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How to add 15kt to cruise speed by adding weight
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n223rv(at)wolflakeairport
Guest

Posted: Tue May 30, 2006 6:12 pm Post subject: How to add 15kt to cruise speed by adding weight

I see the same thing in my -4.  Put about 100-120 lbs in the back seat

and gain about 10 kts.  It is very noticeable.  Next time you fly solo,

trim out the plane and look at the level the elevator sits relative to

the HS.  Add a passenger and look again.  In my plane with a 120lb

passenger, the elevators will be almost level with the HS, but flying

solo they are quite a bit different.



-Mike



--

martin(at)gbonline.com
Guest

Posted: Tue May 30, 2006 6:21 pm Post subject: How to add 15kt to cruise speed by adding weight

Joe and others,

5 years ago when I first began racing  the Air Venture race and others, I 

added a lead pig (approx 10 lbs) to the tail  area of my RV8 to improve the 

CG.  I mounted it just aft of the tail wheel in the tail cone.  It fit very 

nicely and did improve the airspeed.  However after a couple hundred hours , 

I noticed that my tailwheel spring  rod was bending (taking a set) .  I 

removed the tail weight and replaced the tailwheel attach rod.  I now use a 

lead shot bag, 25 lbs strapped to the baggage floor and installed or removed 

as needed with a heavy passenger.  The speed improvement is about the same 

with either of the about the same.

On a separate note:  I am getting ready for the Air Venture race this summer 

and would encourage all of you who have flying airplanes to particiipate. 

Don't worry about not having the fastest airplane.  You will learn a lot by 

participating  and  competing with the other guys.



Dick Martin

RV8 N233M

the fast one

---

pbesing(at)yahoo.com
Guest

Posted: Tue May 30, 2006 6:46 pm Post subject: How to add 15kt to cruise speed by adding weight

I fly my -4 with a 40lb bag of salt in the baggage

compartment (sans passenger of course)...haven't

noticed the speed difference, but it does fly

better...I'll have to check that out.



Paul B esing

--- Mike Kraus <n223rv(at)wolflakeairport.net> wrote:



[quote] 

 <n223rv(at)wolflakeairport.net>

 

 I see the same thing in my -4.  Put about 100-120

 lbs in the back seat

 and gain about 10 kts.  It is very noticeable.  Next

 time you fly solo,

 trim out the plane and look at the level the

 elevator sits relative to

 the HS.  Add a passenger and look again.  In my

 plane with a 120lb

 passenger, the elevators will be almost level with

 the HS, but flying

 solo they are quite a bit different.

 

 -Mike

 

 --

jebrick(at)comcast.net
Guest

Posted: Tue May 30, 2006 8:09 pm Post subject: How to add 15kt to cruise speed by adding weight

What are we to make of the speeds that Van gives for solo and gross weights?

About one mph slower at gross, tandem or side-by side.



jb

LessDragProd(at)aol.com
Guest

Posted: Tue May 30, 2006 8:35 pm Post subject: How to add 15kt to cruise speed by adding weight

Van's cruise performance testing is usually done at a 8,000' density  

altitude using full throttle and 2500 RPM.  (It helps to remove as  many variables as 

possible when doing performance testing.)

 

I have used a 7,500' density altitude for my RV-3 performance  testing.  This 

has been a station altitude of 5,500', at times.  I  have an RMI MicroEncoder 

in my RV-3, so I can get a direct readout on density  altitude (I believe the 

outside air temperature is even corrected for  compressibility effects).

 

Jim Ayers

 

In a message dated 05/30/2006 9:11:04 PM Pacific Daylight Time,  

jebrick(at)comcast.net writes:






What are we to make of the speeds that Van  gives for solo and gross weights?

About one mph slower at gross, tandem or  side-by side.



jb

Ron Schreck

Joined: 10 Jan 2006
Posts: 94
Location: Gold Hill, NC

Posted: Wed May 31, 2006 3:05 am Post subject: How to add 15kt to cruise speed by adding weight

I like both Dan and Rick's explanations and throw in a specific example

of a very unstable airplane to illustrate the aft CG phenomnon.  I used

to fly an airplane that had the CG well aft of the center of lift (CL).

In this configuration the tail plane needed to produce lift in order to

keep the aircraft level.  The advantage of this configuration was that

both the wing and tail plane created lift in most every flight regime

rather than the wing producing lift and the tail plane producing down

force as for a conventionally balance aircraft. This made for some

extremely tight turns and rapid response to control inputs but also made

the aircraft impossible to control by the most experienced pilots.

Solution:  Put a computer in charge of stability and let the pilot input

his desires through an electronic input to the computer.  Thus you have

fly-by-wire technology and the only way to control an F-16.

 

Ron Schreck

RV-8 "Miss Izzy"

Gold Hill Airpark, NC

 

 

 

 

 

 

      

      

      I like Dan's explanation, but will add a bit more.

