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Oct 08, 2018, 11:28 AM
Hates Palm Trees
Discussion

Sub 11 oz. 2M Contest Plane Possible?


Yep......................I'm back with another 2M project that's sure to have some of you asking "Why?"

A sub-11 oz 2 M ship might be a pointless "wild goose chase" or it just might be.......................some magical anti-gravity machine that will bring the local thermal contest flying community to it's knees! Okay, not likely, but it seemed like it would be a fun challenge so, "Why not?"

What got me thinking about this were the two Yellow Jacket hybrids I built which matched Corky Miller's superb 2m wing design with an extra Mad-RES fuse I had laying around gathering dust. The RTF weights for the finished planes were 13.6 oz with a spoiler equipped wing and 13.1 oz for the non-spoiler wing. That's light for a F3RES legal plane and includes a very strong wing. In fact, I've personally launched the Mad-YJ's using a 9lb highstart and the wing barely flexes. Of course, I think 8lbs is the max allowed in F3RES, so one could probably get away with a lighter wing design.

I was intrigued and got on the job immediately.
Last edited by SteveK123; Oct 08, 2018 at 11:35 AM.
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Oct 08, 2018, 11:58 AM
B for Bruce
BMatthews's Avatar
Yeah, I think it's possible and I think that the Mad-YJ has a lot of wood you could remove to get there.

Start at the tail. These are solid sheet that is swiss cheezed with some holes. But there is still far more wood in the tail surfaces than you need. I don't know if you weighed the tail surfaces before installing them but with a light but strong enough "free flight" like construction the tail surfaces would be roughly 1/3 to 1/2 what they weigh currently. And of course it's the old story that a few grams at the tail means about 3 times more than that out of the nose. People punch or drill holes like this all the time thinking that they are making a sizeable difference. But really at best they put in all that effort for about a 10% saving. The wood left behind has enough volume that if that same weight was converted to strip and sheet stock for a more conventional built up structure that we could easily build TWO sets of tail surfaces and still have scrap left over. So potentially half or less the weight of the all sheet option shown. Now the first thing brought up is the weight of the glue. But if done correctly with the proper amount the glue weight does not break this less than half the weight relationship.

The wing's trailing edge is wider than it needs to be. And the wing tips could be formed as an outline from 1/32 x 1/4 strip wood in 4 or 5 layers soaked in hot water and a good dash of ammonia then bent and laminated around a form to save a couple of more grams.

The covering on a model of this size can really add up if the wrong product is used. I'm assuming that it's covered in one of the park flyer films. If so a few more grams could be shaved off by careful selection of a different covering. But if this is Monokote or Ultrakote or something equivalent then you could easily save a bunch of weight by switching to a lighter covering.

On the radio equipment grams count too. I've seen some receivers that are only .3 to .5 of a gram with no connectors. Instead you cut away the connectors from the servos and solder the wires directly to pads on the board. Now these are generally less than full range receivers. But if we're trying to shave grams then buying the lightest workable receiver and servos then modifying them to remove the connectors by soldering the wires directly will save a couple of more grams.

You would want to play around with carbon tube vs built up wood fuselages. There may be some grams to be saved their too. And by built up I don't mean sheet balsa. I mean spruce longerons with balsa diagonal bracing to build up a lift crane's boom like structure. These can be very stiff and light and surprisingly strong. But not if they are made too skinny. That would be the only downside. But a truly light but workable fuselage could be produced with a modest increase in cross section. And at the speeds such a light model would fly I doubt if the slight increase in cross section would have as big an impact on the performance as one would think. And a somewhat larger cross section also permits an even lighter method of mounting the tail surfaces. So a win on that end too. The trick is to build up such a tail boom and fuselage in order to tell for sure.
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Oct 08, 2018, 01:05 PM
Hates Palm Trees
Great suggestions Bruce!

I have a kevlar pod and a short kit for an old-school style 2M wing that I'll be using for this project..............It won't be F3RES legal but if I can get below 11 oz, I'll consider making an F3RES legal version.

