Landing gear weight

[Doggitz]

Hello everyone!

I put in a deposit on a 7 SS about a month ago. Due July 2020, can’t wait to start building. I have this dream (spelled - hallucination) that I will do some “gentle” back country flying with it - not up to cowboys level, but I want to give it a try. I want to build it asp an LSA. I have been looking at videos and doing as much reading as possible. I really like the shock monster/cabane v arrangement. I have time in cubs, so I’m somewhat familiar with how a cabana works and feels. I have virtually no experience with Grove. I have flown Aeroncas with spring gear.

The combined weight of my wife and I, full fuel, and 25 pounds of camping gear would come to about 520 lbs. using the current LSA maximum (AOPA AND EAA say it’s going up) of 1320, that means the build (I plan a 914 engine) can be no more than 800 lbs. does any one have figures on the relative gear weights? I plan 26 inch tires and likely a bushwheel tail wheel, maybe a Beringer anti ground loop tail wheel.

i would appreciate any thoughts.

Thanks

[Av8r3400]

I won't be popular for this answer, but I see no realistic reason for the "shock" style gear for most situations. If you are doing extreme STOL, off-airport ops, maybe, but for most it is a lot of money, excess drag, and complexity.

I am running Grove spring gear and couldn't be happier with the system for my needs. You can look at my YouTube channel and see how the gear works for me.

[HighWing]

I once contacted Grove to determine the installed weight of their gear for a Model IV. Their website at the time indicated 25 lbs. for the gear. I was told that including mounting brackets and hardware it would be a little over 32 lbs.

[Esser]

Cabane gear is a couple pounds lighter than the Grove (Grove is close to 40lbs I think) but slower. I have a 914 powered Model 7 with a lithium battery, constant speed prop and when I did the weight and balance on 26" tires it came to 878. I have a new project I'm slowing picking on and my goal is under 800lbs and I'm going pretty extreme on the plane's diet to get there. Not to say it isn't possible but just to be realistic, you need to be conscious about saving weight everywhere you can.

[Doggitz]

Thanks to everyone. I’m hoping to get the plane around 825 empty weight. May not be possible with options and reasonable avionics.

[DesertFox4]

Just finished weight and balance on my 7SS. Came out 763 lbs. empty weight. My goal was 750 lbs. I’m very happy with those numbers. 😀 That’s with the Grove gear BTW. I think I can still shave off another 4 lbs. or so with carbon turtle deck in the future and a couple other little items.

[efwd]

Holy cow! thats nearly 80# lighter than mine and you painted it. When you going to reveal it DF4?
Doggitz, 825# is doable. Remove my autopilot system and the second EFIS and Im nearly there. Those little servos weigh a ton. Use Oratex as you mentioned to me before. Other than the Carbon Fiber stuff DF4 has, I am surprised at the result. His plane is well equipped. He didn't use the plastic strut fairings either though. Those aren't light. I watched him put a lot of elbow grease into his fiberglass ones though. Can't wait to see it finished and flying. I have begun making arrangements for the AZ trip. Maybe 23 September. :D

[aviator79]

825 is doable, but I think to get there with big tires and a 914 means some tough compromises. The 914 really wants a constant speed prop to make the most of the turbo.

My airplane is pretty loaded with bells and whistles and weighs in at 875:

914/Airmaster
Autopilot
Poly Fiber
T3 tailwheel
Desser Aero Classic 8.5 x 6 Tundra tires
Plastic fairings on lift and HS struts
Single display Skyview HDX panel
All the comfort/convenience options from Kitfox. (Heater, cabin air, upholstery, etc)


With that as a baseline, carbon cowls, Oratex, no autopilot, and a fixed pitch prop would shave close to 50 lbs, but you're going to gain ~17 lbs back with 26" Airstreaks. I really want those Airstreaks, but if I were concerned about weight and only doing "gentle" backcountry, I'd probably stick with the Dessers. If I weren't flying out of high elevations often, was not going to install a CS prop, and if I was really concerned about keeping weight down, I'd be looking at a 912ULS, perhaps with an aftermarket EFI system to further reduce weight, and get you a little more punch.

If you can, you should go to Stick and Rudder and fly the 914 with a FP prop, and then fly the 912iS with a CS prop before deciding on and engine/prop combo.

[michaega]

Not going to get into the landing gear preference or wheel sizes but do you really need a 914? Had 914 that happened to be more problematic then I cared for. Fortunately I found a 912uls (salvaged motor/ totally rebuilt) and put the zipper big bore 1484cc kit and I’m very happy. Flown into the Sierra mountain and happy with motor. I need to add that the engine is a later 2007 model with thru bolt cases and the cam was replaced with the zipper big bore high performance cam.

[fastfred]

Can you share the list of what you end up doing to it? Hopefully the FAA with boost the gross weight up petty soon for the LSA and won't be an issue for me. I rarely would ever get myself in afield short enough to have a problem. Why do you need it so light with all that power ?You must be off in 150 feet most days?

[GuppyWN]

Not going to get into the landing gear preference or wheel sizes but do you really need a 914? Had 914 that happened to be more problematic then I cared for. Fortunately I found a 912uls (salvaged motor/ totally rebuilt) and put the zipper big bore 1484cc kit and I’m very happy. Flown into the Sierra mountain and happy with motor. I need to add that the engine is a later 2007 model with thru bolt cases and the cam was replaced with the zipper big bore high performance cam.

What’s the HP now?

