Why is an ARF not an ARF? - RC Groups
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Sep 20, 2002, 06:47 PM
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Why is an ARF not an ARF? / GRUMBLER

-----Original Message-----
From: Roy
Sent: Friday, September 20, 2002 15:32
To: Pat
Subject: Why is an ARF not an ARF?

My dearest wife,

You wanted to know why it took me days (30+ man hours) to build an RC airplane that is supposedly "Almost Ready to Fly". Here is a sample of the adversities I experienced building the Bohemia Grumbler from Hobby Lobby. These are not all, nor in this order, just those that come to mind. By the way, apparently it's called a "Grumbler" because that's what the builder becomes from the moment they open the box. :-)

+ MotoCalc said that the retailers recommended motor (speed 400) was barely adequate with either the 1700 mah NIMH or 1000 mah NIMH batteries I already had (8 cells both). I considered my existing Speed 600 motor, but was not practical. MotoCalc revealed that a speed 480 motor would be ideal, so I ordered one.
+ The model is designed to use only an MP JET flush mount gearbox. Jury rigging one of my existing gearboxes was not practical, so I ordered one. First had to use MotoCalc to determine best gear ratio. Ordered a 2.33:1 MP JET ball bearing geabox.
+ I researched how to retune a motor for reverse direction required for gearbox. When MP JET gearbox arrived discovered it's designed such that there is no need to reverse the motor after all. No mention of this on either manufacturers or retailers web sites.
+ The instructions are two pages of tiny pictures, with text in bad English, and not in a practical building sequence. After a while I gave up on the instructions and just built the plane in a logical order.
+ I wanted larger wheels (2-7/8" foam) for our rough grass flying field, and had to make tubing spacers to allow bigger wheels to work on smaller landing gear wire.
+ All of the plastic parts were still in their flashings and had to be cut out and sanded.
+ The nylon bolts for holding the horizontal tail were too rubbery to screw in. I tried tapping the holes. Finally to get them to go in was so loose they stripped on tightening. Tried hardening the wood receiver holes with CA (which ran all over inside of airplane) - no luck. Had to cut open the covering, use metal bolts/nuts, and tape up incisions.
+ The rudder was not pre-hinged. Had to CA in hinges.
+ Control horns not pre-installed. Had to install all control horns.
+ German/Chek control clevises were a joke. Sloppy fit would allow controls flutter, and design was problematic. Replaced with standard nylon locking clevis from previously crashed airplanes.
+ The CA (super) glue that ran while trying to harden the stabilizer holes got into the tiny plastic tubes that the brass control wires run through. One had the control wire in it (elevator), which was frozen. Had to cut open the covering, carefully cut out the control wire without cutting it, cut back clogged outer tubing, and splice in new outer tubing. Had to do the same on the other side for the rudder tubing (no wire was in that side). Then glue in new tubing, then tape up incisions. Repaired control wire to straight and smooth.
+ While setting up and testing motor, discovered my Hitec 555 receiver was not working (the one that came out of the crashed BoxFly 20 converted to Speed 600). Finally narrowed problem down to bad crystal. Cannibalized crystal out of radio in Eagle 56. Went online and ordered new crystal.
+ One of the servos that came out of the crashed Sky Scooter (converted to Speed 480 with sheeted wing bottoms and extended wing and 2 pounds of latex paint) did not work. Luckily had two new servos on hand. Could not use HS-81 servos from boxfly, as all had stripped gears. Used HS-55 servos all around.
+ No instructions with MP JET gearbox, nor on their website, nor Hobby Lobby's on how short to cut the motor shaft for gearbox. Contacted HL by email, and got answer within a few hours.
+ While testing drive system (motor, ESC, battery) with Whattmeter and Tachometer to verify MotoCalc numbers, vise tipped over, prop came off, and almost cut my arm off. BTW: MotoCalc predicted amps, watts, and RPM right on.
+ Single piece of lite-ply motor bulkhead looked too flimsy with no bracing. Added 3/8" stock balsa bracing to make bulkhead more crash-worthy.
+ While testing elevator/rudder direction and throws, brand new micro EZ connector on servo arm broke (pin that goes into servo arm broke off). Cannibalized EZ connector from IFO.
+ Precovered wings badly warped (and differently). Had to figure way to heat both sides of wings simultaneously, and single-handedly, while twisting to flat (with slight wash-out). Bolted center of wing to edge of workbench so wing stood vertically. Heated and corrected wing warp in both wings.
+ Discovered could not use two aileron servos (flapperons) as plans called for. New Hitec Eclipse 7 computer radio is "hard wired" to use second aileron servo on channel-6. Receiver being used only 5 channels. Spent extensive time trying to figure out if radio could be reprogrammed to use aileron on channel-5. Not possible. Fell back to installing one aileron servo. Subsequently had to redesign (trim) plastic servo cover for different control rod angles.
+ No instructions, method, or clue for attaching center plastic wing/servo covering. Had to install balsa blocks to receive tiny screws (not supplied).
+ One aileron servo control rod was missing from kit. Cannibalized both control wires from Sky Scooter (which were exact right length).
+ Entire design of kit looked fragile and flimsy (not crash-worthy). Used 1/3 large bottle of thin CA to harden all stress points/areas.
+ The nylon bolts for holding the wing on were too rubbery to screw in. I tried tapping the holes. Finally to get them to go in was so loose they stripped on tightening. Tried hardening the wood receiver holes with CA - no luck. Used teflon coated bugle screws for a while, then they stripped out. Went to store and bought larger and finer thread self-tapping screws to hold wing on. Cut holes in center wing cover so could remove wing for transport without having to remove cover.
+ Tested all mechanical and electrical operations. Reversed aileron servo. Doubled amount of control throw shown on plans (10mm !!), and set transmitter to 30% incremental throws.
+ Discovered 1700 mah battery pack would not slip into fuselage opening. Kit not designed for easily removable battery. Installed left/right screws by corner of windshield to hold battery in vertical position with rubber bands. Glued in closed cell foam for battery cushioning.
+ Tested Center of Gravity (CG) - perfect. Weight: 31-32 oz. Double checked finished data in MotoCalc. Predicted to take off easily in grass, and loop from level fight (oh boy)! Either a 9x6 or 9.5x7 prop would work good. Decided to go with 9x6 APC "E" (thin) prop.
+ Topped off motor and transmitter batteries.

