# What is worth a few pounds?

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#### GESchwarz

##### Well-Known Member
What is the max AGL that geese have been found to fly?

Weight?...

My seats are custom; designed to compress vertically about 10" in a high g vertical impact with the ground. That costs some weight in tracks and foam blocks and related structure.

Folding wings for transport on the highway and storage.

Aft tandem seat 360 swivel feature for awesome rear view experience and to shoot down bogies on my six.

Three piece sliding canopy (like the T-28) so my tail gunner can ride in an open cockpit if he or she desires.

##### Well-Known Member
What is the max AGL that geese have been found to fly?
High above my maximum planned altitude (FL250)..

#### DarylP

##### Well-Known Member
The glass windshield would be heavy, but if you have the cash it would be an interesting test. I want to make a comfortable very lightweight seat, as seats are so heavy. Now by lightweight I do not intend to imply that it would not be strong.

Of course you could always fill your tires with helium. :roll:

#### JimCovington

##### Well-Known Member
One thing that hasn't been mentioned, and makes you much safer in a crash, is pilot weight.

Before I go any further - I'll say that I have a few pounds to drop myself.

Want to save 10 lbs in a 1000 lb plane? Skip the expensive carbon cowling and hit the gym. Being fitter and carrying less weight to the scene of a crash does wonders for your survivability.

##### Well-Known Member
Of course you could always fill your tires with helium. :roll:
And end up flying upside down :gig:

Want to save 10 lbs in a 1000 lb plane? Skip the expensive carbon cowling and hit the gym. Being fitter and carrying less weight to the scene of a crash does wonders for your survivability.
Good remark! Unfortunately I'm 135 lbs and 5'10"

You can also save a considerable amount of weight by throwing out all non-electrical instruments. Something like the Garmin G3X is incredibly light, especially compared to all those analog instruments.

#### WBNH

##### Well-Known Member
On the topic of polycarbonate (lexan) windscreens...there are many films that appear invisible/nonexistent when applied correctly - many subway trains use them - they are easily replaced when one wants to rid the windows of graffiti. They are a lot better than the tear-offs Nascar uses. Most government buildings now, and some private buildings, have this film on the outside of their windows and anchored to the window frames to prevent glass spawl from becoming a cuisinart to the occupants inside in the event of another OK City. The million frame for second footage of the testing is impressive. I just don't know of vendors that sell in small enough quantities to accommodate a home builder.

#### WonderousMountain

##### Well-Known Member
Fuel efficency. I don't care how much I weigh, I'm being carried any case. Only how much it takes me to get to where I'm going.

Wonderous Mountain

#### GESchwarz

##### Well-Known Member
I recently spent about two weeks (a couple of hours per night and several hours on Saturdays) of what would have been devoted to building, on milling off excess steel from my wing hinges. Total weight loss was about 8 pounds. Was it worth it? I think so.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Reasonable weight gains? These are flying machines.

That being said, my items that added weight above minimum in a serious traveling machine that can also do gentleman's aerobatics:

1/4 Plexi Windshield, compound curved, and well supported. This cuts down on prop noise and makes it more bird-strike resistant than just about any other combination and it cost me about two pounds;

Canopy/Roof is designed as a rollover structure. If the poor thing ends up on its back sometime, I want enough room to survive the upset and be able to squirm out, added maybe seven pounds;

Gullwing doors that are stiff with quick release pins. They allow easy baggage access including bags of skis and snowboards, and can be jettisoned for emergency egress. My doors have 3/4" thick sections and weigh five pounds apiece. I have seen flimsy doors that weigh two, so I added maybe six pounds here and they are stiff enough to keep the seals seated at high cruise;

Wittman style landing gear - they weigh a few pounds more than oleo struts, but have to be lower maintenance than a self designed oleo strut set - ten pounds?

Push-Pull Rod controls for aileron and elevator control - much lower control friction than cables, and only cost me a couple pounds - all those pulleys and their mounts weigh something, and the bellcranks have to be there anyway;

6G design in fiberglass means 12G overall design - Mostly this is beefier main spar and inboard drag spar. Most other places, like tail parts, minimum gage of lamina had already got me there. Why 6 G? First is those aerobatics, and then the cruise to stall speed ratio is kind of high - a 4 g airplane would have a Va that was just way too low to be a useful traveling airplane. This cost me about 16 pounds;

Cockpit and seat mounts designed to stand a 19g crash landing stroke. Better the bird than me, and it added 6 pounds;

Total added weight is about 50 pounds on 1200 pound empty weight bird. I probably would have added that stuff anyway, but I justify this weight to myself because I went after weight savings in my construction. By vacuum bagging and using knitted fabrics for virtually the whole airframe, and carefully tailoring sections to follow the loads, I have saved 80-100 pounds over conventional wet layups and straight tapered structures.

