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Author Topic: FMS Fox 3 meter, a fine long winged aerobat!  (Read 1576 times)
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Heron pilot
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« Reply #50 on: January 28, 2019, 10:53:44 PM »

Sadly, many will buy the FOX 3meter ,  Place the battery where the straps are provided and fly with a grossly nose heavy plane for as long as they own it not ever hearing of such a thing as a dive test. Unwilling to question the manual,  their flight reports will say "needs a lot of up elevator and wants to climb out of a dive all the time, won't glide, hold speed or trim, don't buy it"
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Konrad
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« Reply #51 on: January 28, 2019, 11:50:13 PM »

That is why I try to post information that if somebody does a search will find helpful.

I’d like to thank you for helping keep it relevant. My knowledge of the model is from one observation almost a year ago. I did notice that it was much stronger than the last large foamy* Horizon Hobbies (HH) brought to market. But what I saw in the way of performance appeared rather lacking. I have to give credit to the pilots, flying for the publication, I was talking with said they weren’t glider pilots.

Now if history is any guide, HH was been very good with issuing Addendum's addressing errors in the manual’s CofG. I’m thinking of models like the E-Flite Carbon Yak 54. But as this FMS Fox 3 meter is not under an HH brand they might not be willing or able to modify the manual or issue an addendum. I’m concerned that this model was campaigned for about a year with a sponsored pilot and this issue of having the CofG 20mm too far forward wasn’t addressed until RC Informer published their video.

I’m amused that guys are surprised that heavy models thermal and that they make note of it. Just about any clean model will thermal and quite well at that. I recall in the 80’s flying FAI F3D pylon ships** and thermalling these 475 square inch racers that had the wing loading kin to a manhole cover while waiting for the race course to clear.

*Heron Pilot, I'd like you to notice I didn’t say Radian XL! Roll Eyes

** These at the time were 2.25 kg Prather Little Toni 6.5 cc piped engine with fixed props and fixed landing gear. Not really all that clean, and using Florsheim 12.5% non-flapped airfoils! (Sorry the last part is a bad joke).

All the best,
Konrad
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Heron pilot
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« Reply #52 on: January 29, 2019, 12:03:54 AM »

Florsheim airfoil .. LOL.. .love it.. Of course anything will rise given a strong enough thermal, I have no idea how strong or how big an area of rising air was found to make the FOX go up but if you actually picked one of these beasts up from the ground, you'd think it would take a hat sucker. Of course I've never had any RC plane with such massive wing area or span either so this will be fun for me, I hope... I can say for certain that I won't be adding ballast regardless.
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Konrad
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« Reply #53 on: January 29, 2019, 01:29:12 PM »

That airfoil, flat bottom thick trailing edge and all that linkage are a problem. Its all about drag. I was surprised to learn that the linkage hanging in the breeze for a four flapped wing is often as close to the same drag as a second stabilizer!

In case anybody is following along the improper implementation of control linkages can result in substantial drag.
https://www.mh-aerotools.de/airfoils/index.htm
See Aerodynamics and then Drag of Aileron & Flap Linkages

The killer from weight is that it forces the wing into a higher angle of attack, causing weight induced drag. Ballast helps by allowing the ship to fly faster. And by the math (Lift Equation) weight is a linear function and lift is a squared function of velocity. So a little weight can help produce a lot of lift. But the sad truth is that drag goes up by the cube of the speed. Here we go again it is imperative to get rid of drag. While weight is an enemy to flight it is nowhere near a detrimental as drag.

This is why my manhole cover racers could thermal. They were aerodynamically clean to try to go fast.

All the best,
Konrad
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Konrad
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« Reply #54 on: January 29, 2019, 09:46:18 PM »

WOW, learned that a rudder and fin don't introduce a roll component to the fuselage. Roll Eyes It has to be true, I read it on RCG. This was from the same guy that thinks a properly trimmed CofG is found when the stab and elevator are aligned in level flight.

Word to the wise this is not true!

