Van's Air Force
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best L/D ?
- Thread starter RV10inOz
- Start date
azcloudflyer
Active Member
See flight testing section of my web page for details.
One notch (0 degrees) of flaps will get you up off the runway a little sooner. Plane accelerates so well you do have to be careful to retract any flaps before exceeding flap down speed.
In my testing I came up with 87 kias for best glide, gross weight, with a likely error bar of plus or minus 5 knots. e.g., in agreement with the above plot.
In my testing I came up with 87 kias for best glide, gross weight, with a likely error bar of plus or minus 5 knots. e.g., in agreement with the above plot.
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az_gila
Well Known Member
Auburntsts
Well Known Member
In the -10 I'd say yes simply because full "up" is the -3 deg reflex position and is the standard "no flap" position. The zero degree position just happens to be a defined position between full up and full down, no different terminology wise than say 15 deg. Confusion may arise from aircraft (eg Cessna's) where zero deg is the full up flap position and reflex is not an option.
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Yes. Vans lists maximum speeds for the 3 standard flaps down positions, including the first one (0 deg).
The reason is structural; with flaps up (-3 deg) the flaps are against the aft spar. In other positions the forces which want to force the flaps up are carried by the flap push rod.
The reason is structural; with flaps up (-3 deg) the flaps are against the aft spar. In other positions the forces which want to force the flaps up are carried by the flap push rod.
RV10inOz
Well Known Member
This is a great wing!
And yes anywhere from 85-95 or a bit more seems to be the target for glide....I have always had trouble picking the difference in there when doing glide approaches. Now I know why!
Great graph, this thread should be a popular search in future I reckon!
And yes anywhere from 85-95 or a bit more seems to be the target for glide....I have always had trouble picking the difference in there when doing glide approaches. Now I know why!
Great graph, this thread should be a popular search in future I reckon!
If doing "glide approaches" presumably they are into the wind, and you are interested in progress over the ground. In this case the optimum speed is increased, the extra speed depending on the wind. For a 15 knot headwind, add about 6 kts, e.g., 96 instead of 90 kias.
RV10Rob
Well Known Member
And this is why you don't want to lower a flap in an attempt to correct for a heavy wing. The flap must be against the rear spar; otherwise, you'll be stressing the flap actuation parts at cruise speeds. That's my understanding, anyway.
-Rob
Two points, if I may:
You are always better off gliding slightly above the nominal best speed. You are more speed stable (right side of the drag curve), you get better penetration into wind and you are further above the stall. The reduction in glide range is minimal.
Secondly, I am totally confused about the flap limits and how the "reflex' position is used. As I understood it, the UP position is zero, ie flush with the wing top surface. This is the position used for TO, climb and GA. I thought that the reflex (-3, flush with ailerons and hard up against the rear spar) position was used just for cruise. I didn't think it was used in the circuit. Hence the "REFLEX" FPS that I have spent a lot of money on and will soon be trying to configure. So if the UP (0) position is limited to 97kts, doesn't this constrain your circuit and climb speeds somewhat? Why cause all this confusion with "Reflex"? Why not simply start with -3 and call it UP ie 0?
As I said - confused......
You are always better off gliding slightly above the nominal best speed. You are more speed stable (right side of the drag curve), you get better penetration into wind and you are further above the stall. The reduction in glide range is minimal.
Secondly, I am totally confused about the flap limits and how the "reflex' position is used. As I understood it, the UP position is zero, ie flush with the wing top surface. This is the position used for TO, climb and GA. I thought that the reflex (-3, flush with ailerons and hard up against the rear spar) position was used just for cruise. I didn't think it was used in the circuit. Hence the "REFLEX" FPS that I have spent a lot of money on and will soon be trying to configure. So if the UP (0) position is limited to 97kts, doesn't this constrain your circuit and climb speeds somewhat? Why cause all this confusion with "Reflex"? Why not simply start with -3 and call it UP ie 0?
As I said - confused......
