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

Battson

Battson

Moderator
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)
 
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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
 
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.
 
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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
 
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!
 
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.
 
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.
 
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."
 
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.
 
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.
 
Wyo Johnson said:
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
Click to expand...

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

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.

Battson said:
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?
Click to expand...

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."
 
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.
 
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.
 
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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?
 
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.
 
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.
 
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So many factors here.

By real world are you talking about I can go here, but not there? In that case, unless you are flying on the edge of what the airplane can do, I don't think the last 30-50lbs that a diet can remove will make a huge difference.

In this video:

https://youtu.be/CrPJac80W9Y?t=208

They mention that there is an 8kt difference in IAS between light and gross when doing the steep approach. Remembering that momentum is roughly mass * velocity, having a light airplane going 8kts slower is for sure going to matter, but that's the difference between empty and gross.....

I personally think that some weight added for bushwheels (higher AOA on takeoff and landing) and for wingtips (more wing area or effective wing area) makes sense because those changes carry there own weight and probably more, for other stuff like skylight, or seaplane doors, or nicer interior I'm willing to give up some weight because I figure having 50lbs of nice stuff or emergency gear is worth more to me than the 50ft of runway it will buy me.

Anyway to your questions, which without my bearhawk flying is pure opinion based on hearing from other builders and my experiences flying in the back country with an underpowered Cessna 170:
  • 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?
Nobody that I've seen is operating as short as you, and much of it is pilot technique, so unless you climb into a 1300lb airplane, I doubt we will know the answer. I know another fellow that has a bearhawk around 1500lbs and he is doing the same 250ft you are.
  • Are CGs in favourable locations, allowing the plane to use more of the 1,100 lbs (or even 1,300lbs take-off) useful load?
The bearhawk is pretty forward CG with the 540 from what I've seen, so with the lighter engine, I would suspect that you would run out of CG before you got to gross. Here are Eric's tests (http://mybearhawk.com/flying/25hours.html) and looking at those numbers it seems the only way he can get to gross and still have a decent flying airplane is 510lbs in the front seats. Me and my wife are barely 300lbs together, which is why I think the 540 is the right engine for the bearhawk.
  • Is there a measurable fuel economy benefit?
Don't know, but I would surely bet that your power settings and willingness to run LOP would make a much bigger difference than trim drag.


My opinion is that if you can swap out a heavy battery and save 20lbs, for sure do it, or if you can reduce weight by cleaning up unneeded wires/hoses, do it, but I personally wouldn't omit the skylight, or more handles, or lights, or seatbelts.

As for my 170, I do fly into one place that can get pretty tight with a 200lb passenger. So much so that I'm really thinking about how much gear I have. When I roll in there with 100lbs less, it's really a bit nicer. In my 170 it's the difference between 900ft and 800 ft and in a 1000ft strip, that means a lot. I actually prefer windy days for this strip, as you know, even a 5kt wind helps a lot.
 
mike t said:
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.
Click to expand...

I'm with Mike! Battson's plane got heavier and his performance gets better. No doubt, lighter is better. More power is also better. Best of all, is practice, familiarity and pilot skill. I’m nothing more than an average pilot and try real hard to know my limits. We don’t have big rocks and tight canyons around here, but there are lots of little private strips. There’s a strip, not far from here, that I’ve been into a few times. The approaches are tall trees and power lines. The wind has to be just right and I have to "feel it". Spooks the crap out of me every time! My Patrol could weigh 300# less and it would still be 'iffy' at best.

In my book, if I had to take stuff out and have light fuel, to get into an airstrip, I don’t think I'd land there. The downside of finding ones limit, could get expensive!

Bill
 
whee said:
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.



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."
Click to expand...

Thanks for your input Jon, I do appreciate your thoughts given you have some hands-on experience.

I am keenly aware that the community on this forum is a very small portion of the flyers in the Bearhawk family, especially off airport. More's the pity!
There are many BHs operating off airport, I hope one day we can coax them onto the forum with interesting questions and thought-provoking content :)
 
schu said:
So many factors here.

By real world are you talking about I can go here, but not there? In that case, unless you are flying on the edge of what the airplane can do, I don't think the last 30-50lbs that a diet can remove will make a huge difference.

In this video:

https://youtu.be/CrPJac80W9Y?t=208

They mention that there is an 8kt difference in IAS between light and gross when doing the steep approach. Remembering that momentum is roughly mass * velocity, having a light airplane going 8kts slower is for sure going to matter, but that's the difference between empty and gross.....

I personally think that some weight added for bushwheels (higher AOA on takeoff and landing) and for wingtips (more wing area or effective wing area) makes sense because those changes carry there own weight and probably more, for other stuff like skylight, or seaplane doors, or nicer interior I'm willing to give up some weight because I figure having 50lbs of nice stuff or emergency gear is worth more to me than the 50ft of runway it will buy me.

