Weight saving builds, are there "real-world" benefits?

[Battson]

Time for a controversial thread... I am toying with the idea of putting the plane on a diet, but I wonder whether I can save enough weight to realise any "real world" benefits.

I am wondering how much extra utility people are getting from the Bearhawks which are built and flying at very low weights. I am thinking the 1,300 - 1,400lb mark or thereabouts versus the 1,500 - 1,600lbs machines.

On paper it looks good to be 200 pounds lighter, but to coin a phrase - what are the "real world" benefits in a purely practical sense?

• Are people getting very short T/O or landing distances which a heavier Bearhawk cannot achieve? Practically are people going places they couldn't take a heavier Bearhawk?
• Are CGs in favourable locations, allowing the plane to use more of the 1,100 lbs (or even 1,300lbs take-off) useful load?
• Is there a measurable fuel economy benefit?
• Measurably better rate of climb?
• Any other benefits which I am missing?

Here is my use case, with my real world practical hat on:

We tried to avoid adding what I considered "unnecessary" weight during the build. We came out at roughly 1,490 lbs if memory serves.
With the inevitable "bloat" or weight growth over time, we are now closer to 1,590 with the plane fully equipped for backcountry operations (survival gear, tie-down gear / covers, repair tools / spares, maps / charts, cleaning gear, stuff to secure the cabin baggage, etc.). We also have modifications which add weight, big tires and larger (slightly heavier) wingtips. All this in spite of my weight-saving carbon prop and electronic ignition.

Practically, we had our shortest landings ever since the modifications. I had more fuel than ever in the tanks during this year's contest, and we are heavier overall with the modifications. So overall, our performance was improved by modifications which also added weight. So I am turning to the community to get more data-points, is the weight saving worthwhile in a practical sense? Or should I just keep flying the status quo?

Edit (fix spelling mistake)

[Mark Goldberg]

It would seem to me that shorter take off, better climb, and slower approach/landing would be the benefit. But finding actual data to verify would seem easy. Try it with a 200 lb person in the plane, and then with just you Jonathan. That would seem to me a good test. Mark

[Battson]

As you get heavier compared to a fixed amount of horsepower, things definitely get worse. However, there appears to be diminishing returns at the light end of the scale. The plane won't keep flying slower and slower as weight is removed, there are non-linear limits. Practically, of the 100% of places I can take the plane with just one person on board, I can also go to 99.9% percent of those places with two persons on board. The extra person isn't stopping me going places.

There will certainly be a small and measurable difference as weight is saved. Lets not argue that in this thread.

I am keen to know if it practically makes a difference to how the plane can be used, in the real world.

[AKKen07]

At my extreme end of the spectrum - the Citabria I fly is heavier and more CG forward than most which resulted in being slightly illegal on floats in some (most) conditions... On wheels too It also runs out of legal weight very quickly limiting the fuel aboard and range. It has a direct effect on the trips I can take and who I take with me. Sorry I don’t have BH specific data yet... working on that though!

[Wyo Johnson]

Jonathan,

Would a comparison of not only empty weight, but engine and airframe configuration...what I mean by that is there seems to be several engine combos, stretch noses, etc.

Just thinking out loud, but wouldn't the aircraft C.G. location in the C.G. range also impact performance? In other words if you build the airplane nose heavy/empty with the intent to load it...but when it's loaded you aren't mid range...wouldn't that affect performance, especially bush performance?

I remember your thread on CG issues...is there a sweet spot for the aircraft for a specific mission profile? I would really like to see "fleet" numbers on CG location empty.

Andy

[svyolo]

Carrying extra weight costs fuel. Every flight plan I flew for the last 15 years at least had a note in the bottom for how much fuel we would burn, for every 1000 lbs of weight increase, during the course of a flight. It is a big number on a long flight. Carrying 1000 lbs extra might cost over 100 - 200 lbs of fuel. They did that to try to get us to carry less fuel. If a new airplane comes in over weight, the customers usually demand reparations, as the lifecycle cost of operating the airplane goes up. Obviously a light airplane is only going to fly for a few thousand hours at most, vs 100,000 hours for a transport.

Equipment that isn't used, is removed as quickly as possible.

Forward CG also costs fuel burn, ROC, speed, due to trim drag. They try to load bigger airplanes to keep the CG farther aft for the same reason. Easy to do with 200 pax and cargo. Not so easy on a light aircraft.