Some airships are just doomed to be improperly trimmed and flown. Shocked

All the best,
Konrad

P.S.
We know what "G" stands for! Please if any of you spend time on RCG please, please help this guy and his Fox!
« Last Edit: January 29, 2019, 10:25:52 PM by Konrad » Logged

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« Reply #55 on: January 29, 2019, 10:44:08 PM »

Good way to get banned on RCG.. Smiley
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Konrad
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« Reply #56 on: January 29, 2019, 10:48:52 PM »

Sad. I guess you're right. Helping lift the veils of ignorance is not appreciated.  Roll Eyes

I guess one could try to link to here or another site with rational moderation policies. Nope that will also get you black listed on RCG.

OK, never mind!

All the best,
Konrad
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Konrad
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« Reply #57 on: January 30, 2019, 07:55:22 AM »

...

The killer from weight is that it forces the wing into a higher angle of attack, causing weight induced drag. Ballast helps by allowing the ship to fly faster. And by the math (Lift Equation) weight is a linear function and lift is a squared function of velocity. So a little weight can help produce a lot of lift. But the sad truth is that drag goes up by the cube of the speed. Here we go again it is imperative to get rid of drag. While weight is an enemy to flight it is nowhere near a detrimental as drag.

This is why my manhole cover racers could thermal. They were aerodynamically clean to try to go fast.

All the best,
Konrad
In the light of a clear new day, see this was clumsily written. My apologies.

All the best,
Konrad
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Konrad
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« Reply #58 on: January 30, 2019, 08:10:30 AM »

WOW, learned that a rudder and fin don't introduce a roll component to the fuselage. Roll Eyes It has to be true, I read it on RCG. This was from the same guy that thinks a properly trimmed CofG is found when the stab and elevator are aligned in level flight.

Word to the wise this is not true!

Some airships are just doomed to be improperly trimmed and flown. Shocked

All the best,
Konrad

P.S.
We know what "G" stands for! Please if any of you spend time on RCG please, please help this guy and his Fox!

Plus one for RCG! A high five to Peter.
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Konrad
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« Reply #59 on: January 30, 2019, 08:53:29 PM »

Guys should not confuse the reflexed airfoils like those found on flying wing planks, with the modern airfoils with the rear cusp (or rear convex) feature. These would be airfoils like the MH-32, S 7012, RG-15 and most of the Quabeck airfoils. These really cut down on the drag compared with flat bottom aft section airfoils. They also really respond well to full wing camber changing.

Flat bottom airfoils really only are of value with simple balsa built up wings. They are easy to make!  There are whole families of flat bottom airfoils derived with these building constraints. But for a foam molded wing this is NOT a concern.

True I don’t know how much performance one can add after the fact with thinning the airfoil and adding this cusp with a sanding drum. But I fail to see why the OEM did incorporate these airfoil features in the mold in the first place. It is very do able as we see this in the Multiplex Heron.

All the best,
Konrad

P.S.
The Fox airfoils may in fact have this feature. I wasn't allowed to really examine the prerelease Fox I saw.
« Last Edit: January 30, 2019, 09:50:54 PM by Konrad » Logged

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Konrad
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« Reply #60 on: February 05, 2019, 09:31:41 AM »

Now I'm reading that the FMS Fox has a thrust line issue. I have to say I did not notice this with the flights I saw nor do I see it in the posted video from RC Informer.

The dive test is performed with the motor off. So with the motor variable out of the equation I'm at a loss as to how would adding washers to the upper corners of the motor mount to change the thrust line would help with the incidence issue?

To test for the thrust line, trim to fly level at full power. Then when the aircraft is in front of you cut the power. Making no other control input. If at the moment you cut power the plane jumps up is an indication that you have too much DOWN thrust. If at the moment you cut power the plane twitches down is an indication that you have too much UP thrust.

This makes sense if you realize that the elevator is compensating for the wrong thrust line. At the moment you pull back the power the wrong force from the thrust line is removed. This reveals the corrective force from the stab.

I'm rapidly coming to the conclusion that there are few folks left that know how to trim a model aircraft. Cry I'm pretty sure most foamy OEMS don't!

