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**rodsmith** · 04-10-2020, 12:04 PM

The biggest factor in controlling weight is what you don't put in it. Plexiglas/lexan is heavy, so a skylight adds weight as does larger windows, lower doors etc. Glass panels are lighter than a panel full of round instruments, but two large screens and associated IFR avionics still adds a lot of weight, bundles of 24 ga wire add more than you might think. The interior is where a lot of weight can be added. Can't beat aircraft fabric for a light interior, especially Oratex if you can afford it. One of the biggest weight savings on the 4-place would be substituting carbon composite doors for the steel frame aluminum covered ones. You need to have the ability/experience to build them or hire some one who does, and accept the additional cost. Weight savings is either what you don't add (saves money) or substitution of materials (how much will you pay to save a pound of weight, titanium firewall instead of stainless etc). The factory does a great job of making a light weight kit, beyond that it is up to you.

**Westward_Flyer** · 04-10-2020, 12:23 PM

rodsmith That makes a lot of sense, when you break it down like that.
Following your post I realize that I'm most interested in areas where substitution of materials can help decrease weight since I really enjoy fiddling with composite construction and don't mind the cost too. Speaking of which I don't know why I hadn't thought of doing the doors in carbon fiber, duh!

Other than the doors and instrument panel are there other common areas of interest for Carbon Fiber aficionados?

**JimParker256** · 04-10-2020, 12:48 PM

Westward,

I think you'd find it pretty tough to build a Bearhawk that is lighter than Bob's prototype... He is the master of minimalism â€“ everything that is required, nothing that isn't. No fancy leather seats, no EFIS or EMS, and a only hand-held radio. I believe that anyone could build a Bearhawk as light as Bob's (especially if you start with the factory QB kit), but most of us won't... We want to add stuff that Bob is satisfied to do without, such as a nicer interior and fancier instrument panels. And big tires... I love the look of tundra tires, but those big tires, double-puck brakes, and tundra tailwheels all add empty weight. If you really need them, then you need them. Folks who really spend time in the back country and need to land on gravel bars, etc. may need them... Battson needs them with some of the places he goes. But for most of us? Well, Bob somehow manages to fly to most of the places we all want to fly, and without the "cartoon tires" on his plane...

As someone once said, the formula for great performance is to "Simplify and add lightness." Or put another way, those features you don't install weigh nothing...

To reinforce Mark G's point above, over on the Backcountry Pilots forum, whenever someone new to backcountry flying asks what they should add to their airplane to be able to fly into those short, high-altitude airstrips, the overwhelming answer is "Avgas â€“ lots of avgas." Go fly the plane as much as you possibly can. Practice in your plane "as is" until you can touch down within 10 feet of your desired landing point â€“ but never land short of that point â€“ 100% of the time. The most capable plane in the world won't help you if your pilot technique isn't at its peak!

In the hands of Mike Patey, Draco is (or was, until it was destroyed in a crash) an incredible short-field performer. In my hands? Well let's just say I won't be trying that any time soon...

**Westward_Flyer** · 04-10-2020, 02:16 PM

JimParker256 I really appreciate your input, it's like you read my mind and then answered the questions that I would of had next. I am really grateful for the many members of this group that have hard earned wisdom and experience and are willing to take the time to share it with us newcomers in a way we can understand. It really helps bridge the gap between where I'm at knowledge-wise and where I hope to be. One of these days I'd love to meet you and see your plane if you'd be willing since I'm pretty close by in Dallas.

**zkelley2** · 04-10-2020, 07:43 PM

I have a full IFR plane at 1395lbs with a 540 in it and 8.00 tires. There's areas I can take some weight off later that the first builder did that added weight and I declined to change initially. I plan on doing the doors in carbon as a seaplane door later this year along with addressing those areas. If you did the most basic panel possible, you could be even lighter. Do the whole cowl out of carbon and have it support itself rather than the u channel would drop some weight to. Not sure you'll ever approach the no electrical system/starter weight, but that's not a reasonable goal.
The real easy ones are fabric - oratex saves somewhere between 15 and 40lbs depending on your skills with the legacy systems, battery - earthx is 10lbs lighter than an odyssey and prop - a carbon 2 blade is about 20lbs lighter than an aluminum.

**Bcone1381** · 04-11-2020, 08:42 AM

So far we have generalities. But The man wants real data. Do we know what a standard finished door weighs? Can someone remove a door and weigh it? Do we know what a composite door weigh? Best practice demands real information. Without info we all we have is speculation.

With that being said, CF is less weight than Fiberglass. But looking at CF over Glass in Dollars it cost per pound of weight savings is very high. We need data on that too. It seems to me like most folk like CF because of appearance, not weight savings.

They say fiberglass is not rocket science. It seems to me that a balsa wood frame door sandwiched in fiberglass would be a good project to try. Throw it out and start over and learn if its ugly. At least we then have some real data for a reasonable cost even it goes in the trash. The sad truth is that the people who are doing the compost modification and could provide the info are in the shop, not on the internet like me to see our request.

