Dune stretch to 700 - anyone tried it?

[HelliYea]

I love the way my Dune flys and am wondering if a stretched version would result in an awesome flying 700 heli.

Has anyone tried it?

Does the Srimok boom, TT etc fit? I saw on RR that both booms are 19mm so should be OK.

Any thoughts?

Thanks.

[wadders248]

Just about ready to fly... it's not a simple stretch though.

I used a Faifa boom, opened-up the Dune block to 19mm ID and removed the end stop. Then there's a Faifa boom clamp, just before the pinion gear support. The Faifa boom block is only fixed at the top clamping point, because the bottom lugs had to be removed for rudder control lever clearance. The Faifa tail control rod also has to be slightly lengthened.

The head height is very low, 15mm lower than the low rider on the Faifa, so it's going to be close to the boom. My intention is to use it for speed, so boom strikes shouldn't be a problem, I'd be tempted to go for a Faifa head block if I was going to use it for 3D.

[HelliYea]

Thanks for the info. Sounds like a great project.

Sorry if this is a dumb question but is it because the Faifa boom ID and OD is different to the Dune's boom dimensions that makes the conversion tricky?

I'm really keen to hear how it flys. Please keep us posted. Cheers.

[wadders248]

Originally Posted by HelliYea

Sorry if this is a dumb question but is it because the Faifa boom ID and OD is different to the Dune's boom dimensions that makes the conversion tricky?

It's been tricky because the Dune frame is so compact around the tail mounting area, when trying to add the additional boom support. The boom support on the Dune is very sturdy, but not enough on its own to hold the longer boom.

I also wanted to use the Faifa boom, because of the thicker walls and if I crash, I can just use stock parts.

[trillian]

Originally Posted by HelliYea

Thanks for the info. Sounds like a great project.

Sorry if this is a dumb question but is it because the Faifa boom ID and OD is different to the Dune's boom dimensions that makes the conversion tricky?

Yeah they're just slightly different OD so that the Faifa boom will not just fit right into the Dune mounts.

I had thought about a stretch a while back because looking at everything else, the drivetrain looks sturdy enough etc. but I also didn't realise the head is so much lower. I don't know where the minimum safe distance is but if it's 15mm lower than even the Faifa lowrider head then it's probably getting into the danger zone depending on how it would be flown.

Another way to get a bigger feel with the Dune would be to go with a three blade head, stick with 600mm blades. Then you'd have the heavier disc mass. It's not the same as longer blades obviously it's a whole different thing but you'd get the added natural stability and could drop the headspeed and pitch a bit.

I was liking mine a lot with 625s on it and have since updated the Vortex firmware and put in a lower KV motor so I am keen to get out flying it again soon.

[HelliYea]

OK thanks for the details. Might still give it a try in the near future and see what I come up with. Out of interest the head height of the Dune is higher than my E7SE so I'm not sure it will be an issue.

I'm interested to see if the Dune becomes a great flying 700 because kits are pretty cheap at the moment and if the 700 flys as great as the 600 then it will be winner. Or I could wait for the new Faifa Or both ....

[trillian]

Just curious where you're measuring the distance between the head and the boom from? I'd say the main thing is from the bottom of the blades to the boom (and in order to have some standard, use zero pitch).

It occured to me as well that some helis might have a bit of an angle between the main shaft and the boom so that the tips get further away. I am doing this with a Robbe Milli I'm converting to electric and even one degree of tilt gives the blades an extra cm or so of clearance at the tips.

When you get a moment I'd be interested to know what the distance is on the E7 and where it's measured from.

Originally Posted by HelliYea

OK thanks for the details. Might still give it a try in the near future and see what I come up with. Out of interest the head height of the Dune is higher than my E7SE so I'm not sure it will be an issue.

I'm interested to see if the Dune becomes a great flying 700 because kits are pretty cheap at the moment and if the 700 flys as great as the 600 then it will be winner. Or I could wait for the new Faifa Or both ....

