Landing gear height

C

CFZVD

New member
Hi Everyone,
I recently joined this group due to a new project that I am working on. I am rebuilding a 7GCBC in a non certified category. I am currently in the process of selecting a landing gear and propeller. I have browsed the forum and have found several discussions with respect to different propeller selections and landing gear height modifications. My current propeller preference is the 8040 which I realize requires extra gear height. I am also aware that the height can be gained either with a different gear leg or larger tire. Does anyone have a measurement of the minimum distance required from the gear U bolt mounting point to the ground required? My measurements indicate that from the gear mount to the propeller centerline is 20", this indicates that from the gear mount to the ground would have to be a minimum of 29"; using a standard 600X6 installation with 7.5" height to the axel C/L, the leg would have to be a minimum of 21.5"? I know the Scout gear has been used on the Citabria, does anyone know how much higher the Scout gear is? Also with respect to handling, what are the consequences of a longer gear and is there an upper limit? I have over 30 years experience messing with different airplanes, however the Citabria is new to me and I certainly welcome your wisdom and expertise.

Thanks,
Brian
 
I don't have specifics for you, but since the Scout with the IO-390 uses an 80" prop, it stands to reason that Scout gear and 8.50x6" tires will get you adequate clearance. You planning a Borer or Sensenich Wood? How do you plan to certify experimental? I've heard even the Cub guys with their non-factory fuselages and such are sometimes challenged to meet the 51% rule.
 
Hi Osxuser,

Thanks for your reply, to answer your questions; I'm planning on one of the Borer props. I've been reading some of the Cub sites and with the 150Hp engines; folks seem to lean toward 8242 to 8245 configurations. I was hoping to get some real numbers from folks with experience using different props. Also, I was looking for a few actual Scout gear measurements; from what I can scale off a basic drawing the Scout gear seems to be about 25" (vertical) from the U-Bolt to the axel centerline and have a stance of about 84"? If anyone can confirm this it would be much appreciated.

With respect to certification, Canada has an uncertified Owner Maintenance Category. Unfortunately this category is not recognized by the FAA and operation in US airspace is forbidden.
 
In the specs pages for the two airplanes the overall height is listed identical at 8' 7". A quick phone call could clear that up though. Even still, a 7GCBC with 8.50x6's can swing a 76" prop, and the scout is listed as a full 11" taller overall. I think he'd be fine with an 82" Borer even.

I didn't know that with those new Canadian rules came the ability to change the design... I thought you could do the maintenance yourself, but still had to follow the book. Learn new things every day.
 
If you go to the Type Certificate Data sheet of the different airplanes it will tell you the combinations allowed by the manufacturer. You could get it certificated in the US but it would be in the experimental category. Unless you could proves the 51% rule. Contact a DAR for more information.
 
There is a proposal to do Owner Maintenance in the US and its reversable as proposed. To reverse it means you have to remove all your unapproved installations to get the airworthiness back. (i.e. keep good records!)

8GCBC Scout gear is the same height aluminum or steel. This is NOT the case for the Citabria/Decathlon gear. There are several heights of the 'short planes'.
 
Actually the owner maintenance category in Canada is very liberal:

http://www.copanational.org/AircraftInCaOwnerMaint.cfm

Reversing back to certified is also possible however totally impractical as it would require rebuild and recertification of all major components plus a complete conformity inspection; for all intentional purposes it's a one way street.

I also own and maintain a certified airplane so I am very familiar with all the normal maintenance and alteration requirements; however I'm looking forward to my Citabria as it is something I can be a bit more creative with.

Jerry, I have read a number of your posts, you seem to have a great knowledge of these airplanes; would you consider providing some project consulting services? If so, please contact me and we can discuss details: canuk1 at nb.sympatico.ca

Thanks
 
On another point, Heights of short planes? How many are we looking at? Are all the steel and all the aluminum the same height at least?
 
Short planes have more history.
Started with the 'straight-leg' 7-1291
Replaced by the slightly taller 7-1404 in about 1970-ish
7-1404 was then used until early 2000's
Then (2003-4-ish) had aluminum 4-2035 and steel 4-2038, both slightly taller yet, to fit the 1950 lbs GW - 8KCAB and 7GCBC
Now in 2012, we have 4-2139 aluminum tapered legs, that are even taller yet for the 76" prop on the Xtreme Decathlon.

At this moment in time, the 4-2139 legs are all thats available as new. Rest is used.

....
And yeah, after 24 years here, I hope I learned something. :)
Usually, my consultant work is to GET certification. But I can help out with whatever.
 
