Thanks for your efforts, Tony. Even if we don’t need parts right away, the entire group is here to support you. It’s a team effort after 30+ years of people pitching in.
Here is some information for you to consider wrt the nose gear, should you want to make some changes. One of our group members, Imraan, is a aero-engineering professor at Oklahoma State. When he was starting his career, he was in Maryland and bought a Tri-Q200. He used his plane to do instrumented drop tests of the gear, and also did a full finite-element based numerical stress workup of loads on the nose gear. He evaluated the shimmy limiting factors too. He published this study and was kind enough to give me a copy of his paper. I will summarize some of the key points as to how they may relate to any improvements you may decide to make. Imraan monitors the group and he can correct me or embellish as needed. I am also attaching a useful paper on shimmy analysis of a castering nose wheel. I have a couple more papers if you are interested.
Imraan found that the maximum stress on the nose gear occurs in the tight bend near where the nose fork pivot slides onto the gear. This is not surprising, but understanding this reveals two facts: 1That location is the most likely failure point (buckling the back side of the tube near the fork) and 2. Whenever the gear leg is loaded It flexes and reduces the forward rake angle (making it more likely to shimmy).
Below is a key figure from his paper showing stress magnitude color coded to reveal the highly stressed areas when loaded. Warmer colors are higher stress (note the location of the red area, which is the highest stress). The practical demonstration of pushing the leg stress far enough for failure was demonstrated by the guy who bought Earnest Martin’s Tri-Q200. He apparently slammed it into the ground hard enough to break off the fork, right where Imraan’s stress analysis showed it would break.
I notice when I am heavy on the brakes and get down below about 40 mph, mine starts to shimmy also. Probably because, the increased nose down load is pushing it into the unstable zone and/or that same load is flexing the bend enough to reduce the rake (also pushing it into the unstable zone). When I let off the brakes, the shimmy goes away (but so does the pavement on my short runway, so I really have no choice).
If I were to recommend a change to the leg. I would recommend placing a gusset in the tightest part of the bend on the leg (near the fork on the trailing side), in order to more evenly distribute the stress to the rest of the gear leg. This should making the tight bend less prone to failure and less likely to flex and reduce the forward rake of the pivot.
Not sure how this would influence the stiffness/springiness of the gear (already too springy!), but maybe Imraan can chime in on that.
Cheers,
Jay
Bruce, I’m based in Mobile AL. I am still active duty in the U. S. Coast Guard so at this point I am not a business. I am just a guy that didn’t want to see these awesome little planes loose complete support. I was hesitant to take this on in the beginning due to personal bandwidth and my erratic deployment schedule. I have remained in the shadows to learn and gain experience with airplanes before reaching out to the community as a vendor. However seeing the email traffic and need for parts I am trying to get set up sooner than initially planned for high demand parts. First step was nose gear being that it seemed to be a hot topic. I will keep the group informed as we get the tooling set up and workable.
On Jan 29, 2021, at 8:15 AM, Bruce Crain <jcrain2@...> wrote:
Welcome aboard Tony! Where do you live?
Bruce
---------- Original Message ----------
From: "Richard Kaczmarek 3RD" <fastlittleairplanes@...>
To: main@q-list.groups.io
Subject: Re: [Q-List] Nose Gear for Tri-Qs
Date: Fri, 29 Jan 2021 09:02:03 -0500
Tony is going to be the source for all the parts. He is the canard guy that has taken all that over from our shop.
On Fri, Jan 29, 2021, 8:57 AM Bruce Crain <jcrain2@...> wrote:
If you have the fixture from Scott you should be good. He built about 10 gears for me around 2004 and they worked great! Glad you are making the nose gears! The main gears are perhaps a bit easier to find although I don't know who to source for them. Any idea?
Bruce
---------- Original Message ----------
From: "Tony Warnock via groups.io" <tony.warnock=yahoo.com@groups.io>
To: main@q-list.groups.io
Subject: Re: [Q-List] Nose Gear for Tri-Qs
Date: Thu, 28 Jan 2021 22:58:55 -0600
Bruce,
These are being fabricated from the updated fixtures designed by Scott after multiple failures of the original nose gear. If there are updates that need to be made to the newer style legs that reduce shimmy, please advise.
Tony
On Jan 28, 2021, at 10:12 PM, Bruce Crain <jcrain2@...> wrote:
Make sure you have the correct angle with respect to the bottom front of the gear being further forward at the bottom. Otherwise it will shimmy
Bruce
---------- Original Message ----------
From: "Tony Warnock via groups.io" <tony.warnock=yahoo.com@groups.io>
To: "main@q-list.groups.io" <main@q-list.groups.io>
Subject: [Q-List] Nose Gear for Tri-Qs
Date: Thu, 28 Jan 2021 04:54:00 +0000 (UTC)
I have just completed all the machine work and bending of 5 new Tri-Q Nose gear assemblies. We will be doing the final welding this weekend and I hope to have them ready by Monday minus heat treatment. Two of these are already spoken for, so I will have 3 available. If interested please email me privately to discuss your specific needs and prices.
<Nose_wheel_shimmy_theoretical_anlaysis_TKL_FEB_2008.pdf>
