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Ollie Krause

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Feb 26, 2020
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Hi Home Built Airplanes Enthusiasts,

My name is Ollie Krause and I'm happy to introduce Flight Club Aerospace, an aerospace design team organized and run by students from several high schools around the San Francisco Bay Area. Over the past couple months, we've been working to design our own part 103 compliant electric ultralight aircraft which we hope to begin constructing this summer. The Home Built Airplanes forum has been an invaluable resource when designing our wing and fuselage and it was suggested we create our own thread to document our progress and get community feedback. We already have a ton of documentation and resources at FlightClubAerospace.com but we'll try to keep this thread updated with any major changes. We ultimately hope that our ultralight project can leave a lasting educational legacy for students and hobbyists alike through our open sourced designs and resources. We are still early in the detail design phase but here are some photos of our current wing and fuselage designs which can be downloaded, remixed, and viewed in 3D in our public Onshape document.
Wing.jpg
Fuselage.jpg

Here are some quick details on the specs of the aircraft (more detailed resources can be found on our website linked above):

General Design Philosophy:
We aren't professionals and, as high school students, our math abilities are limited at those provided by our school's honors calculus classes. With these limitations in mind, we believe the best way to approach designing our ultralight aircraft is conceptually, basing our design decisions off similar aircraft. Once we have a complete draft of the entire aircraft, we'll follow up with our design mentors and engineers to verify the safety of the airplane before beginning construction.

Wing:
Our wing was heavily inspired by the general wing geometry used by the BeLite ultralights as well as the Affordaplane. Also, the Home Built Airplanes community was super helpful in our wing design process and the thread can be found here. As of this post, we are planning to construct the wing ribs of house insulation foam boards which we will coat in fiberglass on either side and then CNC mill. The rest of the wing is pretty self explanatory and more details can be found in the blog section of our website: FlightClubAerospace.com or on our public Onshape document. We also made our wing fully variabilized so its geometry can be easily adjusted. Here are some general specs of our wing based off some simple calculations and similar aircraft:

Wingspan: 32ft
Chord: 5ft
Dihedral: 3 degrees
Wingtips: Hoerner

Fuselage:
Our fuselage was inspired by the Legal Eagle and uses 6061 T6 aluminum tubes gusseted together. We are designing the fuselage such that no coping is needed to minimize design complexity and make it easier to construct. Please note the fuselage is in a much earlier design phase than the wing and we are yet to determine our wing attachment method.

Powertrain:
We are going to use a 20kw electric powertrain composed of the Rotex Electric REB30 motor, MGM Compro 80120-3EI speed controller, and a 7.08kWh custom battery pack made of 504 Samsung 40T 21700 lithium battery cells. Our current estimates suggest the entire powertrain will weigh around 94 pounds. We've done some pretty extensive research and detailed comparisons to select these exact components and more details can be found from our Powertrain Blog Post.

REB30.jpgHBC.jpg

We'd love to hear the Home Built Airplane Community's thoughts on our designs and are open to any suggestions, concerns, comments, questions, etc. The rest of our team also has Home Built Airplanes accounts and they'll be chipping in below as well.
 

Little Scrapper

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Excellent! Looking forward to your progress. Don’t be shy about asking for advice, materials or money. Many of us here love to donate and help in all 3 areas as long as you have proper initiative and there’s progress being made.
Good luck.
 

Jay Kempf

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I wish you and your team all the best luck moving forward. Hope you can find a way to work on the project even though the school is closed.

I have a question about your fuselage: is the tubing aluminum and how do you plan to join?
 

Ollie Krause

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Feb 26, 2020
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103
I wish you and your team all the best luck moving forward. Hope you can find a way to work on the project even though the school is closed.

I have a question about your fuselage: is the tubing aluminum and how do you plan to join?
Thanks! The tubing is 6061 T6 aluminum and will be connected using CNC milled gussets and rivets. The tubing is 1" in diameter and 0.065" in thickness. We estimate the fuselage will weigh between 30 and 35 pounds once all the gussets and wing attachment beams are added (fuselage pictured above weighs 26 pounds).
 

flywheel1935

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Nov 1, 2018
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Downham Market, Norfolk, Great Britain.
Hi Ollie, I'll be keeping a look at your progress while I re-design my existing LMA kit to comply with a UK microlight spec.
Just a thought, why no go single door, thus keeping the cockpit structure more integral, and allows throttle/trim/etc to be better placed???
good luck.
 

jedi

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Aug 8, 2009
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Sahuarita Arizona, Renton Washington, USA
Triangular tail cone is a good move. 0.065 wall on the one inch tubes may be more than necessary but is more easily sourced. I hope you plan a tailwheel design.

