Landing gear thoughts - retract or fixed?

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09-09-2011, 09:21 AM
Mike Switzer

Landing gear thoughts - retract or fixed?

One of the major engineering (and cost) challenges for the design I have been working on is retractable landing gear. Life would be a whole lot simpler if I just went with fixed gear.

What are peoples thoughts on retract vs fixed gear for a 2 seat 200mph design with performance similar to (but slightly heavier than) a Long EZ, RV, Thorp, Mustang II, etc?

How much benefit would you actually see from retractable gear? I know with production 4 seaters it appears to be approx 20 knots difference, (but they aren't as fast as what I am looking at here)
09-09-2011, 09:30 AM
Chad Jensen

IMHO...the weight and complexity of a retractable system to be installed on an airframe that has fantastic performance like those you listed with fixed gear, is not worth the time, effort, money. I used to be a guy that wanted all airplanes to have retractable gear, and I have lots of time in RG airplanes. Other than the "cool factor" of putting the little gear handle in the up position, it's not that big a deal. With an FG airplane, you'll never land it gear up (I hope!), and you won't have gear boxes, hydraulic pumps, actuators, bungees (if needed), etc to worry about.

All that being said...I do think that RG airplanes are fantastic looking in the air (who doesn't think this!?), but you never see it that way in the cockpit.

Also, I am fully supportive of anyone making their airplane RG is the spirit of homebuilding, so either way, you win!

My vote would be to stick with the simple FG design though...
09-09-2011, 09:44 AM
Mike Switzer

Quote:

Originally Posted by Chad Jensen

My vote would be to stick with the simple FG design though...

I'm beginning to think that would be a whole lot easier...
09-09-2011, 11:00 AM
Dana

You get more performance gains by reducing weight than anything else. Retract mechanisms are heavy. Careful attention to drag reduction elsewhere can give you as much benefit as retractable gear, without the added weight, cost, and complexity. But there is the undeniable "cool" factor...
09-09-2011, 03:47 PM
Neil

I for one do not care for the added weight and complexity of the retract gear aircraft. Insurance companies are more than happy to charge more for hull insurance as well.
As for the performance aspect of the retract, look at this years Oshkosh race winner. Bruce Hammers Glasair I with a fixed gear and fixed pitch propeller on a 360 Lycoming was the fastest airplane in the field. I think the speed was over 250mph. There are some Glasair IIIs with 540s and retracts that aren't as fast. I know Bruce and his airplane is not a "Race Only" hanger queen. In fact it is his only airplane. Flys it every where he goes. He even piled a tubing bender and some tubing into it and came up to help build an exhaust system on a friends airplane.

Save the cost and additional weight and pay attention to the wheel pants and intersection fairings.
09-09-2011, 05:08 PM
Eric Witherspoon

I'm with the other guys. Just look at the examples you list. Other than the retract nose gear on the Long, they're all fixed. And I believe those canards don't get hit with much of an insurance penalty because nose-gear-up is designed to be not much of an event (scrape the hockey puck, no prop strike). When it's my money buying every last pump, limit switch, linkage, bearing, etc. I'd much rather be buying a machined steel tube and be done with it. Reminds me of a quote attributed to Bill Lear - "You don't have to fix what you leave out."
09-09-2011, 05:22 PM
Mike Switzer

OK, I'm convinced. Fitting tubular main gear from a 172 would make things a whole lot simpler. (I thought about gear from a 150/152 but that might be a bit light for what I have in mind)

Just gotta decide if I want a steerable or castering nosewheel. I figure castering is probably lighter (and simpler)
09-09-2011, 05:40 PM
steveinindy

Quote:

As for the performance aspect of the retract, look at this years Oshkosh race winner.

Is that limited to piston aircraft?
09-09-2011, 05:45 PM
steveinindy

Quote:

I'd much rather be buying a machined steel tube and be done with it.

The only issue with that is that if you land hard, your spine will be absorbing most of the shock. Worse case scenario, that steel tube is driven back into the cockpit. I've seen this in one crash I went to the scene of; luckily the rod missed the pilots knee (and the large artery located right behind it) by about an inch. One really has to weigh whether you think simplicity is better than an improvement in crash safety or at least figure out how to strike a balance between the two.

Whatever you do, make sure the landing gear are positioned in such a way that if they are driven upward in a crash that they will not strike the fuel tanks or penetrate the cabin. This goes for both fixies and retracts.
09-10-2011, 12:48 AM
Frank Giger

I'll put my vote on fixed gear as well.