All the best,
Konrad

P.S.
So far the foam products (Gliders) from Multiplex appear to have proper force arrangements for their intended market.
« Last Edit: February 05, 2019, 09:46:08 AM by Konrad » Logged

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Konrad
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« Reply #61 on: February 05, 2019, 11:45:01 AM »

Ops, I can see how the last post could look like a paradigm shift without a clutch!

A lot of guys are finding that as they move the CofG aft (115mm) to get something that resembles a proper CofG location that the elevator is trimming way out of profile. (Lots of down trim is needed) This is a classic indication that the decalage is off. The leading edge of the stab needs to be raised to get the stab and elevator in line to lower the the trim drag.

Many of the early adaptors to the FMS Fox are having issues isolating the various forces involved in trimming an RC aircraft. Gliders are particularly sensitive to trim issues as the power available for flight is limited to the energy in the air.

I think the FMS Fox 3 meter will fill a niche in the market place as long as she is understood for what she is, and doesn't get a bad reputation for being something she isn't. I think having early adaptors that don't know how to fly and or trim a glider hasn't helped. Rich Baker's (RC Informer) has done more to help sales just with his video moving the CofG aft than the previous 6 months of sales blitz.

She is a long winged aerobat that has the potential to thermal should one want.

All the best,
Konrad
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« Reply #62 on: February 05, 2019, 12:11:56 PM »

Well said.. Oddly, people have no idea why they need down trim in level flight and seem to think it's all related to motor thrust line. When asking what the plane does at WOT in level flight when the motor is cut? No response.The thrust line may be "off" too but pretty easy to check. Decalage is a mystery to most so they just scratch their heads and wonder why the EL isn't in line w/ the horizontal stab all the time
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« Reply #63 on: February 05, 2019, 06:20:07 PM »

Definitely agree with both of you. I would suggest tongue in cheek that some of these fellows would benefit from some FF experience and then also reading the trimming advice from the pattern masters. Jim Kirkland many years ago wrote some very informative articles on the subject. I'm sure it's been done many times since.
Basically these fellows just need to do some study and thinking.

John
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Konrad
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« Reply #64 on: February 08, 2019, 02:14:49 PM »

John, There was a publication called the "K" factor for the pattern crowd. It had a real good trimming chart.


I’m always impressed at how the internet is forever September*.

I’m reading about blade failures and potential modification to the blades on the Fox 3 meter.

In the beginning that would be the 80’s we (the hobby) standardized on two blade root sizes. I believe these were the 2mm x 6mm for the “Speed 400” class  good for about 300 watts**. And the 3mm x 8mm root good for about 1200 watts. I think around the mid 90’s the  2mm x 6mm root was dropped as far to many folks where trying to drive these past 600 watts will injection molded blades. Even 2mm x 6mm fiber reinforced injection blades would fail. Hand laid continuous fiber blade would hold up fine but most folks wouldn't pay for them at the lower 600 watt power settings.

The 3mm x 8mm  root holds up fine with properly engineered chopped carbon fiber in the plastic matrix to 1200 watts. Hand laid continuous  fiber lay up are good well past 2 kw. I don’t think that the toy grade unreinforced plastic prop will withstand 1.2 watts.

Over the years I’ve has close to 18 folding prop failures. None of them has been by the pin pulling through the back side of the root. Most have been right where the blade joins the root and some have been right where the blade is starting the thicken to flair into the root.

Please note that all manufactures give a formula for determining the safe rpm limit for their prop construction and diameter. This usually has a safety factor 3 built into it.

I don’t know if FMS is using a none standard size hub for marketing reason, to force you to buy their prop assembly. But the standard 3mm x 8mm hub is adequate for the power available from the stock supplied motor.

I’m not saying that the modification of any brands props is safe or dangerous. Just be aware of the forces on the blade and limits of construction. I haven’t seen any failed prop blades off the FMS Fox 3 meter so I don’t know its failure modes.

*”Always September" is a term used by upper classmates to describe the same questions the freshman class always asked when first coming on campus.
**Even at 150 watts throwing a prop blade would tear up a fiber glass fuselage!

All the best,
Konrad
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Re: FMS Fox 3 meter, a fine long winged aerobat!
« Last Edit: February 08, 2019, 02:58:11 PM by Konrad » Logged

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Konrad
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« Reply #65 on: February 09, 2019, 11:44:46 AM »

Dents in EPO foam.
No good deed goes unpunished!
Guys don’t think or follow directions.

