thread OP
Quote:
Originally Posted by birdofplay
Tony,
About those motors:

the 2826-6 has a max current or 34Amps and watts listed at 342
the2205-34 has a max current of only "8" amps and no watts listed , but 12vx6a = 120W

It seems obvious to me that, just from the specs, the 2826-6 is going to HAUL !

I used to use a motor test stand when these motors 1st came out, as I was WINDING MY OWN from kits et al and needed a performance comparison for my efforts.

It was essentially DR Kiwi's 3rd design and worked out well.

I regularly use an onboard 100amp data capture board and
on the bench I use an HK Watt meter that they are apparently NOT selling any more.

It all helps TUNE IN the PAK/MOTOR /PROP combo - keeping everyone happy.

Bob
Thanks Bob, I must admit, I can't get my head around these electric motors and volts and watts and amps, I was brought up with glow motors and heavy models that would fly in any weather

Quote:
The Aqua Jet is a good flyer but you do lose a lot of the things people like about the Polaris/Aqua Cat, namely low wing loading. You have to "fly" the AJ more and landings are trickier. The vertical fin is not a problem in terms of power loss. The EDF we use delivers 42 oz. of thrust and the plane weighs 32 oz. RTF. However, EDF's are very particular when it comes to inlet air interruptions and ducting.

No doubt you will figure it out with your skills

Scott
Thanks Scott, I appreciate your input

I guess I will do as I always do ... suck it and see ...

Trial and error seems to be the best for me ... not always the quickest though and I DO appreciate all your suggestions and help guys

I can't help thinking ... not everything is alway as it seems .. as I said earlier, who would have thought you could get a plane to fly using a flat piece of foam board as a wing ... Amazing really

Quote:
One thing you will really need to plan for is the CG and battery placement. On the Aqua Jet, the battery needs to be pushed very far aft to get her to balance. With your fan location, this issue may be worse
I intend to try a couple of different EDF's on one of my existing models first Scott and see how and where I have to make modifications, hey ... it might not work at all, in that case I will have a play with the EDF on something else ... LIKE a MIG15 or a Sabre .... I had a MIG15 with a ducted fan when I played with glow motors, it needed a LOOOOOOONG runway but flew nice once in the air

Lockey
Last edited by Lockey; Jul 08, 2013 at 09:02 AM.
Jul 08, 2013, 02:34 PM
Rick
Quote:
Originally Posted by Lockey
Thanks Kadil

Now ... how do I test the thust of a motor/prop etc against a EDF? or even one motor and prop against another motor prop

For instance ... I tried this motor https://www.hobbyking.com/hobbyking/s...idproduct=5684 on the new build and with a 2 bade or 3 blade 6 x 4 it didn't seem to have much thrust at all ... (holding the model at the front and giving it full throttle) compared with this https://www.hobbyking.com/hobbyking/s...dproduct=12919 which I use all the time and it has LOTS of thrust

Lockey
The most important difference between these motors is the kv. The 2826 is 2200kv which is the recommended setup for a Polaris with a 6x4 prop. The 2205 has a kv of only 1500. This means that with the same battery the 2826 will be turning almost 50% faster. This makes a huge difference in the thrust on an electric or a glow motor. A 6x4 prop is much too small for the 2205, the prop recommended by HK is an 8x4. In order to get comparable performance you would need to use a much larger prop on the 2205 than the 2826. Or upping the battery to 4 cells on the 2205 would approximately equalize things.

This brings us to the second important factor, the current rating. If you increase the prop size on the 2205 until it matches the thrust of the 2826, it will be drawing approximately the same current as the 2826. But the 2205 is only rated for 8A where the 2826 is rated for 34A. This means that the 2205 will fry before it matches the maximum output of the 2826.

I find these current and wattage ratings from HK and other sellers are often overstated and not very reliable (the KV ratings usually are reliable). In this case I believe the 2205 probably can handle 8A at 12V = 96W as specified, but I am definitely not believing the 34A/342W rating on the 2826. By the way, on 3 cells with a full charge 34A*12V=408W, an awful lot for a motor that only weighs 50g. Even though I don't believe the ratings on the 2826, such a large difference in ratings certainly suggests it is a much stronger motor than the 2205.