[michaega]

The zipper 1484 big bore kit will give you 114 hp, add the performance cam and that will bring up to 120 hp. The cylinders are a thing of beauty if your a gear head like me with better finning. Of course I didn’t stop there I have the SDS electronic fuel injection and variable timing also by SDS. Not having a dyno available to me like the Zipper folks have, I can only guess another 5 hp or so.
Pulled out my W&B for the Kitfox 7, it’s 826lbs (nose dragger) with Grove gear, magnum whole airplane parachute, MGL 10” EFIS, a210 com, transp, and iPad.

Zipper makes a bigger bore kit but I still like looking out and seeing the wings in the right place.

btw: I have no stake in either company.

[GuppyWN]

The zipper 1484 big bore kit will give you 114 hp, add the performance cam and that will bring up to 120 hp. The cylinders are a thing of beauty if your a gear head like me with better finning. Of course I didn’t stop there I have the SDS electronic fuel injection and variable timing also by SDS. Not having a dyno available to me like the Zipper folks have, I can only guess another 5 hp or so.
Pulled out my W&B for the Kitfox 7, it’s 826lbs (nose dragger) with Grove gear, magnum whole airplane parachute, MGL 10” EFIS, a210 com, transp, and iPad.

Zipper makes a bigger bore kit but I still like looking out and seeing the wings in the right place.

btw: I have no stake in either company.

I’ll be in San Diego Thursday and Friday. I’d like to chat about your upgrades if you’ve got time. I can rent a car and come up. PM me if that is doable.

[redbowen]

I think there is a great argument for the Shock monster gear, but it is a trade off with cruise speed for sure, you will loose 7-10 mph depending on tires. The gear is far safer and can make a bad grove gear landing look good. It allows for a greater angle of attack on take off and landing because of the higher stance, but hurts the visibility out the front. The TK1 gear legs move the wheels forward a couple inches which really improves the ground handling making it very stable.

The TK1 gear legs and Shock monster shocks are 1.6 lbs lighter than the Grove spring gear. You can shave an additional 4.12 lbs off by using the Beringer wheels and brakes. If you are interested in the Airstreaks in a 26" but plan on using the Kitfox at the LSA gross weight of 1320 lbs than look at the Alaskan Bushwheel Ultralights, the 26" is 3.5 lbs lighter per tire than the Airstreaks. the 29" Ultralight is 6lbs lighter per tire than the Airstreak 29."

Just some ways to save weight.

[Av8r3400]

When I converted my old model IV-1050 from Bungee gear, ATV tires with Douglass wheels and Matco brakes to Grove Gear, wheels, brakes and 21-800/6 tires the net weight gain was:


12 pounds.

[72chevy]

I think there is a great argument for the Shock monster gear, but it is a trade off with cruise speed for sure, you will loose 7-10 mph depending on tires. The gear is far safer and can make a bad grove gear landing look good. It allows for a greater angle of attack on take off and landing because of the higher stance, but hurts the visibility out the front. The TK1 gear legs move the wheels forward a couple inches which really improves the ground handling making it very stable.

The TK1 gear legs and Shock monster shocks are 1.6 lbs lighter than the Grove spring gear. You can shave an additional 4.12 lbs off by using the Beringer wheels and brakes. If you are interested in the Airstreaks in a 26" but plan on using the Kitfox at the LSA gross weight of 1320 lbs than look at the Alaskan Bushwheel Ultralights, the 26" is 3.5 lbs lighter per tire than the Airstreaks. the 29" Ultralight is 6lbs lighter per tire than the Airstreak 29."

Just some ways to save weight.

Not to derail but doesn’t moving the gear further from the CG make the plane less stable?

[redbowen]

Not to derail but doesn’t moving the gear further from the CG make the plane less stable?

It does move the CG aft on the ground which puts more weight on the tail, for ground handling this helps, it also allows for much more aggressive braking. In flight it does move the CG very slightly forward. It is very close to the datum so it doesn't have a noticeable effect. I was skeptical but it really does handle much better.

[Esser]

More weight behind your main wheels in theory should make the plane less stable with ground handling as the weight wants to swap ends. This is why tail draggers ground loop. The weight tries to swap ends. The more weight aft, the worse it it. I understand what you are saying about a longer coupled wheel base which does make the plane more stable. It's be interesting to find out where the sweet spot is.

[RV6flyer]

Cabane gear is a couple pounds lighter than the Grove (Grove is close to 40lbs I think) but slower. I have a 914 powered Model 7 with a lithium battery, constant speed prop and when I did the weight and balance on 26" tires it came to 878. I have a new project I'm slowing picking on and my goal is under 800lbs and I'm going pretty extreme on the plane's diet to get there. Not to say it isn't possible but just to be realistic, you need to be conscious about saving weight everywhere you can.

Josh,

I am building a 5 with a 914/Airmaster. Do have a weight & Balance that you could share with me? What tailwheel do you have?

[Delta Whisky]

I've captured reported weights for some time now and as of now my very limited data base shows:








w/o outliers





w/o outliers


Model

KF4

KF5

KF5

KF6

SS7

SS7


average

676

841

820

906

836

827


Max

793

1,013

890

906

963

878


min

560

777

777

906

736

763


sigma

76

69

35

0

56

33


count

5

9

8

1

19

16


The columns labels "w/o outliers" represent me taking out variants caused by what could be "scale dreaming" and heavy engine choices but still only makes a 9 pound difference for the SS7.






BTW - when I converted to TK-1 shocks (only, not their gear) it cost 8 pounds.