Wicked powered SR-71 - Page 2

Doubletap · Nov 25, 2008, 12:47 AM

Don, how does it look for going with 70mm fans? Does it have enough material to remove?

Doubletap

RemE · Nov 25, 2008, 12:55 AM

Subscribing, looks good!

The Don · Nov 25, 2008, 12:57 AM

Quote:

Originally Posted by Doubletap

Don, how does it look for going with 70mm fans? Does it have enough material to remove?
Doubletap

70s should go in.

Don

RemE · Nov 25, 2008, 01:11 AM

I've got the airframe coming from Nitro as well, tomorrow. I'll go with the wicked 4800's, they look great and solid with those EDO plugs. May I ask the normal amp draw on these, and what size 3 cell packs you are using? Just trying to get a feel for runtime. I'll be adding the retracts and probably a few more goodies.

In looking at the tailcones, are the oversize outlets just supposed to be cosmetic, with the "real" exit being back-set inside? I take it you think this will mess with the outflux? If you add thrust tubes, how far out will you take them?

Thanks!

The Don · Nov 25, 2008, 01:19 AM

The 4800s on 3S will pull about 35 amps and be about 360 watts each. I plan on using two 3S 2200 lipos, maybe two 2600s . I am not sure why they did what they did on the tailcones. I am going to make my outlets 80% on these. Once I have them drawn I will post the templates for the tailcones and for the centering ring. They will end at the current exit but will just smaller in diameter.

Don

fly_boy99 · Nov 25, 2008, 01:19 AM

It's too bad they just didn't set this up for 70mm because looking up that intake shows it could easily be done.

Exhaust tube shouldn't be bad to pull down the exhaust size to 54mm for each side.

Doubletap · Nov 25, 2008, 01:39 AM

I'm thinking the tail cones are actually there just for cosmetics; they are much larger in diameter than the actual molded exhaust duct but that's why it shouldn't adversely affect the performance. They are there just for looks but are not functional in any way.

Doubletap

RemE · Nov 25, 2008, 01:43 AM

Right, but I gather that even the smaller "live" duct is too big, and could use a smaller tube still.

The Don · Nov 25, 2008, 01:54 AM

Well it is a sudden expansion and I remember sitting in my Fluid Dynamics Labs and measuring pressure losses in sudden expansions and contractions. So for me it is just taking the outlet energy we have and throwing some away for no good reason.

RemE · Nov 25, 2008, 02:00 AM

Two 4800's and two pentium 40's ordered!

I will go with a modified E-Flite F-15 nose retract and Great Planes 0.10's for the mains . I had great results with them on my modified HL F5-E Camo and this plane's a pound lighter. The stock retracts are too delicate, the plastic gear wire holder's with grub screws are a weak link as is the wire itself, too soft and no spring coils.

RemE · Nov 25, 2008, 02:05 AM

Don, I like the way you think

Looking at the pics of the tailcones again, would those intakes that flow into those turbulent zones act as venturi's, drawing an air cushion around the outflow and relieving some of that "trapped" turbulance? Aaaa my head is beginning to hurt, I'm an electronics guy....

Also, looking in the box, were there decals (with correct USAF spelling) and red trim tape??

Doubletap · Nov 25, 2008, 02:17 AM

Quote:

Originally Posted by The Don

Well it is a sudden expansion and I remember sitting in my Fluid Dynamics Labs and measuring pressure losses in sudden expansions and contractions. So for me it is just taking the outlet energy we have and throwing some away for no good reason.

I understand what you are getting at but although jet turbine and ducted fans are both "reaction" type engines, they are different in that the turbine jet benefits from the expansion of hot gases which doesn't exist with the ducted fan. But then again, it's been over 2 decades since my aerospace engineering days in college and almost a decade since I last worked in the industry, so I am a bit rusty.

Doubletap

The Don · Nov 25, 2008, 02:54 AM

Quote:

Originally Posted by Doubletap

they are different in that the turbine jet benefits from the expansion of hot gases which doesn't exist with the ducted fan.

Actually I was referring to simple shop air being blown down a clear acrylic tube. At least that is what we had in my labs. No turbines or hot gases, we would burn ourselves for sure

I recall we had ~3" diameter clear tubing with shop air blowing down it then we measured the head losses from expansions going from say a 3" to 4" tube then compared our measured head loss "K" factors to what was published in our textbooks based on the expansion area ratios. Lots of fun

I need to grab my Fluids book and take a look to refresh (been 13 year myself). Might be fun to see what is going on. My Eeagletree can get me airspeed then that leads to Reynolds number and so on....

Don

Petefoss · Nov 25, 2008, 08:06 AM

Quote:

Originally Posted by The Don

I weighed all the parts on the scale. Here is my weight break down.