I will also be using:

- A 3mm depron vertical stab and rudder
- Pull spring controls
- Mini 2S lipo battery from a micro drone
- Solarfilm SoLite covering film

This'll be fun!

Steve
Oct 08, 2018, 02:22 PM
B for Bruce
BMatthews's Avatar
Steve, just for giggles I weighed a couple of my free flight model stabilizers that are roughly the same size as what I'd expect to use on an F3RES. One from a old rubber model is 6.3gms covered with tissue and dope the other is 6.8 covered again with tissue and dope. Another stab built up lightly but covered with Solarfilm (lighter than ultracote but heavier than parkflyer films) is a whopping 14.4gms.

As it happens I've got a flat foamy flippy flyer kit here that is made using 3mm depron. I weighed one of the ailerons which is roughly the size of the 6.3gm stabilizer and it's 3.9 grams. But I consider the depron to be too flimsy by itself to be trusted. So by the time some sort of leading and trailing edges are added or some manner of skin is added I'm guessing it would end up in the mid 6gm range like my free flight stabilizers.

One thing for sure though. The difference between the tissue and dope covered stabs and that one plastic film covered stab clearly points out the importance of the right covering in your quest for a sub 11oz final weight. Likely the biggest single factor in fact.

A story to aid in pointing this out. Years ago I built a little 36" span sport model. The airframe came in at something like 6oz (for sake of example). But more importantly about half the total surface area as an F3RES. I covered it with a mix of Monokote and Ultracote in complimentary colors I had on hand. Between the base covering and some overlaid trim I added 1.5 oz to the weight. I did not expect that at all! ! ! So that same covering on all the surfaces of an F3RES would be roughly 3 oz of added weight. I'd say the choice of covering can easily be the make or break factor on this 11oz target weight mission.

Along the way you will also want to carefully weigh and choose whatever balsa you use to ensure it's light where you can be light and rather weaker but stiff and somewhat stronger on the parts that need to be stiff and somewhat stronger. Such as picking a good grade of lighter C grain for the trailing edges so they can still be stiff across the grain when shaped to a thin trailing edge and the like.
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Oct 08, 2018, 04:04 PM
Registered User
SteveK123:

Go for it, sir!

Yours, Greg
Oct 08, 2018, 04:51 PM
Hates Palm Trees

Lightweight Coverings


Bruce,

You're totally correct about the covering.......................I never built a kit until this year and was fortunate enough to have discovered Microlite by Coverite which I used on all my builds..............I really like it............Unfortunately they are no longer operating as of about February 2018.

Fortunately, some detective work led me to Solarfilm, which had apparently provided Coverite with their product for years .............Unfortunately, Solarfilm appears to be planning on discontinuing business and is in the process of selling their existing inventory..................I ordered a bunch of Transparent Red and opaque white from Solarfilm and received the shipment last week. That's what I'll use on this project.

The 2 meter wings I've built have only gained approx. 1 oz after covering with Microlite / Solarfilm (SoLite brand).

Steve
Last edited by SteveK123; Oct 08, 2018 at 05:23 PM.
Oct 08, 2018, 04:58 PM
Hates Palm Trees
Quote:
Originally Posted by glidermang
SteveK123:

Go for it, sir!

Yours, Greg
Thanks for the encouragement Greg............Since I'm new to kit building, it all seems like fun to me.
Oct 08, 2018, 05:12 PM
Hates Palm Trees

Lightweight Battery Setup


I have been using 300mah NIMH batteries for my 2M contest planes but these are typically a minimum of 1.1oz / 30 gm with the leads. However, if I move the servos and receiver forward in the pod and lengthen the nose of the plane a 1oz battery is too heavy.

How do I know this? Because when I built my MAD-RES, I lengthened the nose and used a 300 mah NIMH battery, I had to add tail weight to get the CG correct.

So I'm going to use this........... Total weight 15 gm RTF !