============ FLYING ============================
Contacted RC clubs wisest and most experienced builder, flyer, and instructor (Jack). He came over and checked construction, alignment/trim, etc. Looked good so went flying. 1 mph wind and clear blue skies so went to closer and better flying field. Jack took off the airplane. IT FLEW BEAUTIFULLY!!! Almost no trim adjustments needed. Checked stall characteristics, engine right thrust, stability, etc. Jack's words: "This plane flies very very nicely!". Jack turned transmitter over to me - flew lazy figure 8's to get feel of plane. Jack landed it (greased it on). I tried a take-off - did not give enough throttle - waddled around in semi stall condition and semi-crashed it on ground (right side up, prop not broken, "chin" of plane dirtied with tiny crack). Jack took off again with about 80% throttle - perfect straight takeoff in about 15 feet! I flew it some more, then let Jack land it. Total flight time on first battery charge: 15 minutes! Just as MotoCalc predicted, held level flight at 50% throttle, and climbed rapidly at 80% throttle! EXTREMELY stable flyer! An excellent aileron trainer, and probably wind-worthy as well (yet untested)! One problem discovered in packing up to come home. The wing panels are held on to each side of the wing center with just the friction of the rods inserted into the wings (easily removable for travel). One wing had slipped out about 1/4 of an inch. Jack suggested a small screw in each wing panel with rubber band between to insure wing security against wing root (alternately a set-screw into the "spar rod"). Jack said all the building grief was worth it, as I have a fine flying and fun flying airplane which should give me hours of enjoyment (assuming no crashes)!

Hopefully this will help you understand why I was holed up in my workshop from morning 'til midnight for days at a time. :-)

I am CC'ing this to Hobby Lobby, as I think some of the above reflect some "ARF'ish" design flaws in the kit they market.

Also noteworthy...
+ It took 12 days from order to delivery for original kit order.
+ When ordered motor and gearbox, paid $15 to get faster shipping. Still took 6 days from order to delivery.

