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Dog Slow RV-7A

G

gshipman

Member
I recently finished my RV-7A and have 30+ hours on it now Horay!

It is dog slow, Boo!

120 KIAS @ 10,000 ft ~144 KTAS (no pants, leg fairings, etc)
134 KIAS @ 10,000 ft ~160 KTAS (with the pants, fairings etc)

Here is my setup:

ECI IO-360 FI, Dual PMAGS
CS Hartzel Blended Airfoil

I'm pulling about 20" MAP @ 2,500 RPM

My buddy in an RV-4 is pulling 17" MAP @ 2,400 RPM just to slow down to my speed. He can pull 21" MAP compared to my 20" MAP at WOT

I am at a loss here, it seems that I am about 12 knots slow according to Van's numbers, any ideas here?
 
Hummm

gshipman said:
I recently finished my RV-7A and have 30+ hours on it now Horay!

It is dog slow, Boo!

120 KIAS @ 10,000 ft ~144 KTAS (no pants, leg fairings, etc)
134 KIAS @ 10,000 ft ~160 KTAS (with the pants, fairings etc)

I am at a loss here, it seems that I am about 12 knots slow according to Van's numbers, any ideas here?
Click to expand...
Click to expand...

Are you at Double Eagle, Moriarty or Sandia Air Park?? Reason is because I will be flying my RV-6 to Albuquerque next week sometime and I could look it over and help you. Sounds like rigging issues or sick engine, does it fly straight? AJ
 
mgomez:

I don't have the speed and MAP @ 2700 I will be flying again sometime this weekend.

AJ:

I will send you an email off line..
 
Your engine set up is what I plan to do.....so I am really interested in your situation.

Questions: 1. Who provided you with your engine? Type of FI? Did you place and set up the Pmags yourself?

The increase of speed with fairings and pants is a real plus!

Keep us informed as you work out the problems. I bet that it is something simple and easy to fix!!!!

Frank @ sgu and slc RV7A
 
I will hold off on saying who I purchased the engine from as I'm not sure this is an engine problem yet and I don't want to tarnish anyone..

When the engine was delivered the settings on the Fuel Injection (ECI Titan FI) was way off. We had to adjust the low and high pressure sides, the idle mixture and the idle. After going back and forth we got a guy at ECI to walk us through the adjustments but I am still not confident it is set correctly.

There is a chance that this is a rigging issue, but this is a QB kit and I don't see how I could have messed this up, please let me know if there are any gotcha's here.

With this in mind I am thinking that this is an engine issue. I must say I don't know a lot about engines. I am developing 20" MAP at 10,000 feet, others see 21" MAP. Is it possible to see higher MAP with the engine running suboptimally?

The other variable is the PMAG's and I talked with Brad at Emagair and we have a few things to try.
 
Multiple losses

Galen,
It may not be a single cause.

Firstly, at 10,000' you will not be getting 75% power According to my spread sheet, you will be getting something like 70-72%.

8000-8500' is the alitude at which you should expect to get 75% at WOT. Higher you will get less power. Lower you will be throwing away TAS.
Vans quotes max cruise speed of 177KT for the RV-7A at 75% at 8000', so you should do your test at that altitude. Assuming you do not have any losses in your intake system you should be seeing around 21"MAP at 8000'.
If you still do not have something near 177KT then you need to look else where.

You might also do a search on the forum for 'SLOW' RVs as there was a post a few months ago on the subject with a lot of useful info. Especially from Kevin Horton
Pete.
 
Speed

One thing to check is a 4 way GPS speed average on a low winds aloft day.
My 4 way GPS average is always 10 knots or so above my Dynon and Airspeed Indicator/temp indication. Apparently I have a pitot/static error of approx. 10 knots. This error is consistant and shows up on long trips substantuating the GPS runs.

Don't give up yet! I'm getting close to Van's published figures.

Mannan Thomason
RV-8 N161RL (No. One Girl) IO-360-A3B6D McCauley Prop
176.75 kts GPS 4 way avg. Tru-Trak on.
8000ft. 2250 RPM, 22in MP About 60% best I can figure.
 
I see a couple replied discussing how my speed calculations should be taken, while I think these are important I have clear evidence that I am not even in the ball park. I have flown with a two other RV's both of which are known quantities in terms of speed in relation to many other RV's at the airport. A "fast" rv-4 and a slower rv-6a, both of these planes leave mine in the dust. If I were close this would be one thing...
Well, I have a few things to look at on the engine, but how does one know if it is producing expected power?

Also, any recommendations of determining if the plane is improperly rigged?

thx..
 
Crude

Galen,
This method might seem a little crude but it is a starting point.

