Weight distribution for maximum speed

[AlanA]

Question about and weight and balance and speed.

 

95% of the time I fly by myself, 165 lbs,  about 30 lbs of baggage and 3/4 tanks.  Will changing the location of my baggage change in any appreciable way my speed?  I have heard some pilots say put the 30 lbs in passenger seat next to you and others have said it's better in the back seat.    For OPTIMAL speed should I just do the weight and balance and put the baggage where it is smack in the middle of CG? I  It's probably such a minimal amount it doesn't make a difference, right?  I have heard different things.  I would appreciate your collective wisdom.

[Hank]

I've always heard that tail-heavy is better for Mooneys. I put my bags in the luggage bay. It reduces the required down-force [lift generated by the tail in the downward direction], and we all know that creating lift also creates drag. Whether this is significant or not, maybe Becca can answer, as I'm sure she has done testing for races in her J.

[carusoam]

Since the tail is an inverted lifting device...

And lift causes drag...

Putting weight towards the back generates less need for inverted lift.

Then putting the baggage in the back would cause less drag.

Then actual weight and balance become more critical. At both full and empty tanks.

Nothing would be worse than being tail heavy.

I never calculated much improvement. I did appreciate using less trim...

Best regards,

-a-

[Hank]

I thought about changing "tail heavy" in my post, but decided that people would realize I meant within CG limits. Shortly after buying the plane, I made a spreadsheet figuring CG with various people and baggage loads, with fuel in 10 gal increments from full down to 10 gals, to cover take off and landing situations. Then I highlighted in red the ones that were out of limits, and I keep it in the plane and on the tablet for reference. Still, anytime I will be close, I calculate it to be sure.

 

Something I remember from my RC airplane days:  nose heavy flies poorly, tail heavy flies once.

[carusoam]

We think a lot alike!

Best regards,

-a-

[mikefox]

Yes - Flying at the aft CG limit is most efficient in any traditional design aircraft (not canard).  As was said, always check the CG with takeoff fuel and landing fuel to make sure you are staying within limits.

 

Keep in mind that stability is enhanced slightly with a more forward CG, while the aircraft will be a bit more "responsive" with a more aft CG.  Flying anywhere within the CG limits should not pose any undue hazard as long as the pilot is comfortable with how the airplane handles throughout the range.

 

Enjoy!

[Super Dave]

As Hank already suggested, for best speed you want the CG to be as far aft as possible while still remaining within the envelope.

In our airplanes, the CG will always be forward of the center of lift, which means that the tail must produce a downward force to keep the airplane from turning into a lawn dart. The downward lift created by the tail creates induced drag, but more importantly, the downward force must be counteracted by the wing producing more lift, resulting in an even greater induced drag. So, if weight can be shifted rearward bringing the CG closer to the center of lift, the tail needs to produce less downforce and the wing doesn't need to produce as much lift to counteract that downforce.

Imagine a 3000lb. airplane with a forward CG that requires the tail to produce 100lbs of downforce. In this airplane the wing actually needs to produce 3100lbs of lift. If weight could be shifted rearward so that only 50lbs of downforce was required, the wing now only needs to produce 3050lbs of lift, and the airplane will be marginally faster.

Realistically, moving 30lbs from the front seat to the baggage compartment will probably not make any noticeable increase in speed.

[Bob - S50]

Looking at the POH for our '78 J, it provides data for 2300# and 2740#.  Looking at the 8000' performance chart, the difference in speed between the two weights varies from as little as 2 knots at high power/high RPM settings to as much as 11 knots at low power/low RPM settings.  Of course this probably assumes a constant CG location.  By moving the CG aft, as mentioned above, you not only reduce drag caused by the requirement for extra lift, but you also reduce drag from the tail as well.  How much?  Good question.

 

Let's say you have 30 pounds you can put in the front seat or the baggage area.  For my J the baggage area is about 46" further aft, call it 4' for simplicity.  4 x 30 = 120 ft-lbs.  Since the plane is about 25' long, again for simplicity, let's guess that the center of lift for the tail is 16' aft of the aircraft CG.  120 ft-lbs/16 ft = 7.5 lbs.  So moving 30 pounds from the front seat to the baggage compartment would make a difference of about 7.5 pounds less down force on the tail, and 7.5 lbs less lift required by the wing.

 

So even if we consider both to create equal drag, that would be the equivalent of 15# less weight.  15/440 = 0.034.  Even if we apply that at the low RPM and low power difference of 11 knots, the difference here would be about 0.375 knots.  At the high RPM and high power setting, it would make a difference of 0.068 knots.

 

Not much difference.  On the other hand, if you are taking a beautiful 110 lb woman and a 250 lb man with you... putting the beautiful woman next to you might be a good idea... for more than one reason.

