As I picked apart
our second Delta XS, bought used, but complete, and nearly new (if those three batteries that came with the deal are new they are worth more then what we paid for the whole package) the conclusion was that with propulsion configured wrong (too cheap) and the heavy (as recommended from Horizon Hobbies) batteries and all, a Speed XS would fly like a pig. If the low rpm bearings (not up to the rpm that 3S LiPos produce for more then just a couple of flights) dragged the performance of the motor even further down (I can measure watts-in, but have to guess at watts-out, a virtual dyno can get a close estimate, but only for quality equipment, the virtual dyno accepts the parameters provided, which are often faked, or just plain never achieved in inexpensive motors), or worse, that approximately 5X5 propeller (optimized for both efficiency and economy at forty watts out, it should never have been on this combination) was a poor match to the motor, it must have been a disappointment. Add to that a servo that either is out of specification (one elevon had one third of required travel), or just not strong enough for the task (we suspect the Delta XS needs servos with more torque then ordinary eight gram servos provide) turned an otherwise wonderful to fly RC airplane into just a piece of junk.
Since the experience with the Multiplex Fun Jet (I kept fiddling with mine after the article was published in the SEFSD newsletter) is directly applicable, a comparison is included. The second, let’s get it really right this time, Speed XS experience follows.
The Horizon Hobbies Speed XS is a worthwhile inexpensive fun RC airplane for Mission Bay. It would be suitable as about the fourth airplane for a beginner, and would be great for the back county too. Although landing and part amps speeds are a little faster then a floater, and while it can be fast, or medium speed, depending on available power and how much of it you use, it’s a bit too wide ranging for most parks, the Speed XS needs a couple of hundred yards to fly in. At least if there are other people not too close, the noise level is way down from any other pusher propeller airplane that can go this fast.
Over revving an inexpensive
parkflier motor won’t due, at least not for long. As inexpensive as the XS airframe is, it’s going to take a motor that can sustain high rpm, and they have to be paid for. Just the same, we had hours of fun with an inexpensive Hype Euro20/$27- motor knowing it wasn’t going to last. For the second in the series, faced with requirements for the motor not currently being met by the market (Hacker has a great combination, but the motor and adjustable timing controler cost twice what the airframe does) a mount are going to be made to allow use of inrunners in the (80) gram class i.e. a NeuMotors 1105 and an almost as good Scorpion outrunner intended for use in helicopters.
Our two airframes, and eight servos
(two pairs of originals, two pairs of torquier, if heavier and larger size replacements) aren’t a big enough sample to decide if we hit a run of under specification servos, or if the nice strong hinges (so good that unlike every other foam airplane I ever touched, I didn’t reinforce them) of the Delta XS are just too much for ordinary servos in the (8-11) gram size. Both times one servo performed ok, the other did fine after we pulled it out (along with some of the foam it was glued to) on the bench, but as installed wouldn’t move the elevon full throw. Although the XS was flyable with one and a half elevons, we went to (16) and (20) gram servos for the replacements.
In an (inadvertent) act of omission
magazine articles not only censor all but the worst of something (in the case of the Speed XS ARF (500) watt version the supplied propeller was junk, which was reported on), the problem arises in that since a vast majority of the time the authors only covering that which works right, and only try one combination, and then usually only for a few flights before wear and tear show up, they create an impression that things are to be expected to just go right all the time. Most published articles also don’t mention things gone wrong like copying the parameters from another airplane (in this case the Multiplex Xeno, which was so little entertaining that so far that it has only been flown twice, and will probably be sold at a swap meet) and forgetting to check the individual, at the transmitter, servo centering.
A typical article also doesn’t account for where a specific RC airplane fits in among the owners other airplanes.
Magazine articles, flight simulators and TV sitcoms, can be a (warped) reality of their own. While researching the XS, I made my first try at the Phoenix RC Flight Simulator at a local RC store.