Personal airplanes are a different animal. Pride of ownership, personal requirements, dreams, etc. If you want a beautiful airplane with a leather interior, it is going to be heavier. If you want "fail operational" IFR capability, it is going to be heavier. But it is also easy to just add pounds due to convenience, and not trying hard.

My dragging racing buddy says the easiest way to get rid of 100 lbs, is to find 1600 ways to remove an ounce.

For a kit builder there aren't that many ways to reduce weight, other than simply installing less. The only things I am changing for sure is the stringer material and floorboards (as time permits). Down the road maybe lighter cargo doors, but that is way down the road.

I am using Oratex to reduce my labor, and make repairs easier. A nice side note is it will save at least 12 pounds, all aft of the CG. I am getting ready to pour lead, I think I will save another 6-8 oz per elevator, plus a similar amount in the aileron balances.

Other than that? Lithium battery. Light prop. Short wire runs. Fabric interior. Thin paint on the wings and cowl. No aux tanks.

I am keeping track of what I add, and subtract. I was heavily in the "subtract" category, until i had a mission creep moment and decided to put a skylight in.

I hope to end up nose heavy. I will just plan to always carry some camping/survival stuff in back. The vast majority of my flying will be over wilderness. I should probably carry it just because it is a good idea anyway.

I don't know what the baseline weight is for a kit. A couple have 540 BH's in the mid 1300 lb range. I am hoping to be there as well. We will see.

So far, here are my "adds":

Skylight 15-20 lbs
EFI 5 lbs
Electrical system 33 lbs (1 lithium battery, 1 alt, 2 VR's) Single EFIS, single com, single xponder, gps.
ext lights 4 lbs

My "subtracts"

CF floorboards 7 lbs
wood stringers 4 lbs
Oratex 15 lbs
Comp Prop 15 lbs
Ti firewall.tunnel 4 lbs

I have also seen several bush planes with some really light looking front seats that look like they are factory made, and comfortable I am going to inquire about them at SNF or Oshkosh.

I was doing good until i decided on the skylight.

My "dream" is max useful load, and passengers who complain about the smell of fish. Others may vary.

[mike t]

Johnno you crack me up, over the last four years your landings at the stol comp have improved yet your airplane has got heavier- at least you haven’t. Best bang for the buck is spending money on avgas .once you’ve got it truly dialled in yes getting rid of some weight will make some difference but not much- but you already know that! I could see losin* some weight making a difference in climb performance but in these type of machines whether you could truly see a meaureable improvement in fuel burn over a trip- I doubt it would be measurable or consistent .Then again as they say no one ever complained they had too much horsepower or there plane was too light.

[svyolo]

Once a plane is built, subtracting weight is very difficult and expensive. Most people won't bother, including me. The day it is weighed the first time, is probably the lightest it will ever be.

One of my "experiences" flying, was the ability to drop 10-25% off the total weight of the aircraft, by hitting one little red button. The airplane instantly felt different, and better. It accelerated, turned, and climbed faster. If you fly a 4 hour flight, and burn 200 lbs (10% of weight of the aircraft) of fuel in a BH, you won't notice it as much because it changed gradually over 4 hours.

I could only come up with a few ways to drop a few pounds from a kit, and I am doing them. On the other hand, I can think of dozens of ways to accidentally, or unintentionally, add weight during a build. I am doing my best to minimize those.

Two of my favorite quotes:

Burt Rutan "When you release something, it should float upwards. If it doesn't, it is too heavy."

Somebody on this forum: "If it isn't there, it doesn't add any weight."

[Chewie]

... And it costs nothing and need never breaks.

[svyolo]

I just did an accurate balancing of one elevator. Bob's estimate for covering/painting is light (10 oz/sq yard) to heavy (20 oz). Oratex is about 6 installed. "Heavy cloth" vs Oratex was 11 oz difference in balance weight. "Light" the difference was 3 oz. Average of 7 oz. So just under a pound out of the tail for balance weight.

[jaredyates]

Can I borrow this for the builder manual? We don't have much input about balancing Oratex.

[svyolo]

I can shoot you a picture by email if you want and I will post it here as well. I think I calculated it pretty accurately. The lead in both elevators is still a little hot. I overshot the pour on one side by probably 6 oz. Maybe 1 or 2 on the other. I will drill some out in the morning until it balances perfectly.

