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Sebart Mini Avanti w/ K45 build thread

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Old 05-13-2015, 10:58 AM
  #26
Henke Torphammar
 
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Quote:
Originally Posted by jfetter View Post
My 6S (stock) setup has about 5.5 lbs thrust and tops out @ 122 MPH flat and level.

I won't comment on if that resonable or not. How ever what I do know is that 5.5lb of thrust from the EDF equals a 2.75lb thrust turbine. Twice the speed needs 4 times the power, so the 10lb thrust K45 will propell the Avanti to roughly 240mph flat and level. A slippery airframe :-)
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Old 05-13-2015, 11:11 AM
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Slippery airframe? If its anything like its big brothers, its a draggy airframe. I can't recall the term used, but jets like the futura and Avanti are purposely draggy so the top speed is somewhat aerodynamically limited. Anyone help a brother out on this?

My big avanti has never remotely approached 200mph. It has near double thrust to weight ratio but thrust is for tricks… Not speed ;-) I want more thrust to take off from rough grass fields, thats it. As the gentleman from Italy above alluded to, the cost of the P20 is a deterrent for a lot of modelers. So, this is a nice option, even if it has … dare I say… too much thrust… LOL
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Old 05-13-2015, 11:29 AM
  #28
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Quote:
Originally Posted by Henke Torphammar View Post
I won't comment on if that resonable or not. How ever what I do know is that 5.5lb of thrust from the EDF equals a 2.75lb thrust turbine. Twice the speed needs 4 times the power, so the 10lb thrust K45 will propell the Avanti to roughly 240mph flat and level. A slippery airframe :-)
No.... Thrust is thrust, 5.25lbs from a P20 is no different than 5.25lbs from an EDF...

Jack
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Old 05-13-2015, 11:31 AM
  #29
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Quote:
Originally Posted by Henke Torphammar View Post
I won't comment on if that resonable or not. How ever what I do know is that 5.5lb of thrust from the EDF equals a 2.75lb thrust turbine. Twice the speed needs 4 times the power, so the 10lb thrust K45 will propell the Avanti to roughly 240mph flat and level. A slippery airframe :-)
It's also NOT a slippery airframe at all, the drag coefficient is quite high and it's designed for F3S aerobatics, not speed. Seba himself doesn't like the idea of anything lager than the P20 installed without a proper warning about the airframe not being designed for more power, being given along with it...

Jack
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Old 05-13-2015, 02:02 PM
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Jack those 10s numbers are fantastic. That thing is gonna be killer at that weight.

Regarding EDF and turbine thrust just because it was brought up: Thrust is thrust. EDF's run up against exhaust speed, true, (like prop pitch speed for warbirds) but it doesn't effect thrust at most normal jet flight speeds as long as the exhaust speed is reasonable and most setups these days give way more than reasonable results.

Most of the fast efflux speed in a turbine is un-usable, because thrust limits will be met by airframe drag well before the efflux speed is matched. The dynamic drag produced by the jet airframe is typically going to very high at around 200mph or so. Often, for 1:1 or higher thrust engines, we meet the equal value of (newtons of ) drag produced by the airframe as produced by the engine thrust below 200 mph on most scale or "beefy" airframes. Even though efflux speeds are 700 mph.

EDF on the other hand, even though we may only get 250mph plus on efflux but we can use it all (well 80 percent of it or so) and top out pretty well sub 200 mph assuming our thrust numbers are high enough to meet airframe drag at speed. 9 pounds thrust is 9 pounds thrust. In flight, thrust will change as efflux speed is approached but assuming we have enough head room and maintain thrust we have excellent performance.

Everything I say is anecdotal and off the cuff, it's just a commentary. There is good published data out there though, for those with interest.

Last edited by Eddie P; 05-13-2015 at 08:17 PM. Reason: My initial iPhone post was garbage.. needed clarification
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Old 05-13-2015, 02:03 PM
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PS dont want to hijak the thread this is an awesome project! Looking fwd to more.
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Old 05-13-2015, 09:40 PM
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K45 kinghtech is more and more overpowered for this jet? ........ Not problem, run at 50% of gas and don't are problem, is not necessary to run at 100% full power, important is only if is possible to balance perfectly the model and the final weight is not more different respect the weight with p20 turbine mounted
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Old 05-13-2015, 11:04 PM
  #33
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I will be pushing the engine as far forward as I can.
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Old 05-13-2015, 11:23 PM
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Quote:
Originally Posted by jfetter View Post
No.... Thrust is thrust, 5.25lbs from a P20 is no different than 5.25lbs from an EDF...

