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thermaldoctor

Osprey f5j build log

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thermaldoctor

Well the Osprey test model is going together well. All parts fit and finish very good. Back in the old days i would have said there is a bit more to do than with other models such as fit your own control surface horns but these day many manufacturers leave it all blank anyway as they dont want to commit to a conventional linkage set up in case people want to put IDS. Anyway the Osprey has very nice molded carbon fibre tunnels onto the top wing surfaces for a conventional linkage at the control surface end. Thus you have to fit your own (supplied in kit) cnc'd G10 control horns. Works well and is easier to fit.

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I used a hybrid method which i believe combines the best of both worlds for a low speed low parasitic drag thermal soarer.  I combined the IDS system at the servo end which is by far the best solution as you can run pushrod pick-ups far closer to the servo hub for better torque and resolution without the hassle of grinding out an arc on the metal clevis to clear the hub of the traditional servo output arm. Plus the 1mm hardened pin on IDS is better than a clevis pin going through an opened out hole on a normal servo horn.

To make it secure lengthwise i drilled a 2mm hole in the IDS mono plastic mono pushrod and made an L bend in a metal 2mm pushrod and wound round with kevlar thread secured with thin cyano. 

I am very happy with this set up and i get full movement on crow brakes and ailerons also full movement with approx 90% servo travel so torque and resolution good. Plus it just feels better mechanically. I will be using this system on my Samba Prestiges no question

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I found the very thin airfoil really suited the 8mm Kingmax CLS0512W servos. In the tip panels a 10mm servo only just fits and it is a bit if a squeeze.

 I used balsa shims bonded between the servo mounts to the underside of bottom wing skins to add a great deal of rigidity to linkage. The wing skins on the Osprey are nice and hard (they are post cured at high temperature) and when you squeeze the leading edge D box the lamination is excellent with none of that sickly cracking sound you get when you squeeze some models but this Osprey is quite a light one and the skins do flex a bit around the servos when you apply force to the control surfaces. By bonding the servo frame to the opposing wing skin this flex was totally eliminated. The servorahmen frames make it very easy to do this as on the bearing end they have a molded shelf for this purpose

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thermaldoctor

With the wing pretty much done except for making up a wiring loom i started on the fuselage. Coming from the Ukraine the Osprey features a fuselage and separate tail boom like the original Optimus and Maxa. But in the case of the Osprey the fit of the boom over the fuselage spigot is a nice close tolerance fit with zero slop. This makes it much easier to glue on as it doesnt need jigging all you have to do is make sure the fin and elevator are all square with the wing.

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The wing sits on a small pylon which I like as it makes it easier to grip the fuselage for launching in windy conditions. As supplied there is an odd small rectangular cut out for the wing wire plug. No plug is supplied so you can choose your own preferred method. I had a 9 pin D connector lying about so used this. Whatever you decide to do you will need to open up this rectangular cut out to suit. In the wing is a very nice oval CNC cut out for the wing plug so you will not need to cut/file/dremel anything out on the wing which is good news.

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The fin comes as a separate moulding for easier transportation/shipping and slides over the end of the tail boom. Again it is a very nice tight interference fit so you have the option of keeping it removeable (but you will have to find your own way of fixing it firmly in place in flight such as carbon push-through pegs and tape) or you can simply glue it on. For speed I glued it on. Either way you need to bolt the elevator in place and eyeball it very carefully to make sure the fin is 90 degrees to the elevator. 

At the base of the fin is a nice moulded carbon tunnel for the rudder pushrod. You have to fit the supplied CNC G10 rudder horn but this is easy especially as the fin and rudder are solid core rohacell. Both elevator and rudder pushrods are the familiar Optimus Vladimir style 2mm carbon pushrods in orange plastic tubing. Both elevator and rudder control runs are very free and smooth in the Osprey.