If you can climb with your mates RV6 -at say 100KT- but he then flies away when you level off, I would assume you have the powerto stay with him in the climb, but you have a drag problem which becomes more apparent as speed builds.
Pete.
 
Recheck your incidence, sweep, and check the wings squared up to the fuselage. Check to see that the HS and VS are also squared up and set properly. Recheck control surfaces with airfoil template (wing). Check wheel pants and fairings are straight. Look at the slip ball when flying to see if the plane is flying straight. If you don't have one, see if you can borrow and temporarily mount one.

You should be able to get at least 170 knots. I get 175+ with an 0-360 and Hartzell BA prop.

Roberta
 
First question, are your gauges accurate? You could be pulling less power due to a faulty reading.

Dan's comment about the fuel flow would be a good indication if this is an issue.
 
dan said:
I might have missed it, but what's your fuel flow at those power settings?
Click to expand...

I'm thinking it was showing 11GPH which is low, it may be off a bit but we have been calibrating it based on actual fuel usage.
 
gshipman said:
I'm thinking it was showing 11GPH which is low, it may be off a bit but we have been calibrating it based on actual fuel usage.
Click to expand...
Wow, 11 gph is HIGH imho at 10,000' with a 360 engine. If that's an accurate flow reading, I suspect you could pick up several knots by leaning to best power. Lean to peak IAS, close the vents, and see what you get TAS-wise.
 
Galen,

I agree with Dan, 11gph at that alt is way too high. My IO-360(180hp) consistently will do 170-172kts @9gph(little less sometimes) and 2400rpm, 19-20"Map at those altitudes.
 
Check the valve timing

A local RV8 driver had a slow 8. It turned out his cam was off by one tooth on the drive gear. Ran great but was slooooow.
 
Wierd

I've got a very similar set up with a 7 with ECI IO360 with Emag/Pmag and Whirlwind RV200 prop. I easily get 165Kts at 2400 rpm and 20 to 21". Fuel burn running 15 to 25 LOP is 7.5 to 8 gph depending on altitude. 165 hours now.

Me thinks you've got a power problem. Although it is possible, I don't think it is a rigging problem. You'd have to work at that to mess it up.

I think the concensus is something is wrong. Start with instrument errors first. See if you can get some to fly with you, (as you did), but log some speeds. Match RPM and Manifold and see what you get.

If not determined, I think you need to pull the engine and have ECI go through it. Secondly, what about the prop? Could it be mis pitched?

Certainly not worth taking any chances.

Good luck and keep everyone updated.
 
I have similar problem

My RV-7a has a mid time1100hr smoh IO-360-A3B6D (out of a Mooney), 1 reg mag/ 1 Light Speed, 200RV WW prop and I haven?t been getting the speeds I think it should over the past 56 hours. After reading this post I went up today and at 8,000ft msl 2640 rpm 21.6 mp my speeds were IAS 136 kts and TAS 153kts. Fuel flow was over 11 gph. Interesting that at 2400 rpm I still maintained the same speeds but fuel flow went to 10.8 gph. I lean to rough then richen till smooth. This is with the leg fairings on but not the wheel fairings.

Will be watching this thread with interest.
 
Timing Issue

I spoke with the engine shop, he said he would be very suprised if it is an engine issue. He is thinking the timing may be a little off. Not so much that the engine is rough but that it isn't developing full power. I have the PMAGS, timing these is dead simple but who knows..

I will be testing a variety of things this weekend and I will report back the results.

Feel free to keep the suggestions coming though..

Thanks,
Galen
 
Wayne, you have the same engine as I do in my RV-6 (not quite flying yet). How did you get a single mag to fit in the dual-mag hole? Are they interchangeable?

Heinrich Gerhardt
 
dual to single mag

hgerhardt said:
Wayne, you have the same engine as I do in my RV-6 (not quite flying yet). How did you get a single mag to fit in the dual-mag hole? Are they interchangeable?

Heinrich Gerhardt
Click to expand...

I sent my engine to Bart at Aero Sport to put on the test stand and install the light speed/single mag. I never put much thought into how they did it but there must be a mod of some type.
 
Didn't I read on here a while back about guys tying their planes to a tree or something with some sort of overgrown fish-scale device and going full throttle to compare pulling power. Seems like this could be used to quickly determine if the cause is engine/prop or airframe rigging. Obviously this would have to be done VERY carefully.
 
Some good numbers to work from

Superior says that 50 degF ROP gives .50 BSFC and best power/peak gives 0.43 BSFC.
Therefor on a 180 HP engine at 75% (=135 hp), 50 ROP is 11.25 gph and 9.675 gph is at peak/best power. I'm going to guess that Lycoming will have similar specs. The famous 8000' is designed to give 75% at maximum rpm. If you are burning more than 9.675 at higher than 8000' DAlt, then you either are too rich and/or you have a problem. I grant that the problem could be instrument error on DAlt, rpm, fuel flow, etc.

