I've been going back and reading threads, seeing how in the last year or so there has been a move toward smaller engines in certain "size categories" of aircraft.

For instance, flyers are finding that 50cc engines easily pull around 16-18 lbs planes, the 100 cc motors can handle 40% planes, and even 35-40 cc engines are "normal" on 80-85" planes weighing 13-15 lbs.

The planes have been getting steadily lighter, now being about 25% lighter than just 3 years ago, and the power output (for an engines weight) has increased tremendously over the last 5-6 years. So, it begs to ask, what size engine IS appropriate for a plane these days? So, here's the question/subject I'd like to bring forward. . .

If you had the money to do it all again (build your current plane, or another "favorite" you had in the past) would a re-think of the engine/airframe combination yield a better flying plane for the same money? Could you have actually SAVED money by going to a smaller/lighter engine and modifying the airframe slightly (single in place of a twin, smaller displacement twin for less money, etc.), and let's have some thoughts on "can it be built TOO light" when the total engine/airframe combination is considered.

In my own personal experience, I've found that my 40 lbs 40% CA330sx, with a 3W150 on the nose, is NO match for my radically lightened 28 lbs 40% CA330 with a BME110 on the nose. Both planes came from the same molds, but the performance difference is startling. The 40lbs plane flies very well, but even the simplest pull-up results in the plane "sliding" through the pull, instead of just changing directions. The same holds true for just about any maneuver, and though it is a very good flying plane, it's just no match for it's 30% lighter sibling. The ligher plane is crisper, more reactive, damps out oscillations faster, and accelerates/decelerates quicker. It also required a lower servo count and less expensive hardware to finish it out.

So, let's hear YOUR thoughts on how far this is going to go, and what is practical and do-able NOW.

Do able and practical -
both subjective
For whom?
13 lb 1300 sq in models with 40s are easily do able by good scratch builders .
They are not available for the BARF crowd - so not yet practical .
Having done 40 stuff at 11 lbs --and 100 stuff at almost 30 lbs (they both worked exceptionally well) the envelope of combos is still awfully subjective.
A local guy has a new 40% Cap with a 160 - and I think with pipes it is 34 lbs -
that is another "do able - but as a practical kit - no way . He likes outlandish power -
In contest work - the "best " setups show up differently than the "do able stuff .
Example
my 40 powered 11 lb model (wing loading was 19 oz ft) was tossed around to various TOC pilots for evaluation
The general concensus - Toooo much power and tooo light ---for FAI pattern.
for just plain fun tho--
-very good .
The 2200 sq in 29+ lb Extra- with a small fast revving prop -on a 100 (no tuned pipes) looked wrong -by most stds- but was a winning setup - and super quiet - many would have said -neither do able or practical
i am doing a 1750 sq model with an 80 single -weight likely (base on building 4 others) 23 lbs - as a 3D model
this one fits both do able and practical - as the kit is an ARF and the engine a inexpensive -powerful well proven design.
I would also like to hear other opinions on do able and practical - the general concensus is - -no general agreement!

I recently built a Midwest 80" Extra 300S. 54cc conversion engine on the firewall. All up weight was over 17lbs when it was done.

At 6000' above sea level- there was NO way it would even approach a hover. I never flew it. Sold the plane on Ebay.

A close friend of mine told me to get the airframe as light as possible. This guy knows what he's talking about. He's designed several kits-- some of you are, no doubt, flying some of his planes. I won't drop his name, because it just seams tacky, but, suffice it to say- the guy knows airplane design. The suggestions he had were to scrap the sides and bottoms of the lite ply fuse. and use balsa longerons instead with balsa formers instead of the plywood formers.

It would have been a radical redesign of an old kit. But, looking back, it would have worked well. I just didn't have the confidence to take on such modifications to the kit.

I can only speculate at the weight savings; had I followed his advise. I'd bet it would have weighed somewhere in the 13-14 pound range.

It takes a 50cc engine to hover 15 pounds here at this altitude. Anyone who says otherwise has never tried it or is a flat out lier.