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No work needed for the elevator and mounting. The fuselage comes factory fitted with the mounting pylon already in place. Elevator actuation is via a moulded control horn that bolts to the underside of the elevator with 2 small bolts. It is very neat and secure and there are no pokey out bits on the elevator to deal with. In this pic you can see the screw mounts standing proud and these locate into corresponding moulded recesses in the main elevator. The elevator itself is like the fin - rohacell solid core with spread tow carbon skins.

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The fuselage comes from the factory already fitted with a strong G10 motor mount. It comes with the central hole in place but you will need to drill it for the gearbox bolt holes. Personally I like the machined metal motor mounts like Graham Wickes (RC Metalbitz) produce better, but this is still pretty good and very well executed. Time will tell how strong it is but G10 material is strong and the mount quite thick (3mm). What I do like is that it is very securely and neatly bonded in place in the mold and then post cured at higher temperature so the glue joint will be very strong indeed.

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thermaldoctor

A few useful lessons learnt about the wing wiring plug on the Osprey. 

The wing features a set of very thin Mark Drela airfoils and even at the root it is quite thin. This fact combined with the Osprey having a ballast tube in the fuselage running underneath the wing pylon means that  if making up a standard 9 pin D connector particular attention has to be payed in making the entire assembly as low profile as possible otherwise the wing wont be able to sit flush on the fuselage.  Once done you can make a fuselage mount out of carbon or plywood so that the plugs automatically connect up as the wing bolts on. Fiddly but worth it. Otherwise you can go old school and have a loose floating connector in the fuselage that you manually have to connect before you bolt the wing on.

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Wing connector bolted in place. To make sure it sits nice and level the front block needs to be 3mm longer than the rear block.

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You can see below to make the D connector as low profile as possible the wires need to come off the pins at 90 degrees. The same goes for the connector in the wing. The connector in the wing then needs to have the plug bolted in place as low profile as possible.

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thermaldoctor

With the wiring loom out of the way it is now just a case of fitting out the fuselage with servos and getting the rest of the gear in. 

With the ballast tube in the fuselage there is not any room under the wing for servos. They have to go in the front. With everything up front you have to be careful of getting the right cg. The recommended cg is 98mm which is also quite far forward so you have to put it together with this in mind otherwise you will need tail weight.

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Here you can see the ballast tube. I decided to maximise the space underneath it by fitting the receiver and then part of the servo tray as far back as possible for cg reasons and also to free space up in the canopy area. No lipo will fit under the ballast tube so i figured best get as much as possible under it for cg reasons. 

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I made up a servo tray that bolts to the bottom of the fuselage so it can be removed to allow the receiver to come out. Also...if you fit servos in the position i have you have to make sure they are mounted low enough so there is still clear access to the ballast tube. Normally i would have used horizontally mounted servos for this but i had 2 vertically mounted servos i wanted to use up so hence the over complicated servo tray. It doesnt need to be like this. Although it does actually work quite well.

If i was to fit horizontal servos (which i will be doing from now on) then i would use the hole in the top of the fuselage meant for the ballast bolt to facilitate this. 

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thermaldoctor

Here is a picture of how the ballast is held in. Anyone familiar with the Supra or Maxa will know this system it works very well you just have to plan around it for f5j.

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So what i will do in future is drill through the bottom of the ballast tube at this point and then this will give me access with a screwdriver/hex wrench through the ballast tube down to the servo bolt.

While i now have some spare bandwidth here are some more detail shots of the build..

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Even flap servos can be fitted without blistered servo covers if you get the control surface geometry right and use IDS at the servo end. Virtually no slop and very neat.

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Flap control surface end. Really nice in-the -mould carbon tunnels perfectly moulded into the top surface of the wing and supplied G10 horns and traditional 2mm clevis in place. 

In this pic you can also see the quality of the post cured surface finish and the pattern of the very latest UHM spread tow carbon.

Remember this is a sub £1k 3.8m competitive f5j model....... 😉

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thermaldoctor

Final stages of fitting out the Osprey. Went with Tenshock Viper, YGE 65LVT esc and nano tech plus 3s 1000mah. With this set up it balances perfectly. I was wrong about getting a lipo under the ballast tube. I was talking 4s. A 3s will fit quite a long way under easily making a 3s set up the best bet.