It would be hard to calculate an exact amount for most builders unless they have done a lot of fabric work, and know how much theirs' weighs. Oratex was easy. It is about 5 oz/sq yard, plus I rounded up to 6 oz for glue, tape, etc. Probably a bit conservative.

[Battson]

Jonathan,

Would a comparison of not only empty weight, but engine and airframe configuration...what I mean by that is there seems to be several engine combos, stretch noses, etc.

Just thinking out loud, but wouldn't the aircraft C.G. location in the C.G. range also impact performance? In other words if you build the airplane nose heavy/empty with the intent to load it...but when it's loaded you aren't mid range...wouldn't that affect performance, especially bush performance?

I remember your thread on CG issues...is there a sweet spot for the aircraft for a specific mission profile? I would really like to see "fleet" numbers on CG location empty.

Andy

Yes, I think it does vary depending on the configuration. I didn't want to cut the cake too thinly though, so all comments are welcome.

CG is definitely a factor, a plane with a very light nose or tail will not perform as well as a well balanced plane. In the BH, you are invariable at the forward CG limit when light and the aft limit when heavy.

A heavy tail is necessary in a STOL comp, but in the bush in a practical world, it's the last thing you want. All weight is always stowed forward.

[svyolo]

Yeah, aft CG is better for performance, but can suck for handling qualities. Some very big airplanes have tanks in the tail to manage CG. If you built a light and nose heavy BH, maybe the best place for aux tanks would be right behind the cargo bulkhead.

[whee]

I am keen to know if it practically makes a difference to how the plane can be used, in the real world.

I think it does depending on your "world".

My world seems to be a fair bit different than your world Battson. The area where I'll fly the most has a lot of improved dirt runways which almost any well performing airplane can operate out of. Off-airport landings are strictly prohibited. Extreme STOL performance is not the priority for me. What I need is an airplane that can carry over 1000lbs, 5 people while operating out of 1000ft of dirt. My airplane will just barely accomplish my desired mission.

Your the only one qualified to answer the question you've posed. You are the only off airport operator that actively participates on the forum.

On paper it looks good to be 200 pounds lighter, but to coin a phrase - what are the "real world" benefits in a purely practical sense?

• Are people getting very short T/O or landing distances which a heavier Bearhawk cannot achieve? Practically are people going places they couldn't take a heavier Bearhawk?
• Are CGs in favourable locations, allowing the plane to use more of the 1,100 lbs (or even 1,300lbs take-off) useful load?
• Is there a measurable fuel economy benefit?
• Measurably better rate of climb?
• Any other benefits which I am missing?

My opinion from flying a measly 40hrs in a very light O360 Bearhawk.
1. No, I don't think your T/O or landing distances will change significantly.
2. While there is a correlation between weight and CG I think there are too many builder variables to say either way on this one.
3. No measurable benefit.
4. Not measurably better.
5, Lighter is always better

I'd say remove any easy/cheap weight and forget about the rest.

What's that Cessna nut on BCP say: "Light as possible. Heavy as necessary."

[svyolo]

I think about it like this. If I was building "me", and the rules of the game said that every pound I add now, I have to carry around for the rest of my life. How much weight would I add, and where would I add it.

Just looking down, I would have left off the beer gut and muffin top.

I am doing the best I can on my airplane build.

[Glenn Patterson]

Battson. Your backwoods flying defines your weight. Sounds like you have taken a lot of reasonable & common sense steps to lighten the weight. Any one of the survival/camping items may be life saving. If a person is in the middle of nowhere then there is some essentials in the weight that no one wants to leave behind. The tundra tires adds about at least 40 lbs over regular tires.
We are on a similar mission in that we have built a flying truck for the outback. We are working at putting together a survival kit. 15 - 20 minutes from home in any direction is many hours or days of walking back if it is even possible because it is all heavy bush and lakes. This time of the year the snow is up to the pockets so walking is not happening so may as well build a big fire, throw up some shelter and have something to eat. It is about +5C these days and down to -15C which is mild. For ice fishing we are dressed warm and wear 100 below boots so we could survive a night or few. Even going town to town here is at a minimum an hour over bush and lakes with zero population so it pays to be prepared. We are going to look at a set of floats next week so if they work out it may allow us to use the lakes in summer for some camping & fishing. If a person lives in the middle of no where then there had better be good fishing. I was offered a set wheels when we were building as aircraft come into this country, the wheels are retired then the planes live on floats and skis for the rest of their lives.