Bill.Peyton
Well Known Member
Paul,
The reflex position (-3 degrees) is the "standard cruise position". Van's limits the max speed on the 0 degree trail position to 122 Kts. As stated above, in the trail position at 0 degrees, the load is transferred from the rear wing spar to the flap actuator mechanism. At 15 degrees, the speed limit is 96 kts and at full flaps, 87 kts. The actuation mechanism is not designed to accept a load beyond the limits imposed by the above speeds. I would not think that you would need to fly a pattern at more than 122 kts. My pattern speed is 80 kts, and short final is 72kts with full flaps.
I do agree with you that the flap extension speed limits require a little planning to slow the aircraft down as you enter the pattern.
The reflex position (-3 degrees) is the "standard cruise position". Van's limits the max speed on the 0 degree trail position to 122 Kts. As stated above, in the trail position at 0 degrees, the load is transferred from the rear wing spar to the flap actuator mechanism. At 15 degrees, the speed limit is 96 kts and at full flaps, 87 kts. The actuation mechanism is not designed to accept a load beyond the limits imposed by the above speeds. I would not think that you would need to fly a pattern at more than 122 kts. My pattern speed is 80 kts, and short final is 72kts with full flaps.
I do agree with you that the flap extension speed limits require a little planning to slow the aircraft down as you enter the pattern.
I agree the terminology can be confusing. I have a placard to remind me of the maximum flap speeds, and it is labeled "one notch" "two notch" "three notch". Up means all the way up, against the spar.
And yes, if you use one or two notches to shorten the takeoff roll, you do need to remember to get the flaps all the way up before accelerating too much.
I disagree that it is best to glide a little on the fast side. At gross weight, no wind, best glide is the best speed. But at lower weights, you want to slow from the gross weight number (like the ratio of the square roots of the weights). Into a headwind, a little faster. But with a tailwind, a little slower. I find that often it happens that the plane is under gross by a fair amount, say, 10%, and you have a 15 knot headwind, so the two effects nearly cancel and published best glide works best. But, it all depends on the particulars.
And yes, if you use one or two notches to shorten the takeoff roll, you do need to remember to get the flaps all the way up before accelerating too much.
I disagree that it is best to glide a little on the fast side. At gross weight, no wind, best glide is the best speed. But at lower weights, you want to slow from the gross weight number (like the ratio of the square roots of the weights). Into a headwind, a little faster. But with a tailwind, a little slower. I find that often it happens that the plane is under gross by a fair amount, say, 10%, and you have a 15 knot headwind, so the two effects nearly cancel and published best glide works best. But, it all depends on the particulars.
OK. First I've heard of this 122kt. Obviously in that case, no problem in the circuit...... I'm not at home at the moment. I assume all these speeds are quoted in the "Flight Testing" section of the build manual. Do you climb at 0 or -3?
As for the glide speed argument (discussion?), I still believe that being slightly on the fast side is preferable. The curve is very flat near the top and for the reasons I gave, the theoretical VERY SLIGHT loss of glide range is more than compensated for by the other benefits. Let's face it, if you are gliding you probably have other things you are dealing with and the very last thing you want is to get slow.
I flew F4s in the RAF and with an engine failure on TO, we did nothing till we got 300kts. I was horrified when I moved to flying big jets that you deliberately fly at V2 in the engine failure case. I understand it's all to do with terrain clearance but it's standard practice even with no obstacles.
SPEED IS LIFE
As for the glide speed argument (discussion?), I still believe that being slightly on the fast side is preferable. The curve is very flat near the top and for the reasons I gave, the theoretical VERY SLIGHT loss of glide range is more than compensated for by the other benefits. Let's face it, if you are gliding you probably have other things you are dealing with and the very last thing you want is to get slow.
I flew F4s in the RAF and with an engine failure on TO, we did nothing till we got 300kts. I was horrified when I moved to flying big jets that you deliberately fly at V2 in the engine failure case. I understand it's all to do with terrain clearance but it's standard practice even with no obstacles.
SPEED IS LIFE
douglassmt
Well Known Member
Me too
First time I've heard of the 122 kias limit on the 0 degree flap position too. When I trained with Mike Seager, I'm nearly certain that he stated clearly there is no Vfe for going from reflex (cruise) to zero, and in fact was not a bad way to bleed down some speed in approach toward an airport. If you have a source for that, please share as I will change my procedure.
