Multiplex Lentus

[Konrad]

I was a bit shocked at how many requests I've receive to start this thread after having mentioned that I had a Lentus kit on this and other forums
I've been a bit reluctant to do this as Aloft doesn't carry this model. But I decided to do this as a way to stay off the news feeds.

I chose to get the “kit” Lentus as I almost never like what the program managers have to do to get a product down to a price point. I will say that Multiplex has a very good RR Lentus at the $690 price point. I just think I can customize my kit to closer meet my desiers for a few hundred dollars less. And as most of the upgrades will be using products sold by Aloft Hobbies we might all benefit from this exersize.

First I need to address an issue that Multiplex had early on with the Lentus wing. Because of the thermal properties of the dual aluminum spars the thin wings often showed over expansion of the EPO beads that were over the spars. My kit shows no such issues. I suspect Multiplex is pre-chilling the spars prior to injection molding the wings. Or they are allowing the wings to stay in the molds until everything has reached equilibrium prior to removing the wings from the molds.

Now the one thing that does bother me is that to meet a price point Multiplex left off the main wheel. Multiplex does offer a retract wheel kit as an option. THIS IS NOT OPTIONAL EQUIPMENT! At the weight of the Multiplex Lentus there needs to be a wheel! Landing a 2.3kg glider on an EPO foam fuse will result in a short lived fuse, even if landing on a sod farm. As this is NOT a scale model I’m not sure why Multiplex didn’t offer a fixed wheel like we saw with the Heron. I can tell you that I change out my Park fliers Plastic belly pan on my smaller 2.6m Cularis on a regulare basis. Multipllex has chosen to offer us a retracting main gear for $90 without the servo. This is a bit dear, but if folded into the value of the Multiplex kit this cost is quickly forgoten.

Now one of the few performance upgrades I perform with all my foam (heck any) molded model is to sand the LE to get rid of the part line. This just seems to allow my wing to stay out of the stall ever so slightly longer. And allows the air to reattach sooner after the stall. I remove these part lines with fresh sharp 400 grit sand paper. I also remove any molding flash from the TE, again with new sharp 400 grit sandpaper.

My kit has a few quality issues with where the mold injection sprue was cut off. You can see that at some locations the knife under cut the TE ever so slightly. At one location it looks like the knife slipped a bit. These are cosmetic issues only and might actually clean up when I sand the TE mold flash off.

 

[gp49]

(Echooooooo... just in case i posted my reply on both of your posts. )

Looks like you and @tic have similar taste in gliders, with Zagis and now Lentus. Alex and I have been flying a stock e-Heron for a couple of years and its a blast. I think i will get a Lentus soon as well. Looking forward to your build.

 

[Konrad]

I don’t know what I did to get a dual thread post.

Yes, I’d like to think I put Tic (Heron Pilot) on the Multiplex trail for real foam gliders.

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www.hippocketaeronautics.com

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I will say that the Horizon Hobbies RadianXL and the FMS 3m Fox gave the 3 meter foam glider a black eye. I’ve been flying a 2.6m Cularis and 2.4m Heron for years and actually love what they are as gliders. No need to use the modifier ”foamy”!

If there is any detail you would like to know please let me know and I’ll try to give us all some details.

I’m going to go back to the first post and finish my initial write up. (The wife (SWMBO)called me away).

 

[Konrad]

In the sales write ups Multiplex claims that the power system they sell will allow the use of 4 cells. I was shocked to learn that they dropped the prop to 8x6. To me this has to be like driving a car in 6th gear off the line. I choose to use a low KV motor, so as to allow for a larger prop. Aloft Hobbies has the E-Max GT2826/05 (860KV). This on 4 cells should allow me to use a 13x8 of 12x10 at about 800watts.

At these power levels and with these prop sizes I like to use an external rear bearing. Because this rear bearing needs a stub shaft to index the rear bearing. I chose the E-Max GT as it has a hidden stub shaft. There are 4 screws that allow the motor to be reconfigured for a bulkhead mount. These screws are used to hold a cover used to keep the centrifugal fan blades working a bit more effective at drawing air through the motor, if configured for nose ring mounting. I like that E-Max uses the stator size for the class nomenclature. This gives me a vauge idea as to the torque of the motor. To this engineer this is so much more informitive than using the motor’s diameter (FYI this has a 35mm OD). While the nose is smaller than the Heron and Cularis there is still plenty of room for the outrunner motors. There is no need for those grotesque glider drives!

Now I do have some reservations about the plastic prop yoke. I’m sure these from Multiplex are safe to at least 600 watts. I’m going to have to think real hard if I want to use this spinner at 800watts. Those 13” blades do pull on the yoke! I do like that the 56mm spinner kit PN 1-00456 from the Fun Ray has a fold back O-ring.