Anyway to your questions, which without my bearhawk flying is pure opinion based on hearing from other builders and my experiences flying in the back country with an underpowered Cessna 170:
  • 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?
Nobody that I've seen is operating as short as you, and much of it is pilot technique, so unless you climb into a 1300lb airplane, I doubt we will know the answer. I know another fellow that has a bearhawk around 1500lbs and he is doing the same 250ft you are.
  • Are CGs in favourable locations, allowing the plane to use more of the 1,100 lbs (or even 1,300lbs take-off) useful load?
The bearhawk is pretty forward CG with the 540 from what I've seen, so with the lighter engine, I would suspect that you would run out of CG before you got to gross. Here are Eric's tests (http://mybearhawk.com/flying/25hours.html) and looking at those numbers it seems the only way he can get to gross and still have a decent flying airplane is 510lbs in the front seats. Me and my wife are barely 300lbs together, which is why I think the 540 is the right engine for the bearhawk.
  • Is there a measurable fuel economy benefit?
Don't know, but I would surely bet that your power settings and willingness to run LOP would make a much bigger difference than trim drag.


My opinion is that if you can swap out a heavy battery and save 20lbs, for sure do it, or if you can reduce weight by cleaning up unneeded wires/hoses, do it, but I personally wouldn't omit the skylight, or more handles, or lights, or seatbelts.

As for my 170, I do fly into one place that can get pretty tight with a 200lb passenger. So much so that I'm really thinking about how much gear I have. When I roll in there with 100lbs less, it's really a bit nicer. In my 170 it's the difference between 900ft and 800 ft and in a 1000ft strip, that means a lot. I actually prefer windy days for this strip, as you know, even a 5kt wind helps a lot.
Click to expand...

Thanks for those thoughts Schu.

On the CG question, I totally agree. The heavy engine makes the plane "work" at 2500-2700 lbs, but only just. I think building super-light would create a problem, because of that situation.

My thinking is much the same in terms of empty weight, if 1000 lbs costs you 8 knots stall speed and it's a diminishing return as the plane gets lighter, best case being 200lbs lighter saves you 1 or 2 knots on the stall for any give payload.

Practically, you are flying the same plane +/- 200 lbs (apart from a small margin, too small to be practically useful).
 
Some real performance numbers - in a C180 -

2000lbs the T/O roll is 295ft. At 2400, 440ft. At 2800, 625ft. SL, no wind, ISA, flaps 20, hard surface.

Interpolating that, in that airplane, each pound added about a half a foot to the takeoff roll.

I can't find landing data for it for multiple weights. I'll take a look at some piper manuals I have tomorrow. I have all kinds of data for larger stuff, but trying to keep it small.
 
I suspect that you could make the 4 place bearhawk work on very short strips using a hot rodded io-370 or whatever and by using minimal interior and avionics and such. If you could get it down in the 1300lb range I bet it would work really really well, especially with the more desirable empty CG due to the lighter engine.

But outside of flying around light and showing off, this airplane would make too many other compromises for my taste. With the 540 you get more cruise speed, you get to load it to gross without 300lb people in the front, you can carry the family and camp or your buddy and a moose out of 800ft safely, then cruise at reasonable speeds on the way home. You can add a skylight or lots of avionics and it's not really going to matter.

So for me, the effort and cost it takes to go super light weight and/or the compromises you need to make to get it there really depend on the mission. If the mission is to land on very short gravel bars for the purpose of playing around with somebody filming like the airplane is a sporty ATV, then I'd argue there are better airplanes for that. If the mission is to land on medium sized gravel bars and bring the family in and out with a critter for the freezer, then you're going to be flying a heavy airplane, one way or another.

I guess it also depends on if your hunting buddy has an airplane too. Many hunters around here fly cubs in packs and can hunt out of 300ft strips, and those that are flying in packs either hunt by themselves and/or they are willing to take 6 trips to get everything out.
 
Schu;
Another problem with added weight, is other than avionics, almost all of it is being added aft of the cg, so you are not just hurting useful load in pounds, you are also losing useful load in CG. Just heavy fabric/paint can cost you almost an inch of cg.
 
Yes I know. Some things don't cost much CG (or even help)

Bushwheels
skylight
seaplane doors (assuming they are actually heavier)
wingtips
Extra fuel tanks
Aluminum under the front doors

However I have added a bit of things that do cost CG:

4 point harnesses in the rear (though removable)
Extended baggage
extra handles on the upper longeron
bush like tailwheel

and so I'll be putting the battery on the firewall (inside).

As for fabric, I've played with oratex, I don't like it that much, I'll be using heavy fabric on the belly, and mid weight on the reset of it, and just work at keeping it as light as I can.

I've also noticed that most builders aren't willing to fly it all the way back at 22.5, but I think that they would be more willing to do so without the servoing trim system. I don't have any hard data on that yet, but I'm inching closer to flying everyday, so hopefully will know more soon.
 
The problem is, can you fit a 70" moose head in a Bearhawk?!

Schu, maybe you need another wing strut with a cabane :)
 
schu said:
As for fabric, I've played with oratex, I don't like it that much, I'll be using heavy fabric on the belly, and mid weight on the reset of it, and just work at keeping it as light as I can.

