Is lighter always better?

[Andrew Tinsley]

I started aeromodeling life as a heavy builder. After a lot of effort and pain, I started to build lighter and was really pleased with myself. I am now starting to think that one can go too far with "lightness is everything". I have a nasty suspicion that some of my planes are too light! Adding ballast at the CG makes a couple of my planes track a lot steadier through maneuvers. When the wind gets up, it is even more noticeable.
Can one overdo this lightness thing?

Regards,

Andrew.

[Brett Buck]

I started aeromodeling life as a heavy builder. After a lot of effort and pain, I started to build lighter and was really pleased with myself. I am now starting to think that one can go too far with "lightness is everything". I have a nasty suspicion that some of my planes are too light! Adding ballast at the CG makes a couple of my planes track a lot steadier through maneuvers. When the wind gets up, it is even more noticeable.
Can one overdo this lightness thing?

  Yes. See numerous threads here and on SSW to that effect.

    Brett

[Bill Little]

Like Brett said, it seems the prevailing current thoughts are less concerned with building it as light as possible.  Although I am still not convinced I would say anything to Bill Werwage or Bob Hunt to that effect. (especially Billy!)

Big Bear

[Robert Zambelli]

No!

Bob Z.

[Dan McEntee]

   Every airfoil has a specific wing loading that it operates most efficiently at. No one knows this better than the R/C sailplane guys, and I learned this as a result of competing in R/C soaring events for almost 20 years. Built several models that were ballasted up to optimum performance weight. Stunt model are no different in my opinion, even though they have an engine pulling it along. I don't profess to know all the math and theory involved or can explain it, but I have experienced it first hand in several disciplines of model aviation. The only way I came about it is by trial and error.
  Good luck and have fun,
   Dan McEntee
 Florissant, MO 

[Andrew Tinsley]

Thanks for the information! Now maybe I can use some of that heavier wood that I have been putting to one side!

Regards,

Andrew.

[Scott Hartford]

If there is very little wind, light seems good. If there is a bit more wind, heavier seems best to me.

[dirty dan]

Uh-oh...Sparky Alert!

I have come to the conclusion that stiff models are the best flying pieces even if they tend to come out a bit heavier. So unless it is an OTS model I very much prefer sheeted foam wings, over the past years expanding this to include sheeted horizontal stabilizers and with Pukey Profiles to also use stressed-skin construction in the fuselages.

The latter, with input from Derek, has been upgraded to include what is called Spyder Foam in the 2-pound range, this sheeted with 8- to 10-pound "A" grain balsa. There is no real good way to build a profile fuselage but the latest is my best effort to date.

Dan
 

[Shultzie]

Hey DD!
"GOT PHOTOS"?
Of that lastest new model of your's to share?

Hey Gang...
You can take Dirty-D's conclusion above.."TODA'BANK!"  
Dan is one of the most talented "moneycoat-UltraCoat etc." artists when it comes to awesome blending of both mylar and painted surfaces.  

[Derek Barry]

I agree with the majority. Yes you can build a plane too light. You can build one too heavy too!

[Will Hinton]

I also think straight is the single most important value in any ship.  Even if it's light but not straight, it's a hog!  (Or is that a toad?)

[Randy Powell]

A straight, rigid and reasonably light ship is best. Ask Paul Walker about too light Impacts. As with anything, there is a performance envelope. Yes, it can be too light or too heavy. Depending on the design, this window can be wide or narrow. As a general rule, at the light end of the envelope is better as long as you don't go past the point. So say the weight envelope for a particular design is from 50oz to 64oz (a very wide envelope), you are probably better off nearer the 50oz end than the 64oz end. But if you build it at 44oz, you will probably have to cut down the size of the control surfaces, stabilizer area and possibly decrease the static lift of the airfoil to get maximum performance.