I don’t know how many RC airplanes I’ve assembled anymore, we still had to be fiddled with propulsion and servos on the Delta XS(s) before they were really right. The following is our adventure with this great little RC airplane.
The Delta XS is a carefree RC airplane
The other member of our local club (The Somewhere out There Fliers, of Wiesbaden 2011 e.V. i.e. the SoTF,oW 2011 e.V.) and I like carefree airplanes. We still wanted something faster, despite the misadventure of our pair of Multiplex Blizzards. His Blizzard made eleven flights and seven crashes, my Blizzard four flights and one crash. That fourth flight of mine was forty five minutes of bliss on a 3S 2200 mAh LiPo, that ended with an abrupt stall from five foot up to bury the nose half way to the wing in the mud. I think our problem with the Blizzard is we have to deploy the ailerons as spoilers to land faster at a steeper angle then we are used to, but we aren’t into that sophistication, or flying an airplane with that hard, abrupt stall, yet.
If you read up on the Blizzard on the Internet what is most disconcerting is accounts where it made a great first flight or two, and then was trashed. My spare Blizzard, bought used, the tail was assembled wrong. By omitting deburing it had positive, instead of the required negative, incidence. I now understand, my report on the Blizzard sits as I don’t usually publish before getting at least fifty flights on an airframe (the exception, a couple of airframes where there just wasn’t any promise of them ever working out), and don’t want to go through three more airframes before I get the hang of the Blizzard, the first half of the report has been ready for a year…
Where we usually fly
near Wiesbaden Germany is across from a quiet village (Igstadt), people going by on foot, bicycle and horseback are part of our scene, we just can’t be flying loud irritating things, or airplanes so fast they are intimidating. Just the same, on a day where the wind was swirling hard enough to have you wandering what could fly, and still be flyable after the landing, I was out with the Fun Jet enjoying life. For a stunt the other club member flew his Twin Star II Brushless (3), the basic version offered here in Germany, with some select reinforcement and a BEC, but, despite the agility of a Twin Star, the wind speed at house height was a little too close to it’s maximum speed for more then just a short hop.
I’m developing the latest Twin Star II, Part III, beyond the latest version three brushless from Multiplex, is still being researched.
The other pilot, unlike me not financially hemmed in, but being middle class has to justify new things. When he’s bored at work he watches videos, we both know about the windy days to come, he had been thinking about an Ultra Fun Jet. Average eyesight and reflexes, now two years after starting a he’s a competent flier who, if the equipment functions, doesn’t crash anymore. As such he’s a representative for half the gang back at the beach. But, despite the improvements, Ultra Fun Jets are fragile, and they have been dumped by the local dealers. Multiplex discontinued the Fun Jet. Since, after a lot of repairs, my Fun Jet now weighs about what an Ultra Fun Jet does, mine give him an idea.
So when we stopped by the local RC store
(to ask if my ordered six months ago replacement Twin Star II wing had arrived) there was a nice looking, almost no assembly required, just a little smaller then a Fun Jet, delta “fighter like” pusher RC airplane in an EPP like material, for Euro 60/$80-. Added to the purchase of the airframe were two Horizon Hobbies (8) gram standard servos at Euro22/$-. The rest we had accumulated, which figured into the seemingly spur of the moment purchase.
I’ve used two servos like that in my low to medium powered Fun Jet for a hundred and twenty flights, including a couple of hard crashes (radio failure) which should have destroyed everything, they are doing just fine. And, two more in my little Hacker flying wing where, although they weren’t as light or precise as that two foot wingspan airplane can use, they did exactly what should be expected at that price.
Precision alternates from HiTek (or Futaba, or Multiplex or), much more accurate servos cost twice as much, weren’t within reach at the store, and the owner wasn’t ready for that financial expenditure, yet. The Horizon Hobby servos are exactly the same size as HS-55s, or their Multiplex equivalents, about the same price, and work about as well. Without precision testing, I can’t tell a difference, I’ve been happy with all three brands. Reportedly the ARF versions of the Speed XS come with (12) gram metal geared servos. So more ability to withstand the impacts of a bungled landing, but no additional torque to actuate the control surfaces.