P.S.
I’m showing the E-flight Power 15 as this is one of the motors I used to power my Cularis on 3 cell at about 600 watts.

 

[Hank GB Z]

Konrad,

Looking good. I’ve thought about the Lentus a lot but it’s out of my price range right now.

Hank

 

[Konrad]

Price is a concern. As with all Multiplex products quality pays it does not cost. But in the last 2 weeks there has been a large price hike ($31). Karlton (Mr.MPX) says this is as a result of shipping. As the kit and RR Lentus cost the same to ship, the kit version has had a disproportionate price increase. As a result Karlton thinks that kit sales will drop off. Again I know nothing of sales and marketing but I’d think $690 for a 3 meter foam glider might give most second thoughts. The Multiplex Lentus is still worth the $690 price, it is just that it isn’t the deal it was at $659.

I hope to show that the kit Lentus really is the way to go, particularly if you source your components and sub-systems from Aloft Hobbies. I hope to show that in the end you will have a better performing and cheeper 3 meter foamy glider. Heck to my way of thinking you will have the best 3 meter foamy ever on the market. I think the only non-Multiplex foamy glider that has a chance against the Lentus is the FMS ASW17. But having seen the FMS ASW17 I think it is a waste of $350 dollars if looking for a flat land thermal ship. So even at $690 the Lentus really is the only option for a RR foamy glider in today’s market.

 

[tic]

We all have to get used to higher prices for everything however MPX sailplanes have always been expensive. Quality does indeed pay and IMO MPX foam gliders are the best on the market. I got my Lentus kit before the price hike and it still seemed like I was over paying for foam. MPX quality is really good though and their kits are excellent. Not only is the Lentus kit a fun "build" it can indeed be completed at a cost well below the ready to fly version and you'll end up with a better sailplane IMO. The RR version's drive system was a little under powered for my liking. The Lentus is no hotliner but I've become spoiled by unlimited vertical climbs with just about every plane I own and wanted the same for my Lentus. 700 watts will do the trick, 800 would be better but beyond that I might start to worry about structural integrity up front. I disagree about the need for the landing wheel on Lentus though. IMO it adds too much weight to an already heavy plane. I probably have 100 flights on my Lentus, all belly landings on our rough grass strip. There is plenty of clearance for the flaps even if you forget to retract them before touchdown and with the included belly protection film and some extra added behind it I haven't noticed any denting or deforming of the foam anywhere. Of course all my landings are greasers and YRMV.

 

[Konrad]

Actually I agree with most of what you say. The Multiplex retractable landing gear weighs close to 10% of the AUW of the Lentus. That’s a bit much for a non-flight feature. I’d have much preferred a much lighter fixed gear like we saw with the Heron.

P.S.
For those of you who may not know Tic, he flies FAI F5B ships for sport! So if he is satisfied with the climb on 700 watts. You can be sure most of us will be ecstatic with the climb on 600watts!

 

[Hank GB Z]

Judging by the fact that you have to assemble the retract i think you could engineer a lighter fixed gear system for you lentus if you wanted too. But the retractable gear does have a certian cool factor and you do hate drag....

Hank

 

[tic]

No doubt the cool factor is there with the retract and the door.. There is some European dealer that does sell a fixed gear kit for the lentus though. For me, I'm happy to belly land it and save the weight of the retract or the drag of the fixed gear. The primary purpose of the retract IMO is to enable ROG but then a smaller prop is needed and from the videos I've seen, the ROG doesn't look very inviting unless you have a putting green surface to work with and who wants a tiny prop spinning like mad on a 3 meter glider?

 

[Konrad]

Judging by the fact that you have to assemble the retract i think you could engineer a lighter fixed gear system for you lentus if you wanted too. But the retractable gear does have a certian cool factor and you do hate drag....

Hank

Yep, but not sure trading parasitic drag for induced drag gains me anything. I have to be careful not to gold plate the trash heap. I've generally built and flown foam gliders because I want a simple flying experience. If I want the ultimate glider I don't start with the foam.

While I like the hitec HS65 that is used in the RR Lentus but I find that they are a bit dated. I plan to use the E-Max ES09MD. These are metal gear, dual ball bearing output and digital amp servos. These are almost a perfect fit for the servo cavity in the Lentus. But there is a little bit of foam that needs to be removed (see blacked out foam).