$100 for some epoxy, glass, and time is an inexpensive educational opportunity. But for me right now, electrical is my front burner task. Maybe later. But if I want to fly, it will have to weight...I mean wait.

Time to go to work.

**Westward_Flyer** · 04-11-2020, 09:16 AM

zkelley2 That sounds like a good, disciplined build to get that weight with those options. Thanks for the specific suggestions on places to save weight, they're all going onto my list for further research.
Bcone1381 I totally agree with your comparison of CF and fiberglass. People get stiffness and strength mixed up all the time when talking carbon fiber and composites. If you don't need an extremely stiff and thin part then fiberglass can be nearly as strong, or stronger depending on your application and type of fiberglass used and much cheaper. Plus, if you make a sandwich panel like you mentioned then you get a ton of stiffness, more than plain carbon fiber sheet.

Hopefully I'll be able to do some actual hands on research into this and report back with my findings.

Attached is a little table that does a pretty good job of showing the actually differences between the common composite fibers for those who are curious.

**rodsmith** · 04-11-2020, 09:39 AM

This is anecdotal, but I have heard 25# weight savings with carbon composite doors from more than one source. This was 2 layers of carbon on each side of a foam core. I had a very experienced composites guy that was going to help me build them but he has disappeared after spending two long days modeling my plane into solidworks. ??

**Westward_Flyer** · 04-11-2020, 11:36 AM

rodsmith Wow, that is a very significant weight reduction. Also that's a bummer about the help disappearing, especially since this group could really benefit from more 3D modeling available for the bearhawk.

It would be so awesome if either someone was commissioned to professionally 3d model the entire plane or if everyone who has modeled parts could share and compile them in a document available to plans holders only. To help with the cost if someone was to do the project alone or commission it there could be a reasonable fee to access the files. It's a bummer that everyone who wants to work on the plane/plan on their computer has to keep reinventing the wheel by starting from scratch.

p.s. I really don't like the comment within a comment feature on here so forgive me for responding with @ at everyone. I feel like it makes it a little easier to follow the flow of a thread that way.

**Ed Welfred** · 04-11-2020, 08:22 PM

My bare carbon fiber doors (no hardware and no windows) weigh 3lb. - 13oz. That is, as Rod said, 25% less than the 3/4 by .035 steel tubing frame suggested in the Patrol plans. It is a weight savings of 1 lb. per door. It was an interesting project but it would be difficult to justify the extra time I spent making the doors. I suppose the real weight in the doors is in the hardware and the windows. You probably can not make the hardware any simpler or lighter than what Bob suggests in the plans. Have fun Ed.

**svyolo** · 04-12-2020, 06:38 AM

My choices for best bang for the buck per pound saved, in order. These were also my choices.

1. Oratex. It also saves probably over 50% labor savings compared to traditional fabric. My elevator and aileron balances were also lighter by about 5 lbs. Almost all of this weight is aft of the CG.
2. Lithium battery. This might be the cheapest weight savings, and no additional labor. 10 lbs less for 200-400 dollars more, depending on brand.
3. Simple glass panel. I have a 10" GRT, single radio, transponder. <6 lbs total in the panel.
4. Titanium firewall and tunnel. 4 lbs, but extra labor if you have a QB kit. It is "buried". If I didn't do it now, I would never redo it to save 4 lbs.
5. I will only paint the first front 25-35% of the wing. Save money on paint and weight.

If it is on the outside of the plane, or easy swap out later (doors and floor boards), I will do it after it is flying, if and when I get around to it. I would rather get it flying first.

I think I weighed my door frames from the kit at about 25 lbs for the front doors and cargo doors. The .032 floor boards I didn't weight but I think I calculated about 14 lbs. You should be able to drop 6-8 lbs off the floor boards with CF sandwich.

The Comfor foam seat cushions that a lot are using are also pretty heavy. I will be using them anyway to start out with.

The CF cowling I would only attempt if I were set up for Vacuum bagging and was very good at it. It would get expensive pretty quick redoing it 3 times like I seem to do. Come to think of it, it was expensive making the boot cowl 2 times out of aluminum.

**schu** · 04-13-2020, 03:02 PM

ugh, is the Oratex worth it? It's sooooo ugly.... But 40lbs is a LOT. 5lbs less elevator/aileron balances? That matters!

**Battson** · 04-16-2020, 09:49 PM

Originally posted by Westward_Flyer View Post

[USER="1347"]
Attached is a little table that does a pretty good job of showing the actually differences between the common composite fibers for those who are curious.

No surprises there, as weight goes down linearly, cost goes up exponentially. More money you could have spent on AVGAS...

But I get you're a carbon guy - so hang the cost, get a QB kitset, and enjoy tinkering.

**Westward_Flyer** · 05-19-2020, 12:57 PM

Sorry to resurrect and old thread but I didn't think it warranted a new thread. Does anyone know the weight of the 4 place landing gear assembly? All included minus the wheel and tires? Or a best guess? Thanks!

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Has anyone seen a detailed weight breakdown for the bearhawk?

Has anyone seen a detailed weight breakdown for the bearhawk?

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