[Htwjr]

There is an app called aircraft weight and balance that you can just plug in the specifics for your plane and it will compute W&B for any combination of passenger, fuel, and baggage loadings. It will then provide an envelope graph including takeoff and zero fuel limits. Makes W&B very simple. I always try to load aft but well within the envelope. My C seems to fly better and maybe a little faster there.

[N33GG]

I used to fly a Piper Saratoga. That aircraft would cruise at least 10 kts faster with some aft loading. I kept some weight in the aft baggage compartment even if I didn't need to carry anything.

I have not noticed Mooneys being that responsive to loading and its effect on cruise speeds.

In general, with most aircraft, an aft cg will result in higher cruise speeds. Some aircraft are more sensitive than others.

[Cruiser]

I believe the optimal balance for least (induced) drag would be when CoL = CoG . 

The problems with that configuration is ithe CoG is always changing and the closer to equalibriam the less stable the plane.

[201er]

Don't forget to slide your seat back in cruise

[SkyPilot]

There is an app called aircraft weight and balance that you can just plug in the specifics for your plane and it will compute W&B for any combination of passenger, fuel, and baggage loadings. It will then provide an envelope graph including takeoff and zero fuel limits. Makes W&B very simple. I always try to load aft but well within the envelope. My C seems to fly better and maybe a little faster there.

Not having my bird nearby I wondered if anybody has the arm locations for an M20F? I just downloaded the app(s) but I am in Borneo at the moment.

[Cruiser]

VII. Model M20F (cont’d)

C.G. Range (+45.0) to (+50.1) at 2740 lbs.

(Landing gear extended) (+41.8) to (+50.1) at 2470 lbs.

(+41.0) to (+50.1) at 2250 lbs. or less

(Straight line variation between points given).

Retraction moment 615 in. -lbs.

Empty Weight C.G. Range None

Maximum Weight 2740 lbs.

No. of Seats 4 (2 at +31.5 to +39.0, 2 at +70.7 to 75.2)

Maximum Baggage 120 lbs. (+95.5), 10 lbs. (+119.0)

Fuel Capacity 64 gals. (Two integral tanks in wings at +48.4)

See NOTE 1 for data on unusable fuel.

Oil Capacity 2 gal. (-11.5)

NOTE 1:The certificated empty weight and the corresponding center of

gravity location must include unusable fuel (not included in fuel capacity) as follows:

15.0 lb. (+48.4) for the M20F and M20J

[Marauder]

Not having my bird nearby I wondered if anybody has the arm locations for an M20F? I just downloaded the app(s) but I am in Borneo at the moment.

Are you talking bout this app?

If so, I can send you my template for a 1975 F.

Sent using Tapatalk

[jetdriven]

Don't forget to slide your seat back in cruise

I guess you could call that 7th hole in seat rail a speed mod

[aaronk25]

The interesting things on our trip across the gulf I was loaded right at Max C.G. cause we had just a ton of stuff and in cruise the trim indicator was almost all the way at nose down.  Normally its about 3/8 the way up.  Was definitely more pitch sensitive but even though we were really heavy (not going to define what that means) even at FL150 I was still truing 150kts....2700rom 10ROP.  I think some of the statements above are true about the wing needing to lift more and create more drag as the farther back CG defiantly offset the speed loss of carrying additional weight.

 

However would certainly not want to get into a spin being aft CG.....might not get out of it.

[SkyPilot]

Are you talking bout this app?

ImageUploadedByTapatalk1395061061.011040.jpg

If so, I can send you my template for a 1975 F.

Sent using Tapatalk

 

That is the one. Please send it when you get a moment. I'm at heavycrude@hotmail.com and will be 2 more weeks in this steaming jungle camp.

 

Thanks,

PK

[SkyPilot]

And thanks also Cruiser. I'll compare the numbers. I wish I had a copy of my W & B with me, but I can edit when I get home.

[garytex]

I had a Cheetah that was a few knots faster with an aft loading.  The tail would align with the horizontal stab.  My M20F not so much.

[phecksel]

I raced my "C" a lot.  My favorite races were the ones where they did a flying speed check.  They always required everything be removed from the plane, and I pulled that seat as far forward as I possible could and still safely fly.

 

During the races, I carred a tool kit, a container filled with lead weights, and flew with both pilot and co-pilot all the way back.  It made a huge speed difference.  Was no where near gross and near the back end of the W&B.

 

If you truly know your plane, take off, retract the gear and accelerate in ground effects, staying 3' off the runway.  It's incredible watching the pitch change as the plane accelerates.  really drives home the point of how much downward force the tail contributes.