I've also found that the Painless 1.5m wing wire loom and the 30cm fuselage wiring fit well. These have the 6 pin green Multiplex connectors that fit the space in the wings and fuselage made for these. I must have been one of the few fliers that actually liked the auto plug in system found in the Cularis. The Heron's connection system is a step backwards in my view. The Lentus has the auto connection without the risk of being damaged like the JR style used in the Cularis and Heron.

 

[Hank GB Z]

I went to the website for Mr. MPX and the kit is going for 350. I felt that should be clarified. I know that makes the RR version just about twice as much but the components in the RR are way better than most RR models on the market. If I were to get a Lentus I would go for the kit too.

Hank

 

[Konrad]

No doubt the cool factor is there with the retract and the door.. There is some European dealer that does sell a fixed gear kit for the lentus though. For me, I'm happy to belly land it and save the weight of the retract or the drag of the fixed gear. The primary purpose of the retract IMO is to enable ROG but then a smaller prop is needed and from the videos I've seen, the ROG doesn't look very inviting unless you have a putting green surface to work with and who wants a tiny prop spinning like mad on a 3 meter glider?

I fly an ST Models 2.2 meter Arcus M with retracting gear. I will say that the performance loss is noticable if I leave the gear down. I also fly the ST Models 2 meter DG1000. I have to say that the smaller, simpler and lighter DG1000 flies as good or better than the larger Arcus M.

Here I'm trying to show what the belly of my Cularis looks like. This model has about 200 landing on her and is on the third Park Flyer Plastics belly pan. The Heron has about the same number of landing and looks almost new. Both models are landing on the same terrain. Based on my experiance with the Multiplex Cularis there is no way the Lentus will survive my landings on my landing fields without a wheel.

 

[Konrad]

I went to the website for Mr. MPX and the kit is going for 350. I felt that should be clarified. I know that makes the RR version just about twice as much but the components in the RR are way better than most RR models on the market. If I were to get a Lentus I would go for the kit too.

Hank

Thanks Hank. $350 does put this in the same price as the RR FMS ASW-17, but a kit verses an ARF. Like you and many others I much prefer the empty foam models. Now what I see is in direct competition with the FMS ASW-17 is the Heron at $450. Having flown both I will say the Heron is still the better soaring machine (not a fair comparison as I didn't set up the ASW-17). While the FMS ASW-17 is $100 less than the Heron I still think the Heron is the better value in a soaring machine.

 

[tic]

I'm going to take a picture of my Lentus belly after approx. 100 flights. Our field is more rough weeds than grass. Sure it has some scratches on it but it's held up really well. Unlike Konrad, I tend to land very smoothly at a minimum sink rate with wings level and a short "roll out" so my Lentus is relatively unscathed

 

[Konrad]

Lol, I’m not a politician, rather I’m an engineer, I can’t argue with the truth!

I often land on bare gravel, if I miss the weed patch I was aiming for. This gravel will punch (tear) holes in polycarbonate as you can all see.

Here in the arid west we don’t have naturally occurring lush green grass. Heck our weeds are often as tough as oak!

One needs to build to one’s limitations, be that landing skills or landings zones!

 

[tic]

As promised.. Lentus belly pic after approx. 100 flights.. Rough weeds for landing area but it is mowed short regularly. All I've done is add a few extra strips of clear tape on either side of the protective film included w/ the kit as I didn't think the strip was quite wide enough

 

[Konrad]

Now I'm no aerodynamicist, but my understanding is that by the time the air on top has reached the control surface it is turbulent. If this is true I'd have thought that Multiplex would have placed the control surface live hinge to be bottom hinged. For reason I don't understand Multiplex has place the flap and aileron hinge on the top surface.

To lower the drag from the bottom hinge gap I'll be using Top Models gap seal tape. I wish Multiplex would have added a 0.075 mm relief to the bottom of the wing to accept this style of sealing tape.

 

[tic]

Agreed. My virage is bottom hinged with gap seals right out of the box but of course it's at a far different price point. The control surface gaps on the top hinged Lentus are huge. I've come to prefer top driven bottom hinged control surfaces for flaps AND ailerons even if they are a lot more work in the assembly process.

 

[Konrad]

Top drive, that would be nice! But I have to remember to not gold plate the trash heap. That is this is a foamy and as such it is aimed at being a low investment type model. Low investment in cost and time. I'll have to pass on that idea. But I wish Multiplex would have used that configuration in the original design.

Now Multiplex is using a "hidden hinge" for the rudder. This looks rather nice. I also like that it is a snap on snap off affair in that it allows easy access to the counter balance weight cavity should it be needed. I like the vertical stiffener tied to the mandrel wound carbon fuselage spine. (not a pultruded tube, quality pays it does not cost!)