[jim ivey]

I'm a light guy, well im not the plane is! I like em to float, kinda glide through the air. My son left my last  airplane in that sylmar fire. It burned up a near new johnson 35 and that airplane i spent 22 yers building it was 54 inches app 540 sq in and weighed 19.5 ozs I knew it was light but that even surprized me.  yep I  like em lite I'm overweight enough for both of us 

[jim ivey]

I'm a light guy, well im not the plane is! I like em to float, kinda glide through the air. My son left my last  airplane in that sylmar fire. It burned up a near new johnson 35 and that airplane i spent 22 yers building it was 54 inches app 540 sq in and weighed 19.5 ozs I knew it was light but that even surprized me.  yep I  like em lite I'm overweight enough for both of us.    jim

[Howard Rush]

possibly decrease the static lift of the airfoil to get maximum performance.

Huh?

[RandySmith]

I think yes and no, a 10 Ounce  SV-11 would be too light,  and  a 62 ounce Nobler would be  too heavy !!    

But seriously what is important is that the model be withing the designed, or actual weight range. I personally like them to be on the light side of the weight range, and think they perform better.... but I have seen some very good performing heavy airplanes.
The control system will also need to be "in sync " with the airplane , meaning the flap/elev. travel and ratio is mostly affected by the same airplane being heavy or light. Another thing people will do, that works, is make the flaps wider for heavier planes

Randy

[Randy Powell]

Howard,

I was thinking in terms of the lifting potential of a particular airfoil. A Trivial Pursuit airfoil can carry more weight that a USA-1 airfoil. Doesn't make it better, just that it can tolerate a heavier plane.

[Howard Rush]

A Trivial Pursuit airfoil can carry more weight that a USA-1 airfoil. Doesn't make it better, just that it can tolerate a heavier plane.

Why wouldn't that make it better?  I ask because thin airfoils are fashionable lately.  I haven't heard a good explanation that I understood.  I've heard bad explanations that I understood. 

[M Spencer]

Lift / Drag ratios .

Thicker blunter airfoils carry more weight .And have more drag .
But under cornering the percentage drag increase isnt to great
unless their overweight.Where the increased control deflections
cause the overall drag to vary excessively .
The forward C.G. required to stop them being all jumpy requires
the greater control deflections.
Once its approaching the stall , the ' gust response ' or varying
airflow starts to make em awkward to fly accurately.
Also youre overcomeing inertia with brute force .

The THINER airfoils in a say 12.5 Oz/ sq. ft . airframe fitted with
reasonable size control surfaces dont require as much deflection.

If theres not all protrudeing edges and irregularities with the
surfaces near fully deflected its capeable of effecient
adheshion of atmosphere , and the increase in drag turning
is not excessive , also it has RESERVES of performance there
enabling the pilot to crank in more control in big gusts down low
without exceeding the aerodtnamic limits ( STALLING ) .

This makes the sucker easier , or less frightening to fly .
Or requires less aptitude , attention and determination .
As theres a degtee of feedback somewhat reasureing .

The highly loaded, highly powered plane with large deflections ,
use these forces to overcome the inertia.When theres enough
consitant grunt to pull it through the gusts and the prop thrust
is CONSISTANTLY forceing air to respond to the control deflections,
The suckers answering the helm .

Comparisons to differant types of horses , motorcycles or vehicals
can be Apt .

The later type like a modernish vehical on slicks , That slips tather little .

The earier more like a more instantly reponsive type that drifts , predictably
and controlably like the early 70s dunlop racing tyres ( cross plys )
which were highly controlable and 4 wheel drifted with throotle steer.

Or a Clydesdale Vs a Hunter . Wouldnt want to be on the wrong end of either.

Or a Big block Camaro Vs a 74 Escort .

------------------------------------
The original 4 - 2 bit was so the power matched the drag increase in turns , to maintain even airspeed .

The differance between drag ( resistance to movement ) in level , or STRAIGHt flight , and that in round
 manouvers and parts of ( tops , boiioms , up , down ) and that in Squares , is the " drag Evvelope " ,
allowing for variaiations in wind and gusts .                                                                           PHEW .

The responce and consistancy of the powerplat and airscrew balance these forces primarily.

A bit of fancy acting by the pilot at the handle , as per fly fishers and kite flyers can influance greatly the
yaw responce / reaction in these turns. Particularrly tight ones in wind and gusts .