Never add a single moving part that isn't absolutely required!
09-10-2011, 04:53 AM
Rick Galati

Quote:

Originally Posted by Mike Switzer

OK, I'm convinced. Fitting tubular main gear from a 172 would make things a whole lot simpler.......

Fitting tubular legs is a sound idea from a practical, economical and efficiency standpoint. Doing so, you should realize that it is very important to install gear leg fairings, wheel pants, and intersection fairings to those tubular legs. In fact, those components are so vital for drag reduction and increased top speed that Van's will tell you fitting those components to an RV will add at least 12 MPH or put another way....the equivalent of adding an additional 27 H.P.!

http://i52.tinypic.com/md2p2r.jpg

Here is an old fluid dynamics video. While the 6 minute video itself is dated, its valuable information is timeless and quite revealing. At the very least, you will come to understand the dramatic drag difference between air flowing over a simple round tube and air flowing over the same tube when aerodynamically faired:

http://www.youtube.com/watch?v=ftq8jTQ8ANE
09-10-2011, 07:52 AM
Mike Switzer

that is a pretty good video
09-10-2011, 04:13 PM
spungey

one hopefully minor issue to consider ... you will also get better insurance rates with fixed gear.
09-15-2011, 08:29 PM
Ron Blum

Awesome videos; check out #2, too!

Quote:

Originally Posted by Mike Switzer

that is a pretty good video

While you're out on YouTube, check out the #2 video of that series, too. Shapiro (the guy doing these experiments) is still used in aerodynamic classrooms today. I especially like the smooth vs. rough ball experiments. It says a lot about turbulent (rough ball) and laminar flow (smooth ball) with respect to positive (back side of ball) & negative (front side of ball) pressure gradients and a little thing called Reynolds Number (illustrated well in the drop tube experiments). These are GREAT videos, Rick! Thanks for sharing! -Ron

Oh, PS, as everyone else has mentioned, I'd go with the fixed gear, too ... unless you're planning to go up in the compressibility (Mach) flight levels.
11-17-2011, 06:45 PM
Mike Switzer

1 Attachment(s)

Well, we took a little trip today to Kankakee & besides getting another 1.9 in the club's Arrow, I picked up these:

Attachment 1117
11-17-2011, 07:27 PM
Bill Barker

1) I agree - Go light with the fixed gear.

2) I vote for steerable nosewheel. With a castoring nose wheel, if the brake fails on one side, you lose steering. Not a pleasant surprise on landing.

Bill
12-29-2011, 03:26 PM
corsair82pilot

Can you get 200 mph with fixed gear?
Here is the gear I built from scratch for my project.

http://www.youtube.com/watch?v=bra3h...ure=plpp_video:
12-29-2011, 03:29 PM
Chad Jensen

Quote:

Originally Posted by corsair82pilot

Can you get 200 mph with fixed gear?

Easily.

Quote:

Originally Posted by corsair82pilot

Here is the gear I built from scratch for my project.

http://www.youtube.com/watch?v=bra3hyUrcuk&list=PL73E6F47D86F72FE7&am p;index= 1&feature=plpp_video:

That's really cool!!
12-29-2011, 09:10 PM
steveinindy

As Chad says, 200 mph in a fixie isn't hard to do. You show me a 350+ knot fixed gear and you can color me impressed. ;)
12-29-2011, 10:43 PM
David Darnell

Well, not aware of many 350 kn homebuilts out there.... About the closest I can think of is/was Wittmans "Bonzo", if you consider a Golden Age Racer to be a homebuilt... Oh, and it had fixed gear..
12-30-2011, 01:22 AM
steveinindy

That's kind of my point. You don't see many 250+ kt let alone 350 kt homebuilts and the few that are out there are general retracts. However, you do see 200 kt homebuilts all the time to the point where the novelty of it has worn off. They aren't quite as reiterative as the various Cub copies but things seem to be rather stagnate at both "ends" of the homebuilt spectrum.

BTW, I had to google this Bonzo as I had never heard of it before. I never realized Wittman did much beyond the various taildragging bug smashers he came up with. Thank you for helping my respect for him grow a little bit more.
12-30-2011, 08:19 AM
Mike Switzer

Quote:

Originally Posted by Bill Barker

2) I vote for steerable nosewheel. With a castoring nose wheel, if the brake fails on one side, you lose steering. Not a pleasant surprise on landing.

That is the route I have decided on. I am now looking for nose gear off a 182 (or a whole plane to strip for parts)