Heavy Forward CG Testing

[Redline]

I'm curious what builders do for "heavy forward CG" flight testing as per the EAA test flight manual. Everything added to the empty weight on a Kitfox contributes to aft CG. Do you just run half tanks, PIC only and call that your most forward CG? I realize the EAA manual is trying to cover a large variety of homebuilts, so maybe this doesn't apply to the Kitfox. Just trying to be thorough.

[Dave S]

Redline,

Been a while since I did my phase 1; however, my DAR requested that I calculate loading for "most adverse forward" and "most adverse aft" configurations within engineered W/B limits. Same thing, different words - the EAA test flight manual didn't exist at the time.

I don't know if it is even possible to exceed the forward limit in a kitfox unless a person has an extremely heavy engine. So what a person does is calculate various loading schemes to get the CG as far forward as possible - eliminating as much weight as possible from the aft end. Max vs min required fuel, baggage, etc. don't forget the seat lockers and cubby hole if you have them. Other than that the necessity of having an actual pilot on board almost precludes the possibility for ever getting near the forward CG limit.

I don't think there is any merit to piling sandbags on the floor ahead of the seat because that is probably never going to happen.

You may not be able to fly at max forward CG, but get it as close as possible with realistic loading.

You are doing well by being thorough.

[jiott]

I did same as Dave in my fwd cg testing; just get it as far fwd as it will ever be possible.

[Redline]

Thanks Dave I appreciate the reply and we've done as you've mentioned. Our build has the 915is, so it is a heavy engine comparatively, but the only way to move the CG forward would be ballast on the floor by the passenger side rudder pedals, which as you say doesn't serve much purpose (and it makes me nervous as there isn't a great way to secure it there).

[Redline]

I did same as Dave in my fwd cg testing; just get it as far fwd as it will ever be possible.

Thanks Jim!

[avidflyer]

These are some of the notes on the bottom of an airplane weight and balance sheet I copied and have used in regards to most forward CG.

1 The most forward and most aft CG limits are calculated using the FAA standard pilot and passenger weight of 170 lbs.

2 Minimum fuel weight is calculated using the formula ((Max continuous hp)/12)x6

4 For most forward CG calculations maximize all weight forward of the forward CG limit and minimize all weights aft of the forward CG limit.

6 Weigh aircraft in level flight attitude.

All the other notes refer to most aft CG and such.

I'm trying to figure out the formula in note #2. I'm thinking you are required to have at least 1/2 hr of fuel remaining when you land. In the 912 ULS, that would be probably about 2-2 1/2 gallons. JImChuk

PS just tested my memory on the 1/2 hr fuel remaining and did a search. Here it is in part:
14 CFR § 91.151 - Fuel requirements for flight in VFR conditions.

• CFR

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§ 91.151 Fuel requirements for flight in VFR conditions.
(a) No person may begin a flight in an airplane under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed—
(1) During the day, to fly after that for at least 30 minutes; or
(2) At night, to fly after that for at least 45 minutes.

[Redline]

2 Minimum fuel weight is calculated using the formula ((Max continuous hp)/12)x6

Thanks Jim. I believe that calculation is stating that a 30 minute reserve requires 1/12th of a gallon per max continuous HP. Multiplying by six gives you the weight (of 100LL). I think this based on less efficient engines. Using that for a Rotax 915is I'd need 11.25 gallons in reserve, which would be about two hours.

[avidflyer]

As far as what it required for minimum fuel, I think the FAA rule I pasted is more correct than the formula listed if we are reading the formula correctly. How often would you be flying with less than 11.25 gallons and just yourself? Often I would guess and that would give you a more forward CG. JImChuk