Comparable to a off road ( Rally ) driver in the old rear wheel drive cars. With Blipping stabing and counter steering
to PREVOKE the REQUIRED response from the vehical .

Now we' ll start compareing it to Danceing !! The mind boggles . Partners everyone . State your aeroplane !        Matt.

   . 

[Dwayne]

It's my thinking is that you can't build light enough as long as the model is stiff and strong, then if it is to light for your liking you can always add weight it's very difficult to take weight out.

[Randy Powell]

Matt beat me to it. But I would add that if you use a blunt, thick airfoil and the plane is really light, it's very hard to control turns and transitions. The thing wants to jump around like a hyperactive kid.

[Dennis Adamisin]

Can one overdo this lightness thing?

Regards,

Andrew.

I will probably never know... 

[Brett Buck]

Why wouldn't that make it better?  I ask because thin airfoils are fashionable lately.  I haven't heard a good explanation that I understood.  I've heard bad explanations that I understood. 

     Because with piped engines it's pretty easy to overdo the parasitic drag and get *too much* speed stability. At least that's the issue I have with it. If you try to overcome it by making the engine more responsive, you can easily get too much boost in some conditions, and still not enough in others.

   Bear in mind, I have had a lot of luck with almost comically thick airfoils. I just think I overdid it and it would be better with something less exaggerated now that I know how to get the engine performance I want.

    Brett

[Dennis Moritz]

There's Art here in stunt design. IMHO. Trial and error. Things looking right that work right. Intuition. Evolution of design. Or evolution of design families. It seems to me that precise calculations always leave something out. Often they leave a lot out. Then there is skill in trimming and tuning. Can make a funky performing airplane perform quite well. Despite weight and some questionable numbers. The "scientific" discussions of stunt design, full of equations and what not, remind me of the super computer models of weather patterns. Won't predict the weather for next week. Only do a so so job of predicting the weather of the next few days.

[Steve Fitton]

Huh?

He means to let some helium out of the wing....less static lift.   

[Dennis Moritz]

Some Al Rabe planes weighed a lot. Didn't they.

[Howard Rush]

There's Art here in stunt design. IMHO. Trial and error. Things looking right that work right. Intuition. Evolution of design. Or evolution of design families. It seems to me that precise calculations always leave something out. Often they leave a lot out. Then there is skill in trimming and tuning. Can make a funky performing airplane perform quite well. Despite weight and some questionable numbers. The "scientific" discussions of stunt design, full of equations and what not, remind me of the super computer models of weather patterns. Won't predict the weather for next week. Only do a so so job of predicting the weather of the next few days.

Art or actual science based on experiments and careful observation of the outcome.  I'd rather see reports on how an airplane feels than an attempt at a theoretical explanation.  The trouble with theory in our crowd is: a) that most guys learned it wrong, and b) folks fling around technical terms oblivious of their definitions.  That makes it hard to figure out what's being described.    

[Howard Rush]

    Because with piped engines it's pretty easy to overdo the parasitic drag and get *too much* speed stability. At least that's the issue I have with it. If you try to overcome it by making the engine more responsive, you can easily get too much boost in some conditions, and still not enough in others.

   Bear in mind, I have had a lot of luck with almost comically thick airfoils. I just think I overdid it and it would be better with something less exaggerated now that I know how to get the engine performance I want.

    Brett

If you send me your airfoil coordinates I might do some actual effort and plug them into one of these free CFD programs.  I think maybe a way to approach this is to see what speed (line length or lap time) difference is equivalent to the Cd difference between yours and an Impact or Igor's.   I reckon we'd have to include size, weight, and Clmax in there, too, somehow.   Speaking of Igor and Impacts, I'm going off now to see John Witt to see his new Impact and to try to talk him into machining me an Igor flap control horn slider.

[Larry Cunningham]

I'm guessing electric powered ships might do a bit better with thinner airfoils due to reduced drag. Whereas a large thrust vector countered by a large drag vector offers speed stability (weight vector is porportionately smaller), electric power is a different critter. Witness the difference in props; motor RPM control is more precise.

