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

[schu]

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.

[Bcone1381]

I'm enjoying this thread.

[Bdflies]

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.

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

[Battson]

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."

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

[Battson]

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.

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).

[zkelley2]

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.

[schu]

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.

[svyolo]

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.

[schu]

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.

[Battson]

The problem is, can you fit a 70" moose head in a Bearhawk?!

Schu, maybe you need another wing strut with a cabane

[schu]

Cows and yearlings are much tastier! :-)

[whee]

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.

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.

[Nev]

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.

[whee]

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.

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.

[whee]

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.

[Brett795]

Where’s your battery placement at? I’m guessing firewall if your trying to move the cg forward?

[whee]

Brett, I mounted two pc680s on the firewall.

[Battson]

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.

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.