In case you were wondering, that spin on landing, so frequently experienced with most RC airplanes flown without landing gear, doesn’t occur with our Speed XS or Fun Jet on long grass. So our servos don’t get yanked from sliding backward into things.
And then again, thanks to the other member of the club’s scrounging (zu Deutsch, es gibt keine präzise ein Wort Übersetzung, etwa Organisieren) by checking the Internet used stuff regularly we came into a second used near new XS that was built out with a motor, prop, motor controller, servos and not one, not two, but three LiPos. That re-build up follows the first XS and the Fun Jet accounts.
Even if you are building an exclusively medium powered
Speed XS (think three hundred watts in at .65% efficiency, or lower down to about a hundred and fifty watts-in) I wouldn’t install Hobby People install house eight gram specials at under ten bucks (each), with their to be expected oddities like the two servos not being centered to each other, slower response speed and so on and so forth. Even more so since if fifteen dollar servos weren’t adequate, six dollar ones… We determined along the way that the hinges of the Speed XS are good solid items, already from the factory taped, but they take too much push for inexpensive servos. When I get back to town, I’m going to try a pair of Hobby People (16) gram servos in a Delta XS.
Just the same, if, like my friend out in Jamul, were we have had to chose between affording to have lunch, or better servos, the house brand servos would perform fine using a computer radio to match their centers knowing that hitting a rock hidden in the long grass likely sets the limit on the life of the airframe and servos rather then wearing them out.
In case you were wondering, wandering the back country with a durable little airplane like the Speed XS is worthwhile, affordable fun.
Unlike the semi-precision Multiplex Parkmaster and Gemini, where you really can tell the difference between average (just good enough) servos and the better resolution ones available at twice the price, the servos for deltas flown at medium speeds need the strength of, but maybe not the precision, of better then average servos. But, we started out expecting to assemble a delta on the slower end of the price scale with no ambition for all out speed. That was what servos the dealer had which fit, they had done fine in my Fun Jet (Lite) and, being middle class, the owner doesn’t reach for the better stuff until he recognizes a need for it. We didn’t really know where the project was going to go.
If we had known we wanted the Speed XS to go really fast, like (500) to (1,000) watts-in, I’d have put in HS-82 Metal Gear servos. Even though that would require enlarging the moulded in mounts for the Speed XS servos. When you have something doing over a hundred miles an hour I don’t want the servos to quit in flight! In an obscure Internet article, somebody ran a Fun Jet in a wind tunnel, somewhere around (125) miles an hour the airframe starts to vibrate violently, even with no propulsion. By the time you have that much power in a Speed XS the weight has climbed to where an additional twenty grams more at the servos doesn’t really matter, you have an arrow.
All that needs to be done to initially
to get a Delta XS together is glue the servos and fins in. You can change propulsion in a Delta XS in an hour or two as many times as you feel like it, but with the servos glued in you need to think it through before you select them. In just a couple of hours the two of us had the Delta XS ready for flight. I taped the leading edges with Tesa brand 4124 clear packing tape heat shrunk on, but otherwise about as the picture showed, even if the two pages of fine print text were written in excellent, idiomatically perfect High German (no Chingledeutsch hier), it seemed to be nothing but legal warnings. Even if one servo didn’t seem to be working right, and one had been glued in one tooth off from the other, which travel adjustment at the transmitter might have evened out.
For initial trials
a nearly new (45) gram Graupner 260Z outrunner (the 7,2 Volt, the higher revving of two available windings) and an APC 5X5 fixed propeller with an indifferent quality Hype (25) amp motor controller drew (20) amps at (10.5) past the initial peak volts on the bench, a combination well tested and enjoyed in my Fun Jet Lite. It has also provided pleasant, if a little low powered, service in the owners armored Mini Mag. That’s about three times the watts-in Graupner rates it at (2S LiPo, 6X3 fixed propeller), at way higher rpm, so if the bearings don’t last long, don’t be disappointed.