Of course, another aspect of thicker blunter airfoils is said to be delayed/softer stall characteristics, but are our stunt ships actually approaching stall during pattern maneuvers? (One might argue that thick/blunt airfoils are responsible?)

Somehow I think the optimum conditions sought for our stunt pattern might be satisfied with only slightly more than "adequate" lift and reduced drag to benefit and take advantage of electric drive.  Smaller, lighter battery packs might be another benefit..

Not having built or flown an electric ship yet, I'm simply surmising. Discuss among yourselves.

L.

"Never play cards with a man named Doc, and never eat at a place called Mom's." -John O'Hara

[RandySmith]

If you send me your airfoil coordinates I might do some actual effort and plug them into one of these free CFD programs.  I think maybe a way to approach this is to see what speed (line length or lap time) difference is equivalent to the Cd difference between yours and an Impact or Igor's.   I reckon we'd have to include size, weight, and Clmax in there, too, somehow.   Speaking of Igor and Impacts, I'm going off now to see John Witt to see his new Impact and to try to talk him into machining me an Igor flap control horn slider.

Hi Howard

What format do you need airfoils to be in?

Randy

[Ted Fancher]

I'm guessing electric powered ships might do a bit better with thinner airfoils due to reduced drag. Whereas a large thrust vector countered by a large drag vector offers speed stability (weight vector is porportionately smaller), electric power is a different critter. Witness the difference in props; motor RPM control is more precise.

Of course, another aspect of thicker blunter airfoils is said to be delayed/softer stall characteristics, but are our stunt ships actually approaching stall during pattern maneuvers? (One might argue that thick/blunt airfoils are responsible?)

Hi Larry,  My work with the Imitation (the bluntest of my designs) and its later derivatives argues against the suggestion of "softer" stall characteristics of the blunt airfoil.  The stall is definitely delayed to a higher angle of attack, but when it does stall it does so dramatically.  Two things were obvious in the glide.  First (I'm assuming this relationship), the form drag of the very blunt airfoil made it sort of a pain to whip after the engine quit.  Flying alone it was more work to get it back to the stooge.  Second, if you tried to extend the glide while whipping, keeping the nose high, when it stalled it just literally quit flying. 

The airplane more than made up for it with the engine running, however,  I did some pretty "compact" maneuvers with it during the hundreds of flights it had with the Enya .46 4S and it never even thought about stalling although the wing loading was quite high at around 65oz on a low 600 Square inch wing.

Re how close we fly to the stall (and this is an enlightening response to an earlier post that characterized high wing loadings as hard to fly) the original Trivial Pursuit is a poster boy for such things.  The airplane now weighs 72 oz on its ~ 660 square inches (dang those new pull test rules) and has an enviable competition record; it won the Team Trials in 1993 and has something like six second place Nats finishes over a number of years when it was being "retired" and then pulled back off the wall because I broke something "prettier" although not necessarily "better".  The airplane has flown with engines as small as a VF .40 and as large as PA and RoJett .61s and was competitive with any of them in the front end.

That record sort of puts the kibosh on the suggestion that well designed stunters with high wing loadings are not competitive or are hard to fly.

The other thing that the T.P. taught us is that it was flying very close to the edge with respect to its critical angle of attack.  At a later team trials we were practicing in some damp weather, not real hard rain but a good drizzle.  This airplane that was competitive with the best all of a sudden was stalling dramatically in the last corner of triangles  and the pullout of the hourglass!  I'm not talking a little "blip" and back to work.  It was trying to rekit itself in those corners.

An interesting result of that experience was the band aid we used to eliminate...or at least delay...the stall.  We cut up a set of .018 cables and taped strips of them at the high point of the wing to act as turbulators.  This semi-aerodynamically inspired WAG seemed to do the trick as the stalls went away and I completed the event but was scared to death in each of the "coffin" corners!

I later did something much more sensible and simply increased the flap throw by slowing down the elevators.  It now has "more" than one to one controls with the flaps being the "more".  The turbulators were removed and the ship has flown in damper condition than at that TT with no subsequent stalls.