Walter A. says you can get your BSFC down to 0.40 by running LOP. At 75% that's 9.0 gph. I'll leave it to you to decide if you want to run LOP right up to 75%.

All the above calculations use 6 pounds per gallon, which is just a little off, per Walter.

If you claim you are doing better than 9.0 gph at 75% I'd like to know how. I find even 0.40 BSFC to be pretty amazing.

I'm not flaming anyone, just trying to inject some known physics into a worthwhile discussion.


 
Updated Information..

So I made it to the hanger this weekend and took a look at a few things. I retimed the PMAGS and checked all the plugs. They were all pretty well fouled up so for $18 I replaced them all (auto plugs). I then took the plane up to 10,000 and did some speed tests. The winds aloft were pretty high, about 30 knots out of the south I believe.

I was running out of daylight so I couldn't do much but I found that I am still around 135 KIAS ~160 KTAS. I verified my fuel flow reads 9 GPH and fuel pressure reads 9 PSI. I had leaned back to 25 deg ROP.

I am going to try a couple different settings on the PMAGs next:

1) max advance 39 deg
2) max advance 34 deg
3) max advance 26 deg

I have been running with max of 34 deg. I haven't tried 39 or 26.


I also want to look into the FI system settings, when we first got the engine it was way off on low end pressure so we had to crank that up a bit. I'm not sure that the high pressure side is adjusted correctly either. One problem I face is that all the ECI documentation for adjusting the system is based on MSL, the plane is currently at 7000 MSL.

Again, I will continue to update this thread as this progresses...
 
Things are getting better

Seems like I am starting to get better performance, not sure if this is the engine breaking in or me learning to lean out to best power more effectively. I have seen about 165 KTAS recently. This is 7 Kts below vans numbers. I do have two com antennas, a vor antenna as well as two steps, while I'm not sure exactly what this costs in terms of TAS, it does cost something.

Hopefully this is just a combination of engine break-in and user error.. I look forward to flying with some of the local RV-7As that are similarly configured to do a more acurate comparison. After I do that I will update this thread.

- Galen
 
gshipman said:
I do have two com antennas, a vor antenna as well as two steps, while I'm not sure exactly what this costs in terms of TAS, it does cost something.
Click to expand...

If you tell me their measurements, or send a photo that I can guesstimate their size form, I'd be happy to do the math and give you a WAG of the speed penalty you're paying.

Or, if you'd like to do it yourself, here's the method:

The equivalent drag area for an RV-7 at cruise is about 2.5 square feet. Take the cross-sectional area of the step, antenna, etc. (this assumes they're ROUND tubes, not streamlined, and they're at right angles to the flow). Convert it to square feet. Then divide that number by 2.5. That's the fractional increase in drag area.

If it's a small number (i.e. you're adding an antenna or a step, not a speed brake, bomb, drop tank, or ECM pod!) divide it by 3. That's the fractional decrease in speed. So if you multiply by the speed you'd without the step, you now have the speed hit in knots, mph, or whatever.

Example:

You have a 200 mph airplane, and you add an antenna that measures 24" x 1/4" in diameter. The cross-sectional area of the antenna is 6 sq. inches, or 0.042 sq. ft. That's an increase in drag area of 1.7%. Dividing by 3, that gives you a speed hit of 0.56%. 0.56% of 200 mph is 1.1 mph.

This is rough, but for small increments in drag it's a good approximation.
 
May be conservative by 2

mgomez said:
Example:
You have a 200 mph airplane, and you add an antenna that measures 24" x 1/4" in diameter. The cross-sectional area of the antenna is 6 sq. inches, or 0.042 sq. ft. That's an increase in drag area of 1.7%. Dividing by 3, that gives you a speed hit of 0.56%. 0.56% of 200 mph is 1.1 mph.

This is rough, but for small increments in drag it's a good approximation.
Click to expand...
Wooo, I hear you Bro but that is WAY too conservative by a factor of 2. Assuming as you did the frontal area of a whip antenna is 6 sq-in and a Cd of 0.5, loss of speed at 200 mph would be 1/2 mph.

However a typical bet whip whip antenna is not near 6 sq-in, its tapered diameter and bent down frontal area gives a 3 sq-in area (with base), therefore:

The drag for antennas at 200 mph is aprox:

COM = 0.25-0.33 mph, (0.53 mph w/ 6 sq-in area)
VOR = 0.50-0.65 mph,
TX = 0.10-0.125 mph.

ANTENNA DRAG DOES NOT EXPLAIN THIS PLANES LACK OF GET UP AND GO.
 
