Would you prefer hollow or solid core? - RC Groups
View Poll Results: solid core or hollow molded wing
sandwhich wing (hollow) 31 51.67%
solid core wing 29 48.33%
Voters: 60. You may not vote on this poll

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Sep 22, 2017, 04:24 PM
1 revolution and throw!
Poll

Would you prefer hollow or solid core?


Simple question , would you prefer to buy a solid core plane or hollow molded?
feel free to give you toughts on both or explain why you made the choise you made

DON'T MAKE A VOTE BASED ON RELAIBILITY OF PLANES YOU OWED OR SEEN BOTH CAN BE BUILD SUFFICIENTLY STRONG

i would like to askfor people who voted to motivate they're choise here please! thanks
Last edited by krikkens; Sep 23, 2017 at 02:39 AM.
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Sep 22, 2017, 04:42 PM
1 revolution and throw!
i'll give my toughts here.

i'm tempted to say the solid core wings are a tempoaray phenomenon in f5j or at least go back to a very small part of the market (i could be very wrong!), i expect a solid win in the poll for hollow (or is this a bit confusing to say;-)

in f3k solid is there for some years and lickely it will stay there!
why does it work in f3k?
-wings are very thin , weight gain is significant!
-f3k planes are fairly light , grabbing the wing does not nesecairly cause a dent , f5j planes are +5 times hevier , not to mention wind impact on the wing in your hand , dents are way more lickely.
-in f3k we see a lot more mid airs and solid core damages (if the planes doesn't crash down) are mostly easier to repair. (i could be wrong about the amount of mid airs maybe??)
agree with me or not but solid core wings look nowhere near as good as hollow molded , especially over time , it can be done super smooth but expect a heavy plane!(thick skin is needed, and i'm talking about a 400-600 gram weightgain here , multiple layers to add up to around 200gr/mē dry weight give you a smooth wing , hollow molded are smooth even with a 30gr/mē layer ;-)
i have molded some propellor blades with solid rohacell core with 300gr+ m/ē and they are smooth and will remain smooth, the skin nees to be stable enough on it's own so the solid core roughness has no effect on it .

to me it does make sense in making the flaps and ailerons solid core and maybe the front part of the tip panels , the front part of the centerpanel and perhaps the front part of the tip panel hollow.

personnaly i hate the cellulite effect of a solid core wing and i'm pretty sure i'm not the only one here , in f3k it got accepted due to the above mentioned gains but my gutfeeling says in f5j people will go for a hollow wing which is smooth.

i don't think there can be a discussion about smoothness , all the hollow wings i know are smooth , all the solid core wings i've seen develop cellulite effect , even from the big manufacturers!
it could be solved with a thicker skin but weight goes up , for flaps and ailerons it will be lighter to build solid core , hollow has 2 layers of skin anyway and without taking the spar/dragspar , etc into account you can say the weight of a hollow molded part has a fixed weight/area ratio where the solid core molded part depends on the volume aswell. rough estimation , going below 6-7mm and the solid part wins.
Last edited by krikkens; Sep 22, 2017 at 05:09 PM.
Sep 22, 2017, 05:04 PM
1 revolution and throw!
my personnal tought about why solid cores develop cellulite and hollow parts don't or do much less altough the rohacell is the same:
Hope someone can chime in and conirm this or prove me wrong :

because skins of a solid core are fixed into position (laminated to the solid core) they have nowhere to go when they expand/shrink, the only way to relief this stress is to stretch in between the bridges they are glued the rohacell (this means the cell walls which are cut open by the cnc.
cell sizes are very small so the the deformation happens on a small scale in each open cell.

hollow molded the complete sandwhich can expand and shrink , no need for the skin the relief it's stress on a small scale thus it remains smooth.

if what i'm writtin is true , hope someone can confirm my toughts as i'm intersted to know. then you can say a solid core wings airfoil is more accurate as a hollow wing deforms by expanding , a hollow wings top and bottom skin is bonded on a few points (spar, dragspar LE , TE) but parts in between can deform due to heat diffrence between top and bottom .
Last edited by krikkens; Sep 22, 2017 at 05:10 PM.
Sep 22, 2017, 05:44 PM
Registered User
Luis Moya's Avatar
Quote:
Originally Posted by krikkens
to me it does make sense in making the flaps and ailerons solid core and maybe the front part of the tip panels , the front part of the centerpanel and perhaps the front part of the tip panel hollow.
I donīt know if this proposal is feasible from a manufacturing point of view or not. If it is, perhaps you need the option "Hybrid" in your poll.

As written, it appers that you want "the front part of the tip panels" be solid core and hollow at the same time. Please clarify.

All the best,

Luis
Sep 22, 2017, 06:18 PM
1 revolution and throw!
Quote:
Originally Posted by Luis Moya
I donīt know if this proposal is feasible from a manufacturing point of view or not. If it is, perhaps you need the option "Hybrid" in your poll.

As written, it appers that you want "the front part of the tip panels" be solid core and hollow at the same time. Please clarify.

All the best,

Luis
it is possible from a manufacturing point of view and it is done like that.
i mean't to me the choise is open for the front part of the tip panel , one can say something for both options...
front part of mid section seems to me most benefit for a hollow part .
flaps and ailerons i see most benefit in solid core .

i'm not sure if a hybrid option is good , might confuse people , i want to let them decide on what they know.

to me basically it's a choise about cellulite and easier permanent dents but easier repair most of the time vs smooth wings which adapt to finger pressure witouth damage but can be a pain to repair after a serious mid air.
Last edited by krikkens; Sep 22, 2017 at 06:26 PM.
Sep 22, 2017, 06:20 PM
1 revolution and throw!
took this image frm the supra produced by vladimir models , it has solid core flaps/ailerons and hollow wing.
Sep 22, 2017, 07:00 PM
Everything's A Compromise
Larrikin's Avatar
Voted and subscribed.