One last thing of interest is that the T.P. has a noticeably less blunt leading edge than did the Imitation (I thought the IMI airfoil was so blunt it looked...well...uh..."blunt" ugly).  I firmly believe the T.P. would not have been stalling had the leading edge radius been just a tiny bit more rounded.

Somehow I think the optimum conditions sought for our stunt pattern might be satisfied with only slightly more than "adequate" lift and reduced drag to benefit and take advantage of electric drive.  Smaller, lighter battery packs might be another benefit..

We agree totally here, Larry.  I've often stated that we need "enough" lift to support the airplane in the hardest corners the pilot is capably of flying consistently.  Lift in excess of that necessary results in force vectors inconsistent with the direction we want the airplane to fly.  Once again, the success of the original Trivial Pursuit flying on the edge of its capability is a good real world example. 

Another good example was the 3/4" of flap we cut off the entire span of a profile Cardinal that a month later won the Junior National Championship.  The airplane had No Need for the lift generated by the big flaps and the negative pitching moment and huge hinge loads required to deflect them made the airplane very, very difficult to fly.  Removing nearly 50 square inches of unneeded "high lift" device was a huge trimming advance for the pilot and his patterns were dramatically improved instantly because the airplane was no longer fighting him.

Ted

Ted

Not having built or flown an electric ship yet, I'm simply surmising. Discuss among yourselves.

L.

"Never play cards with a man named Doc, and never eat at a place called Mom's." -John O'Hara

[Howard Rush]

What format do you need airfoils to be in?

I'd just use JavaFoil.  Profili may be more wonderful and just as easy, but I haven't used it. Here is the default NACA 0012 in JavaFoil:
1.00000000   0.00000000
0.99726095   0.00038712
0.98907380   0.00153653
0.97552826   0.00341331
0.95677273   0.00596209
0.93301270   0.00911073
0.90450850   0.01277464
0.87157241   0.01686084
0.83456530   0.02127128
0.79389263   0.02590486
0.75000000   0.03065806
0.70336832   0.03542434
0.65450850   0.04009273
0.60395585   0.04454642
0.55226423   0.04866201
0.50000000   0.05231025
0.44773577   0.05535862
0.39604415   0.05767604
0.34549150   0.05913940
0.29663168   0.05964120
0.25000000   0.05909742
0.20610737   0.05745444
0.16543470   0.05469379
0.12842759   0.05083398
0.09549150   0.04592861
0.06698730   0.04006079
0.04322727   0.03333431
0.02447174   0.02586248
0.01092620   0.01775595
0.00273905   0.00911102
0.00000000   0.00000000
0.00273905   -0.00911102
0.01092620   -0.01775595
0.02447174   -0.02586248
0.04322727   -0.03333431
0.06698730   -0.04006079
0.09549150   -0.04592861
0.12842759   -0.05083398
0.16543470   -0.05469379
0.20610737   -0.05745443
0.25000000   -0.05909742
0.29663168   -0.05964120
0.34549150   -0.05913940
0.39604415   -0.05767604
0.44773577   -0.05535862
0.50000000   -0.05231025
0.55226423   -0.04866201
0.60395585   -0.04454642
0.65450850   -0.04009273
0.70336832   -0.03542434
0.75000000   -0.03065806
0.79389263   -0.02590486
0.83456530   -0.02127128
0.87157241   -0.01686084
0.90450850   -0.01277464
0.93301270   -0.00911073
0.95677273   -0.00596209
0.97552826   -0.00341331
0.98907380   -0.00153653
0.99726095   -0.00038712
1.00000000   0.00000000

Looks like it's pairs of points starting at the TE, going forward over the top, then back to the TE on the lower surface.  All numbers are fraction of chord. 
 
My intention was to compare Brett's to something thinner.  You would probably enjoy fiddling with these programs yourself.  Just replace the default numbers with numbers of your own.