Jerry,

This is really funny, being a complete rookie concerning Citabria's, I did not realize that I was talking to Mr. ACA himself. Regardless, Chad already has my credit card info so I think we are already doing business.

Brian
 
My 1970 had the Straight leg when I got it. I've found it to be somewhat problematic. All the variations are interesting. I've very strongly considered the Aluminum gear. Would really like Scout Alu gear, but nobody seems to have an approval basis.
 
How about Mr. ACA Jr. :p
Anyway, we do what we can. I like the type club as an outlet to see whats happening in the fleet. Need more members!

Scout gear (even the steel) sets up a significant change in geometry. Such that the gear is all happy, but the fuselage becomes an unknown. Obviously, if you grease every landing, you can have gear made of folded paper and be fine. What makes me suspicious, is all the extra meat of the scout frame. Its much more than just 500 lbs of load and it evolved over the years (likely through feild experience). So my feeling on scout gear on a Citabria is that its fine for light/regular duty, but you cannot take it as far as the real 8GCBC can go (not just load, but terrain, treatment, and number od cycles). I have never done any analysis or testing (as you need to measure the dynamics just to get the loads in the first place...'drop testing'). So I cannot quantify how significant the difference is. There are a few stiffeners that fit on the Citabria frame that would change that difference.

That said, the latest 4-2139's should give you about 2 inches; plus the brake line elimination; and about 13-14 lbs. of weight reduction. Its designed for a 76" prop clearance (on the Xtreme Decathlon). They ain't cheap at all, but they are good looking, highly functional, and bolt-on approved. Plus, you can brag about all the 7075 aluminum you now have...okay fine, you wont pick up chicks with that. :p

Leads to the next bush question, and thats tires. The evil you face there is the size of Citabria brakes. 8GCBC's have the double pucks. The single pucks start to get weak once you get to an 8.50x6 tire. Once you consider brakes, Cleveland locks you into different rims too...which leads to different axles for spacing...Yeah, Murphey's Law has full control of you there. I once jested that we should put double puck brakes on all the models so that we can pull in more flip over repairs. My own experience in a 8GCBC landing from the back, I learned how its too much brake...I lost a pair of shorts that day.
 
As far as my research indicates, there is no approval basis for a tire bigger than 7.00x6 on the standard one puck brakes. The sidewall gets into the caliper on the bigger tires. I've been down that road and JUST dropped $2200+ on the "big brake kit" that involves the Cleveland 199-62 (Cessna 180) kit, new solid Alu axles from ACA, as well as some goofy spacers and other odd assorted bits. Now with drawing 4-2042 I'm factory approved up to 29" ABW's. It's particularly nice to have the factory approval so I don't have to mess with an STC, insurance companies want to know about bushwheel STC's...

That was what I was referring to with the "Straight" early gear legs. The normal Citabria mount on the drawing has the calipers behind the gearleg, which I would prefer. They hit the leg in the straight area in back however, so I had to mount them Scout style, in the front. Fortunately, the 1970 model still has heel brakes, so I'm hoping to save the nose-over for another day. I know so many people (especially newish taildragger pilots like me) want toe brakes, but having been forced by my cheapness to buy an old airplane, I quickly learned that heel brakes are FANTASTIC for when you are learning the concepts of tailwheel. Keeps you from dragging brakes before it's necessary... like when you run out of rudder.

Anyway, I don't really NEED the ground clearance for anything, my main desire for the Alu gear stems from wanting to save the weight, and the fact that my steel gear isn't straight, it sits wing-low all the time. The 5K at the moment is going to be going toward the engine fund, since it just hit 2450hrs TTAF/Eng... dang priorities.
 
Indeed. In collage I learned the areodynamics that make airplanes fly. I now know that money is what makes airplanes fly.
 
I just replaced the original steel gear on my 1993 8KCAB with the newest aluminum gear to get the 150lbs gross increase. I am not sure if it is compatible with your project, but if so let me know if you are interested in purchasing the old set.

-Phil
 
philav8or said:
I just replaced the original steel gear on my 1993 8KCAB with the newest aluminum gear to get the 150lbs gross increase. I am not sure if it is compatible with your project, but if so let me know if you are interested in purchasing the old set.

-Phil
Click to expand...

Thanks, but I'm going to save my pennies for the Alu gear, since I've not really had a problem landing the crooked gear much. Unfortunately, the gross weight increase needs metal spars too, which is one solid groundloop away still for me.
 
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