|Feb 26, 2014, 09:44 AM|
Joined Mar 2009
Precedent Hi-Fly Build advice needed
I posted this post in the wrong place the other day so here it is in the right place.
I have had these parts of a Precedent Hi Fly my Dad build a long time ago. Now I am able to fly RC planes, know a bit more about them now and with the summer coming up I would like to finish it and get it flying and give him a nice surprise!
It looks like a nice little park flyer.
The original kit was for 2 channel control and a brushed motor using a Nicad battery pack, using that plastic motor mount.
I would now like to use a brush-less motor, perhaps an in-runner that would fit in that mount or an out-runner for cooling and perhaps run it from a 3 cell 2200Mah battery as I have a few of these already for my AXN Floater and My Blade 450 3D Heli. They fit in the fuselage well too.
However perhaps I should think about saving weight using a smaller 2 cell Li-Po.
The mount will allow for a prop diameter of about 140mm's.
I am almost totally new to building Balsa kits but I have finished a couple RTF's and repaired and re-covered some wings before.
I am looking from some advice on how to proceed with this project. Any tips on the following would be really appreciated:
I now at least know what it is thanks to GeeW!
I now have the plans and the tail fin, stabilizer and elevator that my Dad made and a bit of balsa for the rudder.
How should I go about finishing this model?
I need to join the wings together with a 4mm steel rod bent at 7Deg to give a dihedral. I am not sure what I could use for this..28SWG Piano wire?
I have also read now that the stock wing joining method is poor with this kit so I might need to beef it up a bit. A fibreglass bandage? (not that I know how to make one)
What kind of motor, prop, battery, esc, and RX should I use?
I use a Spektrum DX7, I was thinking an Orange 3or4 CH RX and a hobbyking ESC and Motor.
What kind of covering should I use and how to proceed with it?
I thought thin transparent solar film on the wings and thicker opaque solar film on the tail and fuselage would be the thing here.
What kind of servos, control horns and servo linkages for the nylon push rods should I use? They measure 3mm in diameter.
I am thinking or something like Hextronik 9g HXT 900 digital servos. But these might be a bit cheap and small....
I would like this model to be a nice slow-flying thermal catching bird with a power train for launching, gaining height, wafting about on half throttle and getting out of trouble with. Nothing too amazing in performance.
I have read now that this is a good slope soarer, does that mean its rubbish at catching thermals ;-)
Also how would I set up the transmitter? I would like to keep the rudder on the left stick with the throttle with the pitch on the right stick. However should I put the rudder on the right stick as there are no ailerons
Anyhow I will look forward to your collective inputs.
Thanks for the original postings on my original post:
|Feb 26, 2014, 02:41 PM|
Joined Jun 2008
You know that plastic motor mount is for a Cox .049 , not an electric motor?
To electrify I'd mount a brushless motor in the nose, I can't see the pod strapped/mounted to the top of the wing being much good for an electric motor.
|Feb 26, 2014, 03:11 PM|
Joined Mar 2009
A motor in the nose! BBB-But How?
Sure that would be very nice to have a motor in the nose. However that might be outside my of my balsa chopping abilities.
I thought I could use that pod and mount it behind the wing. The plan says it should be over the CofG, on the wing. Your right it looks a bit dodgey to me as well.
There is room inside the pod for a cylinder 20mm in diameter and 30mm long. That might be OK to hold an in-runner.
But yeah a motor in the nose. hummmmm I will have a look and see how this could be done.
|Feb 26, 2014, 03:44 PM|
Joined Jun 2008
You could probably make a pod like this one:
Almost any iron on covering film would be fine to cover the plane.
|Feb 27, 2014, 02:21 AM|
Romania, Dolj, Craiova
Joined Sep 2007
The inrunners of this size have too big rpm to be useful for such task.
You should mount the motor outside, exactly as the cox, on a ply plate that is screwed in the four external mounting points.
What is the prop size you can fit with this pod ?