[Howard Rush]

Matt beat me to it. But I would add that if you use a blunt, thick airfoil and the plane is really light, it's very hard to control turns and transitions. The thing wants to jump around like a hyperactive kid.

That's better.  You mention turns and transitions.  Was it difficult to change direction in the horizontal eight?  Was it difficult to hold shape on round loops or do accurate corners?   

[Howard Rush]

We agree totally here, Larry.  I've often stated that we need "enough" lift to support the airplane in the hardest corners the pilot is capably of flying consistently.  Lift in excess of that necessary results in force vectors inconsistent with the direction we want the airplane to fly. 

I totally agree that you've often stated that, but I still don't know what you mean.  You seem to be experiencing some real phenomenon, but it's impossible to figure out what it is.  Brett, can you translate?

[Randy Powell]

Howard,

Both. I've actually built a plane that was way too light. A profile with a Trivial Pursuit wing and some tricks I was working on at the time. It was just in clear dope as I figured I'd be cutting and trying different things. weighed about 42oz with a 40VF. It was impossible to smoothly make a transition from inside to outside. The thing would jerk and pop off track (best description I can come up with) and every turn the thing would levitate. You start to make the turn and the thing would almost seem to pull to the center of the figure (sort of the opposite of sliding out of the corner). Very hard to keep on track. Reducing the size of the control surfaces helped a little, but not much. So, after messing with it for a bit, I put it up and forgot about it. After I read description that Ted gave of his plight with the Tucker Special, I pulled the thing out of the rafters and tried it again with about 10oz of ballast at the CG. I have to say when I was originally working on it, it never occurred to me that it was just too light. I didn't think it was possible for a plane to be too light. It actually flew have way decent then. At least it stayed on track and I could put in a reasonably decent pattern with it. Sure convinced me that a plane can be too light.

[Howard Rush]

Interesting comparison.  It ain't like you were comparing different planes with different structures.  Thanks. 

[Dwayne]

Howard,

Both. I've actually built a plane that was way too light. A profile with a Trivial Pursuit wing and some tricks I was working on at the time. It was just in clear dope as I figured I'd be cutting and trying different things. weighed about 42oz with a 40VF. It was impossible to smoothly make a transition from inside to outside. The thing would jerk and pop off track (best description I can come up with) and every turn the thing would levitate. You start to make the turn and the thing would almost seem to pull to the center of the figure (sort of the opposite of sliding out of the corner). Very hard to keep on track. Reducing the size of the control surfaces helped a little, but not much. So, after messing with it for a bit, I put it up and forgot about it. After I read description that Ted gave of his plight with the Tucker Special, I pulled the thing out of the rafters and tried it again with about 10oz of ballast at the CG. I have to say when I was originally working on it, it never occurred to me that it was just too light. I didn't think it was possible for a plane to be too light. It actually flew have way decent then. At least it stayed on track and I could put in a reasonably decent pattern with it. Sure convinced me that a plane can be too light.

Hi Randy
Isn't that kinda what we want though a model light enough so we can trim it by putting the weight on the CG?
An honest question
Dwayne

[L0U CRANE]

...and, if we can build a straight, light model strong enough for the flight conditions, and it turns out too light, we CAN ballast it heavier.

If we'd built it straight and strong enough ...yada, yada... but too heavy, it ain't easy to de-ballast that...

Better to find the approx weight (within a reasonably small range) that design prefers, and build the next one it to almost that weight so you'll have minimum need for ballast to final-trim. IMHO. Never 'been there/done that' but I do examine the comments of those who have and who have the background to understand what's there.

[Bill Little]

It seems the answer to weight lies in the "total package".  A thick/blunt airfoil, "heavier" model can be powered adequately (and then some! LOL!!) so its advantages can be used. 

Maybe that wasn't the case 40-50 years ago when everyone seemed to say "build it light".  The development of power systems has brought about a change in the parameters we have at our disposal when we choose(or draw our own) design these days, IMHO.  I have seen 80 plus ounce airplanes fly quite well, which is something I would have never thought possible.  Building to the "design weight" is the main priority now. 

