Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
May 26, 2019, 11:19:21 PM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: 1 2 [3]   Go Down
Print
Author Topic: Boston Beagle  (Read 3268 times)
0 Members and 1 Guest are viewing this topic.
Yak 52
Titanium Member
*******

Kudos: 61
Offline Offline

United Kingdom United Kingdom

Posts: 2,412


Topic starter
Free Flight Vagrant



Ignore
« Reply #50 on: March 20, 2013, 05:52:28 AM »

I was wondering if the forward CG (for weight reasons) is keeping the inner wing stalled in 'race track mode', which would prevent the ROG quite nicely  Grin

Sorry that's a typo: I meant forward undercarriage...
Logged
Yak 52
Titanium Member
*******

Kudos: 61
Offline Offline

United Kingdom United Kingdom

Posts: 2,412


Topic starter
Free Flight Vagrant



Ignore
« Reply #51 on: April 27, 2013, 09:42:47 AM »

A couple of videos from Impington last month. One good flight:

http://www.youtube.com/watch?v=eupOL9_3Djo

It was very sensitive to torque and rudder and hard to get the turn radius right. On modest power it would do a minute nicely but racking up the turns gave issues with the ROG. It couldn't handle the torque, hence the race track pattern:

http://www.youtube.com/watch?v=Epu6mwEjx_A

(buzzed by a Bonanza too!)

Opening the turn in a bigger venue would be easier. Moving theUC back, reducing the fin size, and adding winglets to give more dihedral effect helped a bit but not enough, so back to the drawing board... The next one will have less focus on motor length and more priority given to stability.
« Last Edit: April 27, 2013, 11:09:03 AM by Yak52 » Logged
FreeFlightModeller
Russ Lister
Titanium Member
*******

Kudos: 64
Offline Offline

United Kingdom United Kingdom

Posts: 3,516


Russ Lister



Ignore
« Reply #52 on: April 27, 2013, 05:57:54 PM »

That first flight's not too far off ideal for Impington  Smiley ... I love that SortaSenator type model that flops into sight! (there is one model that is based on a model like the Senator ... it might be that?)
Logged
danmellor
Titanium Member
*******

Kudos: 54
Offline Offline

United Kingdom United Kingdom

Posts: 2,208




Ignore
« Reply #53 on: April 27, 2013, 06:10:16 PM »

Cool vids! The Planarian canard is one of my fave Bostonians; I need to build another!

Cheers,

Dan.
Logged
FreeFlightModeller
Russ Lister
Titanium Member
*******

Kudos: 64
Offline Offline

United Kingdom United Kingdom

Posts: 3,516


Russ Lister



Ignore
« Reply #54 on: April 27, 2013, 06:15:15 PM »

I think I saw that flying at Nottingham a few years ago?
I remember Joshua doing one on SFA .... I think I would have been tempted if I wasn't into brewing my own so much at the time.
Logged
OZPAF
Palladium Member
********

Kudos: 175
Offline Offline

Australia Australia

Posts: 4,842



Ignore
« Reply #55 on: April 27, 2013, 08:27:20 PM »

I can see the frustration Jon. The first flight seems to show promise of much longer flights but for the inability to handle the torque. I'm not all that experienced in indoor but wonder if a combination of inboard washin - half way out on the wing and an appropiate amount of right thrust would help control the high torque?  At slow and cruising speeds the drag from the wash in would reduce the need for rudder for cruise turn.
I guess you have probably tried all this anyway but thought it may have beeen worth a mention.
John
Logged
Yak 52
Titanium Member
*******

Kudos: 61
Offline Offline

United Kingdom United Kingdom

Posts: 2,412


Topic starter
Free Flight Vagrant



Ignore
« Reply #56 on: April 28, 2013, 08:18:45 AM »

John, it did have a wash out tab on the outer panel of the left wing, but it ended up more or less in line with the mean camber line ie not much deflection needed, at least with that thrust setting and turn radius. The problem with the tab was that a slight stall lead to right wing drop, opening out the pattern (not wise at Impington)

You can see this happening here, when I was trying to slow it down:

http://www.youtube.com/watch?v=d-aTVv3lM5Q&list=UUyJKGlH0WQ0bPDyiplgI-1g&index=1
(Look out for Howard's Sukhoi at 0:18 Cool)