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Drag on the aircraft

Martin please calculate the following:

RV7A model
3"stub transponder antennae
90 degree bent whip comm from Commant
(2) external steps

Thanks from a math idiot
Tad Sargent
180 hours since 2-3-2006 and loving it.
 
We aim to please...

Comant antenna costs you 0.3 mph (assuming it's the one whose diagonal portion is 8.5" tall)

Each step costs you 0.33 mph also (I guessed at the dimensions and airfoil shape from Van's web site. I took it to have a total length of 18" -- strut plus step -- and have an airfoil section of 2" x 0.9"...found that in Aircraft Spruce. As best I can tell from Hoerner, the Cd is ~0.1 at this Reynolds number.)

The transponder antenna I assume is one of those little wires with a ball on top? Like an R.A. Miller AV-22? The manufacturer says the drag is 0.41 lbs at 250 mph, so in your 200 mph RV-7, that costs you less than 0.1 mph.

So, adding it all up,

Comm: 0.3 mph
Two steps: 0.66 mph
Txp: 0.1 mph

Total: 1 mph


Note that adding them all up like that only works for small drag producers like this. If you tried to add huge drag items, you can't use this method.

You're welcome from a riveting idiot,
Martin
Hundreds of hours of building time and looking forward to loving it!
 
Not dog slow

The RV-6A that walked away from Galen was mine and that was before his wheel pants and gear leg fairings were installed. After they were put on I made one less than ideal speed check with his 7A and the two speeds were close as best as I could determine in the 10 seconds or so that we may have stabilized our speeds. Since I have done multiple 8000' DA runs (75% power) and mine is in the 196-197 mph range Galen's is in that ballpark.

Never assume that your instruments are correct unless you check them against a known accurate source. That applies to airspeed, manifold pressure, etc.
 
Ron!

ronlee said:
The RV-6A that walked away from Galen was mine and that was before his wheel pants and gear leg fairings were installed. After they were put on I made one less than ideal speed check with his 7A and the two speeds were close as best as I could determine in the 10 seconds or so that we may have stabilized our speeds. Since I have done multiple 8000' DA runs (75% power) and mine is in the 196-197 mph range Galen's is in that ballpark.

Never assume that your instruments are correct unless you check them against a known accurate source. That applies to airspeed, manifold pressure, etc.
Click to expand...

So you were still pulling ahead of me a bit in that speed run, perhaps not by much. I'm still learning so this could be a simple issue of not making the right calculations. I'm going to go up tomorrow with a group here in ABQ, perhaps I will get to do some speed comparisons with a similar airplane, as Ron points out, this is the best method.

- Can't wait to get back up and fly with you Ron.. - galen
 
dan said:
Wow, 11 gph is HIGH imho at 10,000' with a 360 engine. If that's an accurate flow reading, I suspect you could pick up several knots by leaning to best power. Lean to peak IAS, close the vents, and see what you get TAS-wise.
Click to expand...

Yeah boy, I never burn that much petro here in our local area. Then again, I'm never running at WOT except on climbout with the fixed Sensenich climb prop on my -8. Has John Nystrom looked over your airplane? He's a pretty sharp dude, based in the row E or F hangars (AEG), RV-7A w/ waaay cool panel and awesome paint scheme visible from Mars. If you're interested in hopping down to Mid Valley, I'm off all next week. Gimme a call 203-1326. I know nuthin' bout FI systems, but rigging and trim stuff, not too shabby.
 
May have spoke too soon

After learning how to dial things in a bit better and by taking both TAS, and Ground Speed numbers things are looking in line with similarly equipped RV-6/7s.
 
gshipman said:
After learning how to dial things in a bit better and by taking both TAS, and Ground Speed numbers things are looking in line with similarly equipped RV-6/7s.
Click to expand...
What do you mean by "dial things in a bit better"? Did you make a few adjustments on the airframe or engine? Or did you learn how to better lean the mixture? Or did you learn how to better measure TAS? Please tell us more so other people can learn from your experience.
 
Kevin Horton said:
What do you mean by "dial things in a bit better"? Did you make a few adjustments on the airframe or engine? Or did you learn how to better lean the mixture? Or did you learn how to better measure TAS? Please tell us more so other people can learn from your experience.
Click to expand...

I was doing several things incorrectly I believe, in determining my top end speed. First, I was running rich, when I leaned to peak power that helped. Next I was running at 2400 RPM, for the top end speed I went full prop. Then it was a question of figuring out my TAS which I did both by the wheel and my EFIS. I also took a look at my GS doing a box pattern. I know, there is still error in this but my speed picked up about 10 mph or so. At this point it seems to be comparable to other RV-7A and RV-6A with 180 HP.
 
You just have to listen to Bubba Ron

Don't let my youthful good looks fool you. I am somewhat smart in some matters.
 
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