Big Bear

[Dennis Moritz]

But the winning design (families) diverge, do they not. Sharks, Nobler derivatives (Bears, perhaps the Moonie planes), Patternmaster progeny, the Berringer (sp?) idea, small twisty (I think) flaps, long tail moment, 4 strokes, the Trivial Pursuits, Impacts, and so forth. These ideas for stunt differ (widely?) and have won. Then there are the Bob Barron planes, at least one powered by a Veco 19, I think. Where is the commonality of approach. The moments, weights, airfoils, engines, dunno how all that gets reconciled. Paul Walker's B-17. My thoughts go this way -- towards the divergence of design as opposed to the convergence of design -- partly because I fly with a fellow who's over size blunted, football fat, airfoil, plane seems to have gone it's own way, unlike the aerodynamics of other stunt stuff. Well, might be considered a way big Twister, in aerodynamic approach. That plane is competitive. Aside from a dead reliable power plant and excellent trim, where is the analogy, what's in common?

Heavy and light factors in as well. Joe Adamusko's and Windy's Spits are built light. Dan Banjok, for one, thinks they're the best flying Stunters he's ever flown. Etc., and so forth...

[Dennis Moritz]

Maybe it's balancing the variables. An Eastern term would fit here. Harmony. Harmonizing. The whole more than the sum of the... irritable, irritating, specifics.

[Bill Little]

Hi Dennis,

I agree that it is a matter, to a large degree, of balance.  A Nobler, Ares, Thunderbird, with a Fox .35 can still be competitive to some degree under the right conditions.  But it is so much easier with the better engines, and "fatter" airfoils, we have now.  The K&B .45 was the big hit when Lew McFarland first used one in the "HUGE" (for the time) Shark.  There are .36s and .40s available now that put out much more "useable" power.  Yet a '59 Ares built at 48 oz. will never fly up to its *potential*, regardless of power. 

I would put the modern airfoils in a group under "blunted/thick".  There are some differences when you lay one over the other, but when put together as a group, they are all different from the airfoils in general use in the '50s-'60s.  Modern power allowed the 650-7-- sq. in. models to be able to fly at higher weights with the new airfoils, and actually be an improvement in "bad" air.  Yes they are all somewhat different, but they have common traits in comparison. 

Big Bear

[Larry Cunningham]

Excessive lift is acknowledged; I have also experienced the condition where there wasn't enough lift, and I saw the model "slide" at crucial points such as entry into a wingover. I concluded that the design simply lacked enough "wing" to fly well at our altitude (~4000'), heat (>90F) and low humidity (~20%) ((where's my density altitude calculator - and where's my barometer?)), while ignoring the fact that my model was also quite HEAVY (it was, however, PRETTY).

But I definitely could see it, lacking lift. By the same token, other overweight models of mine (a Mo'Best, with ST51 power) never really experienced that problem with its 28% root and 26% tip NACA00nn wing and relatively large flap areas. And at lower altitudes like Tucson, Phoenix or Dallas, it felt like it was flying in "honey" as we would say, clearly the extra drag associated with the thick wing was noticeable.

The other effects that Ted mentioned, need to whip the model when the engine quits, and abrupt stall to drop were also noted in that design. However, I feel this is a worthwhile compromise and easily adjusted to.

The question comes about, say, if I were to consider an "e-Mo'Best" - profiles are inherently more draggy to start with, and an oversized, overly thick wing seems less likely to be optimum.. The whole stunt IC paradigm of powering the daylights out of a deliberately draggy design with excess lift is likely less applicable.

If more is good, then even more is better - but anything can be overdone - our models are (hopefully) well evolved "optimum" sets of compromises. I'm guessing that changing our power component disturbs the current optimum.

L.

"Unless a man undertakes more than he possibly can do, he will never do all he can do." -Henry Drummond

[Howard Rush]

I'm guessing that changing our power component disturbs the current optimum.

Me, too.  I wonder how.  As a slow builder, I'd like to be able to shortcut a decade or so of experimenting.