Billski

#### orion

##### Well-Known Member
That's an interesting number - 50 pounds. When I was still associated with the CAP back in high school I remember a lecture we attended that looked at aviation safety and crash survivability. The presenters analyzed a slew of accidents whose impacts were not overly severe and yet in which instances all on board were killed. Part of their analysis was concerned with airframe durability and based on that they came up with recommended modifications to classic airplane design techniques that would result in a greater number of survivable forced landings. The results were interesting (and counter to the typical aero class where weight shaving is everything) in that there were several configurational changes recommended to the typical reinforced monocoque structure that for only a slight weight penalty would have made it more of a crash cage rather than just a reinforced fairing. In relation to the subject at hand, the conclusion of the presentation was that just about every four place airplane in production would benefit greatly with a structural weight increase, especially in the area of the cabin. Their data resulted in an average empty weight increase of about 50 pounds.

#### Marc Bourget

##### Well-Known Member
The results were interesting (and counter to the typical aero class where weight shaving is everything) in that there were several configurational changes recommended to the typical reinforced monocoque structure that for only a slight weight penalty would have made it more of a crash cage rather than just a reinforced fairing. In relation to the subject at hand, the conclusion of the presentation was that just about every four place airplane in production would benefit greatly with a structural weight increase, especially in the area of the cabin. Their data resulted in an average empty weight increase of about 50 pounds.
Interesting. Alexander Schleicher did a lot of research on safety (in composites) in the 90's, resulting in their safety cockpits. Instead of making it a "safety cage" (gliders lack the available volume anyway) they used most of the front part of the fuselage to deflect/break, absorbing a lot of the stresses. Then you get something like this. It doesn't look good, but the pilot survived pretty well. It's amazing that sink rates of 10 m/s are surviveable in such a tight cockpit. What amazes me is that so many pilots trade off safety for slightly better looks, or a bit more space.

To add some more points; wheel pants (lower drag), large(r) drag brakes, cabin heat, airco, redundant batteries, adjustable seats.

#### orion

##### Well-Known Member
Wow, that's one of those short field landings I've heard so much about.

##### Well-Known Member
A question in a trade/mission study has always intrigued me.

What would you sacrfice weight for on a design? I'm wondering about were would one add weight specifically.

Assuming a weight conscience builder aiming for the safest low weight possible what would you add for convenience, improved component materials, and for simple whims? I'm looking as much for peoples wish or complaint list as much as a logical choice based on a benefit study.

Me. I am always looking at simple homebuilt designs for cheap recreational flying. Here are some ideas that I often consider.

1- Utilize auto windshield glass rather than the usual plastics. The care required for the plastics and the degraded view with time bugs me. The clarity and easy care of safety glass seems worth a few pounds. I'm refering to the simple flat panel screens like a Fly Baby or a Wittman design.

2- After squezzing my trim 6'2" 280# 56 year old arthritic body head first into the bowels of my Fly Baby cockpit I am willing to sacrfifice weight to allow removeable panels on the sides and bottom of the cockpit area like crop dusters have so one can work on thier machine easily.

3- Designing a comfortable cockpit with a comfortable seat for a fat butt, mine of course. I would never imply anyone else here has a wide rump.

4- The tough engineering questions like how much added weight to sacrifice for lowering drag, ie. cantilevered versus braced surfaces. Or decisions like electric flaps versus manual flaps versus no flaps. Tight tolerance construction suitable to utilize laminar flow airfoils as compared to less critical turbulent airfoils.
For 1- Think about tear-offs such as race cars have on there lexan wind screens, Pull one on your pre/post flight and your clear..... also available with tint.
2-3 My plan to shave weight and build comfort is using trampoline [free from a friend] material laced with bungy or 550 cord to the bottom and back seat frames. This should allow for cool summer and easily warmed spring/fall no extra padding needed seating.... Like your favorite lawn chair.

