Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
November 19, 2017, 05:25:18 AM *
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]   Go Down
Print
Author Topic: Bar Fly Legal Eagle  (Read 2579 times)
0 Members and 1 Guest are viewing this topic.
piecost
Gold Member
*****

Kudos: 6
Offline Offline

United Kingdom United Kingdom

Posts: 262

Topic starter


Ignore
« on: April 28, 2014, 07:54:49 PM »

I intend to enter the UK BMFA Nationals with a Legal Eagle model and selected John Barker's Bar Fly to build.

I read from the HPA forum that 5lb/ft3 balsa was recommended for this model but wanted to experiment with lighter wood. I obtained some excellent balsa from Nick Aikin “Greenman Balsa”; requesting as light as possible for the wheel and some 4.5 lb/ft3 for the structure. I cut the wheel from 4.1 lb/ft3 and the wing and tail ribs. The fuselage structure was cut from 4.5 lb/ft3, I stripped some 4.1 lb/ft3 wood for this but it felt far too fragile and flexible. Wing spars were made from my best model shop wood of 6lb/ft3 balsa with Stiffness Coefficient of 100. The lighter wood felt far too flimsy. The tail spars may have been made from the same stuff as the fuselage.

I slightly regretted the very light wood employed for the fuselage longerons when I broke one of them in the nose during initial flights. Glue was added to the break and extra vertical and horizontal members were added.

I used thinned Ambroid throughout the construction.

I incorrectly positioned the dihedral breaks on one wing – one bay too far outboard - and decided to make the other to match rather than start again. So; only the outboard bay has dihedral, the wingtip raised the same amount as the plan. The starboard wing had 1/8” washin added as recommended elsewhere on this forum. The model flys well with this change.

The windscreen was made from the plastic wrapping round a box of chocolates attached with a thin strip of double sided tape. The tape being rather heavy. Canopy glue would have been better.

I may a few changes from the plan to suit my building style. In particular, I left out the wing and tail tip gussets/braces to save weight.

I added camber to the wing and tail tips for aesthetic reasons; negating the practical design of using wing ribs turned on their side. I sanded a sheet of ¼” to the rib camber and pinned the strips (wetted in boiling water) between camber templates and put in a hot oven.

The fin trailing edge was attached to the right side of the fuselage tail-post to give some right turn

The tissue for the fuselage was water-shrunk once on a frame with an airbrush, attached with thinned aliphatic glue and shrunk a second time with rubbing alcohol. The tissue for the flying surfaces was water-shrunk twice on a frame and attached with Spraymount. The covering on the leading edges of the flying surfaces was wrapped round the front and glued with thinned Ambroid. Some of the other edges were starting to peal off.

I don't like Spraymount for this application since it is difficult to apply enough to stop the tissue lifting without adding allot of weight.

The propeller blades were not sanded to section since I was getting short of time. The propeller was formed with their axis at 15º from vertical on a can of Spraymount (not put in an oven!).

3/32” square bass was used for the propeller spar, tapered and inset into the blades. I had not tried this before and it proved very neat. A strip of tissue was glued over the joints. A reverse Z-hook was bent into 1/32” wire. I found that the trailing edge of the blades clashed with the nose block so had to be cut away. I used a nylon bush to hold the propeller, not being able to find any thin tin plate. The nose block to hold this from soft balsa. I was worried about the nylon bush pulling through so glue 2 layers of the thin wood from cigar tubes cross grained onto the face of the block.

The tailplane was built as per plan except that the single central tailplane rib was used rather than two matching the fuselage taper. The tip braces/gussets were ommitted.

The upper surface of the leading edges of the flying surfaces were sanded to a radius.

Weights were as follows:

                              Uncovered     covered
Fuselage                    0.61g           1.26g
Wing                           0.27g           0.68g
Tailplane                    0.15g           0.20g
Fin                              0.10g           0.20g
Undercarrage             0.13g              ---           
Propeller                    0.65g             ---           
Propeller Block           0.12g             --- 
Peg                             0.11g

Rubber                  0.082” Tan Super-Sport 0.89g
Stint                       1.13g

AUW                      5.65g
CG at AUW

Airframe without Rubber 3.45g

My model has CG 8mm forward compared to plan (with rubber)

Trimming

The model flew straight off the board and the adjustable tail incidence proved very convenient. The tailplane was set to give a nose-up climb. I added some more fin offset, moving the leading edge about 1mm to the right and 1/64” right thrust added to tighten the turn. I plan to enter this model in the nationals in June and generally fly in 24’/25’ ceilings so use a stint to trim with a shorter motor.