[HelliYea]

Sorry guys I have given you a bum steer. My first "measurement" was a rough eyeball. Today I setup both helis with 0 degrees pitch and actually measured them.

Dune: 146mm at root of blade and 143mm towards tip of blade
E7SE: 156mm at root of blade and 154mm towards tip of blade

[trillian]

Originally Posted by HelliYea

Sorry guys I have given you a bum steer. My first "measurement" was a rough eyeball. Today I setup both helis with 0 degrees pitch and actually measured them.

Dune: 146mm at root of blade and 143mm towards tip of blade
E7SE: 156mm at root of blade and 154mm towards tip of blade

Thanks a bunch for doing those measurements. I've never known just exactly what the truly safe distance is (obviously it depends on the headblock and damping as well as the blades themselves).

Most of mine are higher but I just put a lowrider head and shaft on the Faifa and it's considerably lower than the stock head. It ends up at about 152mm

[wadders248]

I'd love to know the same measurements for the speed TDRs, because they look low... I'll have to ask Jamin on RCHA.

[wadders248]

Finally got the stretched Dune finished and setup. I'm going for a speed setup, though baby steps at first! It's running around 2100rpm and 13° +/- pitch and already feels quick. That's with a Quantum 4530 motor on 12s. The next step is to run 14s and increase the head speed :-0

The mains are very low to the boom, so I was a bit worried about a boom strike, though some gentle 3D didn't show any problems. The blades are 710mm and 95mm and although they don't overlap, it's pretty close. If I was going to setup for 3D, I'd go for 690mm and 105mm.

I'm using 5000 OptiPower packs, which make the CoG slightly nose heavy, apparently this is a good thing for speed flying. Using 4300s would enable a perfect CoG.

Overall it's very nice to fly, with the same confident feel of the stock Dune. I think with running 5000 packs the disc loading is similar, but it's more stable and damn quick!

[trillian]

Cool! It should be really light relatively speaking, it's bound to be a rocket at those headspeeds!

From this angle it doesn't really look massively stretched.

[wadders248]

I think the Dune canopy, which is quite large, helps to keep the stretched Dune looking proportional. Here's a comparison with my stock Dune and 600mm mains.

[trillian]

Originally Posted by wadders248

I think the Dune canopy, which is quite large, helps to keep the stretched Dune looking proportional. Here's a comparison with my stock Dune and 600mm mains.

Yeah it's just at the point where without something to compare to it still looks enough in perportion. Whereas the Beam, for example, almost looks stretched as a 600, it would look seriously strange if stretched any more.

I like that F-Nine canopy as well.

I think sometime soon I'll get a few pics of my whole Kasama fleet, currently two Faifas and a Dune (and a spare Dune airframe but it will stay disassembled and most likely I'll pare down to just one flying Faifa to be practical).

[wadders248]

Well after gaining confidence in how well it performs, I've been upping the power! It's now running 14s and 14° of pitch, at around 2,400rpm.

It's at the stage where although it's very stable and very smooth, you can't just dip the nose and go. There's a real skill involved in coming down from a dive, find the right angle and then hold that across the course. Then at the end of a run, slowly move to zero pitch and pull-back on the elevator.

In theory this all sounds very simple, but when you're at speed, it all happens very quickly. Out of probably 30 runs this morning, there were only a couple that where perfect, but when you do get it correct, it makes a big difference to the speed. I really need to get a GPS tracker (or off duty traffic cop) to guesstimate the speed, because I think the smooth sounding Dune belies the actual speed.

The motor is starting to get warm, but not bad and the ESC is almost cold. So the next steps are 15° pitch and and increase the cyclic range. Also swapping to Faifa grips, which will add a bit more to the overall disc size and some Rail 716s if I can find any stock.

Power cables look a bit messy, but it's normally all hidden :-)

[trillian]

Wow, that's pretty heavy duty! A lot of plumbing with those wires to the extra pair of packs :-)

I was going to mention about using Faifa grips but what about the grip arms, can you fit the Dune arms on the Faifa grips?