Jack
It is diffrent Jack, I have prooven it many times. EDF static thrust needs to be twice of the turbine to perform equal in flight.

Last edited by Henke Torphammar; 05-13-2015 at 11:28 PM.
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Old 05-13-2015, 11:28 PM
  #35
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Quote:
Originally Posted by DrScoles View Post
Slippery airframe? If its anything like its big brothers, its a draggy airframe. I can't recall the term used, but jets like the futura and Avanti are purposely draggy so the top speed is somewhat aerodynamically limited. Anyone help a brother out on this?

My big avanti has never remotely approached 200mph. It has near double thrust to weight ratio but thrust is for tricks… Not speed ;-) I want more thrust to take off from rough grass fields, thats it. As the gentleman from Italy above alluded to, the cost of the P20 is a deterrent for a lot of modelers. So, this is a nice option, even if it has … dare I say… too much thrust… LOL
I know I know, I just did the maths from numbers we got from Jack. He is a strange person to argue with. But I think you agree if the Avanti mini does240mph on the K45 it's a slippery airframe. Faster than a Skyrunner 300 :-)


Quote:
Originally Posted by jfetter View Post
It's also NOT a slippery airframe at all, the drag coefficient is quite high and it's designed for F3S aerobatics, not speed. Seba himself doesn't like the idea of anything lager than the P20 installed without a proper warning about the airframe not being designed for more power, being given along with it...

Jack
I know that very well Jack. Either your top speed is not true or your thrust to low. I just did the maths that I can proove are correct.
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Old 05-14-2015, 12:19 AM
  #36
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Quote:
Originally Posted by jfetter View Post
No.... Thrust is thrust, 5.25lbs from a P20 is no different than 5.25lbs from an EDF...

Jack
On a bench going nowhere...With a fan once you get to the pitch speed maximum its just drag!
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Old 05-14-2015, 12:33 AM
  #37
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Quote:
Originally Posted by Henke Torphammar View Post
It is diffrent Jack, I have prooven it many times. EDF static thrust needs to be twice of the turbine to perform equal in flight.
That is just not true, the P20 and stock electric setup produce about the same thrust and perform almost identically. I don't want to hijack the thread with electric discussion but it's all physics, has nothing to do with propulsion type ;-)

Jack
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Old 05-14-2015, 04:40 AM
  #38
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Jack the thing to remember is on a ducted fan the efflux speed is around 230 mph on the turbine its over 650mph so the faster you go the better the turbine will perform against the electric setup.When your plane gets over 130mph the difference between the efflux and aircraft speed are not that great anymore. Static thrust means nothing unless you want to get bench numbers.

When I flew electric planes it was all about static thrust. Now with turbines I don't even care about static thrust. I flew a 32 pound thrust turbine in my plane and a 48 pound thrust turbine in my plane . Guess what the top speed was about the same on them both. The takeoff run was shorter and in the vertical it accelerated.

Quote:
Originally Posted by jfetter View Post
That is just not true, the P20 and stock electric setup produce about the same thrust and perform almost identically. I don't want to hijack the thread with electric discussion but it's all physics, has nothing to do with propulsion type ;-)

Jack
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Old 05-14-2015, 06:39 AM
  #39
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Had a chance to play with fuel tank positions. The intakes are very thin glass, they can deform easily. The 16oz dubro fits on the rails almost perfectly without pushing on the intakes. The 20oz does constrict them a little more than I'm comfortable with. So, I'm going to go with a 16 and 14 on top of each other. The cockpit floor that is provided will not fit without adjustment with the tanks in this configuration. I don't like cockpits on sport jets and will be painting the canopy glass a solid color like I did on its big brother. I'll do a small cutout on the tray for the UAT to sit flush. The fuel pump and UAT will be near the rear nose gear bulkhead.

I looked over the build thread I did for the medium sized avanti last year. I thought I would get 8-10 minute flights with the 150oz of fuel on board. Not even close. I only use full throttle on uplines and when I'm doing tumbles and flat spins, the rest of the time I cruise around at half throttle. with 150oz, I probably have 10-20 oz left with a 6 minute flight. So, I am skeptical of the published fuel burn. It would make sense if it was an average, not at a full throttle measurement.

With the turbine as far forward as I can put it, without making new rails, the distance for the pipe is 475mm from the back edge of the fuse. The two pipes that WREN offers are the wrong size. Already sent an email to Ilja at Grumania for a custom one. Price is around 100 euros.