The thrustlines could have been tweaked but after another long and frustrating session at Whittlesey I've decided it's had it's chance. It was just spirally unstable - a combination of not enough dihedral, short tail moment arm and flying at a higher CL due to the airfoil improvement. I hadn't realised when I was designing it how much these factors would be 'eat into the spiral stability from both ends' as it were. But looking at the 'B' parameter shows it as significantly lower than the Cub. (I should have done this before as opposed to using TLAR with the dihedral  Roll Eyes)

It was pretty squirrelly to trim. Every so often it would go from that nice pattern into a slight spiral dive pattern. I was able to fly it slower than that good flight (about CL0.6) but it was more stable when trimmed faster. The tail volume was about 0.7 but even so it was sensitive to CG shift from the long motor.

It was frustrating because that good flight was about 2000 turns on a motor that should have handled 3000 easily. But if you can't get the power into the air you can't use it...
Logged
OZPAF
Palladium Member
********

Kudos: 175
Offline Offline

Australia Australia

Posts: 4,842



Ignore
« Reply #57 on: April 28, 2013, 08:01:55 PM »

Thanks Jon. Impington does appear to be a turn circle nightmare Grin

That was an interesting description of the trimming problems. Its interesting to see the outside wing slightly stalling.

It was frustrating because that good flight was about 2000 turns on a motor that should have handled 3000 easily. But if you can't get the power into the air you can't use it...

Yes I suppose thats the challenge in a nutshell - the design needs to allow all the high performance features to work. Whether it is a balancing the airfoil CL's against planform shape and AR or power against stability and duration.

Here's looking to the next version.

John

Logged
Yak 52
Titanium Member
*******

Kudos: 61
Offline Offline

United Kingdom United Kingdom

Posts: 2,412


Topic starter
Free Flight Vagrant



Ignore
« Reply #58 on: April 29, 2013, 05:22:23 AM »

Its interesting to see the outside wing slightly stalling.

The tab was big enough to make a difference to the area I think (I meant wash in tab not wash out)
Logged
Haoyang Wang
Bronze Member
***

Kudos: 0
Offline Offline

United States United States

Posts: 10



Ignore
« Reply #59 on: May 01, 2013, 11:26:47 AM »

The tab was big enough to make a difference to the area I think (I meant wash in tab not wash out)

The wash-in tab increases camber, which increases both drag and lift for the inner wing. In this case since the wings are already cambered, maybe the wash-in tab result in too much camber for the inner wing?
Logged
Yak 52
Titanium Member
*******

Kudos: 61
Offline Offline

United Kingdom United Kingdom

Posts: 2,412


Topic starter
Free Flight Vagrant



Ignore
« Reply #60 on: May 01, 2013, 12:33:23 PM »

Do you mean too much camber for the ROG or in the stall? The wash in tab was not deflected very much - it just followed the mean camber line so the increase in camber wasn't very much.

The area increase on the left wing tip due to the tab would be enough to cause asymmetric stall and the right wing to drop. Especially since the planform has tapered tips.
Logged
Haoyang Wang
Bronze Member
***

Kudos: 0
Offline Offline

United States United States

Posts: 10



Ignore
« Reply #61 on: May 01, 2013, 01:13:26 PM »

Do you mean too much camber for the ROG or in the stall? The wash in tab was not deflected very much - it just followed the mean camber line so the increase in camber wasn't very much.

I was thinking on the ROG. (By the way, the same problem would happen when you hand-launch it with lots of turns, right?)
Logged
Yak 52
Titanium Member
*******

Kudos: 61
Offline Offline

United Kingdom United Kingdom

Posts: 2,412


Topic starter
Free Flight Vagrant



Ignore
« Reply #62 on: May 01, 2013, 01:24:40 PM »

I can't remember if I tried that, it's a little while ago. I did think similarly, that the ROG geometry with forward UC was holding the inner wing stalled but you can see from one of the videos that the race track pattern is still present with the tail up and flying. And moving the UC back didn't make that much difference. Which lead me to the lack of spiral stability. It had a critical bank angle that was exceeded in the full power ROG in a tight radius turn. Just needed more dihedral I think.
Logged
Pages: 1 2 [3]   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!