All foam parts and EDF units: 14 ounces
Two Wicked 4800 motors : 4.2 ounces
Two Pentium 40 ESCs: 2.5 ounces
Two servos and servo extension: 1.0 ounce
Receiver: .3 ounces
Two 3S lipos: 6.8 x 2 = 13.6 ounces

Total: 35.6 ounces plus ~2 oz for other stuff so lets call it 38 ounces. I should be getting about 700-750 total watts. So that is about 300 watts per pound

Just how I like my EDFs!

Don

What is the inner diameter of the motor mounts?

jet-ster · Nov 25, 2008, 08:20 AM

ALright GREAT you started this thread. Getting really tried of people bitchin.

Nov 25, 2008, 01:54 AM	#24
The Don Wonderfully Wicked Join Date: Jan 2002 Location: Willoughby, Ohio Posts: 7,928	Well it is a sudden expansion and I remember sitting in my Fluid Dynamics Labs and measuring pressure losses in sudden expansions and contractions. So for me it is just taking the outlet energy we have and throwing some away for no good reason. Attached Thumbnails 6.0 KB · Views: 86

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Nov 25, 2008, 12:47 AM	#16
Doubletap Si Vis Pacem Para Bellum! Join Date: Jul 2005 Location: PRC (People's Republic of Commiefornia) Posts: 5,798	Don, how does it look for going with 70mm fans? Does it have enough material to remove? Doubletap

Nov 25, 2008, 12:55 AM	#17
RemE Tweaker Join Date: Sep 2005 Location: Corona Del Mar Posts: 2,685	Subscribing, looks good!

Nov 25, 2008, 01:11 AM	#19
RemE Tweaker Join Date: Sep 2005 Location: Corona Del Mar Posts: 2,685	I've got the airframe coming from Nitro as well, tomorrow. I'll go with the wicked 4800's, they look great and solid with those EDO plugs. May I ask the normal amp draw on these, and what size 3 cell packs you are using? Just trying to get a feel for runtime. I'll be adding the retracts and probably a few more goodies. In looking at the tailcones, are the oversize outlets just supposed to be cosmetic, with the "real" exit being back-set inside? I take it you think this will mess with the outflux? If you add thrust tubes, how far out will you take them? Thanks!

Nov 25, 2008, 01:19 AM	#20
The Don Wonderfully Wicked Join Date: Jan 2002 Location: Willoughby, Ohio Posts: 7,928	The 4800s on 3S will pull about 35 amps and be about 360 watts each. I plan on using two 3S 2200 lipos, maybe two 2600s . I am not sure why they did what they did on the tailcones. I am going to make my outlets 80% on these. Once I have them drawn I will post the templates for the tailcones and for the centering ring. They will end at the current exit but will just smaller in diameter. Don

Nov 25, 2008, 01:19 AM	#21
fly_boy99 Flying motor mount master Join Date: Oct 2004 Location: San Jose, California, United States Posts: 8,457	It's too bad they just didn't set this up for 70mm because looking up that intake shows it could easily be done. Exhaust tube shouldn't be bad to pull down the exhaust size to 54mm for each side.

Nov 25, 2008, 01:39 AM	#22
Doubletap Si Vis Pacem Para Bellum! Join Date: Jul 2005 Location: PRC (People's Republic of Commiefornia) Posts: 5,798	I'm thinking the tail cones are actually there just for cosmetics; they are much larger in diameter than the actual molded exhaust duct but that's why it shouldn't adversely affect the performance. They are there just for looks but are not functional in any way. Doubletap

Nov 25, 2008, 01:43 AM	#23
RemE Tweaker Join Date: Sep 2005 Location: Corona Del Mar Posts: 2,685	Right, but I gather that even the smaller "live" duct is too big, and could use a smaller tube still.

Nov 25, 2008, 02:00 AM	#25
RemE Tweaker Join Date: Sep 2005 Location: Corona Del Mar Posts: 2,685	Two 4800's and two pentium 40's ordered! I will go with a modified E-Flite F-15 nose retract and Great Planes 0.10's for the mains . I had great results with them on my modified HL F5-E Camo and this plane's a pound lighter. The stock retracts are too delicate, the plastic gear wire holder's with grub screws are a weak link as is the wire itself, too soft and no spring coils.

Nov 25, 2008, 02:05 AM	#26
RemE Tweaker Join Date: Sep 2005 Location: Corona Del Mar Posts: 2,685	Don, I like the way you think Looking at the pics of the tailcones again, would those intakes that flow into those turbulent zones act as venturi's, drawing an air cushion around the outflow and relieving some of that "trapped" turbulance? Aaaa my head is beginning to hurt, I'm an electronics guy.... Also, looking in the box, were there decals (with correct USAF spelling) and red trim tape??

Nov 25, 2008, 08:20 AM	#30
jet-ster I LUV CROSSWINDS Join Date: Jun 2006 Location: Arlington, TX Posts: 546	ALright GREAT you started this thread. Getting really tried of people bitchin.