First heat expands the beads. So pouring hot water on the surface will expand the beads it makes contact with. The pressure of an iron will HELP keep the beads that it makes contact with  from expanding above the surface. The steam should expand the dent spanned by the the iron. The paper towel supplies the water for the steam. This way there is no hot water flowing away the the repair area to expand any adjacent  foam, damaging the surface.

I’ve never had any luck with the frozen (0°C) spoon method of suppressing the alligatoring of the EPO surface. True I haven’t tried dry ice of liquid nitrogen.

I find that with this Beacon product I can hide most of the surface damage. It even blends in well (for a toy) with the white of EPO foam.
https://alofthobbies.com/foam-finish.html

Guys EPO foam is crap for making a model aircraft! Particularly if you want it to perform like traditional modeling materials. EPO foam is fine for making trainer aircraft and toys in in general. Other than the Sensei trainer* I reviewed, all other EPO models I’ve had and reviewed here on HIP fall squarely in the “Toy"  segment of the hobby. Their finish is poor! No OEM has a paint process that actually allows paint to bond to the EPO foam. None will pass the tape pull test. The surface is very susceptible to surface dents.  To my way of thinking it is unconscionable to offer a flying model without supplying a means to repair the model! I suppose buying a replacement is their way of getting around the repair question.

Remember EPO is for low emotional investment modeling. Don’t for a moment think one is getting, with EPO foam, a concourse caliber product that one can be proud to own.

*EPO foam can make a great trainer as it is structurally rather durable, making most learning mishaps minor. It structurally repairs easily with CA glue and some fiber reinforcement. Other than replacing parts, repairs will not look as good or better than new and maintain any surface durability.
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=22768.0

Some of my other reviews of EPO models. (Yikes, I need sand more balsa!) Shocked
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=20999.0
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=21046.0
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=21682.0
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=21198.0
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=21593.0
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=21197.0

All the best,
Konrad

P.S.
This might make a good "R/C general" post, rather than just a FMS Fox 3 meter post.
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Konrad
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« Reply #66 on: February 11, 2019, 10:02:23 AM »

Don’t know what some of these guys are thinking when it comes to trimming. Lighter is almost always better! Less weight will improve the rate of climb. It also means that one needs less control deflection to perform any maneuver. Less surface deflection means less cross coupling of controls; which means less mixing needed to correct these coupled control responses.

If one is looking for better energy retention in a glider the best way to do this is to minimize drag. Such as control arm covers, proper decalage and a minimum margin of stability. Ballasting is another practice, but has all the issues associated with weight. To ballast a glider one adds weight to the the center of mass; NOT the nose! The goal is to NOT effect the models trim with the added weight. In the case of the FMS Fox 3000mm* there is a hollow carbon tube near the center of gravity. This might make a good location to add tungsten slugs to ballast the aircraft. But as the Fox has a prop I’m not sure why one would want to add ballast when just the blip of throttle would pull the model through the air without the penalties of weight. Besides she is already starting out with 4.7 Kg of mass!

Still haven’t read what is the neutral balance point.  By the dive test this would be near the point that the model starts to tuck, rather than pull out by itself as the model builds up speed in the dive.  Looking at RCInformer’s video this neutral balance point is still aft of the 115mm balance point in Rich’s video. Moving the CofG further aft will necessitate lowering the control throws. Again this lowers the drag profile of the aircraft. And if one cuts down the throw by moving the push rod closer to the servo axis this helps with servo resolution.  Win Win!

Remember the CofG in the manual is only to help one get past the maiden flight; to start the trimming process!


*FMS calls it a 3000mm rather than the standard convention of calling her a 3m ship. I guess to the American marketing machine 3000 looks like a better buy than 3.

All the best,
Konrad
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Konrad
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« Reply #67 on: April 11, 2019, 10:55:58 PM »

Heron Pilot, have the snow drifts in Zambia receded enough to throw your Fox into the air. I've been reading a lot about the low land flooding from this year's snow melt.

All the best,
Konrad
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