Speed varition - RV14A

I took a two hour X-country trip yesterday to buy a tug. The tugs weighs about 65 lb which was in the luggage area. What I noticed about my speed, for the same power settings/altitude, I was about 5 knots faster on the way to then coming back when I had the tug. Now, I doubt the added weight can effect the speed that much.

My question, would the tail heaviness attribute to that much speed difference? or would it be the added weight?

I would guess it's the weight more than the tail heavy position. Induced drag (drag resulting from lift generated to carry weight) is probably the main culprit.

But 5 knots seems like a lot. Are you sure all other conditions the same? I've found with other aircraft the most consistent correlation with TAS is LOP fuel flow.

Bavafa said:

I took a two hour X-country trip yesterday to buy a tug. The tugs weighs about 65 lb which was in the luggage area. What I noticed about my speed, for the same power settings/altitude, I was about 5 knots faster on the way to then coming back when I had the tug. Now, I doubt the added weight can effect the speed that much.

My question, would the tail heaviness attribute to that much speed difference? or would it be the added weight?

Click to expand...

An aft CG should actually result in better performance than a more forward CG.

You didn't say whether you were looking at true or indicated but if the CG shift had your pitot tube at a different angle it could result in a different reading .. just a thought

Need to consider down drafts. When your speed is low and the AP is on, take a look at your attitude indicator. If it is slightly above the horizon, or wherever it was when you were getting the higher airspeed, that is the reason for the speed reduction.

Also possible you had an updraft on the faster trip.

Larry

If you are using true speed calculated by your efis then you might consider that your calibration is off just a wee bit.
If this was a round trip and wind was 180 on the return trip that would be your answer.

My guess would be that there were other influences that would have given you the same result whether you had the extra weight or not.

As already mentioned, a further aft C.G. should make the airplane slightly faster.

It got pretty warm here yesterday. Was the OAT noticeably warmer on the return trip? When you said the same power, did you actually adjust MP and/or RPM to account for temperature differences? Since this was a round trip, is it fair to assume that you flew at different altitudes to vs from? What were the density altitudes? Same fuel load both ways? Lots of variables!
As someone else noted, aft cg should be faster than forward cg, everything else held constant, due to the decreased angle of attack on the wing due to the smaller down force on the tail.

Thank you all for your feedbacks.

Bob,
You are correct on the temp, it was certainly much cooler in the morning than my return trip which was just around noon or after and was considerably warmer, upper 80s.

My altitude was different but within a 1K feet. On the way south I was at 11500 and 13500 and return was steady at 12500, both legs were LOP. The fuel burn rate was a bit lower on the return for the same RPM which also explains the lower speed.

For those interested, my burn rate was 8.2G @165knots TAS.

Speed

The horizontal tail on most airplanes carries a significant download, which equals drag. IE the entire horizontal tail is producing downward "lift". Aft CG results in less download on the horizontal tail which results in at least a slight speed increase.
This does not apply to canards. One of the claims for canards is that the wing and the canard are both lifting surfaces and to some degree reduce trim drag.
An interesting experiment would be to duplicate your two flights with and without the weight and note elevator position and trim tab position in both configurations. Measure true airspeed in both cases and make a short run at the same altitude with and without weight. Another option is to do an accurate wt and balance calculation with and without maximum weight in the baggage compartment and do the test. Some accurate speed readings close to the aft cg limit would also be interesting.

Temperature