You want a high rpm motor
you have to pay for it, the cheap, and even the medium priced stuff is really intended for low rpm use on 2S or 3S LiPos. That’s why the low and even medium quality stuff they omit any rpm or temperature ratings. Even sport level Scorpion and Hacker rate motors in this (28) mm size have a maximum of (25,000) rpm, which the manufacturers are quite clear about. Readers, in a Delta XS, we are going to be turning the motors that fast! Even at a higher rpm/v (zu Deutsch kV) rated same weight Graupner the bearings are the same, mine went about seventy five flights (each and every one of which contributed to my enjoyment of life) before the bearings about gave out. We just wanted to get the XS in the air and to get some first experience with it, that combination was in our collective inventory, from experience with the slightly larger Fun Jet we expected it to function well.
New, that Graupner motor costs Euro42/$57-. We acquired our first two, along with matching (18) amp Graupner motor controllers, with a Graupner airframe called the Rookie, the third used like new at a swap meet. The Graupner 260Zs come in two windings, labeled 7,2 and 11,1 Volts. Good news, they have the same bearings as the similar motors from Robbe, for which Boca Bearings out of Florida offers replacements. While we didn’t enjoy the similar to the Easy Star Rookie’s airframe, made out of too soft foam (which is never, ever, mentioned in magazine reports) all that much (well, we dumped them quick), the motors, and their well matched controllers, have been fun. Graupner and Aero-Naut both offer propellers made out of synthetic materials suitable for the Speed XS, that don’t easily break and are rated for the lower half of the expected rpm in the 12,000 to 22,000 range.
That having a selection of propellers (APCs included) so you can change things, is something the magazine reports leave out. I often have to make a several tries to get things right. I had to remove some material from an APC 5.25X4.75 for it to fit on the bell end mount, the 5X5 went on as supplied.
Only recently have affordable motor controllers
with adjustable timing and frequency become available. Although the current Graupner (18) amp motor controler has no timing adjustments, and at Euro32- for the 2-3S LiPo version, it’s more expensive then most (about double a comparable Robbe or the old style Multiplex), of the half a dozen inexpensive motor controllers I’ve run the (45) Graupner motors on, they perform the best with the Graupner controller. It’s not so much more power as more duration and a cleaner response to changes in power.
If I may quote our in club manufacturer of the worlds best RC racing electric motors; “You get what you pay for”. But, for first flights, I don’t install my best propulsion equipment!
There are two things stopping me from getting a suitable Hacker motor controller for this project: Money, and the suitable sized ones are only for 2S to 3S LiPos, and I want to run 4S from now on.
The Speed XS aluminum motor mount
is easily adjustable for both side and vertical thrust. Use two motor mount screws for the low powered version, or all four for higher power, and that’s all there is to it. It takes the smaller bolt circles typical of (28) mm diameter motors.
Have you ever noticed magazine articles never mention things like taking half an hour determining and finding the correct length screws? And I have a selection on the bench, without having to go to one of the decreasingly common stores.
It must be an outrunner
The Speed XS motor mount is recessed in from the trailing edge, no inrunner I know of will bolt up, the output shaft would be sticking into the fuselage. And, it has to be a high rpm capable outrunner which can mount a propeller on the rotating bell end of the case. Which, as it turns out, is a hard to source item.
The first flight without the parameters
Since we missed the instructions included with the airframe for balance or control surface throws, we were flying with the left side traveling about (8) mm up and down, and the other side less then half of that. Due to one servo being a tooth off from the other, it took about 50% of the individual travel adjustment at the computer transmitter to both servos to get them even with each other. For the first flight the servos were set at right angle to the wing, no differential travel. Reflex was set at (2) mm up.