I started with 0.092” rubber, with a 60% stint, equivalent to 200% propeller to peg length. The model proved overpowered and 0.082” was substituted.

I was slightly concerned about the RoG ability of myself and the model. The model quickly established a nose low attitude on it’s wheel and took about 1/3 of a turn before lifting off into a steep climb. From a hand launch the model flys at low incidence for a second or two before settling into a nose high climb.

More trimming awaits...
Attached files Thumbnail(s):
Bar Fly Legal Eagle
Logged
piecost
Gold Member
*****

Kudos: 6
Offline Offline

United Kingdom United Kingdom

Posts: 262

Topic starter


Ignore
« Reply #1 on: April 28, 2014, 07:56:27 PM »

Completed model
Attached files Thumbnail(s):
Re: Bar Fly Legal Eagle
Logged
jhnwdwrd
Bronze Member
***

Kudos: 0
Offline Offline

United States United States

Posts: 32



Ignore
« Reply #2 on: November 23, 2014, 10:07:23 AM »

Good looking plane. Where can one find plans for the "Bar Fly"
Logged
IndoorFlyer
Guest

« Reply #3 on: November 23, 2014, 11:34:23 AM »

John Barker, aka "Hepcat" on this forum, designed the Bar Fly.  There is a .jpg of the plan in this thread:

http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=1281.msg48705#msg48705
Logged
jhnwdwrd
Bronze Member
***

Kudos: 0
Offline Offline

United States United States

Posts: 32



Ignore
« Reply #4 on: November 23, 2014, 12:12:30 PM »

Thanks for the link.
Logged
IndoorFlyer
Guest

« Reply #5 on: November 23, 2014, 01:09:20 PM »

Plan on one sheet, (.jpg again) here:

http://www.creativesweb.co.uk/Clayton/images/John-Barker-Bar-Fly_web.jpg
Logged
piecost
Gold Member
*****

Kudos: 6
Offline Offline

United Kingdom United Kingdom

Posts: 262

Topic starter


Ignore
« Reply #6 on: October 14, 2016, 09:58:23 AM »

Bar Fly

I had only put in the occasional flight in with this model over that last few years and had not really tapped into its full potential. I entered it into the the 2016 nats, but not too seriously. I had not even build a spare mode (I have a habbit of hanging models in the roof). I had been very confident in my first nats (in 2014) the model was the lightest in its class. But my first flight landed the model on the centre boss of the roof structure! It only being retrieved at the end of the competition.

I had found that the best times were achieved with a 26.5" motor length. This had a potential duration of over 4 minutes, but was limited by the motor bunching at the rear hook and landing out of turns. The narrow rear fuselage being more akin to a Peanut scale model than to an indoor duration type. I started using a lightweight bobbin, akin to a Wobbly Peg,  made from  a drinking straw and with depron disks. Unfortunately, this tended to break rather than offering an improvement. So, I had to remove it.

For the competition; I had prepared a number of identical motors , but not did break them in. The idea being to perform lower powered trimming flights in quick succession and resting each for an hour before the competition flights.

I intended to spend the last day of the competition with this model. My first wind was a disaster when a new motor broke in the model. I was trying to break the motor in; not break the motor up!  It had gone at the knot, which was positioned under the wing to avoid bunching at the rear peg. But it left a mass of rubber at the rear peg just waiting to burst into flayling strands to mash the mashmellow-like 1/16th square balsa structure. So, I constructed an external blast tube of 2mm depron taped around the rear fuse. The idea being that this external splint would prevent the structure moving outwards and breaking when hit by the rubber. This worked and I extracted the motor without any further damage. The only repair being an unpright at the wing trailing edge. My third burst motor in this model! I had clearly used up all my luck.

With the model back together, I was going to progressively increasing my times and I was confident of eventually reaching the 4 minute mark.  A first competition time was 3m15s, only reaching 45'  (about 10' below the girders).  This was a solid start to build on, but then I noticed the nice yellow Cassutt Nocal flying which caused me to rush a final conservative Legal Eagle flight of 3m18s before breaking out my NoCal. This was good enough to put me in third place.

