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Old Jan 13, 2013, 01:57 PM
Red Merle ALES
Curtis Suter's Avatar
United States, Mt, Helena
Joined Apr 2002
5,638 Posts
Ian,

Your drag, if any, would be in the fuselage. Now how do you determine what the optimum angle is for the fuselage? Is it zero, slightly up or down? That's a question that can be answered in the wind tunnel.

I attached a photo I drew up for you. The planes on the left all have full flying stabs and all of them have the same angle between the wing and the tail. So which one has the least amount of fuselage drag? "B" or "C" look better than "A" to me.

Are you certain of the balance point/location for you model? If not, as soon as the balance point moves a corresponding change to the elevator trim will be needed and this will change the decalage. Same goes if you change the trailing edge camber, the decalage will change after a corresponding elevator trim change.

I suggest before you start working on adjusting the wings angle to the zero datum line make sure she's balanced and trimmed how you like it.

While on the subject:
The planes on the right have an articulated horizontal tail. There is little or no drag difference between A -A, B-B, or C-C.

Curtis
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Old Jan 13, 2013, 04:57 PM
"...certainty is absurd."
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Joined Jan 2007
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For a given airspeed and model weight, the wing has to fly at a fixed Cl to generate the require lift to support the airplane. This fixes the wing AoA for that airspeed and weight. Moving the CG over the normal range does not alter the wing AoA required, except for a very small change in the stabilizer Cl.

The lowest fuselage drag will be with the fuselage aligned with the wing streamlines. This means the pod should be angled nose down several degrees with respect to the wing at it's best L/D angle of attack. The boom should also be angled down slightly. The streamlines are curved, so without making a curved boom and pod the fit is only approximate.

http://aerade.cranfield.ac.uk/ara/19...report-648.pdf

The up and down wash is proportional to inverse of the aspect ratio, so the higher AR ALES gliders will have less down wash than the DLG in this movie:

DLG onboard camera vol.4 (2 min 26 sec)


The Opus designed by Michael Selig is the most obvious example of this type of design (claimed 30% fuse drag reduction over a straight pod and boom,), but the Icon appears to follows this idea as well.

XFLR5 will plot streamlines that show the wake curvature, but I'm not sure how accurate they are. They show less down wash than the NACA reports indicate, and that in air testing seems to show.

The down wash angle at the tail is usually taken to be the down wash angle at infinity, which is:

Down wash angle, degrees = 114.6*Cl / (pi*AR)

Putting the boom at this angle when the wing is at best L/D AoA is a step in the right direction. Of course the whole airplane is descending downward at the glide slope angle, but that can be ignored when setting the angles since the wing's AoA at best L/D is set including this angle already.

Kevin
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Old Jan 14, 2013, 06:49 AM
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Scotland UK
Joined Jan 2005
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Thanks guys
food for thought here.
I had the Aspire glider pretty well optimised for our conditions and the electric conversion still has a motor change to come. I will focus on getting the handling and thermal hunting aspect right CG wise then address any perceived AoA issues.
Thanks again for your feedback
Ian
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Old Jan 16, 2013, 10:42 AM
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Hi all

After the input from folks I made some minor mods to the plane and managed to get the CG back another 5mm.
I had a flying opportunity today, very light wind 2/3 mph and only 0 degrees C.
Low cloud-base and the ground frozen.

Several models out Supra, Explorer,Graphite and a Reichard Cirrus.

The AspiringBuzrd managed very well in the conditions and despite its weight it out hung everything there even the lightweight Cirrus.

Flying from a 175m motor cut I had 3 flights over 10 minutes and one over 20 minutes no spectacular lift but very gentle little bumps which could be worked to maintain altitude.

Landing was a different matter ,everything from stopping dead if you hit a frozen rut or 10 metres slides along the ground.
A worthwhile day out even if I am now still trying to thaw out.

I will report further when the new gearbox arrives and I fit the new motor and speed controller.
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Old Jan 20, 2013, 09:52 AM
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Hello again Ian,

It took me a long time since my post #40, but I did finally get round to building a fuselage along the lines you have described.I was originally interested in a producing a lightweight model for my Pike Perfect ET wings but in the event decided to make a fuselage to suit both the Pike wings and those from my 4m Hyper Ava.I have followed what you have done very closely so will only give details of any areas of difference.