That clear and windless December afternoon, some sun shining under the thin clouds, four inches of new fallen snow on the ground when we climbed a hill to have some automatic altitude, we had LiPo batteries in the 3S size at (135) grams and 1600 mAh, (150) grams and 1800 mAh, and (185) grams at 2200 mAh. The standard 3S 2200 mAh LiPos are too wide for the fuselage. Although it’s a good thing that there are some grips, giving it a good heave isn’t possible, nor is it necessary. That’s when we discovered that the little casting marks at the throw grips, are half an inch back from the real balance point. I thought something was wrong with the motor at first, it was so quiet! Cut the power, and it just sails right along. After just a couple of minutes flying with it dangerously tail heavy, and using the maximum of the down elevator trim, the Speed XS was landed. At which we found out that, although the snow was soft, that plowed field’s dirt clods just under the snow were frozen into rocks. It was scraped and dented just a little.
The Speed XS is the only elevons flying thing I ever encountered where the two control surfaces are installed in the plane with the wing, the reflex was taken out. After we moved the Center of Gravity forward and correctly centered the elevons we found ourselves with a delightful little airplane, even with one balky servo.
One aspect we weren’t expecting, it was only slightly louder then a Mini Mag mounting a similar combination, and it held on to it’s speed after cutting the power better then the Fun Jet. So despite the disconcerting issue of the right servo only delivering a third of the expected travel, on a late December day when the sun never gets more then 21 degrees above the horizon and it’s dark before 5 p.m. we had a satisfying time flying.
Read all about it, or not
As of December 2012 there was almost nothing written about the Delta XS in either German or English on the Internet. There are many vendor’s offers, pictures included, they are sufficient to identify the airplane, they complement this club publication. And by the end of year 2012 the number of You Tube videos exploded. There seems to have been a race to get the first pictures of stock Speed XS footage covered.
I knew I had read about the Speed XS, afterwards I found my copy of a German publication (Foamie) dedicated to all radio control things made out of foam that fly. In an early 2012 issue, the ARF (500) watts (in) version was detailed. Evidently there are two ARF versions, in addition the basic airframe, in (150) and (500) watts. The difference being 2S and 3S LiPos. I take it that through censorship by omission that means watts-in. The ARF Delta XS comes with (12) gram metal gear servos. Although I have often put in print my observations of censorship by omission, among what was left out was how quiet, for a pusher prop the Speed XS. To somebody that assembled (54) flying wings and a dozen high powered howling Easy Stars to date, that is astounding, the Speed XS is hardly any louder then if the prop were in front. We can use it unrestricted Under Igstadt. That and the Speed XS maintains it’s momentum well after cutting the power.
They exactly identified the balance being (20) mm forward of the two dots. As it turns out we like it better at (17) mm forward of the centers. I take it the instructions to the other author included the neutral setting as there was no mention of the reflex, which every single other flying wing I’ve assembled required.
Evidently, recommended is (10) mm up and down with 35 percent exponential, for those with a computer transmitter. When we reread the instructions it includes going to as much as (20) mm up and down elevon throw. A first, there are no provisions for those yard long MHz receiver antennas we used to use, this is a GHz only airframe. It was the Foamie authors evaluation of the (500) watts ARF that with the same propulsion that the Speed XS was faster then the slightly larger Fun Jet. But that (500) watts Speed XS ARF was being flow heavier then ours, with batteries in the 3S 2500 to 2700 mAh range, and no doubt, the motor, being much more powerful, is also heavier.
The other author did have the nerve to mention that the supplied propeller was of insufficient quality, at least for his judgement at (500) watts-in, he used APCs.
Not mentioning
the reduction of noise to a reasonable level and maintaining momentum was the first occasion of censoring something positive I have yet to encounter in an RC publication! And that although the author had done a comparison to the Fun Jet. That reduction in noise was critical to our being able to use and enjoy the XS, in addition to the expected benefits of modern molded energy absorbing foam airframe. Packing crate materials suite me just fine. I was unable to find any information on the (500) watts ARF motor, from other article it was pulling as much as (45) bench amps on 3S with a 5X5 propeller.