Final MotoCalc...
MotOpinion - Grumbler 3 / 100ft above Sea Level, 70F
Motor: Graupner Speed 480 Race 7.2V #6330; 3213rpm/V; 0.129 Ohms; 2A idle.
Battery: SANYO HR-4/5AUP NIMH; 8 cells; 1700mAh @ 1.2V; 0.006 Ohms/cell.
Speed Control: Electrifly C-30; 0.0028 Ohms; High rate.
Drive System: MPJET GEARBOX; 9x6 (Pconst=1.11; Tconst=1) geared 2.33:1.
Airframe: Grumbler; 390sq.in; 31.6oz; 11.7oz/sq.ft; Cd=0.057; Cl=0.46; Clopt=0.71; Clmax=1.2.
Filter: 18A max, 30A max (ESC), 300F max, 50% min efficiency, 18oz min thrust, 35mph min, 300sec min, 0.8 max pitch:diam.
Stats: 72 W/lb in; 41 W/lb out; 16mph stall; 21mph opt @ 51% (32:51); 26mph level @ 60% (24:22); 649ft/min @ 20.5; -195ft/min @ -6.

Grumbler: http://www.hobby-lobby.com/grumbler.htm

:-) ROY (-:
Last edited by royp; Sep 22, 2002 at 07:11 PM.
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Sep 20, 2002, 07:13 PM
tic's Avatar
Wow, I'm not alone!.... I got into this hobby about 2 yrs. ago and what an education it's been.. I look at ANY potential new plane for my hangar w/ skepticism based on hard lessons learned.. My fav. quote is "can be assembled in one pleasurable evening".. which I've seen several times, I just laugh.. So many pitfalls, and parts you need, that you don' know you need... etc. etc.. My newest plane is a vip racer, I bought this after carefully looking one over at the NEAT fair, I have to say, as far as ARF's go, this little gem has to be one of the best, most complete "arfs" out there. Dieter said the reason he's carrying them is because of the completeness of the kit.. He didnt' mention how fun they are to fly.. but every vendor that had a vip racer sold out of them at NEAT..
Sep 20, 2002, 09:17 PM
Rehab is for quitters
LuckyArmpit's Avatar
Thats my favorite line..."builds in one pleasurable evening"...
Many times its not the case. Been putting together my Raven
sailplane. Not bad however, I have the Vee tail version and the instructions have no mention of it. Figured it out for myself.
Another thing, instructions say CG is 2 11/16 from leading edge which, according to instructions is directly behind the main spar.
Who measured this? Mister Magoo? The CG according to instructions is way behind the spar. I think it'd be tail heavy.
Guy at Dymond told me that HS-300's will fit perfectly in the servo cutouts on the wing. Wrong! No way in hell will they fit. So, I threw in 2 HS-81's with metal gears. Other than that, its a pretty
good model. I got all the throws setup with dual rates and adjusted the epa's for 1st flight since I don't know how the model will fly. I like the look of it!

Sep 20, 2002, 09:27 PM
Registered User
Jeff Meyers's Avatar
I did the review on this model for the E Zone. It has not been published yet.

The first thing that crossed my mind when I got this kit was I thought the quality of workmanship was outstanding.

The second thing that crossed my mind was that there was no way a geared speed 400 would fly this plane. I am glad to say I was wrong. After some flights on the speed 400, I installed a Jeti 15/4 and was disapointed. The additional weight of the motor killed the planes best flight characteristic.....slowly cruising around. I see you used a 480 race...should be more than enough power....I like the 400 for floating around.

I thought the instructions were more than adequate. This is my opinion....I suppose many others have their own.

The nylon bolts were fine on my stab. The wing bolts were a little more like you described....however, I was patient and kept at it. After them being screwed in the first time...they were fine after that.

I've had quite a few of the MP Jet gearboxes and they always had a detailed diagram on or in the packaging showing what length to cut the shaft. I never even cut mine....I just wrap the motor in tape to keep metal shavings from entering the can. Then, I use my grinder to grind down the shaft.

Cutting out plastic molded parts always makes me nervous. (and there's a lot of it in this kit) I wish the molding lines were a bit more obvious to the eye.....anyhow...I did get thru this with some good canopy scissors.