If I get round to building a new model I will consider the following changes:
   Widen the nose (to the same width as at rear peg) to fit a blast tube
   Spacer between leading edge of tailplane and bottom of fuselage to allow more nose up trim.
   Single attachment on leading edge of tail to save weight (to pay for the wieght of the previous change)
   lighter tissue
   more refined noseblock (had to trim propeller trailing edge to miss corners of noseblock!)
   Higher propeller pitch to use shorter/fatter motor to alleviate bunching
   3D printed bobbin/wobbly peg
   Extra upright/lateral spacers in first bay of nose to prevent buckling of longerons

I may try to beat 4 minutes in the next session. I will report here if I do
Logged
piecost
Gold Member
*****

Kudos: 6
Offline Offline

United Kingdom United Kingdom

Posts: 262

Topic starter


Ignore
« Reply #7 on: July 26, 2017, 03:52:14 PM »

for HPA

I really like the Bar Fly design but was disappointed in that I had not wrung out its full potential. I decided to build another Bar Fly incorporating some improvements. These were mainly to save weight relative to my first model (which was already pretty light). The major change was the ability to accommodate a blast-tube. This entailed widening and deepening the nose to the same dimensions as at the rear peg.  The fuselage cross section at the peg was considered the minimum fuselage width around the motor as badly bunched motors had contacted the structure. I made a blast tube from 2 telescoping sections of a Selfie Stick that matched the fuselage cross section at the rear hook, 15mm diameter. The front fuselage was widened and deepened to accommodate it and the canopy almost disappeared, to be only 2mm deep.

I carefully examined the structure with an aim to removing redundant parts, to remove weight. The fuselage cross-member at the base of the windscreen was deleted it was so close to the member at the top of the canopy.  The  base of the Ultra-film windscreen  was joined to the tissue  on the top of the nose with canopy glue. I also removed the diagonals at the edges of the canopy and got away with folding the film onto the side of the fuselage before gluing. Not a neat solution, but very light. The root rib was removed from the fin, the tissue being kept taught by the  careful  spacing of the leading and trailing edges onto the  fuselage. The rear fuselage was tapered to 1/8 inch high and 1/6 inch wide saving structure and tissue weight. This created a potential weak point in that the trailing edge of the fin had a small gluing area onto the back of the fuselage. This has not proved to be a problem. The trailing edge of the fin was glued to the right side of the fuselage, with the leading edge central, to give a right turn. It was extended below the fuselage and rounded to form a post for mounting the tailplane trailing edge tube. This replaces the separate peg attached to the tailplane on the first model. The fuselage structure was built from 4.2 lb/ft3 balsa with Stiffness Coefficient of only 85. This felt very delicate, but was significantly better after covering. It withstands the load from the rubber, even with fairly slack tissue. Most care is needed in handling and not taking out cross members  when fitting the blast tube.

The model was covered with Gampi tissue, attached onto the flying surfaces with 3M77 sprayglue, with the edges  stuck down with thinned Ambroid. The tissue was attached to the fuselage with thinned PVA. The fusleage tissue was pre-shrunk with water and then re-shrunk with rubbing alochol when in place. It was held in a jig to prevent warps. The fuselage tissue was still slack after covering. Perhaps a second water shrinkage should be applied. The tissue for the flying surfaces was preshrunk with water twice and left to dry (not on a frame). It was ironed to get the worst of the wrinkles out. This did not work well and the flying surfaces had a bumpy texture. The ironing was done some hours prior to covering so that the tissue would be at ambient water absorption and not further slacken after covering. Tissue sagging often occurs in cold and damp hangers and must degrade the flying surfaces and increase the camber. I didn’t demonstrate any weight saving in employing Gampi tissue over Esaki, even though it should be 15% lighter IIRC. It seems that weight glue used to attach the tissue is more important than the difference in tissue weights.

The ribs were cut from my lightest balsa of 3.59 lb/ft3. This sheet was also used for the nose sheeting and that holding the motor peg (the hole was hardened with cyano). The peg was 1.5mm OD aluminium tube; a smaller diameter tube/rod would possible tear through the balsa.

On my first model 22% of the airframe weight of the first model was taken-up by the propeller and noseblock and it was clearly over-engineered at 0.77g. I had employed a relatively heavy nylon nose bush which, even worse, necessitated weighty 1/32 piano wire. So, on the new propeller I switched to using 0.022" piano wire (as per my LPP model) and 0.010" steel shim bearings in place of the nylon bush. This is the first time I have tried this, but they seem to work OK without incurring any slop. The fat nose necessitated a large nose block which would be far too heavy if made from sheet and so a space-frame construction was used rather than  a solid lamination. I did use a sheet for the baseplate, but cut lightening holes. It was tissue covered.