Steve
Oct 08, 2018, 09:44 PM
who has rabbit ears down
Captain Canardly's Avatar
This is gonna be interesting! Hang in there Steve! I've only been (previously) experienced in 'heavy' birds- let's see how tthis pans out! ( I'll be using some Monocote on my Yellow Jacket)
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Oct 09, 2018, 01:59 AM
Registered User
Mr. Junji Ishii, known for his 900 mm 80g DLG started evaluating a 1.5-2m, under 250g version.
Oct 09, 2018, 09:05 AM
Hates Palm Trees

More Battery Stuff


When I pitched the idea of using an unregulated 2S Lipo to power this rig to a flying buddy, he was convinced I was going to fry the receiver.

I've been using 2S Life (nominal 6.6V) batteries to power my (very expensive) F3F planes for years and haven't had any issues with receiver function......................I did resolve however, to test the receiver with a fully charged 2S Lipo for 30 minutes to see if there were any glitches................So far no issues so I'm going unregulated.

Steve

PS: The servos are MKS HV 6100's so no issues with voltage.
Oct 09, 2018, 09:30 AM
Registered User
Steve:

You can use 2S unregulated with many servos and receivers (but not all - check the warning labels!). Examples include Dymond D47 small servos, which are perfectly happy at 2S, while an otherwise robust Hitec HS6 will loose all its smoke within minutes of connecting to the same power.

You can also use 1S - a single LiPo cell - and still get perfectly fine performance. Many flyers in F3K (which are hugely more dynamic than our F3RES birds) use single-cell set ups. A single cell LiPo can still carry a capacity of several hundred mAh, and provide power for a couple of hours to two or three servos. Again, look at the specs for your equipment.

The same cautions about power use applies to receivers, of course.

Yours, Greg
Oct 09, 2018, 11:39 AM
Registered User
banjo328's Avatar
In addition to the D47s, the Lemon 0034 rcvr. and the new Spextrum anntenna-less rcvrs. will support 2S unregulated.

The weight reduction attempts are interesting and worthwhile technical exercises but will have little or no visible effect in 'real world' flying, I predict as a curmudgeon.
Oct 09, 2018, 12:37 PM
B for Bruce
BMatthews's Avatar
Quote:
The weight reduction attempts are interesting and worthwhile technical exercises but will have little or no visible effect in 'real world' flying, I predict as a curmudgeon.
Yeah, that's a whole other issue ain't it..... If we're already seeing 16 to 18 oz models quite regularly then hitting 10.5 oz is about a 50% reduction. It'll fly noticeably slower for sure. And it SHOULD be able to stay up in milder conditions that the other models come down in. And likely the dead air duration would be longer. But in any manner of wind the lower weight will affect the penetration ability. Now badly? That'll have to be seen.

I think I'd add in a way to ballast up the center section of the wing. That way you can find the happy weight for each weather condition range.

I know that on the foggy early mornings of fall that my free flight models have often climbed up and just "sat" at some altitude. It's something about the moisture coming up off the ground. Not thermals but lift nontheless. An 11 to 12 oz F3RES model launched in such conditions then trim levered into a slow open circle and left alone should be able to sit on this "fog pillow" for many minutes at a time.... .or until the sun burns the fog away.

Have any of you F3RES types found that your 16 to 18 oz models can do the same?
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Oct 09, 2018, 12:53 PM
B for Bruce
BMatthews's Avatar
If you are already planning on using carbon tubing as the wing spars I'm thinking that the tube in the center panel could double as a holder for ballast rods. Assuming plug on wing tips if the joiners are secured in the tubes of the outer panels that leaves you access to fill up the inside of the spar of the center panel with slugs of steel rod and spacers as needed to keep the steel centered.

A 20 inch length of 1/4" drill rod I've got here weighs 4.5 oz. And some 5/16 drill rod is 4 oz/ft.

And there's many sizes of ground drill rod stock available. So there's options for filling up any size carbon spar tube with some slide in weights is wide open.
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