My wings were straight as can be....however I did add a little washout as they did show this in the insructions.

I just taped on my wing servo cover. tape not included

Applying the decals was a surprise.... I tried to float them on with Windex....wrong. Peel 'em and stick in on.

All in all....it sound like you like the end result. Enjoy it....you deserve it after all your work.


Sep 20, 2002, 09:58 PM
Registered User
fumblethumbs's Avatar

Royp, it's all a misunderstanding......

You see, after recently going through a very similar set of experiences with another Czech plane (which will remain anonymous), I've come to understand that "ARF" means "Almost Ready To Fix"! Yep, thirty hours is about right, but think of the fun you've had, and the time you saved by buying an ARF, not to mention the mere pocket change you've spent versus a kit! -thumbs
Sep 20, 2002, 10:35 PM
Registered User
Jeff Meyers's Avatar
Everybody has different expectations of how long it should take to install your equipment in an ARF I guess.

I think it took me a total of 5 hours or so to do mine. However, it took me 16 hours to build a Kwik E from start to finish. It took other guys only 6-8 hours to do what I did in 16.
Sep 20, 2002, 11:49 PM
Registered User
Andy W's Avatar
I LOVE building models, especially laser-cut ones (SR in particular). What I HATE is installing equipment, and whether "A"RF or not ("A" as they're nowhere near almost ready to fly!!), it takes a long time to install servos, linkages, etc. properly. I've framed and covered an IFO tonite while watching a ball game. I dread servo, linkage, radio and motor installation in the morning!
Sep 21, 2002, 05:01 AM
Single-task at best...
tim hooper's Avatar
I'm with Andy on this.

Although I dislike all aspects of this hobby - building, covering, flying & crashing - I have a particular revulsion for fitting the radio gear.

Thankfully, having discovered the E Zone I can now just sit here and prattle inanely, instead of going in The Shed and fitting that elevator servo into the Bandits fin.

Sep 21, 2002, 05:57 AM
Registered User
Patrick Plawner's Avatar
There are ARF, I've seen them

Multiplex NEVER disapointed me in this. The TwinJet is ARF, the Pico Jet Combat was ARF, and the Movie-Star is even more ARF, if any possible.

Ok, you say these are made of Elapor so it's easy.

So made from different material:
My Nebula Electric was THE most ARF plane seen to date. and guess what, all the places to put the equipment, servos, and batteries were already prepared for you. Just put them...

As for the wires, already put in place for you to, just to attach to the servo and the horns....

This is ARF !!!

The JR Mosquito was also pretty ARF

On the other side of the fence, many so called ARF are not ARF, if you consider anything ARF about up to 5 hours of easy work max and that does not require unregular tools.

I guess maybe the definition is not clear, and some manufacturers consider ARF when it is covered and you still need plenty of hours to work ?

Anyway, there are real ARF outthere, just ask, before you buy.

Last edited by Patrick Plawner; Sep 21, 2002 at 07:18 AM.
Sep 21, 2002, 09:41 AM
Registered User
ARF , Almost Ready to Fly

What's the key word here ? Think like ex-prez Clinton ! What's the word that allows you to wiggle out of any taking responsibility for the quality/completeness of this kit ? What would be a lawyer's favorite word here ??? The word > ALMOST

After building both ARF kits now and also kits that require
alittle more work but come complete with a blueprint-like set of 1 to 1 scale plans, I have to say that I am liking the older idea of what a model plane kit should be..... yup, lazer cut parts for the initial quick build, along with blueprints to replicate a broken part is the way to go !
Sep 21, 2002, 11:31 AM
Mr Mootsie
Mr Mootsie's Avatar
Originally posted by Andy W
I LOVE building models, especially laser-cut ones (SR in particular). What I HATE is installing equipment, and whether "A"RF or not ("A" as they're nowhere near almost ready to fly!!), it takes a long time to install servos, linkages, etc. properly. I've framed and covered an IFO tonite while watching a ball game. I dread servo, linkage, radio and motor installation in the morning!
concur....putting in multiple servos in the wings of my Xenath made me sweat.... I hated it! The building, sanding, covering of anything is great, but its the bits that go inside (gubbins, I think, is the UK word) is a pain right square.
Sep 21, 2002, 11:54 AM
Registered User
fumblethumbs's Avatar

Please don't misunderstand...

