Hello Home Built Airplanes Forum!,
Sorry for the lack of updates from the fuselage side these past few months!
Fuselage Updates
We’ve been designing and simulating our 4130 Chromoly Steel fuselage through Fusion 360. We needed to
redesign our fuselage because our center of
gravity was too far back, making the plane dynamically unstable in flight.
After simulating our plane at 3gs during flight, we’ve decided to stick with 0.625” (⅝”) diameter tubing with a 0.035” wall as many other ultralights, such as the Legal Eagle, have done. Based on our simulations and other comparable ultralight designs, the plane will be able to withstand these forces. To double check we’ll be joint testing, since Fusion’s simulations can be inaccurate around coped tubes.
Most recent design of the Fuselage:
Fuselage Simulation at 3.8 gs:
We’re working this week to add the struts and spars to the simulation since they will be working with the fuselage as one structure, hopefully helping everything withstand the forces.
Tail Questions
Simulations using XFLR5 told us that we needed a tail with an area of 4650 square inches, and our current design reflects this. However, after seeing the tails of the Legal Eagle and other ultralights, we are concerned by our tail size. At what point do we trust industry standard tail size over our calculations? Does anyone have any advice in terms of calculations to run to determine how large our tail area should be?
Our old fuselage incorporated a 1” OD aluminum tail to match the rest of the truss, however now that we’ve moved to ⅝” steel, we’re unsure of our next steps. We’re trying to keep the tail as light as possible so our center of gravity is as forward as possible (according to our XFLR5 simulations, the optimal center of gravity is at least 5.8” in front of the quarter chord). Until this point we’ve planned to use Airdome extruded aluminum hinges this forum previously recommended, however they only come in one size at 1” OD.
Below is an example from
@radfordc back in May 2020:
We have a couple of possibilities for this which we’d love to get your opinions on:
Option 1
We could keep the same aluminum rudder, elevator, horizontal stabilizer, and vertical stabilizer at 1” x 0.035”:
We’re not expecting massive forces on our tail (likely under 50lbs), and the 1” aluminum should be comparable to the Legal Eagle’s ⅝” steel tail. The advantage of this method is to keep the tail as light as possible, as we could very easily weld our own hinges. For ease of transportation, we’re thinking of attaching the vertical stabilizer with a U channel so it is easily removable. We’re wondering if this forum can see any concerns with this?
Option 2
If a detachable vertical stabilizer would be unstable, we could keep it 5/8 OD steel then weld our own custom attachments between it and the rudder.
Again, the disadvantage would be weight as 5/8 “ steel weighs twice as much as 1” aluminum both of 0.035” wall.
Option 3
Just to throw it out there, the EMG-6 attaches their control surfaces using fork and eye bolts with a rotator bolt.
The advantage of this would be simplicity, however, it would have a lot of pressure and we mostly just wanted to put it out there in case there’s strong opinions for/against.
Option 4
Our last option would be to weld our own attachments and keep the tail 5/8 tail, however, the only advantage to this would be preventing galvanic corrosion and allowing us to weld. It would be more expensive and roughly twice as heavy.
Right now, our biggest concern is keeping our center of gravity as far forward as possible, since our calculations tell us we need it to be around 5.8” in front of the Quarter Chord. Because of the weight concerns, we’re leaning more towards the aluminum tail, however, we’d love to hear from the experts what would be more practical.
Galvanic Corrosion:
Basically all of these options result in aluminum and steel being in very close contact, so we were wondering if this forum had any suggestions in preventing galvanic corrosion?
Thank you as always for all your insightful feedback!
