View Full Version : HRII Gear leg fairing cracks

12-07-2016, 07:05 AM
I'm doing some glass work on a friends rocket. The leading edge of both gear leg fairings are cracked at about the half way point. I suspect gear leg flexing during landing is putting stress on the fairings casuing them to crack at the leading edge. Is there a history of this with Rockets and are there better fairings out there that prevent this?

Bob Martin
12-07-2016, 07:33 AM
Can't comment on Rocket fairings but my -6 fiberglass fairings cracked on the top side midway. I wondered why myself but figured it was from gear flexing. Oddly though only one side did it, guess which side?
Now my -6 had 1000+TT with numerous landing and some not so nice. Of course the bad ones were the other guys.:rolleyes:

While doing a FWF update I removed the engine mount to install the vans supplied gussets on the bottom of the gear socket connection. While doing that I cleaned and repainted the landing gear. While handling it I noticed they were not straight. And yes, the left one was bowed or bend more than the right. I was amazed and took them to the machine shop/welder and he used a 100ton press to straighten them. It was slow process but after an hour they were straight. I made new fiberglass fairings and so far so good, but have only flown 10 hours. At some point in the future I will remove the load the check for straightness again to see how they are holding up. Because I am not sure about the affects of spring steel being bent and then restraightened again.
Short answer to your question is check your landing gear to see if it is bent!
Given the Rockets legs are longer then the -6's, seems likely.

RV Jerry
12-07-2016, 09:29 AM
The repair I have done is put a couple of layers of carbon fiber in appropriate places and let the fairing float have done many GLF this way , of course anything can break if hard enough landing. Have used different suppliers and all are about the same

12-07-2016, 10:35 AM
Do the gear legs have wooden stiffeners attached? If not, perhaps there is enough flex to cause this problem. Wonder if he experiences the shimmy some of the Rockets have, might be a factor in cracking the GLF. Again these stiffeners seem to resolve this issue.

12-07-2016, 12:57 PM
If your GLFs get too gnarly to fix, we have more:


12-07-2016, 02:53 PM
Let's discuss this a bit. Think about how the legs on the Wittman gear bend in service: They mostly bend aft and outboard - except in a ground loop, where they bend inboard and aft...bad things happen almost immediately in this situation...

So, if the legs bend outboard, and aft, they will need room to do so inside the fairing - else the fairing will deform, and crack. Thus, the leg needs room to do it's dance without touching the leg fairing.

In flight, the leg is straight, so it can touch the fairings along its inside/lower surface. It should have about 1/2" clearance between the upper/outer surface of the leg and the upper/outer surface of the fairing. This 1/2" of 'wiggle room' keeps the leg from trying to bend the fairings, and the fairings can then live long and prosper (Thank you Mr. Spock).

Builders can shoot about 3-4" of expanding foam inside the fairing to make this space happen, using a small block of wood as a spacer while shooting the foam in place. The spacer can stay in place after the foam hardens.

if you are building an F1 with the supplied upper and lower fairings, the instructions will tell you to have those fairings in place quickly after shooting the foam in so the shape stays correct.

If you are using those same fairings on a different type of plane, it would be a good idea to follow these same directions.


Carry on!

12-07-2016, 09:58 PM

What is this fixation on fixed gear???
So slow...

:-0 btw in fun

12-08-2016, 08:13 AM

Be careful. Retractable gear done less than perfectly is often FAR slower.

If your gear doors don't fit PERFECTLY..... you've just built a very nice, heavier, more expensive, and maintenance unfriendly AIR SCOOP.

There's a reason that fixed gear is still the #1, by far, configuration on anything less than 250mph.

Now.... back to the talk about gear leg fairings....

12-08-2016, 08:24 AM
They do fit perfectly with "hooks" to keep up (lessons learned from a wise Reno man & lovely CF too) and yes you are correct <250 for the fixed gear crowd. I am more interested in 400ish.
:-) Sorry for drift, it was too easy though.....I'll be good now.