Guys, I have no qualms about assembling and installing, It's the REPAIRING things that should have been done correctly to start with that trips my trigger! For instance, I don't think it unreasonable to expect that two pre-covered wing halves should be the same length and chord as designed (one was 1/2" longer and 3/8" wider!), nor do I feel that pre-assembled landing gear should be 1" shorter than allows ground clearance for any prop, or that virtually every square inch of covered surface had to be re-tacked and shrunk, and in some cases removed and replaced altogether. Vacuumed formed parts should at least be usable, not a token afterthought, and last but not least, there simply has to be someone in Czechoslavakia with a command of the English language that could earn a relative fortune writing instruction booklets for models! I knew I was in trouble when the Czech version of the instructions were twice as long as the English set! Some minor details were completely absent (not simply unintelligable), like where the CG should be (I know, main spar, but still!), Rx location, batt. pack mounting info (where?), etc., ad infinitum. This is my second ARF of a similar type but different maker, thinking the first was a fluke, and I have to say it will be my last. It was not a cheap purchase either, at least $100 is not cheap to me for a parkflyer ARF, but that was just the start of escalating expense as the inevitable "extra needed items" were gathered accordingly. I've learned my lesson, next time, laser cut kit for me! -thumbs
Sep 21, 2002, 06:22 PM
Registered User

Wait, there's more...

Fun and informative reading the experiences of others. I mainly posted this so's we could all get a good laugh at ourselves. As indicated, many of the delays were caused by me shooting myself in the foot (my favorite saying is: "When the heads dumb, the whole body suffers"). My wife gave me a T-shirt that says "Mr. Make It Worse". I was wondering if I was the only one who has these kinds of experiences, and now it's confirmed -- I'm not. :O)

In spite of it all, I enjoy the hobby immensely (especially the flying part). Sure, the vendors get a little optimistic with the term "ARF" at times, but I guess I need to remember - I didn't have to cover it! AND -- it flies great! (the 480 is perfect for it - gives you enough power to get yourself out of trouble, and cope with some degree of wind)

This AM our club was invited to fly at an open-house at the local airport. The Grumbler (not me, the plane) got lots of compliments for looks and handling (let some of the RC old timers get some stick time on it and they were impressed).

P.S. Just for grins, add these newly discovered items to the above list:
+ DO NOT use the method for applying the decals that are in the instructions (soapy water). That was another disaster! Just peel them off and carefully apply them dry, being very careful to SLOWLY press them on bottom to top to prevent bubbles.
+ Even with the large wheels, the original landing gear gave insufficient prop clearance. So I bent them down more. Well after only two landings the gear wire is back to no prop clearance. It's a soft (non tempered) wire, and bends easily on landing. No work around - just re-bend them after every landing.

:-) ROY (-:
Sep 22, 2002, 03:06 PM
Registered User


+ The horizontal stabilizer was not horizontal. Was off by about 15 degrees. Reduced it to 5 degrees using a shim made from heavy plastic bag (4 layers).
Sep 22, 2002, 03:18 PM
Registered User


Jeff Meyers,

Have you tried to loop the Grumbler you made? Will the spar rods take more than 1.2 G's (more than normal turns and landings)? It feels to be very capable of loops, spins, and perhaps even inverted flight, but am not sure it's up to the stress. What do you think?

The reason I dropped back to a more docile airplane is that I've found that at age 60 I'm not up to the hotter planes I was trying to fly. I want to make the Grumbler last, and hone my flying skills, but would also be fun to do simple low-G aerobattics. :-)

Also, what was the final weight on yours with an S400? Mine is about 31.5 oz with the S480 Race / BB Gearbox (S480 is .9 oz heavier than S400). S480 also about 50% more "torque" than an S400, is why I went with it.

MotoCalc says "cabable of loops from level flight and almost all aerobatics", but wanted to get your take on it's robustness since it has the appearance of being fragile.


:-) ROY (-:
Last edited by royp; Sep 22, 2002 at 03:52 PM.