I used a 1/16 bass propeller spar 0.063” round at the centre tapered to 0.020" and blades from 0.8mm A-grain balsa. They were PVA glued to the spars without being let into slots in the blades (I found that the slots tended to split the blades) The blades were made from 0.8mm A-grain sanded to 0.022" and proved too delicate; the blades broke off when the model hit a wall. I replaced the broken propellers with a 0.100" diameter bass spar tapering down to 0.022" and 0.8mm thick blades weighing about 0.100g each. They have withstood wall/floor impacts and are now just strong enough. I managed to sneak in an extra 3mm on propeller radius and used a 44º pitch at 75%. The plan had plenty of room for a longer blade radius, but was limited to an additional 3mm on the undercarriage length without encroaching to the 3mm margin around the wing on the plan.

The lighter propeller moved the CG aft, this was compensated by the larger tail area. with no loss of stability noticed. I managed to add 32mm to the span of the tailplane; 16mm added to each trailing edge with the leading edge and trailing edges projected outwards.  A single, central, leading edge attachment hook was used, wedges being added to the tailplane leading edge to prevent it sliding sideways.

The 1 inch diameter balsa disk was replaced by a light 1/16 stick bent around a hair curler into a  circle. A cross bar was added and glued to the wire. The first wheel I built does not rotate, subsequent wheels do at no real weight disadvantage. The gear leg is removable and on the original model about 10mm sticks into a box in the fuselage. On the latest model I reduced the length of the piano wire slotting into the fuselage to about 4mm and correspondingly reduced the height of the box in the fuselage. This proved too wobbly, the model barely stands on its gear, so perhaps 6mm of wire sticking into the fuselage would be better:

I was so pleased with the second model that I build a third. This proved slightly heavier as I had used up my lightest balsa. Weights came out as follows:
                                                  Bar Fly bis 2                      Bar Fly bis 3
                                          uncovered   covered        uncovered   covered
Fuselage                                 0.492            1.123            0.503      1.249
Undercarrage                       0.087               0.087            0.090      0.090
Propeller                              0.325               0.451             0.431
Nose block                            0.105              0.140            0.108       0.148
Fin                                        ?                    0.065             0.023       0.077     
Tailplane                              0.14                0.315             0.119       0.338
Wing                                    0.22                0.623            0.281        0.734
Peg                                      0.11               0.110            0.094         0.094
Total                                                          2.914                             3.161

I test flew the model under a 25' ceiling with a 1/3d motor and a 2/3 spacer  to match my high ceiling site. 

Apart from propeller breakages and the wobbly undercarriage; I was delighted with the model. It trimmed without any tedious thrust line adjustments, only the tailplane setting being changed.

The model needed a thinner motor than the previous plane (1.63g/m compared to 2.00g/m) of the same 8” length.

I flew the models in the high temperature of 24ºC during July. I recorded the following flights under a 25’ ceiling:

17 Jan 2014 Super Sport
1.59g/m by 0.65g (8” loop) 1/3 motor with 2/3 spacer
Wind to 930 & back-off 20
RoG
1m58s no touch
80 landing turns

June 2016 Super Sport
1.63g/m by 0.67g (8” loop) 1/3 motor with 2/3 spacer
Wind to 940 & back-off 35
RoG
2m02s no touch
30 landing turns

I also got the identical times from winding to 95 & backing off 45 and winding to 96 & backing off 55. There being no advantage to winding more and backing off to the same launch turns. But, from plotting the winds onto a curve of torque versus turns I notice that I am only employing the linear part of the rubber torque curve. Winding up the non linear part of the torque curve and backing off may yield improvements. Since I am not pushing the motor hard; perhaps a reduction in g/m could yield an increase in duration.

From comparison from a previous session at 17ºC where my best duration was 1m55s; it seems that the 7ºC increase in temperature was worth 3% duration and the switch to Jun 16 rubber worth another 3%.

It irked me that I had not achieved 4 minutes with the original model under a high ceiling and I am delighted that this new model looks like it would comfortably top 5 minutes on a full motor. I am supprised that it has achieved a 53% improvement in duration for a 12% reduction in airframe weight! This is astonishing considering that the propeller is the same and there are no other significant differences other than the increase in tail area.