I flew my Dune today for the first time in a couple months. This time with a Pyro 700-45 and version 3 firmware in the Vortex. Still using Radix V2 625s and radix 95s on the tail. I brought the Beam out as well and the difference in the way they fly is quite imediately obvious. The Dune flies 'bigger' and smoother. I estimate my current idle-1 headspeed to be about 1663 (based on Mr Mels showing 1734 at 55% throttle and I'm at 51%).

It flies really nicely at that headspeed but needs just a little more pitch. I think I have about 14 available but limited my curves to about 13 to try at first so I need to up them all the way before the next time. The VX1 needs just a little tweaking, I can't quite put my finger on it now, it's very minor though and in general it's darn good right now with just the default '3D' preset.

[wadders248]

Originally Posted by trillian

I was going to mention about using Faifa grips but what about the grip arms, can you fit the Dune arms on the Faifa grips?

The Dune arms don't fit the Faifa grips... annoyingly the bolt holes are different. Though there's a custom set of Faifa grips lurking at Kasama UK that had been made to work direct to swash.

It must have been the day for Dune flying! After early morning speed flying, I got two flights on my stock dune after work. It's been a while, but it really is a pleasure to fly... probably my favourite heli :-)

Not matter how well the Beam performs compared to the Dune, it looks great with the three blade setup!

[trillian]

Just to add, it's a serious endorsement for the Dune drivetrain if it can handle 700mm blades at 2400rpm! That's so much more power being put through there than you're likely to encounter with 600/620mm blades.

Next time out with my Dune I'm going to see if I can bump down about 100 rpm in headspeed if I up the pitch to 14 degrees. That might be too low, we'll see. I know the Jives are quite good at lower throttle but I'm not sure what kind of power is available when you're running that low (below 50% throttle). But the only other way to go lower would be either to run less cells or a lower KV motor. I'm thinking around between 1600 and 1700 might be the sweet spot where you gain flight time but don't have to start flying completely different to compensate.

I was flying for 6 minutes on 2700mah packs and they're only down to about 50%.

In any case I'm not going to go to any lengths to get super low headspeeds on the Dune as I can play around with that on other helis, I just want to find the best balance of headspeed and pitch for my idle-1 and then have my idle-2 at the full 63% (or whatever that number is for the Jive gov) for that kick in the rear now and then.

On the Faifa I really want to go for that 'TDR esque' ability to run really low and just flip a switch to a normal headspeed. With the Dune this may be possible as well.

[wadders248]

Originally Posted by trillian

Just to add, it's a serious endorsement for the Dune drivetrain if it can handle 700mm blades at 2400rpm!

Amazing really, though I'm sure over time it will shorten the life of the thrust bearings and main shaft bearings... just got to make sure everything is really well balanced. The main gear is also showing some slight wear, though I didn't have it meshed tight enough.

I think the best way to get longer efficient flying time and usable power is with a lower Kv motor. Though I think with the 450kv Pyro you're using it should be well suited.

The Jive 80 in my stock Dune seems to hand a throttle curve right down to 25% and still be flyable. It's not the kind of flying that I think you're looking for, it's more the 'how the hell is that flying' blade speed!

I also like dropping to 8s on a 520kv motor, which is very efficient in terms of duration, but also delivers enough power for even gentle tic-tocs.

[trillian]

It would be interesting to see some logs to compare the amount of power needed for a comparison of the two blade sizes. So for example, the average and max amps drawn with 600mm blades at say 2200 rpm vs 690mm blades at the same headspeed. And then it would put in perspective what kind of loads are going through the drivetrain.

I only have logging on the Kosmik at the moment and no idea what the power draws are on the Dune with 625s. I'm not obsessed with logs but I do like knowing what's going on in there.

I do remember reading something not long ago about headspeed and drag, that drag goes up exponentially, so to up the headspeed by X percent may require double that percentage of power.