1
$\begingroup$

I'm doing some pre-planning for a bush flight with the Icon A5, and I'm at CoG calculation.

This is the W&B form from the A5's POH: Image of Weight and Balance Loading Form

I weigh 225 lbs. I'm simulating 111.6 lbs of gear which can be distributed between the luggage shelf and the passenger's seat. I then will bring the aircraft to MTOW with fuel.

My W&B looks like this:

Moment Calculation

Position Weight Arm Moment
Dry Weight 1080 154.75 167130
Pilot 225 128.5 28912.5
Passenger 0 128.5 0
Usable Fuel 91.7 153 14030.1
Baggage 111.6 157 17521.2
Garmin 1.7 109.7 186.49
Totals 1509.6 227780.29

TOW 1,510
CG Pos 150.85"

Which puts the CG nearly 3 full inches outside the envelope:

enter image description here

I've messed with the numbers a several ways, but no matter how I do, I can't get the CoG back in the envelope.

Am I missing something about the calculation process here, or is there basically no safe configuration of the A5 with a 225lb pilot?

I will note that MS Flight Simulator 2020 doesn't consider the CoG out of limits (it gets mad at you if it does) but I can definitely tell that takeoff performance is greatly impacted and god help me if I try to takeoff with any kind of right crosswind.

Improve this question
$\endgroup$
8
  • $\begingroup$ The pilot station is a good ways forward of the CG range, are you sure that’s right? Because even though you’re a pretty big dude, two adults will generally exceed 225. Does the POH mention a weight limit for people? I’m trusting your math, but the crew arm seems suspect to me. (although in photos you do sit fwd of the quarter chord.) What’s a twitch channel? $\endgroup$
    – Michael Hall
    Commented Jun 1, 2022 at 15:22
  • 1
    $\begingroup$ Where did you get the dry weight arm? $\endgroup$
    – GdD
    Commented Jun 1, 2022 at 15:46
  • 3
    $\begingroup$ P.S. If you don't get a good answer here call Icon - present the same question and tell them you are thinking about buying one, but only if you can fly with CG in limits! $\endgroup$
    – Michael Hall
    Commented Jun 1, 2022 at 15:49
  • 3
    $\begingroup$ I'm putting this in a comment as I don't have time to write anything definitive. I think your dry weight arm is incorrect. You've used the reference datum from the POH, where the actual CG is measured using a process defined in the POH section "EMPTY WEIGHT AND CG MEASUREMENT WHILE ON GEAR". $\endgroup$
    – GdD
    Commented Jun 1, 2022 at 15:54
  • 1
    $\begingroup$ the CG is too far forward, which is surprising. Something is wrong with your empty weight numbers. What's the source? $\endgroup$
    – 300D7309EF17
    Commented Jun 2, 2022 at 1:13

2 Answers 2

Reset to default
5
$\begingroup$

Yes, you are doing something wrong.

Your biggest mistake is using 154.75 as the empty weight moment. As shown in my last image (from the Icon A5 user manual), 154.75 is just a reference datum marking where the forward face of the spar is located. It has nothing to do with the empty weight moment.

Your second mistake is putting too much weight in the baggage area.

I have included here an actual weight and balance done by the NTSB of an Icon A5 that was involved in an accident. The empty arm was 163.8 and is probably typical of all Icon A5 aircraft.

As you can see from the calculations, the Icon A5 has a poor useful load and it is difficult to carry 2 pilots, with a reasonable amount of fuel and baggage and remain under the 1510 lbs max gross weight.

NTSB report for N663BA, ICON A5 enter image description here

enter image description here

enter image description here

Improve this answer
$\endgroup$
1
  • $\begingroup$ That REALLY is a limited useful load. If the pilot weighs much over 200 lbs, you can have a child in the other seat at most, or else you're flying solo. Wow! $\endgroup$
    – Ralph J ♦
    Commented Jun 2, 2022 at 23:49
4
$\begingroup$

First, the reference datum for the spar is of no consequence in W&B calculations.

For Empty Weight and Moment, you have to refer to the actual W&B record for the specific aircraft. It is part of the POH or the Approved Flight Manual (the one with the a/c serial number on it.) I suspect (reinforced by the exercise below) that not having the proper values for the empty weight is the root of your problem.

The other issue is that as you stated; "111.6 lbs. of gear which can be distributed between the luggage shelf and the passenger's seat." Yet, in your W&B calculation, you put it all under baggage. For this exercise, I'll assume your original empty weight numbers to be correct.

The problem is that the POH limits the cargo shelf/baggage area to 60 lbs., with the following:

WARNING: Loading a concentrated weight fully aft in the baggage area may cause an unsafe aft CG condition.

If you put 60 lbs. in the baggage area (@ 157 in.) and 51.6 lbs. in the passenger seat (@ 128.5 in.) it will move the CG forward. Without changing any of your other numbers, that will result in a CG at 149.9 in. which is even further out than your first effort.

Improve this answer
$\endgroup$
2
  • $\begingroup$ @MikeSowsun You are correct. I have updated my answer. $\endgroup$
    – Gerry
    Commented Jun 2, 2022 at 21:38
  • $\begingroup$ Yeah, I forgot to mention that I'd stress-tested the assumptions by overloading the baggage, for the reasons that you arrived at. I'm still waiting for ICON to get back to me, because the problem with simulation is you don't have an aircraft to weigh. $\endgroup$
    – William Walker III
    Commented Jun 3, 2022 at 12:56

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .