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Old Jan 09, 2013, 06:30 AM
Flying is Freedom
Sky_Captain's Avatar
Annandale, VA
Joined Jul 2007
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Originally Posted by Joe 1320 View Post
The speed of the air moving out the tailpipe.
Ok.... so narrowing the neck down will create more thrust? Of course if I'm right, it would only be to a certain extent.
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Old Jan 09, 2013, 07:18 AM
Addicted to building...
Freddie B's Avatar
Omaha Nebraska
Joined Feb 2006
5,992 Posts
My understanding and attempt to explain in a way to possibly understand it a bit further is, Eflux actually is a speeding up of the air exiting the tailpipe. The tailpipe is tapered in shape behind the EDF unit, usually from 80% up to 90% of the FSA (Fan Swept Area). This will usually decrease the static thrust, not increase it because a fan does not compress air like a turbine does. It does increase the speed of this exiting air, thus increasing ultimate top flight speeds.

FSA is caculated by taking the diameter of the EDF Shroud, minus the diameter of the motot/rotor hub, and caculating surface area. After determining the FSA, reduce your caculation down to say 80%, and then determine the new diameter needed to make the tube right at the aft end where the air exits into the airstream.

This is often why you notice an EDF 'Getting on step' after launch.

Fred
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Old Jan 09, 2013, 08:19 PM
Flying is Freedom
Sky_Captain's Avatar
Annandale, VA
Joined Jul 2007
6,114 Posts
ahhh, I thought it was just the smaller prop that caused the speed up lag
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Old Jan 11, 2013, 07:53 PM
that's gonna leave a scar
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United States, NC, Mooresville
Joined Aug 2007
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Originally Posted by www.hobbyb.com View Post
Sorry, maybe we missed your email. Could you please send a PM with the order number. We will follow up on that.
awesome support from these guys !!
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Old Jan 11, 2013, 09:39 PM
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United States, TN, Jackson
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awesome support from these guys !!
Yep!!!---I'm sold on these guys---They REALLY pay attention to the customer!!!..

Kevin
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Old Jan 11, 2013, 10:20 PM
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United States, TN, Jackson
Joined Mar 2007
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Getting my F-15 kit version together from Hobby B---The plane will be 4S powered!!!......

I painted my plane flat white to hide the styrofoam beads...After applying the decals I will apply a clear coat to the plane...

I got the ESC's fitted---They are Turnigy Plush 12 amp units rated for 4S with the heat shrink removed...Relief cuts were made in the foam intakes to get cooling air to the ESC's...I have the FET's facing towards the intakes...I made a cutout in the back of the plane to relieve air from the inside of the plane and will use the nose gear cutout widened a bit to allow air in the front of the plane to cool the batts and the VR side of the ESC's...

I'm going to use an 850mAh NanoTech pack to power the plane on 4S...The pic shows the batts in place...I did have to remove some foam to get the pack to fit...

These motors/fans can easily handle 4S as the REAL WORLD kv rating on the motor is more like 5600-6000kv---NOT 9000kv as advertised...I'm flying my MiG 15 on 4S...

Tomorrow I'll get the soldering done to the ESC's/motors...All of the components are just placed in position for the pics...

Kevin
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Old Jan 11, 2013, 10:52 PM
that's gonna leave a scar
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United States, NC, Mooresville
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look forward to some flyin' vid of that badboy !
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Old Jan 12, 2013, 09:26 AM
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Chicago, IL
Joined Nov 1999
2,049 Posts
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Originally Posted by Kevin Greene View Post
Getting my F-15 kit version together from Hobby B---The plane will be 4S powered!!!......
Is that really necessary? I would think 3s would be plenty. With 4s, you have more weight and less flight time.
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Old Jan 12, 2013, 09:56 AM
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United States, TN, Jackson
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Is that really necessary? I would think 3s would be plenty. With 4s, you have more weight and less flight time.
Less flight time???...I'll be @ 1/3rd throttle on 4S and it would take about 1/2 throttle for the same speed on 3S...I should easily get 5 minute flights which is plenty...