For foldable small props you should be interested by a three blades solution, like this:
Was able to takeoff a 2.7m 2 kg monster using such propulsion: three blades 7.5*4.5 turned by a 1500kv 28 class motor.
|Feb 27, 2014, 07:13 PM|
Sweden, Stockholm County, Sollentuna
Joined Aug 2010
It's a nice plane you've got. The Hi-Fly was my first plane built in the early 90'ies, but back then I didn't learn how to fly it. Around 2006 I returned to this hobby but electrified my Hi-Fly and had a lot of fun with it.
When I added my motor I also did this:
For power I chose a 52 grams 2830-motor with a kV of 1300. The Hi-Fly is no rocket with this motor, but she was able to climb to 200m before I fell asleep. As I like to use the motor only for climbing, not for cruising, I like to use as small batteries as possible to save weight. To the Hi-Fly I used 3S-450mAh which - if I recall correctly - is enough for two or three climbs to 150-200m. From my notes I can see I used to get a climbing speed of 4-5 m/s and a sinkrate slightly better than 1 m/s.
My Hi-Fly suffered from a very heavy tail and with the small motor I used I had some problem getting the CoG in the correct spot. I'm not sure if that was because I had built her unusual tail-heavy or if it it inherent to the model, I just mention it so you could keep an eye on it. Since the stabiliser on my plane is held in place with rubberbands I did some rather successful experiments where I replaced the original sheet-balsa stabiliser with one made of depron.
That being said, I don't think you should have any thick covering on the tail, at least not unless you really need som weight there. I used standard cover all over the plane. If I should build another I think I would use a light-weight cover on the wings and on the tail.
I have never had any problem with the wing joiner. Please remember it is originally designed to be launched with a rubber highstart, the loads during a motorassisted climb is much smaller. So unless you intend to do some aerobatics I don't see any reason to beef it up. The 4mm steel rod is of the kind that is sold in ordinary hobby shops (but I don't know the correct english name for it).
I think the Hi-Fly was originally designed as an allround beginners glider and thus equally at home on the slope as on a flat field. Mine has only been used for thermalling and my first thermal ever was caught with her. Of course that makes her very special to me and I intend to keep her for a long time to come. She was very forgiving for my beginner mistakes, as well as surprisingly crash-resistant. It's a bit of coincidence you are asking about a Hi-Fly now, because I dug her out from my storage-room a couple of days ago with the intention of replace the broken motor and test-fly her this weekend.
Please feel free to ask as many questions you have
|Feb 28, 2014, 11:27 AM|
Joined Mar 2009
Brilliant! A very help full post indeed! Thanks very much for that. It has given me some more ideas. I do like the idea of a nose mounted motor with a folding prop. I just wonder how strong the plywood bit at the front is....I guess it could be beefed up a bit. I still haven't had a good look at it.
I am going to weight it and try to guesstimate the all up weight, then measure the wings then I can try to work out how much power I will need. I am terrible at maths so this might not work ;-D but it will be a good exercise in futility if nothing else.
I am thinking about drilling/cutting some holes in the tail and stab to make the tail lighter too especially if you found it to be quite heavy. Is this a good idea?
Your battery and motor choice is interesting, its a very small 3c flight battery indeed. I think I would like to use my 3c 2200mAh batteries for it if possible however these are quite heavy and large but they do fit the fuselage well.
Putting the servos on the outside of the tail is an interesting idea too but I think I will stick with the plastic snakes. Is there any reason why not to use them?
I have read that the rudder is quite weak, would it help to make the moving part of the rudder bigger? If so how much bigger....
Its possible my Dad kept that wing joiner, he might have found it by now. How are the wings supposed be joined anyway? Are they supposed to be glued together? If so with what sort of glue? Slow set epoxy?
Do you have any of the original build instructions/documents you could scan for me? I do have the plan now for it, just not the build instructions.
|Feb 28, 2014, 04:07 PM|
Sweden, Stockholm County, Sollentuna
Joined Aug 2010
Yes, check out the strength of the firewall, but if it glued all right there is no need to add any extra strength.
Do an estimate of your AUW. As a guide I just weighted mine: the fuselage, including motor, propeller and ESC (but no receiver, it's been borrowed to another project) is just above 400 gram. Each wing is approx 105 g including modification for aileron and a 9g servo.