Attached files Thumbnail(s):
Re: Bar Fly Legal Eagle
Re: Bar Fly Legal Eagle
Re: Bar Fly Legal Eagle
Re: Bar Fly Legal Eagle
Logged
piecost
Gold Member
*****

Kudos: 6
Offline Offline

United Kingdom United Kingdom

Posts: 262

Topic starter


Ignore
« Reply #8 on: July 26, 2017, 03:57:52 PM »

This post includes a graph of the June 2016 rubber (on-dimensional) torque versus turns with the turns for my best flight superemposed. I was supprised that I was not employing anywhere near the full energy potential of the motor. However, it gave a very gradual climb and descent and good duration. The descent started at 60% of the flight time, whereas my other models with non-flairing propellers top out after 25% of the duration. Maybe I am on to something here...
Attached files Thumbnail(s):
Re: Bar Fly Legal Eagle
Logged
Hepcat
Platinum Member
******

Kudos: 207
Offline Offline

United Kingdom United Kingdom

Posts: 1,678



Ignore
« Reply #9 on: July 27, 2017, 01:53:38 PM »

Piecost,
(sometime I hope I shall understand that sobriquet .  Being born in Grantham I know that Lincolnshire pork pies are luxuries beyond price but apart from that . . . ?)

I have followed your rapid rise to success in Indoor flying and am tickled pink that the ‘Bar Fly’ has played a part in it. Your success is well deserved. You note and record, think of improvements and then, unlike so many of us, you actually carry out the improvements. I think you found the faults in ‘Bar Fly’ before I did. The propeller blade, if shaped as the plan, did hit the noseblock, the cross section of the fuselage at the front hook and rear peg was far too small, a bit more room to put negative on the tail would have been better.

As well as saying the above I want to ask you if you have any thoughts about the new ‘Osprey’ class.  Some of this has already been mentioned on HPA, indoor free flight, Legal Eagle, Penthouse Lady.  Very briefly, I said the ‘Legal Eagle’ rules in the BMFA Indoor rule book were not suitable for our purpose and should be replaced with rules for a Duration model with a fuselage that was suitable for the small halls where we almost always have to fly.  Bob Bailey and I talked quite a lot about this some months ago and we thought the following rules were a start. Total surface area of wing and tail 60 sq in, minimum airframe weight 4 g. maximum rubber weight 1.5 g. Minimum area of maximum fuselage cross section 1.5 sq.in. Motor must be completely enclosed (this will require some rewording about access) .  Existing ‘Legal Eagle’ models eligible to fly for a period as long as the minimum airframe and maximum rubber weights were met.
I understand at the last Indoor Tech Committee meeting there were questions about limiting fuselage length, propeller diameter, wing span, materials and so on. My hopes are for as little restriction as possible; balsa, carbon, foam ,pushers, canards, tailless all permissible in the quest for high performance in a small hall.  Are you in touch with any ITC members because it would it would be good to get something settled before the Indoor season gets started next month.

John 
Logged
piecost
Gold Member
*****

Kudos: 6
Offline Offline

United Kingdom United Kingdom

Posts: 262

Topic starter


Ignore
« Reply #10 on: July 31, 2017, 05:51:38 PM »

Hi John, I tried sending you a PM. Let me know if you cannot see it and I'll resend

Cheers
Logged
Skymon
Bronze Member
***

Kudos: 0
Offline Offline

United Kingdom United Kingdom

Posts: 56



Ignore
« Reply #11 on: August 14, 2017, 05:02:21 AM »

One of the cool factors of the legal eagle class was the whole plan on a single piece of paper thing.
If there's a move to a class suitable to UK small halls perhaps it could be based on a sheet of A3?
Best regards
S
Logged
piecost
Gold Member
*****

Kudos: 6
Offline Offline

United Kingdom United Kingdom

Posts: 262

Topic starter


Ignore
« Reply #12 on: August 20, 2017, 09:36:06 PM »

Skymon,

I consider the legal Eagle to be very suitable for small sports halls, apart from the tendancy for the undercarrage to get caught in the netting that often hangs in these buildings. A removable undercarrage helps as it can detach when the model is tapped and allow the model to release. Care is needed with all duration models to avoid the ceiling.

I enjoy the take off requirement as it offers unique (to indoor duration) trimming challenges. I use a partial motor with a spacer as an aid for practicing under low ceilings in preparation for competitions under a higher ceiling. There is nothing stopping you using a full motor in a small sports hall. The model can easily turn in tight enough circles for a small venue.  There are many plans to build, but is needed with printing or copying to get the correct scale.

Hepcat is proposing a new class, which will have a minimum weight and will allow more design freedom; see the "Penthouse Lady" topic in the Legal Eagle thread. It removes the take-off requirement and the minimum weight removes the advantage of very light and delicate balsa and special tissue. Foam models might proove competative. I you enjoy designing you own models then this is a good time to create the definative model, as the class is brand new.

Have you recieved an email with the nationals entry form? If not, and you are interested then email Tony from the Indoordurationgb.
Logged
Pages: [1]   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!