I have used all the same components :-

M2A-e pod from http://www.kristoffair.co.uk/products
Tailboom,V mount,pushrod components,carbon from http://www.hyperflight.co.uk/
Balsa etc from my 'bits box '

Wing seat

The wing fixing hole centres on my Pike and Ava wings are 127.5 and 120 mm respectively.These are right at the limit of the seat opening on the pod and so I could not use the same fixing as you did.I built up a sort of outrigger at the back of the opening to house the captive nuts.This is shown on the attached photos.The nuts are in the form of tapped(M4) aluminium sleeves about 5.75mm dia and 19mm long.They are expoxied into the wooden inserts.I made them up myself but commercial steel ones could easily be substituted.
The wing seat itself is made from two layers of 0.8mm ply and one layer of 200 gsm carbon.It is the same dimensions as the Hyper Ava seat.
As you can see from the photo I had to sand it away quite a bit at the front to get a snug fit.If I did another I would use three layers of ply.The Pike wings are fitted with the aid of an adaptor plate made from a couple of bits of balsa.

Tail set

The fin and rudder are simply an enlarged copy of a Bubble Dancer tail.The linear dimensions have been increased by about 15% which gives an area increase of about 32%.This gives a vertical tail with a slightly larger area than the Hyper Ava tail.The construction is all balsa ,with the exception of the fin spar which is reinforced by a full length carbon strip.I though this might give a bit more strength for the larger tail.

Originally I was going to make a BD horizontal stab,which I have used on a couple of other models.In the event I took the easy way out and decided to use the stab from my Hyper Ava.It can easily be switched between models using only one screw.
The finished weight of the complete tail set including horn etc was 56 gms-Very similar to yours.

Pushrods

Pushrods are externally mounted on the top of the boom.They comprise 1mm carbon rods in 1.3 mm etched teflon tubes.As the moment they are taped to the boom until such time as I can get a test glide to make sure the stab is at the right angle.I will then glue them with thin cyano.
Weights

The total ready to go weights worked out slighly lower than my initial targets.

The weights with the Ava and Pike wings are 1486 gms(52.5 oz) and 1733 gms(61.2 oz) respectively giving corresponding wing loadings of 5.6 and 7.2 oz/ft2 .

Balance.
The Rx is mounted on a balsa tray just under the front of the wing seat .It is high enough to allow the battery(TP 1300 3S 65C) to slide underneath right as far back as the servo tray.Despite this, when I fitted my original drive(Mega 16 EDF on Reisenauer box-113gms) the model would not balance.Reluctant to add weight to the tail I replaced the motor with a Hyperion Heli motor(HS 2216) on the same box.This drive weighs 89 gms and with it in place the model will balance with both sets of wings comfortably.I have given it a good work out and it looks to be good for 400 Watts or so without getting too hot.This power should be fine for the Ava wings.It might be a bit light for the Pike wings-Time will tell.
As it stands the model is best suited to a lightweight set up.To use a heavier drive or battery would need either tailweight or the nose cutting a bit shorter.

So, it has all worked out very well.I have finished up with an alternative lightweight set-up for a couple of my models at a very reasonable cost.As you have also demonstated, this route is well suited to producing an Esoaring model using an existing pair of wings.

I have yet to try it out but as it is aerodynamically similar to the Hyper Ava(which I have also flown with the Pike wings) I am not expecting any real surprises.It will be interesting to see what differences the ligher overall weight and lighter extremities make.

Spencer.
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Old Jan 20, 2013, 11:34 AM
Red Merle ALES
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United States, Mt, Helena
Joined Apr 2002
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Very nice Painter S!

Please keep us updated on the flights.

Curtis
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Old Jan 20, 2013, 01:24 PM
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Scotland UK
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great stuff Spencer.
I look forward to your flight report.

I have fitted the lighter motor set up to my AspiringBuzrd.
The test showed 45 amps and 575 watts, I fear I am pushing the motor way over the manufacturers limit.
At least the cg is now where it should be. That's makes two flight test to be made.
Come on guys from the number of hits on this thread many of you are looking, please join in with your knowledge and experiences.
Ian
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Old Jan 21, 2013, 07:15 AM
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Chipping Norton, UK
Joined Jul 2006
393 Posts
Cheapskate Supra