First time I've heard of the 122 kias limit on the 0 degree flap position too. When I trained with Mike Seager, I'm nearly certain that he stated clearly there is no Vfe for going from reflex (cruise) to zero, and in fact was not a bad way to bleed down some speed in approach toward an airport. If you have a source for that, please share as I will change my procedure.
Bob Kuykendall
Well Known Member
The RV-10 wing profile was designed by Steve Smith (scsmith on these forums), a NASA engineer with a Phd in aerodynamics and also a sailplane pilot. Steve did a lot of the aerodynamic design and validation for my HP-24 sailplane project.
Thanks, Bob K.
Bill.Peyton
Well Known Member
Bryan,
I am a home and don't have access to the documents, but as I recall, the speeds are in the documents that come with the final kit
Bill
I am a home and don't have access to the documents, but as I recall, the speeds are in the documents that come with the final kit
Bill
hevansrv7a
Well Known Member
L/D Max vs. Best Glide V vs. Engine-out V
I must sound like a stuck needle on a 33 RPM record. First of all, L/D is a ratio, not a speed. The L/D max for a given wing (and usually a given airplane) does not change with weight. The speed at which it is obtained is higher with greater weight. With a few easily obtained facts and one reasonable estimate, both can be approximated with my "triangle" spreadsheet - the latest version. If any -10 owner would like to work with me on that I would be delighted to provide the "answers" on this forum.
A L/D max of <10 for a "10" is significantly low of reasonable since a -6 has a ratio >12. See the CAFE report if you doubt this.
The L/D max and the V for it are useful in planning a flight profile but they are pretty much useless when the noise stops. If there is any thrust, then they apply. That goes for approach speeds except perhaps with the throttle totally closed.
The best glide ratio and the best glide speed with a prop (stuck or windmilling) out front are both lower than without a prop. See the Norris-Bauer experiments in 1995.
The glide ratio and best speed with engine out must be determined experimentally and if the prop is CS then the no-power prop pitch must be simulated. Duh.
I can't comment on the discussion of flap settings. Sorry.
For much more about this, please refer to my website and drill down to the Oshkosh presentations, especially the most recent. On the same page you will find links to the references above, too.
Has anyone really worked out the best L/D for an RV10? assume 2700lbs.
Just never seen it anywhere on the forum.........
I must sound like a stuck needle on a 33 RPM record. First of all, L/D is a ratio, not a speed. The L/D max for a given wing (and usually a given airplane) does not change with weight. The speed at which it is obtained is higher with greater weight. With a few easily obtained facts and one reasonable estimate, both can be approximated with my "triangle" spreadsheet - the latest version. If any -10 owner would like to work with me on that I would be delighted to provide the "answers" on this forum.
A L/D max of <10 for a "10" is significantly low of reasonable since a -6 has a ratio >12. See the CAFE report if you doubt this.
The L/D max and the V for it are useful in planning a flight profile but they are pretty much useless when the noise stops. If there is any thrust, then they apply. That goes for approach speeds except perhaps with the throttle totally closed.
The best glide ratio and the best glide speed with a prop (stuck or windmilling) out front are both lower than without a prop. See the Norris-Bauer experiments in 1995.
The glide ratio and best speed with engine out must be determined experimentally and if the prop is CS then the no-power prop pitch must be simulated. Duh.
I can't comment on the discussion of flap settings. Sorry.
For much more about this, please refer to my website and drill down to the Oshkosh presentations, especially the most recent. On the same page you will find links to the references above, too.
Bob Kuykendall
Well Known Member
Color me skeptical, but given the RV6's much lower aspect ratio I have to accept that assertion only with an apples-to-apples data set. Or a big grain of salt.
hevansrv7a
Well Known Member
which assertion?
Bob, if you are questioning the CAFE data I suggest you review it first. If you are skeptical of the 6A result because you accept the <10 for the 10 as correct then I ask that you review the part of my post where I note that the presence of a prop that provides drag alters the result significantly.
I also suggest you review the other CAFE tests that used the Norris-Bauer device. Not all did. The Thorp T-18 did. All the ones that did are listed on my site.