Keep it light. Not easy to do.

How are you addressing the 254# limit versus battery weight issue? Have you contacted Earth Star aircraft for Mark's comments. Hope I got my names right here. Got to run.
 

Ollie Krause

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Feb 26, 2020
Messages
103
Hi Ollie, I'll be keeping a look at your progress while I re-design my existing LMA kit to comply with a UK microlight spec.
Just a thought, why no go single door, thus keeping the cockpit structure more integral, and allows throttle/trim/etc to be better placed???
good luck.
I totally didn't think of that! We were actually thinking of just leaving it open on both sides but maybe adding some sort of simple door might help make it more aerodynamic or at least more comfortable for the pilot. We'll adjust the height of the cabin structure to be at a comfortable height to install our throttle and any other necessary instrumentation. Thanks for the feedback!
 

Jay Kempf

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Triangular tail cone is a good move. 0.065 wall on the one inch tubes may be more than necessary but is more easily sourced. I hope you plan a tailwheel design.
Seen a lot of older designs with the triangular tail boom with the point on top. Seen others more recently with it the other way round. So this drives into loads and structural sizing to counteract loads. In wing spars we normally size the upper spar cap for buckling and the lower spar cap for tensile loads cause most airplanes are designed with the wheeled part down.

For a tail boom the load case is a small downward force at the back meaning the top is in tension bottom in compression. That makes sense but it seems to me that landing loads are the larger consideration. If tail dragger landing shock loads are direct. If not then still tail strike is the worst case mode to consider. Either the weight and cantilever with aero loads plus impulse from a bad landing are the worst case far more than flight loads.

So which way: triangle up or triangle down... ?
 

proppastie

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For a tail boom the load case is a small downward force
pull up from a dive would be a large air load. Glider Criteria has chart based on speed gust loads included, based on sq ft of horizontal tail....You need to load test your whole aft structure to limit load, weights on horizontal tail will also test the tail,...The single tube in compression might be the worse case, so you might load the tail upside down.
 

Jay Kempf

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Landing load most times people us 3G's min. For an ultralight, some have no suspension, just tires the structure can take the hit directly. Tail strike cold be more due to impulse. I always end up convincing myself that landing loads are the worst case when I am looking at a tail dragger. Tri-gear can go either way depending on how you factor the tail strike.
 

Ollie Krause

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Feb 26, 2020
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103
How are you addressing the 254# limit versus battery weight issue? Have you contacted Earth Star aircraft for Mark's comments. Hope I got my names right here. Got to run.
We've been taking a more liberal interpretation where there isn't any battery weight limitation since it isn't technically fuel. We haven't reached out to Earthstar aircraft yet but I've done a little research into the E-Gulls and they all seem to use a battery above the 30lb limit. I came across a magazine article a while back that I've attached to this post which references a 2012 legal interpretation by the FAA where they said the batteries don't count as fuel and instead must be part of the 254lb frame weight limit.
 

Ollie Krause

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Feb 26, 2020
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103
Rearrange the aileron to the end of the wing. The flap will have a large length.
Sorry could you clarify a bit please? We don't have any flaps but we might wanna extend our ailerons since we'll be flying at such low speeds they might not have enough of an effect at their current size.
 

proppastie

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Landing load most times people us 3G's min.
Glider Criteria calls out 4G min. Limit load. Does one want a safety factor of 1.5?.......then design for 6G.....unless its composite where the safety factor is 2....8Gs.....and 3Gs will work if you do not have any 4 or 5 G landings.
 

bifft

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So which way: triangle up or triangle down... ?
I've been running loads on my aerobatic ultralight napkin sketch, and because the vertical stab/rudder extends above the tail the loads end up being higher on the top than the bottom (air loads). My worst case so far has been outside snap rolls which is probably a loading the aircraft being discussed won't see, don't know what the standard part 23 loadings are.

I haven't considered landing loads, but they also put the top in compression, which is often the critical state for a truss. Makes me want to put the single pole on the bottom.
 
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