I am using a lion 2600 pack from duralite, and a small duralite inline regulator. The ECU pack is a 2100 LiFe pack from Kingtech. This battery is not supplied with the turbine, so don't forget to order it.

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Old 05-14-2015, 06:53 AM
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Quote:
Originally Posted by gunradd View Post
Jack the thing to remember is on a ducted fan the efflux speed is around 230 mph on the turbine its over 650mph so the faster you go the better the turbine will perform against the electric setup.When your plane gets over 130mph the difference between the efflux and aircraft speed are not that great anymore. Static thrust means nothing unless you want to get bench numbers.

When I flew electric planes it was all about static thrust. Now with turbines I don't even care about static thrust. I flew a 32 pound thrust turbine in my plane and a 48 pound thrust turbine in my plane . Guess what the top speed was about the same on them both. The takeoff run was shorter and in the vertical it accelerated.
Gun,

You know me, I am not turbine stupid just because I love EDF. What he said was "thrust is not equal" from EDF to turbine, even if rated identically and that's flat wrong. Physics says thrust is thrust, and that was the issue being put forth by me as his statement was simply not accurate. Of course with 600 MPH+ efflux there will be some differences in top end but it's minimal, all one has to see to prove it is fly a BVM Electra, Bandit, F-86/Fury, Mig 15, T-33 or any other jet where BVM makes a turbine and EDF version for the same exact airframe. They fly almost the same and their speed and operating envelopes are very similar and guess what, it's on the same installed thrust (one has to measure something, you guys say "yeah, it's the bench" and that's true but there has to be SOME measurement taken somehow!) :-o Let's not hi-jack the thread anymore ;-)

Jack

Last edited by jfetter; 05-14-2015 at 06:56 AM.
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Old 05-14-2015, 06:59 AM
  #41
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Watching with great interest. Would really like to install one in my jtm viper if it does well in the mini Avanti. My current setup with 12s4400 batts flies it very well @ nearly 11.5lbs
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Old 05-14-2015, 07:02 AM
  #42
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That is why I am watching also. I am picking up a JHH A7 next week and going to rip out the electric set up and install the new K45. Very interested in fuel tank size and fuel burn. Good work so far Doc!

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Watching with great interest. Would really like to install one in my jtm viper if it does well in the mini Avanti. My current setup with 12s4400 batts flies it very well @ nearly 11.5lbs
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Old 05-14-2015, 07:30 AM
  #43
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My Avanti XXL has a P200 and feels like its about to fall out of the sky unless im above 3/4 throttle. Its a darggy airframe which is the intent of the design due to the low speed qualities.
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Old 05-14-2015, 08:25 AM
  #44
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Dr Scoles.... can the retracts (door servos) handle Lipo direct. Since you are using A4030, as they are HV servos, I'm hoping to avoid a regulator...
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Old 05-14-2015, 08:36 AM
  #45
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Quote:
Originally Posted by LA jetguy View Post
Dr Scoles.... can the retracts (door servos) handle Lipo direct. Since you are using A4030, as they are HV servos, I'm hoping to avoid a regulator...
if not mistaken, a VR would be needed.

Chatty
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Old 05-14-2015, 11:51 AM
  #46
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Does this have the thrust vector option?
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Old 05-14-2015, 12:03 PM
  #47
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Quote:
Originally Posted by LA jetguy View Post
Dr Scoles.... can the retracts (door servos) handle Lipo direct. Since you are using A4030, as they are HV servos, I'm hoping to avoid a regulator...
The factory-installed electric retracts, nose gear door servos and steering servo can NOT be powered by more than ~ 6.0V. So if you use HV servos for the control surfaces and want to power them with a 2S 7.4V LiPo you'll need to use a regulator to power the retracts, nose gear door servos and the steering servo. But because all of the retract units and the nose gear door servos plug into the included sequencer, you can plug the one lead from the sequencer and the steering servo into this Spektrum VR5203 two-channel/dual output regulator like Jack did in the EDF version build thread here:

http://www.spektrumrc.com/Products/D...odID=SPMVR5203
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Old 05-14-2015, 12:35 PM
  #48
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Quote:
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Does this have the thrust vector option?
Not currently, but myself and a few others are thinking about it for the future...

Last edited by Jason W M; 05-14-2015 at 12:46 PM.
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Old 05-14-2015, 06:30 PM
  #49
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Hello everyone,

Just a quick note to let you know that I updated post #9 with links to some videos, specs, photos and more.
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Old 05-14-2015, 09:43 PM
  #50
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Thanks Jason.... I'll use "LiFe" or "A123" direct...
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