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Slow 7A

R

rwtalbot

Well Known Member
G?day Everyone,

I?ve been test flying my 7A over the last few weeks and starting to form the opinion that it is a bit slower than I expect.

I have a 180 hp updraft engine and Hartzell Constant Speed Prop - with blended airfoil. The gear fairings and wheel pants are not fitted yet.

I have been treating the engine nicely for 10 hours or so but performance seems slow. The ASI has been calibrated and found to be correct. Also the TAS calculated by the EFIS aligns with ground speed from GPS.

Last weekend I was able to get her to 7000? PA and do a couple of runs. With Prop 2600, WOT, leaned for best power, OAT 5 degrees C maximum observed TAS was 149 kts. CG was towards the forward end (170lb pilot + half tanks).

According to Vans I should see around 175 kts in this configuration so I am down approximately 25 kts.. I expect about 12 kts of this can be made up by the installation of gear leg fairings etc.

I have also observed the elevators are not neutral in this configuration. The horns sit approximately 0.5 - 0.75? down. I.e. to neutralise the elevators requires I push forward on the stick resulting in 1200 fpm descent rate or so.

I have no heavy wings and all the control surfaces/fairings are in alignment. The rudder seems to be in trim as well.

My first thought was that the shim on the HS may need adjustment, but the more I think about it that may not be the case. Should I wait till the fairings are on to asses what is required? What should I check first to find some more speed? Am I just overthinking this at this point in the process?

Thanks
Richard

RV7A ? Phase I Flight Testing
 
Hi Richard,
I'm about at the same point you are...10 hours into my Phase 1. I've got almost the same config as you, with the exception of the prop. I have a 3 blade Catto. My numbers are almost identical with yours, except I'm typically flying around 4,500 - 5,000 ft.

Same thing here...no fairings or wheel pants, 180 hp. I've been told that this speed with no pants is typical.
 
Don't touch the HS. Don't do anything to the plane until you have all the gear fairings installed. The flying characteristics will change completely after all is installed. If things aren't right, then start to see where the faults are otherwise you will spend hours chasing phantom faults.
 
Hi Richard
My 8A gained 20 Kts once all the gear fairings were installed. It also needed some more down trim to stay level. Sounds like your fine. Those round gear legs throw out a lot of drag.

Paul Danclovic
Jamestown NC
 
I will of course agree to not worry about it until you get those fairings on. Yes, the flying characteristics of the airplane will change and you will notice it. I flew my airplane for about 30 hours with no fairings and when I put them on the decreased drag was noticeable, especially while landing.

I saw a very considerable increase in TAS once my fairings were installed (about 19kts). I have the same setup as you, updraft 180hp w/ Hartzell blended airfoil prop.

Just for comparison, I flew back home this weekend from Sun-n-fun. I was WOT, 11,500ft, 2400RPM and 170kt TAS cruise.

The absolute *best* way to test your TAS is to use this spreadsheet . It uses four way runs at any heading and will actually tell you how accurate your numbers are (it really only needs three legs to do the calculation, but uses the fourth for validation).

This spreadsheet will also give you a very accurate winds aloft calculation and TAS which you can compare against the data the EFIS is calculating.

For what it's worth, in my case the TAS calculated by the spreadsheet was within one knot of the TAS displayed on the EFIS.
 
My concern is....

rwtalbot said:
. ........ The horns sit approximately 0.5 - 0.75? down. I.e. to neutralise the elevators requires I push forward on the stick resulting in 1200 fpm descent rate or so.



Thanks
Richard

RV7A ? Phase I Flight Testing
Click to expand...

......why the half to three quarter inch up elevator, (if I understand it correctly). Mine and others' elevators are slightly down when flown solo and pretty near streamlined with two aboard. It sounds nose-heavy and the up-elevator is bound to cost some speed.

Put 50 lbs in the baggage area toward the rear and go check the trim position, maybe? As you probably know, a rear CG biased airplane is faster.

Regards,
 
pierre smith said:
......why the half to three quarter inch up elevator, (if I understand it correctly). Mine and others' elevators are slightly down when flown solo and pretty near streamlined with two aboard. It sounds nose-heavy and the up-elevator is bound to cost some speed.

Put 50 lbs in the baggage area toward the rear and go check the trim position, maybe? As you probably know, a rear CG biased airplane is faster.

Regards,
Click to expand...

Hey Pierre - Couldn't the naked gear be pushing the nose down?
 
pierre smith said:
......why the half to three quarter inch up elevator, (if I understand it correctly). Mine and others' elevators are slightly down when flown solo and pretty near streamlined with two aboard. It sounds nose-heavy and the up-elevator is bound to cost some speed.
Click to expand...

Hi Pierre,

I agree and it is a nose heavy airplane... CG is almost 1" in front of the forward limit without pilot/fuel. However, there are no real signs of nose heavy condition. I haven't had any issues keeping the nose off the runway and the stall is pronounced. i.e. it doesn't refuse to drop the nose like a C152stalled solo.

Richard
 
2600 rpm at cruise?

Why so high? High prop rpm, low pitch, at cruise, will slow you down for sure, but never tested how much. I run my RV6/180hp/CS prop at approx 2300 rpm in crz. Note that there is an avoid range below 2250. Brings the fuel burn way down also, with MP held constant.
 
Yeah, I suppose it could...

Webb said:
Hey Pierre - Couldn't the naked gear be pushing the nose down?
Click to expand...

...Webb, but our -6A did 162K/186 MPH with no pants or fairings at 7500' and 2700 on the Catto. Our elevator was near neutral then and we picked up 16 MPH or better, fully faired to 202 MPH, as Craig said we would.

I still think his CG needs to come back some.

Regards,
 
2700 rpm for max HP

wv4i said:
Why so high? High prop rpm, low pitch, at cruise, will slow you down for sure, but never tested how much. I run my RV6/180hp/CS prop at approx 2300 rpm in crz. Note that there is an avoid range below 2250. Brings the fuel burn way down also, with MP held constant.
Click to expand...

For a max speed test you need to run a C/S full throttle and near 2700 RPM to get full available HP from the engine. This should be the fastest configuration.
 
You probably want to play around with the settings a little. With max MP, you may find that at higher airspeeds, the props happy-place may be around 2600 or so, not the full 2700 RPM.
 
Richard,

I'm with Rusty on this one! Unless your RPM is at 2700, you will not be developing rated power of your engine. Not sure what the difference is between 2600 and 2700rpm though it means the HP available is less hence less max TAS.

Cheers, Greg:)
 
rwtalbot said:
G?day Everyone,

IMy first thought was that the shim on the HS may need adjustment, but the more I think about it that may not be the case.

RV7A ? Phase I Flight Testing
Click to expand...

Richard,
I doubt that the Tailplane incidence has any effect on your TAS.

When I set my tailplane incidence, I inserted the appropriate spacer (a 1/4" drill bit from memory.
The plans called for an incidence of 0?, but like all Vans measurements there was no tolerance. ie. plus or minus 20 minutes.

When I checked the incidence it was not 0? and so I added slightly larger drill bits until the incidence was close to zero.
I checked with my mate and he simply used the advised 1/4" bit, so my tailplane ought to have been closer to 0? than his.

However, to my dismay, his RV7 was a few knots faster than mine.

Pete.
 
Once your engine is broken in & add the fairings, you should gain about 20kts. I had the same concerns and speeds you're seeing.
 
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