[phil c]

One thing not mentioned so far is the size and weight of the lines.  The plane has to generate enough pull to keep the lines tight enough- which is about 2-2.5 degrees  of leadout angle, pretty much regardless of the line diameter.  Typical numbers are 60 oz. for 65ft x .018 lines, or 48 oz for 60ft x .015 lines.  Putting 65 ft. x .018 lines on a light Vector will require over 4.5 degrees of leadout angle, and the plane will still want to come in all the time unless it is coaxed just right.  A 36 oz. Nobler has to fly around 65mph to generate enough pull to fly well, but most people are way uncomfortable flying the pattern at that speed.  The ground comes up too fast.

[Randy Powell]

Dwayne,

Well, I've built 5 of what is essentially the same design. I can tell you pretty well what the optimum weight is for that design. I'd rather not ballast, but then, it's unlikely that that will come up again for me. More like trying to figure out how to generate more lift on a overweight plane without going 70 mph.

[Brett Buck]

A 36 oz. Nobler has to fly around 65mph to generate enough pull to fly well, but most people are way uncomfortable flying the pattern at that speed.  The ground comes up too fast.

   Its even worse than that - the faster you fly it, the more control load there is, and that neatly negates the benefits of flying your light airplane faster. That's what Ted and I realized that led us to the ballasted Tucker experiment - that you could fly it faster and faster and get more line tension, but you still didn't gain any margin over the Netzeband wall and the airplane didn't fly much better.

    Add ballast, and now the ratio of the line tension to the airspeed was improved and the airplane could actually turn. It could also be flown more slowly, since now the tension was adequate even at lower speeds. The more we added, the better it got in every respect - as far as we went, which was *8 ounces* - half a pound - or something like 20% of the unladen weight. it was TREMENDOUSLY better at ~46 oz than it was at 38. It wasn't close, it wasn't subtle, it was *tremendously* better.

    I don't suggest randomly adding dead weight is necessarily beneficial in all cases, but this case unequivocally proves that stunt planes can easily be too light to fly well.

    I note that there are a lot of other ways to affect this ratio, like a huge yaw angle (induced however it might be induced) or excess tipweight, differential flaps, etc. But all of those have far worse, essentially show-stopping, effects on the trim. As long as you have enough ponies to limit speed loss in a square corner, and haul the airplane to the top of the circle smartly, extra weight has very minimal side effects.

    Brett

[Brett Buck]

I totally agree that you've often stated that, but I still don't know what you mean.  You seem to be experiencing some real phenomenon, but it's impossible to figure out what it is.  Brett, can you translate?

    I think "too much lift" is best read as "more lift capability than you need for the rotation rate you are going to use" which is more-or-less a fixed ratio given that the rotation and translation is coupled. The net result being that you track through at a low AoA and generated more hinge moment and adverse pitching moment than would be ideal.

     Brett

[RandySmith]

One thing not mentioned so far is the size and weight of the lines.  The plane has to generate enough pull to keep the lines tight enough- which is about 2-2.5 degrees  of leadout angle, pretty much regardless of the line diameter.  Typical numbers are 60 oz. for 65ft x .018 lines, or 48 oz for 60ft x .015 lines.  Putting 65 ft. x .018 lines on a light Vector will require over 4.5 degrees of leadout angle, and the plane will still want to come in all the time unless it is coaxed just right.  A 36 oz. Nobler has to fly around 65mph to generate enough pull to fly well, but most people are way uncomfortable flying the pattern at that speed.  The ground comes up too fast.

Hi Phil

I have here a 45 ounce ship that flies 6.0 and 6.2 lap times on 66 foot lines eyelet to eyelet, Has very good line tension and is not yawed out much, has zero problems with coming in at you and does not wiggle, or do much of anything abnormal, how are you figuring these numbers? Is there wiggle room for higher thrust with low speed?

Regards
Randy

[Dennis Moritz]

Yeah. I have a 38 ounce Tanager kit bashed into a JD Falcon. Powered by an LA46. Lines are .015 by 63', eyelet to eyelet.  I've been running it in a dead four stroke, little burps in the overhead eight. It was timed at 6 second laps. Definitely stays out on the lines.