Weight savings can get like hp in a hot rod. After the common things the equipment for hp gain gets expensive for little gain. Weight savings and exotic means to save weight fit in the same category. At the end of the day we put a lot of money into the airplane from our perspective and happy our wives still kept us. I think if I had to do it again that I would use Stewart Sytems up to the final coat then use Endura urethane for aircraft fabric to top coat the airplane. Probably half the material cost and more conventional to spray so it would cover & gloss in less coats. I can buy it locally without paying crazy shipping for heavy wet weight. We were half done when I learned of Endura. Hardener in waterborne and solvent urethane is isocynate based which is the same deadly component so may as well go solvent based as it requires the same personal protection and breathing environment controls to stay safe. Endura is Canadian and is an excellent paint line that sprays like normal paint. The waterborne turned out okay but was an exercise in patience and took some practice whereas I could have sprayed the Endura with ease. The Endura tech will recommend the product code for the flexible urethane for fabric. Each gallon of unnecessary paint adds pounds. Paint looks first class and would say it is the best at the flying club but it comes with a penalty.

We added Hall Bros vortex generators on the wings and under the tail to see if we can land slower and get in the air quicker. We have about 20 hours of the 25 hours for Transport Canada to get the conditions lifted off the C of A. Then we will gather some data and put it in write up for the forum completed section.

[svyolo]

I live in "civilization" , but 10 miles in any direction and I am in the middle of nowhere, in very rugged terrain. I will almost always have a basic kit of survival and camping gear, semi permanently installed in the airplane.If I want to take 3 friends on a weekend getaway, and I need the weight, I can remove it. That "kit" will keep my plane well within CG tolerance.

[svyolo]

The effect of trim drag on performance? I had to think about this, hard. I know it adds drag, but how much? I had to simplify it as much as I could to understand it myself.
Here is what I came up with. Feel free to call BS on it I make a bad assumption. This is literally my explanation that I came up with to understand it myself.

Take Jonathons BH, Jonathon, and a full tank of gas For simplicity, lets call it 2000 lbs, and at the forward CG limit. Jon wants to move the CG back 6 inches, and do it as efficiently as possible.
2000 lbs x 6 inches is 1200 inch/lbs.. The tail is 12 feet back. 144 inches. Jon mounts 80 pounds of lead x 144 is close to 1200 inch/lbs.

Which one performs better? 2000 lbs at forward CG, or 2080 lbs at middle CG?
Climbing and cruisng, the 2080 lb airplane does better. The wing on both has to generate 2080 lbs of lift to support the airplane plus 80 lbs of downforce on the tail. The one with 80 lbs of lead in the tail, because of the weight. The lighter airplane the same because the tail has to generate 80 lbs of negative lift to balance the plane. The tail is a horrible wing. Just over 1 to 1 aspect ratio. L/D is probably around 3. To generate 80 lbs of negative life, it is also generating 25-35 lbs of drag. The airplane with the lead doesn’t have this drag.

Takeoff the lighter airplane should win. Same takeoff speed, but the lighter one accelerates faster.
Landing not sure. Landing speed will be the same.

Takeoff at FWD CG might cause some controllability issues. Pitch authority, and pitch rate. If neither of those are a factor, the lighter plane should do a little better. On landing, the forward CG might not allow you to hit the brakes as hard, less weight on the tail. Aft CG might help on landing distance, but this is a bit of a guess.

Real world example? It would take 200 lbs in the last foot of the baggage area to give the same 1200 inch/lbs. Now, the wing has to life 2200 lbs. An extra 120 over the other examples, and the wing will be generating additional induced drag doing so. Probably not worth it.

Mark claims the model B is faster than the A model. I can’t remember, 3-5 mph? If I remember right, he claimed it was due to reduced trim drag. The new wing airfoil requires less downforce, plus the airfoil shaped tail is a bit more efficient?

[Glenn Patterson]

The std Bearhawk horizontal tail is down 4 degrees. We added the flying tail ribs and raised ours to 3 degrees. We were told or read that the tail can be set 2 degrees so we built it with shims that can be removed for the extra degree. The plan is to stick with 3 for now until there is more experience with std BH's flying with 2 degrees.. If the new BH flying tail is at 2 degrees then that is a lot of surface with less forces at play. If the tail is not level then would there would not be drag from some back drafting and the back drafting would get worse with a steeper angle? Just a thought not that I have any real aerodynamics knowledge.