A 200g 2200mAh LiPO might be good to enhance penetration on a windy day, but it won't enhance the sinkrate on a sunny day. That being said, there is nothing that says you can't use it that way (I sure have) and sometimes it's preferable with long times between battery changes, just be aware of what you gain and what you lose so you don't get dissapointed. Make a mark in the fuselage where each batterysize is to be positioned to get the CoG in the right spot.
I'm afraid I didn't express myself properly. My servos is not mounted in the tail, they are just below the wingspar. From there they operate via a carbon rod to the controlhorns of the tail. I changed the original rather heavy bowden cables to the carbon rods to save weight. But that were the cables that were included in my kit, I get the impression you're kit is a few years younger and may well have different fittings.
I have never felt the rudder to be weak, not even when I had a rather conservative CoG. I haven't heard this thing about the Hi-Fly myself, but when I had an Easy Star I read the same thing in several forums. I'm not sure, but I think that many of them complaining about the rudder have the CoG a bit to far forward, since such a position makes the plane overly stable and more like a turkey than a falcon. A more neutral CoG makes the bird more responsive both to control surfaces and signals thermal activities better. But please be aware that a too agressive CoG makes the plane hard to steer.
My wings are just joined with the steel rod and can thus svivel around it. However, when attached to the fuselage and held in place with rubber bands the wings stays in place during the flight, but are loose enough to flex a bit in a less-than-perfect landing. I use six rubber bands: two diagonally, two straight, and two diagonally. I'm not sure if that is optimal, but that is how I do it. I've read somewhere that the last pair should be diagonal to ensure that the bands can't creep out of the 'stick'.
Yes, I have the build instructions and could scan them for you. Send me a PM with your mail adress and you'll get them during next week. But be warned, they are very brief. The instruction leaflet is eight pages, including first page, parts list, and two pages of flight instructions.
|Mar 04, 2014, 03:32 PM|
Joined Mar 2009
Thanks for all the responses so far. Great stuff!
I have decided I would like to use a front mounted motor driving a folding prop using my 3 cell 2200mAh batteries.
I have a few more questions:
If I am going fit a motor onto that thin looking firewall I guess I will need to "beef it up" a bit. How would be the best way to do this? How should I attach the motor onto it?
SBS_Pilot, You said you modified the wing to give it ailerons, how did you do that? Ailerons would be nice.
Now the big question is which motor and prop should I go for?
I have been crunching some numbers using this guide:
and this calculator:
Here are the results:
Estimated Weight 19.5 Oz
Wing Area 62'x6.5' = 403 Sq-inch
Wing Area square feet = 403/144 = 2.79 SqFt
Wing Loading= 19.5Oz\2.79SqFt= 6.989 Oz/SqFt
SqRoot of 6.989 = 2.643
Stall speed: = 13.215Mph
Target Top speed 13.215 x 2.5 = 33Mph
Ready-to-fly Weight (oz)=19.5
Total Wing Area (sq in)=403
Number of propellers=1
Maximum prop size (inches) = 8
Flight mission: Gentle Scale Flight
Desired top speed (mph)= 32
Desired thrust (oz)=15
Motor efficiency (%) =Average Outrunner 75%
Cell Type, Li-Po Count 3c, C-rate: 20
Battery Voltage (V) =10.8v
Desired current per motor (A)=5.5A
Motor Kv (rpm/volt) =1100
Power Level: Mild aerobatics.40 degree climbouts.
Minimum Pilot Skill Needed: Easy Beginner level.
Minimum Flying Field Size: 650 x 470 feet.
Minimum Battery Capacity: 300 mAh, 20 C, lithium polymer.
Suggested ESC Rating: 7 A to 8 A.
Power Into / Out of Motor:59.4 watts in / 44.6 watts out.
Power To Weight Ratio: 48.74 watts/pound.
Estimated Stall Speed: 12.9 mph.
Wing Loading: 6.97 oz/square foot.
Cubic Wing Loading: 2.77 oz/cubic foot.
Motor KV 1100Kv
Suggested Prop Sizes (approx):
Type -------Dia (In)-----Pitch(In)-----RPM-----Vpitch(Mph)----- Thrust(Oz)
So what would you people recommend I get?
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