Another nice plus of the Speed XS, with reasonable prop sizes, the propeller can’t hit the ground (rightfully included in the Foamie article) and it would be a lot harder to hit the person launching it. We here in Wiesbaden are landing mostly on grass as a crop, prop wear on landing was never an issue with the Fun Jet. At Mission Bay what we land on is more like sandpaper, that not abrading the prop is an important aspect of the XS.
We wanted more climb
then just top speed in level flight. From experiments with the Fun Jet Lite, a larger diameter propeller with the pitch equal to the diameter works well in the range from 4.7X4.7 through 7X7.
Part of my development program for the Delta XS is to find some really good propellers in higher pitches. There might be better then the Graupner, Aero-Naut and APCs we are currently using, even if they cost (more) money.
As the people who race cars put it, nobody races (virtual) dynos, you have to try it. Among other things, in climb, the motor will be turning at a lower rpm then maximum speed in level flight, and the “slip” the relative speed of the propeller will be higher to the air it is cutting into during steep climb.
To date, with Aero-Naut folding propellers in suitable sizes being limited to around (16,000) rpm (a couple of thousand rpm higher then sport level Graupners, the (7X4) size), I haven’t been willing to make more then just a couple of trials at high power levels. Installing a folding propeller in this pusher configuration required a long output shaft, which a NeuMotors 1105 series in my possession had. Even though the virtual dyno indicated it would rev up higher (about twenty thousand rpm) then the sixteen thousand rpm Aero-Naut certifies their blades for. Although I recommend against it unless you really have the education and the experience to estimate the risks, sometimes, running something at above it’s certified value for just a short period is ok. And sometimes it isn’t. It makes me wonder about the F5D gang and their APC 4.7X4.7s, APC doesn’t give any rpm specifications. Just don’t get complacent and run that prop too fast forever.
Long ago in Costa Mesa I heard a first hand account of death caused by a F5B thrown blade. And our own SEFSD newsletter recently included an account of an impeller being run correctly, but hand held, exploding to throw a blade right through safety glasses to ruin an eye. With the power levels easily available these little RC airplanes of ours are now potentially dangerous things. Even a (55) gram motor turning 21,000 rpm can shred fingers.
Fact is, a folding propeller, at least subjectively (too many other variables involved to decide with just a few flights), didn’t seem to make much difference in a Fun Jet. The (6X3) size didn’t really do it either.
A virtual delta
without the nominal expense of buying a physical one is available as an add on package to Real Flight 5.5 in the for of the Multiplex Fun Jet. Although I haven’t tried it, it should be possible to delete the fake “tip tanks” and increase the weight to model an Ultra Fun Jet. There is a selection of propulsion, one way or another it should function. Even if the software still displays the same airframe to the screen, you can make changes to how virtual airplanes fly.
So we began making adjustments
as we became more comfortable with the XS, the nose up climb on application of thrust became a bother. But first we had to come to grips with the somewhat narrow balance range. There’s a spread about three or four millimeter wide that works well, beyond that and the handling turns unpleasant. Not dangerous, but just a very slight change makes the difference between gee, this thing flies really well, and yuck. Something not mentioned in the one report in Foamie.
Neither in manufacturing, or aerodynamics, to you get much (if anything) for free. To date, with the exception of the too crash prone Blizzard, everything we flew from Multiplex had a wide range in which the balance was ok, stalls, if they are possible at all, are mild. As far as we can tell, a medium powered Speed XS does most things better then the Fun Jet, BUT, you must get the CG correct, the range is only three or four millimeters (zu American three sixteenths of an inch) wide. They may have chosen a more critical airfoil for the Delta XS, you need to be just a little better versed at tuning things to get it to fly right. The balance range if the Speed XS i