      

      Specifically, we require the CG to be forward of the center of

lift (CL) in

      order to have a stable aircraft (and one whose nose drops when the

wing is

      stalled).  The closer the CG gets to the CL, the less induced

drag, but the

      less stable the plane will be.  If the CG should go aft of the CL,

all bets

      are off in terms of controllability.

      

      Another e-mail commented on Bonanzas and how their CG moves with

fuel burn.

      Whether the CG moves aft with fuel burn should depend on the CG of

the tank

      and its fuel relative to the CG of the plane.  I fly an A-36

Bonanza, and

      when weight is up (hence, realistically, with a CG farther aft

than when

      lightly loaded), I have indeed noticed greater pitch sensitivity

after a

      long flight.  When I plan flights at higher weights, I check my

loading by

      calculating CG for zero fuel, just to be on the safe side.  For

extra

      margin), I try to land with fuller tanks, too.

      

      Rick

      A-36, RV-7 in process

      

      --

khorton01(at)rogers.com
Guest

Posted: Wed May 31, 2006 4:14 am Post subject: How to add 15kt to cruise speed by adding weight

Anyone who is thinking about moving the CG aft by

adding some weight needs to keep two things in mind:



1. The weight should be properly secured.  You don't

want it coming loose during turbulence or an off-field

landing and hitting you in the back of the head.



2. Adding weight aft will increase the moment of

inertia on the yaw axis, and this will probably

degrade the spin characteristics.  I.e the results

from any spin testing you did without that weight are

now invalid.



Kevin Horton

RV-8 (Finishing Kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

cjensen(at)dts9000.com
Guest

Posted: Wed May 31, 2006 4:38 am Post subject: How to add 15kt to cruise speed by adding weight

To say nothing of having unsecured weight in the tail that, during a

steep climb-out, slips even further back.  You have now just been

promoted to test pilot; one that may have his hands...and shorts full.



Chuck Jensen

[quote] --

dreel(at)cox.net
Guest

Posted: Wed May 31, 2006 6:39 am Post subject: How to add 15kt to cruise speed by adding weight

To answer a few questions that came up, I was leaned out during both tests

but I lean by ear and have no fuel flow meter.  At 5,500 ft, I have measured

9.2 to 9.4 gph using the 'fly it half an hour on one tank then see how much

it takes to refill the tank' method.  To get the aft CG, I added weight to a

fixture I built for the aft baggage shelf and added a 50 lb sand bag to the

aft seat.  Total 142 lb.  I can refly the forward CG test at the higher

altitude & will report the result.  But it will probably be a while because

I'm flying the RV to Brady TX for paint.  I'll have to leave it there about

a month.  Of course, I'll put everything in the aft baggage compartment for

the flight!



Dave



---

low pass

Joined: 10 Jan 2006
Posts: 32
Location: Houston

Posted: Wed May 31, 2006 7:30 am Post subject: Re: How to add 15kt to cruise speed by adding weight

 	  martin(at)gbonline.com wrote: 	
		  Joe and others,

5 years ago when I first began racing  the Air Venture race and others, I 

added a lead pig (approx 10 lbs) to the tail  area of my RV8 to improve the CG.  	


I sure don't need any corrective ballast, but am thinking I might see what the effect of moving my battery aft (with an O-320 up front) would have on the CG envelope...  Gotta carry it anyway.

batfinks(at)mchsi.com
Guest

Posted: Wed May 31, 2006 9:42 pm Post subject: How to add 15kt to cruise speed by adding weight

I'll bet there are a lot of replies, but that is exactly what you should 

expect.  With more weight in back, the tail has to produce less lift 

(downward) with it's associated lift drag.  Just don't move the CG too 

far back, there be dragons there.



Scott



DAVID REEL wrote:



 	  Quote: 	
		  



I've been exploring the CG range in flight testing of my RV8A and have found

an unanticipated cruise speed effect.  At 85.9 inches, I was getting 155kias

with 2300rpm, 23 in mp, 5,500 ft, and 42 degrees F outside.  At 79.6 inches,

I got 142kias with 2300rpm, 23 in mp, 4,500 ft, and 64 degrees F outside.

My whiz wheel gives true airspeeds of roughly 169kt and 154kt.  Quite an

improvement just by adding some weight in back.  Yes, the fast flight was

with a little bit higher weight!



There's lots of discussion of speed improvements in the archives, but

nothing related to CG location that I could find and certainly nothing so

easy to get and of this magnitude.  So, my question to everyone is have you

had similar experience?  Do you know anywhere this has been quantified or

further detailed?  After all, I'm just comparing two test flights here, but

theoretically, I'd guess the decrease in drag due to decreased pitch

stability requirements as the CG moves aft would explain the speed increase.



Excited!



Dave Reel - RV8A

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