For example, the C-152 without a prop can be compared to the C-152 POH. There is a huge difference. I provide the actual numbers on my website.
The Norris-Bauer zero thrust method, which CAFE used for the 6A, is a proven way to correctly simulate the absence of the prop.
Lastly, I suggest this test: use the 9.6 L/D and the speed at which it was obtained and the weight of the airplane. Compute the sink rate and use the sink rate times the weight divided by the HP value to get the true thrust HP at that speed. Convert that to drag. Now, since parasite and induced drag must be equal at the speed where L/D is max, then project the two drag curves and compute the THP needed to get to the airplane's known top speed. Be sure to keep CAS and TAS straight. Use some reasonable estimate of prop net efficiency (85%? 90%?) and thus compute BHP. You will find that the BHP needed to match the airplane's known performance is greater than what is actually available.
However, if you use CAFE's values you will find a reasonable result.
If this sounds like a lot of difficult math, just use my triangle spreadsheet and it will be very easy. PM or email me if you want to go over this in more detail.
Bob, if you are questioning the CAFE data I suggest you review it first. If you are skeptical of the 6A result because you accept the <10 for the 10 as correct then I ask that you review the part of my post where I note that the presence of a prop that provides drag alters the result significantly.
I also suggest you review the other CAFE tests that used the Norris-Bauer device. Not all did. The Thorp T-18 did. All the ones that did are listed on my site.
For example, the C-152 without a prop can be compared to the C-152 POH. There is a huge difference. I provide the actual numbers on my website.
The Norris-Bauer zero thrust method, which CAFE used for the 6A, is a proven way to correctly simulate the absence of the prop.
Lastly, I suggest this test: use the 9.6 L/D and the speed at which it was obtained and the weight of the airplane. Compute the sink rate and use the sink rate times the weight divided by the HP value to get the true thrust HP at that speed. Convert that to drag. Now, since parasite and induced drag must be equal at the speed where L/D is max, then project the two drag curves and compute the THP needed to get to the airplane's known top speed. Be sure to keep CAS and TAS straight. Use some reasonable estimate of prop net efficiency (85%? 90%?) and thus compute BHP. You will find that the BHP needed to match the airplane's known performance is greater than what is actually available.
However, if you use CAFE's values you will find a reasonable result.
If this sounds like a lot of difficult math, just use my triangle spreadsheet and it will be very easy. PM or email me if you want to go over this in more detail.
hevansrv7a
Well Known Member
A flight testing issue
I just did a quick look at Mike Andresen's flight testing that produced the L/D numbers at the start of this thread. If I understand it correctly, he used engine power as given by the EFIS to compute HP and convert it to drag.
The good news is that he is using a method that eliminates prop DRAG. The bad news is that I don't see any correction for prop efficiency. A typical prop will give a max of 85%, often less. If you take 9.6 and divide it by 0.85 you get about 11.3. That is a much more reasonable result. If prop efficiency at those low speeds is 80% then the corrected number would be 12.0.
I think it should be greater than 12, maybe even 12.5, but I will test it using my spreadsheet and report back on this thread later.
I also noticed that he has a link to my stuff. Thanks, Mike!
BTW - Mike does a very nice job of collecting, organizing and presenting data. I only wish I could do as well. I think that I can use his data in my triangle spreadsheet (plus published dimensions for the -10).
I just did a quick look at Mike Andresen's flight testing that produced the L/D numbers at the start of this thread. If I understand it correctly, he used engine power as given by the EFIS to compute HP and convert it to drag.
The good news is that he is using a method that eliminates prop DRAG. The bad news is that I don't see any correction for prop efficiency. A typical prop will give a max of 85%, often less. If you take 9.6 and divide it by 0.85 you get about 11.3. That is a much more reasonable result. If prop efficiency at those low speeds is 80% then the corrected number would be 12.0.
I think it should be greater than 12, maybe even 12.5, but I will test it using my spreadsheet and report back on this thread later.
I also noticed that he has a link to my stuff. Thanks, Mike!
BTW - Mike does a very nice job of collecting, organizing and presenting data. I only wish I could do as well. I think that I can use his data in my triangle spreadsheet (plus published dimensions for the -10).
