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Old Apr 02, 2011, 11:56 PM
Go invisible pink unicorn!
Ara Tidwell's Avatar
United States, OK, Stigler
Joined Oct 2010
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Thats pretty cool but I would rather have the fuse scaled up to have proportinate engine nacells.
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Old Apr 03, 2011, 01:13 AM
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Maple Valley, WA
Joined Apr 2006
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Originally Posted by Ara Tidwell View Post
Thats pretty cool but I would rather have the fuse scaled up to have proportinate engine nacells.
As would I. My biggest beef with the current foamy. So out of scale looking.
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Old Apr 05, 2011, 11:21 PM
Go invisible pink unicorn!
Ara Tidwell's Avatar
United States, OK, Stigler
Joined Oct 2010
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Glad you agree, kind of felt bad about down talking someone elses project.
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Old Apr 05, 2011, 11:42 PM
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Nah, it is what it is. Cheap foamy. Overall not bad job, semi-scale but yeah those oversized nacells drive me nuts.
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Old Apr 07, 2011, 03:14 AM
Pointy end at the front.
benjo's Avatar
Joined Aug 2009
663 Posts
Meh, I like big engines, makes it look tough. I am pretty sure they did this to make it fly better, You can imagine the backflip phenomenon with a scale length and size foreward fuselage???

The whole aircraft resembles a balance between everything, but in the air it doe look really good no one can deny that.
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Old Apr 07, 2011, 04:01 AM
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Lincolnshire, UK
Joined Oct 2009
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Originally Posted by Aros View Post
As would I. My biggest beef with the current foamy. So out of scale looking.
Good effort with the SR71. I tried and failed to scratch-bulid one and it backflipped on launch. My biggest issue on build was maintaining the scale appearance. Working around 70mm fans and then scaling the jet accordingly gave me a surprisingly large jet (about 5ft long iirc) yet the fuselage was surprisingly thin which lead to a lack of bending strength in the pitch plane where the forward fuz meets the wing. It was also a real struggle to get a pair of 4s 2200 batts in line behind the cockpit.

For all these reasons I reckon you are far better off with the "adjusted scale" foamy you have as it's a minimal hassle to build and still looks pretty good. If you want genuine scale then you'll need to go to a huge airframe with a high-end power system so match. As hand-launchable SR71 foamies go I reckon you've probably got it right.

Si
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Old Apr 07, 2011, 04:46 AM
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lipoflyer's Avatar
Australia
Joined Nov 2010
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does look nice but i havn't been brave enough fly anything that looks like a dart!

the shape is classic and would be a real head turner. well done!
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Old Apr 07, 2011, 08:29 AM
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Yeah I definitely understand why the nacelles are over sized. A much larger airframe would be problematic to hand toss since I fly at a bumpy/mucky/grass field. Overall, it looks really good and quite impressive in the air that is for sure (especially on those low WOT 100+mph passes)!
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Old Apr 07, 2011, 11:05 AM
You win again gravity!
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UK
Joined Jan 2010
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Originally Posted by Paul5910 View Post
Aros, I think I see what you are talking about with the delta style planes pitching up while trying to flare. I even think that I may have read in one of the threads about the squall doing something similar. Thank you for taking the time to explain that to me.. Rest assured if I ever find myself behind the sticks of a delta type, I will remember that very good explanation. I will need considerably more stick time before you will catch my transmitter bound to an SR71 though.

Paul
The tendency is there because deltas pitch around a point off the nose of the aircraft. Concorde, the space shuttle, SR-71 all have the same problem.........you pull back on the stick but because the elevators are on the wing you get a pitching moment change, that you request, but the wing also dumps a load of lift, which you don't! - net result is that you can have a very hard landing.
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Old Apr 07, 2011, 11:18 AM
miniture aircraft pilot
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United States, FL, Tampa
Joined Oct 2007
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i have been flying on eof these stock, getting a feel of it to build a LARGE one. 11' long off plans.

the biggest problem i found that is true with most foamies, it is so light that there is no momentum on landing. the foam slows down quickly and an stiff breez can make it interesting. almost like trying to land a feather in the wind.
But as long as it is flown in a scale like manner it is fine. and if you linger to long and your escs cut off power to the engines ... your down quik.
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Old Apr 07, 2011, 11:49 AM
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I have found that I really have to fly her down to the ground with about 1/4 throttle or she will nose up. Wing rock is another symptom of the SR-71. It feels so weird not to flare on landing so I have to fight against my instinct and keep a touch of down elevator all the way to the ground. I reinforced the bottoms of my nacelles to handle the shock...I think I am going to add little skids as well.
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Old Apr 07, 2011, 08:43 PM
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Ran a pack through her this evening. Unfortunately the grey sky/clouds made orientation especially difficult and boy it didn't take but a split second and I lost orientation. Was it coming towards me? Away from me? What was it doing? I couldn't gain it back fast enough and the ground was rising to meet her so dang fast so I dropped the throttle and she went over the embankment.

Luckily she landed dirty side down but on a road so she split in a few different places. All the splits were extremely clean and a few minutes with CA and she will be ready to go again.

Whew!
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Old Apr 07, 2011, 11:06 PM
Aka: Tom Jenkins
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Palm Beach County, Fl.
Joined Aug 2008
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Thanks Apex...What would this do exactly?
First you take the diameter of the inside of your fan to get the area then deduct the area of the motor housing to give you fan swept area. Reduce the area of that by 20% for an 80% exit area for your tail pipe. Now you take the front diameter and plug it into one end of the program, ad the total length of the pipe and ad the exit diameter and hit print, take the print and ad 1/4" to the lap edge and 1/4" to the lap to the fan for tape. Overlay some acetate or mylar and cut it out for your custom made cone, roll it up to the overlap and tape into place on the back end of the fan housing, re install the fan set and go fly!
Tom
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Old Apr 09, 2011, 01:05 PM
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Thanks Apex. Looks like I will have to try that on a new airframe. Her expiration date came today.

Every hand launch has been a real adventure. For whatever reason, no matter how smoothly and perfect pitch and level it left my hands, it would bank heavily to the right almost smashing to the ground every single time. But once I counter-corrected and got her some more altitude, she would fly beautifully. So it wasn't a trim issue, nor a CG issue.

Today, she banked again to the right but this time my counter inputs did nothing. She slammed into terra firma with a sickening thud with black bits of foam spraying everywhere. I glued her all back together like Frankenstein at the field and tried again (I'm nothing if not determined). Same thing but worse. This time the airframe simply wasn't worth saving. So I yanked all the components out and will pick up a new airframe in a few weeks.

If anyone has ideas what could cause such extreme banking regardless of my hand toss ability I would love to have some insight. I did carve out two finger tip sized holes close to the CG for easier hand tossing but I wonder if it was actually contributing to the problem.

I'll need to find out so I don't have these issues with my next airframe.
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Old Apr 10, 2011, 12:41 AM
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USA, TX, Houston
Joined Jul 2002
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Sorry to hear about the loss Aros. I have been watching this thread and have been encouraged from your reports of a nice flying SR. I don't have any ideas on hand launching to offer. I personally can't stand to hand launch because for me, every one is a near disaster. I do so much better with a rolling takeoff. I am looking forward to seeing you get this bird flight ready again.

Paul
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