I've also noticed that most builders aren't willing to fly it all the way back at 22.5, but I think that they would be more willing to do so without the servoing trim system. I don't have any hard data on that yet, but I'm inching closer to flying everyday, so hopefully will know more soon.
Click to expand...

I think you can end up with a really nice paint job that is quite light if you are careful and lay the paint correctly on the first try. We struggled with our paint and therefore have several extra pounds of it. Had we got it right I think out CG would have landed closer to where I wanted it.

I am really excited to see how our BH flies with the none servo trim tabs. We will be thoroughly testing the aft CG to see if we can comfortably fly at the aft limit. I know BHers that will and some that won't fly at the aft limit due to pitch sensitivity so I think it is all relative to the pilot. 21.5 was as far aft as I was willing to go.
 
If I were to lighten my aircraft weight now it would be difficult. I deliberately kept it light during the build, but I wanted an IO540 (I read on the forum that it was the best choice for CG), skylight, and decent avionics. That was my compromise and the final empty weight was 1498lbs. With 29" tires it's now 1508lbs. Currently I'm trying a more aft CG position with an extra 12 lbs added to the tailwheel (This improves the low speed handling a lot, without compromising the payload).

If I built again I'd probably go with an IO390 or similar, but would still have the avionics and skylight. The change in engine selection would be all about improving the empty CG whilst maintaining a good power to weight ratio. I think doing it that way I would also shed 100lbs and move the CG aft to where the full CG range coincides with the full payload envelope. Currently on mine the payload tends to max out before the aft CG limit, and on O360 powered BH's the aft CG limit often restricts the payload.

My Bearhawk gets me into all the airstrips that I want or need to operate into, which is typically 250m -300m at a landing weight of 2200lbs. This allows me a comfortable safety margin.
 
Nev said:
If I were to lighten my aircraft weight now it would be difficult. I deliberately kept it light during the build, but I wanted an IO540 (I read on the forum that it was the best choice for CG), skylight, and decent avionics. That was my compromise and the final empty weight was 1498lbs. With 29" tires it's now 1508lbs. Currently I'm trying a more aft CG position with an extra 12 lbs added to the tailwheel (This improves the low speed handling a lot, without compromising the payload).

If I built again I'd probably go with an IO390 or similar, but would still have the avionics and skylight. The change in engine selection would be all about improving the empty CG whilst maintaining a good power to weight ratio. I think doing it that way I would also shed 100lbs and move the CG aft to where the full CG range coincides with the full payload envelope. Currently on mine the payload tends to max out before the aft CG limit, and on O360 powered BH's the aft CG limit often restricts the payload.

My Bearhawk gets me into all the airstrips that I want or need to operate into, which is typically 250m -300m at a landing weight of 2200lbs. This allows me a comfortable safety margin.
Click to expand...

The thing I like about experimental aviation is we can easily adjust and modify as suites us individually. Nev’s post here exemplifies this.

My Continental IO360 lies right in the between a Lyc 360 and a 540 weight wise. I thought this would give me a great balance in CG and performance. I got what I thought I wanted and have a nicely balanced airplane that flies great with a bit of a load and has wonderful performance. Unfortunately, nearly all of my flying is with my family of 5 and whatever stuff we manage to cram in the plane with us. I’m always running at the aft end of the CG and wishing I had a more forward empty CG. If I were building now or if my use is the same when my engine needs replacement I’d choose a IO470 or 520.
 
Interesting Whee. Could a different heavier prop be a potential solution?
Btw I'm working on a spreadsheet to estimate weight and balance during the build. It's a bit late for you and I, but will hopefully help those currently building.
 
My current prop weighs the maximum amount allowed for my engine. I was going to swap it out for a metal 3 blade until I looked up what the max allowable was. Good thought though.

Good on you for developing a spreadsheet that will help others. I think it will be very useful.
 
Nev said:
If I were to lighten my aircraft weight now it would be difficult. I deliberately kept it light during the build, but I wanted an IO540 (I read on the forum that it was the best choice for CG), skylight, and decent avionics. That was my compromise and the final empty weight was 1498lbs. With 29" tires it's now 1508lbs. Currently I'm trying a more aft CG position with an extra 12 lbs added to the tailwheel (This improves the low speed handling a lot, without compromising the payload).

If I built again I'd probably go with an IO390 or similar, but would still have the avionics and skylight. The change in engine selection would be all about improving the empty CG whilst maintaining a good power to weight ratio. I think doing it that way I would also shed 100lbs and move the CG aft to where the full CG range coincides with the full payload envelope. Currently on mine the payload tends to max out before the aft CG limit, and on O360 powered BH's the aft CG limit often restricts the payload.

My Bearhawk gets me into all the airstrips that I want or need to operate into, which is typically 250m -300m at a landing weight of 2200lbs. This allows me a comfortable safety margin.
Click to expand...

I think that's the point of this thread, as it turned out.
With the IO-540 the plane is perhaps 100lbs heavier, but the sheer power and performance outweighs the weigh.
Pun absolutely intended.
 
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