As for weight---All I gained was 3/4 ounce by adding the extra cell...There are many guys flying this plane on 4S but with 650mAh packs that only weigh a few grams less than my pack...

Performance---I flew my MiG 15 on 3S and it was "OK"...When I went to 4S the plane performed like a jet SHOULD!!!......Loops as large as you want with plenty of vertical...

Here's an old vid that I did with my cellphone...I didn't have anyone to hold the camera so it is a stationary vid...I posted it a while back to get someone to Dopler it for me...This flight was before I did a "nip/tuck" on the exhaust...You can hear the difference in RPM on mine vs those that have posted 3S vids...As fast as this hotrod is flying straight and level you can imagine how much vertical it has...

The flying starts about 1:10...

Kevin

MiG for Doppler (4 min 32 sec)
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Old Jan 12, 2013, 10:50 AM
CV-15 VB-16
giuseppi's Avatar
USA, TX, Friendswood
Joined Jul 2007
1,371 Posts
Coming along nicely, KG. Looking forward to seeing the maiden video.

g
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Old Jan 12, 2013, 11:44 AM
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United States, AR, Jacksonville
Joined Jul 2004
424 Posts
Kevin,

Do you plan on any kind of full flying taileron mod? If you do please share some photos.

My F-15 kit has been shelved for quite a while now.
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Old Jan 12, 2013, 03:03 PM
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United States, TN, Jackson
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Originally Posted by Whiskey Whiskey View Post
Kevin,

Do you plan on any kind of full flying taileron mod? If you do please share some photos.

My F-15 kit has been shelved for quite a while now.
No full flying stab mod...The only mod I'm thinking about trying is to cut away the ailerons and run them on separate servos...I would have the "flaps" and elevators still coupled together but used as elevators only...I'm going to fly it with the stock control system first to see if I like it...It just seems soooo odd, though!!!

With the extra power the little MiG 15 has so much more grunt that if you try to launch at full throttle it will try to swap ends on ya.......You launch at 3/4 throttle and then go to full when the plane gets on step---Which happens pretty quickly!!!

Kevin
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Old Jan 12, 2013, 03:25 PM
FireHawx
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United States, FL, Jacksonville
Joined Oct 2011
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Just dusted off a few of my 35's today and I put a small 4S pack in my T45 and all I can say is WOW. This is the first time I have put a 4S in my 35's. This is how they should have come. I thought the step-up to 3S was fun, 4S is great. I read about KG running his Mig on 4S so I had to go for it. Total Blast!
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Old Jan 12, 2013, 05:22 PM
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United States, TN, Jackson
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Originally Posted by FireHawx View Post
Just dusted off a few of my 35's today and I put a small 4S pack in my T45 and all I can say is WOW. This is the first time I have put a 4S in my 35's. This is how they should have come. I thought the step-up to 3S was fun, 4S is great. I read about KG running his Mig on 4S so I had to go for it. Total Blast!
Glad to hear it works for you as well!!!............

The motor in these planes is very under-rated kv-wise...They are advertised as 9000kv but test out to being between 5500-6000 kv...Hence, the reason they perform so well on 4S without burning up...I have run my MiG 15 on 240mAh Hyperions to 350mAh ThunderPower packs...I'm thinking that the best pack would be the Babbel Batt 325mAh TP 65C 4S packs...Running larger packs will require you to modify the battery compartment to accept larger packs...The Dremel is your friend!!!......

Kevin
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Old Jan 12, 2013, 06:04 PM
FireHawx
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United States, FL, Jacksonville
Joined Oct 2011
1,066 Posts
Yeah I put together 2 nano-tech 360 2S packs. Stripped'em down and wrapped them once in alumi tape and added a 4S balance tab. I could hear the ESC hitting a few "hiccups" at the top end. I have a 30mm inrunner/fan from my Arttech F86 that I have been fiddling with. The fan seems to be put together well, I just don't know if it will outperform the SA fan/motor on 4S.
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