Ok Ian Iíll crawl out of the shadows, I have been very impressed with your builds and clearly share your approach. Last year I made a Bubble Dancer and as a follow on am building a Supra based soarer at the moment. The plan being to have something suitable for slightly windier days than the Bubble Dancer can cope with.
The fuselage is made up of a home-made moulded pod, same as Bubble Dancer but stronger and heavier. It has a Kevlar, carbon tow and glass layup. Boom and V mount from Neil at Hyperflight. Internal carbon pushrods and servos in the pod(MKS 6100).
Fin and Rudder are built up with a Supra outline and Stabiliser is an extended Bubble Dancer item.
Wings are from Barry at foamwings.co.uk. They are Supra outline stretched to 3.7m with sections AG 40-43, cut from blue foam and covered with veneer. Spar is a carbon tube. Wing joiners are bent aluminium tubes with carbon incidence pins. Covering will be iron on. Ailerons top hinged, flaps bottom hinged, live hinge on flaps but not ailerons. Centre section has Multiplex 6 pin socket in centre for connection to fuselage and standard 3 pin plugs for connection to ailerons, no loose wires all fixed in wing roots, plug and play. Wing servos are Turnigy 777MG, will have to see if these are up to the job.
Motor Hobbyking-NTM Prop Drive 35-48 Series 900KV / 815W
ESC Turngy 60 AMP Plush
Battery Turnigy Nano Tech 45/90c 1300 or 2200 3S
FrSky Rx
Total weight so far 1850g without battery. Still needs covering and some bits and bobs so will see where we end up. Most of the weight is the wing.
Should be finished in a couple of weeks or so and will then find out if its any good!
Graham
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Old Jan 22, 2013, 08:42 AM
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Hi Graham,
That is great, I am looking forward to seeing the finished model photos.
I have very little knowledge of the use of outrunners in big models so I really look forward to your flight reports.

One very small thing I have found that supporting the pushrod outer right up to the end is worthwhile in the flex reduction stakes. Here is a photo of mine plus note the belt'n'braces approach on the pushrod end, as well as expoxying the end I expoxy the heat shrink tube over then heat it.

Your model looks very like Curtis Suter's Red Merle, read the thread on his approach it is well worth it.
Ian
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Old Jan 22, 2013, 10:31 AM
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Quote:
Originally Posted by sandist View Post

One very small thing I have found that supporting the pushrod outer right up to the end is worthwhile in the flex reduction stakes. Here is a photo of mine plus note the belt'n'braces approach on the pushrod end, as well as expoxying the end I expoxy the heat shrink tube over then heat it.


Ian
Yes, agreed!
I'd also suggest adding a piece of light fiberglass over the end of the pushrod housing and balsa wedge, and onto the boom.
Otherwise, the balsa wedge has a tendency to split if you have a hard landing, and create slop in the elevator linkage.

Good luck,
Lenny
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Old Jan 22, 2013, 10:45 AM
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Graham 65's Avatar
Chipping Norton, UK
Joined Jul 2006
393 Posts
Hi Ian,

I'll add a fillet of wood to support the pushrod, good idea.

I would like to copy Chris's build but need to get up to speed on cutting and bagging first. Thinking of starting with 2m models for that and work up.

Added an in focus picture of push rod, I agree about glueing carbon rods into couplings, it does not fill me with confidence.When I do use them, at the servo end, I crimp them with pliers before the epoxy sets so that the lump has to pull out past a constriction to come free. At least thats the plan!
Graham
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Old Jan 22, 2013, 04:17 PM
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Scotland UK
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Hi all,
A good idea Lenny ,I will add a fillet of glass cloth to support the pushrods wedge and in future crimp the pushrods .
I too am looking at a glass surfaced 2 metre model. I got Barry at Foamwings.co.uk to cut me blue foam cores and I now have to teach myself how to glass them. I have been reading all the threads on glassine wings and am now somewhat filled with trepidation at the prospect.
I am sure we are all looking forward to a flight report or three.
Ian
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Old Jan 22, 2013, 04:38 PM
Red Merle ALES
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United States, Mt, Helena
Joined Apr 2002
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Ian,

Whatever questions you have about glassing wings please don't hesitate to ask.

Curtis
Montana
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Old Jan 23, 2013, 01:49 PM
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Scotland UK
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Thanks Curtis,
if I can get my steam driven computer to run your video sample, I will down load first and ask questions afterwards.
Ian
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Old Feb 13, 2013, 07:56 AM
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Scotland UK
Joined Jan 2005
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Hi

Firstly, my apologies to anyone who is awaiting a flight report.
I have been held up on two fronts, one,our weather has been very poor and whilst I dont mind flying on snow , flying in snow is different, if it hasn't been snowing it has been wet or windy.
Secondly, due to a piece of bad luck my Graupner MC 24 Tx is now dead. The costs of repair exceed the value of the TX.:
Decision time, what do I buy? new or second hand ?

I like Graupner and JR gear, I have no knowledge of the programming of Futaba and I have had too many issues with my old Multiplex.
No one round here uses Sanwa/Airtronics but I believe it is good from all I have read.
I will go off and do my arithmetic and see what I can come up with.
So much for soaring on a budget !!!!!!

Ian
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