In a Polaris a similar 2200kv motor with a 6x4 prop typically draws around 23A more or less at full throttle. So 23A*12V=276W. Compared to the maximum rating of the 2205 of 96W, no wonder it isn't producing enough thrust.
Jul 08, 2013, 03:15 PM
Altitude is my friend...
Depronicus's Avatar
Quote:
Originally Posted by Lockey
The low tail Dualis (apart from the rudder) had little or no control surface in the prop wash and it seemed to do OK...
Well, I dunno, but it looks to me like you have a pretty good percentage of the tops of the elevons in the wash. It doesn't take much prop wash to do it, and it appears that you have enough to provide sufficient low-speed control.
Jul 08, 2013, 05:51 PM
Tony Audsley Retired Locksmith
Lockey's Avatar
Thread OP
Thanks for that great rundown Choochoo ... I sort of understand what you are saying

Depronicus, if what you say is true, then would it be better to have the tail a little lower as in pic 2 ? ... (just a quick move to show what I mean) this would be in the EDF blast .. or would this interfere with the efficiency of the fan?

Lockey
Jul 08, 2013, 06:09 PM
Altitude is my friend...
Depronicus's Avatar
Quote:
Originally Posted by Lockey
...would it be better to have the tail a little lower?...this would be in the EDF blast .. or would this interfere with the efficiency of the fan?
The lower horizontal stab would certainly give you all sorts of elevator control at any speed.

That's a very good question, though, about how it might affect thrust. I have no idea. Anybody out there have some thoughts on that?
Jul 08, 2013, 09:40 PM
Rick
Quote:
Originally Posted by Depronicus
The lower horizontal stab would certainly give you all sorts of elevator control at any speed.

That's a very good question, though, about how it might affect thrust. I have no idea. Anybody out there have some thoughts on that?
I would think you wouldn't want both the center vertical fin and the horizontal stab in the fan blast, especially since the intersection can add drag as well.
Last edited by choochoo22; Jul 08, 2013 at 09:52 PM.
Jul 08, 2013, 10:08 PM
unconventional :-)
kadil's Avatar
Quote:
Originally Posted by choochoo22
I would think you wouldn't want both the center vertical fin and the horizontal stab in the fan blast, especially since the intersection can add drag as well.
Yeah but..... if you did not have the centre fin, and only had the hstab in the fan blast then you would gain low speed elevator control. You will get enough lateral stability from the side vstabs, but may have to add some complexity with 2 rudders. My 2c
Jul 08, 2013, 10:31 PM
Tony Audsley Retired Locksmith
Lockey's Avatar
Thread OP
Quote:
Originally Posted by kadil
Yeah but..... if you did not have the centre fin, and only had the hstab in the fan blast then you would gain low speed elevator control. You will get enough lateral stability from the side vstabs, but may have to add some complexity with 2 rudders. My 2c
Yes kadil, this was my thoughts ... to leave out the centre fin would complicate matters a little, it means finding a way to get control to the elevator and the rudder / s

Also, remember it is a water plane and where is it going to get its steering when on water ?

I will give this some more thought ... any ideas?

Lockey
Last edited by Lockey; Jul 08, 2013 at 11:57 PM.
Jul 09, 2013, 12:04 AM
Tony Audsley Retired Locksmith
Lockey's Avatar
Thread OP
This would be the general configuration of the ducting ... any thoughts?

Lockey
Jul 09, 2013, 12:07 AM
unconventional :-)
kadil's Avatar
Quote:
Originally Posted by Lockey
This would be the general configuration of the ducting ... any thoughts?

Lockey
another 2c intakes look a little restrictive, just by eye.
Jul 09, 2013, 01:45 AM
Tony Audsley Retired Locksmith
Lockey's Avatar
Thread OP
Quote:
Originally Posted by kadil
another 2c intakes look a little restrictive, just by eye.
Should be big enough Kadil, its much more than 50% each side and I believe the rule is minimum 100% of the fan area air intake ... please correct me if I am wrong

Lockey


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