I have just recently completed the maiden flight on the World Models 300S with my 54cc engine up front. I haven't weighed it, but I suspect 16lbs or maybe a bit more. It won't hover.

Just to dispell any doubt, the 54cc conversion engine will turn a 22-8 prop at 6900RPM-- just as good as any DA or BME here. So, it's not that I'm low on power, the engines just loose so much at this altitude that it really takes a lot to hover and do 3D with any authority.

The ARF is just to heavy. I'd have been better off with the MW kit and modified it to lighten the airframe.

Denver elevation and SLC are about the same - so your comments are very understandable
50's hauling 18 lb models is a bit --well -- optomistic.and up here - a no go setup for decent 3Dstuff
Here is a easy to do -unscale project .
Get one of the new H9 LiteSticks - a couple of hundred bucks I think.
buy, beg ,borrow or rent - a 40 gasser .
This setup will give you a model of 1200+ squares and a few lbs lighter than your previous attempts.
This is not a recommended setup for blasting around the skies ---but will give you a good 3D power to weight setup -
For Denver -you will have something that works

any gasser which will spin a 20 x8 at over 6000 will fly it well .
If you are good at conversions -make yer own -
I did a few cloned Midwest Extras - (same size -but my own construction) --they ranged from 11 lbs to 14 lbs .
It can be done but the constructuion is not like the kit -
No carbon needed either .

I have never seen a 40% with a 100cc on it, and nobody I know would do it. I know you did, but your the only one I have ever heard of. If it were me, Id put a 150 on it. But I like big engines.


I have a zdz80 on my Sukhoi, and its a great combo, but Id prefer to have more power, so if I did it over a DA100 would be on its nose, I just got a H9 33% cap, and its getting a DA100. I want more power... I also have a DP Extra with a Brison 3.2 on it. Is it a large engine for its size? you bet it is, is it fun to fly? you better believe it! Id never go back to the Moki 1.8 on it, but I did notice a difference in how it handles.

John - we have had plenty of hands on camparisons of the DA100's to the 80 -- If the 80 has a good exhaust system -it is hard to see the difference in power between that and good running DA100. for example --
If the airframes are both light - - The 100 's typically are stronger -as should be expected .
On the very light airframes - where either setup goes like stink straight up - you have to toss a coin.
The DA100 in any of the H9 models really works - but H9 really frowns on engines over 80 cc for these .
Ask em.
The problem?
guys who fly at one speed - flat out .
Iknow about claimed structural problems - which are simply a result of careless , fast flying
I am doing a new 330 with the 80 and a quiet non tuned can - keeping the weight to mins - but no surgery on structural parts.
At this altitude - they work well to about 26 lbs - after that - just too heavy for sharp performance with the 80's.
My next 100 powered model will be in th low twenties - I am spoiled by the 3D setups I have been building --from Himax powered foamies to big stuff -
We just did a Cap -40% glass fuselage foam wings etc.. with a 210 and large quiet cans -
It should be a good 3Dsetup

If all I was gonig to do was show off how fast the plane was, John, a 150, or larger even, would be the ticket. But, this isn't about mongo-vertical drag races, this is about the entire package and performace envelope. My "normal" 40% with a 3W150 on it has no better performace in either speed or vertical acceleration, yet loses out very badly when it comes to every other aspect of the flight envelope. It can't fly as slowly, smoothly, or turn as precisely as the lighter plane, and every maneuver shows the extra weight when compared to the lighter plane. There are even maneuvers, such as a KE loop, that the heavier plane just can't do anywhere nearly as well, even though the heavier plane has a much stronger servo setup on control surfaces that are the same size, and a lot more power.

This is a direct comparison between aircraft A, and aircraft B, in this case. I already know what the outcome is, but having others voice their opinions and ideas, and to start people thinking "outside the box" is one of the purposes of this thread.

Never mind what I've done, or what others won't do, let's see what CAN be done, envisioned, or set into motion. Only in that way can we go beyond what is already proven, and make it better.