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A 1mm GRP plate set on 2mm x 6mm spruce runners was made up and epoxied to the bottom of the fuselage. Holes in the GRP plate were made to 1) help pull the esc and altis wires through and 2) save weight.

 

 

 

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thermaldoctor

So with the battery in the cg came out at what i wanted 98mm to 100mm.  With my chosen configuration there is room for a multitude of different batteries you just have to be careful of length - thickness does not matter. 

Please bear in mind, if i had i envisaged a 3s set up from the start i would have mounted the servos in front of the battery and had the battery under the ballast tube to help balance it. But i didnt i wanted 4s so have ended up with a perfectly okay but not optimum configuration. But what is really really good about the Osprey is that it is not a stupidly tight fuselage to get your gear into. It is slim enough to be efficient yet large enough to get all sorts of set ups in. This is a very big bonus and makes it a lot easier to put together..

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Now ready for the first flights...

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Marc RC pilot

Great build/ write-up on the Osprey Neil. Thanks for sharing.

Did you get a chance to fly her yet?

:popcorn:

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thermaldoctor

It flies! Well of course that was expected, but I was very keen to try the Osprey 2 out and put it through its paces before being able to personally recommend it and sell it.

I wanted to put one together to be in a position to offer customers assistance if needed and also to think of better or alternative ways to get an Osprey 2 in the air. In the end however it went together very well the only 2 areas to pay particular attention to were the wing wiring connector profile and the potential to be a bit nose heavy if care not taken.

So how does it fly?  Extremely well. One of the main reasons I needed to try one for myself is that the Osprey features an extremely thin airfoil. It has been designed by Mark Drela so of course should be excellent but sometimes very thin airfoils can have quite a narrow envelope where it works at its best efficiency but i needn't have worried. I found the Osprey could fly very slowly indeed with a nice flat floaty glide. Camber definitely was needed to do this (thermal 1 set at 3mm thermal 2 set at 6mm) but its manners were impeccable with no signs of tip stalling. Occasionally when it was almost pulled up to a halt in the air it would gently nod and produce a slight straight ahead benign  stall. So this was pleasing.

The thin airfoil would of course move well and I had no concerns over this. In the light to moderate breeze the Osprey moved around the sky effortlessly with very little loss of height. It has a feeling of low drag and efficiency about it  at neutral flap. I set cruise 1 at 1mm reflex and cruise 2 at 2mm reflex and whilst it definitely moved around faster but it also felt like the glide was not quite as  flat on the 2mm setting  but of course it is all very subjective and there were no other models around to compare it against just experience of flying lots of similar models over the years. I think the reflex settings needs a bit more work but I have every confidence the Osprey  2will come forward very  well in wind from a downwind thermal where you can trade a bit of glide angle to cover more ground. 

In terms of overall handling the elevator is smooth but surprisingly powerful. I settled on 12mm up and 14mm down. Ailerons up 25mm down 20mm so little differential was needed and roll control was more than adequate. Rudder was set at 40mm each way and it seemed happier on coupled rudder (20mm each way) rather than separate rudder input. It seemed to benefit from snap flap (approx 10mm down with full up) but there is still plenty of room for experimenting here.

Brakes were effective but it wont land quite as slow as a big flap model. With the flaps set up totally linear on the throttle stick, the elevator needed the usual non linear compensation. Approx 7mm down at half flap and 10mm at full flap. I never use any up aileron for the brakes.

So overall extremely pleasing. If it had been a £1500 model I would have still been pleased but less impressed. The fact the Osprey will sell at £960 (confirmed price) it is quite an amazing model for the money. Given it features many current design features, a high quality finish, is built from natural spread tow and UHM carbon,  has rohacell solid core tail parts and has excellent performance and handling the Osprey 2 offers unbeatable  value for money.

 

 

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