#### SVSUSteve

##### Well-Known Member
Part of their analysis was concerned with airframe durability and based on that they came up with recommended modifications to classic airplane design techniques that would result in a greater number of survivable forced landings. The results were interesting (and counter to the typical aero class where weight shaving is everything) in that there were several configurational changes recommended to the typical reinforced monocoque structure that for only a slight weight penalty would have made it more of a crash cage rather than just a reinforced fairing. In relation to the subject at hand, the conclusion of the presentation was that just about every four place airplane in production would benefit greatly with a structural weight increase, especially in the area of the cabin. Their data resulted in an average empty weight increase of about 50 pounds.
Hugh DeHaven, more of less the father of crash survivability research once famously stated "We have 40 g people, sitting in 8 g seats, strapped into 10 g airplanes". Now if you revise the g factor upwards to reflect current knowledge of human tolerances, it's more like 90-110 g people which is about where the limit for survivability is believed to lay in your average person with reasonable restraints, etc. Keep in mind that there have been some crashes with data available on them that have shown that individuals can survive a far greater impact. I believe the current record is something on the order of 175-180 g keeping in mind that the person in question was pretty badly injured in that crash which involved a Formula One car into a wall.

#### Aircar

##### Banned
Your windscreen problem can be addressed by using Marguard Lexan (A GE brand) there is also Rhinohide and other surface treated polycarbonate sheet --it cannot be compound curved by heat forming but is easily cut and can be bent gently in one plane. I designed a racecar based on the Chevy Monza body shell in 1982 and substituted the original stock glass windscreen for a Lexan Marguard one that was bent to provide far better aerodynamics with the original "A" pillars becoming faired into aerodynamic slots --the mod was first challenged by the rules committee but conceded to comply with the rules (they changed the rules next year but the car --the Bob Jane Monza -- won the Australian GT class two years in a row ) --they added one requirement for durability --in this case throwing a bucket of wet sand on the screen with the wipers going --no scratches.

You can compensate to some degree by increasing span if the weight is to be increased -- weight is not a direct factor in performance (we even carry three or four hundred pounds of water ballast in gliders --the least likely to add weight on purpose you might think ) -- if you figure out the real effect of slowing down by ten knots say on your typical cross country flight it is most likely only a handful of minutes or the time you take to drink a coffee and the most important area is likely in climb angle (in which case adding winglets might more than pay off or if you are able to justify it structurally adding some span ) sitting more upright might be a good trade off in some gliders --extreme supine seating can detract from pilot performance and if you think you have a canopy clarity problem check out the angle of vision through a glider like a HP 18 --you look through some inches of effective thickness at a very shallow angle .

An adjustable and ventilated seat would be worth a pound or two as would a better undercarriage damper (rigid gear on a fly baby isn't it ?) This sort of thinking touches on the same issue with flying cars --the average four seat car can weigh in at 1800 kilograms (4000 lbs) -- a bicycle can carry one person on road for 18 kilograms --most cars only actually carry one person --where do you draw the line for 'extra comfort' etc here ? An electric bike will add under 10Kgs for example ... the sort of gram by gram weight conciousness as used in man powered aircraft is the opposite end of the spectrum. If the L/D of your aircraft is high you can tolerate more weight and the drag equivalent of weight is smaller --weight times sink rate = drag times airspeed (in the same units ) so you can figure out your trade off .

#### topspeed100

##### Banned
I intent to make the lightest single engine aircraft possible.

Winscreen will be 1-2 mm plexi..and replacaple every summer if necessary.

Braces/struts will be just just 1 meter long ( an hour ago I was still thinking 2 metre ) as short as the design possibly allows.

One wheel buried in the fuse.

5-20 hp engine ( 5 hp at first and if necessary heavier 20-22 hp ).

Aim is to keep it under 70 kg with 3-4 gallons of fuel ( 1-2 if weight goes up ).

Cockpit will be by the nature of the design be "heavily" fortified for safety as well.

Engine will be at the front for the safety ( won't hit you at the back if collided with mother earth ).

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#### topspeed100

##### Banned
Hugh DeHaven, more of less the father of crash survivability research once famously stated "We have 40 g people, sitting in 8 g seats, strapped into 10 g airplanes". Now if you revise the g factor upwards to reflect current knowledge of human tolerances, it's more like 90-110 g people which is about where the limit for survivability is believed to lay in your average person with reasonable restraints, etc. Keep in mind that there have been some crashes with data available on them that have shown that individuals can survive a far greater impact. I believe the current record is something on the order of 175-180 g keeping in mind that the person in question was pretty badly injured in that crash which involved a Formula One car into a wall.
Mika Häkkinen was kept in coma for few days after crashing into a wall at 250+ km/h. I bet he did close too 200 Gs.