I know Kris, a lighter plane always flies better. We have discussed this at the field, and we would just slam the plane together with a big engine for simplicity. If this was wrong nobody would do it. I personally would love to see yours go, and see what it feels like on the sticks. But its great for others to keep experimenting for everyones better future.

Dick, I know H9 frowns on it, DP frowns on gassers in his planes but I have a 50cc in his DP Extra... Its all about throttle management. I wany my planes to ROCKET out of the hover, I like vertical drag races, and mine loses. Id like to beef up the zdz80 on my sukhoi, but I dont want a hidous tuned pipe setup hanging on the bottom of the plane. Tell me what I can do in the cowl and I might try it out.

As to the "hideous" tuned pipe on the bottom of a plane:

"Beauty is in the eye of the beholder - rocketing out of a hover on a ZDZ-80."

IN the cowl?

Dare I suggest. . drop a 110 Xtreme in there with standard muflers?

The term "rocket" would be an understatement.

Dave Patrick's Edge is almost made to order for a 50 -and is very strongly built.
I did one a couple of months ago - and it was truly a rocket -
frankly I simply didn't care for the model so I sold it -same day - less engine .
The funny part was it is NOT designed for gas - yet--built bone stock -it was tail heavy with the 50 and an in cowl header and large can muffler I made.
I had to move the batts way forward to get a decent snap recovery .
It could be good 3 D model - with some time spent setting up throws .etc.
This one was exactly 15.25 lbs and no add ons whatsoever.
The ne owner just bolted in a 40 and Pitts muffler -and it still goes very well.
As for the horrible pipe setups - yes -they can be a pain but a decent setup can be done with a short can , which fits partway into and along the cowl bottom and over the gear plate.
Better than blowing a bunch for another engine
We have to hold in air noise down here - so the short muffler (not a tuned setup) works pretty good . Also you really can't see it on the ground and is not noticable in the air.
Another trick is do some prop experimenting with shorter blades -and different pitches .
Your 80 should work well on say a 26x12 Menz's clipped and thinned a bit .
I have tried that combo and was very pleased with the results.
Mike McConville- who did the H9 stuff -told me about the various combos they run .
His , has an 80 single with in cowl stuff and works very well - but the one with the GT 80 - which they sell also does a good job once they redo props and mufflers to spin it up over the 7000 mark a fair bit .
The Zenoah's have to really rev to work well.
I have a stack of props I play with which sometimes produces a prop once thought of as a ho hum -which becomes a winner - on the right model /emgine combo
It' fer sher all the chatter about a "best prop"- is just that -
you have to match the setup .
On 3D-- too many times - the flier goes to a large prop - the engine is really not running up in its best power band on hover/ high alpha stuf etc., -so some prop re think can can change things .

I haven't been doing this long so I will say that I have done. Most of my engine selections was basked on the weight needed to balance the plane with the equipment where I wanted it. Sometime this has lead me down a road I don't like having to have a lighter engine than I could find. What I don't want is to get a plane/engine combo then have to put lead in the nose or tail.

Is this not of any concern or do todays engines have enough power to haul around todays monsters of the sky!

Maybe the thing we should be discussing is how the two approaches fly.

I used to build my planes as light as possible.

Aeroworks edge 33% KIT built as light as I could get it with holes everywhere and a BME 6.2
24 1/4 lbs 1950 sq inches if I remember right.
The plane flew very very light but would not enter snaps well. The leading edge was VERY sharp to promote the stall.

Carden edge 35% built stock with DA100 28 1/2 lbs on just over 2000 sq in
The plane does not fly as light as the aeroworks but the snap entry and exit is first class.

In the IMAC schedule I think there are 8 snaps in the advanced schedule so I am very content with the carden.


I think it depends on what you want from the aeroplane.........I did hear that when Somenzini first flew the aeroworks extra at 34lbs he was not happy with some of the flying characteristics and added weight to around 38 or 39 lbs. I think Doug Cronkite would be able to tell us more about this.

Kindest regards IanB