I'd like to see a performance comparison between a nominal profile, maybe a (Syner) J-100 and a dimpled simulation of the cellulitis.
I'd do it myself but I don't understand XFLR5 well enough.
D.
Sep 22, 2017, 07:11 PM
Registered User
Sensoar's Avatar
I am looking forward to getting a better understanding of the advantages and disadvantages of the two vastly different approached to construction for the F5J planes. I would imagine that anything over 3 meters is a challenge engineering for structural integrity .

Although at the 1.5 m end of the scale. It seems that for F3K solid core Rohacell is the clear cut victor.
Sep 22, 2017, 07:43 PM
E sailplane thermal hack
A well made hollow core just looks better,, seems the Foam would trap heat and cause problems.
Sep 22, 2017, 07:53 PM
Cognitive dissonance
kcaldwel's Avatar
Quote:
Originally Posted by Larrikin
Voted and subscribed.

I'd like to see a performance comparison between a nominal profile, maybe a (Syner) J-100 and a dimpled simulation of the cellulitis.
I'd do it myself but I don't understand XFLR5 well enough.
D.
XFLR5 will not tell you anything about the effect of surface roughness. It doesn't even really work with turbulators. It only models the lift increase, not the drag increase.

Basically, if the surface roughness is thicker than the boundary layer, the flow will be tripped to turbulent, and the drag will be higher than laminar flow. The boundary layer is very thin at the leading edge, and progressively gets thicker further back. Smoothness will be very important for the first 30% of the wing, and probably the first 70% of the bottom surface.

The profile drag will go up with a rough surface, as long as the airfoil didn't have a separation bubble without the roughness, but I don't know of a good way to characterize it. There is some data in the UIUC wind tunnel testing for turbulaors, but on older airfoils, some with laminar separation bubble issues.

For example, the RG15 shows about a 15% increase in drag at a Cl of 0.3 between the clean condition and a 0.17%c (about 0.27mm on a 160mm chord) high upper surface trip at 20% or 40% of the chord. They also tested with bare balsa surfaces compared to a film covered surface, with similar results. Once the trip was back past 40%, the drag increase disappears.

Kevin
Last edited by kcaldwel; Sep 22, 2017 at 08:06 PM.
Sep 22, 2017, 09:08 PM
Registered User
Working at SUSA, I have the opportunity to handle every model that comes in and out the doors, and also fly as many as I can. I have the luxury of pushing these models far past what they are designed to do. By now, I have flown nearly every hollow, and solid core model on the market.
At this time "for me at least", hollow models have proven to be a bit more stiff than the solid core models in F5J. As far as I see it, if you deploy crow at a reasonable airspeed and the wing flexes to the point where you now have anhedral, something is wrong..

I will also say from my experience, that higher aspect designs are not the only way of the future. Far from it. You buy what suits your flying style!
Sep 22, 2017, 10:05 PM
Registered User
Luis Moya's Avatar
Quote:
Originally Posted by Alex Breaux
I will also say from my experience, that higher aspect designs are not the only way of the future. Far from it. You buy what suits your flying style!
Could you provide some examples in which this proved to be true? Not challenging, just curious.

Al the best.

Luis
Sep 22, 2017, 10:10 PM
E sailplane thermal hack
I've seen a solid core wing flex to anhedral the way Alex describes when Flaps were deployed,,SCAREY
:-O
Sep 23, 2017, 01:52 AM
1 revolution and throw!
Quote:
Originally Posted by Alex Breaux
Working at SUSA, I have the opportunity to handle every model that comes in and out the doors, and also fly as many as I can. I have the luxury of pushing these models far past what they are designed to do. By now, I have flown nearly every hollow, and solid core model on the market.
At this time "for me at least", hollow models have proven to be a bit more stiff than the solid core models in F5J. As far as I see it, if you deploy crow at a reasonable airspeed and the wing flexes to the point where you now have anhedral, something is wrong..

I will also say from my experience, that higher aspect designs are not the only way of the future. Far from it. You buy what suits your flying style!
flexing when deploying flaps has nothing to do with solid core or hollow!
it's just the spar build up in combination with spar height.
make a solid core xplorer(just an exapmle) with the same spar as they use now and it will flex the same way!

the airfoil of f5j wings are at least on some parts more volumous then what's beneficial in terms of weight to a solid core model , thus they need to build heavier for the same strenght/stiffness. how much i don't know , the thicker the foil , the heavier it needs to be solid core.

in f3k most of the wing is thinner then this optimum , in f5j for sure most of the wing is thicker then this optimum
Sep 23, 2017, 02:08 AM
1 revolution and throw!
Quote:
Originally Posted by Larrikin
Voted and subscribed.

I'd like to see a performance comparison between a nominal profile, maybe a (Syner) J-100 and a dimpled simulation of the cellulitis.
I'd do it myself but I don't understand XFLR5 well enough.
D.

yes i would like to see it too, but can it be done,

another thing i like to discus is the shape stability of hollow wings and thermal expension due to sunlight radiation on it!

i made a quick drawing to show my toughts on this one , these are just asumptioms don't take them for granted!!!!

looking for someone who did tests/calculation on this, maybe in full scale this has been done???



airfoil with sun radiation on top,
the upper part of the airfoild expands due to heating up +++++(i only did the part in front of the hingeline)
the bottom part of the wing remain cool so the wing should defrom i think?
because it expands it will get longer pushing the LE forward and down , after the spar pushing the hingeline down.
causing a flatter bottom part of the airfoil.

Could there be any thruth in this???


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