Landing Gear shock absorbing leg design 7

[Drkwing]

I have recently started working in a project about the design of an anmanned Aerial Vehicle (UAV). My responsibility is the design of the Retractable Landing Gear. Based on my lack of previous experience on design of Landing Gears, I started reading on the topic and examination of different uavs on the market today.

The landing gear will be a tricycle one with the main lg legs are probably retracting into the fuselage. For the sake of simplicity regarding main landing gear, I plan to use composite legs without shock absorbers (just like in the GA series, gnat, predator, altus..)
In the concept phase, I calculated the main landing gear load, max kinetic energy to be absorbed, energy to be absorbed by tires. But in the literature the following procedure is the calculation of shock absorber stroke, which is absent on m design.
What is the procedure for calculating the length and section of the gear legs which will absorb the landing energy by deflection?

Any help will be greatly appreciated..
Thanx in advance.

 

[plasgears]

Explore the merits of trailing gear with springs. Jet trainers have this feature to good effect.

Cessna has made use of the spring gear approach in many of their light models. A component of the landing load acts on the gear leg as a cantilever beam. You can go from there.

 

[aerodog]

A landing gear without a shock asorber is a pogo stick.

The Cessna spring gear works because the tires scrub
outboard on landing and act as a shock absorber.

 

[aerodog]

If you have questions about
landing gear loads, FAR Part 23
appendix D has useful equations
for light aircraft.

 

[Drkwing]

aerodog,
Landing gears without shock absorbers are being used on GA UAVs like the predator. They are mostly made of kevlar to absorb landing shocks and they also deflect toward the wings on landing.
Anyone has an idea how to analyze the loads and deflection on these types of main landing gear lags?

 

[aerodog]

Drkwing

In 1964, I designed spring main gears for the Alon Aircoupe. They deflected aft towards the tail. The design replaced the original struts which used Bellville springs. The Bellville's acted as both springs and shock absorbers.

For the first flight, the test pilot was able to log one take off and eight landings. Boing...Boing...Boing, well you get the idea, a pogo stick with wings. There was no damping (shock absorber) in the system.

After we sorted thru the problem, we slimmed down the strut near the axle, so that on landing, the strut would twist causing the tire to scrub and dampen the rebound.

The most interesting aspect of the project was the industrial espionage it took to acquire Cessna's spec on their spring gear. It was a special steel alloy purchased in mill runs. The gears were formed, heat treated to 220,000 psi then shot peened if my memory serves.

 

[FranAle]

Hi,

I suggest you check "landing gear for light aircraft" written by Pazmany. It solve your doubts and give many clues about design and solutions.

Francis

 

[WKTaylor]

You need resources on landing gear design ASAP.

GO TO AIAA website [

http://www.aiaa.org,

publications, educational series] for the following book:

Aircraft Landing Gear Design: Principles and Practices
Norman S. Currey (Author)
AIAA Education Series
Published by AIAA, © 1988, 373 pages, Hardback
ISBN: 093040341X

Also go to SAE website [

http://www.sae.org,

aerospace standards, browse by technology, landing gear & tires/wheels] and review the SAE document lists. You WILL be surprised at data available!!!!

NOTE: MOST SAE documents [ASxxx, AMSxxxx, AIRxxx, ARPxxx, etc] are on-line with IHS "specs and Standards"

Regards, Wil Taylor

 

[Drkwing]

Thank you Taylor, but I already have Currey's book and also Roskam's Part IV on LG design. Although Currey's book is a real good one, the spring gear type that I want to use is not in that book. I am trying to grab a copy of Pazmany's book on light a/c LG.

I will surely look into sae's site.

 

[WKTaylor]

Drkwing...

Also on SAE website... for documents... do an advanced search on "landing gear" and ~150 SAE documents [papers, AIRs ARPs, ASs, etc] are listed.

Regards, Wil Taylor

 

[plasgears]

Go to EAA.org for Pazmany's book and others.